RBU is atime signal radio station located inMoscow (56°44′00″N37°39′48″E / 56.73333°N 37.66333°E /56.73333; 37.66333 (RBU transmitter)).[1] It transmits a continuous 10 kW time code on 66⅔ kHz.[2] This is commonly written as 66.66[1] or 66.666 kHz,[3] but is actually 200/3 kHz.[2] Until 2008, the transmitter site was nearKupavna55°44′04″N38°9′0″E / 55.73444°N 38.15000°E /55.73444; 38.15000 (RBU) and used as antenna three T-antennas spun between three 150 metres tall grounded masts. In 2008, it has been transferred to theTaldom transmitter at56°44′00″N37°39′48″E / 56.73333°N 37.66333°E /56.73333; 37.66333 (Taldom transmitter).[4]
RBU is controlled byAll-Russian Scientific Research Institute for Physical-Engineering and Radiotechnical Metrology. It is operated byRussian Television and Radio Broadcasting Network.[5]
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 | CarrierPM 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 (100 Hz tone) |
| 300 ms | |
| 400 ms | |
| 500 ms | |
| 600 ms | |
| 700 ms | Always 0, except 1 before start of minute. Minute marker |
| 800 ms | |
| 900 ms | Always 1 (312.5 Hz tone). Second marker |
Each minute, the two bits of time code encode the local time of the following minute (likeDCF77) 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.[8]
| Second | Data bit 1 | Data bit 2 | Second | Data bit 1 | Data bit 2 | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Weight | Meaning | Weight | Meaning | Weight | Meaning | Weight | Meaning | ||||
| 00 | 1 | Always 1 | 1 | Always 1 | 30 | 4 | Year (00–99) | 8 | Truncated MJD (0000–9999) | ||
| 01 | 0 | Unused, zero | +0.1 | DUT1 (+0.1–+0.8 s) Unary encoding, bit set if DUT1 ≥ Weight | 31 | 2 | 4 | ||||
| 02 | 0 | +0.2 | 32 | 1 | 2 | ||||||
| 03 | 0.02 | dUT1 (±0.02–±0.08 s) Bit set if mod(dUT1) ≥ Weight[9] | +0.3 | 33 | 10 | Month (01–12) | 1 | ||||
| 04 | 0.04 | +0.4 | 34 | 8 | 0 | Unused, zero[10] | |||||
| 05 | 0.06 | +0.5 | 35 | 4 | 0 | ||||||
| 06 | 0.08 | +0.6 | 36 | 2 | 0 | ||||||
| 07 | ± | +0.7 | 37 | 1 | 0 | ||||||
| 08 | 0 | Unused, zero | +0.8 | 38 | 4 | Day of week 1=Monday 7=Sunday | 0 | ||||
| 09 | 0 | −0.1 | DUT1 (−0.1–−0.8 s) Unary encoding, bit set if DUT1 ≤ Weight | 39 | 2 | 0 | |||||
| 10 | 0 | −0.2 | 40 | 1 | 0 | ||||||
| 11 | 0.02 | dUT1 (±0.02–±0.08 s) Bit set if mod(dUT1) ≥ Weight[9] | −0.3 | 41 | 20 | Day of month (1–31) | 0 | ||||
| 12 | 0.04 | −0.4 | 42 | 10 | 0 | ||||||
| 13 | 0.06 | −0.5 | 43 | 8 | 0 | ||||||
| 14 | 0.08 | −0.6 | 44 | 4 | 0 | ||||||
| 15 | ± | −0.7 | 45 | 2 | 0 | ||||||
| 16 | 0 | Unused, zero | −0.8 | 46 | 1 | 0 | |||||
| 17 | 0 | 0 | Unused, zero | 47 | 20 | Hour (00–23) | 0 | ||||
| 18 | ± | ΔUT Moscow time minusUTC Fixed+3 since 26 Oct 2014 | 8000 | Truncated Julian Day (0000–9999) Last 4 digits of Modified Julian day number | 48 | 10 | 0 | ||||
| 19 | 10 | 4000 | 49 | 8 | P1 | TJD bits 18–25 | Even parity over | ||||
| 20 | 8 | 2000 | 50 | 4 | P2 | TJD bits 26–33 | |||||
| 21 | 4 | 1000 | 51 | 2 | 0 | Unused, zero | |||||
| 22 | 2 | 800 | 52 | 1 | 0 | ||||||
| 23 | 1 | 400 | 53 | 40 | Minute (00–59) | P3 | ΔUT bits 18–24 | ||||
| 24 | 0[11] | Unused, zero | 200 | 54 | 20 | P4 | Year bits 25–32 | ||||
| 25 | 80 | Year (00–99) | 100 | 55 | 10 | P5 | Month/DoW bits 33–40 | ||||
| 26 | 40 | 80 | 56 | 8 | P6 | Day bits 41–46 | |||||
| 27 | 20 | 40 | 57 | 4 | P7 | Hour bits 47–52 | |||||
| 28 | 10 | 20 | 58 | 2 | P8 | Minute bits 53–59 | |||||
| 29 | 8 | 10 | 59 | 1 | 0 | Unused, zero | |||||
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.
