NavList:

Bill,

GPS satellites have their own cesium clocks contained in the satellite. Shortwave time ticks from land stations use land based cesium clocks. Not sure on the UT/UT1 but anything within a second is more than good enough for celestial navigation.

The main problem with atomic clocks and watches is that the quality and strength of the synch signal is not displayed. I use a Seiko atomic clock for convenience but always compare the minutes with my conventional digital. I have been spoofed on more than one occasion with the atomic clock minute display being one minute slow in each case.

During Santa Ana's here in Southern California 90* dry winds blow over 55* ocean waters. Under these conditions I have observed dip errors as high as 4 moa from a height of eye of 16 ft. Dip errors of 10 moa seems excessive to me but plausible.

Greg Rudzinski

[NavList] Re: Extremely poor conditions??
From: Bill B
Date: 22 Mar 2012 19:38
On 3/21/2012 5:36 PM, Alexandre E Eremenko wrote:
>
> Greg,
>
>> I have had two different digital atomic clocks jump a complete
>> minute on me out of the blue for no reason.
>
> Are you serious... But Bill was comparing. (All electronic toys,
> except a Casio calculator are his).
>
>> I still think you are a minute out in your time rather
>> than having a horizon 3.5 miles away elevated 11 moa.
>
As I write to Alex: "Spring break on a beach in Michigan in winter. 80+
F and people in swimsuits and swimming. If you can believe that, 10'
ought to be a easy!

I have two "clam shell" clocks (folds up like a travel clock). The first
did a horrible job of picking up the time signal from Colorado, so i set
it to UTC Zulu and to keep it next to my main computer to keep me honest.

The second has been excellent. It automatically polls Colorado about
midnight. I keep it facing CO on a three-seasons porch so it
re-calibrates every day if needed. approached the list with the
following question(s) about six years ago, but never really understood
the "why" despite mentions of satellites corrections for gravity wells etc.

The "atomic clock" (actually a clock that polls the atomic clock) is
usually about a second different than my Garmin marine GPS, even when
DUT1 is supposedly 0. Why?

(I have just checked the GPS against the clock at UTC 23:34:xx, and they
are so close I cannot see a difference. I will recheck right after the
clock re-calibrate tonight.)

A few side questions:

Is Colorado transmitting UTC with leap second adjustments?

Do satellites carry their own clocks, or are they synced up with CO and
then making on board adjustments for speed/relativity and gravity well?

Does GPS show UTC or UTC1 time?

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