so ive been messing with satellites for a few weeks now, started with the FM birds just to get a feel for the passes and doppler and all that, and those went pretty well. figured id try AO-73 since its been pretty active lately and people keep saying linear transponders are where the real fun is.

my setup is an FT-818 with a pair of arrow antennas, one for 2m uplink and one for 70cm downlink, running them into a diplexer into the rig. i know some people split them but this is what i had lying around. i can hear the beacon fine so i know im pointed in the right direction more or less.

the problem is when i transmit i cant find my own signal in the passband. ive been using gpredict for tracking and the doppler corrections look right, or at least they match what the beacon is doing. tried bumping power up a bit but then someone on the mailing list said that's bad practice on linear birds and i should back off. so now im at like 1.5 watts output and still nothing.

is the arrow diplexer combo just not going to cut it for this or am i missing something obvious about how to tune for your own downlink signal

the diplexer thing might be worth looking at but honestly i dont think thats your main issue. on AO-73 specifically the passband is pretty narrow and finding yourself is genuinely tricky at first because your downlink is shifted from your uplink by the transponder inversion. so if youre tuning the downlink to the same frequency youre transmitting on youre going to be way off. the transponder is inverting, meaning LSB up and the signal comes out flipped in the passband. you really have to find the beacon first as a reference point and then work relative to that.

also 1.5w with an arrow should be plenty if your elevation is decent, ive worked AO-73 with less on a good 30 degree pass. the main thing is patience and slow tuning on the downlink while youre transmitting a continuous tone or just saying your callsign slowly. once you find yourself once it clicks and you wont lose it again

yeah what he said about the inversion is the big thing, caught me out too when i first tried it. gpredict will do doppler on both vfos if you set it up right but you have to tell it which mode the transponder is using otherwise its just guessing. theres a transponder database file you can load in and that helps a lot. also i found it easier to start with a high elevation pass, like 40 degrees or more, because youve got more time and the doppler rate isnt as crazy right at AOS and LOS when the bird is low on the horizon