"Garage door opener" remote

[Don Y]

[Poor choice of subject line but closest I could come up with]

Most (all?) US cars seem to have a three-button "programmable remote"
embedded (typ above the rear view window) to handle garage door
openers without having to clip a "remote" to the vehicle's visor.

I'd like to know what that device is capable of -- by understanding
the sorts of things that it would likely control (and the requirements
imposed by those things).

I see GDOs operating in the 300-400MHz band -- "intermittent duty".

I've seen a report of a 2.4GHz opener but I think that to be in error
(more research required).

Nearest I can tell, a typical user would "pair" these with GDOs and/or
"electric gates" (a GDO in another form?).

[I have one of the three buttons "bound" to the garage light as the
light on the GDO is lame and only of use in certain circumstances]

Anything else that *might* see such use? I.e., something to control
from within the car in order to enter/depart from a property?

Any idea what this seemingly universal 3-button device is called,
in the trade? I.e., how to chase down further information (USPTO)
on it?

Or, ideas as to how it is trained? (do all remotes follow some
preordained data pattern?)

[Dave Platt]

In article <scssvd$ieb$1...@dont-email.me>,

Don Y <blocked...@foo.invalid> wrote:

>I see GDOs operating in the 300-400MHz band -- "intermittent duty".

I believe that most commonly you will see them operating at, or around
433.920 MHz. This is one of the bands in which Part 15 operation is
allowed.

The primary frequency-user here is military radar, and secondary is
amateur radio. One occasionally sees stories about military radar
operations disrupting peoples' garage door openers and car
alarm/locking systems in some areas. The commonest problems seem to
be "they don't work" (the strong radar signals saturate the receivers)
but "undesired operation" occurs occasionally (garage doors opening
"by themselves").

>I've seen a report of a 2.4GHz opener but I think that to be in error

>Nearest I can tell, a typical user would "pair" these with GDOs and/or
>"electric gates" (a GDO in another form?).

>Anything else that *might* see such use? I.e., something to control
>from within the car in order to enter/depart from a property?

Disarming the anti-intruder mines and lasers? :-)

>Any idea what this seemingly universal 3-button device is called,
>in the trade? I.e., how to chase down further information (USPTO)
>on it?

"Garage door opener", "car alarm key-fob", etc.

>Or, ideas as to how it is trained? (do all remotes follow some
>preordained data pattern?)

Your best bet is probably to open up either the transmitter or
receiver and find the FCC Part 15 registration ID. You can look this
up on an FCC web site and get at least some information about the
frequency and modulation pattern.

Commonly, these days, each button push will transmit a "rolling code"
packet... a header, a transmitter ID number, a sequence number of some
sort, a button code, and (in good ones) a cryptographic authentication
of some sort (cheaper ones omit this). The reciever is "trained" to
accept a specific transmitter ID (or set of IDs).

The better ones have some sort of transmitter-specific secret (known
to the receiver via the training/programming process) which creates a
cryptographic "signature" in the packet that's difficult to spoof.
The receiver validates this, and also looks at the sequence number to
provide "anti-replay" protection, so somebody can't record one of your
"open the garage door" transmissions and play it back later when
you're away from home. For these, the training process requires
giving the receiver both the transmitter ID and shared secret (and
often the starting sequence number).

Cheaper/older ones lack this sort of strong signature authentication
and anti-playback defense. There are plenty of stories about people
using off-the-shelf receiver dongles (e.g. the RTL-SDR type) to
receive transmissions, PCs to analyze them, and cheap transmitters to
re-send them. Want to unlock your neighbor's car? Want to "fast
forward" your neighbor's transmitter's sequence number a few thousand
times, effectively locking your neighbor out of the car? Not hard to
do, alas.

[Don Y]

On 7/16/2021 3:46 PM, Dave Platt wrote:
> In article <scssvd$ieb$1...@dont-email.me>,
> Don Y <blocked...@foo.invalid> wrote:
>
>> I see GDOs operating in the 300-400MHz band -- "intermittent duty".
>
> I believe that most commonly you will see them operating at, or around
> 433.920 MHz. This is one of the bands in which Part 15 operation is
> allowed.

I've looked at various (incl legacy) GDO remotes and they seem to
operate (or HAVE operated) at a variety of bands: 310, 315, 360,
380, 390MHz. I.e., it doesn't appear that *one* band is all a
"remote control emulator" would need to handle.

[Part of the reason for my asking is to understand what's happening
inside the "universal remote" without trying to reverse engineer
it (being an automotive product, the volumes are high enough for the
entire design to be fully custom!)]

I'm assuming the "key fob" uses a different subsystem to provide
it's functionality (though it seems the two could easily be integrated).

> The primary frequency-user here is military radar, and secondary is
> amateur radio. One occasionally sees stories about military radar
> operations disrupting peoples' garage door openers and car
> alarm/locking systems in some areas. The commonest problems seem to
> be "they don't work" (the strong radar signals saturate the receivers)
> but "undesired operation" occurs occasionally (garage doors opening
> "by themselves").

I read of one frequency change being prompted by military *radio*.
Not sure how common such interference would be (given that we're not
located on a battlefield!). Nearest military base is some distance away
so no easy way to verify...

>> I've seen a report of a 2.4GHz opener but I think that to be in error
>
>> Nearest I can tell, a typical user would "pair" these with GDOs and/or
>> "electric gates" (a GDO in another form?).
>
>> Anything else that *might* see such use? I.e., something to control
>>from within the car in order to enter/depart from a property?
>
> Disarming the anti-intruder mines and lasers? :-)

Doors, gates, lights -- and a colleague suggested "security systems"
(probably NOT involving mines! :> )

>> Any idea what this seemingly universal 3-button device is called,
>> in the trade? I.e., how to chase down further information (USPTO)
>> on it?
>
> "Garage door opener", "car alarm key-fob", etc.

Colleague offered "HomeLink". That has produced a few hits.
I've been chasing them down to see what they might yield.

>> Or, ideas as to how it is trained? (do all remotes follow some
>> preordained data pattern?)
>
> Your best bet is probably to open up either the transmitter or
> receiver and find the FCC Part 15 registration ID. You can look this
> up on an FCC web site and get at least some information about the
> frequency and modulation pattern.

Yeah, I found a few hits on the fccid website. It will take a while
to sort out which might be most productive/informative. One (which
may not be The One) shows 5 frequency ranges: 286-303, 307-321,
336-398, 411-440 & 902-926. I'll have to see which of these are
likely "legacy support".

[A (previous) neighbor works for Chamberlain. I will chase him down and
see what he can offer regarding their current products -- and, any
history that he can add]

> Commonly, these days, each button push will transmit a "rolling code"
> packet... a header, a transmitter ID number, a sequence number of some
> sort, a button code, and (in good ones) a cryptographic authentication
> of some sort (cheaper ones omit this). The reciever is "trained" to
> accept a specific transmitter ID (or set of IDs).

Yes. And the receiver *tries* to remain in sync with the transmitter
by looking ahead some number of codes (256?) in case the transmitter
had been activated (repeatedly) without the receiver "seeing" those
activations.

This suggests surreptitiously pressing your "friend's" remote button
a few hundred times will leave the transmitter and receiver out of sync
with each other (i.e., "breaking" the control). The receiver can't
look *backwards* in the code sequence as that would allow a replay
attack.

> The better ones have some sort of transmitter-specific secret (known
> to the receiver via the training/programming process) which creates a
> cryptographic "signature" in the packet that's difficult to spoof.
> The receiver validates this, and also looks at the sequence number to
> provide "anti-replay" protection, so somebody can't record one of your
> "open the garage door" transmissions and play it back later when
> you're away from home. For these, the training process requires
> giving the receiver both the transmitter ID and shared secret (and
> often the starting sequence number).

I think (?) the "sequence number" is implicit in the actual code
sent. I.e., if the series of random codes (LPRNG) is:
5, 93, 387, 443, 3726, 423, 445, 9088, 244, 768, ...
then if YOU think the "next" code is "93", you will accept any of the
(256?) codes AFTER "93" as valid -- and, synchronize to THAT point in the
sequence, thereafter. So, if "445" was received, all of those codes up
to ("before" in the sequence) would be invalidated.

This raises some interesting implementation questions:
- if a 'second" remote is in use, does it use an entirely different sequence?
(if not, how does *it* know that the next number is now 9088 instead of 93
or even 387?)
- how does the trainable remote (emulator) know what the sequence is?
are all sequences (from all remote control vendors) using the same
polynomial? (if so, a hacker could anticipate the next code just by
"listening" to your remote, now)

> Cheaper/older ones lack this sort of strong signature authentication
> and anti-playback defense. There are plenty of stories about people
> using off-the-shelf receiver dongles (e.g. the RTL-SDR type) to
> receive transmissions, PCs to analyze them, and cheap transmitters to
> re-send them.

Hmmm... I will have to research that. It's not germane to the problem
I'm trying to address but it "is a puzzlement" (Brynner) worth exploring.

> Want to unlock your neighbor's car? Want to "fast
> forward" your neighbor's transmitter's sequence number a few thousand
> times, effectively locking your neighbor out of the car? Not hard to
> do, alas.

Only a fool bets against the hacker! :< Too often, designers rely on
easily violated assumptions in their designs. Once identified, they
can easily be subverted. So, the security only applies to prevent
casual theft/abuse; a mildly determined adversary is unimpeded.

[I particularly like the hacks of keyless entry devices that simply
require the user to *possess* the key, no button presses required!]

In my case, I just want to leverage what is becoming a ubiquitous feature
in vehicles to provide a "non-wired" link between a vehicle and another
device (avoiding the design, certification, manufacture and PACKAGING
of said device). It is almost second nature to reach up and press
one of these buttons as entering/exiting a property. So, a likely candidate
to "overload" for other functionality!

Thanks for your comments! I'll see what else I can find... I was
hoping to get a feel for what the trainable device COULD do (there is
no formal specification available, that I can find -- it works, or it
doesn't). Then, contemplate how they would implement such functionality.

Then, figure out how to verify that as well as leverage it for MY needs.

[Don]

test

Don Y wrote:

<snip>

> Yeah, I found a few hits on the fccid website. It will take a while
> to sort out which might be most productive/informative. One (which
> may not be The One) shows 5 frequency ranges: 286-303, 307-321,
> 336-398, 411-440 & 902-926. I'll have to see which of these are
> likely "legacy support".

418 MHz is good and cheap and probably provides the best "legacy"
support because it was formerly widely used in Europe until newer
products migrated to 433.92 MHz.

Which frequency should I use when planning to design a RF
(Radio Frequency) product in the United States?

...

418MHz is a good frequency to use in the US as it is not
very crowded. This gives the least likely chance for
interference and therefore the best performance.

...

https://www.solidremote.com/blog/rf-remote-control-frequency-selection-315mhz-418mhz-433-92mhz-or-915mhz/

Danke,

--
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.

[Don Y]

On 7/16/2021 8:43 PM, Don wrote:
> test
>
> Don Y wrote:
>
> <snip>
>
>> Yeah, I found a few hits on the fccid website. It will take a while
>> to sort out which might be most productive/informative. One (which
>> may not be The One) shows 5 frequency ranges: 286-303, 307-321,
>> 336-398, 411-440 & 902-926. I'll have to see which of these are
>> likely "legacy support".
>
> 418 MHz is good and cheap and probably provides the best "legacy"
> support because it was formerly widely used in Europe until newer
> products migrated to 433.92 MHz.

I'm actually trying NOT to design such a device. The HomeLink units
in vehicles already have the ability to masquerade as any number of
such devices. I would want to have them masquerade as devices that
are "new (modern) enough" that support for them wouldn't be elided
from the next iteration of the HL design.

[E.g., HL can emulate devices that emit *fixed* codes; I suspect these
are increasingly rare (i.e., GDOs), "in the wild", and that capability
may be bred out of the HL design's evolution -- in favor of support
for even more "clever" future designs.]

Once I can settle on a "safe" remote to be emulated (or, remote
*technology*), I'd have to build a "programmer" -- essentially a
remote with just enough output power to be seen by the HL device
when in programming mode. Hopefully, this can be low enough
that the device doesn't pose a nuisance attracting FCC attention.

[I suspect the HL device is intentionally crippled to only
detect signal in very close proximity -- less than a foot -- so
this may be a challenge]

[Piglet]

On 17/07/2021 09:56, Don Y wrote:
>
> [I suspect the HL device is intentionally crippled to only
> detect signal in very close proximity -- less than a foot -- so
> this may be a challenge]
>

In units I have seen the close range reception in programming mode is
achieved by merely using a crystal radio type diode detector - not any
"proper" receiver at all!

piglet

[Clifford Heath]

Don,

IDK if it's useful to you, but the open source "rtl_433" software can
demodulate and decode many of these types of keyfobs. Hundreds, anyway.

I suspect that reading the code would give you a lot of insight into the
variety of encodings used. You could even get an RTL dongle and listen in.

CH

[ABLE1]

On 7/16/2021 6:46 PM, Dave Platt wrote:
> The primary frequency-user here is military radar, and secondary is
> amateur radio. One occasionally sees stories about military radar
> operations disrupting peoples' garage door openers and car
> alarm/locking systems in some areas. The commonest problems seem to
> be "they don't work" (the strong radar signals saturate the receivers)
> but "undesired operation" occurs occasionally (garage doors opening
> "by themselves").

Hello, I find this VERY interesting. I won't go into the whole story
since it is very long but I have a customer that has an alarm system
that I installed. It has wireless sensors for doors and such.
There has been a few times that the system does not receive signals
from the transmitters for periods of time from 45 minutes to 2 days.
During this time their garage door opener remote does not work unless
you hold it in you hand reach up to within 18" of the opener antenna
and then it will work.

During that time the problem or source can't be determined.
In discussions with neighbors it has be determined that at least
4 others, next door and across the street have experienced the same
with there openers.

Then it all stops and goes back to normal operation???

This happened about 2 years ago and then again about a month ago.
That I know about that is.

Needless to say when it IS NOT happening it is absolutely impossible
to find. When it IS happening it is absolutely impossible to find.

The openers have a red LED on the unit that is used for learning in
a remote button. Normally it is off until it receives a signal from
a remote to open. During these events the LED is solid red for the
entire time frame. Then during the end of the event it starts to
flicker and then off.

The security devices are on 319.5 Mhz and the door opener is on 318 Mhz.

Is there any thoughts here as to what other than Military Radar that
could be causing this issue with such intensity in a small area??

There is a local airport with control tower about 2 miles away.

I say a small area (200' square box maybe??) but it could be effecting
a larger area but I have no way to know or to find out without having
a town meeting.

Any thoughts on the subject would be most helpful.

Thanks,

Les

[Rick C]

Here's my two cents worth. My home town, Frederick, MD is host to Fort Detrick. Maybe 10 or 20 years ago they announced some change in their emissions (no details provided I believe) so that these garage opener type devices may malfunction. With a number of homes in close proximity of the base there were garage doors opening at will and remotes no longer functioning. I believe at that time there were many fixed code devices and few, if any rolling code devices. It's not clear to me if that makes a difference, but a rolling code may be more suseptable to jamming in that if enough triggers are received as valid I believe the rolling code can desync your remote requiring you to sync it up again.

