so i finally got around to trying satellite work after talking about it forever. did a couple SO-50 passes this week with my FT-65 and a homemade eggbeater-ish antenna i threw together from some old coax and pvc. actually heard myself come back through the bird which felt pretty cool even if the audio was rough.

anyway now i want to try the linear transponder satellites, like FO-29 or AO-73. and this is where i get lost. with SO-50 its just a repeater basically, you tx on one freq and it comes out on another, same mode. but with a linear transponder i keep reading that the passband is inverted and you have to do the doppler correction differently for both uplink and downlink independently and honestly my brain is melting a little. like if im running SSB, which side do i use on which end. ive been reading the amsat pages but some of it assumes you already know stuff i dont know yet.

also im using gpredict for tracking which seems to work fine for SO-50 but im not sure how to set it up properly for the dual doppler thing on a linear sat. does it handle that automatically or do i have to manually tune two separate rigs. right now i just have the one radio and would have to split the job somehow i think.

yeah the inverted passband thing trips everyone up at first. basically on a linear transponder, if you tune your uplink higher in the passband, your downlink signal comes out lower. so doppler correction has to go in opposite directions on the two ends, which is why you really want two vfos or two radios eventually. gpredict does handle the dual doppler correction and it can drive two separate radios via hamlib, one for rx and one for tx, which is the typical setup people use.

for mode, most of the linear birds you want LSB on the uplink and you'll hear USB coming down, or the reverse depending on the sat. FO-29 is USB uplink i think but dont quote me, check the amsat freq chart. AO-73 is the one thats only active in eclipse periods too so timing matters there. with a single radio what some people do is use two vfos and manually track doppler by ear which is totally doable on a short pass if you're quick about it, annoying but works fine for learning.

the main thing is your signal in the passband is just one of many, the transponder is linear so everyone shares the same chunk of spectrum. so keep your power reasonable or you'll be that guy who desenses the whole passband for everyone else on the pass.

im in roughly the same boat tbh, been doing SO-50 for a few months and just started messing with FO-29 last week. honestly just dive in, the first few passes you wont work anyone but you'll figure out the doppler feel pretty fast. i was surprised how manageable it was just tuning by ear once i got the rough frequencies dialed in before the pass. gpredict is solid for predictions, i just use it for that and do the tuning manually for now.