Satgen50  13 Mar 90  Comparative Assessment of Pacsat Operating Features

With Jas1-B, Lusat, Pacsat and Webersat now offering BBS, Digipeater or
Picture facilities, it has become possible to do comparative tests.

JAS1-B's good features are its operating height , with its provision of
long periods in range, slow doppler rate and more orbits above the station
horizon. Signal/Noise ratio for consistent printing is very good = very
low at 3 to 5 dB for consistent print. By contrast its problems are, deep
fades roughly every 25 seconds as the antennas appear to be obscured. It
also has a QRM problem from its own non linear transmitter whereby SSB
signals 45 Khz below the JD signal are sometimes repeated on top of or
just below the JD signal. Last but not least the BBS software appears to
have the old JAS1-A fault of leaving the message sender in limbo at times.

Lusat needs a better higher signal to noise than JAS1-B before it will
print ( roughly 7 to 10 dB ) but it has very little fading

Pacsat reception by contrast, needs a very high signal to noise for
consistent screen print copy. Is this a feature of Raised Cosine
modulation? For the first few days after launch Pacsat was easy copy as it
sent Manchester coded signals.

Webersat has a very rough signal and needs to be S9 before it will print.
This is not due to AFC inconsistencies as some reports suggest. It is
equally bad on low doppler rate orbits and seems to have surplus carriers
in its signal.

General Remarks  At least one report claims Pacsat can be received on
simple antennas unassisted by pre amps. I do not find this to be true. I
suggest purveyors of this sort of misdirection try operating the
satellites themselves or at least read the equipment reports being logged
on the sats by JD users. Eg typically 2 x 10XY down , 2 x 5XY up, or if 
helical 12 or 16 turns. Equally important , most successful users have
gone over to direct input of Tx audio at or near the transmitter varactor,
NOT THE MIKE SOCKET. In addition some transceivers as reported by G3RUH
seem to have Tx delay problems ( a nasty which can also apply to VOX
operated linears ).

The situation is not static. Doubtless much of the above will change as
the satellites stabilize and come fully operational.73 de GM4IHJ@GB7MAC