Message-ID: <4C6566E7.5090207@charter.net>
Date: Fri, 13 Aug 2010 11:38:15 -0400
From: John Andrews <w1tag@charter.net>
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Subject: Re: LF: A question about loops for 136 and 500kHz TX
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Roger,

Even in an area with very poor ground conductivity (such as mine), 
environmental losses will be reduced by elevating the lower conductor. I 
would suggest 2-3 meters as a minimum. In general, loop shapes having 
the lowest proximity to ground are the best, with circular being very 
desirable. The late Reg Edwards, G4FGQ, wrote several programs dealing 
with loops for transmit use, and RJELOOP1 would apply the best to your 
situation. You can download it from:
http://www.we0h.us/page3.html#S301%22

Your actual feedpoint impedance will probably differ, but the program 
allows you to play with various options in advance, perhaps saving some 
money, and certainly time.

The loop is an excellent option for a lot with so many trees that a 
Marconi-style antenna would have excessive environmental losses at these 
frequencies.

John, W1TAG


On 8/13/2010 11:08 AM, Roger Lapthorn wrote:
> Having considered the antenna options for my small garden, I'm going to
> erect a TX loop antenna rather than a Marconi vertical for 136kHz: the
> earthing issues are removed and it is easier to build a capacitor
> selection box (to tune and match the loop) than wind a huge loading coil
> and match it. I've seen some of the webpages dealing with these and
> understand basically what is needed (large loop area, thick wire,
> capacitor match-box, dealing with high RF currents, etc). I understand
> the loop will have directionality and nulls.
>
> My question is this. *Is there any reason why the bottom of the loop
> cannot be laid along the ground rather than elevated a few metres?* Most
> designs show the bottom elevated a bit, but if laid on the soil I could
> use thick coax or multiple wires for part of the loop so reducing the
> loop resistance.
>
> Views appreciated, although it may be a case of "suck it and see".
>
> 73s
> Roger G3XBM
>
> --
> http://g3xbm-qrp.blogspot.com/
> http://www.g3xbm.co.uk
> http://www.youtube.com/user/g3xbm
> G3XBM   GQRP 1678    ISWL G11088