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 = 66.6̅ 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:

RBU tenth second format[6][7]

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:

RBU second format[6][7]

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]

RBU time code[6][7]
Shaded bits are fixed

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

1. Markus Kuhn (2006-05-10), Low-frequency radio time signals, retrieved 2011-09-20
2. 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".
3. William Hepburn (2006-10-29), VLF time signal brioadcasts, retrieved 2011-09-20
4. "Москва". Vcfm.ru. Retrieved 2012-10-24.
5. "Главный Метрологический Центр Государственной Службы Времени и Частоты (ГМЦ ГСВЧ (НИО-7))". VNIIFTRI. Retrieved 23 July 2018.
6. 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.
7. Standard Time and Frequency Signals (PDF), pp. 5–6, 18–20, retrieved 2018-07-15 -- official signal specification, in russian.
8. 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.
9. National Geospatial-Intelligence Agency (2005), PUB 117: Radio Navigation Aids, pp. 2–5, retrieved 2011-09-20