so after like three weekends of messing around i finally made my first contact through AO-73 last sunday, which was pretty satisfying after all the frustration. but honestly the doppler correction is still giving me more grief than i expected.

im using gpredict on a linux box tied into my ft-818 via hamlib and most of the time it works fine but every now and then the freq correction just seems to stop updating mid-pass and i lose the downlink completely. not sure if its a hamlib timeout or something with my usb-serial adapter flaking out. the pass was only like 8 minutes to begin with so losing 90 seconds of it is pretty annoying.

also wondering if anyone has tips on actually finding the linear transponder passband when youre new to this. i kept hunting around and occasionally heard voices but couldnt always tell if i was hearing my own signal in the downlink or someone else. the inverting transponder thing messes with my head a bit still — so if i tune up on uplink my signal goes down on downlink, right? i think i have that correct but during an actual pass its easy to second-guess yourself.

anyway just wanted to share that it actually works and see if anyone has dealt with the gpredict/hamlib dropout thing before

yeah the inverting transponder thing trips everyone up at first, you have that right — USB on the uplink means LSB on the downlink effectively, and tuning higher on tx moves your rx signal lower. once it clicks it becomes second nature but during a busy pass with doppler correction happening at the same time its a lot to juggle.

for the gpredict dropout issue, ive seen that before with cheap prolific usb-serial adapters, they have a tendency to disconnect under load or just randomly reset. if you havent already, check dmesg during a pass and see if youre getting any usb disconnect messages. swapping to an FTDI-based adapter basically fixed that problem for me. also worth checking your hamlib polling interval — if its set too aggressively sometimes it overwhelms older rigs.

AO-73 is a good bird to start on, the transponder is pretty forgiving. FO-29 is worth learning too when its healthy, better signal margin in my experience. congrats on the first contact, it gets way more addictive from here.

the usb serial thing is almost definitely your problem, had the exact same issue last year. also just want to say finding your own signal on the downlink is kind of the hardest part honestly, what helped me was to start a pass by just transmitting a carrier briefly with no audio and hunting for the het in the passband before actually trying to make a contact. once you can hear yourself its much easier to work the doppler manually even if the software glitches out