so i've been wanting to do LEO satellite work for probably two years now and last weekend i finally just did it instead of reading about it more. used my FT-818 and one of those arrow antennas, nothing fancy for the first pass. managed to hear myself in the downlink which was pretty exciting honestly.

the doppler correction thing is what i'm struggling with though. i was doing it manually by just nudging the dial every 30 seconds or so but obviously that's not really workable when you're also trying to point the antenna. i've got a windows laptop i could bring outside, is gpredict actually usable for real time correction if i connect the radio via cat? i've seen people mention it but not sure how well it actually works with the 818 specifically.

also the linear transponder on AO-73 — i know its inverting so USB on uplink means LSB on downlink or whatever, but does the passband shift noticeably during a pass or do you kind of pick a spot and stay there. i was all over the place and couldn't tell if that was me or doppler or what

gpredict with CAT works great with the 818, just make sure you've got the hamlib stuff configured right and set the poll interval low enough that it's actually keeping up — i think i run mine at like 500ms or something. the doppler tracking on a 10 minute LEO pass is pretty aggressive especially near AOS and LOS so manual just doesnt cut it once you've tried full auto.

for the inverting transponder thing yeah you basically pick a spot in the passband and try to stay there, the whole passband shifts together with doppler so if you're set up right your signal should stay in roughly the same place relative to other stations. the confusing part is that when you tune your uplink up, your downlink goes down because of the inversion, so it feels backwards until it clicks. just takes a few passes to get the muscle memory.

the arrow antenna is honestly all you need for the low inclination LEOs, people way overthink the antenna side of things when starting out. i ran the arrow for like two years before i built anything else and worked plenty of stations through AO-73 and SO-50. the hardest part is just pointing and tuning at the same time, some people duct tape the radio to the antenna handle which sounds ridiculous but actually kind of works for a single-band pass.

what elevation was your pass? anything under about 20 degrees is gonna be rough just from path loss and horizon noise, the high passes are way more forgiving when you're still figuring out the doppler thing