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LF: Loops on TX

from [Roger Lapthorn] [Permanent Link][Original]
To: [email protected]
Subject: LF: Loops on TX
From: Roger Lapthorn <[email protected]>
Date: Mon, 27 Sep 2010 18:24:26 +0100
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Good to see the reflector back again.

For the last week or so I've been running my vertical "fully in the air" TX loop (1mm diameter wire, 80m sq area) on both 137 and 500kHz. Now, the bottom of the loop is laying right on the lawn with no attempt to raise it off the ground. Weather has been mixed and yesterday it rained all day. Results on 500kHz suggest it is every bit as good (actually better) than my top loaded Marconi used last winter with best DX so far with 2mW ERP being LA3EQ last evening (heavy rain all day and evening). Results on 136kHz with <20uW ERP have been encouraging too with 6 different WSPR reports out to 148km. I clearly know that improving the wire diameter will improve the ERP simply as a result of reducing resistive losses. What I'm less clear about is why people say all of the loop should be raised above the ground.

My questions are these:
  • What additional losses, if any, do I suffer having the loop on the ground (even wet ground)? How do these arise?
  • Could I bury the return part of the loop wire in the ground and maybe gain a few more square metres of area?
  • Is there anywhere where I can get a simple explanation of loop losses due to ground presence and foliage presence?
In the last year a lot of accepted theory/beliefs, for example on earth electrode antennas, has proved to be questionable and I am wondering if the "loop must be in the air and away from foliage" is another accepted "fact" which needs to be questioned.

73s
Roger G3XBM

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