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TDR pulse or squarewave ?
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amdx
Jun 14, 2018, 2:53:29 PM6/14/18
to
I'm on a quest to find the proper termination for my Beverage on
Ground antenna (BOG)
My MFJ-259 is just not accurate up near 500 ohms.
I see two different styles of TDR a pulse and a square wave.
The square wave is neat in that you can watch the square wave get square
as you adjust the termination and the pulse about the same you watch the
reflection disappear when you get the proper termination.
Is there any other reason to pick one over the other?
Also, Is the output impedance important? I see many set to 50 ohms,
using four drivers with series 220 ohm resistors. Then I see other
circuits that add additional series resistance for 75 ohm, 100ohm, and
120 ohm, etc.
So if my antenna is actually 250 ohms, do I need to raise the output
impedance of the pulse driver?
Some use a 74AC14, which would be fine, but if I build it, is there a
fast edge chip that will run at 4.5 volts or even 3 volts.
I understand the layout is important to the fast edges.
Thanks, Mikek
Here's a square wave generator,
> http://marcusjenkins.com/tdr-pulse-generator-for-testing-coax/
Here's a pulse generator,
> http://support.fccps.cz/download/adv/frr/Reflectoprobe/reflectoprobe.html
Ground antenna (BOG)
My MFJ-259 is just not accurate up near 500 ohms.
I see two different styles of TDR a pulse and a square wave.
The square wave is neat in that you can watch the square wave get square
as you adjust the termination and the pulse about the same you watch the
reflection disappear when you get the proper termination.
Is there any other reason to pick one over the other?
Also, Is the output impedance important? I see many set to 50 ohms,
using four drivers with series 220 ohm resistors. Then I see other
circuits that add additional series resistance for 75 ohm, 100ohm, and
120 ohm, etc.
So if my antenna is actually 250 ohms, do I need to raise the output
impedance of the pulse driver?
Some use a 74AC14, which would be fine, but if I build it, is there a
fast edge chip that will run at 4.5 volts or even 3 volts.
I understand the layout is important to the fast edges.
Thanks, Mikek
Here's a square wave generator,
> http://marcusjenkins.com/tdr-pulse-generator-for-testing-coax/
Here's a pulse generator,
> http://support.fccps.cz/download/adv/frr/Reflectoprobe/reflectoprobe.html
Joerg
Jun 14, 2018, 3:01:18 PM6/14/18
to
On 2018-06-14 11:53, amdx wrote:
> I'm on a quest to find the proper termination for my Beverage on
> Ground antenna (BOG)
> My MFJ-259 is just not accurate up near 500 ohms.
> I see two different styles of TDR a pulse and a square wave.
> The square wave is neat in that you can watch the square wave get square
> as you adjust the termination and the pulse about the same you watch the
> reflection disappear when you get the proper termination.
>
> Is there any other reason to pick one over the other?
>
Either is fine. Just don't eat the whle can of Altoids in one session.
> I'm on a quest to find the proper termination for my Beverage on
> Ground antenna (BOG)
> My MFJ-259 is just not accurate up near 500 ohms.
> I see two different styles of TDR a pulse and a square wave.
> The square wave is neat in that you can watch the square wave get square
> as you adjust the termination and the pulse about the same you watch the
> reflection disappear when you get the proper termination.
>
> Is there any other reason to pick one over the other?
>
> Also, Is the output impedance important? I see many set to 50 ohms,
> using four drivers with series 220 ohm resistors. Then I see other
> circuits that add additional series resistance for 75 ohm, 100ohm, and
> 120 ohm, etc.
> So if my antenna is actually 250 ohms, do I need to raise the output
> impedance of the pulse driver?
>
reflections there as well. If both ends are mismatched it'll run back
and forth.
> Some use a 74AC14, which would be fine, but if I build it, is there a
> fast edge chip that will run at 4.5 volts or even 3 volts.
> I understand the layout is important to the fast edges.
>
super fast logic. 74HC would be ok, whatever you have.
> Thanks, Mikek
>
> Here's a square wave generator,
>
>> http://marcusjenkins.com/tdr-pulse-generator-for-testing-coax/
>
>
>
> Here's a pulse generator,
>
>> http://support.fccps.cz/download/adv/frr/Reflectoprobe/reflectoprobe.html
>
--
Regards, Joerg
http://www.analogconsultants.com/
amdx
Jun 14, 2018, 3:16:52 PM6/14/18
to
I might as well get the fastest edge chip as long as it will work on 3V
or 4.5v.
>
>> Thanks, Mikek
>>
>> Here's a square wave generator,
>>
>>> http://marcusjenkins.com/tdr-pulse-generator-for-testing-coax/
>>
>>
>>
>> Here's a pulse generator,
>>
>>> http://support.fccps.cz/download/adv/frr/Reflectoprobe/reflectoprobe.html
>>>
>>
>
> Those should work fine but adapt the resistors to your cable impedance.
>
measuring device to properly measure my cable. But, I expect I will see
the end reflection and the driving device mismatch reflection, I can
adjust to get rid of the device mismatch reflection.
Thanks, Mikek
Joerg
Jun 14, 2018, 3:33:30 PM6/14/18
to
and live with 2.7V or less but then you might as well use ECL for the
real speed.
>
>>
>>> Thanks, Mikek
>>>
>>> Here's a square wave generator,
>>>
>>>> http://marcusjenkins.com/tdr-pulse-generator-for-testing-coax/
>>>
>>>
>>>
>>> Here's a pulse generator,
>>>
>>>> http://support.fccps.cz/download/adv/frr/Reflectoprobe/reflectoprobe.html
>>>>
>>>
>>
>> Those should work fine but adapt the resistors to your cable impedance.
>>
> Ok, seems a little odd I need to measure my cable then adjust the
> measuring device to properly measure my cable.
behaves upon encountering a mismatch. Whether it'll invert or not, et
cetera. Then you can use that knowledge to gauge impedances and matching
without bothering to have the source well terminated.
> ... But, I expect I will see
> the end reflection and the driving device mismatch reflection, I can
> adjust to get rid of the device mismatch reflection.
Bingo. Sometimes on a long cable I actually use only the driver source
> adjust to get rid of the device mismatch reflection.
impedance. I change that until I only just one reflection left (the one
at the end of the cable) and then I know the cable impedance. Mostly for
cases where there is no spec on the cable but we need to use it for RF
stuff.
BTW, now it dawned on me what your handle "amdx" means :-)
I still have to build some sort of outdoor loop for the Drake SSR-1
downstairs in my brew house. Inside there is too much noise. I'd like to
keep it passive though, maybe 20ft or so of wire looped around under the
deck.
In the evening I can pick up radio stations in the tropical band around
5MHz.
Tom Gardner
Jun 14, 2018, 4:01:32 PM6/14/18
to
On 14/06/18 20:16, amdx wrote:
> I wasn't very clear on that, the 74AC14 is fine, but if I'm building, I might as
> well get the fastest edge chip as long as it will work on 3V or 4.5v.
74lvc1g* will work from 1.5V (and lower) to 5V
> I wasn't very clear on that, the 74AC14 is fine, but if I'm building, I might as
> well get the fastest edge chip as long as it will work on 3V or 4.5v.
If you drive a 50ohm cable with three parallel
(74lvc1g* + 143ohms in series) then the risetime
is <<1ns (probably <300ps, but I can't measure
that).
Joerg
Jun 14, 2018, 4:16:24 PM6/14/18
to
RF-transistor with it but there comes a point where the lack of
measurement tools for the RX side makes all this irrelevant. Even the
reflection from a 74AC pulse requires a scope north of 200MHz BW which
most hobbyists don't have.
amdx
Jun 14, 2018, 7:41:52 PM6/14/18
to
I removed the termination from my just measured at 253ft long BOG.
(I thought it was 300ft)
I measured it at 500kHz, 1000Khz, 1500kHz and 2000khz using my MFJ 259
with wire brought out to drive a DVM. I recorded the readings, then went
back to the shack and found a resistance to match what I read on the DVM
at the antenna. The reading was very close to 500 ohms.
This is much higher than the expected 250 ohms most of the BOG URLs
mention. Not sure why, Maybe I need a better ground, it's only 5ft long
in very wet dark soil. Maybe because it's a wet area I have more losses
on the wire.
I made up a termination of 500 ohms and installed it. I'll check
performance tonight.
Question,
I measured the wire open, and got 500 ohms.
Now I terminated it with 500 ohms, will I still measure 500 ohms
as the impedance?
Grabbing my equipment to go measure, I think it will.
Mikek
Joerg
Jun 14, 2018, 8:01:50 PM6/14/18
to
On 2018-06-14 16:41, amdx wrote:
> On 6/14/2018 3:16 PM, Joerg wrote:
>> On 2018-06-14 13:01, Tom Gardner wrote:
>>> On 14/06/18 20:16, amdx wrote:
>>>> I wasn't very clear on that, the 74AC14 is fine, but if I'm building,
>>>> I might as well get the fastest edge chip as long as it will work on
>>>> 3V or 4.5v.
>>>
>>> 74lvc1g* will work from 1.5V (and lower) to 5V
>>>
>>> If you drive a 50ohm cable with three parallel
>>> (74lvc1g* + 143ohms in series) then the risetime
>>> is <<1ns (probably <300ps, but I can't measure
>>> that).
>>
>>
>> For the ultimate pedal-to-the-metal feel you can bang a xxGHz
>> RF-transistor with it but there comes a point where the lack of
>> measurement tools for the RX side makes all this irrelevant. Even the
>> reflection from a 74AC pulse requires a scope north of 200MHz BW which
>> most hobbyists don't have.
