[evlatests] ant 16 bandpasses from Tests, July 21

[Vivek Dhawan]

Ant 14 not working. Barry got some data on ea16.  Looks like
polarization LL (?), IF C(?), at BW (resolution) of:

50 (3.125) MHz;   25 (0.78);   12.5 (0.195);   6.25 (0.0488).

The phase looks (deceptively) flat in the 50MHz case, i.e.
nearly zero delay residual - black points in plot#1.

At all narrower BW, the phases have a sawtooth with corresponding
amplitude jags. Ant 16 is the only one with this shape. all VLA ones
look good. Correlator problems were reported in work orders # C116570
and C116538, but appear to be unrelated.

I believe the smooth 50MHz plot is a result of having the teeth be
just 3.125MHz apart, corresponding to delay offsets of 320ns i.e.
32 samples at 100MHz (please check my math).

The next 2 plots are the cross correlation of antenna 16x17,
and the autocorrelation of ant 16, both from the 25MHz data.

The 'false' correlation spikes lie in chans +_ 16 here, at +_8 in the 
12.5MHz, and +_4 in the 6.25MHz data. I think, as above, they are at
chan +_32 i.e. aliased to the 0-channel, in the 50MHz data.
(AIPS refuses to label this plot in physical units).

Mark Claussen reported (July 12) large delay offsets in a previous
round of tests. The band-passes looked similar (I was hovering) but
I do not have a copy of those. I also think we saw similar shapes on
July 7 on both IFs A&C when the same hardware  -or some of it- was
on antenna 14.

Vivek.



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