Talk:WWVB/Archive 1

Archive 1

HISD in Houston Texas

All HISD schools in Houston use clocks which are controlled by transmitted from somewhere in Colorado, presumably from WWVB. However, at all the schools I have been to, the clocks have either not been working properly or, as in most cases, showing the wrong time. Is this station still operating correctly? —Preceding unsigned comment added by 69.151.247.10 (talk) 22:01, 8 August 2008 (UTC)

WWVB is still transmitting properly, because my own WWVB radio-controlled clock is showing the correct time. Perhaps they dial in to the USNO master clock in Colorado? --  Denelson83  22:32, 8 August 2008 (UTC)

[The current status can be monitored here]--CMG (talk) 22:44, 8 August 2008 (UTC)

Request additional opinions on DST bits.

There's an edit war brewing; this is the latest (earlier, earlier, introduced), over the definition of the DST bits broadcast in seconds 57 and 58. Specifically, the definition included in the table. The two rival definitions are:

1. Defining the bits individually
   • Bit 57 is set if DST is in effect as of 24:00Z today.
   • Bit 58 is set if DST is in effect as of 00:00Z today.
2. Defining them as a 4-state status value, with bit 57 having weight 2 and bit 58 having weight 1.
   • 2 = DST begins today.
   • 3 = DST is in effect
   • 1 = DST ends today
   • 0 = DST is not in effect.

The two definitions are equivalent. The former has the advantage of being more compact, while the latter mirrors how NIST describes it. The former provides an alternative to the explanation given in the WWVB signal format diagram, while the latter reiterates it.

Discussion between the rival editors can be found at the end of their respective Talk pages here and here.

Additional (tie-breaker) opinions on which form is preferred are solicited. 71.41.210.146 (talk) 08:14, 1 April 2009 (UTC)

Hello, I'm responding to your request for a third opinion. I think that both formats make sense, and while there is no technical difference between them, I think it is clearer to to treat them together as a 2-bit number and provide a table similar to the second format above. However, I think the values should be ordered correctly and that the actual labels in the table are a little vague; if "DST begins today", what time exactly does it begin? Would it be better to write something like this?

• 3 = DST is in effect.
• 2 = DST begins at 24:00Z today.
• 1 = DST ends at 24:00Z today.
• 0 = DST is not in effect.

How does that look? AlekseyFy (talk) 07:55, 7 April 2009 (UTC)

It looks great, but is incorrect. DST rarely starts at 24:00Z. In much of North America, for example, DST starts at 02:00 local time, which can be anywhere between 05:30Z to 10:00Z. The original definition of "is in effect as of 24:00Z today" may not be the most intuitive, but at least it is accurate. Owen× ☎ 12:14, 7 April 2009 (UTC)

Yes, it may help to read the text (which gives a third explanation) for a lengthier explanation, which includes the fact that the change is actually applied at 02:00 local time. The dispute here is primarily about what to put in the table, although overall clarity, including all versions, is obviously the ultimate goal. As for the ordering, the Gray code ordering given lists the values in the order in which they appear over time, which I think is more important than numerical order. You can rotate the list to start at 0 if you like, though. 71.41.210.146 (talk) 15:52, 7 April 2009 (UTC)

Sorry, I didn't realize that the vagueness of the description there was necessarily to match what really happens. I had assumed (incorrectly) that the switch must happen at 24:00 from the way the first format above was written, which isn't what it's really saying. I probably wouldn't be the only person to make that mistake from just looking at that description, however.

I still think the table format is the clearer of the two. Also, when looking to decode the bits in the message, I first form the number 0-3 in my head, then consult the table. Having the table out of order, even for a good reason, makes this less clear. I know that I didn't notice that the table was out of order at all when I first looked at this page, so when I worked the meanings through the first time, I thought I'd misunderstood when the text didn't match what I expected. Again, I probably wouldn't be the only person to make that mistake either. If you think it is really important to preserve the sequence the code would occur in, why not just write them out in binary instead of base 10:

• 10 = DST begins today.
• 11 = DST is in effect
• 01 = DST ends today
• 00 = DST is not in effect.

