Hello EVN-NREN group members,
The aim of yesterday's run was to test sustained "normal" operation
referencing) and to track down any correlator problems caused by
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
Again there were some initial problems and it took a little longer get
up and running. Torun and Onsala suffered connectivity loss at times
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
stations time for calibration and to avoid wasting recording medium
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
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
Correlation was quite stable (when the system finally was up). Arpad
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
With a work around for the gap problem established it will be possible,
a future test, to try real sustained operation and look more carefully
the state of the system when it falls over.
In all an excellent effort, we learned plenty, and set some records
we were at it. Thanks to all involved!
(Above is a summary of Arpad's more detailed report to the
S M Parsley _______
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