ok so ive been licensed for about 3 years now mostly just doing HF and some local 2m stuff but i finally decided to try working through one of the LEO birds with a linear transponder. picked up a funcube dongle plus a cheap yagi and figured id give it a shot with SO-50 first but then someone told me SO-50 is FM not linear so i switched focus to AO-73 or maybe FO-29 i cant remember which one my tracking software was showing as having a good pass this weekend.

anyway the doppler correction is what's killing me. i understand the concept, signal comes in higher frequency as the sat approaches and lower as it moves away, fine, i get that. but in practice when im trying to work a linear transponder i need to be adjusting both my uplink AND my downlink simultaneously? and they drift in opposite directions? that just seems incredibly annoying to manage in real time especially when the pass is only like 9 minutes long and you gotta actually make a contact in there somewhere.

using gpredict right now linked to my ft-818 via hamlib and it seems to be doing something but honestly i cant tell if its actually correcting or just showing me pretty numbers. did anyone else go through this learning curve or am i missing something obvious

yeah the doppler on linears is a bit of a head trip at first. the thing to remember is that for a typical LEO like FO-29 or AO-73, the downlink shift over a whole pass can be something like plus or minus 10 kHz on the 70cm downlink, and the uplink on 2m will shift maybe 3-4 kHz the other direction. so if youre tuning your downlink up to chase the signal as the bird approaches, your uplink needs to go down slightly at the same time.

gpredict with hamlib should actually handle most of this automatically if you have it configured right. the key thing a lot of people miss is that you set your "nominal" frequency in gpredict, which is the transponder passband center basically, and then let it calculate the corrected TX and RX freqs. when it's working you mostly just tune your RX a tiny bit to keep your own downlink signal centered and gpredict handles the coarse correction. its not perfect but it gets you in the ballpark and for a 9 min pass thats usually enough to actually make a few contacts once you get used to it.

also FO-29 has been sketchy lately with power issues, might have better luck targeting AO-73 for initial attempts, the transponder on that one seems more consistent in my experience

dont stress too much about getting perfect doppler correction your first few passes honestly. i spent way too long obsessing over it and then realized the biggest problem was my antenna pointing was way off. like yeah the doppler matters but if your yagi is aimed at where the sat was 30 seconds ago youre not gonna hear anything regardless of how good your freq correction is.

what tracking software are you using for the antenna side of things, separate from gpredict or same thing? im still doing it all manually which is probably dumb but i kind of enjoy it