so ive been chasing LEO sats for a few months now, mostly FM stuff on SO-50 and the like, got pretty comfortable with that. decided to step up and try working AO-73 and some of the other linear transponder birds and man it is way harder than i expected.

the problem im having is i can hear the downlink fine on 145 MHz, signals sound decent when the bird is high enough, but i cant seem to get my uplink to actually land where i want it in the passband. ive got doppler correction running through gpredict and that part seems okay but when i transmit i either cant find myself or by the time i do the pass is like halfway over. also the inverting transponder thing is tripping me up, i keep forgetting which way to tune and end up going the wrong direction.

im running an ic-9700 and a pair of small yagis on an az-el mount, so the hardware should be up to the task i think. is this just a practice thing or am i missing something fundamental about working linear birds vs FM repeater sats

the inverting transponder thing is what gets everybody at first, dont feel bad. basically if you drift down in the passband on rx you need to tune UP on tx to compensate, it feels completely backwards and your brain fights you on it. once it clicks it becomes automatic but it takes a few passes to rewire yourself.

for finding yourself — easiest trick is to use a very short low power transmission, like just tap the PTT for half a second with like 5 or 10 watts, and really listen for where you land. dont try to hold a full over until youve actually located yourself in the passband. a lot of guys new to linear birds just key up and wonder why they cant find themselves and its because they blasted a 10 second transmission before verifying anything.

also with the 9700 and gpredict, make sure you have the doppler correction actually set up for the right VFO assignments. the 9700 has that CAT setup where you can have it track both uplink and downlink simultaneously but you have to tell gpredict which is which and i've seen people have them swapped without realizing it. check the tracking module settings, there's a control port configuration that matters.

yeah what he said about the inverting transponder, that took me a embarrassingly long time to get sorted out. the other thing i'd add is honestly just spend a pass or two not even trying to make contacts, just sit on rx and watch where signals are, listen to how the doppler sounds, get a feel for how the passband is moving during the pass. i found that really helped me before i started stressing about actually working someone.

AO-73 can be kind of finicky depending on power levels too, the transponder will start to saturate if too many people are running too much power and then everything gets muddy. some passes are just rough because of that, nothing wrong with your setup.