Moodyjim
Well-Known Member
navigation; been looking on the net but there is such variety of clocks and watches it's difficult to decide. What do you use and recommend?
Timers for astro
- Thread starter Moodyjim
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snowleopard
Well-Known Member
Basically any quartz watch or clock will do as long as it has a second hand/display. Back in the 70s I used one of the early kitchen clocks, mounted where I could see it from my bracing position. I see no reason to have a mechanical chronometer except for nostaligic reasons.
I bought a combined analog/digital clock to act as ship's colck (analog) and chronometer (digital). It was hard to find a digital clock with a seconds display. Frustratingly, while the analog keeps good time the digital is rubbish!
I always have a mechanical sailing stop watch on the chart table for timing light characteristics so that also serves to take on deck for timing sights.
I check my 'chronometer' by comparing it to the gps display each day. Once I know the rate of gain/loss I can continue if the gps dies.
I am told the gps time signal is out by about 1 sec. Good enough for my level of astro skills.
I bought a combined analog/digital clock to act as ship's colck (analog) and chronometer (digital). It was hard to find a digital clock with a seconds display. Frustratingly, while the analog keeps good time the digital is rubbish!
I always have a mechanical sailing stop watch on the chart table for timing light characteristics so that also serves to take on deck for timing sights.
I check my 'chronometer' by comparing it to the gps display each day. Once I know the rate of gain/loss I can continue if the gps dies.
I am told the gps time signal is out by about 1 sec. Good enough for my level of astro skills.
30boat
N/A
I have a large digital chronometer that has a very clear display.I think it's perfect.
T
timbartlett
Guest
I go with snowleopard: any quartz clock or watch that can indicate seconds will be fine. If in doubt, try it out for a month or so first, and see how much it "drifts" compared with the BBC pips.
But beware of using GPS to set the clock. GPS is fine to monitor changes, but GPS system time is about fifteen or sixteen seconds ahead of UTC. Your GPS receiver may or may not apply the correction.
And don't use web clocks or DAB radios, either: they both tend to be a few seconds behind the definitive time signal
Fair winds
But beware of using GPS to set the clock. GPS is fine to monitor changes, but GPS system time is about fifteen or sixteen seconds ahead of UTC. Your GPS receiver may or may not apply the correction.
And don't use web clocks or DAB radios, either: they both tend to be a few seconds behind the definitive time signal
Fair winds
snowleopard
Well-Known Member
Just confirmed that with a google. Interesting that Stokey Woodall told me the difference was only 1 second (in 2001).
So - use GPS to check the accuracy of your clock but set it using the pips or WWV.
Neil
Well-Known Member
I bought a Precision radio controlled watch - not too expensive, and it's dead on when in range of either the German or UK (or even the Colorado, US or Tokyo ones) time signal. I haven't used it in anger yet, and I don't know how accurate it is in the absence of the time signal. Not that I have any immediate plans to move out of reception range..........
mcframe
Well-Known Member
Only if you're on LW and within 400 miles of R4....
AIUI, the difference is between UTC[0] and GPS *reference* time, and that the offset is broadcast as part of the almanac/ephemeris data.
http://www.kowoma.de/en/gps/data_composition.htm
I've never seen a (modern) GPS receiver that didn't display ~1 sec accurate UTC.
[0] For the differences between UTC and UT{0|1|2}, STFW; note that UTC is never "live" - it's always voted on monthly, in arrears...
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snowleopard
Well-Known Member
WWV Colorado broadcasts on 2.5, 5, 10, 15 & 20 MHz. You should be able to get it pretty well anywhere.
BrendanS
Well-Known Member
you are always going to get delays on any radio broadcast. GPS has built in ephemeris data to calculate the local time from the satellites, so it's only the delay from receipt of data to processing and display that you need to worry about. Even digital radio has a processing time from receipt of signal to output.
I'd use gps over most forms of accurate times displayed unless the chronometer has been set to an accurate non radio signal very recently, and the chronometer keeps good time without external input.
I'd use gps over most forms of accurate times displayed unless the chronometer has been set to an accurate non radio signal very recently, and the chronometer keeps good time without external input.
grumpy_o_g
Well-Known Member
Except that you might be using Astro because GPS is unavailable of course....
mcframe
Well-Known Member
Fair point:
http://www.ucolick.org/~sla/leapsecs/timescales.html
or
http://www.youtube.com/watch?v=ib8nH4kHjxk
Your choice, I'm off to bed ;-)
BrendanS
Well-Known Member
Yes, that was assumed. I was commenting on setting chronometers from a time signal
T
timbartlett
Guest
Your GPS receiver may or may not apply the correction.
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BrendanS
Well-Known Member
Do you have a list of gps units available to the general public that don't? I've never seen any that do not apply the correction, though some basic receivers used commercially that might apply their own corrections downstream are conceivable.
Neil_Y
Well-Known Member
Casio £15.00 with soft backlight/glow and another as spare.
Still better than H4, which is good enough for me.
Still better than H4, which is good enough for me.
snowleopard
Well-Known Member
The point is that you use the gps time signal to check the accuracy of your chronometer and log your lat/long. Then when the gps goes on the blink you have an accurate starting point to continue with the old-fashioned astro.
st599
Well-Known Member
The problem with GPS time is not the propagation delay, it is the lack of leap seconds being added since launch. I'm not sure this is corrected for.
geoid96
Well-Known Member
I'm fairly sure the default time dislayed by all GPS receivers manufactured in the last 20 years will be UTC. The GPS / UTC offset is included in the message broadcast by each satellite and applied automatically by the receiver. Either way, as the offset is currently 15 seconds, it is easy to check.
Additionally the NMEA 0183 standard specifies that GGA, GSA and RMC messages used to send GPS data to other equipment, contain UTC time.
T
timbartlett
Guest
I'm afraid I don't although I know there certainly were some that didn't. I can't remember which one(s) they were, and I accept that they are almost certainly out of production by now, but there could well be some still kicking around.
FWIW, the reason I noticed the problem was that I had just been loaned a crop of the (then) current production hand-helds to test for a magazine, and as it was my turn to be race officer for my local club at the time, I thought I'd be clever by using one of them as the race timer. Then some smart alec protested the "race committee (me!) for starting the race at the wrong time!
So I checked all of them, and found that some of theses super-accurate time pieces didn't agree with the "Greenwich" time signal. And that's what made me look into the difference between GPS and UTC time. But all this happened way before the year 2k "crisis" that never happened.
That's why I said "may or may not" in my original post: I wasn't intending to frighten anyone, just suggesting that it was worth a few seconds to check.
Moodyjim
Well-Known Member
Was this a drift thread?