what material reflects microwave?
jgy2001
cellular and wifi signals?
I am thinking simple laminated material, such as film, or tape or
plastic sheets?
Can I embed simple film with some kind of simple metal to reflect
microwave signals?
Thank you.
Tim Wescott
Metal, or just about anything that's metalized. Aluminized mylar would
certainly count as a "simple film", and is somewhat conformal if you
don't mind cussing a bit.
If you can't find it anywhere else find a hobby shop that caters to
model airplane builders and ask for metallic Monocoat, or check out the
hobby websites (Tower Hobbies is good).
You can also get aluminum backed duct tape (you _don't_ want 'regular'
silver-colored duct tape -- you want the stuff that looks like aluminum
foil).
Or you could make a form, spray 3M 77 contact cement on it, and apply
aluminum foil.
Come to think of it, even something like silver paint might -- although
if it did it'd probably scatter quite a bit.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
John Fields
wrote:
---
Yes, of course.
---
>Thank you.
---
You're welcome.
---
JF
mpm
The material that is embedded in some microwave popcorn bags (which is
why they always say "This Side Down".
Ditto for some microwave frozen dinner entres.
-mpm
John Larkin
wrote:
>On Aug 26, 1:49 pm, jgy2001 <jgy2...@gmail.com> wrote:
>> What kind of simple material reflects microwave energy, such as
>> cellular and wifi signals?
Anything metallic.
>> I am thinking simple laminated material, such as film, or tape or
>> plastic sheets?
>> Can I embed simple film with some kind of simple metal to reflect
>> microwave signals?
>> Thank you.
>
>The material that is embedded in some microwave popcorn bags (which is
>why they always say "This Side Down".
>Ditto for some microwave frozen dinner entres.
Those things are designed to absorb, not reflect.
John
mpm
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Thu, 26 Aug 2010 12:11:53 -0700 (PDT), mpm <mpmill...@aol.com>
Maybe for frozen dinners, but I'm pretty sure the popcorn bag variety
reflects?
I'm trying to remember the "technical" name for it.....
Getting old is a bitch.
John Fields
---
I disagree.
AFAIK, "Those things" are designed to reflect the RF into the food, in
order to heat the food, instead of heating the packaging and causing
the heat generated there to heat the food by conduction.
---
JF
Rich Grise on Google groups
> On Aug 26, 1:49 pm, jgy2001 <jgy2...@gmail.com> wrote:
>
> > What kind of simple material reflects microwave energy, such as
> > cellular and wifi signals?
> The material that is embedded in some microwave popcorn bags (which is
> why they always say "This Side Down".
> Ditto for some microwave frozen dinner entres.
>
microwaves - aluminum
foil does that admirably (I saw a photo shoot in an early microwave
oven cookbook -
they wrapped an ice cube in foil, set it in the oven next to a cup of
water, boiled the
water and the ice cube was virtually untouched.) But that stuff on the
bottom of the
popcorn pack is designed to _absorb_ the microwaves and turn them into
just plain
ol' heat. Sometimes you get those "hot pocket" thingies with reluctor
wrapped around
them to brown the crust.
I have a suspicion that the reluctor stuff is somehow related to
"radar-absorbent
materal" paint for stealth aircraft. ;-)
Cheers!
Rich
Rich Grise on Google groups
wrote:
> On Thu, 26 Aug 2010 12:14:57 -0700, John Larkin
> >>On Aug 26, 1:49 pm, jgy2001 <jgy2...@gmail.com> wrote:
> >>> What kind of simple material reflects microwave energy, such as
> >>> cellular and wifi signals?
>
> >Anything metallic.
>
> >>why they always say "This Side Down".
> >>Ditto for some microwave frozen dinner entres.
>
> >Those things are designed to absorb, not reflect.
> I disagree.
>
> AFAIK, "Those things" are designed to reflect the RF into the food, in
> order to heat the food, instead of heating the packaging and causing
> the heat generated there to heat the food by conduction.
>
No, John, they're designed _exactly_ to heat the packaging (hence the
"this side down" admonition) and cause the heat generated there to
heat
the food by conduction, thus popping the corn on the bottom or
browning
the crust of a hot pocket thingie.
