[evlatests] 25 MHz correlator offset poblem

[Gustaaf van Moorsel]

Gustaaf van Moorsel wrote:

> Some time last week Ray swapped samplers, and I did a test observation
> this weekend to see if the problem moved with the sampler.  It does not.
> The off-set-like problem stays with IF A (IF 1, Stokes 'RR').

Last night I did the same test using 12.5 MHz bandwidth instead of
25 MHz bandwidth.  The offset-like behavior is no longer there, as
shown in the two attached postscript files.  Although the rms noise
in the 12.5 MHz maps is obviously higher, the effect, if present,
would have been clearly visible.

Note that the fact this effect is specific to 25 MHz bandwidth is
reminiscent of the more serious correlator offset problem (which
affected all antennas) which was solved by turning off selftest.

Gustaaf
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