Re: Topband: High Impedance RX Antennas

[Jim Brown]

On 4/3/2023 10:20 AM, Tree wrote:

I guess most people have some kind of small antenna analyzer that has a TDR
kind of function.


In my professional life in pro audio, I started doing Time Domain 
Spectrometry in 1982, so I have a pretty good handle on how it works. 
There is a mathematical relationship between the frequency response of a 
system and its time response -- one is the inverse of the other. The 
Fourier Transform of the time response yields the frequency response, 
and the Inverse Fourier of the frequency response yields the time 
response. Modern antenna analyzers produce a swept frequency response, 
and associated software running on the computer does the Inverse Fourier 
Transform of a sweep to produce the TDR.


For more than 10 years, the best of the low cost Vector Network 
Analyzers has been the VNWA3SE, built and sold as a finished and tested 
unit, by SDR Kits, run by hams in UK. The unit, its firmware, and 
associated software, was designed by DG8SAQ, an EE prof. Support from 
both DG8SAQ and SDR Kits is excellent -- both read and respond to their 
support email reflector. Current cost with shipping is about $560 
(depending on currency).


https://www.sdr-kits.net/introducing-DG8SAQ-VNWA3

Greatest precision (ability to see small things) is provided by a sweep 
over a very wide frequency range. I usually sweep from 50-500 MHz. Once 
the sweep is done, the TDR is simply a few more button pushes in the 
menu system.


73, Jim K9YC
_
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector

Re: Topband: [PVRC] 2-element receiving arrays

[Dave Cuthbert]

It seems that padding the element capacitance as needed for equal
capacitance would help.

  Dave KH6AQ

On Thu, Mar 30, 2023 at 4:48 PM Frank W3LPL  wrote:

