Just to add a little more information on LF transmitting loops:
Paralleling conductors is usually more effective than creating a multi-turn
loop. The extra copper loss from another turn can easily negate the increase in
field strength from that turn.
With paralleled conductors, keep them separated so that the current will flow
over the complete outer surface of each conductor. 10cm spacing seems
reasonable as a minimum.
My experience is limited to a single-conductor loop, and 500 watts transmitter
output. I've had two experiences with tree fires. Both were caused by my
earlier method of running the lower leg of the loop through PVC fittings at
each tree. Long screws through the fittings provided sharp edges to scrape
insulation and increase the voltage gradient between the screw and the wire. I
have long since switched to porcelain insulators for the lower supports, with
no trouble. All other contacts with the trees are directly between the wire and
the tree. I do worry about a lot of insulation damage done last winter during
and after an ice storm, but thus far there have been no issues.
Major starting difficulties are the voltage and current ratings of tuning
capacitors and coupling transformers. Your senses of touch and smell will help
in knowing if you have succeeded! While the voltages and currents can be
accurately calculated in advance, you may have limited information on the
components, particularly the current rating of capacitors. In general, think
big.
And just one random thought on multi-turn receiving loops: As Jim Moritz has
pointed out a number of times, a loop of N turns can be quite nicely replaced
by a loop of one turn and an N step-up transformer. A one-turn loop is easier
to construct, and may provide a wider tuning range.
John, W1TAG
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