RBU (radio station)

RBU is a time signal radio station located in Moscow (56°44′00″N 37°39′48″E).^[1] It transmits a continuous 10 kW time code on 66+2⁄3 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:

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
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	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 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 18–24
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.