Tuesday, March 8, 2022

Artificial Ground or Tuning the ground or neutralizing the reactance in the ground loop.

 The antenna tuner can have a section to tune the antenna and a section to tune the ground. You can search and find several commercial products and some created by hams. They are mainly for transmitter applications but could help a receiver too. Some popular home brew sets have tuners with matching. Anywho I assembled a little monitor and ran some test on my 7 foot whip using the chassis ground on my DX-160.

It is fairly simple but does a good job. I am using the NanoVNA to sweep the circuit but you can use a signal generator. The sweep allows the operator to see where he is on the curve a fixed frequency will require a little searching. 

The antenna lead is simple threaded through the core. The core was from a core test. It was wound and tested to see the core properties. I did not count them but about 15 - 20 turns. I did measure to coil. It is 100uh. The meter is set to 50ua. You could use a DVM set to its lowest range. Use the pot to adjust the reading. (keep it on scale)

This is the circuit I used. The blue is RF. The lighter trace is DC output.I am using nanovna-saver to control and monitor the test. The program attaches to the vna, displays and records data. In the following shots I tested the whip against ground and then added a Vcap in series with the vna and ground. You will see the dip shifting as I change the Vcap setting.

When I have more time perhaps a dual circuit to monitor the antenna and the ground?  

Tune the antenna with a PI network and the ground with a series LC?

That would require 3 or 4 Vcaps and some tapped coils. I thinking a simple arrangement would consist of 3 or 4 (yellow/white) cores with 1T, 2T, etc. and 3 or 4 (green) cores with 1T, 2T, etc.

I did a test board with 6 green cores and found the following reading at the taps.

1- 2.5uh

2- 12.8uh

3- 29.8uh

4- 68.7uh

5- 133uh

6- 213uh

It could use a switch or simply a clip lead to select the tap.

Um? more on that later.