[evlatests] new '3-dB' step test results

[Rick Perley]

    Ken/Michael ran a new '3-dB' step test.  The attenuators in the T304 
were adjusted to increase the power to the 3-bit samplers in steps of 
3dB ( a doubling of the power for each step).  Five sequential steps 
were made.  For each step, the resamplers were adjusted to give the same 
rms level (effectively, the same number of bits in the resampling).  The 
goal was to detect what the change in SNR is as the 3-bit samplers 
becomes increasingly highly populated.  Because of the adjustments made 
in the requantizer, no effective change in cross-correlation, or 
auto-correlation power is expected. 

    Results:

    Indeed, no significant changes in the auto- or cross-powers were 
seen.  (More correctly, increments were seen at the moment the 
attenuators were changed, but the output powers quickly returned to the 
earlier level as the requantizers adjusted). 

    Very little change -- if any -- in blank-field rms values were 
noted.  Antenna 22 was out of the array now (as its samplers have been 
returned here for diagnosis).  Antenna 12RCP gives higher noise than the 
others, as previously noted. 

    The detailed noise results are below. 

Baseline-IF    Low    +3dB   +6dB   +9dB   +12dB(high)
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12 x 15 R        .23        .21      .23      .23         .23
12 x 28 R        .23        .24      .24      .24         .23
15 x 28 R        .19        .18      .17      .18         .19
12 x 15 L        .18        .17      .15      .17         .17
12 x 28 L        .17        .16      .18      .17         .18
15 x 28 L        .17        .16      .16      .16         .17
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