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Subject: e-VLBI, 26 May
From: Steve Parsley <[log in to unmask]>
Reply-To:European VLBI Network discussion.
Date:Fri, 27 May 2005 14:31:49 +0200
Content-Type:text/plain
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text/plain (87 lines)


Hello EVN-NREN group members,

The aim of yesterday's run was to test sustained "normal" operation
(phase 
referencing) and to track down any correlator problems caused by
running 
such a "normal" schedule in eVLBI mode. 

Participating telescopes were: Arecibo, Cambridge, Jodrell Bank (MkII),

Onsala, Torun and Westerbork. For the first two hours the data rate was

limited to 64M/s, with Arecibo participating. The second part, without

Arecibo, was done at 128Mbps. 

After a few minor problems the experiment went smoothly. Arecibo and 
Onsala lost connectivity at  times but always came back.  Good fringes

were obtained to all stations. 

When Arecibo became unavailable the data rate was increased to
128Mbps.
Again there were some initial problems and it took a little longer get
the system
up and running. Torun and Onsala suffered connectivity loss at times
but
fringes were detected on all baselines.  

Throughout these tests the biggest problem was that the system did not

recover from gaps in the schedule. Gaps are normally introduced to
allow
stations time for calibration and to avoid wasting recording medium
when 
telescopes are moving between sources. At the correlator, for e-VLBI, 
none of this is relevant so a change was made to make the correlator 
control code ignore gaps and consider the complete time range as one 
continuous scan. This seemed to do the trick and it was possible to do

actual phase referencing using a realistic schedule. 

In conclusion: we did 64Mbps trans-Atlantic correlation with 6
telescopes, 
and 128Mbps with 5 telescopes, both of which have not been done before 

we believe. And we did 128Mbps to two telescopes in the UK, also a
first.
Correlation was quite stable (when the system finally was up). Arpad
has 
added a feature that lets one reconnect the Mk5s at the station to the

correlator, which is very useful when connectivity is lost because of 
packet loss.

With a work around for the gap problem established it will be possible,
in
a future test, to try real sustained operation and look more carefully
at 
the state of the system when it falls over.

In all an excellent effort, we learned plenty, and set some records
while 
we were at it. Thanks to all involved!

(Above is a summary of Arpad's more detailed report to the
participants.)

Steve.



================================================
S M Parsley                              _______
Manager, Technical Operations and R&D    ___|___
Joint Institute for VLBI in Europe        / | \ 
Radiosterrenwacht                        /__|__\
Postbus 2                                 |___| 
7990 AA Dwingeloo                         |___|
Netherlands 
+31-(0)521-596519 (direct)               __|_|__
+31-(0)521-596500 (switch)                _|_|_ 
+44-7970-654092 (mobile)                  \\  / 
+31-(0)521-596539 (fax)                  ___|___
[log in to unmask]                           / | \ 
http://www.jive.nl                       /  |  \
================================================

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