I KNOW it's not diy but ...

Yes.

Depends what you mean by "not very". On a broadband connection to a Stratum

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.

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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Only a minute? I thought it was more like 30 years..... ;-)

.andy

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Even if it's "bounced" off a satellite, the geostationary are about 22,500 miles high, giving a round trip if 50,000 miles.

at propagation speed, around 186,000 miles per second, that only puts in about a quarter of a second of the delay, so much more of it is due to processing

mike r

Assuming transmitter and receiver are both vertically below the satellite, or nearly so....

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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At Northern Europe latitudes (assuming uplink and reception) about

The additional delays are as a result of the MPEG1 layer 2 compression and the various forms of error correction and other processing employed in the transmission path.

.andy

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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.

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

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

.andy

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"Bob Eager" wrote in news: snipped-for-privacy@rikki.tavi.co.uk:

Never thought of that, you'd have to be at the right place on the equator.

However, given the diameter of the earth at roughly 4000 miles, and allowing tangential sight (to give me a right angle triangle, it's 50 years since school) it couldn't be as much a 27000, which wouldn't add much,

My point, which my brain wishes it hadn't tried to show off with, was that all the processing causes most of the lag - now I need a bevvy and a lie down

mike r

Oh, I accept that...just making an observation!

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.....)

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

-snip-

That's what I thought.

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:

So the bottom line is that the GPS receiver gives the time with atomic clock accuracy.

Err, I thought the earth was about 8000 miles diameter?

My mathematics is a bit on the rusty side now, but Australia is about

As circumference = PI x diameter then circumference / PI = diameter, which is 24000 / 3.14, approx 8000.

Professor PoP

Replying to the email address given by my news reader will result in your own email address being instantly added to my anti-spam database! If you really want to contact me try changing the prefix in the given email address to my newsgroup posting name.....

I was wondering what I'd started!

Mary

I was wondering what I'd started!

Mary

Well it was a DIY project...... :-) .andy

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