From vicente@cay.oan.es Tue Oct 26 15:04:59 MET 1999 Received: from siva.cay.oan.es (siva.cay.oan.es [193.146.252.16]) by picasso.geod.uni-bonn.de with ESMTP (8.8.6 (PHNE_14041)/8.8.8) id PAA18030; Tue, 26 Oct 1999 15:04:57 +0200 (METDST) Received: from polifemo (vicente@polifemo [193.146.252.30]) by siva.cay.oan.es (8.9.3/8.9.1) with SMTP id PAA09508; Tue, 26 Oct 1999 15:03:35 +0200 (METDST) From: Pablo de Vicente Reply-To: vicente@cay.oan.es Organization: Observatorio Astronomico Nacional To: Brian Corey , petrov@picasso.geod.uni-bonn.de (Leonid Petrov) Subject: Re: YEBES and question marks Date: Tue, 26 Oct 1999 14:29:54 +0200 X-Mailer: KMail [version 1.0.28] Content-Type: text/plain 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, vlbi@oan.es References: <199910251920.PAA21049@dopey.haystack.edu> In-Reply-To: <199910251920.PAA21049@dopey.haystack.edu> MIME-Version: 1.0 Message-Id: <99102615033401.17720@polifemo> Content-Transfer-Encoding: 8bit Status: R Dear Brian and Leonid, Concerning all the messages received tonight: 1) We can make the test Brian suggests. We do have the cable cal ground unit. and we are already measuring now. I will send the results later today or tomorrow and explain you the setup we have used. >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. 2) I do not know the characteristics of the 5MHz distributor (A. Barcia knows those, when he is available he may through some light on them). However the nominal temperature stability of the delay is 10 ps/deg C 3) In the Europe51 observation we fed 5 MHz from the maser and through the VLBA 5MHz distributor to: the MKIV formatter, the VLBA and the LO. The 5 MHz from the auxiliary distributor fed the phase cal and the 1pps box. This box gives 1pps to the MKIV formatter and the VLBA rack. 4) The VLBA equipment is close to the auxiliary 5MHz distributor and therefore it is also affected by the same temperature variations. However I would expect less sensitivity to oscillations of temperature since it is enclosed on closed rack together with other elements that dissipate heat. It would show more dependence on temperature if the temperature changes were larger and with a longer cycle. 5) We have looked at the 5 MHz signals coming from both the maser and the auxiliary 5 MHz distributor. No apparent degradation is seen. For exmaple there are no bands at 50Hz.. 6) We can avoid using the auxiliary 5 MHz distributor for next observation. We could use all 5MHz VLBA outputs, we have enough outputs. If the temperature is the problem I am almost sure that we will not need the air conditioning next time, since it will be colder. 7) We could make a test on Tuesday, and with some problems on Friday, but we need to clarify what we have to measure at the station. Measuring everything and logging the data is not trivial. I can log some variables but not others. I can log temperature but I do not know if I can log the voltage of the power supplies in a computer for next friday. So I would conclude that we can perform the test if we have a clear proposal. For example observe without air conditioning and/or avoid the 5 MHz auxiliary distributor and register the temperature at the racks. I remind you we have an observation for begining of november (CORE). Regards, Pablo. ________________________________________________________ Pablo de Vicente (vicente@oan.es), http://www.oan.es, OAN Spain