so ive been chasing this for like three weekends now and im pretty frustrated honestly. got a funcube dongle plus and a cheap yagi i built from a tape measure design, using gpredict to track and the timing seems right but i just cannot hear anything on the downlink. tried AO-73 and also FO-29 since someone on the club net said FO-29 was in linear mode again.

my setup is the yagi feeding into the funcube, running SDR# on the side and gpredict doing doppler correction through the CAT interface... or at least i think it is, i followed a youtube tutorial but honestly not sure the correction is actually being applied properly. elevation was like 35 degrees max on the pass i tried yesterday which should be enough right?

is there some trick to the linear transponder passband i'm missing? like do i need to be listening on the exact inverted frequency or something? and how much does the doppler actually shift things in practice, i know it's like 10khz-ish at LEO but i've read conflicting stuff about how SDR# handles the correction versus if you need to tune manually

the doppler thing trips up almost everyone starting out. on FO-29 the downlink is around 435.800 and yes the shift can be close to ±10kHz at the start and end of a pass, so if your correction isnt actually working youll be chasing the signal the whole time and probably miss it entirely especially on a low elevation pass like 35 degrees which goes by really fast.

one thing worth checking — in gpredict go to Edit > Preferences > Interfaces and make sure you actually have a radio device configured there, a lot of people set up the CAT port but forget to actually connect it to the SDR# virtual cable or whatever routing youre using. the doppler correction wont do anything if that handshake isnt established.

also on the linear transponders, yeah youre uplink and downlink are inverted so USB on uplink gives you LSB on downlink or however the particular bird is set up, the amsat status pages have the current mode for each satellite. FO-29 has been a bit sketchy lately in terms of when its actually in linear mode vs beacon only so worth double checking before a pass. try a high elevation pass first, anything over 50-60 degrees will give you a much longer window to actually hear something and sort out the tuning.

35 degrees is workable but yeah its not ideal for troubleshooting. i spent like two months thinking my setup was broken and it turned out gpredict was using a TLE file that was like 6 weeks old and the pointing was just off enough that i was missing the pass. update your TLEs like right before the pass, celestrak has a current amateur sat file. sounds dumb but that fixed it for me.