Message-ID: <000f01c26abe$62710620$70e4fc3e@l8p8y6>
From: "hamilton mal" <g3kev.ham@virgin.net>
To: rsgb_lf_group@blacksheep.org
References: <5.1.0.14.0.20021002093944.00a8c768@gemini.herts.ac.uk>
Date: Thu, 3 Oct 2002 10:21:56 +0100
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Subject: Re: LF: Whoops 137.31 self-inflicted
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----- Original Message -----
From: "James Moritz" <j.r.moritz@herts.ac.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, October 02, 2002 11:41 AM
Subject: Re: LF: Whoops 137.31 self-inflicted


> Dear Alan, LF Group,
>
> At 01:09 02/10/2002 +0100, you wrote:
> >  There is something there I have seen for some time
> >(months) which looks like a very weak 100Hz  RTTY shift  signal, but this
> >could be a more distant TV or PC, but this is down at the level of the
Loran
> >sidebands ( which are fairly weak here).
> >
> >Cheers de Alan G3NYK
> >alan.melia@btinternet.com
>
> A while ago, I had a problem with a weak FSK signal around 137.4kHz - it
> turned out to be a 3rd order intermod between the "DCF" stations on 138.83
> and 128.93, and DDH47 on 147.3, so:
>
> 147.3 - 138.83 + 128.93 = 137.4
>
> The result was FSK, just about audible, with gaps when the data bursts
> occurred on the DCF signals. The problem was due to the rather wide 1st IF
> filter in the RA1792 (about 20kHz), in combination with a fairly wide-band
> antenna - when tuned to 137.4kHz, all 3 signals reach the early IF stages
> and 2nd mixer with little attenuation, resulting in the intermodulation,
> allthough they are removed by the main IF filters. The solution was to add
> preselection with a BW of a few kHz - if the antenna is sharply resonant,
> this is enough to do the trick. If you are using an antenna that has
> relatively low Q, there are several possibilities for this type of
> intermodulation to appear.
>
> Cheers, Jim Moritz
> 73 de M0BMU
Hi Jim and all
The signal here on 137.3 khz is not coming from my computers. It is there
when they are switched off. It could be coming I suppose from another some
distance away but its there all the time, and never seems to go off. This is
a recent thing, it is strong but not a real problem with what appears to be
a 6 hz shift transmitting revs(equal mark/space)
73 de Mal/G3KEV

>
>
>