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
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