> Hi Dave,
>
> Anyone who has experimented with a high impedance antenna such
> as an end fed half wave has experienced the extreme environmental
> influence on the feedpoint impedance of a high impedance feed.
>
> The required spacing to trees and buildings is very difficult to predict
> with any confidence. The impedance of a high impedance element
> -- and hence the amount of voltag if feeds into the preamp --
> is heavily influenced by its immediate environment.
>
> If all of the high impedance verticals in an array do not produce the
> same voltages from the signals received by the array, the pattern
> of the array and especially its nulls are significantly degraded.
>
> 73
> Frank
> W3LPL
>
>
>
>
>
>
>
> From: "K3ZJ David Siddall" 
> To: "Frank W3LPL" 
> Cc: "topband" , "PVRC" ,
> "Pete N4ZR N4ZR" 
> Sent: Friday, March 31, 2023 12:34:28 AM
> Subject: Re: [PVRC] Topband: 2-element receiving arrays
>
> Frank,
> " wrt to-negative effects of nearby trees and buildings." for high
> impedance verticals:
>
> Is there any data measuring how much loss if placed in the woods? Minimum
> distance from a tree to minimize the loss? Are their other effects too,
> such as less directionality?
>
> 73, Dave K3ZJ
>
>
>
> On Thu, Mar 30, 2023 at 1:38 PM Frank W3LPL < [ mailto:
> donov...@starpower.net | donov...@starpower.net ] > wrote:
>
>
> Hi Pete,
>
> For a monoband receiving array, you might consider using low impedance
> resonant verticals rather than high impedance verticals.
>
> The primary advantages of high impedance verticals are
> - very short verticals (but taller verticals produce stronger signals)
> - multi-band operation
> - no radials
>
> The primary disadvantages are
> - reliability issues with outdoor electronics
> - lightning susceptibility of outdoor electronics
> - higher cost
> - much lower signal levels
> - extreme care required to suppress common mode signals (buried feedlines
> are highly recommended)
> - negative effects of nearby trees and buildings.
>
> The primary advantages of low impedance verticals are
> - much stronger signal levels
> - much less criticality of common mode signal suppression,
> - much lower cost
> - much higher reliability
> - immunity to lightning damage
> - much less affected by nearby trees and buildings
>
> The primary disadvantages are
> - taller verticals (typically about 24 feet)
> - radials (they can be very short if many radials are used)
> - mono band operation (switchable matching networks can be used for
> multi-band operation).
>
> I highly recommend the DX Engineering Receiving Antenna Phasing System.
> Its expensive but well worth the investment especially for a small array.
>
> [ https://www.dxengineering.com/parts/dxe-ncc-2 |
> https://www.dxengineering.com/parts/dxe-ncc-2 ]
>
> If you have 120 feet for a three element array, the YCCC array is a great
> choice
> It can use high impedance or low impedance verticals
> Unfortunately its no longer available from DX Engineering
> The nine element YCCC array uses only three active elements at any time,
> so its really a three element array switchable in many directions.
>
> [
> https://static.dxengineering.com/global/images/instructions/dxe-yccc-switch.pdf?_gl=1*1cv0fc9*_ga*MjEyMDA1Nzc3MS4xNjUyMzAyMjc0*_ga_NZB590FMHY*MTY4MDE5NTk1OC40My4xLjE2ODAxOTYwNTYuNTAuMC4w
> |
> https://static.dxengineering.com/global/images/instructions/dxe-yccc-switch.pdf?_gl=1*1cv0fc9*_ga*MjEyMDA1Nzc3MS4xNjUyMzAyMjc0*_ga_NZB590FMHY*MTY4MDE5NTk1OC40My4xLjE2ODAxOTYwNTYuNTAuMC4w
> ]
>
> [ https://www.youtube.com/watch?v=dl-crM5Kb6A |
> https://www.youtube.com/watch?v=dl-crM5Kb6A ]
>
> [ https://www.youtube.com/watch?v=lVW1CmrzP7c |
> https://www.youtube.com/watch?v=lVW1CmrzP7c ]
>
> A two element array occupies only 60 feet or even a little less.
>
> 73
> Frank
> W3LPL
>
>
> - Original Message -
> From: "Pete N4ZR N4ZR" < [ mailto:pete.n...@gmail.com |
> pete.n...@gmail.com ] >
> To: "topband" < [ mailto:Topband@contesting.com | Topband@contesting.com
> ] >
> Sent: Thursday, March 30, 2023 12:54:30 PM
> Subject: Topband: 2-element receiving arrays
>
> Thinking ahead to next winter on 160, I'm interested in replacing my
> K9AY Loop with a 2-vertical phased array. I'd like to homebrew the
> antennas and just buy or build the remote control unit for the shack.
> I'm looking for sources of components (antenna-located preamps and an
> in-shack controller), and would prefer not to completely homebrew them,
> but the prices at the usual suspects are awfully high. Any ideas?
>
> I have pretty reasonably-priced access to 25 and 31-foot fiberglass
> poles (used for wind-socks by model airplane enthusiasts). I'm thinking
> that one relatively low-cost approach might be to attach, say, #14 wire
> to the poles, with preamps at the base, but wonder if there is a
> downside to using such 

Re: Topband: High Impedance RX Antennas

[John Kaufmann via Topband]

Another tool I've found indispensable for setting up and troubleshooting phased 
vertical RX arrays is a two-port VNA.   I use an Array Solutions VNA-2180 (now 
discontinued) for critical measurements.  I also have a NanoVNA H4 
(https://nanovna.com/) which is a very "affordable" VNA that can be used as a 
portable, handheld, standalone instrument and that you can take out in the 
field.  In most cases, the NanoVNA H4 is more than good enough.

There is a learning curve to using a VNA.  However, once you learn it, you'll 
be able to make very accurate measurements of delay line lengths, preamplifier 
gain and phase, phase combiner gain and phase.  Most VNA's also have a TDR 
function, although it is usually based on frequency domain measurements that 
are transformed to the time domain.

I'm running a homebrew RX array and it would have been almost impossible to get 
it running as well as it is now without a VNA.

73, John W1FV
_
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector

Re: Topband: High Impedance RX Antennas

[Don Moman VE6JY]

A used Tek 1502 TDR is the "gold standard" to me anyway and they can be
quite cheap at flea markets etc. They are "arm held" and self contained
portable so ideal for up to 1000' runs and have enough resolution that you
can "see" defects that you don't really need to worry about.  The advantage
over some of the VNWA's that have a TDR function, is that the 1502 is real
time so intermittents can easily be spotted. And it measures impedance so
you can easily see how long and what Z that unknown roll of flea market
coax is!

