QO-100: the PSK beacon on 10489.750 MHz, the heartbeat of the geostationary transponder

What you hear

In USB the beacon is a steady rushing sound, like a tap left running, without rhythm or pitch; on the waterfall it is a band about a kilohertz wide with a flat top, sitting exactly in the middle of the transponder at 10489.750 MHz, with the SSB voices on either side. It never stops and never changes. Inside is a 400 baud BPSK data stream with the satellite's telemetry, unreadable by ear. Its value to a listener is simpler. If the rushing sound is there, the path to the satellite works; its loudness tells you how good the dish and the receiver are; and its exact position on the dial is the ruler by which every other frequency on the transponder is measured. Web receivers lock their tuning to it, and operators keep their own signals no stronger than it.

Who transmits and why

QO-100 is the amateur radio payload of Es’hail-2, a commercial communications satellite of Qatar launched in November 2018. The two amateur transponders were built by AMSAT-DL, the German amateur satellite organisation, in a project with the Qatar Amateur Radio Society and the satellite's operator, and the payload received the amateur designation Qatar-OSCAR 100. It is the first amateur transponder in geostationary orbit and so far the only one: the satellite hangs over Africa at 25.9 degrees east, so there are no passes to wait for and no Doppler shift to chase. The footprint covers Europe, Africa, the Middle East and India, from eastern Brazil to Thailand.

The narrowband transponder is linear: it takes a 500 kHz slice of the 2.4 GHz band sent up from the ground and sends it down again at 10489.500 to 10490.000 MHz, everything at once, as if the whole footprint shared one shortwave band. The beacons are sent up from AMSAT-DL's ground station at Bochum in Germany: a CW beacon at each edge and this PSK beacon in the middle. Between them the band plan puts CW just above the lower beacon, FT8 and other narrowband digital modes above that, a mixed segment with SSTV, SSB below and above the middle beacon, and an emergency frequency near the top. A wideband transponder beside it carries amateur digital television, which a web receiver cannot pass on.

When and where to listen

Any hour of any day. The limit is geographical: you need a dish inside the footprint. At home that means a 60 cm satellite-TV dish with an ordinary Ku-band LNB and a receiver tuned 9750 MHz below the published frequency, because the LNB's local oscillator converts 10489.750 MHz down to 739.750 MHz; that oscillator drifts with the weather, which is why the beacon serves as the reference. Without a dish, the public receivers do the work: a KiwiSDR near Paris run under the callsign F6BIR and a few OpenWebRX servers with a QO-100 profile share what their dishes hear.

In ShackDeck

Station catalogue → QO-100: the Es’hail-2 satellite → QO-100: the PSK beacon 10489.750. The program picks a public receiver that has a dish on the satellite and does the converter arithmetic for you: the dial shows 10489.750 MHz while the receiver is actually tuned to its converted frequency behind the LNB, 739.750 MHz or lower still if there is a second converter in the chain. It sets USB with a passband of 300 to 1500 Hz and shows the waterfall. No dish, LNB, receiver or account of your own is needed. The rest of the transponder, from the edge beacons to SSTV and the emergency frequency, is in the same rubric.