so ive been playing with FO-29 and AO-7 for a few weeks now using my ic-9700 and a pair of arrow antennas handheld which i know isnt ideal but its what i have. got the basic FM birds figured out pretty quick, SO-50 and those are easy enough. but i wanted to try the linear transponders because everyone says thats where the real operating is.

the problem is the doppler correction is driving me insane. i understand the concept, uplink and downlink shift in opposite directions on a linear transponder, so you cant just throw a single doppler correction at the whole thing like you can with a FM bird. im using gpredict for tracking which is solid but im still losing my own signal constantly. i tune around on the downlink trying to find myself and by the time i do the pass is half over.

is there a trick to this that im missing or do i just need more practice. feels like everyone else makes it look easy in the videos i watch but in practice its chaos trying to hold the antenna, watch the screen, and tune simultaneously. do most people run this stuff full duplex or are some people actually doing it simplex and just getting lucky

yeah the doppler on linear birds is genuinely a bit of a puzzle the first few times. the thing that helped me most was just forgetting about the uplink doppler correction at first and only correcting the downlink. find your own signal on the downlink, lock onto it, and then make tiny adjustments to stay on frequency as the pass progresses. the uplink will drift relative to your transmitted frequency but on a linear transponder the transponder itself handles the inversion so you kind of chase your own signal on the receive side rather than trying to predict both shifts simultaneously.

gpredict does have doppler correction built in and if you have it talking to your radio via CAT it can handle both VFOs separately which is the real solution honestly. once i got that set up on my 9700 my pass success rate went way up. you set the downlink on VFO A and uplink on VFO B and let gpredict chase the frequencies automatically while you just focus on the antenna and actually making contacts. the manual tuning approach works but its a lot to juggle especially handheld.

also AO-7 mode B is more forgiving for beginners imo, the transponder is pretty sensitive and the passband is wide enough that you have some margin for error. FO-29 is a bit pickier.

honestly i gave up trying to do it manually after like three passes of chasing my own tail. got gpredict connected to the radio over CAT and it was like a completely different experience. the doppler tracking isnt perfect but its close enough that you can actually have a qso instead of just tuning around the whole time. the arrow handheld setup is totally workable btw, ive made plenty of contacts with one, just gotta nail the elevation angles and not block yourself with your own body which sounds obvious but yeah.