so ive been messing around with LEO sat work for a few months now, started with the easy FM birds like SO-50 just to get the hang of passes and the doppler thing, and i finally decided to try one of the linear transponder birds, specifically AO-73 since i keep hearing its pretty active.

my problem is i can hear the downlink fine on 145.935 or wherever it is at the start of the pass, got my FT-817 and a handheld yagi, but when i transmit on the uplink i either hear nothing come back down or i completely stomp on other guys who are already working the transponder. i know you have to tune around and compensate for doppler on both ends which is where i think im losing it — im trying to do it manually and it just feels like chasing my tail the whole time.

is there a simpler way to set this up without a full station and rotor system? ive seen people work these things with just handheld yagis so i know its possible, im just clearly missing something fundamental about how to manage the tuning. also not sure if my uplink power is too high, i read somewhere you should barely tickle the transponder but i dont know what that actually means in watts.

the power thing is real and it trips up a lot of people starting on the linears. you want maybe 5 watts into a decent yagi as an absolute ceiling, honestly less if you can manage it. the transponder on AO-73 has an AGC that will compress everything if one station is hogging the passband, so if youre running 25w you're basically just making everyone else quieter including your own downlink. its a shared resource and the transponder doesnt care who you are.

for the doppler on a split-frequency transponder it takes some practice but the trick i use is to find a beacon or another qso already in the passband and use that as your reference point to check how much youre off. SDR# or even just SDRConsole running alongside your logging software helps a ton if you have an SDR dongle lying around, you can watch the whole passband at once and find a clear spot before you even key up. gpredict will do the doppler correction automatically if you connect it to your rig via hamlib but that's a whole other rabbit hole.

yeah the handheld yagi thing totally works, i did my first AO-73 qso with a cheap arrow antenna and the ft-817 just holding it up by hand, it was a mess but it worked lol. the key for me was just accepting the first couple passes are going to be chaotic and using them to listen only, get a feel for where signals actually sit in the passband before you try to put your own in there.

one thing nobody told me — the transponder is inverting so if you tune your uplink higher your downlink signal goes lower in frequency, that messed with my head for a long time. once that clicked the manual doppler chasing started making more sense even if its still a workout