Message-ID: <2000011120594668199@zetnet.co.uk>
Date: Tue, 11 Jan 2000 20:59:46 GMT
To: rsgb_lf_group@blacksheep.org
From: "Peter Dodd" <g3ldo@zetnet.co.uk>
Subject: Re: LF: Loops
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>
Content-type: text/plain; charset=windows-1252; format=flowed
MIME-Version: 1.0
Content-transfer-encoding: 8bit


> If you're building a loop don't forget that a lot off turns side-by-side 
> constitutes electrically another loop at right angles to the main one, much 
> smaller perhaps but quite enough to knock the notch down from a possible 50 
> dB to only 15-20 dB. For this reason flat "pancake" loops are better.

Provided you are not too bothered about the deep nulls loop antennas 
with side-by-side windings are good for DX if they are over a metre 
in diameter. This construction (see the PA0SE design in the RSGB 
Communication Handbook and the G3LNP design in Radcom July 1999) 
allows the individual wires of the windings to be spaced to reduce 
the loop internal capacity and increase the Q.
In the early days of experimenting with 73kHz, G3XDV and I used 
ferrite loopsticks from transistor radios for with mobile receivers. 
While these antennas, even with an FET amplifier, are no good for DX 
they do have very sharp nulls.
Ferrite loop antennas can be used for DX. See the 160m design, using 
lots of ferrite, by Richard Q, Marris, G2BZQ, in the ARRL Antenna 
Compendium, Vol 6. Could this be modified for 136kHz?
Has any one seen, or even posses, one of the large flat slab ferrite 
DF loop antennas used in the RAF (circa 1960)? 
I can confirm that a 1.5m LF loop antenna made from computer multi 
colour ribbon performed badly.


-- 
Regards, Peter, G3LDO

<g3ldo@zetnet.co.uk>