so ive been chasing this for a few weeks now and i can hear the downlink fine on my FT-817 with a handheld yagi but i cannot for the life of me get my uplink to actually hit the bird. im using AO-7 in mode B mostly because the pass times work out better for me and ive got it set up in SO-239 split mode or whatever its called.

the thing thats killing me is the doppler. i know i need to apply doppler correction on both uplink and downlink but every time i try to do it manually i feel like im chasing my own tail — i tune the downlink, then my uplink drifts, then i cant find my own signal anymore. ive been using Gpredict for tracking and it seems accurate enough, at least the pass predictions match what im actually hearing.

someone told me i should just let the downlink sit and only correct the uplink but that doesnt feel right either? also not sure if my uplink power is even making it through, like how do you actually know if youre hitting the transponder or just shouting into the void. running maybe 3-4 watts out of the 817 to a 3el yagi on 70cm, downlink on a 5el on 2m. any thoughts appreciated, been lurking here for a while and finally just had to ask

yeah the doppler thing on linear transponders trips everyone up at first. the trick is basically the opposite of what feels natural — you leave your downlink VFO alone and you move the uplink to find your signal. the transponder inverts the signal so as your uplink drifts one way the downlink goes the other, which is actually useful once you get your head around it because the doppler effects kinda cancel partially depending on the geometry of the pass.

for AO-7 mode B your uplink is 432 and downlink is 145 so the doppler on those two bands is different enough that you really cant treat them the same. Gpredict can actually output doppler corrected frequencies if you have it set up to talk to your rig via hamlib, that helps a ton and takes most of the manual work out of it. even just having Gpredict open and manually nudging the uplink every 30 seconds or so is way better than trying to chase both at once.

on your power question — 3-4 watts to a 3el should be enough to hit it on a decent pass, but near the horizon you might struggle. listen for other stations on the downlink passband first to confirm the bird is actually live, AO-7 has no battery so it only works when its in sunlight and it can go dark mid pass sometimes.

just to add to what the other guy said — i spent probably two months frustrating myself before i finally just hooked up a second receiver to monitor my own uplink reflected back down. once i could actually hear myself it all clicked. if you have a second radio or even an SDR dongle you can run it as a dedicated downlink monitor while you operate, makes a huge difference.

also dont sleep on FO-29 if you havent tried it yet, the transponder on that one always seemed a bit more forgiving to me when i was starting out, though the pass windows are shorter and tracking it is a bit twitchier. AO-7 is a great bird but it can be moody.