[amsat-bb] PSK-31 satellite

["Howie DeFelice" <hdefelice@xxxxxxxxxxxxxx>]

Last night I tried a small experiment to get a feel for how the proposed SSB
to FM transponder might work work. I connected the headphone output of my HF
receiver (an Atlas 110, single conversion with audio derived AGC) to the
external FM modulation input of a signal generator. I connected the signal
generator to the my UHF HT. I then tuned the HF receiver to a "pack" of
PSK-31 signals on 20 meters. I connected my computer, running Digipan, to
the earphone jack of the HT. I set the signal generator for a full quieting
signal on the HT, about .5 uV, and proceeded to copy PSK-31 signals. At one
time I had six different signals of widely varying signal strengths in the
passband simultaneously and could jump between them at will by clicking on
the waterfall display. I then reduced the signal level to the HT to .3uV to
see the effect of increasing the noise floor. The increased white noise was
visible on the waterfall display but I could not detect an appreciable
reduction in performance. I didn't have a way to measure the SINAD of the
channel, but intuitively I don't believe it was better than 8 to 10 dB. I
further reduced the signal generator to .2uV, producing a very noisy signal
in the HT. I could still copy PSK-31 conversations, but the degradation was
noticeable.

This was not a very scientific experiment but it was enough to get me
excited because:

1. Even with a simple receiver, there was no evidence of "power hogging" or
adverse AGC effects even with a large variation of typical signals. One
station was actually running 1W QRP.

2. I could maintain good copy with signals on the FM receiver in conditions
similar to those I currently get from UO-14 or AO-21 using an omni antenna.

3. Anyone with an FM receiver, (scanner,HT,etc.) and a computer with sound
card can copy the satellite and be almost guaranteed of receiving something
intelligible.

4. Forget chasing doppler on the 10M uplink, just use the mouse to click
over a few KHz. on the waterfall display at the start of the next exchange.

 I think this could be allot of fun.....

Howie
AB2S

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