so ive been chasing LEO satellites for a few months now and mostly sticking to the FM birds because they're forgiving but i finally wanted to try AO-73 with its linear transponder and i'm losing my mind a little bit. like i can hear the downlink fine at the start of the pass, SSB signals coming through pretty clearly, i dial in my uplink, get my signal going, and then maybe 30-40 seconds in the whole thing just shifts and i can't find myself anymore.

i know about the doppler and i'm compensating manually which yeah is probably part of the problem but i feel like it's more than just doppler drift. my radio is a 705 and i'm using a handheld yagi which i know is not ideal but it's what i've got right now. is there something about how linear transponders work that i'm missing? like does the transponder invert the sideband or something because someone mentioned that to me and i kind of ignored it and now i'm wondering if that's been my whole issue this whole time.

also using gpredict for tracking and the doppler correction plugin thing but only on the downlink frequency, i didnt set it up for uplink yet. anyway any pointers appreciated

yeah the sideband inversion is almost certainly your problem or at least a big chunk of it. on AO-73 the transponder inverts, so if you're transmitting USB on the uplink your signal comes out as LSB on the downlink. a lot of guys get tripped up by this. so you transmit USB, tune the downlink in LSB, and then here's the fun part - when you compensate for doppler on the uplink you actually move the dial the opposite direction from what feels natural. it's counterintuitive until it clicks and then it becomes second nature.

the gpredict doppler plugin can handle both uplink and downlink simultaneously if you configure it right, definitely worth doing that before your next pass because manually compensating both at once while also steering a yagi by hand is basically juggling. i ran a handheld yagi for my first six months of sat work and it's totally doable but your passes are short so any confusion about which way to tune costs you a big chunk of usable time.

the inversion thing caught me too when i started on the linears. took me like three passes of being totally confused before someone on the cluster told me. also worth checking that you're not transmitting too hot into the transponder - AO-73's transponder is pretty sensitive and if you're running too much power the AGC kicks in and stomps on everyone else on the pass, you end up hearing yourself kind of weirdly and everyone else disappears. on a handheld yagi you're probably fine but just something to keep in mind as you get the rest of it sorted out