so ive been wanting to get into satellite work for a while now and finally got a setup together this weekend. im using a FT-847 for both uplink and downlink, two separate yagis (one 2m one 70cm) and i built a simple az/el mount out of some TV rotors. tracking with gpredict and it seems to be working pretty well, the antenna follows the pass okay.

the issue is when i actually got on a linear transponder sat - think it was AO-73 - i could hear signals down on the downlink but my own signal sounded really weird. like there was this warbling or fluctuating thing going on and i couldnt hold a QSO for more than a few seconds without somebody telling me i was drifting all over. ive got doppler correction set up in gpredict feeding CAT to the radio but im not sure its actually working right because the shift doesnt feel right.

is this a common thing when starting out or did i mess up the doppler config somewhere? i had the sat mode set to inverting linear which i think is right for AO-73. honestly not sure if the problem is the doppler correction, the antenna tracking, or something else entirely. any help appreciated

yeah the doppler thing bites everyone when they start. the tricky part with inverting linear transponders is that you need to correct doppler on BOTH uplink and downlink but in opposite directions - if you just let gpredict do it automatically and you have the mode set right it should handle that, but double check that you actually have the right TLE loaded and that it's current. stale TLEs will make your doppler correction lag and you'll chase the signal all pass.

also one thing people miss - on an inverting linear if you tune UP on the uplink your downlink signal moves DOWN. so if you're hearing yourself drift one way, try tuning the other direction than you think you should. takes a while to get your brain used to it honestly. AO-73 has a pretty narrow passband too so even small errors are obvious.

what TLE source are you pulling from and how old were they when you did the pass?

the warbling could also be multipath if your yagis are close together or if theres something reflective nearby - i had that problem for months before i figured out my downlink yagi was basically pointing at a metal shed at certain elevations. drove me crazy. not saying thats definitely it but worth ruling out before going deep on the doppler config rabbit hole