Topband: Loop on the ground as a counterpoise

[K4SAV]

Without more detail of your system, the cause is only a guess.  Here are 
some possibilities.

A single wire isn't much of a ground plane.  It will make a vertical 
directional.  When you change from a single wire to a different ground 
system you will change the antenna pattern. You should expect some 
difference in noise performance.

Since a single wire is a poor ground system, if it is closer to a local 
noise source than a different ground system, it could be picking up more 
noise.

Since a single wire is not a good ground system, and if you don't have a 
very good choke at the antenna feedpoint, the coax could be acting as 
part of the antenna.  Changing the ground system also changes the 
effects of the coax.

A longer wire used for ground will have a lower resonant frequency and 
may provide a lower impedance at the frequency of interest, providing 
more decoupling for the coax.

Those are all just possibilities.  Further experimentation may determine 
the real answer.  It's not likely that NEC will show the answer.

Solution: Change to a good ground system as suggested by some of the 
other responders.

Since you have been playing with loops on the ground as receiving 
antennas, you may be interested in reading the results of my experiments 
here:
http://lists.contesting.com/archives/html/Topband/2018-08/msg00019.html

Jerry, K4SAV


On 5/4/2020 3:57 AM, Chris Moulding wrote:
> I've developed a High Z Antenna Amplifier for 160m and other HF use as 
> previously mentioned on the list.
>
> Usually these would be used with a ground rod and 5m vertical element.
>
> With the lockdown it's not possible to nip to the shops for a ground 
> rod so I looked at supplying a 10m wire as a counterpoise.
>
> At home and the workshop I have Loop on the Ground antennas from 
> previous antenna experiments so I also tried using these with both 
> ends of the loop connected to the amplifier ground terminal.
>
> On testing this gave significantly better signal to noise ratios than 
> using a ground rod or a single wire counterpoise. Checking with a SDR 
> receiver I could see that the usual local VDSL internet hash had 
> disappeared.
>
> Both loops on the ground are 3m or 10' square.
>
> I've also tried it using a G7FEK vertical antenna at home with two 3m 
> or 10' square loops on the ground with similar results seeing much 
> reduced local noise compared with the ground radials I had before. 
> Topband Dx might be a possibility for me now.
>
> I've never seen this mentioned in ham magazines before and I can't 
> find anything with an internet search. Usually I find that all my good 
> ideas have already been thought of 50 years ago.
>
> I suspect that the RF voltage in the loop counterpoise is much reduced 
> over the voltage at the end of a radial wire reducing noise pickup in 
> the radial system.
>
> I would like to model the loop on the ground counterpoise in a 
> modelling tool. I use 4NEC2 but only have access to NEC2 so wires on 
> the ground don't model correctly.
>
> Is there any one out there with access to suitable software that could 
> model it for me?
>
> 73, Chris G4HYG
>
>
>
>
>
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