so ive been licensed for about 3 years now mostly doing HF and some 2m local stuff but last week i finally tried working through one of the AO satellites after a buddy at the club kept bugging me to try it. used my handheld and a tape measure yagi i built from that old ARRL article and honestly it was way more chaotic than i expected

i could hear the linear transponder fine, found my downlink on 70cm no problem, but i could not for the life of me figure out how to actually make a contact. like i was transmitting on the uplink and i could sort of hear myself come back down but by the time i figured out the doppler correction i needed to apply i missed the whole pass. the satellite was only above my horizon for like 6 or 7 minutes and i wasted most of it fumbling with my radio

been using Gpredict to track and that part actually works great, got the TLE data updated and the footprint display is really helpful. but whats the deal with doppler on linear transponders exactly — do i need to correct both the uplink and downlink or just one of them? i've seen different things online and some of it is from like 2009 so i dont know whats still accurate. any advice from people who actually do this regularly would be really appreciated

yeah the doppler thing trips everybody up at first. so with a linear transponder the short answer is you really need to correct both sides, but in practice a lot of guys just correct the downlink and leave the uplink fixed or let the transponder passband do the work. the passband is wide enough on something like AO-73 that you can get away with a static uplink frequency for shorter passes if you're not too far off.

what i'd actually recommend is set Gpredict to do the doppler tracking on both VFOs if your radio supports it and you have it CAT-connected. that changes everything. i was doing it manually on a 817 for months and it was a nightmare, soon as i got the CAT cable sorted and let Gpredict drive the radio it became way more manageable. you still have to tune yourself on the downlink to find your own signal but at least you're in the ballpark instead of chasing the whole passband around

also 6-7 minute passes are rough for learning, try to target passes that are at least 10 degrees max elevation or higher, you get more time and the geometry is easier to work with. low horizon passes are good for experienced guys who already know what they're doing but for learning just skip anything under like 20-25 degrees max el if you can

the tape measure yagi for LEO work is totally legit btw, i used one for over a year before i built anything fancier. if you're hearing the downlink clearly you're probably doing better than you think. the contacts will come once the doppler stuff clicks

one thing that helped me was just spending a couple passes listening only, not even trying to transmit. get comfortable with where signals are sitting in the passband and how they drift, you'll start to develop an instinct for it. also the passband on AO-73 is inverting so if you tune up on the uplink your signal moves down on the downlink, that freaks people out the first time