Message-ID: <20090721111004.NESLM.2165994.root@mp07>
Date: Tue, 21 Jul 2009 11:10:04 -0400
From:  <w1tag@charter.net>
To: rsgb_lf_group@blacksheep.org
In-Reply-To: <57a24ca70907210620v6f208cf2t898ce58cab2e9776@mail.gmail.com>
MIME-Version: 1.0
Sensitivity: Normal
Subject: Re: LF: Loop (was Re: IGBT in 136 KHz TX?)
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org


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