so i've been messing around with LEO sat ops for maybe 3 weeks now, started with SO-50 just doing FM passes to get my feet wet and that went fine, but i wanted to try a linear transponder bird and AO-73 has been pretty cooperative lately with decent passes over my QTH in the mornings.

my setup is nothing fancy — a yaesu ft-817 and a pair of handheld yagis i built from that arrow copy design, one for 2m uplink and one for 70cm downlink. the issue im running into is the doppler correction. i know the transponder is inverting so if i tune up on uplink my signal comes down lower on the downlink, got that part sorted in my head finally after reading about it for an hour. what i cant figure out is whether im supposed to be chasing my own signal by moving both vfos or just the downlink vfo as the pass progresses. i was using gpredict to get the doppler shifted frequencies printed out beforehand and kind of pre-programmed some memory channels but that feels really clunky and i definitely missed a chunk of the pass fiddling with the radio.

also heard a few stations working each other but couldnt tell if my signal was even getting in — no one came back to me. is the 817 putting out enough power for a reasonable pass? i was running maybe 2-2.5w on uplink, not full 5w because i didn't want to be that guy hog the transponder.

yeah doppler on a linear transponder confused the heck out of me too when i first started. the way i do it now — i lock my uplink frequency and only chase on the downlink. the idea is you pick a spot in the passband and stay there, so other stations can find you. if you're moving both vfos you're kind of all over the place and it gets messy. gpredict is great but real time doppler correction is the way to go if your radio supports CAT control, i run mine through a laptop and it makes a huge difference, basically hands free tuning.

2 to 2.5 watts should honestly be fine for a decent elevation pass, people work these birds with less. if you're not hearing yourself in the passband thats the first thing to sort out before you call anyone — you gotta hear your own downlink echo before you can really operate effectively. the delay is tiny but its there and it tells you your signal is actually getting in.

AO-73 can be picky depending on the time of day because of the solar panel situation — it goes into transponder mode when the battery is charged enough which isnt always predictable. sometimes i'll have a great 8 minute pass and it's dead, then the next one it's wall to wall signals. worth checking amsat's status page before you go out.

also dont stress too much about 2w, i've had solid QSOs on that bird with similar power and a 3 element handheld yag. pointing accuracy probably matters more than a watt or two honestly, especially near the horizon at the start and end of the pass where a lot of people give up too early.