so ive been chasing the FM birds for a while now and decided to step it up and try working one of the linear transponder sats, specifically FO-29 since it was supposedly in a decent pass this week. got my Arrow antenna, FT-817 for downlink on 2m and an old FT-857 i borrowed from a buddy for the uplink on 70cm. ran it all into a duplexer which in retrospect was probably not ideal but whatever.

i can hear SSB signals on the downlink, like clearly there are people talking, but my own signal is just not coming back to me no matter what i try. ive been reading about the full duplex thing and how you need to hear yourself on the downlink to do the doppler correction properly but i genuinely cannot tell if im even hitting the transponder at all. the uplink is supposed to be 435.900 to 435.800 inverted right? so SSB on 70cm goes in and comes out on the 2m downlink inverted? im confusing myself.

also how much power are people actually running into these things. i started at like 5 watts on the uplink because i didnt want to be that guy who blows out the transponder AGC but maybe thats too low with a handheld yagi and the satellite only being maybe 15 degrees elevation at best during that pass.

yeah FO-29 is tricky and its definitely not the most forgiving bird to start on, transponder has been flakey for years honestly. but the inverted thing you mentioned — yes thats right, USB in on the uplink shows up as USB on the downlink but the sense of doppler is flipped so as the sat comes toward you the downlink frequency is rising while your uplink needs to go DOWN to stay in the passband. a lot of guys get burned by that at first.

5 watts into an Arrow at low elevation is probably borderline, i usually run closer to 10-15 on the uplink for FO-29, it can take it. the AGC thing is real but youre not gonna hurt it with 15w from a handheld yagi, you'd need like 50+ probably to start causing problems. the bigger issue is probably your doppler correction if your not actually hearing yourself — are you manually tuning the downlink in real time or did you set it and forget it? because at a 10 degree pass the doppler on 2m alone can be like 3-4 khz across the whole pass, enough to wander out of the passband if you're not chasing it.

also what software are you using for tracking? gpredict is solid if you havent tried it, it'll at least tell you exactly where the sat is and some rigs can do the doppler correction automatically if you set it up right.

low elevation passes on the linears are basically practice runs imo, dont get discouraged. i tried working AO-73 for like two weeks before i finally heard my own signal come back and honestly it was kind of an accident when it happened, i was just randomly tuning around on the downlink and there i was. the full duplex monitoring really is the whole game with these birds, once you can hear yourself everything clicks.

one thing that helped me was switching to holding the Arrow by hand and physically pointing it rather than trying to track on a tripod — gives you way more control especially at low elevation where the geometry is changing fast. probably not everyones thing but it worked for me.