That avoids the look-up problem for my eyes, at least, and also makes the Gray code progression clear.

Since I'm sure you both have been looking at this page for a while now, I hope that bit outside perspective helps. AlekseyFy (talk) 17:57, 7 April 2009 (UTC)

Helix Information

We need to recruit an expert to write on helix (electronics) page which I started. I flagged the dubious claim that the helix is 4100 feet long. I have seen them with my own eyes and know better. Helical inductors are not even MENTIONED on the inductor page. Every one of the hundreds of millions of televisions in the world has a dozen of them in their tuners. It would be nice is someone could give the helix currents which are on the order of a few hundred amps. Thousands of watts are lost in the helix and their design is not trivial.Trojancowboy (talk) 22:18, 1 May 2009 (UTC)

When I say "amount of cable used in each antenna", I'm referring to the length of the top-hat and downlead in the air, not the "helix". I'll clarify. --  Denelson83  00:36, 2 May 2009 (UTC)

You did a good job except for a basic misunderstanding. The length of the down lead is negligible. The helix inductor is in series resonance with the diamond capacitance to ground, about 1 nFd. Its physical length is irrelevant and could be only a few feet with some inductor designs.

See below for the enormous voltages and currents. The tower would have to be nearly a mile high otherwise. A normal 50 ohm antenna would have a current of 30 amps and a voltage of 1500 volts for 50 kW. I used to talk to Mr Maxton 15 years ago wwhen he was running his old transmitter with only 13 kW. It was running 150 amps of helix current then into one antenna.Trojancowboy (talk) 02:39, 2 May 2009 (UTC)

Well, the downlead needs to be that long simply to connect the helix house to the antenna top hat at 122 metres AGL. --  Denelson83  04:45, 2 May 2009 (UTC)

Antenna System

I added a link to the antenna system in reference 1.WWVB IMPROVEMENTS It shows the details of the tuning. With a 1 nFd top hat, X_c is about 2,652 ohms. Each helix should be about 7 mH. With 25 kW to each antenna and a radiation resistance of 0.85 ohm, helix current is about 170 amps and top helix voltage is 454 kV. It would be nice if someone could confirm my calculations and add the appropriate text. This is not an everyday helix. Trojancowboy (talk) 23:49, 1 May 2009 (UTC)

Why don't you just e-mail someone at NIST who can confirm your calculations? I'm not an electrical expert. --  Denelson83  04:47, 2 May 2009 (UTC)

How sound the signal?

A sound of the signal in an AM receiver capable of receiving its frequency

Nothing would be audible on an AM receiver, as the carrier is amplitude modulated but at a sub-audible rate (1 cycle per second). On a receiver with CW (Morse) mode you would hear a tone, sounding a little like very low speed Morse, but the tone is not "the sound of the station" as it is not being generated at the station. It's being generated in the receiver, just as in regular Morse Code reception. (In other words, if you set your receiver to produce a 400 Hz tone for Morse, it would... but there's no 400 Hz, or any other audible tone, in the RF from the station.) Instead of the tone clearly stopping and stopping you would hear it decrease markedly in volume and then come back, once per second, for varying durations. The different durations of reduced signal strength are the encodings of the bits, one bit per second. You could also notice the signal strength modulation on the S-meter, assuming the meter wasn't damped enough to hide it. Jeh (talk) 01:38, 30 September 2011 (UTC)

How much Radio clocks

exists using WWVB? --Itu (talk) 17:23, 31 August 2012 (UTC)

In 2011, NIST estimated the number at 50 million. Owen× ☎ 19:11, 31 August 2012 (UTC)

phase modulation

The WWVB article currently says "A 1 bit is encoded by inverting the phase (a 180° phase shift) of the last 0.9 seconds of each UTC second."

My reading of ref 4 "Enhanced WWVB Broadcast Format" is that the ONLY phase shift occurs .1 seconds into each second so the phase (if inverted) stays inverted for 1.0 seconds (and .1 second into the next second).