>>
>
> I'm lucky to have come across at Tektronix 2465 CTS, 300MHz scope.
>
Those are nice scopes but still barely justifying anything faster than 74AC.
> On 6/14/2018 3:16 PM, Joerg wrote:
>> On 2018-06-14 13:01, Tom Gardner wrote:
>>> On 14/06/18 20:16, amdx wrote:
>>>> I wasn't very clear on that, the 74AC14 is fine, but if I'm building,
>>>> I might as well get the fastest edge chip as long as it will work on
>>>> 3V or 4.5v.
>>>
>>> 74lvc1g* will work from 1.5V (and lower) to 5V
>>>
>>> If you drive a 50ohm cable with three parallel
>>> (74lvc1g* + 143ohms in series) then the risetime
>>> is <<1ns (probably <300ps, but I can't measure
>>> that).
>>
>>
>> For the ultimate pedal-to-the-metal feel you can bang a xxGHz
>> RF-transistor with it but there comes a point where the lack of
>> measurement tools for the RX side makes all this irrelevant. Even the
>> reflection from a 74AC pulse requires a scope north of 200MHz BW which
>> most hobbyists don't have.
>>
>
> I'm lucky to have come across at Tektronix 2465 CTS, 300MHz scope.
>
The Tek 2465 is "the" scope, IMHO one of the best ever built. Except for
its delayed trigger clutch which they shouldn't have made out of
plastic, but there is always something.
> I removed the termination from my just measured at 253ft long BOG.
> (I thought it was 300ft)
> I measured it at 500kHz, 1000Khz, 1500kHz and 2000khz using my MFJ 259
> with wire brought out to drive a DVM. I recorded the readings, then went
> back to the shack and found a resistance to match what I read on the DVM
> at the antenna. The reading was very close to 500 ohms.
> This is much higher than the expected 250 ohms most of the BOG URLs
> mention. Not sure why, Maybe I need a better ground, it's only 5ft long
> in very wet dark soil. Maybe because it's a wet area I have more losses
> on the wire.
> I made up a termination of 500 ohms and installed it. I'll check
> performance tonight.
>
AM frequencies it shouldn't make a difference, the cable is the same
impedance at all of them. Though you probably meant something different
here.
> Question,
> I measured the wire open, and got 500 ohms.
> Now I terminated it with 500 ohms, will I still measure 500 ohms
> as the impedance?
> Grabbing my equipment to go measure, I think it will.
>
from the end if terminated.
mike
Jun 14, 2018, 8:07:54 PM6/14/18
to
I assume that any antenna system has a terminal impedance that is a
STRONG function of frequency.
Sounds like you're trying to use a time domain measurement to solve
a frequency domain problem.
You haven't mentioned anything like high resolution data acquisition
and FFT-like domain conversions.
So, just how do you plan to use the time domain information when you
get it?
TDR is a great way to adjust frequency-independent termination
resistances. For antennas, not so much.
As for pulse vs square wave, there ain't much difference as long
as the pulse is long enough to get the info you want.
Frequency hasn't been mentioned. I'm assuming it's LOW.
Impulse response is another issue.
I you get the pulse short enough, you can approximate a wide range
of frequencies and get something useful from a FFT, if you have super
acquisition capabilities.
I have 2 minutes of google experience with BOG antennas ;-)
Looks like you feed a matching transformer with low impedance coax.
Sounds like you need to match the wire at BOTH ends.
First thing I'd try is to listen to a signal and tweak the termination
for (whatever your best criteria are). If you can't tell
the difference, it don't matter.
I submit that a fast-rise pulse generator won't help you at all.
I was going to suggest a frequency burst, but you probably
can't get any useful information if the period of the burst
frequency isn't much shorter than the length of the wire.
amdx
Jun 14, 2018, 8:12:59 PM6/14/18
to
little rain storm since my last measurement. I'll try this on another day.
Mikek
Jeff Liebermann
Jun 14, 2018, 9:48:23 PM6/14/18
to
On Thu, 14 Jun 2018 13:53:20 -0500, amdx <noj...@knology.net> wrote:
> I'm on a quest to find the proper termination for my Beverage on
>Ground antenna (BOG)
> My MFJ-259 is just not accurate up near 500 ohms.
Use a 4:1 transformer or balun on the MFJ-259 to connect to your zip
> I'm on a quest to find the proper termination for my Beverage on
>Ground antenna (BOG)
> My MFJ-259 is just not accurate up near 500 ohms.
cord transmission line. Make sure the balun covers well beyond your
operating frequency range so that the balun doesn't contribute extra
inductance or capacitance to the measurement.
> I see two different styles of TDR a pulse and a square wave.
>The square wave is neat in that you can watch the square wave get square
>as you adjust the termination and the pulse about the same you watch the
>reflection disappear when you get the proper termination.
> Is there any other reason to pick one over the other?
impedance. One uses a TDR to measure transmission line impedance.
As Mike (ham...@netzero.net) mentioned, the load impedance is
frequency sensitive. Since the impedance of the antenna changes with
frequency, the frequencies near the characteristic impedance of the
transmission line will not reflect, while the one's that are some
complex impedance, will produce some rather other ugly looking
reflections. When combined, they really look ugly on the scope. The
only termination that will look reasonable is a purely resistive load.
You have that in the load, but combined with the BOG antenna, it's no
longer resistive.
I've built numerous TDR boards. For me, it's an obsession to NOT buy
a dedicated TDR instrument. The last few were based on this 74HC14
design:
<http://www.epanorama.net/circuits/tdr.html>
<http://www.epanorama.net/newepa/2010/07/17/tdr-circuit-kit-available/>
My only major change was replacing the 4.5 battery with a AA cell to
5.0v regulated step-up inverter.
<https://www.ebay.com/itm/232784790136>
74AC14 also works.
More (and probably better):
<http://www.qsl.net/g4usp/Time%20Domain%20Reflectometer/TDR%20SCH.htm>
<http://support.fccps.cz/download/adv/frr/Reflectoprobe/reflectoprobe.html>
<http://marcusjenkins.com/tdr-pulse-generator-for-testing-coax/>
<https://www.youtube.com/watch?v=9cP6w2odGUc>
Or, you can build one that uses an avalanche diode:
<https://www.youtube.com/watch?v=I1gfUNh5PJQ> (20:04)
--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
amdx
Jun 14, 2018, 10:13:12 PM6/14/18
to
On 6/14/2018 7:01 PM, Joerg wrote:
> On 2018-06-14 16:41, amdx wrote:
>> On 6/14/2018 3:16 PM, Joerg wrote:
>>> On 2018-06-14 13:01, Tom Gardner wrote:
>>>> On 14/06/18 20:16, amdx wrote:
>>>>> I wasn't very clear on that, the 74AC14 is fine, but if I'm building,
>>>>> I might as well get the fastest edge chip as long as it will work on
>>>>> 3V or 4.5v.
>>>>
>>>> 74lvc1g* will work from 1.5V (and lower) to 5V
>>>>
>>>> If you drive a 50ohm cable with three parallel
>>>> (74lvc1g* + 143ohms in series) then the risetime
>>>> is <<1ns (probably <300ps, but I can't measure
>>>> that).
>>>
>>>
>>> For the ultimate pedal-to-the-metal feel you can bang a xxGHz
>>> RF-transistor with it but there comes a point where the lack of
>>> measurement tools for the RX side makes all this irrelevant. Even the
>>> reflection from a 74AC pulse requires a scope north of 200MHz BW which
>>> most hobbyists don't have.
>>>
>>
>> I'm lucky to have come across at Tektronix 2465 CTS, 300MHz scope.
>>
>
> Those are nice scopes but still barely justifying anything faster than
> 74AC.
>
> The Tek 2465 is "the" scope, IMHO one of the best ever built. Except for
> its delayed trigger clutch which they shouldn't have made out of
> plastic, but there is always something.
>
I'll be careful with mine from now on.
> On 2018-06-14 16:41, amdx wrote:
>> On 6/14/2018 3:16 PM, Joerg wrote:
>>> On 2018-06-14 13:01, Tom Gardner wrote:
>>>> On 14/06/18 20:16, amdx wrote:
>>>>> I wasn't very clear on that, the 74AC14 is fine, but if I'm building,
>>>>> I might as well get the fastest edge chip as long as it will work on
>>>>> 3V or 4.5v.
>>>>
>>>> 74lvc1g* will work from 1.5V (and lower) to 5V
>>>>
>>>> If you drive a 50ohm cable with three parallel
>>>> (74lvc1g* + 143ohms in series) then the risetime
>>>> is <<1ns (probably <300ps, but I can't measure
>>>> that).
>>>
>>>
>>> For the ultimate pedal-to-the-metal feel you can bang a xxGHz
>>> RF-transistor with it but there comes a point where the lack of
>>> measurement tools for the RX side makes all this irrelevant. Even the
>>> reflection from a 74AC pulse requires a scope north of 200MHz BW which
>>> most hobbyists don't have.
>>>
>>
>> I'm lucky to have come across at Tektronix 2465 CTS, 300MHz scope.
>>
>
> Those are nice scopes but still barely justifying anything faster than
> 74AC.
>
> The Tek 2465 is "the" scope, IMHO one of the best ever built. Except for
> its delayed trigger clutch which they shouldn't have made out of
> plastic, but there is always something.
>
>
>> I removed the termination from my just measured at 253ft long BOG.
>> (I thought it was 300ft)
>> I measured it at 500kHz, 1000Khz, 1500kHz and 2000khz using my MFJ 259
>> with wire brought out to drive a DVM. I recorded the readings, then went
>> back to the shack and found a resistance to match what I read on the DVM
>> at the antenna. The reading was very close to 500 ohms.
