so ive been trying to work AO-73 for the past couple weeks with mixed results. got a yaesu ft-818 and a pair of m2 antennas on an az/el rotor, doppler correction running through gpredict talking to the radio via hamlib. pass predictions look good, elevation is fine, im getting good arcs most of the time.

the problem is when i actually try to make a contact i can hear a ton of signals in the passband but nobody seems to come back to me, or ill get a partial and then lose it. ive read that the transponder compresses when loaded so i try to keep my uplink pretty modest but honestly im not even sure what level im putting in. the inverting passband thing took me a while to wrap my head around too, had my doppler correction backwards for like the first three passes lol.

is there a sweet spot for uplink power on this one or is it just that everyone is fighting for space during the better passes? feels like trying to shout in a crowded room sometimes. wondering if other peoples experience is similar or if i have something fundamentally wrong with my setup.

the crowded room thing is pretty accurate honestly. AO-73 gets hammered on good passes especially anything over like 30-40 degrees max elevation. the AGC on that transponder will pull everyone down if a few lids are running full power so yeah keeping your uplink conservative is the right call, but what that actually means in practice kind of depends on your antenna gain and feedline losses.

the inverting transponder thing trips everyone up at first, dont feel bad. once you get the doppler sorted and tuned correctly you should hear yourself in the downlink which is really the sanity check — if you cant hear your own signal you either arent in the passband or youre way too low power for that point in the pass. i usually aim to just barely audible on the downlink rather than trying to boom in. also worth trying some of the passes at lower elevations, counterintuitively you sometimes get fewer lids on the marginal passes because casual ops skip them.

yeah gpredict with hamlib to the 818 is basically the standard setup so thats not your issue. one thing i'll mention is that the 818 split mode behavior can be a little weird when hamlib is driving it depending on which version you're running, i had an issue a while back where the vfo tracking wasnt doing what i thought it was doing and i spent like two whole passes confused. might be worth confirming with a known signal on the downlink that your rx doppler is actually tracking right before blaming everything else.