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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: "mal hamilton" <[email protected]>
Date: Tue, 21 Jul 2009 16:48:44 +0100
References: <[email protected]>
Reply-to: [email protected]
Sender: [email protected]
Use a vertical and avoid all the specified LOOP problems and directional
Loops maybe for RX but for TX vertical systems, ie inv L, T top is probably
the best approach on LF and MF.
One wave loops on the frequency of interest on HF is a different story.

----- Original Message ----- From: <[email protected]>
To: <[email protected]>
Sent: Tuesday, July 21, 2009 4:10 PM
Subject: Re: LF: Loop (was Re: IGBT in 136 KHz TX?)

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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