From bec@haystack.mit.edu Mon Oct 25 19:22:33 MET 1999
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From: Brian Corey <bec@haystack.mit.edu>
Message-Id: <199910251719.NAA19613@dopey.haystack.edu>
Subject: RE: RE: Yebes talk. Proposals.
To: petrov@picasso.geod.uni-bonn.de (Leonid Petrov)
Date: Mon, 25 Oct 1999 13:19:14 EDT
Cc: 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,
        tme@cygx3.usno.navy.mil, vicente@cay.oan.es, vlbi@oan.es,
        weh@ivscc.gsfc.nasa.gov
In-Reply-To: <199910251641.SAA12046@picasso.geod.uni-bonn.de>; from "Leonid Petrov" at Oct 25, 99 6:41 pm
X-Mailer: Elm [revision: 109.18]
Status: RO

Dear Leonid,

> We will try manual
> phase cal, but it helped marginally in Europe50 (wrms reduced from 140 to 130ps
> for some baselines) -- and we don't expect it would solve the problem of
> Europe51 neither.

You may not, but I do!  If the problem is with the 5 MHz distributor,
then with the receiver LO's being driven directly from the maser in
Europe-51, manual phases should do much better than normal phase cal.

> But if to look attentively we find that peak-to-peak
> 3C fluctuation occurred from 13:00 till 14:40 while the largest variations
> in phase cal rate (2.D-6) occurred in the interval 13:00 16:00.

Maybe so, but that's not what the plot on the web shows.  The phase
cal rate plot there has large scatter from ~13:00 to ~14:40, then two
points with low rate before 15:00, and no points at all between 15:00
and 16:00.  The plot of Medicina/Yebes delay rate does have points in
the 15:00-16:00 range, and they all have relatively small scatter.  Do
you have additional phase cal rate points not shown in the web plot?

>  ...  What would you do were you in YEBES now?

The idea of a test with nearly continuous observations of a single
source is a good one.  That should pinpoint the problem, unless of
course the problem is associated with the receiver or antenna and only
appears when the antenna is moved from source to source.  A useful, but
less complete, test that could be done without any VLBI observations is
to measure the phase difference between the receiver LO 5 MHz and phase
cal 5 MHz for a few hours.  But that test requires an instrument capable
of ~10 ps precision and stability, such as a vector voltmeter or the
picosecond phase comparator circuit in a Mark III cable cal ground unit,
and I don't know whether Yebes has either.

 --Brian