>> This is much higher than the expected 250 ohms most of the BOG URLs
>> mention. Not sure why, Maybe I need a better ground, it's only 5ft long
>> in very wet dark soil. Maybe because it's a wet area I have more losses
>> on the wire.
>> I made up a termination of 500 ohms and installed it. I'll check
>> performance tonight.
>>
>
> I don't quite understand, not sure what a BOG is. Regarding the various
> AM frequencies it shouldn't make a difference, the cable is the same
> impedance at all of them. Though you probably meant something different
> here.
>
OH, sorry, conversations on several groups. A BOG is a 'Beverage
>> I removed the termination from my just measured at 253ft long BOG.
>> (I thought it was 300ft)
>> I measured it at 500kHz, 1000Khz, 1500kHz and 2000khz using my MFJ 259
>> with wire brought out to drive a DVM. I recorded the readings, then went
>> back to the shack and found a resistance to match what I read on the DVM
>> at the antenna. The reading was very close to 500 ohms.
>> This is much higher than the expected 250 ohms most of the BOG URLs
>> mention. Not sure why, Maybe I need a better ground, it's only 5ft long
>> in very wet dark soil. Maybe because it's a wet area I have more losses
>> on the wire.
>> I made up a termination of 500 ohms and installed it. I'll check
>> performance tonight.
>>
>
> I don't quite understand, not sure what a BOG is. Regarding the various
> AM frequencies it shouldn't make a difference, the cable is the same
> impedance at all of them. Though you probably meant something different
> here.
>
Antenna' On the Ground. So you lay a long piece of wire on the ground.
put a transformer at one end and termination resistor at the other.
amdx
Jun 14, 2018, 10:28:57 PM6/14/18
to
characteristic impedance as the wire. Thus I need to measure or use some
technique to find the proper termination resistor.
Go to 8:40 of this video below, That looks like it will do exactly
what I want use a square wave circuit.
> https://www.youtube.com/watch?v=Il_eju4D_TM&t=92s
> I assume that any antenna system has a terminal impedance that is a
> STRONG function of frequency.
> Sounds like you're trying to use a time domain measurement to solve
> a frequency domain problem.
> You haven't mentioned anything like high resolution data acquisition
> and FFT-like domain conversions.
> So, just how do you plan to use the time domain information when you
> get it?
>
> TDR is a great way to adjust frequency-independent termination
> resistances. For antennas, not so much.
>
> As for pulse vs square wave, there ain't much difference as long
> as the pulse is long enough to get the info you want.
> Frequency hasn't been mentioned. I'm assuming it's LOW.
>
> Impulse response is another issue.
> I you get the pulse short enough, you can approximate a wide range
> of frequencies and get something useful from a FFT, if you have super
> acquisition capabilities.
>
> I have 2 minutes of google experience with BOG antennas ;-)
> Looks like you feed a matching transformer with low impedance coax.
> Sounds like you need to match the wire at BOTH ends.
>
> First thing I'd try is to listen to a signal and tweak the termination
> for (whatever your best criteria are). If you can't tell
> the difference, it don't matter.
>
> I submit that a fast-rise pulse generator won't help you at all.
> I was going to suggest a frequency burst, but you probably
> can't get any useful information if the period of the burst
> frequency isn't much shorter than the length of the wire.
>
Thanks, Mikek
amdx
Jun 14, 2018, 11:13:31 PM6/14/18
to
On 6/14/2018 8:48 PM, Jeff Liebermann wrote:
> On Thu, 14 Jun 2018 13:53:20 -0500, amdx <noj...@knology.net> wrote:
>
>> I'm on a quest to find the proper termination for my Beverage on
>> Ground antenna (BOG)
>> My MFJ-259 is just not accurate up near 500 ohms.
>
> Use a 4:1 transformer or balun on the MFJ-259 to connect to your zip
> cord transmission line. Make sure the balun covers well beyond your
> operating frequency range so that the balun doesn't contribute extra
> inductance or capacitance to the measurement.
> How about if we assume my 500 ohms is correct for now and I wind a 500 to 50 ohm transformer and connect it to the BOG and ground and to the MFJ-259 for the measurement? Then I should be seeing around 50 ohms on the scale, and make more accurate tests. And if the impedance is very far from 50 ohms, I can adjust the transformer.
> On Thu, 14 Jun 2018 13:53:20 -0500, amdx <noj...@knology.net> wrote:
>
>> I'm on a quest to find the proper termination for my Beverage on
>> Ground antenna (BOG)
>> My MFJ-259 is just not accurate up near 500 ohms.
>
> Use a 4:1 transformer or balun on the MFJ-259 to connect to your zip
> cord transmission line. Make sure the balun covers well beyond your
> operating frequency range so that the balun doesn't contribute extra
> inductance or capacitance to the measurement.
Just noted something else that makes me think the 500 ohms is pretty
close. I measured at 4 frequencies with my MFJ-259, 500kHz-102.3mv
1000kHz-107.4 1500kHz-106.9 and 2000Khz-98.4mv. This is with a 250 ohm
termination. The mv readings are for comparison, I'll add a note* about
there values.
When I had a 500 ohm termination 500kHz-104.5mv, 1000kHz-105.6,
1500kHz--104.5, 2000kHz--104.1
I'm assuming them being about the same means something, could be wrong.
*105.9mv = 430ohms
106.9mv = 479ohms
107.9mv = 510ohms
I know, you thought it would vary with frequency, and I don't know why
it doesn't.
>> I see two different styles of TDR a pulse and a square wave.
>> The square wave is neat in that you can watch the square wave get square
>> as you adjust the termination and the pulse about the same you watch the
>> reflection disappear when you get the proper termination.
>> Is there any other reason to pick one over the other?
>
> Is neither one a choice? One doesn't use a TDR to measure antenna
> impedance. One uses a TDR to measure transmission line impedance.
>
very similar to a transmission line impedance, it's L-C-L-C-L-C,
and will have a reflection from the end or not if terminated properly.
Please watch the two minutes from 8:40, I think that is what I'm after.
> https://www.youtube.com/watch?v=Il_eju4D_TM&t=92s
Joerg
Jun 15, 2018, 9:58:17 AM6/15/18
to
and also this clutch for th 2465.
>>
>>> I removed the termination from my just measured at 253ft long BOG.
>>> (I thought it was 300ft)
>>> I measured it at 500kHz, 1000Khz, 1500kHz and 2000khz using my MFJ 259
>>> with wire brought out to drive a DVM. I recorded the readings, then went
>>> back to the shack and found a resistance to match what I read on the DVM
>>> at the antenna. The reading was very close to 500 ohms.
>>> This is much higher than the expected 250 ohms most of the BOG URLs
>>> mention. Not sure why, Maybe I need a better ground, it's only 5ft long
>>> in very wet dark soil. Maybe because it's a wet area I have more losses
>>> on the wire.
>>> I made up a termination of 500 ohms and installed it. I'll check
>>> performance tonight.
>>>
>>
>> I don't quite understand, not sure what a BOG is. Regarding the
>> various AM frequencies it shouldn't make a difference, the cable is
>> the same impedance at all of them. Though you probably meant something
>> different here.
>>
> OH, sorry, conversations on several groups. A BOG is a 'Beverage
> Antenna' On the Ground. So you lay a long piece of wire on the ground.
> put a transformer at one end and termination resistor at the other.
>
quite rocky. It would change as the properties of the ground change. Wet
dirt, dry, rocks, sand.
[...]
amdx
Jun 15, 2018, 10:57:21 AM6/15/18
to
grounds and a desert in between. I can only work with what I have, and
what I have is a clandestine beverage on someone else's pretty wet
property. But I'm happy with what I have so far, I have less noise
and cochannel interference, than my Active antenna at 24ft or my long
wire at 35ft.
Here a story,
"The Case of Declining Beverage-on-Ground Antenna Performance"
> http://rudys.typepad.com/files/qst-june-2016-bog.pdf
Mikek
amdx
Jun 15, 2018, 11:23:33 AM6/15/18
to
On 6/14/2018 8:48 PM, Jeff Liebermann wrote:
I left with comparing the BOG to a transmission line, your argument is
that it is frequency dependent. Your probably right, but I'm not see
much change over a 4 to 1 frequency range now that I have the
termination resistor at 500 ohms.
I will build the TDR even if it's only to check my speaker wire feed
line impedance.
I'm in the market to buy a better Antenna Analyzer, I've looked at
video of the RigExpert AA-30, but I don't see any info about how it does
at 500 ohms. I have a suspicion that most analyzers lose accuracy the
farther from 50 ohms you get.
Any comment about this ground rod resistance measuring method?
See last 1/3rd of page.
> http://www.mwcircle.org/mw_loop_beverage.htm
Mikek
>
> I've built numerous TDR boards. For me, it's an obsession to NOT buy
> a dedicated TDR instrument. The last few were based on this 74HC14
> design:
> <http://www.epanorama.net/circuits/tdr.html>
> <http://www.epanorama.net/newepa/2010/07/17/tdr-circuit-kit-available/>
> My only major change was replacing the 4.5 battery with a AA cell to
> 5.0v regulated step-up inverter.
drive voltage?
Johnny B Good
Jun 15, 2018, 11:38:37 AM6/15/18
to
On Fri, 15 Jun 2018 09:57:13 -0500, amdx wrote:
====snip====
> Here a story,
> "The Case of Declining Beverage-on-Ground Antenna Performance"
>> http://rudys.typepad.com/files/qst-june-2016-bog.pdf
>
I have to say that my reaction to reading that article was "Well, Duh!".
