Results of TADU4 test
What we did
On Monday 28th Oct we had another in the series of tests of the new
tied-array hardware for Westerbork. The setup used 4 bands (out of a
maximum possible of 8) so that we can record at least the dual-pol of
64MHz IF that the old hardware was capable of.
We observed at 6cm
- one 22min pass 3C345 (WB and MC)
- one 22min pass 1739+522 (WB, MC, JB)
- In parallel with the tape WB and MC did a recording
to hard disk (not looked at yet)
Results of correlation
Bob Campbell of JIVE handled the correlator output
- Phasecal in RCP only (expected)
- Amplitude level was good, and stable on each source.
- Phase OK. The drifts is less than 1 turn in 22min and
behaves consistently in all bands, so it is probably
atmospheric.
- Autocorrelation bandpass shows a slight artefact from
insufficient supression of an LO (at 120MHz in the IF entering
the VLBI rack). We will try to improve on this.
- Delay differences between the 2 sources a small fraction of 1ns
(probably atmospheric)
- cross polarized amplitude much less than 20% of parallel
(a better number to follow)
- Cross polarized spectra look reasonable and stable
In all cases the data looks at least as good as (and in respect of
bandpasses very much better than) the old tied-array's output.
Other notes
- The new correlator at Westerbork has lower offsets than the old
correlator, so local synthesis data taken in parallel
was usable for calibration.
Conclusions
- We plan to use the new tied-array hardware for the coming
(Nov 2002) VLBI session. Correlators note: the extra delay in
the new tied-array hardware is 1000µs
- Anyone wanting parallel WSRT observations should contact me
before the observations are made.
Finally many thanks to people who worked paryicularly hard to get this
running, particularly Albert Bos, Harm-Jan Stiepel, Hans van Someren
Greve and Teun Grit. Also thanks to those helping to test it:
Alessandro Orfei, Paul Burgess and Bob Campbell.
Tony Foley <foley@astron.nl>
Last modified: Fri Nov 1 14:25:01 2002