so ive been doing FM sats for about a year now, mostly SO-50 and the PSAT2 stuff, and i finally decided to give AO-73 a real shot last weekend. got a decent pass, around 35 degrees max elevation from here in ohio, and i could hear the transponder beacon no problem. pulled up gpredict and had it running doppler correction through hamlib to my 817.

heres where i got confused though — i was tuning around the passband and i could hear a few stations but when i tried to transmit i could never find myself in the downlink. i know you have to work the doppler on both uplink and downlink independently which is different from FM birds, and im pretty sure i was doing that, but honestly i might have been doing it wrong. is there a good way to verify youre actually hitting the transponder without someone else telling you? also does the 817 have enough drive for this or should i be running a small amp on the uplink side

i was using a pair of Arrow yagis by the way, handheld, which worked fine for FM so i figured itd be ok

yeah the linear birds are a whole different world compared to FM sats, took me a while to get my head around it too. the trick i use to find myself is to transmit a short carrier and listen for it in the downlink — but you have to account for the fact that the transponder is inverting, so if youre on the low end of the uplink passband your signal shows up on the high end of the downlink. gpredict should handle most of that if its set up right but i found i still had to manually nudge things a bit during a pass especially near AOS and LOS when the doppler rate is changing fastest.

as for the 817, its plenty. im running barefoot into an arrow and getting into AO-73 without much trouble. the transponder isnt super sensitive but its not deaf either. i'd actually say the bigger issue for most people starting out is just antenna pointing — if youre off even a bit on a low elevation pass you lose a lot. dont worry about an amp yet, get the technique down first

the inverting transponder thing bit me hard when i first started. i kept tuning the wrong direction chasing my signal around. what helped me was just drawing it out on paper honestly — uplink is 435 range downlink is 145 range and the passband is like 40khz wide, and as you go up in uplink freq you go down in downlink. once that clicked it made more sense in practice.

one other thing — are you sure gpredict was actually sending doppler corrections to the 817 via CAT? i had a USB cable issue for a while where it looked like it was connected but wasnt actually changing the rig frequency. worth double checking that the freq on the radio matches what gpredict says during the pass