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.
It could use a switch or simply a clip lead to select the tap.
Um? more on that later.
Post a Comment