One man's ground is another man's antenna

07/09/2014

After a year and a half of no earth antenna experiments, I decided to get back to it. So far, all experiments have been done during the day for both 137 kc and 475 kc. The plan this time is to construct a low duty, low power (10 watts or so), remote controllable WSPR transmitter and try to get a feeling of the performance of the earth antenna.

In order to do this, I though it would be good to have some impedance values, for both bands, using both configurations: terminated remote end and unterminated remote end. The same ~250 m wire was used, as in the previous experiments. It was installed in the same path as before. The results are as follows:

The dam/container locations relate to the following configuration:

It is not surprising that the results are different depending on which end of the wire the transmitter is connected. I believe this may be explained by the non-homogeneous ground and its influence, which is greater closer to the transmitter. The other observation is the big change in the impedance between this test, and the one conducted on 475 kc, on the 23/01/2013. There are changes in both the real part of the impedance, which I assume is dominated by the losses, and the reactance. The change in the reactance may imply that the antenna is now using a different configuration, possibly due to the change in the moisture content of the various layers below. Perhaps, a layer that is lower or higher in the stack is now carrying more current?

It seems that the earth antenna is constantly changing and that should be an encouragement to try again, even if the first time the results have not been very good. I was initially planning to use only the terminated end configuration, but seeing the very low resistive part of the unterminated impedance, I am tempted to try this instead. In fact, I should try both and compare - it's easy to connect/disconnect the end of the antenna.

Go back to the main earth antenna page.

Dimitris Tsifakis, VK1SV