so ive been wanting to get into satellite work for a while and finally had a free weekend to give it a shot. been using gpredict for tracking and it seems solid enough, got my ft-847 set up with the rig control and everything seemed like it was talking to each other okay. pass was AO-73 i think, came over around 70 degrees elevation so should have been a good one.

the problem is i could hear the linear transponder fine on the downlink, people were actually making contacts and it sounded pretty normal. but when i tried to transmit i either couldnt hear myself in the passband or i was way off and stepped on someone. i was using a fixed yagi for both uplink and downlink which i know isnt ideal but its what i have right now.

my question is basically about the doppler correction - is gpredict supposed to be moving both VFOs simultaneously or do i need to set something up differently for a linear transponder vs a FM bird? i feel like i read somewhere that you have to keep your downlink frequency fixed and let the uplink chase but i might be misremembering that. any help appreciated, dont want to be that guy wrecking contacts on the bird

yeah youve got the right idea about which VFO moves. for a linear transponder you want to keep your downlink fixed and tune the uplink to compensate for doppler. the reason is that if you move the downlink you lose your own signal in the passband and then youre chasing your tail. gpredict should handle this automatically if you configure the transponder correctly in the tool - there's a transponder editor in the satellite config where you tell it the passband limits for uplink and downlink and whether its inverting or not.

AO-73 is inverting by the way so if you tune up on uplink you go down on downlink, which trips people up a lot at first. also with a fixed yagi youre going to lose the signal near the horizon anyway so dont sweat the low elevation parts too much. the middle chunk of the pass is where you want to be making contacts. once gpredict has rig control working right it really does move things automatically, just make sure you have the right satellite config loaded and the doppler correction is enabled in the radio control panel, theres a checkbox that sometimes gets missed

i went through basically the exact same thing a few months ago lol. took me like 4 or 5 passes before i actually completed a contact. one thing that helped me was just listening for my own signal in the downlink before the pass even starts - when the bird is still low on the horizon the doppler shift is changing fast so thats actually the hardest time to stay locked in. once its higher up things settle down a bit and you have more time to find yourself in the passband.

also are you doing full duplex? because if youre not monitoring your downlink while you transmit you really cant tell if youre in the right spot. the 847 can do it but you have to make sure its configured for that, i think theres a setting in the menu for satellite mode that enables the split receive