so ive been meaning to get into LEO satellite work for a while now and last weekend i finally dragged out my arrow antenna and gave FO-29 a shot. managed to hear myself in the passband which was pretty exciting honestly, made one contact with a guy in ohio but then lost the bird before i could work anyone else.

my doppler correction was kind of a mess though. i was using gpredict and had it set up to do split doppler on my IC-9700 but i kept getting confused about which VFO was doing what. i think i had it backwards for part of the pass because my signal kept drifting around and the other station had to chase me a bit. also the inverting nature of the linear transponder caught me off guard, i knew about it intellectually but in practice keeping track of which way to tune while also managing doppler is a lot to juggle on a short pass.

anyway my question is mostly about the doppler correction setup in gpredict. is there a good guide specifically for the 9700 with the hamlib interface? i got it sort of working but not confident i have it right. also curious how much of the doppler you actually need to correct on your transmit side vs just letting the other station deal with it, ive seen different opinions on this.

yeah the inverting transponder thing bites everyone the first time. FO-29 specifically, you tune down on the uplink when you hear yourself going up in the passband, which feels completely wrong until it clicks.

for gpredict and the 9700 i actually dont bother with hamlib, i use satnogs rotator stuff for my antennas but for radio control i just let gpredict do its thing through the rigctl interface. the main thing to check is that you have the downlink frequency set as your primary and gpredict is correcting both VFOs. there was a thread on the amsat-bb list maybe two years ago where someone spelled out the exact settings for the 9700, might be worth digging through the archives.

as for transmit doppler correction, convention is you correct your downlink and keep your uplink roughly fixed, or let gpredict handle both. the other station is doing the same thing so it more or less works out. the passes are short enough that if your doppler is slightly off at the start its not a huge deal, just adjust as you go.

FO-29 has been getting flaky lately btw, i've had a couple passes where it just wasnt on, not sure if its a power issue on the bird or scheduling thing. might want to check the amsat status page before you plan a session around it. AO-73 has been more reliable for me lately when its in sunlight.