[evlatests] More on compression and switched power

[Ken Sowinski]

>     So what can cause the closure failure?  I note that Cyg A quadruples
> the system temperature -- and that the T304s are running 'hot' -- the
> output attenuators are typically at 25 to 31 dB.   Are we overflowing
> something in the digital system?  Overflowing the requantizer seems
> unlikely to cause a closure problem, but what if we are overflowing the
> cross-multiplier accumulators.  Note that Cyg A has a correlation
> coefficient of over 75% at L-band ...

If the downconverter output is too hot, the sampler will
be over driven a little but we have about 10 dB of headroom
there.  The subband requantizer output will also be too high.
That may put is in a less linear regime of the multipliers.
If the multipliers or LTAs were to overflow, that would surely
produce a recognizably weird result in frequency space.