[evlatests] Modcomp-Free Tests, 25 May

[Jim Jackson]

Providing the FRM is positioned correctly, I can see no reason in the
hardware for Antenna 14 not fringing. Everything is locked and
synchronized and levels look good all the way thru to the T5's.

Jim


>     Now that power is back, and all the antennas are moved to, and are
> working at, their new positions, we can restart the Modcomp-free tests.
>
>     A quick look was done, in the standard way.  Because the weather is
> poor, and pointing/delays are not yet accurately determined for many
> antennas, the tests were done at P, L, C, and X bands only.
>
>     It was immediately found that the continuum data (taken at 50 MHz)
> was not useful for testing, as the amplitudes were highly variable on
> baseline/antenna.
>
>     Reducing the line data quickly gave the answer -- there are very
> large delay errors amongst all antennas -- the typical value being about
> 100 nsec (huge!).
>
>     Concentrating on the line results, I find:
>
>     0) Antennas 14 and 22 gave no fringes at any band, or any
> frequency.  The operator confirmed that antenna 22 was out of the array,
> but states that 14 was in, and should have been working.  Antenna 19 was
> out at the time.
>
>     1) No sensible data from Pband at all.  Something is significantly
> wrong.
>
>     2) At Lband:
>
>           - All antennas (other than 14, 19, and 22) gave good, steady
> fringes.  All bandpasses, except #25, gave normal looking bandpasses.
> Antenna 25 has an especially high delay errors-- over 250 nsec.
>           - The EVLA and VLA were again incoherent with each other, in
> IF#2 only!!!  This is a line mode effect -- there are good fringes seen
> between EVLA and VLA in the continuum data.
>
>     3) At CBand:
>
>           - In addition to 14, 19 and 21, antenna 23 gave no fringes.
> No receiver, I presume.  Antenna 25's bandpass was very odd (worse than
> at L-band).
>
>     4) At X-Band:
>
>        - Fringes are rather rattier than hoped -- probably weather
> related.  Bandpass from 25 is hugely weird.  (Sorry for the ad hoc term,
> but I can't think of a better descriptor).    Otherwise, all looks about
> as expected.
>
>     Overall:
>
>      Stable data, on all antennas, are being provided.  The delays need
> to be straighted out before more exacting tests can be done.
>
>
>
>
>
>
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