Below is a WWVB subcode record of the leap second in the middle of 1997. The question I was trying to answer is what subcode bit is transmitted during the leap second; a '0' bit or a '1' bit, or a position marker bit. The answer is a position marker bit. Since the positive leap second is inserted into UTC at the top of the minute, this is the only time three position markers are broadcast back-to-back.
From: Tom Van Baak <tvb veritas.com> Subject: Re: WWVB to Logic RF Circuit / Chip Date: 1997/10/21 Message-ID: <344D489A.4D6@veritas.com>#1/1 References: <34490871.AD6@pacific.net> To: email@example.com Organization: VERITAS Software Reply-To: tvb veritas.com Newsgroups: rec.radio.amateur.homebrew,sci.electronics.design Brooke wrote: > > I would like to receive the time code from WWVB on 60 kHz (not the > carrier frequency). Does anyone know of a simple circuit and/or > chip that outputs the time code? > > Thanks, > Brooke > N6GCE Brooke, An excellent 3 part article by Bob Roehrig on building a WWVB receiver can be found in the Jan/Feb/Mar issue of '73 magazine. The old HP 117A VLF receiver has a signal level output that can be used to decode the subcode. The manual has an example where a strip chart recorder is used to decode the signal. See http://www.bldrdoc.gov/timefreq/pubs/sp432/s_appc.htm for a description of the 60 second WWVB time code format. See http://gorzarg5.phy.bnl.gov/~scott/radio-clocks.html for a bibliography of time and frequency radio receivers. Perhaps the easiest way these days is to extract the raw subcode from one of the many battery-powered desktop WWVB radio clocks on the market. I have been unable to decode the VLF receiver output of the Oregon Scientific, Brookstone, or Junghans WWVB radio clocks, but have had great success with the Arcron Zeit. There are two ICs inside the desktop model of the Zeit: one is the 60 kHz VLF receiver and the other, hidden under the LCD, is the uP which decodes the 1 Hz subcode and drives the display. One of the traces that runs between the two ICs is the receiver enable and the other is the 1 Hz subcode output. Logic low (0 V) on this line corresponds to full WWVB power and logic high (3 V) to 10 dB reduced power. When the receiver is on and reception is good the 0.2, 0.5, and 0.8 second width bit frames are clearly visible on the 1 Hz subcode output. This output can be sampled and decoded by a PC or microcontroller (such as a Basic Stamp). At the end of June 1997 I used this technique to observe how WWVB handled the leap second. In the following log the date and time are PC local time (PST), "P" indicates a frame or position marker (0.8 second of 10 dB power reduction), "1" indicates a binary one (0.5 second power reduction), and "0" indicates a binary zero (0.2 second power reduction): 1997-06-30.16:55.P10100101P001000011P000101000P000100010P010101001P011100111P 1997-06-30.16:56.P10100110P001000011P000101000P000100010P010101001P011100111P 1997-06-30.16:57.P10100111P001000011P000101000P000100010P010101001P011100111P 1997-06-30.16:58.P10101000P001000011P000101000P000100010P010101001P011100111P 1997-06-30.16:59.P10101001P001000011P000101000P000100010P010101001P011100111PP 1997-06-30.17:00.P00000000P000000000P000101000P001000101P010101001P011100011P 1997-06-30.17:01.P00000001P000000000P000101000P001000101P010101001P011100011P 1997-06-30.17:02.P00000010P000000000P000101000P001000101P010101001P011100011P 1997-06-30.17:03.P00000011P000000000P000101000P001000101P010101001P011100011P 1997-06-30.17:04.P00000100P000000000P000101000P001000101P010101001P011100011P Use SP432 to decode the :59 and :00 minute frames: 59 minutes, 23 hours, 181 days, UT1 = -0.5 seconds, year 97, leap second pending, and DST active. 00 minutes, 00 hours, 182 days, UT1 = +0.5 seconds, year 97, no leap second pending, and DST active. /tvb
The above was an old posting of mine found in the Google Usenet archives.