I suppose popcorn in a microwave _without_ the reluctor on the bottom
of the
pack would pop eventually, but it'd probably burn the corn before the
rest
of it pops.
Who wants to volunteer to do this experiment? Take a microwave bag,
dump
the corn out into a (microwave-safe!) plastic plate, dump some plain
ordinary
popcorn on another (microwave-safe) plastic plate, and start them up?
Please report back with results.
Oh, wait - you'd need two ovens. Or a stopwatch! ;-)
Thanks!
Rich
David Eather
> On 08/26/2010 11:49 AM, jgy2001 wrote:
>> What kind of simple material reflects microwave energy, such as
>> cellular and wifi signals?
>> I am thinking simple laminated material, such as film, or tape or
>> plastic sheets?
>> Can I embed simple film with some kind of simple metal to reflect
>> microwave signals?
>
> Metal, or just about anything that's metalized. Aluminized mylar would
> certainly count as a "simple film", and is somewhat conformal if you
> don't mind cussing a bit.
>
> If you can't find it anywhere else find a hobby shop that caters to
> model airplane builders and ask for metallic Monocoat, or check out the
> hobby websites (Tower Hobbies is good).
The "Emergency Space Blankets" beloved by rescue and emergency services
are aluminized mylar and cost something like one or two dollars per
square yard.
David Eather
Popcorn contains too little water (about 10%) to effectively absorb
microwaves. Hence the "this side down" panel absorbs microwave energy
and heats up.
Tim Wescott
> On 27/08/2010 5:08 AM, Tim Wescott wrote:
>> On 08/26/2010 11:49 AM, jgy2001 wrote:
>>> What kind of simple material reflects microwave energy, such as
>>> cellular and wifi signals?
>>> I am thinking simple laminated material, such as film, or tape or
>>> plastic sheets?
>>> Can I embed simple film with some kind of simple metal to reflect
>>> microwave signals?
>>
>> Metal, or just about anything that's metalized. Aluminized mylar would
>> certainly count as a "simple film", and is somewhat conformal if you
>> don't mind cussing a bit.
>>
>> If you can't find it anywhere else find a hobby shop that caters to
>> model airplane builders and ask for metallic Monocoat, or check out the
>> hobby websites (Tower Hobbies is good).
>
> The "Emergency Space Blankets" beloved by rescue and emergency services
> are aluminized mylar and cost something like one or two dollars per
> square yard.
Of course! Why didn't I think of that?
(please don't answer).
mpm
>
> - Show quoted text -
Maybe "susceptor" is the right term I was thinking about, but it
doesn't ring a bell.
To the OP, US Patent # 6,559,430 is worth a look.
I of course, could not resist the temptation to do a patent search on
"Inventor = Orville Redenbacher".
Boy was I disappointed. :)
tm
"jgy2001" <jgy...@gmail.com> wrote in message
news:5177ada3-35d5-48b5...@v6g2000prd.googlegroups.com...
How about single side PC board material? The real thin
stuff, 0.008 inch FR4 with 1 Oz copper is cheap. Check ebay.
tm
--- news://freenews.netfront.net/ - complaints: ne...@netfront.net ---
whit3rd
> What kind of simple material reflects microwave energy, such as
> cellular and wifi signals?
A conductor, or a material with high magnetic susceptibility,
will block radiation.
> I am thinking simple laminated material, such as film, or tape or
> plastic sheets?
There are aluminized films, of course (but beware, the long
wavelengths
you are referring to will tunnel through a very thin film).
Construction
materials like aluminized foam insulation have thick-enough metal,
and there are nickel-containing conductive paints that do a DANDY
job, they both have conductivity and susceptibility on their side.
Seams must be made conductive, too, of course (there's a line of
3M tapes for this purpose). Doors with conductive gaskets are
used in screen rooms, those gasket materials are NOT cheap.
Nor, for that matter, are the tapes.
