From bec@haystack.mit.edu Tue Oct 26 23:14:41 MET 1999
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From: Brian Corey <bec@haystack.mit.edu>
Message-Id: <199910262111.RAA01990@dopey.haystack.edu>
Subject: Re: Little test at Yebes with distributor
To: vicente@cay.oan.es
Date: Tue, 26 Oct 1999 17:11:18 EDT
Cc: petrov@picasso.geod.uni-bonn.de, aen@haystack.mit.edu,
        baa@casa.usno.navy.mil, dgg@aquila.gsfc.nasa.gov,
        hase@wettzell.ifag.de, mueskens@mpifr-bonn.mpg.de,
        nothnage@picasso.geod.uni-bonn.de, sorgente@hp138.mpifr-bonn.mpg.de,
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In-Reply-To: <99102621511800.18208@polifemo>; from "Pablo de Vicente" at Oct 26, 99 9:46 pm
X-Mailer: Elm [revision: 109.18]
Status: R

Dear Pablo,

> Does this sensitivity explain the values seen at the correlator?

Yes, I think it does!  Very nice work -- thanks for doing the test so
quickly.  (Like Leonid, I was surprised to learn you had a ground unit,
as I too had noticed that the Yebes logs contain no cable cal data.)

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.

If you have nothing better to do and would like to play with the
setup a bit more, you might try comparing two outputs (say, the ones
used in Europe50 to drive the receiver LO and phase cal) from the
auxiliary distributor.  But the test you've done was the critical one.

 --Brian

P.S. to Leonid: What do the fringe phases look like during Europe50
  scan 228-135300 (the scan for which you've plotted the phase cal)?