Previous: Appendix 3: EVN CAL Observations Up: EVN TWG/Friends Meeting Next: Appendix 5
If you recall there was in a long-gone TWG meeting the suggestion of doing a calibration experiment including polarization. Well I have done a little simple analysis of that, I think it was done in February. The polarisation performance at 6cm is much the same as that measured by Foley and Strom some years back. That data has also been investigated by Maria Massi. Here are some figures for LR and RL i.e. crossed circulars as a percentage of LL and RR fringe amplitudes. Most of these figures are high and show little change with hour angle, so this is just excess ellipticity of feeds.
Base % Base % Eff-Jod 1-6 Jod-Noto 6 Eff-Med 20 Jod-Wsrt 7 Eff-Noto 10 Med-Noto 20 Eff-WSRT 10 Med-WSRT 12 Noto-WSRT 12
The Eff-Jod figure shows variability across the band, peak frequency to next peak is 35MHz, which seems rather large to be caused by reflection from telescope back into the horn. The pattern moves in frequency with the difference in B-J parallactic angle (the observations were done near zenith at both stations). So all baselines with Jodrell look pretty healthy, particulary Eff-Jodrell. Note that the larger figures will give rise to closure errors of about 0.5 degrees on typical triangles. Clocks are worth noting:
Station clock rate offset millihz Eff 0 (ref) 0 Jod -13 -3 Med -7 -15 Noto -15 -8 WSRT 43 +35
(for VLBA operation these should really be a lot nearer to zero, or at least have a known constant offset, e.g. for combined synthesis antennas).
Here are the parallel-hand amplitudes (LL) for various bases, in units of 0.01% correlation, after b-factor correction. The values are given for the sources: 2030+547/1739+522
Eff-Jod : 52/135, Ef-Med: 75/170, Eff-Noto: 60/170 Eff-WSRT: 100/210, Jod-Med:23/66, Jod-Noto:21/65, Jod-WSRT:37/88 , Med-Noto,37/78, Med-Wsrt: 37/100, Noto-WSRT:32/100.
Dave Graham