From vicente@cay.oan.es Wed Oct 27 08:51:55 MET 1999
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From: Pablo de Vicente <vicente@cay.oan.es>
Reply-To: vicente@cay.oan.es
Organization: Observatorio Astronomico Nacional
To: Brian Corey <bec@haystack.mit.edu>, vicente@cay.oan.es
Subject: Re: Little test at Yebes with distributor
Date: Wed, 27 Oct 1999 08:44:42 +0200
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Dear Brian

>I do have a quibble with a couple of your numbers, however.  As you say,
>a change of 200 us on the counter corresponds to a real change in delay
>of 1 ns (divide by 2e5, not 2.5e5).  But with a corresponding temperature
>change of 12.4 K, that makes the sensitivity 80 ps/C, not 8 ps/C.  If
>I did the math wrong and the sensitivity is 8 ps/C, then the auxiliary
>distributor is not to blame.  But if it really is 80 ps/C, then I think
>it explains most (although certainly not all -- I'm working on the
>epicycles, Leonid) of the correlator anomalies, including the high delay
>rates and discrepant multiband delays.  At 80 ps/C, the delay rate will
>be 1 ps/s for a temperature change of 1 C in 80 seconds, which is
>consistent with the temperature rates right after the air conditioner
>turns on or off.  And at 1 ps/s over a few minutes, delay errors of 
>several hundred ps can accumulate.
>

 Of course Brian, I am ashamed to have made such a silly fault. the 
scale factor is 2e5 (5MHz/25Hz)  and I dialed one 0 excess in my calculator
and that made 8ps/C. The correct value is of course 80ps/C, which means the 
distributor does not comply with its specifications.

Pablo.
________________________________________________________
Pablo de Vicente  (vicente@oan.es),  http://www.oan.es,  OAN Spain