The article comment of "0.9 seconds of each UTC second" is misleading as it seems to imply that a reverse phase shift occurs at the end of the second... — Preceding unsigned comment added by 76.90.10.170 (talk) 17:50, 14 December 2012 (UTC)

The article comment is correct, because a reverse phase shift does occur at the end of the second. Figures 2–5, beginning on page 3, make that clear. 71.41.210.146 (talk) 12:29, 8 April 2013 (UTC)

Antenna location discrepancy

WWVB antenna coordinates (from NIST, unknown datum))
North	40°40′51.3″N 105°03′00.0″W
South	40°40′28.3″N 105°02′39.5″W

A NIST press release gives antenna locations different from those in the article. The article's work well with Google maps, while NIST's do not. As they do not mention a datum, it is possible they are correct, but in whatever pre-WGS84 datum was used for the initial survey in 1962. I'm not inclined to fix what doesn't appear to be broke in the article, but I thought I'd mention it here for other people's comments.

71.41.210.146 (talk) 05:24, 13 May 2013 (UTC)

Removed text

I noticed that another person removed this text that someone else added. I don't have enough knowledge on WWVB signal to know if this is important or not, so I copied it here. • Sbmeirow • Talk • 03:34, 29 January 2014 (UTC)

Shortcomings of the current signal format

• Unlike MSF and DCF77, WWVB does not have a built in tick around the minute mark to discipline clocks that are in continuous reception mode.
• What MSF does (and almost identical DCF77) to indicate the start of a minute
• If each second is considered as ten 100 ms pieces, the minute marker is transmitted as 1111100000, while all other seconds are transmitted as 1AB0000000.

The first statement is not true. WWVB transmits two consecutive periods of reduced-carrier signal, each 800 ms long and starting on the second, to indicate the top of the minute. The start of the second of these periods is the exact top of the minute. --  Denelson83  03:49, 29 January 2014 (UTC)

I'm the one who removed it and I of course agree with Denelson83 re the first statement. Re removal of the rest, we wouldn't put details of the WWVB format in the MSF or DCF77 articles; nor do their details belong in the WWVB article. Jeh (talk) 04:54, 29 January 2014 (UTC)

Removals were appropriate. Glrx (talk) 00:11, 30 January 2014 (UTC)

Re "one bit per symbol"

I strongly object to this edit. Yes, some modems are "many bits per symbol"; that's the point! "symbol" is not "less informative," it is more correct.

In the AM code one bit is not sent per second. If you consider only the data bits, it's an average of less than one bit per second, since only 53 data bits are sent per minute. But that is an incorrect analysis as you can't interpret the data bits without recognizing the marker symbols. Fact is there is one symbol per second, each symbol having three possible values, not two. That's about 1.6 bits per symbol (1.6 being the log base 2 of 3), so the effective bit rate would be 95 b/s! Better to just say "symbol per second" and explain what a symbol is. Note that we're already using "symbol" in the description of the AM format. Jeh (talk) 09:57, 7 December 2015 (UTC) it.

The first reason I prefer the "bit" language is that it's describing both amplitude and phase modulation, and for phase modulation, "one bit" is exactly correct.

Regarding the amplitude modulation, I agree that from a low-level perspective, there are three possible symbols and thus it's not binary.

However, from a high level perspective, at most one payload bit is sent per second, so it very much is a one bit per second code.

I note that NIST's own documentation describes the AM format as "broadcast continuously at a rate of 1 bit per second" (p. 17).

There are many line codes which use additional low-level symbols for framing, spectrum shaping, forward error correction, or other purposes, but are still described in terms of their payload data rates.

The one that leaps immediately to mind is alternate mark inversion as used on T1 lines. There are three line levels used, yet a T1 line is universally referred to as "1.544 Mbit/s", because the additional state is not used for data transmission.

Another example is USB 1.x. Frames are terminated with a "single-ended zero" which is distinct from the usual 1 and 0 bits. Yet it's called 12 Mbit/s, the specification talks about "bit times", and so on.

