[evlatests] More on Switched Power 'Saturation'

[Bob Hayward]

Rick Perley wrote:
> 
>    Although the expected effect was seen, its magnitude is quite a bit 
> less than expected -- the 'on/off  Cyg A' experiment -- which triples 
> the cold-sky system temperature --  showed a considerably larger 
> reduction in PDif than the ~8% reduction seen in the experiment.   No 
> simple explanation for this comes to mind.
> 

My guess is that it has something to do with the LO settings.

In our experiment on Ant 24 we tapped off the signals at the input and 
output of the T304 module and fed them into narrow 100 MHz filters 
before being detected by an Agilent power meter. To ensure we were 
looking at the exact same signal we forced the L301 & L302 synthesizers 
to use different frequencies from what had been used on the Cygnus 
observation. We still need to evaluate what sort of effect different LO 
settings cause on the T304.

Even more confusing was that we saw a *larger* Y-Factor at the output of 
the T304 than what we saw on the input. We would normally expect it to 
be exactly the same or slightly smaller (the T304 will add a little bit 
of noise thus increasing Tsys and decreasing the Y-Factor). Either our 
test setup was nonlinear or it's all thanks to some odd nonlinearity 
within the T304.

More tests are planned...

-Bob