If enough units use the same brand of receivers/remotes is it possible that frequent use causes rolling code collisions that desync remotes? I'm thinking the wrap around count is sufficiently large that this is a near impossibility.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

[Joe Gwinn]

I've never had a GDO, but for programming it may have near-field only
antennas, precisely to make programming from the street outside
impossible.

Joe Gwinn

[Ralph Mowery]

In article <vjs5fg9im19ln3hsk...@4ax.com>,
joeg...@comcast.net says...

>
> I've never had a GDO, but for programming it may have near-field only
> antennas, precisely to make programming from the street outside
> impossible.
>
>
>

Most garage door openers have very low power so not much over 100 to 200
feet of range.

If someone has a much more powerful transmitter then a mile or two would
be possiable. I am not talking about 1000 or more watts but maybe 10
watts for the transmitter.

Much like the key thing for the cars . They have a very short range. The
transmitter is very low power because of the size of the battery. No
one would want a key FOB the size of a 2 or 3 cell flashlight.

[Don Y]

On 7/17/2021 8:10 AM, Joe Gwinn wrote:
> On Sat, 17 Jul 2021 01:56:58 -0700, Don Y

>> [I suspect the HL device is intentionally crippled to only
>> detect signal in very close proximity -- less than a foot -- so
>> this may be a challenge]
>
> I've never had a GDO, but for programming it may have near-field only
> antennas, precisely to make programming from the street outside
> impossible.

Note that the HL device is not a GDO; it's a GDO *remote* (emulator).
For the GDOs that are push-button programmed (press button to
enter programming mode), they use the existing receiver design
to "capture" the signal from the remote. So, you can program
the GDO at the same distance as you could normally actuate the
opener.

Many years ago, we discovered that *our* remote would open our
GDO *and* the neighbor across the street! I'm still unsure
as to how this could have happened. I.e., even if he happened to
have been in "programming mode" when we (drove in/out and) actuated
*our* GDO, he would have known that his remote wasn't working properly
and would have tried again.

Unless his GDO "saw" our remote's action, responded and he
never verified that his remote *would* operate his (i.e.,
a pure coincidence?)

[Don Y]

On 7/17/2021 9:19 AM, Ralph Mowery wrote:
> Most garage door openers have very low power so not much over 100 to 200
> feet of range.

The HL devices are rated at 2mW.

> If someone has a much more powerful transmitter then a mile or two would
> be possiable. I am not talking about 1000 or more watts but maybe 10
> watts for the transmitter.
>
> Much like the key thing for the cars . They have a very short range. The
> transmitter is very low power because of the size of the battery. No
> one would want a key FOB the size of a 2 or 3 cell flashlight.

No, there are other reasons for the limited range.

- you wouldn't want the car NEXT to you to respond to your signal
(or interfere with your vehicle's response)
- you want to know the HAND that is now grasping the door handle
belongs to the individual with the fob on their person (~30 inches)
- you want to know that the fob is located:
by the driver side door (so the driver's door will unlock when the
driver's door handle is sensed)
by the passenger side door (so the passenger's door will unlock when
the passenger's door handle is sensed)
[you don't want an adversary approaching your vehicle to be able to
let himself *in* on the passenger side just because "you" happened
to have brought the fob close to the vehicle]
by the "hatchback" (so the hatchback can be opened when commanded)
close to the ignition switch (so the vehicle could be started)
is no longer contained within the confines of the vehicle (so
the occupants aren't locked out of a RUNNING vehicle)

My other half and I frequently travel together. Each of us carrying
our own fob (driver's fob adjusts the car to that person's preferences).
Owing to the way that we park in the garage, the passenger usually passes
by the driver's door on their way to their spot. If the driver
(following the passenger) grabs the door handle too soon after the
passenger (and fob!) has passed the driver door, the car will think
hat the *passenger* is driving and will set things up for the
passenger-as-driver.

This is annoying. The driver has to close the door and repeat the
exercise to "change the car's mind" (this also takes a few moments
as the seat and mirrors have to be repositioned from that false
input)

[Thankfully, the car doesn't get confused with the passenger *seated*
near the driver! So, very near-field operation]

[Don Y]

On 7/17/2021 4:53 AM, Clifford Heath wrote:
> IDK if it's useful to you, but the open source "rtl_433" software can
> demodulate and decode many of these types of keyfobs. Hundreds, anyway.
>
> I suspect that reading the code would give you a lot of insight into the
> variety of encodings used. You could even get an RTL dongle and listen in.

Hmmm... I don't know. I will have to think about what I could do with that
capability. And, if I could use it "in production" to make the device
more usable (?). Maybe I could use it to *receive* commands issued
by the HL device (though I'd still have to sort out how to "program"
the HL device -- with a "synthetic remote")

My current thinking is that the GDO (and any other "remote activated"
device) should NOT be responding to a remote (because then there is the
possibility that it will perform and/or enter a state that "I" don't
endorse). "I" should capture the commands from the remote and decide
what to do with them.

E.g., I am frequently working in the garage. I don't want someone
"coming home" to open the door and drive in (I may be accessing the
ceiling area ABOVE the raised garage door so would be harmed by its
opening).

Folks with multiple garage doors (I have a buddy with *8*) could
use the remote to signal "open *a* door" and which door may be
determined by noting which stalls are "in use".

[Ideally, it would be nice to be able to lock the remote XMIT "on"
and use this to sense the *presence*/approach/departure of a
vehicle. But, not an allowed use so rely on other technologies
to do that!]

Someone else might use *a* button (recall there are three) to
signal they are waiting "out front" and the occupant should
come out (for their ride to work).

I'll have to think on this. And, collect more data on "remotes".
Thanks!

[Don Y]

I can clearly see an antenna trace in the FCC filings. One has to
wonder why (given that it is obviously produced in HUGE quantities
and can be damn near anything it WANTS to be) they made the deliberate
effort to limit the device's *receiving* range. Yeah, you want to
have some assurance that the signal you are receiving is INTENDED for
you (while "learning") but even a mmistaken capture could easily be
verified: "when the red light stops flashing (signaling the
remote has been programmed) press the button to verify the GDO operates..."

[Phil Hobbs]

I'm sorry, but in an electronic design newsgroup, 'GDO' has got to mean
'Grid Dip Oscillator' and nothing else.

Garages, humph. ;)

Cheers

Phil Hobbs

(Whose garage is opened and closed fully manually)

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

[Jasen Betts]

On 2021-07-17, ABLE1 <some...@nowhere.net> wrote:

> The security devices are on 319.5 Mhz and the door opener is on 318 Mhz.
>
> Is there any thoughts here as to what other than Military Radar that
> could be causing this issue with such intensity in a small area??
>
> There is a local airport with control tower about 2 miles away.
>
> I say a small area (200' square box maybe??) but it could be effecting
> a larger area but I have no way to know or to find out without having
> a town meeting.
>
> Any thoughts on the subject would be most helpful.

Build or borrow a directional antenna for 318 MHZ, get a portable receiver
that provides signal strength information, and go on a fox hunt.

--
Jasen.

[Don Y]

On 7/17/2021 6:07 AM, ABLE1 wrote:
> Hello, I find this VERY interesting. I won't go into the whole story
> since it is very long but I have a customer that has an alarm system
> that I installed. It has wireless sensors for doors and such.
> There has been a few times that the system does not receive signals
> from the transmitters for periods of time from 45 minutes to 2 days.

2 *days*? Are you sure someone isn't (illegally) operating
a transmitter, nearby?

> During this time their garage door opener remote does not work unless
> you hold it in you hand reach up to within 18" of the opener antenna
> and then it will work.
>
> During that time the problem or source can't be determined.
> In discussions with neighbors it has be determined that at least
> 4 others, next door and across the street have experienced the same
> with there openers.
>
> Then it all stops and goes back to normal operation???
>
> This happened about 2 years ago and then again about a month ago.
> That I know about that is.
>
> Needless to say when it IS NOT happening it is absolutely impossible
> to find. When it IS happening it is absolutely impossible to find.
>
> The openers have a red LED on the unit that is used for learning in
> a remote button. Normally it is off until it receives a signal from
> a remote to open. During these events the LED is solid red for the
> entire time frame. Then during the end of the event it starts to
> flicker and then off.

Verify the *complete* behavior of the indicator. Usually, when
in "learn mode" (activated by a button on the RECEIVER), the
indicator will flash (until it times out).

Some flash when they detect an obstacle in the path of the door
(either photoelectrically or by sensing an increased current
draw by the motor)

Does "lit" coincide with the *entire* open/close cycle? I.e.,
the behavior you are seeing SHOULD be accompanied by the door
moving (?)

> The security devices are on 319.5 Mhz and the door opener is on 318 Mhz.
>
> Is there any thoughts here as to what other than Military Radar that
> could be causing this issue with such intensity in a small area??

Almost anything can be an "unintentional radiator" -- even things like
christmas lights!

I'd wonder if someone wasn't (naively) putting a bunch of hash out.
The "45 minutes" sounds like someone might be "doing something"
(or USING something) for a short period. The "2 days" suggests it
got left *on*!

I lived in a house with the garage located beneath the master bedroom.
Vacuuming the carpet in the MBR would often result in the garage door
opening. We'd come out, the next morning, to leave for work and
wonder which of us had "*left* the door open"! (Ans: neither)

> There is a local airport with control tower about 2 miles away.

Possible. Why not go sniffing for signals? TV or radio stations
nearby?

> I say a small area (200' square box maybe??) but it could be effecting
> a larger area but I have no way to know or to find out without having
> a town meeting.
>
> Any thoughts on the subject would be most helpful.

When the problem next manifests, try to shield the affected unit.
This would at least give you an idea if the interference was radiated
or conducted. In most places, several homes are fed from a single
transformer. So, your line is a direct reflection of what's happening
in your neighbor's homes. Neighbors served by *another* transformer
will have two transformers acting to attenuate signals between your
home and theirs.

[Here, it's 4 homes per xformer -- and I can easily deduce which homes are
serviced "together" (or service is all below grade)]

[boB]

Buy one of those $50 (ish) Tiny SA Spectrum alalyzers and see if
there is any RF signals around that frequency above the level there is
when the door IS working and compare.

That would tell you something. Then you could either get a
directional antenna for it or possibly drive around the neighborhood
trying to find where the signal gets stronger.

But first you need to see if nearby RF interference is even the issue
and what it looks like.

I wonder if there are any high power transmitter near by on another
frequency that could de-sense this garage door receiver ? Overload,

boB

[Clifford Heath]

On 18/7/21 6:03 am, Don Y wrote:
> On 7/17/2021 4:53 AM, Clifford Heath wrote:
>> IDK if it's useful to you, but the open source "rtl_433" software can
>> demodulate and decode many of these types of keyfobs. Hundreds, anyway.
>>
>> I suspect that reading the code would give you a lot of insight into
>> the variety of encodings used. You could even get an RTL dongle and
>> listen in.
>
> Hmmm... I don't know.  I will have to think about what I could do with that
> capability.  And, if I could use it "in production" to make the device
> more usable (?).

I don't think you want to run an SDR as a receiver. I only meant that
you could read the code to learn about the types of encodings that have
been used.

> E.g., I am frequently working in the garage.  I don't want someone
> "coming home" to open the door and drive in (I may be accessing the
> ceiling area ABOVE the raised garage door so would be harmed by its
> opening).

Door openers have "stuck" detectors that shut the motors down when there
is a blockage. If your door is installed in a way that any operation is
unsafe, you should fix that before worrying about how to control it.

> I'll have to think on this.  And, collect more data on "remotes".

The data you probably want is in that code.

CH

[Joe Gwinn]

I was not worrying about the battery. My issue is to hinder criminal
misuse.

Joe Gwinn

[ABLE1]

On 7/17/2021 5:19 PM, Don Y wrote:
> On 7/17/2021 6:07 AM, ABLE1 wrote:
>> Hello, I find this VERY interesting. I won't go into the whole story
>> since it is very long but I have a customer that has an alarm system
>> that I installed. It has wireless sensors for doors and such.
>> There has been a few times that the system does not receive signals
>> from the transmitters for periods of time from 45 minutes to 2 days.
>
> 2 *days*? Are you sure someone isn't (illegally) operating
> a transmitter, nearby?
>

That is a possibility. Again finding and proving is the challenge.

This LED is primary for learning in a remote. And just blinks when the
remote is pushed. Which is seeing the RF Signal. Normally the LED
is off. During my observation at the 45 minute period. The handheld
remote would not work unless it was held up within 18" of the antenna.
Also the Subaru header button did not work. There were two house doors
that would not communicate the doors were open or closed to the security
panel during this time. At the same time the next door neighbor's
garage remote would not work. Then the LED started to blink and then
off. Door contacts then worked as they should. The event was over
and as I am aware has not returned.

>> The security devices are on 319.5 Mhz and the door opener is on 318 Mhz.
>>
>> Is there any thoughts here as to what other than Military Radar that
>> could be causing this issue with such intensity in a small area??
>
> Almost anything can be an "unintentional radiator" -- even things like
> christmas lights!
>
> I'd wonder if someone wasn't (naively) putting a bunch of hash out.
> The "45 minutes" sounds like someone might be "doing something"
> (or USING something) for a short period. The "2 days" suggests it
> got left *on*!

I agree, but when it is not on it can't be found.

> I lived in a house with the garage located beneath the master bedroom.
> Vacuuming the carpet in the MBR would often result in the garage door
> opening. We'd come out, the next morning, to leave for work and
> wonder which of us had "*left* the door open"! (Ans: neither)
>
>> There is a local airport with control tower about 2 miles away.
>
> Possible. Why not go sniffing for signals? TV or radio stations
> nearby?

No Radio or TV nearby. Closest TV station is 6 miles as the crow flies.
But I would think that if something that far away would have a much
broader area effected rather than this very small area of maybe 6 homes.
At least that I know about at this time.

It would make more sense that what ever it is would be located in
one of the nearby houses that is radiating out 306 degrees, but What??
And Where??

>
>> I say a small area (200' square box maybe??) but it could be effecting
>> a larger area but I have no way to know or to find out without having
>> a town meeting.
>>
>> Any thoughts on the subject would be most helpful.
>
> When the problem next manifests, try to shield the affected unit.
> This would at least give you an idea if the interference was radiated
> or conducted. In most places, several homes are fed from a single
> transformer. So, your line is a direct reflection of what's happening
> in your neighbor's homes. Neighbors served by *another* transformer
> will have two transformers acting to attenuate signals between your
> home and theirs.
>
> [Here, it's 4 homes per xformer -- and I can easily deduce which
homes are
> serviced "together" (or service is all below grade)]

This a new 55 and over community that was new in the past 3 years or so.
Houses are rather close and streets are narrow. As things always seem
to go it was first thought that the new security system that I was
installing was the cause of the problem with the Door Opener.........

