[evlatests] P-band sampled voltages

[Walter Brisken]

Ken noted strong spectral features at P-band on antenna 14.  I explored 
the deformatter sampled voltages...

Antenna 14 was set up in the standard P-band mode.  I captured 
4096 voltage samples from each IF from the D351 module.  Histograms of the 
sampled data showed a distribution consistent with a single dominant 
sinusoid.  In IFs B and D this dominant feature is at exactly 1/4 the 
sample rate (that is one half the nyquist rate).  For IFs A and C the 
feature lies 6 MHz lower in frequency as is expected for the default 
setting if the feature is present in the RF.  About 99.8% of the total 
power across the 1 GHz sampled band is in this one spectral feature.  IFs 
A and B also have spectral features at 646 and 640 MHz respectively above 
baseband containing approximately 1/500 the total power.  This is likely 
aliased power since the feature appears at higher frequency in the A/C 
IFs.

-Walter