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Re: LF: Loop (was Re: IGBT in 136 KHz TX?)

To: [email protected]
Subject: Re: LF: Loop (was Re: IGBT in 136 KHz TX?)
From: <[email protected]>
Date: Tue, 21 Jul 2009 11:10:04 -0400
In-reply-to: <[email protected]>
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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 

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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