I have more time in this problem trying to find the source or just
pondering the problem than I want to think about. Total LO$$!!

It is horrible when you can't measure it, see it, touch it, taste it
or even smell it!!!

BTW I may have forgotten to mention that there are two Door Openers in
this house and both react exactly the same way.

From what I gather at this time is that it may be one of the following.

Military Radar
RF Newbie building a new toy
TV tower sending out a bad signal
Christmas lights turned on during the spring/summer
Old bad Florescent Light Ballast producing bad RF
Electronic Music Box with no FCC approvals turned on infrequently
Something else that I can fathom!!!

Question: How would I "shield the affected unit" as suggested??
Tin Foil around the opener??
Tin Foil over the wireless door transmitter??
Place a metal box over the antenna on the security receiver??

How is that going to determine if the interference was radiated or
conducted??

Thanks for any input!!

Les

[ABLE1]

boB wrote:

Buy one of those $50 (ish) Tiny SA Spectrum alalyzers and see if
there is any RF signals around that frequency above the level there is
when the door IS working and compare.

That would tell you something. Then you could either get a
directional antenna for it or possibly drive around the neighborhood
trying to find where the signal gets stronger.

But first you need to see if nearby RF interference is even the issue
and what it looks like.

I wonder if there are any high power transmitter near by on another
frequency that could de-sense this garage door receiver ? Overload,

boB

===================================================================
I got a $20 (ish) thingie that has a colored LED bar when RF is
detected. It has a adjustment knob that you can dial up or down the
signal strength. Presently the customer has it but the nasty is not
going on so using it doesn't find anything other than the microwave is
turned on and it lights up when close.

The challenge is that it may not happen for another 2 years. Really
difficult/impossible to find the source when it's not there.

Thanks for the input!!

Les

[Don Y]

On 7/17/2021 5:07 PM, Clifford Heath wrote:
> On 18/7/21 6:03 am, Don Y wrote:
>> On 7/17/2021 4:53 AM, Clifford Heath wrote:
>>> IDK if it's useful to you, but the open source "rtl_433" software can
>>> demodulate and decode many of these types of keyfobs. Hundreds, anyway.
>>>
>>> I suspect that reading the code would give you a lot of insight into the
>>> variety of encodings used. You could even get an RTL dongle and listen in.
>>
>> Hmmm... I don't know. I will have to think about what I could do with that
>> capability. And, if I could use it "in production" to make the device
>> more usable (?).
>
> I don't think you want to run an SDR as a receiver. I only meant that you could
> read the code to learn about the types of encodings that have been used.

I've already planned several SDR-based receivers. It lets me adapt the
hardware to the *present* reception needs.

But, watching for a "remote" to be activated is something that can't
easily be "scheduled" (like listening to an HD FM broadcast vs. tuning
a TV's audio or listening to WWV/CHU or...). So, it would require
pretty much dedicating a receiver to that purpose (or, sharing one with
some other low-occurrence use)

>> E.g., I am frequently working in the garage. I don't want someone
>> "coming home" to open the door and drive in (I may be accessing the
>> ceiling area ABOVE the raised garage door so would be harmed by its
>> opening).
>
> Door openers have "stuck" detectors that shut the motors down when there is a
> blockage. If your door is installed in a way that any operation is unsafe, you
> should fix that before worrying about how to control it.

Most detection is focused on preventing the door from closing on
an obstacle in its path. Often, their remedy is to *open* when
that is detected. It's not as common for someone to be in the path of
a *rising* door!

I've also noticed that the "sense" is pretty sluggish wrt activation.
E.g., if I was working directly in the plane of the door but *above* it,
I am sure I would be injured before the door even noticed that it had
hit me or knocked me from my ladder.

The point is to provide ADVANCE knowledge of problem situations
instead of relying on the opener itself to detect them, after the
fact. The methods that it uses are pretty crude (like
parking a car by noticing when you *hit* something!)

[Don Y]

IIRC, the fob (or at least *some* fobs) have a handshake with the
vehicle. So, the fob doesn't have to be emitting signal constantly;
instead, it waits to be "woken up" by the car.

I read of an attack whereby a tag team of hackers can gain access to
a vehicle by shadowing the owner as he/she exits the vehicle. The
party closest to the owner has a transponder in their possession
while their accomplice has the other end of the link in his
possession -- and has placed himself in close proximity to the vehicle's
door.

The probe from the car jumps the gap between the two accomplices
and makes the car think the owner is located nearby -- because
it acts as a simple "range extender" for both car and fob.

The accomplice at the vehicle opens the door and then steps in
to the driver's position and engages the ignition. Again, the
transponders extend the range so the car thinks the owner is
seated within. Car starts. Driver goes around to fetch his
partner and they drive off.

All is well until the engine is shut off -- at which point,
it can not be restarted. But, if your goal is to drive it
to a chop-shop (or use it to rob a bank), that single use
may be all you need!

[Clifford Heath]

Stop, is as common as reverse.

> It's not as common for someone to be in the path of
> a *rising* door!

Right, the overload sensor is weaker or inactive on open, because it's
safer for a door to be open than closed, so more important to reach that
state against whatever resistance.

> E.g., if I was working directly in the plane of the door but *above* it,

Then your door is unsafe already. It should be boxed in so that you
cannot be above it. There's not a good electronic solution to that.

Clifford Heath.

[Rick C]

On Saturday, July 17, 2021 at 9:54:28 PM UTC-4, Don Y wrote:
> I've already planned several SDR-based receivers. It lets me adapt the
> hardware to the *present* reception needs.
>
> But, watching for a "remote" to be activated is something that can't
> easily be "scheduled" (like listening to an HD FM broadcast vs. tuning
> a TV's audio or listening to WWV/CHU or...). So, it would require
> pretty much dedicating a receiver to that purpose (or, sharing one with
> some other low-occurrence use)

You don't need to dedicate a receiver if there are other tasks that can be done on a duty cycle. The first step is to scan for energy above a threshold. That can be done over the band of interest on a low duty cycle. When energy is detected it then needs to have a drop receiver tuned to see if it is a signal of interest. I don't know the modulation scheme used in these things, probably ASK which doesn't even need a dedicated receiver. The signal can be sampled periodically to recover the modulated data.

> Most detection is focused on preventing the door from closing on
> an obstacle in its path. Often, their remedy is to *open* when
> that is detected. It's not as common for someone to be in the path of
> a *rising* door!

They do care if the door is stuck for any reason. It can signal a failure that might prove dangerous, so the door is stopped. That's how mine works. I think it is a bit crude though since it relies on the motor pulling on it's mounts. The sensitivity is limited by the natural factors in the mechanism.

> I've also noticed that the "sense" is pretty sluggish wrt activation.
> E.g., if I was working directly in the plane of the door but *above* it,
> I am sure I would be injured before the door even noticed that it had
> hit me or knocked me from my ladder.
>
> The point is to provide ADVANCE knowledge of problem situations
> instead of relying on the opener itself to detect them, after the
> fact. The methods that it uses are pretty crude (like
> parking a car by noticing when you *hit* something!)

Yeah, when your sidewall scrubs against the curb. Isn't that how everyone does it? I had a boss once who had to replace tires because he wore out the sidewalls. He might have learned the lesson, or maybe not. It's odd that Teslas don't let you see the sides at the curb when parking. But then if you have the time to let it, the car will in theory parallel park itself!!!

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

[Rick C]

On Saturday, July 17, 2021 at 10:00:28 PM UTC-4, Don Y wrote:
> IIRC, the fob (or at least *some* fobs) have a handshake with the
> vehicle. So, the fob doesn't have to be emitting signal constantly;
> instead, it waits to be "woken up" by the car.
>
> I read of an attack whereby a tag team of hackers can gain access to
> a vehicle by shadowing the owner as he/she exits the vehicle. The
> party closest to the owner has a transponder in their possession
> while their accomplice has the other end of the link in his
> possession -- and has placed himself in close proximity to the vehicle's
> door.
>
> The probe from the car jumps the gap between the two accomplices
> and makes the car think the owner is located nearby -- because
> it acts as a simple "range extender" for both car and fob.
>
> The accomplice at the vehicle opens the door and then steps in
> to the driver's position and engages the ignition. Again, the
> transponders extend the range so the car thinks the owner is
> seated within. Car starts. Driver goes around to fetch his
> partner and they drive off.
>
> All is well until the engine is shut off -- at which point,
> it can not be restarted. But, if your goal is to drive it
> to a chop-shop (or use it to rob a bank), that single use
> may be all you need!

That won't work well for a Tesla. The car reports it's location all the time. I can tell when my friend drives it. It would result in the location of the chop shop being the last reported location before they ripped the car apart.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

[Lasse Langwadt Christensen]

you mean the location where they made a stop to cut the GPS antenna

[Rick C]

Where's the GPS antenna?

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

[Lasse Langwadt Christensen]

I don't k now, people who steal and chop Teslas will know

[Rick C]

And how many are there of those?

In addition to being very hard to steal, the car has access to all the serial numbers of all the parts. So put a stolen part in your car and it can be reported to Tesla where stolen part serial numbers are noted. There's no market for stolen parts, so no Tesla chop shops.

Maybe stolen parts will be a bigger business when Tesla goes under and no longer tracks part SNs.

All you had to do was do a simple Google search and you would have learned a bit about this rather than post a bunch of nonsense.

[Don Y]

The doors I have seen reverse when detecting an object on closing.
You wouldn't want to STOP and *pin* a young child between the
door and the ground.

>> It's not as common for someone to be in the path of
>> a *rising* door!
>
> Right, the overload sensor is weaker or inactive on open, because it's safer
> for a door to be open than closed, so more important to reach that state
> against whatever resistance.

But *any* activity of a rising door would easily topple a person
standing on a ladder, body in the path of that door.

>> E.g., if I was working directly in the plane of the door but *above* it,
>
> Then your door is unsafe already. It should be boxed in so that you cannot be
> above it. There's not a good electronic solution to that.

There is no way to avoid this -- it is common for most "torsion spring"
doors (the spring is located directly above the door, in the plane of the
door). The GDO typically fastens to the front/outer wall of the garage
above this spring.

<https://www.doormaticgaragedoors.co.uk/wp-content/uploads/2019/02/garage-door-torsion-spring-e1549368222571.jpg>

[Note that to be a UK source so I suspect it is not uncommon for
MOST garage doors to be implemented in this fashion!]

In *this* house, there isn't much "above the door" that would
need to be accessed. But, other homes in the neighborhood have
"storage spaces" (attics) above the door (the horizontal tracks
depicted along the side of the door pictured above). I grew up
in a home where it was not uncommon for someone to have a tall
ladder sited below the opening in the garage ceiling to climb
into the attic space. Any motion of the door would easily
topple that person from the ladder

I like being overly cautious in designs, implementations, etc.
I have several down-facing cameras located in the garage to
"examine" the floor when each "stall" is vacant. Prior to opening
the door, the area to be occupied by the vehicle (as determined
from a union of all previous images of the vehicle parked *in*
that spot) is checked for "differences" (from "clear of any
obstacles"). If anything is found (even if it is a *leaf* cuz
I haven't invested much time in the detector), the driver is
alerted to the presence of a potential hazard.

I have the RGBW version of this:
<https://www.lumenpulse.com/products/2242/lumenbeam-lbx-color-changing>
outfacing in the garage to attract the driver's attention. Along
with a 120dB siren (which might not be audible to a deaf driver! But,
ANY driver should be able to *see*! :> )

Had I been more forward thinking, I would have grabbed a couple more
of them ("What the hell can I use a 100W LED floodlight for?? <shrug>
Dunno. But, it looks cool so I'll take one and figure out if I
can use it, later...")

I've watched a lot of "accidents", over the years, that could have
been prevented if someone could have better seen the environment
in which they were operating.

[On one occasion, I *watched* a neighbor run over his young son (!).
Sadly, I was helpless to do anything to warn him -- or the son -- as
I was under my vehicle, at the time, replacing the starter. Even
my scream was muted by the two tons of steel on top of me!]

Given that cameras and other tech are relatively cheap, it seems
foolish *not* to deploy them liberally -- if you can have something
"smart" monitoring the images!

Unfortunately, I didn't have any of this kit in place when my other half
drive out of the garage with the hatchback open -- striking the
garage door in the process! (didn't she notice the car telling
her that the hatch was open??? <rolls eyes>)

[Don Y]

On 7/17/2021 6:14 PM, ABLE1 wrote:
> On 7/17/2021 5:19 PM, Don Y wrote:
> > On 7/17/2021 6:07 AM, ABLE1 wrote:
> >> Hello, I find this VERY interesting. I won't go into the whole story
> >> since it is very long but I have a customer that has an alarm system
> >> that I installed. It has wireless sensors for doors and such.
> >> There has been a few times that the system does not receive signals
> >> from the transmitters for periods of time from 45 minutes to 2 days.
> >
> > 2 *days*? Are you sure someone isn't (illegally) operating
> > a transmitter, nearby?
> >
> That is a possibility. Again finding and proving is the challenge.

You need to go on a snipe hunt! :>

(seriously, though) Don't rule out something that shouldn't exist
(i.e., illegal or undesirable). Remember, there are lots of things
that are legit but that have to take measures to mitigate their
interference *if* they are interfering (this inherently assumes
there WILL be such things!)

In the 80's, a neighbor once inquired, "What the hell have you got
in there?" (meaning my house). I looked at him, puzzled. Apparently,
when he'd drive by, his scanner (?) would unsquelch with lots of
hash. At the time, everything that I had was COTS gear (though a
fair bit of it!) so I didn't feel like it was something I'd *designed*
that was giving him grief.

But, it is likely a processor/sequencer that is driving the LED; not
an "RF detector". (?) So, one has to wonder what assumptions went into
that design aspect.

I.e., if you use a WRONG remote (when the interference is not present)
and hold the remote actuated, does the LED stay lit? I.e., indicating
RF even though it is not CORRECT RF?

> Normally the LED
> is off. During my observation at the 45 minute period. The handheld
> remote would not work unless it was held up within 18" of the antenna.
> Also the Subaru header button did not work. There were two house doors
> that would not communicate the doors were open or closed to the security
> panel during this time. At the same time the next door neighbor's garage
> remote would not work. Then the LED started to blink and then
> off. Door contacts then worked as they should. The event was over
> and as I am aware has not returned.

You need to understand the criteria that cause the LED to illuminate.
Not just the *intended* criteria but the ACTUAL criteria -- as it is
the only EASY indicator to which you have access.

You're still going to need to go on a snipe hunt. If you had a spare
GDO ("parts"), you could wire the controls to a battery and wander around
the neighborhood using the LED as your crude indicator.

