[evlatests] First full bandwidth data!

[Ken Sowinski]

On Thu, 15 Mar 2012, Rick Perley wrote:

>    Seven antennas are now outfitted with the full complement of 3-bit
> samplers.  I prevailed upon Ken to generate a script to see if we are
> getting good data across the full 8.192 GHz of bandwidth now available.
>
>    He ran a short test script this afternoon, which worked (almost)
> flawlessly.  All 16384 channels for each baseline are present (4096 is
> each of four polarization), for all 21 baselines.
>
>    A few things are clearly not right.  First, some nomenclature:
>
>    According to BDFLIST, the data are arranged in four 'chunks' (IFs)
> with 16 subbands each.  The four chunks are each 2.048 GHz wide, and are
> listed in reversed frequency order:  the first is the highest frequency
> (24.0 -- 26 GHz), the second is the next highest (22 -- 24 GHz), etc.
> The subbands within each of these four chunks is within proper frequency
> order, however.  In any event, BDF2AIPS will (if requested) resort the
> order of all the subbands, so all comes out as expected.    I number the
> IFS from lowest frequency
> to highest.
>    Each IF (chunk) has 16 subbands of 128 MHz each, numbered from 1
> through 16.

I don't know about these chunks.  The LO system requires that
AC tune the top half and BS the low half of K band.  AC will be
LSB, and BD USB.  The observation was arranged so that:
AC1: 24 - 26 GHz
AC2: 22 - 24
BD1: 20 - 22
BD2  18 - 20

Some of the problems reported below were caused by some filter FPGAs
haveing been left in a funny state after phased-array testing today.
That has been repaired.  It will be interesting to see if the residual
problems are all the same as what Rick reports.

Delays have not yet been adjusted.


>    1) On the RR correlations, four subbands are giving no signal on
> most of the antennas:
>
>    subband 4 on IFs 1 and 2
>    subband 13 on IFs 3 and 4.
>
>    2) On the LL correlations, most antennas also have four subbands
> with low signal, or unusual shape:
>
>    subband 1 on IFs 1 and 2
>    subband 16 on IFs 3 and 4.
>
>    3) Delays are very, very large -- as expected.  The AIPS task
> 'FRING' cannot do a multi-subband delay solution for these data, since
> it doesn't (yet) know about four IFs being present within a single
> database.  (It knows about 1 or 2 IFs).  No big deal -- FRING will work
> on each subband separately.
>
>    4) Some IFs have powers that are wrong by up to 5 dB.  Notably:  IF
> 1L, on ea 17 is low by -5 dB.  IF 3L on ea 25 low by -4 dB.
>
>    5) A very large spectral power slope is seen on ea21, LCP, on
> subband 2 (=#3 in the original ordering).  The slope is about 15 dB
> across the 2 GHz.  Bad slope filter value, evidently.
>
>    Ken's observation was on 3C84, whose flux is not exactly known.  He
> plans to run this test tonight on 3C286, after which I can derive
> sensitivities, etc.
>
>
>
>
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