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.[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]
StartDurationSignal
+0 ms10 msUnmodulated carrier
+10 ms80 msCarrier PM modulated with 100 Hz or 312.5 Hz tone, modulation index 0.698
+90 ms5 msUnmodulated carrier
+95 ms5 msCarrier 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]
StartSignificance
0 msTime code data bit 1
100 msTime code data bit 2
200 msAlways 0 (100 Hz tone)
300 ms
400 ms
500 ms
600 ms
700 msAlways 0, except 1 before start of minute
800 ms
900 msAlways 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
SecondData bit 1Data bit 2 SecondData bit 1Data bit 2
WeightMeaningWeightMeaning WeightMeaningWeightMeaning
001Always 1 1Always 1 304Year
(00–99)
8Truncated MJD
(0000–9999)
010Unused, zero +0.1DUT1
(+0.1–+0.8 s)
Unary encoding,
bit set if
DUT1 ≥ Weight
312 4
020 +0.2 321 2
03+0.02dUT1
(+0.02–+0.10 s)
Bit set if
dUT1 ≥ Weight[9]
+0.3 3310Month
(01–12)
1
04+0.04 +0.4 348 0Unused, zero
05+0.06 +0.5 354 0
06+0.08 +0.6 362 0
07+0.10 +0.7 371 0
080Unused, zero +0.8 384Day of week
1=Monday
7=Sunday
0
090 −0.1DUT1
(−0.1–−0.8 s)
Unary encoding,
bit set if
DUT1 ≤ Weight
392 0
100 −0.2 401 0
11−0.02dUT1
(−0.02–−0.10 s)
Bit set if
dUT1 ≤ Weight[9]
−0.3 4120Day of month
(1–31)
0
12−0.04 −0.4 4210 0
13−0.06 −0.5 438 0
14−0.08 −0.6 444 0
15−0.10 −0.7 452 0
160Unused, zero −0.8 461 0
170 0Unused, zero 4720Hour
(00–23)
0
18±ΔUT
Moscow time
minus UTC
Fixed +3 since
26 Oct 2014
8000Truncated
Julian Day
(0000–9999)

Last 4 digits of
Modified Julian
day
number
4810 0
1910 4000 498 P1TJD bits 18–25Even
parity

over
208 2000 504 P2TJD bits 26–33
214 1000 512 0Unused, zero
222 800 521 0
231 400 5340Minute
(00–59)
P3ΔUT bits 18–23
240Unused, zero 200 5420 P4Year bits 25–32
2580Year
(00–99)
100 5510 P5Month/DoW bits 33–40
2640 80 568 P6Day bits 41–46
2720 40 574 P7Hour bits 47–52
2810 20 582 P8Minute bits 53–59
298 10 591 0Unused, 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
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