A better solution is to just get proper kit and do it right.
If you find an "offender", lodging a complaint will likely
have more standing if you can say "he was putting out X at Y MHz"
instead of "my GDO didn't work because of something I *think*
he was doing"

> >> The security devices are on 319.5 Mhz and the door opener is on 318 Mhz.
> >>
> >> Is there any thoughts here as to what other than Military Radar that
> >> could be causing this issue with such intensity in a small area??
> >
> > Almost anything can be an "unintentional radiator" -- even things like
> > christmas lights!
> >
> > I'd wonder if someone wasn't (naively) putting a bunch of hash out.
> > The "45 minutes" sounds like someone might be "doing something"
> > (or USING something) for a short period. The "2 days" suggests it
> > got left *on*!
> I agree, but when it is not on it can't be found.

Capture the available data when you can -- even the "normal" situation
may reveal an offender some N dB down! Without any real data, you're
just "complaining" and hoping something else identifies (or eliminates)
the problem.

> > I lived in a house with the garage located beneath the master bedroom.
> > Vacuuming the carpet in the MBR would often result in the garage door
> > opening. We'd come out, the next morning, to leave for work and
> > wonder which of us had "*left* the door open"! (Ans: neither)
> >
> >> There is a local airport with control tower about 2 miles away.
> >
> > Possible. Why not go sniffing for signals? TV or radio stations
> > nearby?
> No Radio or TV nearby. Closest TV station is 6 miles as the crow flies.
> But I would think that if something that far away would have a much
> broader area effected rather than this very small area of maybe 6 homes.
> At least that I know about at this time.
>
> It would make more sense that what ever it is would be located in
> one of the nearby houses that is radiating out 306 degrees, but What??
> And Where??

Ask yourself what the afflicted homes share in common.
Note that one of the "victims" may, in fact, turn out to be the
*culprit*!

> >> I say a small area (200' square box maybe??) but it could be effecting
> >> a larger area but I have no way to know or to find out without having
> >> a town meeting.
> >>
> >> Any thoughts on the subject would be most helpful.
> >
> > When the problem next manifests, try to shield the affected unit.
> > This would at least give you an idea if the interference was radiated
> > or conducted. In most places, several homes are fed from a single
> > transformer. So, your line is a direct reflection of what's happening
> > in your neighbor's homes. Neighbors served by *another* transformer
> > will have two transformers acting to attenuate signals between your
> > home and theirs.
> >
> > [Here, it's 4 homes per xformer -- and I can easily deduce which homes are
> > serviced "together" (or service is all below grade)]
> This a new 55 and over community that was new in the past 3 years or so.
> Houses are rather close and streets are narrow. As things always seem
> to go it was first thought that the new security system that I was installing
> was the cause of the problem with the Door Opener.........
>
> I have more time in this problem trying to find the source or just
> pondering the problem than I want to think about. Total LO$$!!

Customers... gotta love 'em! (not!)

> It is horrible when you can't measure it, see it, touch it, taste it
> or even smell it!!!
>
> BTW I may have forgotten to mention that there are two Door Openers in
> this house and both react exactly the same way.
>
> From what I gather at this time is that it may be one of the following.
>
> Military Radar

Or radio

> RF Newbie building a new toy

Or, some COTS bit of kit that was shoddily made, operated with
it's covers off, etc.

> TV tower sending out a bad signal
> Christmas lights turned on during the spring/summer
> Old bad Florescent Light Ballast producing bad RF

New *electronic* ballast

> Electronic Music Box with no FCC approvals turned on infrequently
> Something else that I can fathom!!!
>
> Question: How would I "shield the affected unit" as suggested??
> Tin Foil around the opener??
> Tin Foil over the wireless door transmitter??
> Place a metal box over the antenna on the security receiver??

You'd ideally like to understand how it's getting *into*
the device. Is it conducted? Radiated? Coming in via
the antenna? Some unintended "loop" in the wiring/PCB?

> How is that going to determine if the interference was radiated or conducted??

If you put it in a box and ground the box, then the only way in is via
"wires". You can verify this, to some extent, by enclosing the
device *now*. Then, try to use the remote to actuate it.
Can the remote penetrate your shield? (it is using *radiated*
emissions only!)

[Don Y]

On 7/17/2021 4:52 PM, boB wrote:
> Buy one of those $50 (ish) Tiny SA Spectrum alalyzers and see if
> there is any RF signals around that frequency above the level there is
> when the door IS working and compare.

Yup. Starting with *data* is always a good plan! If this is a
business, then it's hard NOT to justify having the necessary tools
on hand. Don't worry... you;ll need them AGAIN, sooner or
later!

[I opted not to use any wireless technologies in my current project.
Instead, ran ~5000 ft of CAT5 so "interference" won't be an issue
(or, if it is, it's likely an EMP the next block over! :-/ ) ]

[Clifford Heath]

On 18/7/21 1:52 pm, Don Y wrote:
> On 7/17/2021 7:49 PM, Clifford Heath wrote:
>> On 18/7/21 11:54 am, Don Y wrote:
>>> On 7/17/2021 5:07 PM, Clifford Heath wrote:
>>>> On 18/7/21 6:03 am, Don Y wrote:
>>>> Door openers have "stuck" detectors that shut the motors down when
>>>> there is a blockage. If your door is installed in a way that any
>>>> operation is unsafe, you should fix that before worrying about how
>>>> to control it.
>>>
>>> Most detection is focused on preventing the door from closing on
>>> an obstacle in its path.  Often, their remedy is to *open* when
>>> that is detected.
>> Stop, is as common as reverse.
> The doors I have seen reverse when detecting an object on closing.

I've had one like that, but the one I have now (major Australian
roller-door brand) just stops.

>>> E.g., if I was working directly in the plane of the door but *above* it,
>> Then your door is unsafe already. It should be boxed in so that you
>> cannot be above it. There's not a good electronic solution to that.
>
> There is no way to avoid this -- it is common for most "torsion spring"

It could still be boxed in, but ok (there's no free space above in the
picture you showed). I was talking about roller doors, not the kind you
have shown. They'd need only a much smaller box. My one doesn't have
space above anyhow - the ceiling is only just high enough for the door
anyhow.

And I understand you're talking about e.g. tall cupboards on the side
wall adjacent to the door.

> Unfortunately, I didn't have any of this kit in place when my other half
> drive out of the garage with the hatchback open -- striking the
> garage door in the process!  (didn't she notice the car telling
> her that the hatch was open???  <rolls eyes>)

Yes, well, there was one time my (learner driver) son decided he could
push the car out of the garage instead of going inside for the key to
start it. The open driver's door hit the side of the opening and bent
the door panel...

You can try as hard as you like to make things foolproof, but fools will
always outsmart you.

CH

[Piglet]

Did the poster describing the 45mins/2 days outage say if other RF
services were affected? Interference is often broadband rather than
narrowband and if 318MHz was blighted by broad noise emitters it may
even have been audible on FM broadcast receivers?

piglet

[Don Y]

On 7/17/2021 11:54 PM, Clifford Heath wrote:
>>> Stop, is as common as reverse.
>> The doors I have seen reverse when detecting an object on closing.
>
> I've had one like that, but the one I have now (major Australian roller-door
> brand) just stops.

Different markets, different products, different expectations.

>>>> E.g., if I was working directly in the plane of the door but *above* it,
>>> Then your door is unsafe already. It should be boxed in so that you cannot
>>> be above it. There's not a good electronic solution to that.
>>
>> There is no way to avoid this -- it is common for most "torsion spring"
>
> It could still be boxed in, but ok (there's no free space above in the picture

Of course there's free space! The tracks don't run *along* the ceiling!
So, the difference between door height and ceiling height is "free space".

Here, I have light fixtures, retractable power cords and cameras mounted
*on* the ceiling in that space above the horizontal rails.

My neighbors have "shelves" (for want of a better word -- platforms
anchored to the ceiling by poles, hanging down above the opened door).
Another has access to the attic space above the garage through a
hole cut in the ceiling above the (opened) door.

> you showed). I was talking about roller doors, not the kind you have shown.
> They'd need only a much smaller box. My one doesn't have space above anyhow -
> the ceiling is only just high enough for the door anyhow.

I've no idea what a roller door is. Most doors, here, are segmented
(so they partially "fold" as they ride up the curved tracks). Some
older ones will be unsegmented and tilt up and in as one solid sheet.
In the country, you might find some doors that open like regular
"people" doors (hinged on the sides).

<https://gds-repair.com/wp-content/uploads/2017/05/Untitled.jpg>

The left being a segmented door; the right being a solid one.

> And I understand you're talking about e.g. tall cupboards on the side wall
> adjacent to the door.

No. In my case, there are light fixtures above the door that are
useless (for throwing light) when the door is raised -- but very effective
at illuminating that front half of the garage when the door is closed.
(otherwise, the lighting has to come from further inside the garage...
out beyond the point where the top edge of the opened door would rest).

As my walls are floor to ceiling industrial shelving, the only place
for electric outlets is *away* from the wall -- which means on the ceiling.
So, I have retractable "cord reels" sited along the ceiling so you
can pull a power cord down to the ground and use it to power some
device. Again, those cords that are close to the garage door *opening*
are obstructed when the door is raised. But, those are typically the
places you would want power -- to work on the engine (we back into
the garage so the front of the car is closest to the door opening)
If you had to access a cord located far enough *into* the garage
to clear the opened door, you'd need another 8 feet of cord to reach
the point you wanted to use the power!

We don't have basements, here -- and the layout of this house is
pretty "open". So, there aren't many places to *hide* things.
The garage (even with an insulated door) tends to be hot much
of the year. So, *what* you store out there has to be considered
carefully.

Big things (my electric wheelchair, power washer, genset, etc.)
obviously need to sit on the floor -- raising them off the
floor would pose a challenge getting them up *and* down, intact.
And, space on the shelving units disappears *fast* (e.g., we store
our paper products out there, insecticides, cables, power cords,
fully one third of the shelving is devoted to hand tools, etc.).

[Did I mention I worked for a hand tool company in a previous life?]

So, anything that is relatively lightweight hangs from the ceiling.
All of my extension cords are stored thusly. They're hard to get
down and put back up (ceiling is very high) but a pole with a
hook is sufficient to "unhook" them from their hangers.

The cargo cover for the SUV (it's like a horizontal window shade
that "hides" what you have in the back of the vehicle) sits up there
when not in the car. There's a giant styrofoam "spare tire" that
came with the car (spare tire was an optional purchase; now that
*it* fills that space in the trunk, where do we put this big piece
of styrofoam that had been there as a "filler"?). Jumper cables.
Drop light. Fruit picker. Extension pole for painting the roof.
Hoses. etc.

The garage door, when raised, obstructs fully half of the ceiling
space. So, stuff ends up above it. Access it while the door is down;
don't let the door raise while you're tinkering around up there!

[The trick is to make it *look* like everything you've "stored"
actually BELONGS there! I'd love to store the ladders up there
but am wary that I'll get careless when taking them down (or putting
them back up) and drop one on one of the cars.]

[[Many people have effectively converted their garages into
"two-car closets"!]]

I frequently find myself looking for "more space"... then remind
myself that I should be getting RID of things, not acquiring
MORE! <frown> (I have *way* too much shit^H^Hstuff!)

>> Unfortunately, I didn't have any of this kit in place when my other half
>> drive out of the garage with the hatchback open -- striking the
>> garage door in the process! (didn't she notice the car telling
>> her that the hatch was open??? <rolls eyes>)
>
> Yes, well, there was one time my (learner driver) son decided he could push the
> car out of the garage instead of going inside for the key to start it. The open
> driver's door hit the side of the opening and bent the door panel...

A neighbor drove his car through his garage door, on returning home
(you're supposed to STOP before you get to the door!)

Another neighbor (different location) backed out of his garage -- before
opening the door.

There are lots of ways to screw yourself without actually being careless.
E.g., I can't tell if the garage door is fully raised when I am backing into
the garage (a modification I need to make to my design). If the GDO
encountered a fault and stopped partially open, I'd not know until the
back of the car (SUV) collided with the lower part of the door.

"Something" watching can eliminate these sorts of problems. And, protect
the "elderly" (senile, dementia, etc.) from the sorts of careless errors
like driving into a closed door!

> You can try as hard as you like to make things foolproof, but fools will always
> outsmart you.

Of course! I worked for a hand tool manufacturer many years ago.
The stories of people using lawnmowers to trim hedges are more fact
than fiction!

Growing up, I had a friend who got the bright idea that he could "explode"
some .22 calibre rounds by hammering on them (!). Yes, it works quite well!
But, leaves you with no control over where the *bullet* goes. In his case,
it went up his arm. Not the sort of thing you want to tell Daddy...

[Spehro Pefhany]

On Sat, 17 Jul 2021 09:07:41 -0400, ABLE1 <some...@nowhere.net>
wrote:

>On 7/16/2021 6:46 PM, Dave Platt wrote:
>> The primary frequency-user here is military radar, and secondary is
>> amateur radio. One occasionally sees stories about military radar
>> operations disrupting peoples' garage door openers and car
>> alarm/locking systems in some areas. The commonest problems seem to
>> be "they don't work" (the strong radar signals saturate the receivers)
>> but "undesired operation" occurs occasionally (garage doors opening
>> "by themselves").

>
>
>Hello, I find this VERY interesting. I won't go into the whole story
>since it is very long but I have a customer that has an alarm system
>that I installed. It has wireless sensors for doors and such.
>There has been a few times that the system does not receive signals
>from the transmitters for periods of time from 45 minutes to 2 days.

>During this time their garage door opener remote does not work unless
>you hold it in you hand reach up to within 18" of the opener antenna
>and then it will work.

Reminds me of when I found one day that my garage door opener would
open, but not close the garage door. After waiting 5 minutes, it would
then close it.

Turns out that replacing the incandescent bulb in the opener with a
CFL bulb (yes that long ago) caused enough EMI to saturate the front
end of the receiver and it would not longer work while the bulb was
on.

I currently have LED bulbs in the other garage lighting and it works
okay, but I guess the bulb physically in the unit, plus the probably
crummy bulb design, was enough to kill the receiver temporarily.

So maybe there is an *unintentional* emitter somewhere that is causing
the loss in sensitivity

--
Best regards,
Spehro Pefhany

[Martin Brown]

On 18/07/2021 02:14, ABLE1 wrote:
> On 7/17/2021 5:19 PM, Don Y wrote:
> > On 7/17/2021 6:07 AM, ABLE1 wrote:
> >> Hello, I find this VERY interesting.  I won't go into the whole story
> >> since it is very long but I have a customer that has an alarm system
> >> that I installed.  It has wireless sensors for doors and such.
> >> There has been a few times that the system does not receive signals
> >> from the transmitters for periods of time from 45 minutes to 2 days.
> >
> > 2 *days*?  Are you sure someone isn't (illegally) operating
> > a transmitter, nearby?
> >
> That is a possibility.  Again finding and proving is the challenge.

One cheap way would be to buy one of the TV tuner dongles that can be
subverted with suitable free software into a broadband SDR with a
waterfall display that will show you if there is anything jamming the
band used by your garage door TX. Or for that matter any very strong
signals that might overload the front end of its receiver.

That several neighbours have the same problem suggests local RF
interference jamming the door opener signal. It might be possible to
move your transmitters close enough to the receiver to overcome it.

