so ive been trying to work the linear transponder birds for a few months now, mostly AO-73 and sometimes IO-86 when its up, and i think i finally got a halfway decent pass yesterday but the doppler correction is still giving me grief. im using SDR# for the downlink and a separate VFO for the uplink and trying to manually tune both at the same time while watching the waterfall and honestly its a mess. i know gpredict can drive a rig with hamlib but ive never actually gotten that working end to end without something crashing or the offsets being weird.

the pass was like 6 minutes and i managed to hear myself in the transponder for maybe 90 seconds of it before i lost the downlink. part of that might be antenna, im just using a handheld yagi for TX and a whip on the SDR dongle which is probably the problem. but also i think my uplink freq was drifting because i was using a cheap baofeng and the TX freq on those things is not exactly stable especially when it warms up.

anyway has anyone got a smooth doppler correction workflow that doesnt require like four hands and three monitors. or is this just one of those things where you kinda have to suffer through it until it becomes muscle memory

yeah the baofeng for uplink is probably hurting you more than you realize, those things can drift 2-3 kHz just from TX heat which on a linear transponder basically sounds like youre sliding around. even a used FT-817 or IC-705 makes a huge difference because the TCXO keeps things stable and you can actually use hamlib properly with them.

for the workflow i run gpredict with two radio instances, one controlling the downlink rig and one for uplink, and i set a manual doppler offset in gpredict for the transponder passband center. its not perfect but its way better than doing it by hand. the thing nobody tells you is you have to account for the transponder inversion on linear birds -- your uplink goes up as your downlink goes down relative to the center, so if you just let gpredict chase both independently it sounds wrong. took me an embarassing amount of time to figure that out.

6 minute pass with a whip on the downlink and a handheld yagi for TX is actually not bad honestly, if you were hearing yourself at all youre closer than you think

IO-86 doesnt have a linear transponder its FM only just so you know, might be thinking of a different bird. AO-73 is linear though and its a good one to practice on when the attitude control is cooperating.

i went through the same thing with gpredict and hamlib for like two weekends before i got it stable. turned out my hamlib rig model was wrong by one digit and it was sending commands to the radio but they werent taking. worth double checking that. also make sure the polling interval in gpredict isnt set too fast, i had mine at like 500ms and it was overwhelming my serial adapter.