Message-ID: <3C8F7E83.7F760276@netscapeonline.co.uk>
Date: Wed, 13 Mar 2002 16:29:55 +0000
From: "gii3kev" <gii3kev@netscapeonline.co.uk>
Organization: Netscape Online member
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To: "rsgb rsgb" <rsgb_lf_group@blacksheep.org>
Subject: LF: loops
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Dave/G3YMC my loop configuration is not like yours and is going to have
a different feed system, therefore your web site would not be of any
interest for my project. I am using parallel capacitor feed at present
as a starting point to resonate the loop on 136 khz,  and then will get
round to transformer matching the loop impedence to my 75 ohm coax and
TX/RX.
The matching network is at the right bottom corner of the loop and not
in the shack.
I am experimenting at present to optimise the received signal. The DC
resistance of the loop without any attachments is just over 1 ohm for
2.5mm insulated wire, and there is nothing I can do about this except
change the wire to heavier guage or use litz. I doubt if the end result
makes that much difference and I have to consider the mechanical
advantage with 2.5mm wire. The capacity needed to resonate the loop on
136.5 khz approx is 3000 pf at the loop corner. (1500 pf resonates it at
the shack end of coax, because of the coax capacity etc, when I setting
it up and testing)
There could also be an advantage putting some insulated ground radials
under the loop. I do not think anyone else around EU has a loop of these
dimensions, therefore capacitor and inductor values would be different,
plus the location environment is different, and nothing would be gained
by trying to copy what someone else is doing. The basic principle for
loop design and installation would be similar and thats about it.
I was thinking of not using any capacitors at all and trying to use a
multi turn loop (turns in series), the same size as the present single
loop, turns space to avoid losses and bring the loop natural resonance
to 136 khz, and use a heavy duty ferrite transformer for impedance
matching to the tx/rx.
I hope I do not pull the trees over with the weight !!
I want to access loop potential compared to my vertical before I launch
into any serious loop business.The vertical is working fb world wide and
the loop is just a fun project, and so far on receive it is doing well.
When I get everything on the nose all matched both on tx and rx I will
publish the results and observations compared to my vertical system.
73 de Mal/G3KEV