Straying further afield, modems routinely use additional states for forward error correction. Most commonly, n bits of payload and 1 bit of FEC are bundled into an n+1-bit constellation. But the modems all talk about the payload' data rate.

Other codes use violations of the usual coding rules for framing purposes. Modified frequency modulation and AES3 (=S/PDIF) are both called rate-1/2 codes, even though there are additional sync symbols which may be sent through the channel, making the rate technically greater than 0.5.

Likewise, 8b/10b encoding actually transmits 8.0444 bits per 10 bit times if you include the additional control codes. But nobody does.

If WWVB used the extra values to transmit more data, in the style of 4B3T, I'd call it a ternary code. But as long as they're framing bits which actually preclude sending a time code bit in those slots, I think the high level "one bit per second" is correct.

The other is detrimental pedantry. It's being technically correct (and even then, only from one specific point of view) at the expense of intelligibly.

The article includes the full details for someone who wants to understand. It's not a secret that there are three possible "bits". But for someone skimming the heading (and the location of the edit is an introduction), "one bit per second" is more informative and more useful.

I can try to rephrase it to make the high-level perspective clearer and remove any implications to the contrary.

(BTW, nice edit getting rid of the "modulation depth" subsection. That definitely cleaned things up!)

71.41.210.146 (talk) 11:06, 7 December 2015 (UTC)

P.S. Another source to look at is the IRIG timecode specification that WWVB is modeled on. And section 3.2.3 of http://irigb.com/pdf/wp-irig-200-04.pdf (p.3-1 of doc, p. 17 of pdf) says "Each pulse in a time code word/sub-word is called a bit." Even though a "bit" can be a 0 bit, a 1 bit, or a "position identifier". 3.2.4 specifically calls the position identifier at the beginning of the frame "a reference bit".

I suppose I could cite that and the NIST spec as reliable sources for the factual assertion that that the code is "one bit per second", but I think that's *also* obnoxious pedantry. I honestly think saying "bit" makes for better exposition. 71.41.210.146 (talk) 11:31, 7 December 2015 (UTC)

"Three possible bits" - you mean three possible symbol values. :) (Awhile ago I edited this, and/or WWV, to get rid of the term "marker bit". If it's a marker, it's not one of the two possible binary digits. To say otherwise contradicts the definition of "bit". Ok, the IRIG doc has its own special definition of "bit", but the reader of these articles is pretty unlikely to know that.)

I don't feel that saying "one symbol per second" is detrimental or obnoxious. On the contrary I think saying "one bit per second" for the AM code is. I know that Wikipedia is supposed to be edited for a general audience, but I'm tired of seeing it watered down on the assumption that the "general audience" is content with approximations and generalities. To put it another way, I hate the "lying to children" concept. (Some of them don't like it when they find out.)

Hmm... How about "approximately one bit per second"? This is more correct than simply "one bit per second", invites the reader to read more if they want the details, but is good enough if they don't. Then the stuff about markers being a possibility doesn't have to be in this intro section at all, it can just appear in the AM subsection. Any mention of "symbols" can be shoved to the AM subsection too.

And likewise BTW, the rest your edits in that session were all good - thanks! Jeh (talk) 11:35, 7 December 2015 (UTC)

To me, it's like replacing a clear word with a vague euphemism. "Boyfriend" means something; "partner" requires extra context to interpret. As I said, from an information-carrying point of view, they are bits; the frame markers are a lower-level detail. Would it be better if I tried to phrase it that "in some seconds, a marker is transmitted in lieu of a bit" without being too awkward?

We're not lying to anyone because the details are right there. Nor is it talking down to anyone. In the field of line coding, special escape codes, comma symbols, or whatever you want to call them are common things, and practitioners call them "bits" without blinking.

Maybe it's a software thing. Hardware engineers are quite familiar with three-state logic. For overkill, see IEEE 1164: nine possible values for one bit!

71.41.210.146 (talk) 11:58, 7 December 2015 (UTC)