Satgen42  17th Jan 90  Microsat PSK Modems, JAS1-B

Whilst we wait for Spot II ( and our Amateur Radio Microsats ), launch ,(
not before 26th is latest forecast I have ), I want to answer queries
received regarding equipment needed to operate Microsats either as an
active transmitting station or as a passive receive only station.
Using presently available G3RUH PCB kit and buying and fitting the
electronics to it, a typical 1200 AFSK up, 1200 BPSK down Microsat/JAS1
system consists of a G3RUH Fuji modem kit, and a Do It Yourself modified
Terminal Node Controller,feeding the mike/ptt inputs of a 2m FM Tx, and
receiving on USB via the phone socket of a 70cm receiver . This receiver
to be DIY fitted with an input to UP/DOWN frequency scanning to permit
Automatic Frequency Control (AFC) of the Rx by the RUH Fuji modem.
This AFC is vital. I find that 50Hz mistuned = No print out. So the AFC 
mod must be done to your Rx. In addition you must modify your TNC, so that
the received data signal from the Fuji modem bypasses the existing TNC
modem. G3RUH explains how to do this in the excellent guide which you get
with his Fuji PCB, but these are not simple tasks despite the guidance.
If you want to go further and use the above for terrestrial PSK you need
to be aware that in addition to the above you must fit an additional DCD
output from the Fuji modem to your TNC to tell it when the channel is
blocked by another signal. Noting that you are no longer using different
send and receive channels. Worse still in the terrestrial case , the use
of a simplex single channel , means you do not have a steady carrier for
your AFC to tune to. Tuning can be very dicey.
I hope the above does not sound too formidable. Anyway , surely just
around the corner are commercial modems which will do all this for you ?
Unfortunately it may not be as easy as that. Purchasers of commercial
modems should check that all the above problems which can be dealt with on
the new modems for Microsats, have been solved. Proposed new Microsat
modems advertised recently still seem to require a separate TNC. In some
cases some of the wiring changes described above are done for you, but it
looks as if it will cost you 100 pounds for your TNC plus at least another
200 for your Microsat modem. Check before you purchase that the  changes
have been incorporated, and remember you will probably still have to do
the AFC Rx mod yourself. Future Satgen bulls will report on this .

Have not yet seen orbital elements for JAS1-B launch 1st Feb 0125 ut
For plotting purposes have been using Epoch 90  32.02 : Inc 99 : Mean
Anom 54 : Mean Motion 13.18 : Ecc .001 : Arg Per 270 : RAAN 96.2 . The
problem of main payload going to 900 kms and then JAS1-B going to 1200
kms if residual fuel permits, means actual orbit could be very different. 
Launch window is 0125 to 0200 ut. So first orbit in range Northern UK
could be sometime after 0642 ut approx.

Have recently had a lot of damage to GM packet links, and GB7MAC, GB7JED
,GB7CQV and others have done miracles to keep traffic moving. So most
parts of world should have seen Satgen 38 to 41 in last month , except the
old familiar Yorkshire problem area. Tnx for feedback go to 30 odd
stations from G to ZL2. Yes , will investigate Pacsat distribution of
Satgen as soon as possible.  73 de John GM4IHJ@GB7MAC