RBU is a time code radio station located in Moscow (55°44′N 38°12′E). It transmits a continuous 10 kW time code on 66⅔ kHz. According other sources http://vcfm.ru/vc/Cities/moskva.htm the transmitter site may be 55°44′04"N 38°9′0"E or on the area of Taldom transmitter

Taldom transmitter

Taldom transmitter is a large facility for longwave and shortwave broadcasting near Taldom, Russia. It transmits on two longwave frequencies, on 153 kHz with 300 kW and on 261 kHz with a power of 2,500 kW. Latter is the most powerful broadcasting station in the world...

 at 56°44′00"N 37°39′48"E. This is commonly written as 66.66 or 66.666 kHz, but is actually 200/3 = 66.6̅ kHz.

Time code

Every 100 ms, synchronized to the UTC second, one bit is transmitted:

RBU tenth second format

Start	Duration	Signal
+0 ms	10 ms	Unmodulated carrier
+10 ms	80 ms	Carrier AM modulated with 100 Hz or 312.5 Hz tone, 70% modulation
+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

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

DCF77

DCF77 is a longwave time signal and standard-frequency radio station. Its primary and backup transmitter are located in Mainflingen, about 25 km south-east of Frankfurt am Main, Germany. It is operated by Media Broadcast GmbH , on behalf of the Physikalisch-Technische Bundesanstalt, Germany's...

) 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.

RBU time code
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) 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) Bit set if dUT1 ≥ Weight	+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 (1–7) 1=Monday 7=Sunday	0
09	0		−0.1		DUT1 (−0.1–−0.8) 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) Bit set if dUT1 ≤ Weight	−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 Moscow Time Moscow Time is the time zone for the city of Moscow, Russia and most of western Russia, including Saint Petersburg. It is the second westernmost of the nine time zones of Russia. Moscow Time has been UTC+4 year-round since 27 March 2011....  − UTC Always +4 since 27 March 2011	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 of month 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.