[evlatests] PDif compression -- more tests

[Ken Sowinski]

On Tue, 5 Mar 2013, Rick Perley wrote:

>    Result:  No change in PDif compression.  These three antennas are
> still as bad as they were before.
>
>    Comment 1:  We must be barking up the wrong tree.  All the tests I
> can recall doing in the past couple years have exonerated the T304.
> Since the problem is manifest in the X-band system, and since the old
> style X-band receivers did not show the compression, while the new style
> ones do, is the problem somehow connected to the receivers, or the
> switched power injection mechanism?

One thought comes to mind.  If we have ruled out the downconverters,
except for passive components, only the receiver and sampler are left
in the X band system.  Are we seeing compression in the sampler module
before the digitizer?  That can be tested by reducing the output power
set point by 3 to 6 dB.  Our conventional set point produces a sampler
RMS of about 11, so there is some room to reduce the power.  Have we
already done this?