ok so ive been licensed for about two years and mostly do HF but my buddy kept bugging me to try working through AO-73 and i finally caved and gave it a shot last weekend. i have an FT-818 and a Arrow antenna so i figured that was enough to at least hear something.

i can hear the downlink no problem, signals are actually pretty strong when the bird is high enough in the pass. but here is where i get confused — i know you have to correct for doppler shift as the satellite comes toward you and then moves away, but like... do i tune the uplink, the downlink, or both? i was reading different things online and some guys say to keep the downlink fixed and tune the uplink, others say the opposite. and im using the 818 which is only one radio so how does that even work with full duplex monitoring.

also i was using heavens-above to predict passes and it worked ok but someone mentioned gpredict is way better for this stuff, is that true? the pass i caught was maybe 8 minutes long and signals totally disappeared for the last minute or so, is that normal or was i doing something wrong with the antenna pointing.

yeah the doppler thing trips everyone up the first time. for a linear transponder like on AO-73, the standard practice is to tune your receiver (downlink) to compensate for doppler and leave the uplink more or less alone — your transmitted signal will drift a little in the transponder passband but thats fine, the guys youre trying to work will just tune to find you. if you have two radios running full duplex you can hear yourself and make small corrections to the uplink too, but with a single radio setup like the 818 just focus on keeping your receive frequency correct.

gpredict is genuinely better for satellite work, heavens above is fine for visual passes but gpredict gives you real-time doppler corrected frequencies and can even drive a rig via CAT which is nice if your radio supports it. the signal dropping at the end of a pass is completely normal, youre fighting lower elevation and more atmosphere at the horizon, anything below maybe 5-10 degrees is usually pretty rough depending on your local terrain.

dont worry too much about the full duplex thing starting out, i worked my first few contacts through FO-29 back in the day with just one radio and it was messy but it worked. you kind of develop a feel for it after a few passes. the arrow is a solid choice btw, i still use mine even though i have a better az/el setup now, theres something satisfying about just hand-tracking the thing across the sky.

one thing that helped me early on was recording the pass audio and listening back after, you can hear where you were on the transponder passband and figure out what you were doing wrong. also check the amsat status page before a pass, AO-73 goes into power saving mode sometimes and the transponder isnt always on.