:-)
--
Johnny B Good
====snip====
> Here a story,
> "The Case of Declining Beverage-on-Ground Antenna Performance"
>> http://rudys.typepad.com/files/qst-june-2016-bog.pdf
>
:-)
--
Johnny B Good
Joerg
Jun 15, 2018, 12:06:33 PM6/15/18
to
watering can, his neighbor coming out with a shotgun "Whaddaya doin' in
my yard?!" ... "Oh, just watering the termination of my beverage". Then
Brutus the dog comes barging out, running to that very spot, sniffing
some, lifting a leg and letting go.
:-)
Jeff Liebermann
Jun 15, 2018, 12:37:23 PM6/15/18
to
On Fri, 15 Jun 2018 10:23:25 -0500, amdx <noj...@knology.net> wrote:
>> I've built numerous TDR boards. For me, it's an obsession to NOT buy
>> a dedicated TDR instrument. The last few were based on this 74HC14
>> design:
>> <http://www.epanorama.net/circuits/tdr.html>
>> <http://www.epanorama.net/newepa/2010/07/17/tdr-circuit-kit-available/>
>> My only major change was replacing the 4.5 battery with a AA cell to
>> 5.0v regulated step-up inverter.
>Did you add the step up for longer battery life or did you need more
>drive voltage?
Neither.
>> I've built numerous TDR boards. For me, it's an obsession to NOT buy
>> a dedicated TDR instrument. The last few were based on this 74HC14
>> design:
>> <http://www.epanorama.net/circuits/tdr.html>
>> <http://www.epanorama.net/newepa/2010/07/17/tdr-circuit-kit-available/>
>> My only major change was replacing the 4.5 battery with a AA cell to
>> 5.0v regulated step-up inverter.
>Did you add the step up for longer battery life or did you need more
>drive voltage?
1. I put an adjustable power supply on Vcc and ran it up and down to
see what range of voltages would work for the 74HC14. 25 ohm
resistive load so that it draws some current (about 0.2A). The data
sheet claims that the 74HC14 will work from 2-7V and I wanted to see
what the output would look like over this range. At the low end, I
lost some risetime. At the high end, I some some oscillations or
ringing. 5V seemed like a good compromise value.
2. The 74AC14 has a voltage range of 2-6v which should work nicely at
5V, but the 74ACT14 is 4.5-5.5v, which requires a 5v regulated supply.
I wanted to try all of them, so 5V regulated was the obvious choice.
3. I wanted to run it off a single cheap alkaline battery to make it
small. If I were to do it again today, I probably would use a LiIon
or LiPo cell and leave out the regulator. It will probably run ok on
3.6v (except for 74ACT14).
4. I couldn't find a three cell AA battery holder that would fit in
the intended box. One AA and an inverter are much smaller.
5. I had some switching regulators left over from another project.
<https://www.ebay.com/itm/232784790136>
There may be something better available. I didn't check.
6. I was thinking of selling the PCB, but never got around to
learning KiCad so that I could make the board. Yet another unfinished
project.
I'll get back to the antenna stuff later. I'm kinda busy today. Two
meetings, lavish lunch, coffee with a friend, drug deal at Costco,
exercise walk, some errands, radio club meeting, etc. If any work
will be done today, it will be under cover of darkness (with the phone
turned off).
Johnny B Good
Jun 15, 2018, 12:39:37 PM6/15/18
to
On Thu, 14 Jun 2018 21:28:50 -0500, amdx wrote:
====snip====
> I want to find the termination resistance that is the same value as the
> characteristic impedance as the wire. Thus I need to measure or use some
> technique to find the proper termination resistor.
It's not the *wire* that has the characteristic impedance, it's the wire
and the ground return circuit that provides the characteristic impedance.
What you have there with your BOG, is effectively an extremely leaky
transmission line feeder that happens to have a useful directional
response to skywave signals (both front and back along its length if the
far end isn't terminated with a dummy load matching its characteristic
impedance).
If you can set up a variable dummy load which impedance can
automatically track the ever changing characteristic impedance of your
'leaky feeder' antenna[1], apart from variations in the signal voltage
transfer function into the Rx's input impedance, whatever impedance
mismatch you have at the Rx end won't matter one jot as far as
suppressing the unwanted reverse direction of signal pickup.
Anything coming in from the 'back' will never bounce back to the Rx due
to the perfectly matched dummy load termination and any signal received
from the forward direction hitting an Rx mismatch will only suffer a
portion of its energy being bounced back to the terminated end, never to
trouble the Rx again.
[1] After reading that pdf on the mysterious drop in performance of a
BOG, I'm guessing that an obvious way to improve performance, as well as
reduce variations in Z, would be to lay down a metre wide 100 metre long
roll of thin copper sheet along the ground upon which to lay your BOG
wire and hammer a pair of grounding rods either side of the copper
groundplane, say every ten metres, to bond the copper sheet to ground for
good measure.
It still won't be perfectly stable with regard to Z but it will come a
damn sight closer to the ideal and reduce losses to boot. :-)
A much cheaper, and more practical alternative to this problem might be
simply to suspend it a few feet above the ground clutter (say 6 to 10
feet, depending on the nature of the ground clutter and how often you
plan on hacking it back).
Incidentally, the Z of a BOG will vary along its length according to
variations in the local ground conductivity. This isn't usually a problem
since in general, these changes in Z tend to be relatively smooth in
nature. It's only step changes in Z that give rise to unwanted
reflections that would spoil the immunity to unwanted signals arriving
from the back end.
This leads on to the idea of an extremely long BOG not needing to be
quite so perfectly matched to its termination dummy load since the
increased return losses will improve the situation of unwanted
reflections spoiling its rejection of signals originating in the reverse
direction.
Given a long enough wire, you can simply bury the last ten yards or so
into a shallowly downsloped trench and forget about adding a discrete
terminating impedance altogether. Just let the ground do the job for
free! :-)
--
Johnny B Good
====snip====
> I want to find the termination resistance that is the same value as the
> characteristic impedance as the wire. Thus I need to measure or use some
> technique to find the proper termination resistor.
and the ground return circuit that provides the characteristic impedance.
What you have there with your BOG, is effectively an extremely leaky
transmission line feeder that happens to have a useful directional
response to skywave signals (both front and back along its length if the
far end isn't terminated with a dummy load matching its characteristic
impedance).
If you can set up a variable dummy load which impedance can
automatically track the ever changing characteristic impedance of your
'leaky feeder' antenna[1], apart from variations in the signal voltage
transfer function into the Rx's input impedance, whatever impedance
mismatch you have at the Rx end won't matter one jot as far as
suppressing the unwanted reverse direction of signal pickup.
Anything coming in from the 'back' will never bounce back to the Rx due
to the perfectly matched dummy load termination and any signal received
from the forward direction hitting an Rx mismatch will only suffer a
portion of its energy being bounced back to the terminated end, never to
trouble the Rx again.
[1] After reading that pdf on the mysterious drop in performance of a
BOG, I'm guessing that an obvious way to improve performance, as well as
reduce variations in Z, would be to lay down a metre wide 100 metre long
roll of thin copper sheet along the ground upon which to lay your BOG
wire and hammer a pair of grounding rods either side of the copper
groundplane, say every ten metres, to bond the copper sheet to ground for
good measure.
It still won't be perfectly stable with regard to Z but it will come a
damn sight closer to the ideal and reduce losses to boot. :-)
A much cheaper, and more practical alternative to this problem might be
simply to suspend it a few feet above the ground clutter (say 6 to 10
feet, depending on the nature of the ground clutter and how often you
plan on hacking it back).
Incidentally, the Z of a BOG will vary along its length according to
variations in the local ground conductivity. This isn't usually a problem
since in general, these changes in Z tend to be relatively smooth in
nature. It's only step changes in Z that give rise to unwanted
reflections that would spoil the immunity to unwanted signals arriving
from the back end.
This leads on to the idea of an extremely long BOG not needing to be
quite so perfectly matched to its termination dummy load since the
increased return losses will improve the situation of unwanted
reflections spoiling its rejection of signals originating in the reverse
direction.
Given a long enough wire, you can simply bury the last ten yards or so
into a shallowly downsloped trench and forget about adding a discrete
terminating impedance altogether. Just let the ground do the job for
free! :-)
--
Johnny B Good
Johnny B Good
Jun 15, 2018, 12:58:12 PM6/15/18
to
On Thu, 14 Jun 2018 22:13:25 -0500, amdx wrote:
====snip====
>>
> I not being argumentative, just want to understand, it seems my BOG is
> very similar to a transmission line impedance, it's L-C-L-C-L-C,
> and will have a reflection from the end or not if terminated properly.
>
Bingo! That's effectively what a BOG is; a very leaky transmission line!
The moment you terminate such an and fed long wire *antenna* into a
ground return dummy load that matches its effective transmission line
impedance characteristic, it stops being a conventional long wire antenna
with antenna like resonances and becomes a leaky feeder *transmission*
line instead.
If both ends are terminated with impedance matching dummy loads, you
won't ever see any resonance effects (unless the construction includes
any step changes of impedance). The effective impedances at each end need
not be the same with such a practical BOG but as long as changes of
impedance from end to end are smooth transitions, it only matters that
each end is terminated with an impedance that matches whatever it happens
to be at each end. This means you won't be seeing any resonant effects
with such a leaky feeder transmission line antenna.
--
Johnny B Good
====snip====
>>
> I not being argumentative, just want to understand, it seems my BOG is
> very similar to a transmission line impedance, it's L-C-L-C-L-C,
> and will have a reflection from the end or not if terminated properly.
