Resonating Your Ground System
The Other Half of Your Antenna
What! Resonate my ground system! Have you gone mad?? Well, not exactly, at least not so you can tell it. Resonant ground systems have not been discussed in any of the ham magazines, or any of the other ham antenna literature that is available. But if you think about it, it isn’t a bad idea when you consider the grounding system is part of the antenna circuit, and rf current flows in the ground as well as the antenna. So, the idea of a resonant ground circuit is not a bad idea at all.
In the diagram below, which shows a series tuned circuit in parallel with a rf choke, there is a variable capacitor in series with a variable inductor and an rf ammeter. The rfc is a must in order to allow the other voltages present to go to ground through the proper path instead of through your carcass, which is rather painful or even fatal. Thus, the rfc is a definite requirement to keep your rig from being a fatal attraction in the true meaning of the word.
If you construct this resonating circuit, be sure to use components large enough to handle the rf currents involved. Rf ammeters are not a stock item in most parts supplier’s inventory, but some of the surplus houses like Fair Radio Sales, do list them in their catalogs. Any other rf current indicating device will do, but it must indicate rf current flow and not 60 hz ac or anything else.
To tune up the ground, first load up the transmitter on your favorite band. Next, set the capacitor to half mesh. This will allow you some leeway in the capacitor tuning. Then key up the rig with enough carrier to get an indication on the amp meter. Once you get some sort of indication unkey the rig and then start tapping up or down the coil. And, then rekey to see which way the current goes, up or down. You are tuning for maximum. When you find out which way to go on the coil, continue until you reach a maximum. Then tune the capacitor to see if there is any improvement. Once you get the maximum for that band, proceed to the next frequency and start again with the same procedure to tune up the ground system.
Here’s some more technical information. One of the chief characteristics of a series tuned circuit is it is a low impedance device at resonance and therefore passes maximum current flow at resonance. This is just the opposite of a parallel-tuned circuit, which is a high-impedance at resonance with a minimum of current and a maximum of voltage present across it. For this application, the series tuned circuit is the way to go. We do want maximum current in that antenna and anything connected with the antenna.
The important thing to keep in mind is there is an image antenna equal to the antenna height, (H) situated below ground at D = H, with currents of equal but opposite phase. Anything we do to increase the current in both the image and real antenna is going to enhance the outgoing signal. So, resonate the ground. The amount of effort to build the series tuned circuit is not too much, but any improvement in signal strength would make it worth while.
The 1/4 wave vertical and the long wire antennas will most likely show more of an improvement than a twenty meter beam at 110 feet, but any improvement is worth while. Keep in mind all connections need to be soldered and/or bolted together with star washers that cut into the metal to form a good solid connection. Weather proof all connections, and measure the dc resistance of the entire ground circuit to check for continuity, and low resistance.
Originally posted on the AntennaX Online Magazine by Richard Morrow, K5CNF
Last Updated : 13th March 2024