> It would make more sense that what ever it is would be located in
> one of the nearby houses that is radiating out 306 degrees, but What??
> And Where??

What is allowed on that frequency in the USA?

--
Regards,
Martin Brown

[ABLE1]

Hi,
Being the OP the answer is during the time I had not thought about
turning on a radio AM/FM to see if any bad noise was happening.
However, now that the suggestion has been made I will keep that in
mind should it happen again.

For me not knowing is there a FM frequency that would be effected more
than another if 319.5mhz and 318mhz was effected?? I have heard of
frequency doubling or something that happens so that a range RF like
159mhz or 79.5mhz could effect 318mhz in someway if it is strong enough.

Is it possible that could hold true in this case??

Thanks,

Les

[Clifford Heath]

On 18/7/21 6:46 pm, Don Y wrote:
> On 7/17/2021 11:54 PM, Clifford Heath wrote:
>>>> Stop, is as common as reverse.
>>> The doors I have seen reverse when detecting an object on closing.
>>
>> I've had one like that, but the one I have now (major Australian
>> roller-door brand) just stops.
>
> Different markets, different products, different expectations.
>
>>>>> E.g., if I was working directly in the plane of the door but
>>>>> *above* it,
>>>> Then your door is unsafe already. It should be boxed in so that you
>>>> cannot be above it. There's not a good electronic solution to that.
>>>
>>> There is no way to avoid this -- it is common for most "torsion spring"
>>
>> It could still be boxed in, but ok (there's no free space above in the
>> picture
>
> Of course there's free space!  The tracks don't run *along* the ceiling!
> So, the difference between door height and ceiling height is "free space".

Ok, yeah, I think my Dad might have had some storage above there too,
but he had a bit more clearance. His door wasn't segmented though and I
recall it was pivoted in a way that the door protruded above the tracks
while opening, before being fully open.

>> you showed). I was talking about roller doors, not the kind you have
>> shown. They'd need only a much smaller box. My one doesn't have space
>> above anyhow - the ceiling is only just high enough for the door anyhow.
>
> I've no idea what a roller door is.

E.g. (first decent picture I found)
<https://www.totalspan.com.au/media/latest-news/clearance-for-roller-doors/>

>> And I understand you're talking about e.g. tall cupboards on the side
>> wall adjacent to the door.
>
> No.

Well, I still wouldn't want to be accessing side cupboards using a
ladder when the door operated.

> All of my extension cords are stored thusly.  They're hard to get
> down and put back up (ceiling is very high)

We made the ceiling 10cm higher in my basement garage by lowering the
floor, but it's still just barely an 8' ceiling (actually enough to be
lined and still be 8'). No real high storage, but I have almost
900foot^2 (76m^2) and only a single-width garage door. That's floor area
for four cars, but access for only one. When we went away for three
months once I got the boat&trailer and *both* cars in there, but it
wasn't easy.

> There's a giant styrofoam "spare tire" that
> came with the car (spare tire was an optional purchase; now that
> *it* fills that space in the trunk, where do we put this big piece
> of styrofoam that had been there as a "filler"?).

Surely you have no good reason to keep it? I mean, is it good as a
swimming pool toy?

Anyhow, this isn't really electronics design any more. Except that most
of my not-yet-started project resources are down there.

CH.

[ABLE1]

On 7/18/2021 5:36 AM, Martin Brown wrote:
> TV tuner dongles that can be subverted with suitable free software into
> a broadband SDR with a waterfall display

TV tuner dongles that can be subverted with suitable free software
into a broadband SDR with a waterfall display

That is totally over my head.

I am sure it may be simple....................?? But??

If this issue were happening frequently or on some schedule putting
together some kind of tracking device may be a way. But with the
present condition of all is good, that can't happen.

Thanks,

Les

[ABLE1]

On 7/18/2021 12:38 AM, Don Y wrote:
> But, it is likely a processor/sequencer that is driving the LED; not
> an "RF detector".  (?)  So, one has to wonder what assumptions went into
> that design aspect.
>
> I.e., if you use a WRONG remote (when the interference is not present)
> and hold the remote actuated, does the LED stay lit?  I.e., indicating
> RF even though it is not CORRECT RF?

Very good thought!! I will try that the next time I am in the area.
Won't find the problem, but will give more information or input.

Thanks,

Les

[ABLE1]

On 7/18/2021 12:38 AM, Don Y wrote:
>

> Ask yourself what the afflicted homes share in common.
> Note that one of the "victims" may, in fact, turn out to be the
> *culprit*!

Good point!! Now that the "neighbor's" have been discussing the
situation that is happening, it is possible the "offender" is now
aware and had stopped or fixed the issue. That would be GREAT!!

Although then it will never be known what or who was causing it!!

And at that point it really doesn't matter anymore.

At least I can sleep nights!!

Thanks!!

Les

[Michael Terrell]

On Saturday, July 17, 2021 at 3:43:08 PM UTC-4, Don Y wrote:
>
> Many years ago, we discovered that *our* remote would open our
> GDO *and* the neighbor across the street! I'm still unsure
> as to how this could have happened. I.e., even if he happened to
> have been in "programming mode" when we (drove in/out and) actuated
> *our* GDO, he would have known that his remote wasn't working properly
> and would have tried again.

The oldest remotes only generated an AM modulated signal. You could adjust the audio frequency to prevent interaction. Linear was one big maker of these systems, well into the '80s. I used to repair the receivers for a local garage door company. The biggest problem was a bad electrolytic, in the unregulated power supply, followed by frequency drift due to aging. After that, the 40673 dual gate MOSFET was bad, or the output relay. Since Wireless openers were still fairly rare, it provided enough security.
One system was real fun. It was for a firehouse, with four bays. I was asked to fix it, since the trucks had to roll up to the doors to get it to work. After a careful alignment, they could open any door from a little over a block, away.

[Tom Gardner]

On 18/07/21 13:07, ABLE1 wrote:
> On 7/18/2021 5:36 AM, Martin Brown wrote:
>> TV tuner dongles that can be subverted with suitable free software into a
>> broadband SDR with a waterfall display
>
>  TV tuner dongles that can be subverted with suitable free software into a
> broadband SDR with a waterfall display
>
> That is totally over my head.
>
> I am sure it may be simple....................??  But??

One of many starting points:
https://www.rtl-sdr.com/about-rtl-sdr/

[Don Y]

On 7/18/2021 5:18 AM, ABLE1 wrote:
> On 7/18/2021 12:38 AM, Don Y wrote:
>>
>> Ask yourself what the afflicted homes share in common.
>> Note that one of the "victims" may, in fact, turn out to be the
>> *culprit*!
>
> Good point!! Now that the "neighbor's" have been discussing the
> situation that is happening, it is possible the "offender" is now
> aware and had stopped or fixed the issue. That would be GREAT!!

They may not be aware that they are *still* doing it. If it
was happening *daily* at 3AM, would anyone know?

> Although then it will never be known what or who was causing it!!
>
> And at that point it really doesn't matter anymore.
>
> At least I can sleep nights!!

Oh, nights are for *work*! :>

[Martin Brown]

And it is almost as simple as read the URL download the software and run
it. Bit of a learning curve but the display is easy to understand.

US Amateur Radio mags probably review slightly more user friendly
versions that cost a bit more and make it more or less plug and play.
(UK ones do anyway)

--
Regards,
Martin Brown

[ABLE1]

Ok as a "starting point". Just doing a search on "rtl sdr"
brings up the following link on eBay.

https://www.ebay.com/sch/i.html?_from=R40&_nkw=rtl+sdr&_sacat=1500&rt=nc&LH_PrefLoc=1

Not that I am going to do this but out of 525 possible choices
which one might be the best choice??

This is all rather foreign to me.

Thanks,

Les

[Don Y]

On 7/18/2021 5:04 AM, Clifford Heath wrote:
> On 18/7/21 6:46 pm, Don Y wrote:
>> On 7/17/2021 11:54 PM, Clifford Heath wrote:
>>>>> Stop, is as common as reverse.
>>>> The doors I have seen reverse when detecting an object on closing.
>>>
>>> I've had one like that, but the one I have now (major Australian roller-door
>>> brand) just stops.
>>
>> Different markets, different products, different expectations.
>>
>>>>>> E.g., if I was working directly in the plane of the door but *above* it,
>>>>> Then your door is unsafe already. It should be boxed in so that you cannot
>>>>> be above it. There's not a good electronic solution to that.
>>>>
>>>> There is no way to avoid this -- it is common for most "torsion spring"
>>>
>>> It could still be boxed in, but ok (there's no free space above in the picture
>>
>> Of course there's free space! The tracks don't run *along* the ceiling!
>> So, the difference between door height and ceiling height is "free space".
>
> Ok, yeah, I think my Dad might have had some storage above there too, but he
> had a bit more clearance. His door wasn't segmented though and I recall it was
> pivoted in a way that the door protruded above the tracks while opening, before
> being fully open.

I'm most often "up there" replacing lights (having completed all the
other wiring). Garage lights see lots of on/off, short cycles.
Apparently not good for fluorescent lamps. (I need to replace the
fixtures but haven't selected an alternative, yet)

>>> you showed). I was talking about roller doors, not the kind you have shown.
>>> They'd need only a much smaller box. My one doesn't have space above anyhow
>>> - the ceiling is only just high enough for the door anyhow.
>>
>> I've no idea what a roller door is.
>
> E.g. (first decent picture I found)
> <https://www.totalspan.com.au/media/latest-news/clearance-for-roller-doors/>

Ah! That would be more common in a business, here.

>>> And I understand you're talking about e.g. tall cupboards on the side wall
>>> adjacent to the door.
>>
>> No.
>
> Well, I still wouldn't want to be accessing side cupboards using a ladder when
> the door operated.

I tried to arrange for the commonly accessed items to be down
at "standing height". The items up high are far less commonly used:
the dozens of king-size bed sheets that we use to cover the citrus trees
in the winter; the laminator; the electric wok and frying pans (still in
original boxes); the ~50 canvas bags that we use when harvesting
fruit; the original bases for the monitors that are presently in use
(currently mounted on multi-headed stands); etc.

>> All of my extension cords are stored thusly. They're hard to get
>> down and put back up (ceiling is very high)
>
> We made the ceiling 10cm higher in my basement garage by lowering the floor,
> but it's still just barely an 8' ceiling (actually enough to be lined and still
> be 8'). No real high storage, but I have almost 900foot^2 (76m^2) and only a
> single-width garage door. That's floor area for four cars, but access for only
> one. When we went away for three months once I got the boat&trailer and *both*
> cars in there, but it wasn't easy.

Garage ceiling is easily over 10 ft. So, it's *really* tempting to
find a use for it -- given that the other storage options *in* the
house are scarce.

OTOH, the ceiling is essentially the roof rafters. So, you don't want
to put lots of load on it. Nor do you want to risk anything that
might fall *on* a vehicle within!

>> There's a giant styrofoam "spare tire" that
>> came with the car (spare tire was an optional purchase; now that
>> *it* fills that space in the trunk, where do we put this big piece
>> of styrofoam that had been there as a "filler"?).
>
> Surely you have no good reason to keep it? I mean, is it good as a swimming
> pool toy?

Keep it for when we sell the car. Without the spare in the trunk,
the "styrofoam spare" acts as a support for the (removable) floor
panel that provides access to that compartment. (when the spare
is in place, *it* acts as that support)

Likewise the "cargo cover" that we don't typically use (~4ft wide so
not the sort of thing you're going to put on a shelf).

> Anyhow, this isn't really electronics design any more. Except that most of my
> not-yet-started project resources are down there.

I still have some of my larger prototypes stored in the garage. But,
for the most part, don't store anything that the heat would
eventually "cook" ('lytics, mechanisms, etc.). Lots of text books
(cringe), the remaining paper files that haven't yet been
digitized, boxes of 9W XMAS lights (to keep the citrus "warm"),
hundreds of quart-sized bottles (to store fresh juice for freezing),
power tools, hand tools, assorted cables/power cords, etc.

WAY too much "stuff"! :< OTOH, it's really nice to be able to just grab
another patch cord, when needed. Or, USB3 cable. Or, VHDCI SCSI
cable... instead of having to go and *buy* one WHEN it is needed!

[Tom Gardner]

R820T2 is a good starting point.

They are a commodity item, all much of a muchness and suitable
for casual use.

There are some with a lower noise floor, but they are more
expensive and change over time. A metal case helps.

[Lasse Langwadt Christensen]

There's a whole industry build on electrifying old cars using Tesla parts, Tesla has no involvement
or any way of tracking those parts if they were stolen

>
> All you had to do was do a simple Google search and you would have learned a bit about this rather than post a bunch of nonsense.
> --

nonsense? I'm just saying that those who still bother with stealing cars probably know what
they are doing or they wouldn't be doing it very long.
Expensive cars have had gps tracking for many years. All the electronics modules, ecu, abs, gearbox, instrument cluster, rfid key, etc. are all matched so they won't work in any other car unless they get enabled with manufacturer codes. And in many places those who deal in used parts are required to track where and from who they got them.

[Don Y]

On 7/18/2021 5:50 AM, Michael Terrell wrote:
> On Saturday, July 17, 2021 at 3:43:08 PM UTC-4, Don Y wrote:
>>
>> Many years ago, we discovered that *our* remote would open our GDO *and*
>> the neighbor across the street! I'm still unsure as to how this could have
>> happened. I.e., even if he happened to have been in "programming mode"
>> when we (drove in/out and) actuated *our* GDO, he would have known that
>> his remote wasn't working properly and would have tried again.
>
> The oldest remotes only generated an AM modulated signal. You could adjust
> the audio frequency to prevent interaction. Linear was one big maker of
> these systems, well into the '80s.

What was so surprising about my neighbor's GDO locking to ours
(or, was it vice versa?) was that these are both rolling code
remotes -- unlikely to "coincidentally" be at the same points
in their code sequences!

[I never verified if they were the same make/model]

> I used to repair the receivers for a
> local garage door company. The biggest problem was a bad electrolytic, in
> the unregulated power supply, followed by frequency drift due to aging.
> After that, the 40673 dual gate MOSFET was bad, or the output relay. Since
> Wireless openers were still fairly rare, it provided enough security. One
> system was real fun. It was for a firehouse, with four bays. I was asked to
> fix it, since the trucks had to roll up to the doors to get it to work.
> After a careful alignment, they could open any door from a little over a
> block, away.

It's tempting to make a "remote" on steroids and war-drive the neighborhood
seeing how many GDOs you could trigger! And, have all those folks wonder
who (why) opened their door -- or, if they simply forgot to close it
the night before (then, return the NEXT day and repeat the exercise!)

[I had a friend who had bought some "super fuel efficient" car in the
70's. All he talked about was how great his gas mileage was -- easy
to beat the rest of us driving LAND YACHTS! He was constantly "topping
off" the tank so he could get a new estimate.

So, a few of us got together. Each night, we'd ADD a little gas to his tank.
He got even MORE unbearable with his boasts as now he was BEATING the best
"manufacturer spec" for his vehicle.

