so ive been messing around with AO-7 and a couple of the other linear birds for a few weeks now and im still not totally clear on the doppler correction thing. i get the basic concept — satellite is moving so frequency shifts — but when people say to tune the downlink to keep it constant and let the uplink drift... is that actually what most people do? or do you tune both?

my setup right now is an FT-847 with a pair of crossed yagis, az/el rotator running off hamlib and gpredict. the tracking part seems to work fine, i can hear signals on the downlink no problem. but when i transmit i feel like im always slightly off and contacts are hit or miss. ive read the wiki stuff but some of it feels like it was written in 2003 and im not sure how much still applies

also curious if anyone has run into issues with gpredict and the doppler plugin being slightly laggy — sometimes it feels like theres a half second delay between where the sat actually is and what the software thinks

yeah the tuning thing trips everyone up at first. the way i do it — and this works for me on AO-7 mode B anyway — is i just watch the downlink beacon and keep that locked in place by tuning my receiver, then i let gpredict handle the uplink correction automatically through rig control. the 847 handles split doppler pretty well if you set it up right in gpredict, theres a setting for it somewhere in the rig control dialog.

the lag you're describing is real though. gpredict isnt doing true real-time doppler, its recalculating on a set interval. i think the default is like every 500ms or maybe a second. you can dig into the settings and lower that interval but honestly for most LEO passes the rate of change isnt so fast that half a second matters much except right at AOS and LOS when the doppler is swinging hardest. mid pass its pretty stable. just dont expect it to be perfect and you'll be fine

the 2003 wiki comment made me laugh because yeah some of that stuff really hasnt been updated. one thing that helped me was just finding a strong signal on the transponder passband — like someone already in a QSO — and tuning around them first so i could hear what full quieting sounds like before i even tried transmitting. gives you a reference point.

also worth double checking your TLE files are fresh, stale keplerian elements will make the tracking drift and if gpredict is pointing your rotator slightly wrong that compounds everything. i update mine every few days when im actively doing sat work