[ntp:questions] Re: Clock accuracy & auto setting : digital television does a crap job of providing time services...

Jonathan Buzzard jonathan at uk.me.buzzard
Thu May 4 17:57:25 UTC 2006

On Mon, 01 May 2006 05:42:07 -0700, Max Power wrote:

>>> LF time services are OK, and are necessary over large transnational
>>> regions -- like Sub Saharan Africa, Australasia and South America ... but
>>> any new LF service needs to be more technologically advanced than WWVB, 
>>> MSF
>>> or DCF77 and its Swiss twin. In these regions 10 LF frequencies need to 
>>> be
>>> allocated, but the signal to be transmitted needs to be more modern than
>>> WWVB or DCF77 -- maybe using some form of low complexity PSK or low
>>> complexity QAM and 240 hz to 480 hz of bandwidth. The signal must be
>>> futureproofed -- as above.
>> ================================
>> OK? What other technology can provide such accurate signals at such a low
>> cost? The simple amplitude modulated nature of the LW signals makes for
>> such low cost implementations. A PSK or QAM modulation is going to put the
>> cost of hardware to decode the signal up to much to be useful.
> For consumer purposes (save cellular telephony) GNSS technology is too 
> costly.
> NTP is OK for computers, but has a learning curve.

But the consumer does not need any better accuracy than LW, and if they do
then GPS is dirt cheap these days. The point is that the SW signals have
very few users. Consider the number of say CHU users to MSF or DCF77.

> I am unaware of WWVB doing this.
> If WWVB does this, its signalling must be very quaint.
> Typical 1983 signalling medthods (bitfields transmitted) would probably not 
> pass modern muster.

The point was that the LW signals can provide better accuracy than the
normal AM pulses used.

> BCD is the universal flaw of LW time stations.
> NTP could fix the problem, but NTP is not perfect for this [without 
> tweaking].
> BCD could be said to use odd signalling in not using {seconds} within a day, 
> albeit seconds are not suitable for LW signalling rates.

All LW signals implicitly signal the second...

> I assume both NTP 
> and BCD signalling medthods are aimiable to 'bit averaging' for LW time 
> service's slow signal rate and error correction condtions.

Not really a 64bit signal cannot be transmitted within one minute for
starters. Secondly a NTP style time signal would be overly complicated for
the simple wall clocks to cheaply decode. I just described a simple binary
coded signal with the year/day/time as separate fields with loads of bits
left over for error correction, which could be taken or left depending on
the power of the decoding device. It is good for a 1000 years. What more
do you need?

> DRM on MW and SW only sends the Julian date and time.
> There is some BCD coding similar to WWVB and DCF77 -- for time and date.
> However, there is no [univeral] NTP or UNIX time packet in DRM.

Probably because it is not suitable for simple decoding.

> SW signals do cover areas LW cannot reach (like Antartica) -- and with 
> adiquate frequency diversity provide a higher time resolution vs LW.

If you need something better than LW then GPS is a better solution than SW
and probably just as cheap, and has global reach. I imagine that a good
view of the sky is not hard in Antartica.

> DRM can 
> cope with ionspheric delay via indicating TX (and at the reciver RX) coords.
> LW time stations are trapped in late 1960s style signalling.

But are simple enough to provide a millisecond accuracy at the receiver
for 20USD.

I personally cannot think of anything dafter than an additional SW
transmitter signal for CHU. Another LW station somewhere in north America
would be infinitely more useful.


Jonathan A. Buzzard                 Email: jonathan (at) buzzard.me.uk
Northumberland, United Kingdom.       Tel: +44 1661-832195

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