Topband: Loop on the ground as a counterpoise

[K4SAV]

Another thought.

Changing to a good ground system with a good choke at the antenna 
feedpoint will make your vertical omnidirectional, but that may not 
solve the noise problem,.  You may need a directional receiving antenna 
to reduce it.

Jerry, K4SAV


On 5/6/2020 8:00 AM, K4SAV wrote:
> 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
>>
>>
>>
>>
>>
>> _________________
>> Searchable Archives: http://www.contesting.com/_topband - Topband 
>> Reflector
>
> _________________
> Searchable Archives: http://www.contesting.com/_topband - Topband 
> Reflector