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Re: Topband: Loop on the ground as a counterpoise

To: topband@contesting.com
Subject: Re: Topband: Loop on the ground as a counterpoise
From: K4SAV <RadioXX@charter.net>
Date: Wed, 6 May 2020 08:17:30 -0500
List-post: <mailto:topband@contesting.com>
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





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