Jim Yanik
news:i56qvb$25jk$1...@adenine.netfront.net:
>
> "jgy2001" <jgy...@gmail.com> wrote in message
> news:5177ada3-35d5-48b5...@v6g2000prd.googlegroups.com...
>> What kind of simple material reflects microwave energy, such as
>> cellular and wifi signals?
household aluminum foil
>> I am thinking simple laminated material, such as film, or tape or
>> plastic sheets?
glue aluminum foil to your plastic sheet;use 3M spray adhesive.
>> Can I embed simple film with some kind of simple metal to reflect
>> microwave signals?
>> Thank you.
>
>
> How about single side PC board material? The real thin
> stuff, 0.008 inch FR4 with 1 Oz copper is cheap. Check ebay.
>
>
> tm
>
>
>
> --- news://freenews.netfront.net/ - complaints: ne...@netfront.net ---
>
--
Jim Yanik
jyanik
at
localnet
dot com
Paul Hovnanian P.E.
Aluminum foil. Preferably hat-shaped.
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
Ask not for whom the <CONTROL-G> tolls.
David Eather
> On 08/26/2010 02:07 PM, David Eather wrote:
>> On 27/08/2010 5:08 AM, Tim Wescott wrote:
>>> On 08/26/2010 11:49 AM, jgy2001 wrote:
>>>> What kind of simple material reflects microwave energy, such as
>>>> cellular and wifi signals?
>>>> I am thinking simple laminated material, such as film, or tape or
>>>> plastic sheets?
>>>> Can I embed simple film with some kind of simple metal to reflect
>>>> microwave signals?
>>>
>>> Metal, or just about anything that's metalized. Aluminized mylar would
>>> certainly count as a "simple film", and is somewhat conformal if you
>>> don't mind cussing a bit.
>>>
>>> If you can't find it anywhere else find a hobby shop that caters to
>>> model airplane builders and ask for metallic Monocoat, or check out the
>>> hobby websites (Tower Hobbies is good).
>>
>> The "Emergency Space Blankets" beloved by rescue and emergency services
>> are aluminized mylar and cost something like one or two dollars per
>> square yard.
>
> Of course! Why didn't I think of that?
>
> (please don't answer).
>
I have lots of time, but little money on hand.
Paul Keinanen
<the_ob...@whitehouse.gov> wrote:
>How about single side PC board material? The real thin
>stuff, 0.008 inch FR4 with 1 Oz copper is cheap. Check ebay.
Radio amateur often make boxes for subassemblies by cutting double
sided PCB boards into suitable plates and soldering these plates into
a box, with slightly overlapping sides. These boxes are mechanically
stable and good EMC isolation, so that small signal subassembly units
can be close to high RF power (10-1000 W) subassemblies.
John Fields
John Fields
<richar...@yahoo.com> wrote:
>On Aug 26, 12:30 pm, John Fields <jfie...@austininstruments.com>
>wrote:
>> On Thu, 26 Aug 2010 12:14:57 -0700, John Larkin
>> >On Thu, 26 Aug 2010 12:11:53 -0700 (PDT), mpm <mpmill...@aol.com>
>> >>On Aug 26, 1:49 pm, jgy2001 <jgy2...@gmail.com> wrote:
>> >>> What kind of simple material reflects microwave energy, such as
>> >>> cellular and wifi signals?
>>
>> >Anything metallic.
>>
>> >>The material that is embedded in some microwave popcorn bags (which is
>> >>why they always say "This Side Down".
>> >>Ditto for some microwave frozen dinner entres.
>>
>> >Those things are designed to absorb, not reflect.
>
>> I disagree.
>>
>> AFAIK, "Those things" are designed to reflect the RF into the food, in
>> order to heat the food, instead of heating the packaging and causing
>> the heat generated there to heat the food by conduction.
>>
>
>No, John, they're designed _exactly_ to heat the packaging (hence the
>"this side down" admonition) and cause the heat generated there to
>heat
>the food by conduction, thus popping the corn on the bottom or
>browning
>the crust of a hot pocket thingie.
---
Tim Williams
news:cp6f76hn57hhan51h...@4ax.com...
> Interesting.
