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Re: LF: Simple receivers for 136kHz

To: "RSGB LF Group" <[email protected]>
Subject: Re: LF: Simple receivers for 136kHz
From: "Kevin Ravenhill" <[email protected]>
Date: Mon, 15 Nov 1999 15:10:32 -0000
Organization: Radiometrix Ltd.
References: <[email protected]>
Reply-to: [email protected]
Sender: <[email protected]>
Mike, G3XDV wrote:

I could hear DCF39 at S9+ and
copied MM0ALM (650km) loud and clear. To a beginner this might
indicate that all was well. But what I could not hear was the Greek
RTTY which was S7 on the converter, the Loran or any static. The
difference was remarkable.

As I have said before, if you don't get a HUGE signal from DCF39
compared to your noise level, and can't hear the RTTY just below
136kHz most of the time, and can't hear Loran and/or static all of the
time, you may need to increase the receiver system gain. This may
also involve improving front end selectivity.

Quite agree Mike. I did originally try this receiver without its 1st RF
preamplifier stage and the performance was very disappointing - no Loran
etc. just as you describe. This despite the receiver having an apparently
adequate sensitivity (<0.2uV MDS) when measured using a 50 ohm feed from a
signal generator. I'll certainly be interested in your findings re. the

With the additional preamp I can hear Loran loud and clear along with
(almost depressing!) amounts of static. The Greek RTTY is always there,
usually peaking at around S6-7 estimated (except at night when it increases
markedly in strength, and particularly this last weekend when it was S9+
during the daytime).

Narrow filtering fairly early on in the audio chain is absolutely essential
with this receiver though, otherwise DCF39 is so strong that it completely
swamps the audio stages!


Kevin, G1HDQ.

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