I KNOW it's not diy but ...

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On Sat, 27 Dec 2003 15:07:58 -0000, "Mary Fisher"

Realistically, if you want to have accurate time for all but high precision scientific purposes there are a few ways:
- Clock with receiver synchronised to the MSF station at Rugby. These clocks are now pretty cheap.
- GPS receiver
- Using a computer connected to the Internet and synchronised using NTP (Network Time Protocol.) There are numerous bits of software around for doing this,
e.g. Tardis http://www.kaska.demon.co.uk /
Care has to be taken with setup of packages like this if you have a dial up connection, because they will initiate dialling frequently if you let them. A typical way is that they only become active when a dial connection is already there because you are transferring email or accessing web sites. If you have an "always on" "broadband" connection it doesn't matter.
.andy
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Many of the cheap clocks are synchronised to a German source.

Does this have to be accurate? Isn't it the time _difference_ in receiving signals from different satellites that is important.

Not very accurate but okay for Internet connections. You request a time from a time server that may be locked accurately to one of the time references but the journey time back to you is variable. It's much the same as pinging a machine over a network. It may take 200ms or many seconds to respond depending on network (ISP) loading..

--
Alan
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On 27 Dec 2003, Alan wrote

It's odd, though: I got a cheap one for Christmas, and the manual *said* it synchronised to Germany -- but it's synched itself properly to GMT, and I can only guess that the unit itself is set for Rugby, but that the manual that came with it wasn't changed.
(Unless the German source knows that I'm calling in from the UK and adjusts accordingly -- but I doubt that. If it's using the German source, though, it's still synchronising fine for me.)
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On Sat, 27 Dec 2003 17:55:50 GMT, Harvey Van Sickle

Probably that, although I suppose it could be set up to subtract an hour when sold in the UK market and still use DCF77.
Even so, the methods of coding the time signal used by MSF Rugby and DCF77 Mainflingen are fairly similar, so the basic electronics will probably be switchable to either according to market. The radio part is probably tuned differently - 77.5kHz vs. MSF's 60kHz

Nope. It's reception only.

.andy
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On 27 Dec 2003, Andy Hall wrote

There's certainly something going on with the factory settings. It has a C/F display switch, but so far I've not found a way to show a 24-hour clock, just am/pm (even though the manual illustrates with a time of 16:20)....must keep looking....
-snip-


That's what I thought.
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wrote

Play around with the clock buttons a bit - I did earlier today (accidentally!) and found one display of -1. When I set that to zero the clock showed CET. I guess they are ready set for the UK market at -1 before despatch.
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Woody

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On 27 Dec 2003, Woody wrote

-snip-

I'll give that a try, but I fiddled around a bit and didn't see an obvious setting. (There's a +12 to -12 setting for an alternative time zone, but that doesn't seem to apply to the main display.)
What makes me think that it's a "wrong manual" thing is that I also can't seem to get a 2400 hour display -- just an am/pm -- even though the manual uses an illustrative time of 16:20. I'll play around a bit more...
(So far, though, I'm quite tickled with it: it displays indoor and outdoor temperatures, with the outdoor temperature through a radio sender. I'm a happy little gadget man.....)
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Frankfurt -I presume that it is internally switchable to put the display an hour backwards.
The guts are probably made by Junghans who were one of the first companies to market reasonably priced radio sync'd clocks
I have a clock which is sync'd to Frankfurt and gives european time, no problem getting the signal, but it does take a bit of thought when setting the alarm when pissed
--
geoff

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[12 lines snipped]

Yes.
[6 lines snipped]

Depends what you mean by "not very". On a broadband connection to a Stratum 1 time server you're likely to get accuracy in the 10's and possibly units of milliseconds.

NTP has "strata" of time sources depnding on how far from a hardware time source you are.

Not very. And NTP takes account by measuring the roundtrip time.
--
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On Sat, 27 Dec 2003 17:45:50 +0000, Alan

DCF77. The signals can be a bit weak as you move further north and west in the UK.

For positioning, yes, but I understand that there is also a time stamp in the transmissions. I believe that the receiver is able to deduce a reasonably accurate time from the signals.

It can become reasonably respectable. You can configure your software to work with multiple time servers. With the better software, each peering is done with a digital phase locked loop and the short term jitter between you and the time server can be averaged out. This is then accounted for as an offset and offsets between peerings compared to produce a fairly accurate time after a few hours of operation.
No it isn't the same as having your own caesium time standard equipment, but you can generally get to few tens of mS accuracy, which is generally OK for purposes apart from precision science.

.andy
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Well, not exactly.
The GPS receiver has to find the distance from each of four satellites to get a fix on your position. It does this by measuring the time taken for the signal to travel from the satellite to the receiver. In order to do this the receiver *must* know the exact time with nanosecond accuracy.
The satellites have atomic clocks and send a message to the GPS receiver which includes the exact time it was sent. By a very ingeneous method the receiver examines the data from at least four satellites and calculates its position and the exact time.
If you want more details: http://www.gpsinformation.org/dale/theory.htm
So the bottom line is that the GPS receiver gives the time with atomic clock accuracy.
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Alan wrote:

I thought there was compensation built in for this, i.e. set clock to time halfway between time request sent and time ack received?

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On Sun, 28 Dec 2003 23:51:15 +0000, The Natural Philosopher wrote:

It's *much* more complicated than that, take a look at RFC1305.
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On Mon, 29 Dec 2003 01:13:30 +0000 (GMT), "Dave Liquorice"

There is a detailed FAQ at
http://www.ntp.org/index.html http://www.ntp.org/ntpfaq/NTP-a-faq.htm
as well as the references from the leading light on the subject, Prof. David Mills of the University of Delaware.
http://www.eecis.udel.edu/~mills/ntp/html/index.html
.andy
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wrote:

.....or if you want accurate pips, use 198KHz Radio 4LW.
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Woody

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wrote:

I used to have a clock that I made that used this Droitwich R4 transmitter when it was on 200kHz as a frequency reference. It worked extremely well because the carrier was a national standard with a caesium (or maybe it was rubidium) reference. Then they shifted to 198kHz. The clock was discrete logic based and so not particularly easy to modify to work at the new frequency,
.andy
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I was wondering what I'd started!
Mary

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I was wondering what I'd started!
Mary

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On Sun, 28 Dec 2003 12:33:11 -0000, "Mary Fisher"

Well it was a DIY project...... :-) .andy
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But after all that - does it sound like bubbling mud, as the FM hi-fi purists insist that it does ?.
--
Andrew

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