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Message-ID: <66D678B54F9F43EA8421AE7B1BB96770@JimPC>
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
References: <4DC527C4.3070903@iup.uni-heidelberg.de> <D0EE688714534219A64EC627262F2114@JimPC> <4DC56FCB.1050509@iup.uni-heidelberg.de> <14CAC29AA012468A844D715FA1A336F8@JimPC> <4DC5AF77.2060706@iup.uni-heidelberg.de>
In-Reply-To: <4DC5AF77.2060706@iup.uni-heidelberg.de>
Date: Sun, 8 May 2011 12:23:49 +0100
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Subject: LF: Re: CW...
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Dear Stefan, LF Group,

The loop I am using is detailed at 
https://sites.google.com/site/uk500khz/members-files/files - see the file 
"BPloops2.pdf". These loops use a 1m x 1m single turn made of copper tube. 
The unloaded Q of the single turn is quite high, >100, provided a very 
low-resistance capacitor (about 400nF for 136k) is used. So the Q is similar 
to a multi-turn loop, although the impedance is very much lower. The low 
impedance means it is easy to feed a 50ohms input, and it is very 
insensitive to de-tuning. The loop is used in a bandpass design that gives a 
flat response over about 10kHz bandwidth without re-tuning, combined with 
better out-of-band rejection.

A single loop gives a figure-of-8 directional pattern with 2 nulls 180 
degrees apart, and it is well known that combining equal-amplitude signals 
from a loop and a vertical with the correct phase gives a cardioid pattern 
with a single null. If the signal amplitude from the vertical is reduced, 
the result is a skewed figure-of-8 pattern, with less than 180 degrees 
between the two nulls. With appropriate adjustment of the vertical signal 
level and the loop direction, you can have 2 nulls seperated by any angle 
from 0 - 180 degrees. I used this type of arrangement when Loran-C was being 
transmitted from Rugby a few years ago - then it was not possible to null 
both the Rugby and Lessay signals with a simple loop at this QTH, because 
the difference in bearing between the transmitters was only 100 degrees or 
so. The procedure was to aim the loop on a bearing half way between the 
bearings of the two transmitters, then adjust amplitude and phase of the 
loop/vertical signals until both signals were nulled. This was quite 
effective, and it was possible to effectively eliminate both Loran signals 
while getting good coverage of Europe. Of course, the usefulness of this 
type of system depends on the direction of the wanted signal being well away 
from the interfering transmitters, but looking at the map, it should be 
possible to make it work quite well for receiving signals to the west of 
Heidelberg while rejecting DCF39 and HGA22

Cheers, Jim Moritz
73 de M0BMU