[evlatests] "2-bit" sampler test

[Barry Clark]

A real 2bit sampler would do a bit better than the "2bit sampler"
because the bad high values leak into the next bit, and hence are more
heavily weighted than a truncating sampler.  So the optimistic case
for a shifted 3bit sampler might be around 0.06 or so.

Vivek Dhawan wrote:
> Here is the last measured 3-bit data, from Rick, and the latest '2-bit'
> comparison from today. (ea15 was pulled off just before). The 2-bit is
> a shade better.
> 
> -------- Original Message --------
> Subject: [evlatests] 3-bit 22RCP all fixed, but ...
> Date: Thu, 16 Sep 2010 14:56:46 -0600
> From: Rick Perley <rperley at nrao.edu>
> To: evlatests at aoc.nrao.edu
> 
>      The repaired sampler is back in the antenna, and the standards tests
> done.  The results are exactly as expected:
> 
> Here's the 'noise matrix', 3bit, from Rick, RR upper right, LL lower left.
> 
>          12        15       22       28
> --------------------------------------
> 12  |   X       .22      .22     .24
> 15  |  .17       X       .18     .18
> 22  |  .17      .16        X     .19
> 28  |  .17      .17      .17       X
> --------------------------------------
> 
> 
> 2bit, today (ea15 removed)
> 
>          12       15      22      28
> --------------------------------------
> 12  |   X        X      .21     .23
> 15  |   X        X       X       X
> 22  |  .16       X       X      .16
> 28  |  .16       X      .15      X
> --------------------------------------
> 
> Ken Sowinski wrote:
>> I rand the usual test program that alternates ons and offs at
>> 3c286 with the T304 gain set to what would be appropriate to
>> drive a 2-bit sampler.  Requantizer gains were set to the optimal
>> RMS of 2.7 for four bit correlation.  I expect that the sampler
>> RMS needed is about 1.0.
>>
>> Ken
>>
>>
>>
>> The name was C2tuned_006
>>
>> 1922 UT  Started script
>> 1927     Requantizer gains all set
>> 1956     Stopped script
>>
>>
>> I recorded the T304 output power and sampler RMS
>>
>>          IFA           IFC
>> ea12  -35.0/0.83   -33.9/1.03
>> ea22  -34.2/1.13   -33.3/1.19
>> ea28  -33.5/1.03   -34.1/1.16
>>
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