>
> http://en.wikipedia.org/wiki/Susceptor
Graphite crucibles are absolutely beautiful for induction melting,
especially of materials that don't normally work well, like copper and
silver (which are too conductive and reflect most of the energy) or
insulators (like if you wanted to do glass, or synthesize diamonds, etc.).
It also has a nearly flat tempco, whereas metals change by more than an
order of magnitude before they melt. (Not to mention steel's additional
hysteresis losses at low temperature.)
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Tim Wescott
You could make a great close-to-parabolic reflector with one of those
things just by sticking it to a round air tight frame and pulling a
vacuum. In fact, even if the frame weren't perfectly round it'd
probably still be an OK reflector.
The downside would be that you'd need to maintain the vacuum, but hey --
nothing in life is perfect.
Jan Panteltje
> On 08/26/2010 11:00 PM, David Eather wrote:
> You could make a great close-to-parabolic reflector with one of those
> things just by sticking it to a round air tight frame and pulling a
> vacuum. In fact, even if the frame weren't perfectly round it'd
> probably still be an OK reflector.
>
> The downside would be that you'd need to maintain the vacuum, but hey --
> nothing in life is perfect.
Or you could take a big tank full of mercury,
and slowly rotate it so the centrifugal force makes a parabolic shape,
allowing you to dynamically adjust the focus.
It has some drawbacks, but maybe you could sell it as 'green',
and they would not notice :-)
GregS
>On 27/08/2010 5:08 AM, Tim Wescott wrote:
>> On 08/26/2010 11:49 AM, jgy2001 wrote:
>>> What kind of simple material reflects microwave energy, such as
>>> cellular and wifi signals?
>>> I am thinking simple laminated material, such as film, or tape or
>>> plastic sheets?
>>> Can I embed simple film with some kind of simple metal to reflect
>>> microwave signals?
>>
>> Metal, or just about anything that's metalized. Aluminized mylar would
>> certainly count as a "simple film", and is somewhat conformal if you
>> don't mind cussing a bit.
>>
>> If you can't find it anywhere else find a hobby shop that caters to
>> model airplane builders and ask for metallic Monocoat, or check out the
>> hobby websites (Tower Hobbies is good).
>
>The "Emergency Space Blankets" beloved by rescue and emergency services
>are aluminized mylar and cost something like one or two dollars per
>square yard.
>
>>
When Hostess used to put HoHo's in foil, it made a electrical storm inside
the microwave. I guess the foil could not take the current.
greg
Jim Yanik
news:i58ltj$q9h$1...@usenet01.srv.cis.pitt.edu:
>
> When Hostess used to put HoHo's in foil, it made a electrical storm
> inside the microwave. I guess the foil could not take the current.
>
> greg
no,you get standing waves and the voltage causes arcing,at sharp points.
the metalization acts as an antenna.
L. Larry
I am interested to learn the material that reflects microwave energy,
cellular and wifi signals, and these specific wavelengths?
I also interested to learn what is best and low cost to collect
cellular and wifi specific wavelength signals?
mpm
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -
Mental note to self: Greg puts Ho-Ho's in microwaves. :)
mpm
Low cost (for collecting) would be an antenna.
High cost (for reflecting) might be something like this:
Link: http://en.wikipedia.org/wiki/File:Signalreflectors.JPG
Near Salt Lake City, UT.
Up close, you can see they have little patterns cut into them to
better reflect certain wavelengths.
They use these as passive repeaters (no electronics whatsoever) to get
around mountainous terrain and other obstructions.
Sometimes you'll see them on old microwave relay towers (antennas on
the ground, passive reflector panels at altitude on a tower)
You wouldn't think they'd work, but they actually work quite well.
I recall in the early days of the space race, they launched a metal
spehere and bounced radio waves off it while it was in orbit.
Pretty much the same concept here.
-mpm
David Eather
"bug-out" bag
L. Larry
>
> Link: http://en.wikipedia.org/wiki/File:Signalreflectors.JPG
>
> Near Salt Lake City, UT.
> Up close, you can see they have little patterns cut into them to
> better reflect certain wavelengths.
