[evlatests] Some results from 3-bit test of Friday evening

[Ken Sowinski]

On Sat, 12 Nov 2011, Rick Perley wrote:

>    5) ea07, on the 3-bit paths, is very troubled.  There is real
> trouble with subband 8 for both 3-bit paths (13872 -- 14000 MHz), which
> the fringe levels are very low, very likely due to a very large
> resonance which appears in that band -- at the same frequency for both
> paths, and for both polarizations.  Unfortunately, this subband is not
> overlapped by the 8-bit path, so I can't tell if it is in the 8-bit B
> and D IFs.  This 'resonance' is very strong and at least 10 MHz wide.
> It is present at all times on both polarizations.  It is only seen on
> ea07, and is thus not external RFI.  I can easily see it in the
> cross-power for all baselines to ea07 -- this may well be radiation from
> ea07 getting into the other antennas, hence to the correlator, and
> visible as common source.

I tried this again this morning using 3C273 and shifting the
8-bit IF pair to cover the center GHz of the 2GHz 3-bit baseband.

The birdie was also seen in the 8-bit BD data.  If I have done
the arithmetic correctly it is at 13988 NHz, resolved, and with
a noticable shoulder on one frequency side.  The obvious
speculation is that it is an example of the "phenomenon" getting
out of the box and seen by the Ku band horn.  However, the
signature persisted in the BD data even when both 3-bit sampler
modules (D301 and D303) were turned off.

There is some evidence of mis-wiring.  When I turned of the 3-bit
samplers in D303, the deformatter reported an RMS of zero for
both samplers.  When the D301 samplers were turned off, only the RCP 
sampler RMS was zero; the LCP sampler remained at around 1.3 with a
funny looking autocorrelation.

For Rick, the dataset is called ku_birdie, rand for about half an
hour and has just finished.  Be aware that the samplers at ea07
were cycled off and on towards the end of that time.