Message-ID: <003f01ca0a1a$ba6fd880$0301a8c0@mal769a60aa920>
From: "mal hamilton" <g3kevmal@talktalk.net>
To: <rsgb_lf_group@blacksheep.org>
References: <20090721111004.NESLM.2165994.root@mp07>
Date: Tue, 21 Jul 2009 16:48:44 +0100
MIME-Version: 1.0
Subject: Re: LF: Loop (was Re: IGBT in 136 KHz TX?)
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Use a vertical and avoid all the specified LOOP problems and directional 
limitations.
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.
mal/g3kev


----- Original Message ----- 
From: <w1tag@charter.net>
To: <rsgb_lf_group@blacksheep.org>
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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