so i've been wanting to do satellite work for a while now and last weekend i finally had a decent pass of AO-7 over my QTH, mode B was active and i figured i'd just go for it with my FT-847 and a pair of yagis on an az-el mount i built from a kit last year. got the tracking going in Gpredict which was pointed at my rotor controller and that part actually worked pretty smoothly, better than i expected honestly.

anyway i found the transponder passband and heard a couple QSOs in progress which was pretty exciting, managed to tune around and heard my own downlink which i know sounds dumb but that was kind of a revelation. the thing im struggling with is the doppler compensation. i understand the concept — uplink and downlink shift in opposite directions on a linear transponder — but my actual experience was kind of a mess. i was chasing my own signal around and i think i was overcompensating on one side and not enough on the other. Gpredict has the doppler tuning feature but i couldnt figure out if it was actually controlling both VFOs on the 847 independently or just doing one. does anyone have this actually set up and working? like what does your CAT setup look like for split doppler correction on a linear bird

yeah the 847 can be a bit fiddly with Gpredict for this. the key thing is you need to have the rig set up so Gpredict sees it as two separate devices in the interface — one for the uplink freq and one for the downlink. there's a setting in the radio interfaces section where you can define the 847 twice, once for VFO-A and once for VFO-B, and then assign one as your rx and one as your tx in the satellite config. if you only set it up once it'll just chase the downlink and your uplink wanders all over the passband which sounds like what you were experiencing.

also worth knowing that AO-7 has an inverting transponder so as you tune your uplink higher your downlink goes lower, Gpredict should handle that automatically once you have the right transponder data loaded but double check the passband limits are correct in the satellites.dat or wherever you have it configured. took me an embarrassingly long time to figure all this out when i first started

hearing your own downlink for the first time is genuinely one of the cooler moments in this hobby imo. thats how it grabs you. i still get a little kick out of it even after doing this for a few years

one thing i'd add on top of what the other guy said — when you're starting out dont chase perfect doppler correction every second, the passband on AO-7 mode B is maybe 40khz wide and the doppler rate mid-pass isn't so fast that you'll lose yourself immediately. let Gpredict handle the coarse tuning and just do small manual corrections on your downlink rx. once you've got a few passes under your belt the muscle memory develops and you stop thinking about it so much. the first few times are always a bit chaotic