RBU (radio station)

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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)Coordinates: 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 = 66.6̅ 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][5]

Time code[edit]

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.

See also[edit]

References[edit]

  1. ^ a b Markus Kuhn (2006-05-10), Low-frequency radio time signals, retrieved 2011-09-20 
  2. ^ 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, 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. ^ "RWM". Dic.academic.ru. Retrieved 2012-10-24. 
  6. ^ 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.
  7. ^ a b c Standard Time and Frequency Signals (DOC), pp. 4, 15–17, retrieved 2014-08-03  -- 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. ^ a b National Geospatial-Intelligence Agency (2005), PUB 117: Radio Navigation Aids, pp. 2–5, retrieved 2011-09-20