RBU (radio station)
RBU is a time code radio station located in Moscow (56°44′00″N 37°39′48″E).[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 near Kupavna 55°44′04″N 38°9′0″E 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 56°44′00″N 37°39′48″E.[4]
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.[5]
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 (100 Hz tone) |
| 300 ms | |
| 400 ms | |
| 500 ms | |
| 600 ms | |
| 700 ms | Always 0, except 1 before start of minute |
| 800 ms | |
| 900 ms | Always 1 (312.5 Hz tone) |
Each minute, the two bits of time code encode the local time of the following minute (like DCF77) 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–+0.10 s) Bit set if dUT1 ≥ Weight[9] |
+0.3 | 33 | 10 | Month (01–12) |
1 | ||||
| 04 | +0.04 | +0.4 | 34 | 8 | 0 | Unused, zero | |||||
| 05 | +0.06 | +0.5 | 35 | 4 | 0 | ||||||
| 06 | +0.08 | +0.6 | 36 | 2 | 0 | ||||||
| 07 | +0.10 | +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–−0.10 s) Bit set if 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 | −0.10 | −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 minus UTC 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 18–23 | ||||
| 24 | 0 | 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.
References
- Markus Kuhn (2006-05-10), Low-frequency radio time signals, retrieved 2011-09-20
- International Telecommunication Union (6 October 2010), Characteristics of standard-frequency and time-signal emissions in allocated bands and characteristics of stations emitting with regular schedules with stabilized frequencies, outside of allocated bands, retrieved 2014-10-30 Supplement to Recommendation ITU-R TF.768 "Standard frequencies and time signals".
- William Hepburn (2006-10-29), VLF time signal brioadcasts, retrieved 2011-09-20
- "Москва". Vcfm.ru. Retrieved 2012-10-24.
- "Главный Метрологический Центр Государственной Службы Времени и Частоты (ГМЦ ГСВЧ (НИО-7))". VNIIFTRI. Retrieved 23 July 2018.
- Klaus Betke (1 August 2002), Standard Frequency and Time Signal Stations on Longwave and Shortwave (PDF), pp. 16–17, retrieved 2011-09-20. Note that there is a modulation type error in this reference.
- Standard Time and Frequency Signals (PDF), pp. 5–6, 18–20, retrieved 2018-07-15 -- official signal specification, in russian.
- See Nils Schiffhauer's radio monitoring pages. Under "Audio Clips — Medium Wave (& Longwave)" are audio samples of several time signal stations, including both an audio clip and a spectrogram "waterfall diagram" of RBU at the top of the hour. It clearly shows the 0.1 second bits producing sidebands straddling the carrier at ±100 Hz and ±312.5 Hz, and the 5 consecutive 1 bits marking the top of the minute. The carrier has been shifted down by 66.0 kHz, so it shows up on the plot at 666⅔ Hz.
- National Geospatial-Intelligence Agency (2005), PUB 117: Radio Navigation Aids, pp. 2–5, retrieved 2011-09-20
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