Dear LF Group,
The maths required to calculate the gain and Rrad of a loop over a ground
plane looks much too difficult... so I cheated and used EZNEC instead to
simulate a 10m square loop 1m above a ground plane - the gain is close to
4.77dBi ( ie. 3), instead of 1.77dBi for a loop in free space, so 3dB gain
due to the ground plane, as one would intuitively expect.
I also tried simulating it with "real" grounds, to find out what the effect
would be on the radiation resistance. Unfortunately, it does not like doing
this, giving an error message saying that the resistance is negative and
the loop is too small. I increased the frequency to 1MHz, where the
simulation ran OK. Comparing Rrad with perfect ground and free space gave a
ratio of about 2:1 as expected. With "high accuracy" ground, either very
low or very high ground conductivity gave lower loss resistance than
intermediate values, which also seems reasonable - the loss reached a
maximum somewhere around 100mS, so this suggests that, with actual grounds
having lower conductivity than this, loops will work best with the lowest
possible ground conductivity. However, one has to take all this with a
pinch of salt because of the simulation errors produced if the frequency is
reduced.
Cheers, Jim Moritz
73 de M0BMU
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