so ive been playing around with AO-7 and a couple of the other linear birds for the past few weeks and i think i kind of understand whats happening but honestly im not 100% sure my doppler correction is doing what i think its doing

my setup is an ic-9700 and a pair of arrow antennas on a pretty janky homemade Az/El mount, works okay but i have to manually adjust which is whatever. i can usually hear the beacon and sometimes catch a bit of SSB activity in the passband but when i try to actually make a contact it feels like im either hunting all over the place or my downlink drifts off right when i think i have someone

the thing i cant figure out is whether im supposed to hold my downlink frequency constant and let the radio adjust the uplink automatically or if i should be manually tuning both. ive watched a few youtube videos and they all kind of say different things. one guy was using gpredict and had it linked to his rig which seemed cool but i couldnt get that working either - the rig control through hamlib kept erroring out on me

anyway does anyone have a simple way to think about this? like a mental model for the doppler thing on linear sats that isnt just "trust the software"

yeah the doppler thing on linears trips up basically everyone at first. the short version is that on an inverting linear transponder like AO-7 mode B, if you tune your uplink UP the passband, your downlink comes out going DOWN, so they move in opposite directions relative to ground. but the doppler shift is happening on both links independently and at slightly different amounts since the uplink and downlink are on different bands - so they dont cancel perfectly

the way i think about it: lock your downlink receive frequency to where you want to hear yourself and adjust your uplink until you find your own signal. once youre there, if you hold the downlink constant and the sat drifts because of doppler, nudge your uplink slightly to compensate. your receive freq stays put and thats your reference. gpredict linked to the 9700 should handle most of this automatically once you get the hamlib stuff sorted, the CAT settings on the 9700 can be finicky - make sure youre not letting two applications try to talk to the radio at the same time, that bites people a lot

also AO-7 is a great bird to learn on but its old and sometimes it disappears into eclipse mode unexpectedly so if you lose it mid pass dont panic

i had the exact same problem last summer, took me like a month of frustrating passes before something clicked. honestly what helped me more than anything was just finding my own downlink carrier before the pass even gets to high elevation so you have time to get settled. trying to find yourself when the sat is overhead and everyones piling on is chaos

the hamlib/gpredict integration is worth getting working though i wont lie. once it actually works its kind of magical watching the radio tune itself. think i had to downgrade hamlib version to get it stable with my setup but that might not be your issue