Satgen 52 The JAS1-B Orbit Tracking by Doppler 9600 bps The JAS1-B launch released the primary payload into a roughly 820 km near circular orbit but the last stage engine was then re ignited in an attempt to use remaining fuel to lift JAS1-B to an Apogee high point around 1200 kms. In fact it went to 1750 kms and descends at perigee to 820 kms. So JAS1-B is in an eccentric orbit which makes its performance and tracking quite different from that of the other Pacsats. At 1750 kms JAS1-B sees 38.3 degs all round. During early March the Apogee near UK allowed UK users access right to Northern JA. But, by the end of May 90 JAS1-B perigee low point will give UK users only 27.6 degs all round access ie a loss of nearly 30% of DX range. So DXers using LSB up 145.9 to 145.97 Mhz for USB down 435.9 to 435.83 Mhz, will find best DX :- To Western USA in early April, late July and early September 90 To Northern Japan in early March and mid August 90. Data mode JD users will be less affected by this 160 day Apogee 81N - Perigee 81N - back to Apogee 81N , cycle, but their access times will drop by 30% when Perigee is near UK 52N, and they will find afternoon Polar passes very poor and in at least one case, probably unreadable. PLEASE NOTE THAT THESE ORBITAL VARIATIONS DO NOT AFFECT OTHER PACSATS Tracking by Doppler Recent Pacsat and JAS keplerian elements have been rather inaccurate. If your computer program predicts Doppler shift you can track much more accurately simply by noting what your AFC controlled Rx Frequency display indicates. Remember your Rx is locking to a 1500 Hz note So if the time is 1143 and your RX says 435.9106 whilst your predictions show :- 1142 +5.2 Khz 1143 +4.0 Khz 1144 +2.4 Khz 1145 +0.6 Khz.Where sat signal frequency with zero doppler is 435.910 Mhz and you earlier found by CPA/TCP calibration (closest approach time,time of zero doppler ,time of maximum doppler rate of change),a 1500 Hz lock occurs at 435.910 on your Rx.You can see the Keps are 2 mins or so behind the satellite. Lusat/Pacsat are providing excellent digipeated sigs for uplink test. If you put up rubbish ,they send it back to you. They do not check it was a good packet.Set your TNC to PASSAL ON, your screen shows the quality of sig the sat sees.Also useful are the 1.5 minutes every 6 minutes of 9600 bps FSK being sent by Uosat D. On FM it sounds like a rise in noise .It comes on screen as "O"s. G3RUH has a summary (on JAS BBS) of how to use this for test of your 9600 modem. JAS BBS is becoming an excellent source for all Packet satellite topics. If you can access or know someone who can, you can keep up to date. 73 de John GM4IHJ@GB7MAC 27 March 90