>
The moment you terminate such an and fed long wire *antenna* into a
ground return dummy load that matches its effective transmission line
impedance characteristic, it stops being a conventional long wire antenna
with antenna like resonances and becomes a leaky feeder *transmission*
line instead.
If both ends are terminated with impedance matching dummy loads, you
won't ever see any resonance effects (unless the construction includes
any step changes of impedance). The effective impedances at each end need
not be the same with such a practical BOG but as long as changes of
impedance from end to end are smooth transitions, it only matters that
each end is terminated with an impedance that matches whatever it happens
to be at each end. This means you won't be seeing any resonant effects
with such a leaky feeder transmission line antenna.
--
Johnny B Good
amdx
Jun 15, 2018, 2:44:07 PM6/15/18
to
On 6/15/2018 11:06 AM, Joerg wrote:
> On 2018-06-15 08:38, Johnny B Good wrote:
>> On Fri, 15 Jun 2018 09:57:13 -0500, amdx wrote:
>>
>> ====snip====
>>
>>> Here a story,
>>> "The Case of Declining Beverage-on-Ground Antenna Performance"
>>>> http://rudys.typepad.com/files/qst-june-2016-bog.pdf
>>>
>>
>> I have to say that my reaction to reading that article was "Well,
>> Duh!".
>>
>> :-)
>>
>
> I can already picture Mike walking onto his neighbors's turf with a
> watering can, his neighbor coming out with a shotgun "Whaddaya doin' in
> my yard?!" ...
Ya, it's the edge of a commercial property and the buffer woods
> On 2018-06-15 08:38, Johnny B Good wrote:
>> On Fri, 15 Jun 2018 09:57:13 -0500, amdx wrote:
>>
>> ====snip====
>>
>>> Here a story,
>>> "The Case of Declining Beverage-on-Ground Antenna Performance"
>>>> http://rudys.typepad.com/files/qst-june-2016-bog.pdf
>>>
>>
>> I have to say that my reaction to reading that article was "Well,
>> Duh!".
>>
>> :-)
>>
>
> I can already picture Mike walking onto his neighbors's turf with a
> watering can, his neighbor coming out with a shotgun "Whaddaya doin' in
> my yard?!" ...
between the commercial property and a subdivision.
My Bog ends near (35ft) the fence line of two houses, one owner has
two dogs. if they are out, I lose my invisibility cloaking.
mike
Jun 15, 2018, 10:43:08 PM6/15/18
to
The video describes how to terminate a (approximately) lossless
transmission line with constant characteristic impedance and no
radiation. In that case, the only significant frequency dependent
characteristics are the length of the mismatched cable.
To the extent that your BOG approximates that, you're good to go.
Stuff a repetitive pulse into a coax. Do A FFT on that pulse train.
You'll see the frequencies and amplitudes that the pulse is putting on
the line.
You'll see the summation of the line characteristics at those and only
those frequencies and amplitudes.
Because the ideal coax is frequency independent, it doesn't matter.
If the BOG has characteristics like resonance or loss/radiation,
you may not be able to relate that to what you see on the scope.
The math relating frequency to time is doable. But the devil
is in the details. It's very difficult to generate the required
pulses and measure with the required resolution to get any useful
data. The dynamic range required is non trivial.
It's often best to solve a frequency problem in the frequency domain,
especially if you want it simple.
Here's a thought experiment.
Suppose I gave you two coaxes connected to identical BOG antennas
except that they had different termination resistors.
I ask you to pick the one that's the best.
How would describe the symptom that distinguishes best from worst?
What if you were to adjust one of the termination resistances
to maximize the goodness and minimize the badness of that symptom?
If there ain't no observable symptom, don't worry about it.;-)
If there is an observable symptom, tweak the load to optimize that.
Please post some pictures of the waveforms you get from the TDR.
Would be interesting to see what it looks like.
Would also be interesting to learn the frequencies you need
and what you're trying to do with it when you get it.
Are we having fun yet?
amdx
Jun 15, 2018, 11:41:24 PM6/15/18
to
when you have the highest F/B ratio, ie the signals from the back are
all dissipated in the termination resistor and don't reflect back to the
transformer.
I just need to run a wire for a Vactrol and then it won't matter.
I will be able to adjust the termination from the shack for the best
(least cochannel interference) signal.
> What if you were to adjust one of the termination resistances
> to maximize the goodness and minimize the badness of that symptom?
>
> If there ain't no observable symptom, don't worry about it.;-)
> If there is an observable symptom, tweak the load to optimize that.
>
> Please post some pictures of the waveforms you get from the TDR.
> Would be interesting to see what it looks like.
>
> Would also be interesting to learn the frequencies you need
> and what you're trying to do with it when you get it.
>
> Are we having fun yet?
we have a small business.
Mikek
>
>
>
>
>
>
>
>
srober...@gmail.com
Jun 16, 2018, 7:46:07 PM6/16/18
to
This pulse generator by Leo Bodnar is all the rage on the EEVblog forum for TDR. About as fast as you
Can get with low cost gear.
http://www.leobodnar.com/shop/index.php?main_page=index&cPath=124&zenid=cc3b955eb339500506754024e5942992
Steve
Can get with low cost gear.
http://www.leobodnar.com/shop/index.php?main_page=index&cPath=124&zenid=cc3b955eb339500506754024e5942992
Steve
mike
Jun 16, 2018, 10:47:15 PM6/16/18
to
You're building a Bird Slug.
It's a directional coupler loosely coupled to the "ether".
In a Bird Wattmeter the sensor is coupled to a relatively
constrained wave.
Your directional coupler has RF coming in at all angles and phase
shifts.
Not clear whether it's a simple summation of cosine relationships or
something more sinister.
What is the 'work' that you're doing in the AM broadcast band?
Stated another way...what is the improvement in your quality of life
that results from this impedance match?
amdx
Jun 17, 2018, 11:28:39 AM6/17/18
to
As it stands now, I have local stations directly West and one directly
East, At night they are both gone on the BOG and 6 S units of more on my
long wire and active whip antenna. That's not a bad thing, As long as I
have good signal of the front.
I'm in the Florida Panhandle and the antenna points at Chicago.
I have noted that the pattern starts reverting back to a more omni
pattern at somewhere above 1MHz. This happens because the antenna is to
short. I hope to add some loading coils to make it seem longer.
I did some antenna measurements using my MFJ-259* through a 500ohm to
50 ohm transformer.
With the far end OPEN, I measured at 500kHz--406ohms,
1000kHz--509ohms, 1500kHz--482ohms and 2000kHz--270ohms.
With a 500 ohm termination, I measured at 500kHz--425ohms,
1000kHz--475ohms, 1500kHz--407ohms and 2000kHz--350ohms.
I don't know what it means, I'm supposed to match the surge impedance
of the BOG. I guess I have to compromise, but at 500 ohms, I think I'm
very close for the 3 to 1 frequency range I'm after.
In the end, I'll have a variable resistor termination so getting this
termination right is just to learn about it
I ordered a new Antenna analyzer yesterday (Rigexpert AA-35), the
MFJ-259 just doesn't cut it any longer.
It will be even more fun with graphs!!
* To get better? measurements, I monitored the 259 output voltage with
my DVM and recorded the number for each frequency. Then back in the
shop, I put variable resistance on the MFJ/transformer assy and adjusted
to match the readings I got in the field, then measured the R with my
DVM. Ya, this is ignoring any reactance, but, I'll get there.
Mikek
Jeff Liebermann
Jun 17, 2018, 1:33:11 PM6/17/18
to
On Sun, 17 Jun 2018 10:28:32 -0500, amdx <noj...@knology.net> wrote:
> I did some antenna measurements using my MFJ-259* through a 500ohm to
>50 ohm transformer.
> With the far end OPEN, I measured at 500kHz--406ohms,
>1000kHz--509ohms, 1500kHz--482ohms and 2000kHz--270ohms.
>
>
>With a 500 ohm termination, I measured at 500kHz--425ohms,
>1000kHz--475ohms, 1500kHz--407ohms and 2000kHz--350ohms.
>
> I don't know what it means,
All that it means is that the feed impedance of the BOG is not the
> I did some antenna measurements using my MFJ-259* through a 500ohm to
>50 ohm transformer.
> With the far end OPEN, I measured at 500kHz--406ohms,
>1000kHz--509ohms, 1500kHz--482ohms and 2000kHz--270ohms.
>
>
>With a 500 ohm termination, I measured at 500kHz--425ohms,
>1000kHz--475ohms, 1500kHz--407ohms and 2000kHz--350ohms.
>
> I don't know what it means,
same as the impedance of your zip cord feed line. If you set the
terminator for best F/B ratio on the BOG, you'll probably end up with
some complex impedance at the feed point. Your zip cord feed line
might match that, but it's unlikely. So, to get it perfect, you'll
need some kind of antenna tuner or at least an LC network at the
antenna feed point to make the antenna look purely resistive.
Incidentally, I've found this T-match Java tuner simulator handy for
160m antenna matching. Probably will work equally well on BCB. Keep
close watch on the tuner losses:
<http://fermi.la.asu.edu/w9cf/tuner/tuner.html>
You can probably live without a tuner and just use resistors to match
the real part of the antenna impedance close to the zip cord impedance
or 50 receiver input. That's because your limiting factor for decent
reception at 1MHz is atmospheric noise. If you install an attenuator
between the BOG and the feed line for matching, the signal level will
go down, but the noise will also go down by the same amount. The
benefit is that the BOG will probably have a better F/B ratio. If you
don't believe me, take your current setup, and estimate the SNR by
watching the audio on an oscilloscope. Then, add a 3 or 6dB
attenuator at the 50 ohm receiver input. Crank up the receiver volume
to get the same peak level on the scope. You should see the same SNR.
