From bec@haystack.mit.edu Mon Oct 25 20:36:41 MET 1999 Received: from dopey.haystack.edu (dopey.haystack.edu [192.52.61.54]) by picasso.geod.uni-bonn.de with ESMTP (8.8.6 (PHNE_14041)/8.8.8) id UAA12751; Mon, 25 Oct 1999 20:36:40 +0200 (METDST) Received: (from bec@localhost) by dopey.haystack.edu (8.8.6 (sendmail_886_v2)/8.8.6) id OAA20543; Mon, 25 Oct 1999 14:33:55 -0400 (EDT) From: Brian Corey Message-Id: <199910251833.OAA20543@dopey.haystack.edu> Subject: RE: RE: Yebes talk. Proposals. To: petrov@picasso.geod.uni-bonn.de (Leonid Petrov) Date: Mon, 25 Oct 1999 14:33:55 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: <199910251756.TAA12563@picasso.geod.uni-bonn.de>; from "Leonid Petrov" at Oct 25, 99 7:56 pm X-Mailer: Elm [revision: 109.18] Status: R Dear Leonid, > But it [manual phase cal] didn't cure Europe50. Why? Because the receiver LO, phase cal, and VLBA rack were all running off the same, drifting 5 MHz, according to the hot/cold 5 MHz distributor theory. In other words, the situation was nearly the same as if the maser were wandering, and in that case there's nothing you can do to fix up that problem at the fringing or analysis stage. But Europe51 is very different, with the LO and rack being driven by a good (I hope!) 5 MHz. That could make all the difference in the world. > Did you try manual phase cal in CORE-B504? did you notice improvement? I haven't tried, and I wasn't intending to, at least for now. From plots of phase cal phases and rates, I don't expect there to be much difference between normal and manual fringing. In other words, I think CB504 will look like Europe49 and 50. > As far as I understand if > the phase fluctuations occur in the 5MHz distribution box then these > fluctuations should drive phase cal and formatter also, right? Therefore time > epochs are undergone by the fluctuations too and it is probably the reason > why we have so awful scattering in group delay residuals. In Europe51 my understanding is that the 5 MHz distributor drove phase cal only. The receiver LO and VLBA rack, including formatter, got 5 MHz straight from the maser. Actually I don't believe the formatter can be blamed for any of this mess -- the fluctuations in its sample epochs would have to be of order 1 microsec to explain the delay rate variations, for instance, and I doubt the singleband delays in Europe50 show fluctuations that large. More critical is the 5 MHz driving the BBC LO's. If that 5 MHz and the receiver LO 5 MHz are OK, then manual phases should work. --Brian