We let this go on for several weeks.

Then (obviously) started siphoning a little OUT of his tank, each night.
The sudden HUGE drop in fuel efficiency had him going nuts! Of course,
we'd deliberately ask him for updates of his current fuel efficiency
(which he had previously been all too eager to provide).
By the time we were "done with him", he was haggard -- having tried multiple
different gas stations, been into the dealership to complain about it, etc.

Yes, totally unrelated to the subject at hand! :> But, brought a smile
back to my face as I think about poor Richard...]

[Don Y]

On 7/18/2021 11:52 AM, Lasse Langwadt Christensen wrote:
> nonsense? I'm just saying that those who still bother with stealing cars
> probably know what they are doing or they wouldn't be doing it very long.
> Expensive cars have had gps tracking for many years. All the electronics
> modules, ecu, abs, gearbox, instrument cluster, rfid key, etc. are all
> matched so they won't work in any other car unless they get enabled with
> manufacturer codes. And in many places those who deal in used parts are
> required to track where and from who they got them.

There are also grey markets where things can be "fixed" (altered)
in ways that you'd hardly imagine!

I know a firm that modifies "stock" car engines -- actually adding and
removing metal from the block to change the dynamics of air flow
through the manifolds, valve bodies to gain a little performance.
Then, "scuffs up" their work so it looks like an original casting
(in case someone wants to verify the engine hadn't been "tampered with"
before they award that "big prize")

Thinking that you can "serialize" components in such a way that
someone with re$ource$ and motivation can't beat is folly. Esp
if you can control *where* the item ends up (and who is likely
to have access to it).

Plain old detroit iron have had serial numbers STAMPED on key parts
of the vehicle for decades. Nothing stopping them from being resold.
Ditto serial numbers on guns...

[boB]

On Sun, 18 Jul 2021 08:00:12 -0400, ABLE1 <some...@nowhere.net>
wrote:

Could be possible but not likely. If so, you can still see the
signals with an SA.

I have heard of interference due to frequency doubling by way of a
rusty fence that was acting as a rectifier and emitting RF at twice
the frequency of a semi-close by transmitter. Pretty weird but
possible. This one might be a very simple problem. OR, could be
difficult to track down especially with the "data" that could be found
with a SA.

boB





>
>Thanks,
>
>Les

[Ralph Mowery]

In article <sd21kl$7km$1...@dont-email.me>, blocked...@foo.invalid
says...

>
> It's tempting to make a "remote" on steroids and war-drive the neighborhood
> seeing how many GDOs you could trigger! And, have all those folks wonder
> who (why) opened their door -- or, if they simply forgot to close it
> the night before (then, return the NEXT day and repeat the exercise!)
>
>

My dad had a house that was in line with a practice air force bombing
run. They did not drop any bombs, just flew over to a dam that was
about 10 miles away. They were usually very low to the ground. About
half the time they flew over, his garage door would open or close.
Probably picking up some of the radio talk of the planes as there were
usually 2 to 4 of them at a time.

[Ralph Mowery]

In article <sd220p$cjp$1...@dont-email.me>, blocked...@foo.invalid
says...

> Plain old detroit iron have had serial numbers STAMPED on key parts
> of the vehicle for decades. Nothing stopping them from being resold.
> Ditto serial numbers on guns...
>
>

While cars have serial numbers (VIN) stamped in seveal places, I don't
know of any modern gun sold to the generl public that has more than one
serial number. That is on a certain part of the gun and is concidered
the gun. Every thing else on the gun can be changed.

You can change barrles on some hand guns in about 60 seconds and even
the caliber of the gun. So you could shoot someone with a 9 mm and in
less than 60 seconds convert it to a 40 caliber. Almost no one would
look for that particular gun.

[Ralph Mowery]

In article <nu29fglt7i65b4i9s...@4ax.com>, b...@K7IQ.com
says...

>
> Could be possible but not likely. If so, you can still see the
> signals with an SA.
>
> I have heard of interference due to frequency doubling by way of a
> rusty fence that was acting as a rectifier and emitting RF at twice
> the frequency of a semi-close by transmitter. Pretty weird but
> possible. This one might be a very simple problem. OR, could be
> difficult to track down especially with the "data" that could be found
> with a SA.
>
>
>

It is possiable that anytime there are 2 different metals joining each
other a 'diode junctiion' could form, especially if one is rusty.
Anytime two or more radio frequencies are on that junction you can get
all kinds of mixing. Usually the sum and difference of the frequencies
are the strongest.

[Don Y]

On 7/18/2021 3:12 PM, Ralph Mowery wrote:
> In article <sd220p$cjp$1...@dont-email.me>, blocked...@foo.invalid
> says...
>> Plain old detroit iron have had serial numbers STAMPED on key parts
>> of the vehicle for decades. Nothing stopping them from being resold.
>> Ditto serial numbers on guns...
>
> While cars have serial numbers (VIN) stamped in seveal places, I don't
> know of any modern gun sold to the generl public that has more than one
> serial number. That is on a certain part of the gun and is concidered
> the gun. Every thing else on the gun can be changed.

The point is that you can change (file) the serial number, redrill
the barrel to change the rifling, etc. Gun A is now Gun B.

Reputable jewelers won't work on Rolex watches without verifying
the S/N. Does that mean you *can't* get a stolen Rolex repaired? :>

[Don Y]

Hmmm... one of the non-profits that I'm affiliated with used to occupy
a facility on the approach path for the local military base. I.e.,
when we were out in the "yard", we could *see* the faces of the pilots
as they flew overhead (quite an unnerving experience knowing that
there are munitions so close by! wonder what it would be like on a
battlefield?)

I don't recall the folks who lived by complaining of radio interference.
(but they sure complained about the audio noise of the engines!)

[Ralph Mowery]

In article <sd29si$ga5$1...@dont-email.me>, blocked...@foo.invalid
says...

>
> I don't recall the folks who lived by complaining of radio interference.
> (but they sure complained about the audio noise of the engines!)
>
>

Dad's garage opener was a very old type. Way before digital codes.
Probable a very simple receiver and probably almost any door opener
would open it. His house was a long way from any other house and thse
did not have a garage door.

[Lasse Langwadt Christensen]

https://en.wikipedia.org/wiki/1977_Dutch_train_hijacking

six low flying F-104s with full afterburner is probably going to get your attention

https://youtu.be/3SH5953iQ6w?t=641

[Don Y]

The base is home of the A10 Warthog fleet:

<https://en.wikipedia.org/wiki/Fairchild_Republic_A-10_Thunderbolt_II>

The plane appears to defy gravity -- it always seems like it is flying too
slowly to remain in the sky! So, when it passes overhead, it seems to
just *linger* there!

It is known for it's massive 30 calibre cannon (gattling gun) which
is the justification for its massive engines (when the cannon is firing,
the plane loses forward airspeed as the recoil exceeds the output of
both engines). The rounds -- up to 4000 per minute -- can weigh up
to 1.5pounds, *each*. (I have a friend who works on them at the base)

<https://en.wikipedia.org/wiki/GAU-8_Avenger>

[Note the photo in comparison to the VW Beetle]

So, when I've been outside watching them "float" overhead, I always
tried to imagine what it would be like hearing ~60 rounds per second
belching from the canon! (the entire magazine -- 1300 rounds -- can
be emptied in less than 20 seconds; that's got to be a hellacious
SCREAM!!)

I find it amusing to see what sheer brute force can accomplish!

[At the time, the US was heavily engaged in Iraq so you could imagine
them on tank-hunts (they can take out a tank from a mile away)

[Lasse Langwadt Christensen]

afaik that's a myth, the recoil is only about the same as one engine and
it would run out of ammo long before it had any big impact on
the planes momentum, the planes weights ~10000kg empty

[Don Y]

"The average recoil force of the GAU-8/A is 10,000 pounds-force (45 kN),
which is slightly more than the output of each of the A-10's two TF34 engines
of 9,065 lbf (40.3 kN). While this recoil force is significant, in practice
a cannon fire burst slows the aircraft only a few miles per hour in level
flight."

So, yes, the plane DOES slow down when the canon is engaged. But,
there are limits placed on how long the pilot can keep the weapon
engaged -- if you throw 100 rounds at a target in a second and
haven't destroyed it, you should probably rethink your strategy
before engaging the weapon again. (the barrels get hot from the
friction of all those rounds passing through; failing to let
them cool between bursts leads to more frequent replacement)

Remember, this isn't a bomber that flies at thousands of feet
in altitude. The aircraft has to point the nose at the target
(typ a tank) and the target must be in the kill radius (~1 mi).
So, it tends to fly low to the ground (not steep dives).

[Rick C]

On Sunday, July 18, 2021 at 4:22:27 PM UTC-4, boB wrote:
>
> I have heard of interference due to frequency doubling by way of a
> rusty fence that was acting as a rectifier and emitting RF at twice
> the frequency of a semi-close by transmitter. Pretty weird but
> possible. This one might be a very simple problem. OR, could be
> difficult to track down especially with the "data" that could be found
> with a SA.

Huh? I don't think you get frequency doubling unless the signal is full wave rectified. What the fence in a bridge arrangement? Or maybe dual diode center tapped?

--

Rick C.

--- Get 1,000 miles of free Supercharging
--- Tesla referral code - https://ts.la/richard11209

[Lasse Langwadt Christensen]

mandag den 19. juli 2021 kl. 04.24.40 UTC+2 skrev gnuarm.del...@gmail.com:
> On Sunday, July 18, 2021 at 4:22:27 PM UTC-4, boB wrote:
> >
> > I have heard of interference due to frequency doubling by way of a
> > rusty fence that was acting as a rectifier and emitting RF at twice
> > the frequency of a semi-close by transmitter. Pretty weird but
> > possible. This one might be a very simple problem. OR, could be
> > difficult to track down especially with the "data" that could be found
> > with a SA.
> Huh? I don't think you get frequency doubling unless the signal is full wave rectified. What the fence in a bridge arrangement? Or maybe dual diode center tapped?

wouldn't pretty much anything non linear do?

[boB]

Yeah, that's a good point about needing to be full bridge rectified.

Non-linear could make a mixer though. Maybe that is what acutally
happened that I heard about.

[Tom Gardner]

On 19/07/21 03:24, Rick C wrote:
> On Sunday, July 18, 2021 at 4:22:27 PM UTC-4, boB wrote:
>>
>> I have heard of interference due to frequency doubling by way of a
>> rusty fence that was acting as a rectifier and emitting RF at twice
>> the frequency of a semi-close by transmitter. Pretty weird but
>> possible. This one might be a very simple problem. OR, could be
>> difficult to track down especially with the "data" that could be found
>> with a SA.
>
> Huh? I don't think you get frequency doubling unless the signal is full wave rectified. What the fence in a bridge arrangement? Or maybe dual diode center tapped?
>

Any non-linearity in the vicinity is sufficient to
create harmonics. In some environments it is a major
problem, e.g. marine with high power transmitters.

It is sufficiently common that it is often called
"the rusty bolt effect"
https://en.wikipedia.org/wiki/Rusty_bolt_effect

[Mike]

In article <dd540fc1-a308-4021...@googlegroups.com>,

Rick C <gnuarm.del...@gmail.com> wrote:
>On Sunday, July 18, 2021 at 4:22:27 PM UTC-4, boB wrote:

>> I have heard of interference due to frequency doubling by way of a
>> rusty fence that was acting as a rectifier and emitting RF at twice
>> the frequency of a semi-close by transmitter.

>Huh? I don't think you get frequency doubling unless the signal is
> full wave rectified.

What about those passive security tags that are an L-C
resonant with a diode in them -- they pick up the transmitted field,
and re-radiate a corrupted version (all those harmonics!) which can
be picked up by a receiver listening for 2 x frequency? No bridge
(or fence!) there ... ?

--
--------------------------------------+------------------------------------
Mike Brown: mjb[-at-]signal11.org.uk | http://www.signal11.org.uk

[Rick C]

Sure, any non-linearity creates harmonics. Even if twice the frequency is generated in some amount, that's not frequency doubling. Heck, the original signal contains harmonics, no?

--

Rick C.

--+ Get 1,000 miles of free Supercharging
--+ Tesla referral code - https://ts.la/richard11209

[Tom Gardner]

On 19/07/21 10:53, Rick C wrote:
> On Monday, July 19, 2021 at 3:52:14 AM UTC-4, Tom Gardner wrote:
>> On 19/07/21 03:24, Rick C wrote:
>>> On Sunday, July 18, 2021 at 4:22:27 PM UTC-4, boB wrote:
>>>>
>>>> I have heard of interference due to frequency doubling by way of a
>>>> rusty fence that was acting as a rectifier and emitting RF at twice
>>>> the frequency of a semi-close by transmitter. Pretty weird but
>>>> possible. This one might be a very simple problem. OR, could be
>>>> difficult to track down especially with the "data" that could be found
>>>> with a SA.
>>>
>>> Huh? I don't think you get frequency doubling unless the signal is full wave rectified. What the fence in a bridge arrangement? Or maybe dual diode center tapped?
>>>
>> Any non-linearity in the vicinity is sufficient to
>> create harmonics. In some environments it is a major
>> problem, e.g. marine with high power transmitters.
>>
>> It is sufficiently common that it is often called
>> "the rusty bolt effect"
>> https://en.wikipedia.org/wiki/Rusty_bolt_effect
>
> Sure, any non-linearity creates harmonics. Even if twice the frequency is generated in some amount, that's not frequency doubling. Heck, the original signal contains harmonics, no?
>

You need to define what you mean by "frequency doubling",
since you are not using in the conventional engineering
sense.

[Ralph Mowery]

In article <v78afgtkcefhmr9kn...@4ax.com>, b...@K7IQ.com
says...

> wouldn't pretty much anything non linear do?
>
> Yeah, that's a good point about needing to be full bridge rectified.
>
> Non-linear could make a mixer though. Maybe that is what acutally
> happened that I heard about.
>
>
>
>

It is not usually a doubling, but a mixing of two or more signals. You
get mainly the sum a and difference of the two. Other signals may be
generted.

[Ralph Mowery]

In article <04e88db5-224e-40f4...@googlegroups.com>,
gnuarm.del...@gmail.com says...

>
> Sure, any non-linearity creates harmonics. Even if twice the frequency is generated in some amount, that's not frequency doubling. Heck, the original signal contains harmonics, no?
>
>
>

The origional signal will contain harmonics, but they are usually so
weak as to be a non issue.

[Dave Platt]

In article <ACAII.13105$0N5....@fx06.iad>,
ABLE1 <some...@nowhere.net> wrote:
>On 7/16/2021 6:46 PM, Dave Platt wrote:
>> The primary frequency-user here is military radar, and secondary is
>> amateur radio. One occasionally sees stories about military radar
>> operations disrupting peoples' garage door openers and car
>> alarm/locking systems in some areas. The commonest problems seem to
>> be "they don't work" (the strong radar signals saturate the receivers)
>> but "undesired operation" occurs occasionally (garage doors opening
>> "by themselves").

