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In the past, experiments on antenna test sites
indicate a vertical loop performs best if the bottom wire of loop is about 7 ft
above ground.
VE2CW I think did comprehensive tests with such
antennas, as an alt there is the grounded loop, half the size at natural
resonance is above ground and earth acting as the other half.
Small loops in relation to freq on TX are
inefficient, but acceptable for RX
All this info has been documented over the years,
some research will reveal results
de g3kev
----- Original Message -----
Sent: Monday, September 27, 2010 6:24
PM
Subject: LF: Loops on TX
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
--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM GQRP
1678 ISWL G11088
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