RBU (radio station)
RBU is a time code radio station located in Moscow. It transmits a continuous 10 kW time code on 66⅔ kHz. This is commonly written as 66.66 or 66.666 kHz, but is actually 200/3 kHz = 66.6̅ kHz. Until 2008, the transmitter site was near Kupavna and used as antenna three T-antennas spun between three 150 metres tall grounded masts. In 2008, it has been transferred to the Taldom transmitter at.
RBU is controlled by All-Russian Scientific Research Institute for Physical-Engineering and Radiotechnical Metrology. It is operated by Russian Television and Radio Broadcasting Network.
Time code
Every 100 ms, synchronized to the UTC second, one bit is transmitted:| Start | Duration | Signal |
| +0 ms | 10 ms | Unmodulated carrier |
| +10 ms | 80 ms | Carrier PM modulated with 100 Hz or 312.5 Hz tone, modulation index 0.698 |
| +90 ms | 5 ms | Unmodulated carrier |
| +95 ms | 5 ms | Carrier off |
100 Hz modulation encodes a binary 0, while 312.5 Hz modulation encodes a binary 1.
Each UTC second consists of 10 such bits. 6 of them are fixed, two encode minute boundaries, and two provide time code information:
| Start | Significance |
| 0 ms | Time code data bit 1 |
| 100 ms | Time code data bit 2 |
| 200 ms | Always 0 |
| 300 ms | Always 0 |
| 400 ms | Always 0 |
| 500 ms | Always 0 |
| 600 ms | Always 0 |
| 700 ms | Always 0, except 1 before start of minute |
| 800 ms | Always 0, except 1 before start of minute |
| 900 ms | Always 1 |
Each minute, the two bits of time code encode the local time of the following minute and some additional information. Because the time code starts with two 1 bits, the top of the minute is uniquely marked by 5 consecutive 1 bits.
dUT1 is an additional, higher-precision correction to DUT1. UT1 = UTC + DUT1 + dUT1.
Bits with a weight of ± are 0 for positive, 1 for negative. The time transmitted is Moscow local time; UTC can be computed by subtracting the value of the ΔUT field.