[evlatests] 3bit test LL replicated

[Doug Gerrard]

After today's tests, the D301 module with the 3-bit sampler is no longer 
in antenna 22.  We removed it and brought it back to the lab for further 
investigation.  Antennas 12, 15, and 28 have the splitters removed and 
are back to "normal" A1 and C1 inputs respectively.

Doug



Rick Perley wrote:
>     For this test, the T304 LCP signal was fed into both RCP and LCP 
> sampler inputs. 
> 
>     If the noise matrix asymmetries are all due to the digital system, 
> they should remain in this test. 
> 
>     And they do.  But there is one notable change -- 22RCP is not nearly 
> so bad in this test as it was in the previous test  (where the RCP 
> signal was replicated into RR and LL).  Perhaps somebody can explain 
> this ...
> 
>     Here's the noise matrix:
> 
>           12          15             22           28
> --------------------------------------------------------
> 12  |     X         .20            .25          .21
> 15  |    .17         X             .21          .18
> 22  |    .16        .15             X           .22
> 28  |    .18        .17             .16          X
> ------------------------------------------------------
> 
> The 'improvement' in 22R is clearly related to the power level.  Here 
> are the power gains applied to the data:
> 
> Ant/IF        Power Gain
> ----------------------------------
> 12R                56
> 12L                42
> 15R                40
> 15L                38
> 22R                57          !!!!!!!!
> 22L                33
> 28R                39
> 28L                36
> ----------------------------------
> 
> -------- Original Message --------
> Subject: 	3-bit test: *C1* fed to A1 and C1
> Date: 	Fri, 10 Sep 2010 11:48:28 -0600 (MDT)
> From: 	Michael Rupen <mrupen at aoc.nrao.edu>
> To: 	Rick Perley <rperley at aoc.nrao.edu>, Vivek Dhawan 
> <vdhawan at aoc.nrao.edu>
> CC: 	Ken Sowinski <ksowinsk at aoc.nrao.edu>, Robert Long 
> <rlong at aoc.nrao.edu>, Doug Gerrard <dgerrard at aoc.nrao.edu>
> References: 	<Pine.LNX.4.64.1009101027280.29329 at scamper>
> 
> 
> 
> Hi folks --
> 
>   Doug & Rob moved the splitter, such that the signal from *C1* is now fed
> to A1 and C1.  Ken adjusted the attenuators at each antenna to get the
> optimal rms for one of the samplers, without over-driving the other sampler:
> i.e., in each case he set the highest-rms sampler to give an rms of 1.7 (the
> theoretically desired value for a Gaussian distribution of state counts).
> 
>  The measured power levels at the output of the downconverters and
> corresponding rms values of the samplers were as follows:
> 
> ea12  initial   -30.3  0.75  1.12
>       final     -25.1  1.27  1.69
> 
> ea15  initial   -29.3  1.23  1.23
>       final     -25.1  1.27  1.65
> 
> ea22  initial   -30.3  1.07  1.28
>       intermed. -25.1  1.62  1.82
>       final     -27.3  1.38  1.59
> 
> ea28  initial   -30.7  1.00  1.24
>       intermed. -22.5  1.68  1.95
>       final     -26.8  1.34  1.61
> 
>   "initial"   --> as set automatically ("set-and-remember")
>   "intermed." --> what happens if we set attenuators to get the weaker
>                   sampler to have rms 1.7
>   "final"     --> final setting used for the rest of the observation
>                   (stronger sampler has rms 1.7)
> 
> After setting the attenuators to the "final" state given above, Ken
> ajdusted the filter scalings & requantizer gains to give an rms of 2.7
> after re-quantization to 4-bits.
> 
> The final attenautor settings & filter scalings & gains were all in place by
> 1714 (scan 13), and remained undisturbed for the following ~20 minutes
> (through the end of the observation [scan 32]).
> 
> The attached figure shows the distribution of state counts as seen at the
> Input FPGAs on the Station Boards (i.e., before subband filtering &
> requantization) for the 3-bit antennas, after converging on the final
> attenuator settings.  The RED (top, Path 0) subplots are for A1; the BLUE
> (bottom, Path 1) subplots are for C1; and the four plots are laid out as:
> 
>         ea12    ea15
>         ea22    ea28
> 
> The observing script is our standard: one subband pair (128 MHz) at C band,
> centered at 7056 MHz. The first scan is 5 minutes on 3C286, to let the
> samplers stabilize.  After that we have pairs of 1-minute scans {3C286,
> off-source}.
> 
> Please DISCARD all data before the attenuators & filters are set up (at
> 1714, or scan 13).
> 
> The data are available at
>   /home/scamper2/WIDAR0/C3tuned_3bit128MHz_001.55449.706552766205
> 
> Enjoy --
> 
>       Michael
> 
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