so ive been wanting to try satellite work for a while now and finally pulled the trigger on building a cheap tape measure yagi from that ARRL design everyone seems to reference. got my az/el figured out from gpredict and i can hear the downlink on 145.950 no problem, pretty clearly actually, but i cannot for the life of me get anyone to come back to me on the uplink.

im running about 5 watts through the yagi on the 435 uplink and i know AO-73 has a linear transponder so im guessing my SSB needs to be on the right part of the passband. ive been transmitting LSB on the uplink which is what i read somewhere but then i heard someone say its USB on the downlink so now im confused about the inversion thing. is it just that the transponder flips it and i should be hearing myself in the passband if i did it right? because i dont think im hearing myself at all which is probably the main issue.

also gpredict is showing the doppler correction and i've been trying to manually tune but the pass goes by so fast i feel like im always chasing it. any tricks for this on a budget sdr setup? i have an rtlsdr for the downlink and my ft-817 for the uplink.

yeah the inversion thing trips everyone up the first time. AO-73 is an inverting transponder so LSB in becomes USB out, which means when youre listening on the downlink you should be in USB. so if you transmit LSB on 435 the transponder flips it and you hear USB on 145. a lot of people get confused because they think they need to match modes on both ends but thats not how it works with an inverting linear.

the other thing - are you actually hearing yourself in the passband? that's step one honestly. dont try to work anyone until you can find your own signal. tune around the downlink while you transmit a quick dit or just say your call in a monotone. if the transponder is on and youre getting in, youll hear yourself with a little delay. if you cant find yourself you might not be getting into the bird at all, could be polarization, could be the uplink yagi pattern, could be youre not pointing well enough during the fast part of the pass.

for doppler with the 817 and rtlsdr combo - gpredict can actually drive both if you set up the rotctld and rigctld interfaces. takes a bit of fiddling but once its working it tracks automatically. totally worth the afternoon it takes to configure.

honestly just wanted to add - low elevation passes are brutal for beginners, even with a decent yagi. i wasted like my first 6 or 7 passes wondering why i couldn't get in and it turned out i was only trying passes that barely crested 15 degrees. anything under 20-25 degrees i basically dont bother anymore unless the geometry is really favorable. find a pass that goes 40+ degrees elevation and you'll have way more time to mess around and figure out where your signal is.