Message-ID: <003801c4c103$70eab870$2101a8c0@AUG2004>
From: "Walter Blanchard" <blanch@pncl.co.uk>
To: rsgb_lf_group@blacksheep.org
References: <E1COlI9-0000WZ-3f@post.thorcom.com> <4186F5A2.9080706@zen.co.uk> <001701c4c0fa$9429c960$48657ad5@derekm3uttnxf9>
Date: Tue, 2 Nov 2004 17:43:16 -0000
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Subject: Re: LF: Rugby Loran station
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----- Original Message ----- 
From: "Derek Atter" <datter@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Tuesday, November 02, 2004 4:39 PM
Subject: Re: LF: Rugby Loran station


> Stewart,
>
> Re : Loran Blankers :
>
> It is not too difficult to build a blanker for Loran. I made one in the
> early days of the 136khz band to try it in comparison with antenna nulling
> techniques and it did work quite well. It used a diode gate in the RF 
> signal
> input fed by an adjustable width monostable fed in  turn by a delay equal 
> to
> the Loran pulse interval triggered via an adjustable signal threshold. The
> diode gate was in effect operated by the previous pulse burst to overcome
> the problem of circuit delays and rise-time effects. From what I remember, 
> I
> found it just as effective to blank the whole of the pulse burst rather 
> than
> try to blank individual Loran pulses. The technique was similar to that 
> used
> on HF to combat the old Russian  "Woodpecker" over-the -horizon radar. The
> diode gate reduced the Loran pulses only down to the average background 
> band
> noise level rather than right down the to receiver noise floor so as to
> minimise modulation of ordinary band noise. In the end. I actually went 
> for
> antenna nulling as being more flexible in also being potentially able to
> null other sources of QRM.such as CFH etc. when it was on.
>
>  73,    Derek Atter
>
>

Yes, the series of 8 pulses only lasts 8 mS  so even if you cut out an 8 mS 
hole there's still
92% of other signals left if the rep rate is 100 mS. Unfortunately if you 
get two strong
signals as you will with both Lessay and Rugby you'll lose another 8% and 
have only 86%
left! However, probably enough using QRSS.

Walter G3JKV.