so i've been wanting to get into LEO satellite work for a while now and last weekend i finally set up enough to give AO-73 a real shot. been doing SSB on HF for years so i kind of assumed the linear transponder stuff would feel familiar but honestly its a bit more disorienting than i expected.

my setup right now is a yaesu 817 for the downlink on 2m and an old ft-2900 feeding a small 5 element yagi for uplink on 70cm. running gpredict on the laptop for tracking and doing the az/el manually just by watching the predictions and spinning the beam by hand. no rotor yet.

the doppler thing is what's really messing with me. i kind of get the concept but in practice i was constantly chasing my own signal around and by the time i found it the pass was like halfway done. is there a trick to pre-tuning or do most people just let gpredict handle the rig CAT control and forget about it? also i noticed my signal sounded inverted at one point — like when i tuned up my downlink rx frequency went down? is that just how inverting transponders work or did i have something set up wrong.

got one qso in, guy in ohio, pretty exciting for a first try but i feel like im barely scratching the surface of whats going on technically.

yeah the inverting transponder thing trips everyone up the first time. AO-73 is an inverting linear transponder so if you tune your uplink higher your downlink comes down in frequency — its counterintuitive but thats just how it works. so you have to tune your rigs in opposite directions when chasing doppler or a qso partner. once that clicks it starts making more sense.

the doppler management honestly gets easier with CAT control, gpredict can drive both radios if they're both connected and it'll handle the correction automatically based on the TLE data. that said plenty of people work LEO sats without it, you just kind of develop a feel for pre-tuning ahead of the pass. AO-73 has a relatively slow doppler shift compared to some of the faster lower birds so its not the worst one to learn on.

one thing that helped me early on — park your downlink rx at a fixed frequency you're pretty confident about and tune your uplink to find yourself. that way you're only chasing one thing at a time. and honestly hand-tracking with a yagi isnt that bad for low-elevation passes if you know where to look, the high-elevation ones are the painful ones where you're spinning constantly.

nice work getting a qso on the first real try tbh. i fumbled around for like three passes before i actually completed anything. one thing i'd add — make sure your TLEs in gpredict are fresh, like updated within the last few days fresh. i had a situation where i was pointing the wrong direction entirely because i hadn't refreshed in a couple weeks and the element set was way off. satellites drift enough that stale TLEs will have you looking in completely the wrong part of the sky especially toward the end of a pass.

also re: the 817 for downlink, i used one for a while and found the AGC behavior kind of annoying when signals were fading in and out on a sat pass. might be worth digging into the AGC settings if you haven't already.