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Satellite passes
A handheld and a home-made antenna are enough for a QSO via satellite, you just need to know when it comes and where to point.
| Satellite | AOS | Duration | Max. elevation | Track | Frequencies |
|---|---|---|---|---|---|
- above your horizon
- below your horizon
- your location
- track for the next 20 minutes
- selected satellite: track for the next orbit
- track so far
- footprint: from here it's above the horizon
Land and borders: Natural Earth (public domain). Map library: MapLibre (BSD). SGP4 orbit model via satellite.js (MIT), orbital data from CelesTrak.
Geostationary satellites don't make passes, they always sit in the same spot. All that matters is where to point your dish.
Some handhelds work out passes themselves and correct for Doppler. For that they need a satellite list with frequencies and fresh orbital data. You get both here as a file for the radio's programming software.
Without programming software, use Rigstudio: there you write the satellites straight into the radio over the programming cable and later just refresh the orbital data. That works with the AnyTone AT-D168UV, the AT-D878UV II with firmware 3.x and the Icom IC-9700 and IC-9100 (satellite memories, without orbital data). For now Rigstudio can only read the AT-D878UV II S and AT-D890UV.
How a satellite QSO works
Depending on altitude, a pass lasts five to fifteen minutes. During that time the satellite rises above the horizon at the given AOS point, crosses the sky and sets again. The higher it gets, the longer and louder you'll hear it. Below ten degrees there's usually a house, a tree or a hill in the way.
There are two kinds. An FM transponder works like a repeater in the sky: one talks, everyone else listens. It's the easier way in, but it gets crowded. A linear transponder relays a whole frequency range and is used in SSB or CW; several QSOs fit side by side there. “Inverting” means the band is mirrored: go higher on the uplink and you come out lower on the downlink, and upper sideband turns into lower.
Why the frequency shifts
The satellite races along at about 7.5 kilometres per second. Coming towards you, you hear it too high; moving away, too low. On 435 MHz that's a good ten kilohertz between AOS and LOS, more than an SSB bandwidth, so you have to retune during the pass. On 145 MHz it's only about three kilohertz.
The rule of thumb: always retune on the higher frequency. During a pass the shift is largest at the start and end and zero for a moment at TCA. The table gives the values for AOS, TCA and LOS for each pass.
Where the numbers come from and how accurate they are
The calculation uses the SGP4 orbit model with the official orbital elements. When fresh, the prediction is accurate to seconds; after a week it's already minutes off, because the upper atmosphere slows the orbit down. The page tells you how old its elements are.
Whether a satellite is actually transmitting right now is deliberately not shown here: transponders get switched off and on again, and a copy of that information would soon be wrong. The current status is on the AMSAT status page, fed by reports from people who have just tried.