> They use these as passive repeaters (no electronics whatsoever) to get
> around mountainous terrain and other obstructions.
> Sometimes you'll see them on old microwave relay towers (antennas on
> the ground, passive reflector panels at altitude on a tower)
>
> You wouldn't think they'd work, but they actually work quite well.
> I recall in the early days of the space race, they launched a metal
> spehere and bounced radio waves off it while it was in orbit.
> Pretty much the same concept here.
>
> -mpm
mpm, very interesting, can you tell me more about this kind passive
signal reflectors? If I can build something myself? how do I figure
out the patterns for WiFi and Cellular signals?
mi...@sushi.com
> On 08/26/2010 11:49 AM, jgy2001 wrote:
>
> > What kind of simple material reflects microwave energy, such as
> > cellular and wifi signals?
> > I am thinking simple laminated material, such as film, or tape or
> > plastic sheets?
> > Can I embed simple film with some kind of simple metal to reflect
> > microwave signals?
>
> Metal, or just about anything that's metalized. Aluminized mylar would
> certainly count as a "simple film", and is somewhat conformal if you
> don't mind cussing a bit.
>
> If you can't find it anywhere else find a hobby shop that caters to
> model airplane builders and ask for metallic Monocoat, or check out the
> hobby websites (Tower Hobbies is good).
>
> silver-colored duct tape -- you want the stuff that looks like aluminum
> foil).
>
> Or you could make a form, spray 3M 77 contact cement on it, and apply
> aluminum foil.
>
> Come to think of it, even something like silver paint might -- although
> if it did it'd probably scatter quite a bit.
>
>
> Tim Wescott
> Wescott Design Serviceshttp://www.wescottdesign.com
>
> Do you need to implement control loops in software?
> "Applied Control Theory for Embedded Systems" was written for you.
> See details athttp://www.wescottdesign.com/actfes/actfes.html
You can get spray-on nickel in aerosol cans. Fry's has/had it for
electronic shielding. I've used it on radios with plastic cases to
keep RF from leaking. I can't say for sure it is good at reflecting
RF, but it seems like it should.
I thought it was GC electronics, but that doesn't seem to be the
vendor.
mpm
>
> - Show quoted text -
Try this: http://www.valmont.com/userfiles/file/specialty_structures/Catalog161A.pdf
Grant
But they have a nice turn off feature, simply release the vacuum. It's
been documented somewhere for a solar reflector whatsit hotspot heater.
Make a drum, metalised plastic for the skin and just add vacuum to focus.
Grant.
Grant
They make lossy coax for passive repeaters too.
Grant.
Phil Hobbs
You don't need a big tank--mercury zenith telescopes use a really thin
layer of Hg on top of a roughly parabolic support, with a small gutter
running round the outer edge to prevent the mercury from breaking up
into drops. You do have to watch out for the vapour from such a large
area, of course.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
jgy2001
apartment, to improve sign reception and transmission, what kind of
pattern should I use for Wifi (2.45GHz) and Cellular (GSM has 4 bands,
do not know what is best frequency for rest others?)
To: mi...@sushi.com, why spray on Nickel? Is Nickel good in absorb or
reflect microwave?
m II
This would be a good starting place. The music leaves a bit to be desired.
http://www.youtube.com/watch?v=vJwOpJjYKqA&feature=fvsr
There are easier ways to do it. Keep looking until you find something
suitable for you. At least the music will never get worse.
mike
JosephKK
wrote:
>On 08/26/2010 11:49 AM, jgy2001 wrote:
>> What kind of simple material reflects microwave energy, such as
>> cellular and wifi signals?
>> I am thinking simple laminated material, such as film, or tape or
>> plastic sheets?
>> Can I embed simple film with some kind of simple metal to reflect
>> microwave signals?
>
>Metal, or just about anything that's metalized. Aluminized mylar would
>certainly count as a "simple film", and is somewhat conformal if you
>don't mind cussing a bit.
>
>If you can't find it anywhere else find a hobby shop that caters to
>model airplane builders and ask for metallic Monocoat, or check out the
>hobby websites (Tower Hobbies is good).