I built the scope based TDR from the QST articles years ago, but that
version isn't even close to the 1502.  I also have a Tek 1503 for checking
longer runs of control cable etc.

73 Don
VE6JY

On Mon, Apr 3, 2023 at 11:21 AM Tree  wrote:

> I guess most people have some kind of small antenna analyzer that has a TDR
> kind of function.
>
> I have not warmed up to them yet as the results I see seem to be "all over
> the place".  Maybe I just don't know how to use them yet.
>
> My goto TDR is homebrew - using an analog scope.
>
> Here is one design pretty similar to what I am using:
>
> A very simple TDR from W2AEW – PierpaLab.com
>   I put a
> switch on it to slow down the rep rate as an option since some of my
> "stuff" is pretty long.
>
> It works wonderfully to check feedlines and beverages.  I have one beverage
> that has transformers and feedlines on both ends and I can see the
> difference between open/short/terminate on the "far end" (which is
> physically in the shack).
>
> 73 Tree N6TR
>
> On Mon, Apr 3, 2023 at 10:11 AM Frank W3LPL 
> wrote:
>
> > Another highly recommended tool is a Time Domain Reflectometer.
> > Tt easily detects any abnormalities in my 8-circle and 4-square
> > arrays and stacked HF Yagi arrays and switches.
> >
> > Other than my hand held antenna analyzer, my hand held TDR is my
> > most often used and most valuable tool for proving that the performance
> > of my antennas and feedlines has not changed from prior measurements
> > and identifying and isolating faults before they cause partial or
> > total failure.  A TDR can detect, diagnose and locate feedline and
> > antenna faults from the comfort of your ham shack.
> >
> > Affordable TDRs are often available on eBay. Some antenna
> > analyzers have rudimentary TDR capabilities but I've never used
> > an antenna analyzer with TDR capabilities comparable in
> > performance to a TDR.
> >
> > Long before moisture causes coax failure, it causes the impedance
> > of the coax to change, a potentially big problem in a phased array
> > or stacked Yagis.  A TDR easily detects and locates the problem
> > before it causes a failure.
> >
> > An antenna analyzer can also detect that moisture has caused
> > an impedance shift in coax cable.  Place a dummy load (with the
> > same impedance as the coax) at one end of the coax cable.  Sweep
> > the antenna analyzer frequency.  As you do a frequency sweep the
> > VSWR and impedance should not change.  If it does, moisture is
> > probably eating away inside your coax.
> >
> > 73
> > Frank
> > W3LPL
> >
> >
> >
> >
> >
> > - Original Message -
> > From: "Dennis W0JX via Topband" 
> > To: "topband" 
> > Sent: Monday, April 3, 2023 4:42:37 PM
> > Subject: Re: Topband: High Impedance RX Antennas
> >
> > There is an old saying "The enemy of good is perfect."  You will be
> driven
> > crazy by chasing down every slight variance from the ideal. That being
> > said, it is important to check out the obvious areas where flaws can
> create
> > big problems. Indeed, the feedline coax, typically RG6 CATV line, is a
> > major contributor to array performance problems.  The cheap, big box
> cable
> > is covered with PVC and that stuff hardens and tightens up over the
> years.
> > This allows water to enter the shield and the water easily migrates for
> > long distances, creating a high resistance. Spend the money upfront and
> buy
> > quality cable that is flooded.
> > The idea of using cable that has a solid copper conductor has merit. But
> > even with that, a bare copper conductor will oxidize over time. I find
> > myself cleaning these conductors on an annual basis with the eraser end
> of
> > a pencil (recommended by Lee K7TJR).
> > I have also had F connector failures on my combiner box and on a common
> > mode choke. Sometimes the imported female connector center contact just
> > fails for no reason. The alternative Amphenol connectors are very
> expensive
> > at about $8+ each but I am considering replacing the connectors with
> these
> > higher grade parts.
> > Also, the so-called "water-proof" compression connectors are often not.
> > The connection must be waterproofed effectively.  Also, condensation from
> > humidity can be a big problem. Here is northeast Ohio, the environment is
> > humid for the majority of the year. I have poured water out of a 75 ohm
> > preamp that was sheltered in a good enclosure!
> > 

Re: Topband: High Impedance RX Antennas

[Tree]

I guess most people have some kind of small antenna analyzer that has a TDR
kind of function.