I suggest you do your measurements at the antenna feed point, without
the zip cord feed line. Once the numbers look sane, then deal with
the feed line and matching to 50 ohms into the receiver.
Your new analyzer looks interesting:
<https://rigexpertusa.com/aa-35-zoom-analyzer/>
I don't know anything about it, but if it's better than my MFJ-269 and
doesn't blow up the input diodes every time I connect it to a big
antenna, I'm interested. Let me know how it works for you.
Good luck.
amdx
Jun 17, 2018, 2:14:31 PM6/17/18
to
On 6/17/2018 12:33 PM, Jeff Liebermann wrote:
> On Sun, 17 Jun 2018 10:28:32 -0500, amdx <noj...@knology.net> wrote:
>
>
>> I did some antenna measurements using my MFJ-259* through a 500ohm to
>> 50 ohm transformer.
>> With the far end OPEN, I measured at 500kHz--406ohms,
>> 1000kHz--509ohms, 1500kHz--482ohms and 2000kHz--270ohms.
>>
>>
>> With a 500 ohm termination, I measured at 500kHz--425ohms,
>> 1000kHz--475ohms, 1500kHz--407ohms and 2000kHz--350ohms.
>>
>> I don't know what it means,
>
> All that it means is that the feed impedance of the BOG is not the
> same as the impedance of your zip cord feed line.
Sorry, I should have been more specific, I measured the BOG only
> On Sun, 17 Jun 2018 10:28:32 -0500, amdx <noj...@knology.net> wrote:
>
>
>> I did some antenna measurements using my MFJ-259* through a 500ohm to
>> 50 ohm transformer.
>> With the far end OPEN, I measured at 500kHz--406ohms,
>> 1000kHz--509ohms, 1500kHz--482ohms and 2000kHz--270ohms.
>>
>>
>> With a 500 ohm termination, I measured at 500kHz--425ohms,
>> 1000kHz--475ohms, 1500kHz--407ohms and 2000kHz--350ohms.
>>
>> I don't know what it means,
>
> All that it means is that the feed impedance of the BOG is not the
> same as the impedance of your zip cord feed line.
no feedline, just a 500 to 50 ohm transformer between the MFJ259 and the
wire.
If you set the
> terminator for best F/B ratio on the BOG, you'll probably end up with
> some complex impedance at the feed point. Your zip cord feed line
> might match that, but it's unlikely. So, to get it perfect, you'll
> need some kind of antenna tuner or at least an LC network at the
> antenna feed point to make the antenna look purely resistive.
>
> Incidentally, I've found this T-match Java tuner simulator handy for
> 160m antenna matching. Probably will work equally well on BCB. Keep
> close watch on the tuner losses:
> <http://fermi.la.asu.edu/w9cf/tuner/tuner.html>
>
> You can probably live without a tuner and just use resistors to match
> the real part of the antenna impedance close to the zip cord impedance
> or 50 receiver input. That's because your limiting factor for decent
> reception at 1MHz is atmospheric noise. If you install an attenuator
> between the BOG and the feed line for matching, the signal level will
> go down, but the noise will also go down by the same amount. The
> benefit is that the BOG will probably have a better F/B ratio. If you
> don't believe me, take your current setup, and estimate the SNR by
> watching the audio on an oscilloscope. Then, add a 3 or 6dB
> attenuator at the 50 ohm receiver input. Crank up the receiver volume
> to get the same peak level on the scope. You should see the same SNR.
>
> I suggest you do your measurements at the antenna feed point, without
> the zip cord feed line. Once the numbers look sane, then deal with
> the feed line and matching to 50 ohms into the receiver.
>
> Your new analyzer looks interesting:
> <https://rigexpertusa.com/aa-35-zoom-analyzer/>
> I don't know anything about it, but if it's better than my MFJ-269 and
> doesn't blow up the input diodes every time I connect it to a big
> antenna, I'm interested. Let me know how it works for you.
>
> Good luck.
>
but the only difference I can find is the upper frequency range.
> https://www.youtube.com/watch?v=Q2HDuv84mkw
Here's a comparison of the 10 analyzers from Rigexperts.
> https://rigexpert.com/antenna-analyzers-comparison-table/
I'm starting to notice some electronics coming out of Ukraine,
which is where this is made.
Mikek
mike
Jun 17, 2018, 3:55:54 PM6/17/18
to
I'm assuming that there's so much noise coming in that you can easily
build an amplifier that doesn't degrade SNR.
Why not put a buffer at the BOG? You can adjust the circuit design
to make the input impedance track what the BOG wants over the frequency
range. The feedline gets matched to 50 ohms, or whatever shielded
cable you use, and those issues go away. Yes?
What if you were to build a reverse directional coupler?
Haven't figgered out exactly how to build it, but as a thought
experiment, consider a coax placed parallel to the antenna.
Not sure how long it needs to be.
Terminate it and send down a signal at the Rx frequency.
Cut a slot along the top of the coax to let the RF leak out
without disturbing the impedance much.
Tweak the BOG termination to minimize the signal leaking out
of the coax at the receiver.
Assume symmetry and use the same termination impedance on both
ends of the BOG.
I'd still like to see the TDR waveforms. It would be hard
to find a pulse generator and scope that wouldn't be good
enough at 1MHz. and 500 ohms.
I thought the probe calibration signal out of the
scope would work, but I tried it. I was wrong. Rise time
too slow.
amdx
Jun 17, 2018, 4:46:30 PM6/17/18
to
I'm getting way beyond my experience, so this is "food for thought."
I'm assuming that there's so much noise coming in that you can easily
build an amplifier that doesn't degrade SNR.
Why not put a buffer at the BOG? You can adjust the circuit design
to make the input impedance track what the BOG wants over the frequency
range. The feedline gets matched to 50 ohms, or whatever shielded
cable you use, and those issues go away. Yes?
What if you were to build a reverse directional coupler?
Haven't figgered out exactly how to build it, but as a thought
experiment, consider a coax placed parallel to the antenna.
Not sure how long it needs to be.
Terminate it and send down a signal at the Rx frequency.
Cut a slot along the top of the coax to let the RF leak out
without disturbing the impedance much.
Tweak the BOG termination to minimize the signal leaking out
of the coax at the receiver.
Assume symmetry and use the same termination impedance on both
ends of the BOG.
I'd still like to see the TDR waveforms. It would be hard
to find a pulse generator and scope that wouldn't be good
enough at 1MHz. and 500 ohms.
I thought the probe calibration signal out of the
scope would work, but I tried it. I was wrong. Rise time
too slow.
************************************************************
I'm assuming that there's so much noise coming in that you can easily
build an amplifier that doesn't degrade SNR.
Why not put a buffer at the BOG? You can adjust the circuit design
to make the input impedance track what the BOG wants over the frequency
range. The feedline gets matched to 50 ohms, or whatever shielded
cable you use, and those issues go away. Yes?
What if you were to build a reverse directional coupler?
Haven't figgered out exactly how to build it, but as a thought
experiment, consider a coax placed parallel to the antenna.
Not sure how long it needs to be.
Terminate it and send down a signal at the Rx frequency.
Cut a slot along the top of the coax to let the RF leak out
without disturbing the impedance much.
Tweak the BOG termination to minimize the signal leaking out
of the coax at the receiver.
Assume symmetry and use the same termination impedance on both
ends of the BOG.
I'd still like to see the TDR waveforms. It would be hard
to find a pulse generator and scope that wouldn't be good
enough at 1MHz. and 500 ohms.
I thought the probe calibration signal out of the
scope would work, but I tried it. I was wrong. Rise time
too slow.
My newsreader is acting up, I could not see any text in your post, I
went to google groups and pasted it above.
>I'm assuming that there's so much noise coming in that you can easily
build an amplifier that doesn't degrade SNR.
are high input impedance 100 ohm output, low noise.
>Why not put a buffer at the BOG? You can adjust the circuit design
>to make the input impedance track what the BOG wants over the frequency
>range. The feedline gets matched to 50 ohms, or whatever shielded
>cable you use, and those issues go away. Yes?
although I would need an adult to figure out the L's and C's to match
the antenna. I haven't got any hints to the reactance of the BOG over
frequency.
Stepped away from coax, I'm using twisted speaker wire for it's much
lower signal ingress. Could move to CAT5 with or without a shield, I've
read the shield is not necessary. Mostly the CAT5 because I can get it
that will standup outdoors. I suspect my speaker wire won't hold up.
>What if you were to build a reverse directional coupler?
it would receive South and central America, Mexico and Cuba, I don't
understand Spanish.
There are plenty of plans for reversible Beverages.
>I'd still like to see the TDR waveforms.
from a company I worked for, I may have it.
>I thought the probe calibration signal out of the
>scope would work, but I tried it. I was wrong. Rise time
>too slow.
Mikek
Jeff Liebermann
Jun 17, 2018, 5:30:13 PM6/17/18
to
On Sun, 17 Jun 2018 15:46:20 -0500, amdx <noj...@knology.net> wrote:
>On 6/17/2018 1:14 PM, amdx wrote:
>> Here's a comprehensive review of the functions of the AA-55,
>> but the only difference I can find is the upper frequency range.
>>> https://www.youtube.com/watch?v=Q2HDuv84mkw
>> Here's a comparison of the 10 analyzers from Rigexperts.
