Re: parameters - ssb receiver and single polarization

[Leif Asbrink <sm5bsz.com; leif@xxxxxxxxxxxxxxxx>]

Hi Phil,

> Hello everyone.  I have Linrad running under windows with a Kenwood
> TS-2000, a 4X12 horizontal array, and a 2.8 GHz AMD Athlon with a
> SoundBlaster card.  I have the screen set up to my liking, and I have
> been studying the fft process and have read many of the web pages on
> Linrad and am beginning to learn my way around.  I plan to perform the
> noise blanker calibration in the next week.  My main interest is 2
> meter and 70 cm EME.  Which parameters should I concentrate on to
> optimize weak signal detection?  My noise background on 2 meters is
> reasonably quiet, but I have a local pulsing interference on 70 cm.

I do not know the TS2000 well. Maybe it has a noise blanker
that operates in a wide bandwidth. If it has, it could be better
to allow it to take care of pulse interference. On HF bands it
may be different because wideband blankers that are built into
transceivers do not work well if there are strong signals anywhere
in the wide bandwidth of the blanker. Then the Linrad blanker
might do much better within the bandwidth it has. Surely more
bandwidth improves greatly, so set the bandwidth as wide as possible.

For the blanker to work, and for other reasons as well, you should
disable the AGC of the TS2000. Set the RF volume for the signal
to not saturate (or engage the AGC) for the strongest signals
or noise spikes you normally have. The lower signal level you
run at, the better dynamic range you will have, but do not set
the level too low because at some point the noise figure of
your system will start to degrade. 60Hz and its overtones might
also become a problem.

In other words, make sure that the TS2000 works in a linear mode
for all signals that you expect while also making sure that the
system NF is OK. (disconnecting the DC power to your antenna
mounted preamp should lower the noise floor by about 15 dB.)

Set the BFO pitch, passband tuning or whatever they call it
on a TS2000 for a somewhat higher pitch than normal. 60Hz
overtones might reach up to 400Hz or so and it would be
a good idea to have them outside the frequency range of 
interest. Make sure you do not loose bandwidth, more bandwidth
is always better.

After you have done the calibration you must NOT change 
the bandwidth tuning or BFO pitch. Even small changes 
will destroy the wider and flatter noise floor that
the calibrated system benefits from.

With a calibrated system you can run the waterfall slower
and increase the waterfall gain to see signals deeper down
below the noise floor. 

Do whatever seems reasonable and use Linrad a little
so you become somewhat more familiar to it. Then press
the 'S' key some time when you have a signal you can not
quite copy. Record it for one minute (or close to.)
Then press 'S' to stop recording,'G' to save a gif file
with what you have on the screen. Finally exit and save
all the parameter files par_* somewhere. Pack the parameter
files in an archive file and make everything available 
to me:-)


73

Leif / SM5BSZ


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