so ive been chasing LEO sats for a few months now mostly doing FM birds like SO-50 and that's been going fine, got a decent pass rate with my arrow antenna and an HT. but i want to try AO-73 or maybe FO-29 since everyone says linear transponders are a whole different thing and i want to learn it properly.

the part im really struggling to wrap my head around is the doppler correction. i get that the sat is moving so the frequency shifts but like... if im using a linear transponder the uplink and downlink are on totally different bands right? so do i have to be manually tuning both at the same time? ive seen people say their radios are linked or something but i dont have a fancy rig, just an FT-817 and an old laptop. is there software that handles this or am i going to be spinning two VFOs at once trying to have a QSO. feels like it would be impossible honestly

also just to make sure i have this right - on a linear transponder if i transmit USB on the uplink my signal comes out as LSB on the downlink? ive read this a couple times but it still doesnt feel intuitive to me

yeah the inverted sideband thing gets everyone at first. basically the transponder flips it so you transmit USB on your uplink and it comes out LSB on the downlink. just kind of how the mixing works in there. once you actually hear it happen on a pass it clicks pretty fast.

for doppler on the 817 with a laptop, look at gpredict. it's free and it has CAT control so it can tune the radio automatically based on the predicted doppler curve. you'll need a CAT cable for the 817 (or a USB one) and then you configure your uplink and downlink frequencies in gpredict and let it handle the correction. it's not perfect and sometimes you still nudge things manually but it gets you 90% of the way there. the key thing people forget is you still have to find your own signal on the downlink and tune to it, gpredict just keeps the nominal frequency correct, your actual signal could be slightly off depending on how well you calibrated.

AO-73 is a good one to start with, passes are reasonable and the transponder is pretty sensitive. just keep your power down, like seriously 5 watts or less on the uplink is plenty, overdriving a linear bird is a quick way to get ignored by everyone on the pass.

the two VFO thing sounds scarier than it is tbh. i did my first linear sat QSO without any CAT control at all, just printed out the doppler schedule from heavens-above and kind of manually stepped the frequencies every 30 seconds or so. its clunky but it works well enough to prove the concept before you go down the gpredict rabbit hole. FO-29 might actually be easier to hear than AO-73 depending on where you are, the downlink seems punchier to me but that could just be my setup