so ive been trying to work FO-29 for about three weeks now and i think i finally got a signal but honestly im not sure if what im hearing is actually the transponder or just terrestrial garbage leaking in. using a homemade turnstile for receive on 435 and a 2m yagi for uplink, both going into an IC-9700 which i have set to sat mode.

the thing that's confusing me is the doppler. i know i need to compensate but my tracking software (gpredict) and the radio dont seem to be talking to me in a way i understand. like i set the doppler tracking up with the CAT interface and it IS shifting the frequencies but when i transmit i still feel like im chasing my own tail. heard what might have been my signal come back downlink but it was way in the weeds and i couldnt tell if it was me or someone else on the bird.

anyone gone through this initial learning curve with linear birds? feels like theres a thing everyone knows that i just havent figured out yet.

yeah the doppler thing on linear transponders trips everybody up at first. the key thing people dont explain well is that on a linear inverting transponder like FO-29 the uplink and downlink doppler corrections go in opposite directions - so if gpredict is set up right it should be handling both but you gotta make sure you configured it for the correct mode (USB downlink, LSB uplink or whatever the bird spec says). if you have it backwards youre fighting yourself the whole pass.

also FO-29 has been pretty sketchy the last year or so, it goes into safe mode randomly and the transponder isnt always on even when the bird is in range. might wanna check the AMSAT status page before a pass to see if anyones reported it active recently. AO-73 is probably more reliable right now if you can work with what you have antenna wise.

went through exactly this about a year ago. what finally clicked for me was just listening to a full pass without transmitting at all - find a strong station working the bird and track THEIR signal manually to understand how the passband drifts. once i did that a few times the doppler intuition kind of just developed on its own. the turnstile on receive might also be limiting you a bit, FO-29s downlink is not super strong and a little beam makes a huge difference on the noise floor even just a small one. but yeah you are definitely on the right track, the fact that you might have heard your own signal come back means something is working.