>
>
>Hello, I find this VERY interesting. I won't go into the whole story
>since it is very long but I have a customer that has an alarm system
>that I installed. It has wireless sensors for doors and such.
>There has been a few times that the system does not receive signals
>from the transmitters for periods of time from 45 minutes to 2 days.

>During this time their garage door opener remote does not work unless
>you hold it in you hand reach up to within 18" of the opener antenna
>and then it will work.
>
>During that time the problem or source can't be determined.
>In discussions with neighbors it has be determined that at least
>4 others, next door and across the street have experienced the same
>with there openers.
>
>Then it all stops and goes back to normal operation???
>
>This happened about 2 years ago and then again about a month ago.
>That I know about that is.
>
>Needless to say when it IS NOT happening it is absolutely impossible
>to find. When it IS happening it is absolutely impossible to find.
>
>The openers have a red LED on the unit that is used for learning in
>a remote button. Normally it is off until it receives a signal from
>a remote to open. During these events the LED is solid red for the
>entire time frame. Then during the end of the event it starts to
>flicker and then off.
>

>The security devices are on 319.5 Mhz and the door opener is on 318 Mhz.
>
>Is there any thoughts here as to what other than Military Radar that
>could be causing this issue with such intensity in a small area??

Here in the US, amateur radio operators have privileges in the 222-225
MHz, and 420-450 MHz bands. Neither of those so close to 318/319 MHz
that it should cause problems for well-engineered receivers... but
security and door-opener receivers may not be terribly selective.
Unless they have band-pass filters before their first RF stage, it's
possible that a strong ham transmission from nearby might saturate the
front end (which would make it far less sensitive to the signals it
should be receiving). I'm not sure you'd see the "red light flashing"
symptom in that case, but that depends on the circuitry in your
receiver.

>There is a local airport with control tower about 2 miles away.

The 318-320 MHz range appears to have primary usage for fixed and
mobile communication, and 326 upwards is an aeronautical navigation
range. So, it's possible that airport operations are responsible.

>I say a small area (200' square box maybe??) but it could be effecting
>a larger area but I have no way to know or to find out without having
>a town meeting.

Another possibility is leakage from a cable-TV system. Cable TV uses a
very wide range of frequencies, putting stations on frequencies which
have other over-the-air uses. If somebody's got a cable TV feed in their
house which has been left "open", or (worse yet) connected in parallel to
a TV antenna, they could be radiating a whole range of frequencies out into
the neighborhood and causing interference.

>Any thoughts on the subject would be most helpful.

You might want to consider investing a small amount of money in what's
commonly referred to as an "RTL-SDR dongle" or "DVB stick". These are
wide-range radio-frequency receivers with USB interfaces. There's
plenty of open-source software which lets them be used as inexpensive
spectrum analyzers/sniffers - either on a PC or on an Android tablet
or phone. They're in the $20-$30 range, depending on quality and
features.

With one of these dongles, a tablet/phone, and a simple two- or
three-element handheld Yagi antenna cut for 318 MHz, you could go
QRM-hunting. You could see a whole slice of the frequency spectrum (I
think these dongles give you about 2 MHz at a time) and look for the
origin of an interfering signal.

[ABLE1]

On 7/19/2021 3:19 PM, Dave Platt wrote:
> Another possibility is leakage from a cable-TV system. Cable TV uses a
> very wide range of frequencies, putting stations on frequencies which
> have other over-the-air uses. If somebody's got a cable TV feed in their
> house which has been left "open", or (worse yet) connected in parallel to
> a TV antenna, they could be radiating a whole range of frequencies out into
> the neighborhood and causing interference.

Some additional input. During the 2 day's of interference a couple of
years ago I driving through the development and noticed a Cable Company
truck sitting on a street a couple of blocks away. I stopped and talked
to the tech and told him what was going on. I asked if there was any
problems in the area. He said, no he was just do some basic service
checks and that he had a device in his truck that can see if there were
any issue as he drove around. I gave him my cell and asked him to drive
past the address and if he saw anything odd to please call me. He never
called be so I can only "assume" his equipment didn't see anything
unusual for the parameters that would concern him. I would guess
that the frequencies are outside what the equipment looks at.

>
>> Any thoughts on the subject would be most helpful.
> You might want to consider investing a small amount of money in what's
> commonly referred to as an "RTL-SDR dongle" or "DVB stick". These are
> wide-range radio-frequency receivers with USB interfaces. There's
> plenty of open-source software which lets them be used as inexpensive
> spectrum analyzers/sniffers - either on a PC or on an Android tablet
> or phone. They're in the $20-$30 range, depending on quality and
> features.
>
> With one of these dongles, a tablet/phone, and a simple two- or
> three-element handheld Yagi antenna cut for 318 MHz, you could go
> QRM-hunting. You could see a whole slice of the frequency spectrum (I
> think these dongles give you about 2 MHz at a time) and look for the
> origin of an interfering signal.

Dave, I agree that the cost would be minimal to maybe get lucky and
find the nasty RFI. Someone else suggested similar equipment/software.
My problem is that I really don't know what to get other than your
description. For me that is only a hint. What I would like would be
to have the Mfg. Name and Model Number for the dongle and the name
of the PC software that will bring up a screen with the "waterfall"
screen as it was mentioned earlier by somebody.

Without that specific information I would be just guessing and more than
likely get it wrong more than once. Now I understand the concern of
promoting a product that might seem like a sales pitch but for the
rookie I see too many mistakes that I could make.

So I respectfully request the following.

RTL-SDR Dongle Mfg. & Model#

Handheld Yagi antenna cut for 318 MHz Mfg. & Model#

Open-Source Software Name/version

I would be installing on my PC Laptop and using USB connection.

I am guessing something here will meet the requirements??

https://www.ebay.com/sch/i.html?_from=R40&_nkw=rtl+sdr&_sacat=1500&rt=nc&LH_PrefLoc=1

Thanks for any input.

Les

[Clifford Heath]

This is the only really reliable place to get a good quality product.
There are many clones, most of which cut corners and have reduced
performance. There are also other reputable brands that are not clones,
but this is the original-and-best, by all accounts:

<https://www.amazon.com/RTL-SDR-Blog-RTL2832U-Software-Defined/dp/B011HVUEME/ref=sr_1_3>

You might not need a Yagi - a dipole will probably suffice despite the
bi-polar radiation pattern. And the dipole is telescopic so you can set
it to the right length for the frequency you're looking at.

The software you need depends on what hardware you're going to use
(Linux, Windoze, or Android phone are all acceptable answers).

CH

[ehsjr]

On 7/17/2021 9:54 PM, Don Y wrote:

<snip>
>
> I've also noticed that the "sense" is pretty sluggish wrt activation.
> E.g., if I was working directly in the plane of the door but *above* it,
> I am sure I would be injured before the door even noticed that it had
> hit me or knocked me from my ladder.
>


The safety problem described above is human error. ALWAYS de-energize
the motor (switch/unplug/flip breaker) or mechanically disconnect the
door from the opener mechanism when you need to work in the area where
the door could knock you off the ladder.

Ed

[Don]

Clifford Heathwrote:
> ABLE1 wrote:

<snip>

>> So I respectfully request the following.
>>
>> RTL-SDR Dongle Mfg. & Model#
>> Handheld Yagi antenna cut for 318 MHz Mfg. & Model#
>
> This is the only really reliable place to get a good quality product.
> There are many clones, most of which cut corners and have reduced
> performance. There are also other reputable brands that are not clones,
> but this is the original-and-best, by all accounts:
>
> <https://www.amazon.com/RTL-SDR-Blog-RTL2832U-Software-Defined/dp/B011HVUEME/ref=sr_1_3>
>
> You might not need a Yagi - a dipole will probably suffice despite the
> bi-polar radiation pattern. And the dipole is telescopic so you can set
> it to the right length for the frequency you're looking at.
>
> The software you need depends on what hardware you're going to use
> (Linux, Windoze, or Android phone are all acceptable answers).

And, for those who prefer to shop at ebay, here's RTL-SDR Blog's ebay
store:

https://www.ebay.com/str/rtlsdrblog

Danke,

--
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.

[Don Y]

On 7/19/2021 8:59 PM, ehsjr wrote:
> On 7/17/2021 9:54 PM, Don Y wrote:
>
> <snip>
>>
>> I've also noticed that the "sense" is pretty sluggish wrt activation.
>> E.g., if I was working directly in the plane of the door but *above* it,
>> I am sure I would be injured before the door even noticed that it had
>> hit me or knocked me from my ladder.
>
> The safety problem described above is human error.

As is *driving* over your child! That doesn't change the fact that
"accidents happen". Being able to *disable* the opener (without
disconnecting power *or* disabling the power feed to the garage)
allows one to easily prevent these sorts of things from happening!

It's a simple matter of an "inhibit" to the opener's control.

[Tauno Voipio]

On 19.7.21 22.19, Dave Platt wrote:
>
> Here in the US, amateur radio operators have privileges in the 222-225
> MHz, and 420-450 MHz bands. Neither of those so close to 318/319 MHz
> that it should cause problems for well-engineered receivers... but
> security and door-opener receivers may not be terribly selective.
> Unless they have band-pass filters before their first RF stage, it's
> possible that a strong ham transmission from nearby might saturate the
> front end (which would make it far less sensitive to the signals it
> should be receiving). I'm not sure you'd see the "red light flashing"
> symptom in that case, but that depends on the circuitry in your
> receiver.
>
>> There is a local airport with control tower about 2 miles away.
>
> The 318-320 MHz range appears to have primary usage for fixed and
> mobile communication, and 326 upwards is an aeronautical navigation
> range. So, it's possible that airport operations are responsible.

The airport radion navigation is hardly the culprit: the 329.15 MHz
to 335 MHz range is for instrument landing system glideslopes (ILS GS).
The signals are directed to the approach sector and they are pretty
low power (typically 2 t0 10 W).

--

-TV

[boB]

Frequency doubling means doubling the frequency

A full bridge rectifier is one way of doing just that.

[Tom Gardner]

Sure, but given what Rick wrote, I'm interested in his definition.

[Clifford Heath]

Yes, but a rusty bolt won't do that.

[Don Y]

This *looks* to be the item I bought as a "cheap admission price"
to tinkering with SDR. It was relatively painless to get started
and "write" my first receiver.

The dongle gets pretty warm, though. And, I'm not sure how much
actual power it is drawing -- how well it would work in a
"portable" application.

[I don't like the USB interface but this was a lot cheaper than some
of the other radios I looked at -- with "better" interfaces]

> You might not need a Yagi - a dipole will probably suffice despite the bi-polar
> radiation pattern. And the dipole is telescopic so you can set it to the right
> length for the frequency you're looking at.

If the effect is as localized as he suggests, I imagine he'll get
"visible" results regardless of the antenna used; "Can you hear me now?"

> The software you need depends on what hardware you're going to use (Linux,
> Windoze, or Android phone are all acceptable answers).

But, he'll need something with a graphic display (unless he wants
to write some code)...

[There are some other, more tightly integrated SDRs with displays.
But, at considerably more money!]

[boB]

If you wire them in a full bridge configuration they might ? :)

[Joe Gwinn]

A rusty bolt is a non-linear conductance, and can easily yield 2nd and
3rd harmonics to appear, plus a forest of intermodulation products.

It's a particular problem on steel ships with powerful S-band (3 GHz)
radars.

Joe Gwinn

[Clifford Heath]

A bit over a watt. They do get warm. A phone's battery will still run
one for long enough for useful DF though.

> [I don't like the USB interface but this was a lot cheaper than some
> of the other radios I looked at -- with "better" interfaces]
>
>> You might not need a Yagi - a dipole will probably suffice despite the
>> bi-polar radiation pattern. And the dipole is telescopic so you can
>> set it to the right length for the frequency you're looking at.
>
> If the effect is as localized as he suggests, I imagine he'll get
> "visible" results regardless of the antenna used; "Can you hear me now?"
>
>> The software you need depends on what hardware you're going to use
>> (Linux, Windoze, or Android phone are all acceptable answers).
>
> But, he'll need something with a graphic display (unless he wants
> to write some code)...

There is software that displays a waterfall for all three operating
systems I listed.

CH

[Jasen Betts]

it will, half wave rectification has half the effect of full wave
rectification:

eg half-wave rectify a signal thenm subtract half the original signal
what you get is a full-wave rectified signal at half amplitude,

so it's still going to produce second harmonic content,
in a simulation there's also a 3rd harmonic at 5 db down abnd 4th at 12 dB down etc...

--
Jasen.

[Don Y]

On 7/20/2021 4:28 PM, Clifford Heath wrote:

>> But, he'll need something with a graphic display (unless he wants
>> to write some code)...
>
> There is software that displays a waterfall for all three operating systems I
> listed.

My point was that he needs a graphic DISPLAY (device) -- unless he wants to
write code. (e.g., I don't use a graphic display with my *radio*)

[Clifford Heath]

Do you know of any "Linux, Windoze, or Android phone" device that
doesn't have a graphic display? Assuming he's not planning to DF with a
headless server...

Please read more carefully :)

[Don Y]

Sure! My radio is plugged into a box under my dresser. As its a *radio*,
all it needs is a frequency/band to tune to and an audio output. An
"interference detector" needs little more!

And, if he is looking for a *tool* to use in his ONGOING
business, he'd likely want something as compact and "to the point"
as possible. E.g., I have a USB dongle about the size of the RTL-SDR
that has a WiFi radio inside *and* a two line display that lets
me probe for hotspots using the battery in the dongle and the
text display (to indicate SSID, encryption, etc.)

Building something from scratch that meets these needs would be relatively
easy with an rPi driving a "VU-meter" or equivalent "signal strength
indicator" (no need for a fancy display if you just are looking for
"signal"/"interference")

> Please read more carefully :)

*Think* about the poster's needs instead of your particular solution.

[ehsjr]

On 7/20/2021 12:55 AM, Don Y wrote:
> On 7/19/2021 8:59 PM, ehsjr wrote:
>> On 7/17/2021 9:54 PM, Don Y wrote:
>>
>> <snip>
>>>
>>> I've also noticed that the "sense" is pretty sluggish wrt activation.
>>> E.g., if I was working directly in the plane of the door but *above* it,
>>> I am sure I would be injured before the door even noticed that it had
>>> hit me or knocked me from my ladder.
>>
>> The safety problem described above is human error.
>
> As is *driving* over your child!  That doesn't change the fact that
> "accidents happen".  Being able to *disable* the opener (without
> disconnecting power *or* disabling the power feed to the garage)
> allows one to easily prevent these sorts of things from happening!
>
> It's a simple matter of an "inhibit" to the opener's control.

Simple? Not from what you have asked and stated in the thread
to this point. It leads to some questions:

What specifically do you have in mind to inhibit the opener's
control that is *simpler* than flipping a switch which removes
power to the opener?

What is the *advantage* of not disconnecting power to the opener,
but instead using the inhibit to the opener's control that you
have in mind?