>
>You can also get aluminum backed duct tape (you _don't_ want 'regular'
>silver-colored duct tape -- you want the stuff that looks like aluminum
>foil).
>
>Or you could make a form, spray 3M 77 contact cement on it, and apply
>aluminum foil.
>
>Come to think of it, even something like silver paint might -- although
>if it did it'd probably scatter quite a bit.
A lot of "silver" paints contain NO metal.
JosephKK
wrote:
>On 08/26/2010 11:00 PM, David Eather wrote:
Pretty much any air pressure differential, use the other hookup on the
household vacuum, and then spray the back with structural foam. After
it hardens you are good to go.
JosephKK
wrote:
>On Aug 27, 12:25 pm, "L. Larry" <larry.py...@gmail.com> wrote:
Yes, the "Echo" ballons. Not quite orbital but they lasted a while.
JosephKK
wrote:
>On Aug 26, 1:49 pm, jgy2001 <jgy2...@gmail.com> wrote:
>> What kind of simple material reflects microwave energy, such as
>> cellular and wifi signals?
>> I am thinking simple laminated material, such as film, or tape or
>> plastic sheets?
>> Can I embed simple film with some kind of simple metal to reflect
>> microwave signals?
>> Thank you.
>
>The material that is embedded in some microwave popcorn bags (which is
>why they always say "This Side Down".
>Ditto for some microwave frozen dinner entres.
>
>-mpm
Actually it is often more absorbtive than reflective.
JosephKK
<richar...@yahoo.com> wrote:
>On Aug 26, 12:11 pm, mpm <mpmill...@aol.com> wrote:
>> On Aug 26, 1:49 pm, jgy2001 <jgy2...@gmail.com> wrote:
>>
>> > What kind of simple material reflects microwave energy, such as
>> > cellular and wifi signals?
>...
>> The material that is embedded in some microwave popcorn bags (which is
>> why they always say "This Side Down".
>> Ditto for some microwave frozen dinner entres.
>>
>Actually, that stuff (called "reluctor") doesn't _reflect_ the
>microwaves - aluminum
>foil does that admirably (I saw a photo shoot in an early microwave
>oven cookbook -
>they wrapped an ice cube in foil, set it in the oven next to a cup of
>water, boiled the
>water and the ice cube was virtually untouched.) But that stuff on the
>bottom of the
>popcorn pack is designed to _absorb_ the microwaves and turn them into
>just plain
>ol' heat. Sometimes you get those "hot pocket" thingies with reluctor
>wrapped around
>them to brown the crust.
>
>I have a suspicion that the reluctor stuff is somehow related to
>"radar-absorbent
>materal" paint for stealth aircraft. ;-)
>
>Cheers!
>Rich
Give that man a cigarette and a blindfold; how dare you reveal
declassified Government sneakrets.
Grant
Not even aluminium dust? But that's possibly non-conductive. The
conductive paints certainly come at a premium price.
My current lappy was given in return for data recovery, what had happened
is that it was dropped because someone tripped over the power cord. Had
been 'repaired' but was unreliable (hence the giveaway). IN servicing the
thing I discovered inside plastic was sprayed with conductive silver paint
for RFI reduction. A small piece of painted plastic had broken off and
shorted hard drive connector pins, creating havoc. Anyway, machine has
not faulted since I properly cleaned it out :) Some of that silver paint
does work as advertised. It's old now, made in 1999. Win98 or Win2k era.
Now crawling along with WinXP SP3.
Grant.
Grant
Frozen vacuum, sounds almost possible ;) Probably good enough for solar
Grant.
mi...@sushi.com
> If I make a flat metal sheet as antenna on window from inside my
> apartment, to improve sign reception and transmission, what kind of
> pattern should I use for Wifi (2.45GHz) and Cellular (GSM has 4 bands,
> do not know what is best frequency for rest others?)
>
> reflect microwave?
You might want to research passive reflectors. Not my field, but I
know they are used commercially. You find passive reflectors generally
in rural areas when they run telecom signals over microwave. Rather
than doing point to point microwave links, they put a reflector in the
middle and keep the transmitter/receiver on the ground. Damn clever of
these phone companies, since that saves them the hassle of driving up
mountain tops to repair their gear.