I have not warmed up to them yet as the results I see seem to be "all over
the place".  Maybe I just don't know how to use them yet.

My goto TDR is homebrew - using an analog scope.

Here is one design pretty similar to what I am using:

A very simple TDR from W2AEW – PierpaLab.com
  I put a
switch on it to slow down the rep rate as an option since some of my
"stuff" is pretty long.

It works wonderfully to check feedlines and beverages.  I have one beverage
that has transformers and feedlines on both ends and I can see the
difference between open/short/terminate on the "far end" (which is
physically in the shack).

73 Tree N6TR

On Mon, Apr 3, 2023 at 10:11 AM Frank W3LPL  wrote:

> Another highly recommended tool is a Time Domain Reflectometer.
> Tt easily detects any abnormalities in my 8-circle and 4-square
> arrays and stacked HF Yagi arrays and switches.
>
> Other than my hand held antenna analyzer, my hand held TDR is my
> most often used and most valuable tool for proving that the performance
> of my antennas and feedlines has not changed from prior measurements
> and identifying and isolating faults before they cause partial or
> total failure.  A TDR can detect, diagnose and locate feedline and
> antenna faults from the comfort of your ham shack.
>
> Affordable TDRs are often available on eBay. Some antenna
> analyzers have rudimentary TDR capabilities but I've never used
> an antenna analyzer with TDR capabilities comparable in
> performance to a TDR.
>
> Long before moisture causes coax failure, it causes the impedance
> of the coax to change, a potentially big problem in a phased array
> or stacked Yagis.  A TDR easily detects and locates the problem
> before it causes a failure.
>
> An antenna analyzer can also detect that moisture has caused
> an impedance shift in coax cable.  Place a dummy load (with the
> same impedance as the coax) at one end of the coax cable.  Sweep
> the antenna analyzer frequency.  As you do a frequency sweep the
> VSWR and impedance should not change.  If it does, moisture is
> probably eating away inside your coax.
>
> 73
> Frank
> W3LPL
>
>
>
>
>
> - Original Message -
> From: "Dennis W0JX via Topband" 
> To: "topband" 
> Sent: Monday, April 3, 2023 4:42:37 PM
> Subject: Re: Topband: High Impedance RX Antennas
>
> There is an old saying "The enemy of good is perfect."  You will be driven
> crazy by chasing down every slight variance from the ideal. That being
> said, it is important to check out the obvious areas where flaws can create
> big problems. Indeed, the feedline coax, typically RG6 CATV line, is a
> major contributor to array performance problems.  The cheap, big box cable
> is covered with PVC and that stuff hardens and tightens up over the years.
> This allows water to enter the shield and the water easily migrates for
> long distances, creating a high resistance. Spend the money upfront and buy
> quality cable that is flooded.
> The idea of using cable that has a solid copper conductor has merit. But
> even with that, a bare copper conductor will oxidize over time. I find
> myself cleaning these conductors on an annual basis with the eraser end of
> a pencil (recommended by Lee K7TJR).
> I have also had F connector failures on my combiner box and on a common
> mode choke. Sometimes the imported female connector center contact just
> fails for no reason. The alternative Amphenol connectors are very expensive
> at about $8+ each but I am considering replacing the connectors with these
> higher grade parts.
> Also, the so-called "water-proof" compression connectors are often not.
> The connection must be waterproofed effectively.  Also, condensation from
> humidity can be a big problem. Here is northeast Ohio, the environment is
> humid for the majority of the year. I have poured water out of a 75 ohm
> preamp that was sheltered in a good enclosure!
> These complex phasing arrays are by no means plug and play. Each
> installation will be unique depending on layout and surrounding objects.
> There are three tools necessary to get them and keep them working:  1.) a
> good portable signal source to feed the antenna preamps (I use an Elecraft
> XG-3 with a home brew impedance transformer at the input);  2.) a portable
> transceiver to measure signal out of the system at various points (My KX3
> does a great job); and an accurate antenna analyzer to measure impedances
> and to measure feedlines and phasing lines for the proper electrical
> lengths. N6RK is right. There can be considerable difference in RG6
> impedance so you need to check it out.
>
>  73 Dennis W0JXMilan, OH
> _
> Searchable Archives: http://www.contesting.com/_topband - Topband
> Reflector
> _
> Searchable Archives: http://www.contesting.com/_topband - Topband
> Reflector
>
_

