so i've been doing HF for about 8 years and figured satellite would be similar enough that i could figure it out on the fly. yeah no. spent about 45 minutes just trying to get the doppler correction working properly in gpredict before the pass even started. i had the tracking set up on my FT-817 via CAT control and the uplink/downlink offsets configured but something was just slightly off and i kept hearing myself either not at all or weirdly shifted.

eventually got a QSO with someone down in florida on the second pass but i was scrambling the whole time. the linear transponder on AO-73 is pretty narrow and people kept drifting into each other, i think some of them werent correcting doppler at all on the uplink side which makes it rough for everyone. also i was using a handheld yagi for the downlink and just kind of holding it pointed at the sky which definitely was not ideal.

anyway my question is basically — is there a smarter workflow for setting up the doppler correction before a pass? i felt like i was always chasing it instead of staying ahead of it. and does the rate of change really get that bad near AOS and LOS or is it mostly in the middle of the pass where things are moving fastest?

doppler rate is actually worst at AOS and LOS for the lower LEO birds, counterintuitive but thats when the geometry is changing fastest relative to you. the middle of a high elevation pass is when things kinda settle down and you get a breather. so yeah the scrambling at the start is normal and you kind of just have to get ahead of it a few minutes before AOS by pre-tuning to where the downlink should be coming in.

for gpredict CAT control, the thing that helped me the most was setting the poll interval lower, like 500ms or less if your radio handles it, so it's updating more frequently. some people also just manually tune the downlink and let the software handle the uplink correction only, which reduces the weirdness of both sides chasing each other. took me probably a dozen passes before it started feeling natural honestly.

the handheld yagi thing is totally doable but your arms are gonna hate you by the end of a good pass lol. i did that for months before i built a simple az/el mount out of some rotor hardware i had lying around. even a crappy az/el setup with manual control is way better than trying to point freehand. also for AO-73 specifically the inverting transponder trips people up sometimes — USB on the downlink means LSB on the uplink or the other way, i always have to double check which one it is before the pass because i mix them up every single time