[time-nuts] Determination of the placement of the first pps

Bob Camp lists at rtty.us
Mon Jan 23 12:07:42 EST 2012


Hi

I think the key point is that they are still using a gizmo made in the
1800's and it works "good enough". There are certainly better ways you could
set it up today, but they use what they have.

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Attila Kinali
Sent: Monday, January 23, 2012 11:57 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Determination of the placement of the first pps

On Mon, 23 Jan 2012 08:43:01 -0800
Chris Albertson <albertson.chris at gmail.com> wrote:


> 
> It's a transit telescope (one that looks up at the local meridian) but
> they don't use the sun.  It looks at every start that passes in front
> of it, thousands of them every night.  Then they reduce the data by
> knowing the exact location of every star and the time is pasted
> directly overhead.  This way they get thousands of measurements every
> day.  If you use the Sun you get only one per day.

Not to mention the solar noon varies by +/- 15min over the year
(don't ask me how this is called...old knowledge from my high school days)
 
> A transit solar scope would be a fun Time Nut project.  I think a
> primitive one would be a photo cell and a length of wire.  Measure the
> time when the shadow of the wire sweeps across the cell.  The trouble
> is that with only one measurements per day it would time years to
> build up uSec level data.    Even if you placed the cell behind a pin
> hold mask and used a fine piano wire, shades and baffles and so on.

Why not use a real telescope with a CCD and get more reliable data?
A friend of mine is into hobby astronomy and uses special type CCDs
for it (ie not even the hobbist look directly into the telescope anymore).
I guess it shouldn't be too hard to rig up some gear, a PC that collects
the pictures at precise instances and calculates the ephemeris time to
UTC/GPS difference. The only issue is that you'd need to put that telescope
somewhere with little light polution, otherwise you'll only get the
brightest
stars.


				Attila Kinali

-- 
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
		-- Tirin, The Dispossessed, U. Le Guin

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