Re: Topband: High Impedance RX Antennas

[Frank W3LPL]

Another highly recommended tool is a Time Domain Reflectometer.
Tt easily detects any abnormalities in my 8-circle and 4-square
arrays and stacked HF Yagi arrays and switches.

Other than my hand held antenna analyzer, my hand held TDR is my
most often used and most valuable tool for proving that the performance
of my antennas and feedlines has not changed from prior measurements
and identifying and isolating faults before they cause partial or
total failure.  A TDR can detect, diagnose and locate feedline and
antenna faults from the comfort of your ham shack.

Affordable TDRs are often available on eBay. Some antenna
analyzers have rudimentary TDR capabilities but I've never used
an antenna analyzer with TDR capabilities comparable in
performance to a TDR.

Long before moisture causes coax failure, it causes the impedance
of the coax to change, a potentially big problem in a phased array
or stacked Yagis.  A TDR easily detects and locates the problem
before it causes a failure.

An antenna analyzer can also detect that moisture has caused
an impedance shift in coax cable.  Place a dummy load (with the
same impedance as the coax) at one end of the coax cable.  Sweep
the antenna analyzer frequency.  As you do a frequency sweep the
VSWR and impedance should not change.  If it does, moisture is
probably eating away inside your coax.

73
Frank
W3LPL





- Original Message -
From: "Dennis W0JX via Topband" 
To: "topband" 
Sent: Monday, April 3, 2023 4:42:37 PM
Subject: Re: Topband: High Impedance RX Antennas

There is an old saying "The enemy of good is perfect."  You will be driven 
crazy by chasing down every slight variance from the ideal. That being said, it 
is important to check out the obvious areas where flaws can create big 
problems. Indeed, the feedline coax, typically RG6 CATV line, is a major 
contributor to array performance problems.  The cheap, big box cable is covered 
with PVC and that stuff hardens and tightens up over the years. This allows 
water to enter the shield and the water easily migrates for long distances, 
creating a high resistance. Spend the money upfront and buy quality cable that 
is flooded.
The idea of using cable that has a solid copper conductor has merit. But even 
with that, a bare copper conductor will oxidize over time. I find myself 
cleaning these conductors on an annual basis with the eraser end of a pencil 
(recommended by Lee K7TJR).
I have also had F connector failures on my combiner box and on a common mode 
choke. Sometimes the imported female connector center contact just fails for no 
reason. The alternative Amphenol connectors are very expensive at about $8+ 
each but I am considering replacing the connectors with these higher grade 
parts.
Also, the so-called "water-proof" compression connectors are often not. The 
connection must be waterproofed effectively.  Also, condensation from humidity 
can be a big problem. Here is northeast Ohio, the environment is humid for the 
majority of the year. I have poured water out of a 75 ohm preamp that was 
sheltered in a good enclosure!
These complex phasing arrays are by no means plug and play. Each installation 
will be unique depending on layout and surrounding objects. There are three 
tools necessary to get them and keep them working:  1.) a good portable signal 
source to feed the antenna preamps (I use an Elecraft XG-3 with a home brew 
impedance transformer at the input);  2.) a portable transceiver to measure 
signal out of the system at various points (My KX3 does a great job); and an 
accurate antenna analyzer to measure impedances and to measure feedlines and 
phasing lines for the proper electrical lengths. N6RK is right. There can be 
considerable difference in RG6 impedance so you need to check it out.  
 
