[evlatests] 3-bit tests -- 7 Sept.

[Barry Clark]

The correlation efficiency is a multiplicative effect, so if the system
temp is high, it will show up as the same percentage.

I agree, 6dB too little power into the digitizer is like going from
a three bit to a two bit sampler, so a 10 or 12 percent effect.  But
6dB too high power should result in a sigma about equal to the edges
of the good bins, or about 30% of samples falling in the overflow bins,
which act like one bit samplers, and their contribution is weighted
up by nearly a factor of two, so more like a 30% effect.  But we knew
from the state counts that things get wonky at high power anyhow.  At
a guess, we are being saved by the zero offset - there are no overflow
high times overflow low products, so the overflow bins do not, contrary
to theory, act like one bit digitizers, but get scraped off into the DC
channel, which we, sensibly, ignore.

Rick Perley wrote:
>     Ken/Michael arranged to supply the samplers with a range of input 
> powers, from -38 dBm to -26 dBm in 5 levels (i.e. steps of 3 dB). 
> 
>     I've reviewed the data.  The power changes are easy to see in the 
> gain solutions.  But the curious (disturbing?) result is that there is 
> no effective change in rms noise in the 'blank sky' histograms between 
> the max and min powers.  The other (disturbing?) effect is that both 
> polarizations are much noisier than in the test of last week -- 
> typically .25 to .35 Jy rms, when 0.16 is the expected value.  Two 
> baselines (22 x 27 and 22 x 28) in RCP have noise over 0.5 Jy. 
> 
>     Ken notes is was raining at the time, so perhaps the elevated noise 
> is from excess cloud emission.  We think that, over the range in power 
> level, the expected effect might be ~10% of the proper noise -- say, .02 
> Jy, which is difficult to see in the high noise. 
> 
>     We should try again tomorrow, in hopefully better weather
> 
>    
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