so i finally decided to give satellite operation a shot after years of telling myself i'd get around to it. been licensed for about 8 years, mostly HF but figured why not. got gpredict set up and pointed it at AO-73 since everyone seems to say thats a good starting point for linear transponder work.

my problem is the doppler correction. i understand the concept, the frequency shifts as the bird moves toward you then away, fine. but in practice i cant figure out if im supposed to be manually tuning both the uplink and downlink in real time or if theres a way to automate it, or if i should just set a fixed offset and chase it by ear. ive been using an ic-9700 so in theory it should be able to handle this but the gpredict to radio CAT interface is giving me fits and half the time it just loses connection.

also not sure if im even hearing the transponder correctly. i heard what might have been a few ssb signals on a pass yesterday around 145.950 ish on the downlink but they faded real fast and i couldnt tell if that was the pass geometry or just me doing something wrong with the antenna. running a simple arrow antenna handheld for now, no az/el rotators or anything fancy.

the arrow handheld thing is totally workable, ive made a bunch of contacts that way on AO-73 and even FO-29. the doppler on the linear birds is manageable once you get a feel for it. with the 9700 and gpredict the CAT connection can be flaky, make sure youre using the right port settings and that rigctld is actually running before gpredict tries to connect, thats usually the issue in my experience. also check that you have the transponder passband entered correctly in gpredict's satellite config, if those numbers are off the tuning will seem weird.

what you probably heard was real, 145.950 is right in the AO-73 downlink range. the signals fade fast on a low elevation pass especially with a handheld antenna since youre not tracking perfectly. try a pass that gets above 30 degrees or so, way easier to work. and yeah you basically tune both vfo's together, gpredict handles the math if the CAT link is working. if its not working just manually tune the downlink and accept the uplink will be slightly off, you can still get on there and listen at least.

just to add one thing about the arrow — when you're holding it and spinning around trying to track the pass, your downlink signal is gonna flutter all over the place and thats completley normal and kind of drives you crazy at first. i spent like three passes thinking my radio was broken before i realized i just kept blocking the antenna with my arm. also AO-73 isnt always on, the operators put it in power safe mode sometimes during certain orbital conditions so if you hear nothing at all on a good pass thats maybe why. the AMSAT status page is worth bookmarking.