 73 Dennis W0JXMilan, OH  
_
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
_
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector

Re: Topband: High Impedance RX Antennas

[Dennis W0JX via Topband]

 There is an old saying "The enemy of good is perfect."  You will be driven 
crazy by chasing down every slight variance from the ideal. That being said, it 
is important to check out the obvious areas where flaws can create big 
problems. Indeed, the feedline coax, typically RG6 CATV line, is a major 
contributor to array performance problems.  The cheap, big box cable is covered 
with PVC and that stuff hardens and tightens up over the years. This allows 
water to enter the shield and the water easily migrates for long distances, 
creating a high resistance. Spend the money upfront and buy quality cable that 
is flooded.
The idea of using cable that has a solid copper conductor has merit. But even 
with that, a bare copper conductor will oxidize over time. I find myself 
cleaning these conductors on an annual basis with the eraser end of a pencil 
(recommended by Lee K7TJR).
I have also had F connector failures on my combiner box and on a common mode 
choke. Sometimes the imported female connector center contact just fails for no 
reason. The alternative Amphenol connectors are very expensive at about $8+ 
each but I am considering replacing the connectors with these higher grade 
parts.
Also, the so-called "water-proof" compression connectors are often not. The 
connection must be waterproofed effectively.  Also, condensation from humidity 
can be a big problem. Here is northeast Ohio, the environment is humid for the 
majority of the year. I have poured water out of a 75 ohm preamp that was 
sheltered in a good enclosure!
These complex phasing arrays are by no means plug and play. Each installation 
will be unique depending on layout and surrounding objects. There are three 
tools necessary to get them and keep them working:  1.) a good portable signal 
source to feed the antenna preamps (I use an Elecraft XG-3 with a home brew 
impedance transformer at the input);  2.) a portable transceiver to measure 
signal out of the system at various points (My KX3 does a great job); and an 
accurate antenna analyzer to measure impedances and to measure feedlines and 
phasing lines for the proper electrical lengths. N6RK is right. There can be 
considerable difference in RG6 impedance so you need to check it out.  
 
 73 Dennis W0JXMilan, OH  
_
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector

Re: Topband: [PVRC] 2-element receiving arrays

[Mike Fatchett W0MU]

Meaning,

We do the best we can and there is no and there will never be a perfect 
solution.  All we can do is attempt to eliminate as many variables as 
possible.   My circle array  works better than all of the other things I 
have tried.  It is near fencing, close to a power line etc.  I don't 
have unlimited flat land in the middle of nowhere.  Not optimal but it 
is what I can do.


I think people get caught up in perfection.  Put up stuff and try it!  
You might be surprised.  What works for me might not be a good solution 
for you, etc.


W0MU


On 3/30/2023 7:47 PM, Frank W3LPL wrote:

Hi Dave,

Anyone who has experimented with a high impedance antenna such
as an end fed half wave has experienced the extreme environmental
influence on the feedpoint impedance of a high impedance feed.

The required spacing to trees and buildings is very difficult to predict
with any confidence. The impedance of a high impedance element
-- and hence the amount of voltag if feeds into the preamp --
is heavily influenced by its immediate environment.

If all of the high impedance verticals in an array do not produce the
same voltages from the signals received by the array, the pattern
of the array and especially its nulls are significantly degraded.

73
Frank
W3LPL



Allow me to quibble a little with this analogy.  The 1/2 wave dipole
is a tuned circuit with a Q in the low double digits.  This leverages
any capacitance change.  The voltage probe antenna is just a plain
non-resonant capacitance.  Still sensitive to nearby conductors, but
probably not to the extent of the EFHW antenna.  I would be more
worried about circuit capacitance in the hi-Z preamp.  In general,
the capacitance of JFET's (or any FET's) is very loosely specified.
The transconductance is also very loosely specified, and can
act as a modulator of input capacitance due to the Miller effect.
As if that isn't bad enough, the DXE preamp comes with tank circuits
that you can optionally activate with jumpers.  This adds another
random variable to the input capacitance.  Ideally, there would be
a "factory select" padding capacitor to make the capacitance the
same on all copies of the preamp.  AFAIK, no preamps have this
feature. And finally, the CB whip moves around wildly in the wind.
If there are nearby objects, this adds a time variability.

