-----Original Message-----
From: Martin Evans <[email protected]>
To: [email protected] <[email protected]>
Date: 25 November 2000 13:26
Subject: LF: Datong VLF Converter
Hi all!
Just as a matter of interest, I've compared the direct reception of 136kHz
using a TS950SD, with a Datong converter using the TS950 as the ten-metre
IF. Using a 40 metre inverted L antenna, untuned, and with 9db attenuation
in front of the Datong to eliminate overloading, I can see no significant
difference in the reception of CFH between the two methods- so the 950
seems
to be a decent 136kHz receiver! Anybody got any comments on this? I would
be
interested in hearing of other opinions of the 950 as a receiver on this
band.
Having tamed a datong converter by adding about 40 db attenuation between
antenna and converter it seemed to work very well. Without the attenuation
it was terrible with severe overload. I understand they were meant to be
used with short antennas and not my 120 ft vertical inv L system.
With my antenna I have tried several receivers direct from antenna and there
is very little difference amongst them. IC746, FT1000MP, TS50, IC706 ( pre
amp on ) TS570.
These receivers are all fitted with the narrowest cw filters available. With
a smaller antenna things might be different regarding signal over noise and
sensitivity.
I also tried a FT847 with narrow filters and it was not as good as the
others. The IC 706 is almost on par with the others with pre amp on and a
large antenna, but you do need the 250 hz cw filter and an external DSP unit
for the required selectivity. I tried a smaller antenna and the sensitivity
was low. I also use the 706 as a stable driver for the tx on 13.6 mhz and
divide down by 100. Use vfo A for tx and vfo B for rx. All controlled from
one switch. The same procedure can be used on 73 khz. Divide down from 7.3
mhz.
I have arranged an extra rx output for another rx if necessary.
This is old hat, others are probably doing the same thing but it is the most
convenient way of driving your big PA and guarantees a stable signal, no
wobbly or jumpy signals.
I key the PA and not the transceiver drive.
73 de Mal/G3KEV
Martin Evans GW3UCJ
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