More about grounds and radials


I have been studying low band(160, 80 and 40 meter) verticals and ground systems a long time. Some of the things I have concluded and info I have found is not exactly common knowledge among hams. Unfortunately there is much info out there that is not exactly correct and even more only half way correct. Let’s say there are a lot of “half truths” out there being passed around as correct.

There is a large void in the knowledge of how grounds and radials for verticals work. It is complicated. All radials do not exactly work the same. From my point of view there are at least four types of radials (uninsulated buried, insulated buried, insulated on the ground, and above ground) They all do the same thing and that is collect ground or return currents. How they do it is sometimes slightly different and sometimes significantly different! Buried uninsulated radials and ground rods do it by being in contact with the ground. Thus the weak point is the size of contact area where the bare conductor touches the earth. The larger the contact point the lower the resistance. With insulated radials there is little to no contact with the earth and the path of current flow is through the capacitor or capacitive reactance that is formed by the earth and the wire or radial system. Return currents flow in the earth and then through the capacitive reactance to the radial conductor and then back to the source. That capacitive reactance varies inversely with frequency among other things.  With above ground radials ( height of say six feet or so on 160 meters, less on the higher bands) the return currents are not through the ground. The vertical and it’s above ground radial or radials act more like a dipole with one 1/4 wave leg vertical and the other 1/4 wave leg (or radial) horizontal. Between radials being directly on the ground and the six feet high elevated radial system is a transition zone where the mechanism by which the radials collect current changes from being a capacitor to one of directly collecting the return currents from the air and not the ground. It is very hard to measure ground resistance or the ground loss resistance as we like to call it. It is also very hard to measure the radiation resistance of the vertical. We usually resort to theory and calculate the radiation resistance over a perfect ground plane. That’s easy. 
We can then build an antenna and measure its impedance. We then know that that measured resistance consists of two parts, the radiation resistance plus the ground resistance. Neither of which we can measure separately. We then take the theoretical calculated radiation resistance and subtract it from the measured Resistance and can assume that the result is pretty close to the loss resistance. The majority of the loss resistance is ground resistance. So at that point we think we have a fairly close number for ground loss resistance. If we make a change to our ground system and that change results in a reduction in measured total R we can safely assume that we reduced our ground resistance (loss) by that amount. Using the classic W1BB inverted L as an example,  we also know by theory that the 3/8 wave wire will have a greater radiation resistance than the 1/4 wave wire. That fact alone increases the efficiency of the antenna regardless of the ground loss. We need to compare the measured R value of our inverted L to the theoretical radiation resistance for this antenna, and the difference between the two R values should be close to our ground loss resistance.

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