73
Rick N6RK
_
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Reflector

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Re: Topband: European broadcast stations

[mstangelo]

I enjoyed listening to the LW stations but unfortunately they are disappearing:

 On 04/03/2023 8:31 AM David Olean  wrote:
> 
>  
> Hello Michael
> 
> I have an old Bendix MN-26C Aircraft Navigation receiver and use it in 
> my workshop that also doubles as my 160 meter ham shack. Of course, I 
> use my Beverage wires on the BC band and have listened to LW broadcasts 
> from Europe.  Over the last few years, many of the stations have 
> disappeared, but the last time I tried it, I could hear Droitwich in 
> England (BBC)  and another station in Iceland. The Icelandic station 
> played all sorts of stuff including rock n' roll. Both stations were in 
> the 200+ kHz range. I used to hear many more stations around Europe and 
> even the middle East and North Africa. Signals vary a lot depending on 
> conditions, just like 160 meters! Droitwich and Iceland were quite 
> listenable at times.
> 
> 73
> 
> Dave K1WHS
_
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector

Re: Topband: [PVRC] 2-element receiving arrays

[Richard (Rick) Karlquist]

On 3/30/2023 7:47 PM, Frank W3LPL wrote:

Hi Dave,

Anyone who has experimented with a high impedance antenna such
as an end fed half wave has experienced the extreme environmental
influence on the feedpoint impedance of a high impedance feed.

The required spacing to trees and buildings is very difficult to predict
with any confidence. The impedance of a high impedance element
-- and hence the amount of voltag if feeds into the preamp --
is heavily influenced by its immediate environment.

If all of the high impedance verticals in an array do not produce the
same voltages from the signals received by the array, the pattern
of the array and especially its nulls are significantly degraded.

73
Frank
W3LPL



Allow me to quibble a little with this analogy.  The 1/2 wave dipole
is a tuned circuit with a Q in the low double digits.  This leverages
any capacitance change.  The voltage probe antenna is just a plain
non-resonant capacitance.  Still sensitive to nearby conductors, but
probably not to the extent of the EFHW antenna.  I would be more
worried about circuit capacitance in the hi-Z preamp.  In general,
the capacitance of JFET's (or any FET's) is very loosely specified.
The transconductance is also very loosely specified, and can
act as a modulator of input capacitance due to the Miller effect.
As if that isn't bad enough, the DXE preamp comes with tank circuits
that you can optionally activate with jumpers.  This adds another
random variable to the input capacitance.  Ideally, there would be
a "factory select" padding capacitor to make the capacitance the
same on all copies of the preamp.  AFAIK, no preamps have this
feature. And finally, the CB whip moves around wildly in the wind.
If there are nearby objects, this adds a time variability.

73
Rick N6RK
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Re: Topband: European broadcast stations

[David Olean]

Hello Michael

I have an old Bendix MN-26C Aircraft Navigation receiver and use it in 
my workshop that also doubles as my 160 meter ham shack. Of course, I 
use my Beverage wires on the BC band and have listened to LW broadcasts 
from Europe.  Over the last few years, many of the stations have 
disappeared, but the last time I tried it, I could hear Droitwich in 
England (BBC)  and another station in Iceland. The Icelandic station 
played all sorts of stuff including rock n' roll. Both stations were in 
the 200+ kHz range. I used to hear many more stations around Europe and 
even the middle East and North Africa. Signals vary a lot depending on 
conditions, just like 160 meters! Droitwich and Iceland were quite 
listenable at times.


73

Dave K1WHS

On 4/3/2023 6:56 AM, Michael Rutkaus wrote:

I wonder if you guys with terrific antenna systems ever use them to try to
listen to European broadcast stations in the 100kc to 300kc area? I've
heard just a few weakly a few years ago.
Mike
K4QET


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Topband: European broadcast stations

[Michael Rutkaus]

I wonder if you guys with terrific antenna systems ever use them to try to
listen to European broadcast stations in the 100kc to 300kc area? I've
heard just a few weakly a few years ago.
Mike
K4QET


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