Message 18/446 Denise Gabuzda                    Oct 10, 2000 10:01:23 am +0100

Date: Tue, 10 Oct 2000 10:01:23 +0100 (WET DST)
X-Sender: gabuzda@juw11
Reply-To: gabuzda@jive.nfra.nl
To: evntech@jb.man.ac.uk
Subject: EVNtech: Frequency flexibility in the EVN
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Report on Current Status of Frequency Flexibility in the EVN

On February 27, 2000, there was a several-hour dual-polarization
experiment (GAH03) designed to test two potential frequency-switching
observing modes:

1) rapid (~70 second) switching between 6cm ad 3.6cm at Eb and Wb

2) slower (~4 minute) switching between 6cm and 3.6cm at Mc

In addition to these three antennas, Jb-2 and Tr observed only
at 6cm, and Nt and On-60 observed only at 3.6cm.

The parallel-hand (RR and LL) data were correlated at JIVE and
analyzed by D. Gabuzda. The only evident problem was that the times
allowed for switching were sometimes slightly too short at Wb (~80
seconds would be better) and Mc (4.5 minutes would be better).
It was verified that the R-L phase differences at Eb, Wb, and Mc at
a given frequency were preserved when the frequency was switched and
then switched back. This is the primary requirement for being able to
perform polarization observations in such a frequency-switching
observing regime.

Based on the success of GAH03, the dual-frequency, dual-polarization
global experiment GG041 was observed on June 5 during the 6cm session,
with the VLBA, Eb, and Wb switching between 6cm and 3.6cm for alternate
scans; Jb-2, Nt, and Tr observing only at 6cm; and Mc observing only at
3.6cm. In this way, simultaneous observations were made with two global
arrays at the two frequencies: 15 antennas at 6cm (the VLBA, Eb, Wb,
Jb-2, Nt, and Tr), and 13 antennas at 3.6cm (the VLBA, Eb, Wb, and Mc).
These data are currently being correlated in Socorro.