so ive been eyeing satellite operation for a while now and last weekend i finally had a clear pass over my QTH with AO-73 at a decent elevation, think it peaked around 52 degrees which is pretty good for me. been using gpredict for tracking and honestly that part worked way better than i expected, doppler corrections were pretty smooth once i got the CAT interface sorted with my 817.

anyway the linear transponder stuff is where i got confused in practice. i understood the theory — you transmit on the uplink passband and your signal comes back on the downlink inverted, so LSB up means USB down or whatever. but i kept chasing my own signal all over the place. like i'd tune to where i thought i was and by the time i got there it had drifted again. not sure if that was doppler not being compensated fast enough or if i was just overdriving the transponder and causing the AGC to squish everything.

also heard what sounded like a few other stations on there but couldnt really pull any callsigns out, the passband seemed pretty busy for a weekday afternoon. is that normal for AO-73 or was i just in a bad geometry for the footprint? i didnt end up making any contacts but i got my own downlink signal which i guess counts for something. any tips from people who actually work these things regularly would be great.

the chasing your own signal thing is classic and it trips up almost everyone starting out on linear birds. what you want to do is tune the downlink to find yourself, then leave the downlink VFO alone and only adjust the uplink. gpredict or whatever you're using should be doing the doppler math on both ends but the key is your reference is always the downlink — if your signal drifts on the downlink you move the uplink to bring it back, not the other way around. sounds backwards but it clicks pretty fast once you internalize it.

the AGC thing is real too, AO-73's transponder is not super high power and if someone is hammering the uplink with too much power it does compress everything. 5 watts is usually plenty, some people work it with less. you were probably fine with the 817 honestly. the footprint being busy is kind of geography dependent, europeans absolutely pile onto that bird when it comes over them.

yeah 52 degrees is a solid pass, you picked a good one to start with. i had the same frustration my first few times and honestly the thing that helped me most was just getting comfortable finding my own signal before worrying about working anyone else. like spend a whole pass just doing that, dont even try to call CQ yet. once you can find yourself and hold your downlink frequency steady then working other stations gets a lot easier because you're not also fighting yourself at the same time.

gpredict is good but i've heard some people have better luck with MacDoppler on mac or even just doing manual doppler with a spreadsheet someone posted over on amsat-bb, though that sounds painful to me. what are you using for the CAT connection, just the standard USB-serial thing on the 817?