Commercially, I've only seen Microflect.
http://www.valmont.com/page.aspx?id=91
If you live in the US and want a strong signal at home, go T-Mobile
and get one of their wifi capable phones. They call the service UMTS.
Some call it GOIP (gsm over IP). I've used the wifi phone service in
locations where there is no cellular service.
Paul Keinanen
>You might want to research passive reflectors. Not my field, but I
>know they are used commercially. You find passive reflectors generally
>in rural areas when they run telecom signals over microwave. Rather
>than doing point to point microwave links, they put a reflector in the
>middle and keep the transmitter/receiver on the ground. Damn clever of
>these phone companies, since that saves them the hassle of driving up
>mountain tops to repair their gear.
Passive repeaters (either simple reflectors or directional
antenna-cable-directional antenna) are useful very close to either end
of the link, but at midpoint, it is usually useless.
The power captured from the transmitter by the reflector is inversely
proportional to the square of distance. Also the power from the
reflector to final receiver is inversely proportional to he square of
the latter distance.
A reflector at the midpoint is equivalent to the situation in the
radar equation, i.e. the received power is inversely proportional to
the forth power of distance from the reflector to either end station.
Moving the reflector closer to one end and we have the bistatic radar
case.
Assuming initial condition with a total distance between end points of
60 km and a reflector at mid point and a certain very small power is
received.
Move the reflector above the receiver antenna on a mountain 3 km away.
Now the distance from transmitter to reflector is doubled and hence
path loss increases by 6 dB, but the path from reflector to receiver
drops to 1/10 and that path loss drops by 20 dB, so the signal
strength increases by 14 dB.
By putting the same reflector on a 300 m tower, the latter path loss
drops with an additional 20 dB and the received power increased by 34
dB compared to the midpoint situation.
A reflector at only 30 m (assuming free path to the reflector) would
give 54 dB stronger signals compared to the midpoint reflector.
Thus, if the signal is just usable with a reflector 30 m from the
receiver, the link will fail, if the reflector is 300-3000 m away or
even at midpoint.
Thus, in order to increase cell phone coverage e.g. in a room below
ground with a passive system, a directional antenna outside on a mast
aimed towards the cellular tower a low loss coaxial cable down into
the room below ground and an omnidirectional antenna in that room
might help.
Assuming minimal cable losses, there is one path loss from the
cellular tower to the directional antenna and an other pass loss
within the room from the omnidirectional antenna to the cell phone. Of
course the gain of the directional antenna also helps a bit. The cell
phone might be usable a few meters from the indoor antenna and there
is no need to directly connect the coaxial to the phone.
Michael A. Terrell
"mi...@sushi.com" wrote:
>
> You might want to research passive reflectors. Not my field, but I
> know they are used commercially. You find passive reflectors generally
> in rural areas when they run telecom signals over microwave. Rather
> than doing point to point microwave links, they put a reflector in the
> middle and keep the transmitter/receiver on the ground. Damn clever of
> these phone companies, since that saves them the hassle of driving up
> mountain tops to repair their gear.
You've never heard of 'Over the horizon microwave telephone relay"?
Search for 'White Alice Network' which was build in the '40s
--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
mpm
> On Thu, 26 Aug 2010 12:11:53 -0700 (PDT), mpm <mpmill...@aol.com>
Learn something new every day!
mpm
>
> - Show quoted text -
That's funny!
I was just thinking a lot of silver-plated, high-frequency RF
connectors don't contain any silver either! :)
I won't name them, but they hail from Belgium. Pure crap.
JosephKK
Not frozen vacuum, air pressure differntial foam casting.
JosephKK
Exactly my point, some do and some don't contain metal.
Michael A. Terrell
Antennas For Communications (AFC) still makes some of those microwave
antennas. The last time I passed their plant, the molds were still
sitting outside in their storage lot. They were owned by Microdyne at
one time, and made the 3 & 5 meter dishes for Microdyne's C-band CATV
and broadcast installations.