so ive been chasing LEO sats for a few weeks now with FM birds and that went fine, but decided to try AO-73 last night since i saw a decent pass coming up, like 58 degrees max elevation which should be plenty. got my two VX-8DR handhelds set up, one for uplink on 435 and one for downlink on 145, using a pair of arrow yagis i built from that online calculator.

here's the thing — i could hear signals on the downlink, faint but definitely there, some SSB voices and what sounded like CW. but whenever i transmitted i couldnt hear myself come back through the transponder. read that you're supposed to tune the downlink while you transmit to find yourself and then keep adjusting for doppler but i just got nothing. i was putting out maybe 3-4 watts on the uplink which i thought was enough?

is there something about linear transponders im missing compared to FM? like do i need to be more precise on the uplink frequency or is 3-4 watts actually not enough for a handheld setup into a yagi? the pass is coming around again tomorrow morning and i want to actually make a contact this time

linear transponders are a whole different animal compared to FM birds yeah. the thing most people trip over first time is the inverting transponder thing — AO-73 is inverting so if you move your uplink up, your downlink signal moves down. so you cant just set and forget the frequencies, you have to continuously chase both ends as the doppler shifts. a lot of guys just use one radio with doppler correction software and then manually tune the downlink on the second rig while transmitting short bursts to find themselves.

3-4 watts into a yagi should be workable but the transponder does have AGC and if the bird is busy with strong signals it can get competitive. try transmitting CW or just a short carrier first since that makes it easier to find your own signal in the passband. also double check your uplink and downlink freqs against the amsat frequency page because sometimes the bird drifts a bit from the published numbers depending on thermal stuff in orbit.

yeah the inverting part got me too when i started on linear sats. i was using gpredict for doppler correction and it helped a lot but honestly even with software you still end up tweaking manually cause nothing is perfect. what are you using for tracking, like do you have a computer in the loop at all or doing it by hand? cause doing full doppler correction by hand on two radios simultaneously while also physically pointing two yagis is... a lot to manage solo. i ended up building a small az-el rotor setup just to deal with that part