RBU: the Russian long-wave time signal on 66.66 kHz

What you hear

In CW mode RBU is a steady note with a short pulse riding on it once a second and a longer mark at the minute; between the pulses the carrier simply holds. There is no voice and no Morse callsign, so the only way to be sure what you have is the frequency itself, which is unusual enough: 66.666 kHz, or 66 and two thirds, a number that never ends when written as a decimal and comes from dividing a standard frequency by three. The full time code, with the hour, the minute and the date, is carried as shifts of the carrier phase rather than as changes you can hear, so a plain receiver gets only the pulses and a decoder gets everything. The exact layout of pulses and phase code is published by the service but seldom written up in the listener literature, so expect small surprises in the rhythm.

On the waterfall the station is a thin line with a faint dotted edge where the pulses are, sitting between MSF on 60 kHz and DCF77 on 77.5 kHz.

Who transmits and why

RBU belongs to the Russian state time and frequency service run by VNIIFTRI, the national metrology institute outside Moscow, the same organisation that puts RWM on shortwave. The transmitter is in the Moscow region; public listings place it at the Taldom site north of the capital, next to the RWM transmitters. Long wave was chosen for the same reason every country chose it: the ground wave at 66 kHz travels hundreds of kilometres with a stable delay, which is what a laboratory needs to compare its frequency standard against the national one to a part in a trillion. Radio-controlled consumer clocks never caught on in Russia the way they did in Germany or Britain, so RBU has always been more of a calibration service than a household one, and today satellite navigation does most of that work. The station carries on as the reference that does not depend on anything in orbit.

Russia has a second long-wave time station, RTZ on 50 kHz near Irkutsk, serving Siberia in the same way.

When and where to listen

By day the ground wave covers central European Russia: receivers in the Moscow region and the surrounding provinces hear RBU at full strength, and so do those in Finland, the Baltic states and Belarus. After dark the sky wave arrives and the signal reaches Poland, Germany, Scandinavia and sometimes Britain and Italy, with the slow swells and fades typical of long wave at night. Winter nights are the best time for a western European receiver; a summer afternoon in Germany may show nothing at all. Pick a receiver as far east as you can find with long-wave coverage, in Finland or the Baltics, and the station is there at any hour.

A narrow CW filter is the right tool, as for any bare carrier; the program's passband of 300 to 2000 Hz keeps most of the long-wave noise out while leaving the pulses audible.

In ShackDeck

Station catalogue → Time signals → RBU (66.66 kHz). The program picks a public receiver that covers 66.66 kHz, tunes it in CW with a narrow passband so that the carrier becomes a note, and shows the waterfall. No receiver, antenna or account of your own is needed; the phase-coded time is not decoded, what you get is the carrier and its pulses.