so i've been chasing LEO birds for a few months now mostly on FM - SO-50, PO-101, that kind of thing. got comfortable with the doppler and the timing and thought ok let me try a linear transponder pass. picked AO-73 since it seems like everyone says start there.

first couple passes were a disaster honestly. i was using gpredict on the laptop and had it set up to do the doppler correction but i think i had the offset wrong or something because i could hear the downlink but my signal wasnt showing up anywhere i expected it to. or maybe it was and i just couldnt find it. the passband is pretty narrow right, like 30 or 40 khz? so if youre off even a little you're just gone.

anyway on the third pass i finally heard myself and it was this weird moment where my voice is coming back at me with a slight delay and i was so surprised i just stopped talking lol. managed a few contacts after that once i got used to it. the full duplex thing is genuinely different from anything else ive operated.

my setup is a yaesu ft-847 into a pair of arrow antennas handheld. nothing fancy. my question is about tracking - im doing it manually which is exhausting and i feel like im always a little behind the satellite. is there a way to set up gpredict to output CAT to the 847 so it does the correction automatically, or do i have to use something else for that?

yeah gpredict can do CAT control to the 847 directly, there's a radio interface built in under Edit > Preferences > Interfaces. you add the radio there and then when you're in the tracking window you can enable doppler tuning. the thing is with a linear bird you need to have the uplink and downlink set as separate VFOs and the 847 handles that pretty well since it's got the satellite mode with independent VFOs.

one gotcha - make sure you have the transponder inverting flag set correctly in gpredict for AO-73. it's an inverting transponder so if you tune up on the uplink your signal moves down on the downlink. if you get that backwards the doppler correction will fight you the whole pass. i made that mistake for way longer than i want to admit.

also with the arrow handheld you're gonna lose some passes just from trying to point and tune at the same time, that's just the reality of it. a lot of guys eventually go to a fixed az/el mount just so they can focus on the radio. but manually working it is actually good practice, you learn the doppler curve pretty fast that way.

the delay thing you mentioned catches everyone the first time haha. i remember the first time i heard myself i thought i was causing some kind of feedback loop and just keyed up going "hello? hello?" like an idiot for half the pass before someone else came back to me instead.

one thing that helped me a lot was just running gpredict on a tablet mounted right next to the radio so i could see the footprint and the doppler curve at the same time. also if you're not already doing it, set your squelch completely off on the downlink receiver - sometimes the signal dips a bit during the pass especially when the bird is low on the horizon and a tight squelch will just cut you off right when you're in a good exchange.