[evlatests] P-band switched power observed at S-band

[Paul Harden]

On 6/17/2016 2:42 PM, Paul Demorest wrote:
> hi everyone,
>
> While looking into various switched power issues recently, I noticed 
> that the state of the low-band (4/P) cal switching causes a 
> significant change in switched power (aka Pdif) measurements done at 
> S-band.

I had addressed this some time ago, in that there is virtually no 
isolation between the noise coupler prior to the LNA, where the 20-30K 
Tcal is injected, and the P-band dipoles.  This would seemingly 
illuminate the subreflector with the Tcal power leaking to the dipole.  
Today, we'll be at the site most all day shutting down the array.  In 
the next day or two, I will see if I can measure the amount of Tcal 
power coming out of the receiver inputs.  The noise source in the LBR is 
only good to around 2-3 GHz, so likely little effect on the higher 
bands.  (I'll measure that, too).

It would be easy to turn off the low band CAL switching when the LBR is 
not in use.  There is no way to remotely turn off the receiver.

Paul