>>> https://rigexpert.com/antenna-analyzers-comparison-table/
The AA-55 will generate an on screen Smith Chart, while the AA-35 does
>On 6/17/2018 1:14 PM, amdx wrote:
>> Here's a comprehensive review of the functions of the AA-55,
>> but the only difference I can find is the upper frequency range.
>>> https://www.youtube.com/watch?v=Q2HDuv84mkw
>> Here's a comparison of the 10 analyzers from Rigexperts.
>>> https://rigexpert.com/antenna-analyzers-comparison-table/
not. The AA-35 goes up to 35MHz, while the AA-55 goes to 55MHz (to
cover 6 meter band). Whether these are worth an extra $100 is
questionable. Smith charts are very useful for antenna and
transmission line matching. Compare:
<https://rigexpertusa.com/aa-35-zoom-analyzer/>
<https://rigexpertusa.com/aa-35-zoom-screen-shots/>
<https://rigexpertusa.com/aa-55-zoom-analyzer/>
<https://rigexpertusa.com/aa-55-zoom-screen-shots/>
Notice that there two very different web piles:
<https://rigexpert.com>
<https://rigexpertusa.com>
>> I'm starting to notice some electronics coming out of Ukraine,
>> which is where this is made.
parts. The USA site points to corporate offices in Carmichael, CA.
> My newsreader is acting up, I could not see any text in your post, I
>went to google groups and pasted it above.
I didn't write the stuff you cited.
Looking at your news header, you're using Thunderbird 52.8.0. That
the current version. What's probably happening is that your indexes
are corrupted. First, rebuild the global database:
<https://support.mozilla.org/en-US/kb/rebuilding-global-database>
Then, compact the news directories (right-click -> compact).
Then if that doesn't work, find the index files for news in the
..\Applications Data\Thunderbird\Profiles\{whatever}\something
I don't have News installed under Thunderbird on this machine so I
can't give you the exact location and file names. Once you've found
them, move just the indexes to an empty directory. When you restart
Thunderbird, it will automagically rebuild the news indexes.
Incidentally, the same problem (no text) happens with email and is
fixed in the same manner.
mike
Jun 17, 2018, 6:11:34 PM6/17/18
to
What if you were to build a reverse directional coupler?
Haven't figgered out exactly how to build it, but as a thought
experiment, consider a coax placed parallel to the antenna.
Not sure how long it needs to be.
Terminate it and send down a signal at the Rx frequency.
Cut a slot along the top of the coax to let the RF leak out
without disturbing the impedance much.
Tweak the BOG termination to minimize the signal leaking out
of the coax at the receiver.
Assume symmetry and use the same termination impedance on both
ends of the BOG.
The purpose is as a tool to adjust the termination.
Haven't figgered out exactly how to build it, but as a thought
experiment, consider a coax placed parallel to the antenna.
Not sure how long it needs to be.
Terminate it and send down a signal at the Rx frequency.
Cut a slot along the top of the coax to let the RF leak out
without disturbing the impedance much.
Tweak the BOG termination to minimize the signal leaking out
of the coax at the receiver.
Assume symmetry and use the same termination impedance on both
ends of the BOG.
Just happens to work like a bird slug directional coupler, only it's
a source rather than an input. The advantage is that you don't have
to match the drive impedance, it's just another received signal with
precisely known parameters.
amdx
Jun 17, 2018, 6:40:22 PM6/17/18
to
> What if you were to build a reverse directional coupler?
> Haven't figgered out exactly how to build it, but as a thought
> experiment, consider a coax placed parallel to the antenna.
> Not sure how long it needs to be.
> Terminate it and send down a signal at the Rx frequency.
> Cut a slot along the top of the coax to let the RF leak out
> without disturbing the impedance much.
> Tweak the BOG termination to minimize the signal leaking out
> of the coax at the receiver.
> Assume symmetry and use the same termination impedance on both
> ends of the BOG.
>
> The purpose is as a tool to adjust the termination.
> Just happens to work like a bird slug directional coupler, only it's
> a source rather than an input. The advantage is that you don't have
> to match the drive impedance, it's just another received signal with
> precisely known parameters.
go about that.
amdx
Jun 17, 2018, 6:59:21 PM6/17/18
to
On 6/17/2018 4:30 PM, Jeff Liebermann wrote:
> On Sun, 17 Jun 2018 15:46:20 -0500, amdx <noj...@knology.net> wrote:
>
>> On 6/17/2018 1:14 PM, amdx wrote:
>
>>> Here's a comprehensive review of the functions of the AA-55,
>>> but the only difference I can find is the upper frequency range.
>>>> https://www.youtube.com/watch?v=Q2HDuv84mkw
>
>>> Here's a comparison of the 10 analyzers from Rigexperts.
>>>> https://rigexpert.com/antenna-analyzers-comparison-table/
>
> The AA-55 will generate an on screen Smith Chart, while the AA-35 does
> not. The AA-35 goes up to 35MHz, while the AA-55 goes to 55MHz (to
> cover 6 meter band). Whether these are worth an extra $100 is
> questionable. Smith charts are very useful for antenna and
> transmission line matching. Compare:
> <https://rigexpertusa.com/aa-35-zoom-analyzer/>
> <https://rigexpertusa.com/aa-35-zoom-screen-shots/>
> <https://rigexpertusa.com/aa-55-zoom-analyzer/>
> <https://rigexpertusa.com/aa-55-zoom-screen-shots/>
> Notice that there two very different web piles:
> <https://rigexpert.com>
> <https://rigexpertusa.com>
>
I don't know that the Smith chart capability would have pushed me to
> On Sun, 17 Jun 2018 15:46:20 -0500, amdx <noj...@knology.net> wrote:
>
>> On 6/17/2018 1:14 PM, amdx wrote:
>
>>> Here's a comprehensive review of the functions of the AA-55,
>>> but the only difference I can find is the upper frequency range.
>>>> https://www.youtube.com/watch?v=Q2HDuv84mkw
>
>>> Here's a comparison of the 10 analyzers from Rigexperts.
>>>> https://rigexpert.com/antenna-analyzers-comparison-table/
>
> The AA-55 will generate an on screen Smith Chart, while the AA-35 does
> not. The AA-35 goes up to 35MHz, while the AA-55 goes to 55MHz (to
> cover 6 meter band). Whether these are worth an extra $100 is
> questionable. Smith charts are very useful for antenna and
> transmission line matching. Compare:
> <https://rigexpertusa.com/aa-35-zoom-analyzer/>
> <https://rigexpertusa.com/aa-35-zoom-screen-shots/>
> <https://rigexpertusa.com/aa-55-zoom-analyzer/>
> <https://rigexpertusa.com/aa-55-zoom-screen-shots/>
> Notice that there two very different web piles:
> <https://rigexpert.com>
> <https://rigexpertusa.com>
>
the AA-55 for the extra $110, maybe then I would need to learn
understand Smith charts.
I also should have bought from Rigexpertusa.
>>> I'm starting to notice some electronics coming out of Ukraine,
>>> which is where this is made.
>
> Yep, which might causes problems when you need repairs and spare
> parts. The USA site points to corporate offices in Carmichael, CA.
>
>> My newsreader is acting up, I could not see any text in your post, I
>> went to google groups and pasted it above.
>
> Hang on while I remove my RF hat and replace it with my PC Repair hat.
> I didn't write the stuff you cited.
to it so I responded to my own post and copied his post into it.
>
> Looking at your news header, you're using Thunderbird 52.8.0. That
> the current version. What's probably happening is that your indexes
> are corrupted. First, rebuild the global database:
> <https://support.mozilla.org/en-US/kb/rebuilding-global-database>
> Then, compact the news directories (right-click -> compact).
> Then if that doesn't work, find the index files for news in the
> ..\Applications Data\Thunderbird\Profiles\{whatever}\something
> I don't have News installed under Thunderbird on this machine so I
> can't give you the exact location and file names. Once you've found
> them, move just the indexes to an empty directory. When you restart
> Thunderbird, it will automagically rebuild the news indexes.
> Incidentally, the same problem (no text) happens with email and is
> fixed in the same manner.
>
have under two email addresses.
I'll google how to delete emails by sender.
Mikek
Jeff Liebermann
Jun 17, 2018, 9:07:15 PM6/17/18
to
On Sun, 17 Jun 2018 17:59:12 -0500, amdx <noj...@knology.net> wrote:
> Looking into it, wonder if I should delete some of the 45,000 emails I
> have under two email addresses.
> I'll google how to delete emails by sender.
Sort the messages by the "From" column by clicking on the "From" tab.
> Looking into it, wonder if I should delete some of the 45,000 emails I
> have under two email addresses.
> I'll google how to delete emails by sender.
Find the first instance of the person you want to delete.
Stomp and hold the <Shift> key.
Scroll down to the last instance of the messages you want to delete.
Left click once. The messages by the person should be highlighted.
Hit <delete> and they're gone.
You might also consider using a program designed for reading Usenet
news. I suggest Forte Agent:
<http://www.forteinc.com/main/homepage.php>
$29 after 30 day free trial.
Jeff Liebermann
Jun 17, 2018, 9:32:57 PM6/17/18
to
On Sun, 17 Jun 2018 15:11:18 -0700, mike <ham...@netzero.net> wrote:
>What if you were to build a reverse directional coupler?
>Haven't figgered out exactly how to build it, but as a thought
>experiment, consider a coax placed parallel to the antenna.
>Not sure how long it needs to be.
>Terminate it and send down a signal at the Rx frequency.
>Cut a slot along the top of the coax to let the RF leak out
>without disturbing the impedance much.
>Tweak the BOG termination to minimize the signal leaking out
>of the coax at the receiver.
