From: "Mike Dennison" <mike.dennison@rsgb.org.uk>
To: rsgb_lf_group@blacksheep.org
Date: Mon, 15 Nov 1999 13:10:37 -0000
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII; format=flowed
Content-Transfer-Encoding: 8bit
Subject: Re: LF: Simple receivers for 136kHz
In-reply-to: <000501bf2f5c$84687c40$6d8fbc3e@default>
Message-ID: <E11nLyu-0000yp-00@mserv1a.u-net.net>
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>

G1HDQ wrote: 

> I've noticed that, whilst there is naturally a lot of discussion on the
> reflector about transmitters and antennas, there is relatively little about
> receivers. Since I have a strong preference for uncomplicated homebrew
> equipment and an aversion to buying expensive commercial gear, I've recently
> been experimenting to find out how simple a receiving setup can be made
> whilst still being capable of useful results on 136kHz.
> 
[big cut]

> The antenna now appears to be the limiting factor. Apart from mains-borne
> QRM/N, Loran chatter is quite a problem here in East Devon and a frame
> (loop) antenna suggests itself as the next step.
> 

Looks like this is a useful receiver if Loran can be heard easily. 
Regulars on this relector will remember my sermons on decent 
receivers in the past. I use a Datong converter (with essential added 
front-end filtering) and an IC-706 Mk1 as an IF at 28MHz. I tried the 
IC-706 out as an LF receiver on its own (not sure why I haven't 
done this before). It covers down to 50kHz which gives both LF 
bands. It is fairly useless at 73 but works better at 136kHz - even the 
pre-amp has some gain.

However, here's where the trap lies. 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.

I will try out the 706 with some preamplification and report back.

Mike, G3XDV (IO91VT)
http://www.dennison.demon.co.uk/activity.htm