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RBU is a time code radio station located in Moscow (56°44′00″N 37°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 near Kupavna 55°44′04″N 38°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 the Taldom transmitter at 56°44′00″N 37°39′48″E / 56.73333°N 37.66333°E / 56.73333; 37.66333 (Taldom transmitter).^[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. Minute marker
800 ms	Always 0, except 1 before start of minute. Minute marker
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 (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	Weight	Meaning	Weight	Meaning	Second	Weight	Meaning	Weight	Meaning
Second	Data bit 1		Data bit 2		Second	Data bit 1		Data bit 2
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	Unused, zero	+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	Unused, zero	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	Unused, zero
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.

References

^ ^a ^b Markus Kuhn (2006-05-10), Low-frequency radio time signals, retrieved 2011-09-20
^ ^a ^b 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, archived from the original on 2012-11-06, 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. Archived from the original on 27 July 2018. Retrieved 23 July 2018.
^ ^a ^b ^c 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.
^ ^a ^b ^c 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.
^ ^a ^b National Geospatial-Intelligence Agency (2005), PUB 117: Radio Navigation Aids, pp. 2–5, retrieved 2011-09-20
^ used to be "seconds of day" (weight 80000 - 20)
^ may be 1/2 (half-hour) weight of ΔUT