>Assume symmetry and use the same termination impedance on both
>ends of the BOG.
>
>The purpose is as a tool to adjust the termination.
>Just happens to work like a bird slug directional coupler, only it's
>a source rather than an input. The advantage is that you don't have
>to match the drive impedance, it's just another received signal with
>precisely known parameters.
Kinda sounds like yet another antenna analyzer. Sweeping the HF bands
>What if you were to build a reverse directional coupler?
>Haven't figgered out exactly how to build it, but as a thought
>experiment, consider a coax placed parallel to the antenna.
>Not sure how long it needs to be.
>Terminate it and send down a signal at the Rx frequency.
>Cut a slot along the top of the coax to let the RF leak out
>without disturbing the impedance much.
>Tweak the BOG termination to minimize the signal leaking out
>of the coax at the receiver.
>Assume symmetry and use the same termination impedance on both
>ends of the BOG.
>
>The purpose is as a tool to adjust the termination.
>Just happens to work like a bird slug directional coupler, only it's
>a source rather than an input. The advantage is that you don't have
>to match the drive impedance, it's just another received signal with
>precisely known parameters.
with the watts of RF that it takes to get an indication on a Bird slug
is probably not the way to make yourself very popular. If you must
sweep or transmit, use low power.
May I suggest some alternatives:
1. Noise Bridge:
<https://www.mfjenterprises.com/Product.php?productid=MFJ-202B>
<http://kv5r.com/ham-radio/noise-bridge/>
<https://qrpguys.com/k7qo-noise-bridge>
<http://users.monash.edu.au/~ralphk/noise-bridge.html>
<https://www.google.com/search?q=rf+noise+bridge&tbm=isch>
2. Return Loss Bridge:
<http://www.qsl.net/kl7jef/Build%20a%20Return%20Loss%20Bridge.pdf>
<http://www.qsl.net/n9zia/rlb/index.html>
<https://www.youtube.com/watch?v=ct_ZUYTRkOA>
<https://www.youtube.com/watch?v=lqd_6s8ZfqM>
<https://www.google.com/search?q=return+loss+bridge&tbm=isch>
Requires an RF source, sweep generator, RF diode detector, and
oscilloscope. It shows the VSWR, but not the load reactance.
I have a bunch of Texscan return loss bridges that I use on the bench
mostly to sweep various antennas:
<https://www.google.com/search?tbm=isch&q=return+loss+bridge+texscan>
<http://www.qsl.net/n9zia/rlb/texscan.png>
mike
Jun 17, 2018, 11:17:36 PM6/17/18
to
On 6/17/2018 6:32 PM, Jeff Liebermann wrote:
> On Sun, 17 Jun 2018 15:11:18 -0700, mike <ham...@netzero.net> wrote:
>
>> What if you were to build a reverse directional coupler?
>> Haven't figgered out exactly how to build it, but as a thought
>> experiment, consider a coax placed parallel to the antenna.
>> Not sure how long it needs to be.
>> Terminate it and send down a signal at the Rx frequency.
>> Cut a slot along the top of the coax to let the RF leak out
>> without disturbing the impedance much.
>> Tweak the BOG termination to minimize the signal leaking out
>> of the coax at the receiver.
>> Assume symmetry and use the same termination impedance on both
>> ends of the BOG.
>>
>> The purpose is as a tool to adjust the termination.
>> Just happens to work like a bird slug directional coupler, only it's
>> a source rather than an input. The advantage is that you don't have
>> to match the drive impedance, it's just another received signal with
>> precisely known parameters.
>
> Kinda sounds like yet another antenna analyzer. Sweeping the HF bands
> with the watts of RF that it takes to get an indication on a Bird slug
> is probably not the way to make yourself very popular. If you must
> sweep or transmit, use low power.
You're missing the point too.
> On Sun, 17 Jun 2018 15:11:18 -0700, mike <ham...@netzero.net> wrote:
>
>> What if you were to build a reverse directional coupler?
>> Haven't figgered out exactly how to build it, but as a thought
>> experiment, consider a coax placed parallel to the antenna.
>> Not sure how long it needs to be.
>> Terminate it and send down a signal at the Rx frequency.
>> Cut a slot along the top of the coax to let the RF leak out
>> without disturbing the impedance much.
>> Tweak the BOG termination to minimize the signal leaking out
>> of the coax at the receiver.
>> Assume symmetry and use the same termination impedance on both
>> ends of the BOG.
>>
>> The purpose is as a tool to adjust the termination.
>> Just happens to work like a bird slug directional coupler, only it's
>> a source rather than an input. The advantage is that you don't have
>> to match the drive impedance, it's just another received signal with
>> precisely known parameters.
>
> Kinda sounds like yet another antenna analyzer. Sweeping the HF bands
> with the watts of RF that it takes to get an indication on a Bird slug
> is probably not the way to make yourself very popular. If you must
> sweep or transmit, use low power.
The BOG IS the bird slug. The parallel transmission line radiates
fractions of a milliwatt to get thru the BOG a few feet away and onto
the receiver is a controlled source
to let you tune the BOG termination. The unanswered question is
just how long does that transmission line have to be to get useful
results. I think I'd use a sine wave. A noise generator works, but
you have to average it. And the total noise power required is WAY
more than you'd need for a single frequency carrier.
As I said, this is a thought experiment. Might turn out to be totally
wrong...
amdx
Jun 18, 2018, 7:07:56 PM6/18/18
to
ohms. I used an old style Vactrol VTL3A27*, padded with a series 100ohm
fixed resistor and a parallel 1,330 ohm fixed resistor.
Will get to test it tonight.
Mikek
*
https://www.datasheets360.com/pdf/-4577744495125923097
Jeff Liebermann
Jun 19, 2018, 12:12:44 PM6/19/18
to
On Mon, 18 Jun 2018 18:07:46 -0500, amdx <noj...@knology.net> wrote:
> I installed a variable termination on the BOG today, 200 ohm to 1300
>ohms. I used an old style Vactrol VTL3A27*, padded with a series 100ohm
>fixed resistor and a parallel 1,330 ohm fixed resistor.
> Will get to test it tonight.
> Mikek
>*
> https://www.datasheets360.com/pdf/-4577744495125923097
What can go wrong? Inside is probably a cadmium sulfide
> I installed a variable termination on the BOG today, 200 ohm to 1300
>ohms. I used an old style Vactrol VTL3A27*, padded with a series 100ohm
>fixed resistor and a parallel 1,330 ohm fixed resistor.
> Will get to test it tonight.
> Mikek
>*
> https://www.datasheets360.com/pdf/-4577744495125923097
photoresistor. If it's like these, the conductive path follows a
serpentine pattern, which kinda looks like an inductor.
<https://www.google.com/search?tbm=isch&q=photoresistor>
The inductance is probably fairly small (I couldn't find a number). At
1MHz, the inductance probably has little effect, especially with the
padding. However, if things act strangely in your testing, you might
want to measure the inductance with a common LRC meter.
amdx
Jun 19, 2018, 12:54:49 PM6/19/18
to
On 6/19/2018 11:12 AM, Jeff Liebermann wrote:
> On Mon, 18 Jun 2018 18:07:46 -0500, amdx <noj...@knology.net> wrote:
>
>> I installed a variable termination on the BOG today, 200 ohm to 1300
>> ohms. I used an old style Vactrol VTL3A27*, padded with a series 100ohm
>> fixed resistor and a parallel 1,330 ohm fixed resistor.
>> Will get to test it tonight.
>> Mikek
>> *
>> https://www.datasheets360.com/pdf/-4577744495125923097
>
> What can go wrong? Inside is probably a cadmium sulfide
> photoresistor. If it's like these, the conductive path follows a
> serpentine pattern, which kinda looks like an inductor.
> <https://www.google.com/search?tbm=isch&q=photoresistor>
> The inductance is probably fairly small (I couldn't find a number). At
> 1MHz, the inductance probably has little effect, especially with the
> padding. However, if things act strangely in your testing, you might
> want to measure the inductance with a common LRC meter.
>
>
I had good success when I used the Vactrols on my Flag antenna, and
> On Mon, 18 Jun 2018 18:07:46 -0500, amdx <noj...@knology.net> wrote:
>
>> I installed a variable termination on the BOG today, 200 ohm to 1300
>> ohms. I used an old style Vactrol VTL3A27*, padded with a series 100ohm
>> fixed resistor and a parallel 1,330 ohm fixed resistor.
>> Will get to test it tonight.
>> Mikek
>> *
>> https://www.datasheets360.com/pdf/-4577744495125923097
>
> What can go wrong? Inside is probably a cadmium sulfide
> photoresistor. If it's like these, the conductive path follows a
> serpentine pattern, which kinda looks like an inductor.
> <https://www.google.com/search?tbm=isch&q=photoresistor>
> The inductance is probably fairly small (I couldn't find a number). At
> 1MHz, the inductance probably has little effect, especially with the
> padding. However, if things act strangely in your testing, you might
> want to measure the inductance with a common LRC meter.
>
>
many have used them for variable terminations, I don't suspect much
inductance.
I didn't have a good night for finding any front to back.
My antennas acted about the same. Sometimes atmospherics will do that,
I'll try another night or two before I revert back to a fixed resistor.
I went to use the Vactrol ass'y I took off my Flag antenna during
testing, I found the 300ohm series resistor was measuring 10Mohm and the
Vactrol resistance section was open, I suspect lightning may have
damaged it.
I installed a new Vactrol and resistors.
I have one Vactrol on the shelf, I can measure it when I get my
Rigexpert. I have an LCR meter, but the highest frequency it goes to is
100kHz.
Mikek
Mikek
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