Will the inhibit you have in mind prevent the opener motor from
starting when the manual (push button/key lock) door opener switch
is operated? Or when some electrical failure within the motor
unit causes it to start?

Ed

[Don Y]

On 7/20/2021 9:13 PM, ehsjr wrote:
> On 7/20/2021 12:55 AM, Don Y wrote:
>> On 7/19/2021 8:59 PM, ehsjr wrote:
>>> On 7/17/2021 9:54 PM, Don Y wrote:
>>>
>>> <snip>
>>>>
>>>> I've also noticed that the "sense" is pretty sluggish wrt activation.
>>>> E.g., if I was working directly in the plane of the door but *above* it,
>>>> I am sure I would be injured before the door even noticed that it had
>>>> hit me or knocked me from my ladder.
>>>
>>> The safety problem described above is human error.
>>
>> As is *driving* over your child! That doesn't change the fact that
>> "accidents happen". Being able to *disable* the opener (without
>> disconnecting power *or* disabling the power feed to the garage)
>> allows one to easily prevent these sorts of things from happening!
>>
>> It's a simple matter of an "inhibit" to the opener's control.
>
> Simple? Not from what you have asked and stated in the thread
> to this point. It leads to some questions:
>
> What specifically do you have in mind to inhibit the opener's
> control that is *simpler* than flipping a switch which removes
> power to the opener?

Removing power to the opener by "flipping a switch" would mean
turning off power to the garage, as a whole. So, if you wanted
to work "above the door" using any power tools, you'd have to run
a cord from some other branch circuit.

If accessing an attic space ABOVE the garage ceiling (via an
access hole IN that ceiling), any lighting up there would
likely draw power from the garage circuit. So, now you'd have
to bring a flashlight or drop light on that extension cord.

> What is the *advantage* of not disconnecting power to the opener,
> but instead using the inhibit to the opener's control that you
> have in mind?

Inhibiting the opener can be simpler and more convenient, from
the standpoint of the user. If so, it will likely be exercised
more faithfully than "flipping a breaker".

An inhibit can also tie in much the same way that the photo-interrupter
does; so, one could "watch" for hazards ABOVE the door instead of
just in the closing path of the door.

> Will the inhibit you have in mind prevent the opener motor from
> starting when the manual (push button/key lock) door opener switch
> is operated?

Inhibit is inhibit. You don't want the motor to start.
If the user wants to operate the door, then he should
have to consciously disable the inhibit.

You can't close the door while you are standing in its path,
period. Why should this be a different set of rules?

> Or when some electrical failure within the motor
> unit causes it to start?

Or when some electrical failure within the motor unit

causes the door to close on a child standing in its path?

(if YOU can hypothesize failures, then *I* can, as well!
Clearly, the EXISTING safety measures must be insufficient?)

[ehsjr]

Ok, now I see your thinking. Now I'll tell you (vs ask you) the
solution I propose. Install (or hire an electrician if you can't
do it yourself) a switch in the garage to turn the outlet
serving the opener on/off. Nothing simpler than flipping the
switch.

Of course, that doesn't cover the situation where you need to work
on the opener itself with power available to it. In that case
you need to disconnect the mechanical link between the opener
and the door such that even if the motor starts unexpectedly
the door can't knock you off the ladder.

>
> If accessing an attic space ABOVE the garage ceiling (via an
> access hole IN that ceiling), any lighting up there would
> likely draw power from the garage circuit.  So, now you'd have
> to bring a flashlight or drop light on that extension cord.
>
>> What is the *advantage* of not disconnecting power to the opener,
>> but instead using the inhibit to the opener's control that you
>> have in mind?
>
> Inhibiting the opener can be simpler and more convenient, from
> the standpoint of the user.  If so, it will likely be exercised
> more faithfully than "flipping a breaker".
>
> An inhibit can also tie in much the same way that the photo-interrupter
> does; so, one could "watch" for hazards ABOVE the door instead of
> just in the closing path of the door.
>
>> Will the inhibit you have in mind prevent the opener motor from
>> starting when the manual (push button/key lock) door opener switch
>> is operated?
>
> Inhibit is inhibit.  You don't want the motor to start.

Ok! There are only two ways to prevent the motor from starting:
1) some mechanical arrangement that prevents it from spinning or
2) preventing electrical power from reaching it.

> If the user wants to operate the door, then he should
> have to consciously disable the inhibit.
>
> You can't close the door while you are standing in its path,
> period.  Why should this be a different set of rules?
>
>>  Or when some electrical failure within the motor
>> unit causes it to start?
>
> Or when some electrical failure within the motor unit
> causes the door to close on a child standing in its path?
>
> (if YOU can hypothesize failures, then *I* can, as well!

Hypothesize all you want - I have been clear about the situation
I am discussing with you. I'll quote it below so we can keep
on track:
You: " I've also noticed that the "sense" is pretty sluggish wrt

activation. E.g., if I was working directly in the plane of the

door but *above* it,I am sure I would be injured before the door

even noticed that it had hit me or knocked me from my ladder."

Me: "The safety problem described above is human error."

I am not talking about a child unexpectedly putting himself in
danger - I am talking about you knowingly putting yourself
in danger.

> Clearly, the EXISTING safety measures must be insufficient?)

Yes they are, from your description: at this time you have
no simple means in place to prevent the door from injuring
you when you are working on the ladder above the door.

Ed

[Don Y]

So, *every* GDO should be installed with a special switch to
cut power to the GDO? Instead of designing the GDO with a
"lockout" capability ON THE INDOOR PUSHBUTTON.

Obviously, GDO manufacturers think otherwise:

<https://www.youtube.com/watch?v=mY3NZtsaTNs>

An "inhibit" prevents electrical power from reaching the *motor*.
So, power can be present in the GDO yet not passed through to the
motor/mechanism.

>> If the user wants to operate the door, then he should
>> have to consciously disable the inhibit.
>>
>> You can't close the door while you are standing in its path,
>> period. Why should this be a different set of rules?
>>
>>> Or when some electrical failure within the motor
>>> unit causes it to start?
>>
>> Or when some electrical failure within the motor unit
>> causes the door to close on a child standing in its path?
>>
>> (if YOU can hypothesize failures, then *I* can, as well!
>
> Hypothesize all you want - I have been clear about the situation
> I am discussing with you. I'll quote it below so we can keep
> on track:
> You: " I've also noticed that the "sense" is pretty sluggish wrt activation.
> E.g., if I was working directly in the plane of the
> door but *above* it,I am sure I would be injured before the door
> even noticed that it had hit me or knocked me from my ladder."
>
> Me: "The safety problem described above is human error."

Because there is no CONVENIENT way to inhibit the door's operation.
DO manufacturers have decided that it is a common enough occurrence
for doors to close on creatures and things and have incorporated
additional mechanisms to "prevent" that from happening. Note that
even those aren't infallible as they rely on the obstruction
being ground-based (as the interrupter is usually located a few inches
off the floor)

I repeat: I *watched* a neighbor RUN OVER his child. He was the
"responsible adult" operating the motor vehicle. It was HIS
responsibility to verify there was nothing in the path of HIS
vehicle as he backed out of HIS driveway -- including HIS
child unexpectedly putting itself in danger.

As a parent, he KNOWS that he should be ever vigilant as to the
whereabouts of HIS kids. (and, as an operator of a motor vehicle,
aware of any damage that HE might cause to others) Regardless of
how INCONVENIENT that vigilance can be.

You'll note that newer vehicles actually "watch" for activity
around them to enhance this "convenience".

> I am not talking about a child unexpectedly putting himself in
> danger - I am talking about you knowingly putting yourself
> in danger.

People put themselves in danger all the time. Usually, because
"safety" is an inconvenience.

Why do people jaywalk -- lose the protections afforded by a traffic
signal inhibiting the flow of traffic WHILE they cross? Why do they
not wait for the "WALK" signal? Why not walk *to* the next
intersection instead of crossing BETWEEN them?

Why do driver fail to "signal" their intentions (clearly, letting
other operators of two ton metal blocks proximate to you is
probably safer than HOPING they react to your unannounced actions)?

If I have to disable the GDO (by walking to the other end of the
house to flip the breaker "OFF"; by reaching up to the ceiling to
unplug the opener from the outlet; by manually disconnecting the
door from the mechanism) each time I climb the ladder to make
an adjustment on the door -- or do any other work "above" the
door -- then human nature will have this process short-cutted.
Each representing an opportunity for injury or other "loss".

If, instead, the GDO (or other) makes safety more convenient,
then the end result is a safer environment DESPITE "human nature".

>> Clearly, the EXISTING safety measures must be insufficient?)
>
> Yes they are, from your description: at this time you have
> no simple means in place to prevent the door from injuring
> you when you are working on the ladder above the door.

You've taken my comment out of context:

"Or when some electrical failure within the motor unit
causes the door to close on a child standing in its path?

(if YOU can hypothesize failures, then *I* can, as well!

Clearly, the EXISTING safety measures must be insufficient?)"

note that I was refering to existing GDO implementations
and the (hypothesized) possibility that a door COULD *close*
on a child standing beneath it (if YOU allow for failures
in the safety mechanisms)

I suspect you will discover that *most* GDO installations have

"no simple means in place to prevent the door from injuring
you when you are working on the ladder above the door".

And, that the way to fix that is to fix the GDO, *not* add a
mains switch to the GDO in the garage! (or, mandate
that all homes be built with such a capability)

[Dave Platt]

In article <55oJI.37633$UR4....@fx37.iad>,

ABLE1 <some...@nowhere.net> wrote:
>Dave, I agree that the cost would be minimal to maybe get lucky and
>find the nasty RFI. Someone else suggested similar equipment/software.
>My problem is that I really don't know what to get other than your
>description. For me that is only a hint. What I would like would be
>to have the Mfg. Name and Model Number for the dongle and the name
>of the PC software that will bring up a screen with the "waterfall"
>screen as it was mentioned earlier by somebody.
>
>Without that specific information I would be just guessing and more than
>likely get it wrong more than once. Now I understand the concern of
>promoting a product that might seem like a sales pitch but for the
>rookie I see too many mistakes that I could make.
>
>So I respectfully request the following.
>
>RTL-SDR Dongle Mfg. & Model#

As others have suggested, the RTL-SDR.com R820T2 RTL2832U dongle is a
solid performer. Their $40 bundle (including several antennas) is a
good all-in-one solution to get you started.

Nooelec makes a similar medal-case premium dongle that's also got a
good reputation...

https://amazon.com/NooElec-NESDR-Smart-Enclosure-R820T2-Based/dp/B01HA642SW

and they also offer bundles with antennas. Their prices are a hair
higher than RTL-SDR.com, though.

>Handheld Yagi antenna cut for 318 MHz Mfg. & Model#

I don't know of an inexpensive commercial one which is cut for this
frequency band. If it were me, I'd make one myself out of scrap wood
and copper wire :-)

Some years ago I made an antenna along the following lines, for use in
the 2-meter band (144-148 MHz):

https://www.jpole-antenna.com/2017/02/07/build-it-2-meter-tape-measure-yagi-beam-antenna/

A similar design would work for 318 MHz. If you just cut all of the
dimensions in half (elements half as long, and separated by half as
much distance) it'd probably work.

As others have suggested, you may not need one. It's possible to do
direction-finding pretty well on these frequencies using a technique
called "body fade". You would:

(1) Connect the dongle to a simple antenna - the little magnetic-mount
wire-whip antenna sold in the RTL-SDR and Nooelec bundles should work.

(2) Stick the mag-mount on a steel pie pan or something like that, to
provide a ground plane and give you something to hold it by.

(3) Stand in a clear area, so you aren't close to building walls or trees.

(4) Hold the antenna a foot or so directly in front of your body, and
observe the interference signal on you PC/phone/tablet screen.

(5) Slowly turn around in a complete circle, looking at the screen to
figure out the direction in which the signal is _weakest_.

(6) When you are facing in that direction, the source of the signal is
(approximately) directly behind you.

Take bearings like this from multiple locations, draw the resulting
vectors on a map, and where the lines cross is probably near the
source of the interference.

>Open-Source Software Name/version
>
>I would be installing on my PC Laptop and using USB connection.

SDR# is the commonest one for Windows use.

On Android, I use an app called "RF Analyzer", which requires a second
app called "Rtl-sdr driver". Both are available from the Play Store.

On a Linux PC I usually use gqrx.

[Don Y]

On 7/19/2021 4:41 PM, ABLE1 wrote:
> Without that specific information I would be just guessing and more than
> likely get it wrong more than once. Now I understand the concern of
> promoting a product that might seem like a sales pitch but for the
> rookie I see too many mistakes that I could make.
>
> So I respectfully request the following.
>
> RTL-SDR Dongle Mfg. & Model#
>
> Handheld Yagi antenna cut for 318 MHz Mfg. & Model#
>
> Open-Source Software Name/version
>
> I would be installing on my PC Laptop and using USB connection.

I think you will find a laptop to be cumbersome to use;
acceptable if you are war-driving but you may not be able to
localize the signal "from the available roadways".

You stated it affects a very small area. So, it likely
emits FROM that small area.

I think you'll (going forward) much prefer something
that you can carry as you WALK the area. You're likely
not going to see a sharp spike WHILE driving but, rather,
will see something "suspicious" and will want to refine
your examination. The sort of thing you can easily
do on foot, scanning the antenna in different directions.

You may also find it hard to identify a particular
"peak" as being the offender (did someone just turn
on an appliance that throws lots of hash? is THIS
hash the stuff that is causing me grief?)

So, you'll want to be able to return to a victimized
site and "look" in the suspected direction FROM THERE
to see if the signal is present in similar magnitudes.
And, try "directional" mitigation to confirm that the
source is verifiably so.

My money is still on one of the homes that are afflicted
(or an immediate neighbor that doesn't have any of the
sort of kit that is bothered by this)

Fish or cut bait. Buy one of the kits. Follow the
instructions to set it up for a particular purpose
(e.g., to receive FM radio broadcasts) just so you
can verify that everything is working ("Hey! I can
hear my local DJ!"). And, so you can familiarize
yourself with how the software (tools) work.

*THEN* start thinking about how you can apply what you've
learned to your real-world situation.

E.g., you can eventually learn to use it to "observe"
the (normal) activities of the devices you install
and verify their proper operation (polling, etc.).
So, it's not just a tool to "look for interference".

[Don Y]

On 7/22/2021 12:54 PM, Dave Platt wrote:
>> Handheld Yagi antenna cut for 318 MHz Mfg. & Model#
>
> I don't know of an inexpensive commercial one which is cut for this
> frequency band. If it were me, I'd make one myself out of scrap wood
> and copper wire :-)

He may find some success just repurposing one of his "modules"
for its antenna; if THEY are "seeing" the signal, then the
sniffer should similarly see it with the same sort of antenna
(admittedly at a different signal strength)

I.e., one alternative way of doing this work is to just
take an instance of the victim hardware around the neighborhood
and watch to see where it misbehaves/behaves. This also
gives you data on areas that may not have "subscribers".