[time-nuts] Earth: An Oscillator and Frequency Standard

Bill Hawkins bill at iaxs.net
Sun Nov 5 15:55:06 EST 2006


Brooke,

I proposed a platform driven by a synchronous motor referred
to a cesium standard. On this platform is an arrangement to
project an attenuated image of the sun onto a mirror that is
attached to a galvanometer. Light-beam galvos used this kind
of arrangement. The mirror projects the solar image onto a split
detector, such that the output of two photocells cancels when the
image is centered. The detector drives a servo to keep the image
centered using the mirror galvanometer. You'll also need a vertical
servo to track the sun through the day.

The signal to the galvo is proportional to the deviation of the
suns image. Remove the equation of time (a few percent) and you
have the deviation from solar time. Do a lot of these and you
can apply statistical methods to find the Earth's wobbles.

Sounds like great fun, but beyond my capabilities. A rotating
platform with no error in angles, for instance. A clear field
of view, for another.

Regards,
Bill Hawkins


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Brooke Clarke
Sent: Sunday, November 05, 2006 1:29 PM
To: Tom Van Baak; Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Earth: An Oscillator and Frequency Standard

Hi Tom:

Thanks for the lab test report on the earth frequency standard.  Since
there are a number of frequency/time standards that have much better
performance I'd like to find a way to directly measure the performance
of the earth standard.  I've thought about a telescope looking at stars
or maybe a photo detector to look at the light from the closest star to
the earth frequency standard.  Do  you have any ideas on how to make
these measurements?

Have Fun,

Brooke Clarke

w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com



Tom Van Baak wrote:

>>>Anyway, how do you compute the Allan Deviation of a sun dial?
>>>      
>>>
>>Oh, God, now someone's going to do it...
>>
>>John
>>    
>>
>
>Well, yes, thanks for asking! I did it a year ago.
>
>The lab report on earth, including Allan deviation is at:
>
>http://www.leapsecond.com/museum/earth/
>
>/tvb
>
>  
>
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