so ive been chasing this for a few weeks now and i cant seem to get it together. im using SDR# to track the downlink on 145.960 and transmitting on the 435 uplink with my handheld through a Arrow antenna. the pass comes up, i can hear the beacon no problem, but when i try to work through the transponder i either cant hear my own downlink at all or i hear it way off where i dont expect it to be.

i know about doppler and i thought i had it figured out with gpredict doing the tuning automatically but something isnt clicking. the satellite is AO-73 by the way. is it possible the linear transponder is inverting my signal and thats why my downlink is in a weird spot? i read something about that but wasnt sure if it applies here. also how much power do people typically run on these, im doing maybe 5 watts through the Arrow and not sure if thats even getting in

yeah the inverting thing is exactly your problem, AO-73 has an inverting transponder so if you tune up on the uplink your signal comes down lower on the downlink passband, not higher. it trips everyone up the first time. so when you're chasing your own signal you gotta go the opposite direction than you'd think. gpredict should handle the doppler math fine but you still need to understand the inversion to find yourself in the passband.

5 watts through an Arrow is honestly plenty for a good overhead pass, ive worked it with less. the bigger issue is usually antenna pointing especially near the horizon when the bird is moving fast. elevation below like 15 degrees is rough, signals get spotty and the doppler rate is high so everything feels chaotic. try a higher max elevation pass first, like 60 degrees or better, way easier to get your bearings and actually hear what youre doing

same thing happened to me lol, spent like an hour one evening wondering why i couldnt find my downlink and it turned out i was tuning the wrong direction the whole time because of the inversion. once that clicked it made way more sense. also make sure gpredict is actually connected and sending tuning commands to your radio, sometimes the CAT link drops and you dont notice and then youre manually tuning a moving target which is basically impossible