[evlatests] WIDAR P-band status update: 13SEP2014

[Paul Harden]

On 9/17/2014 1:10 PM, Barry Clark wrote:
> I presume this means the power at the correlator, and therefore
> after the level setting in the T304.  So it means a really low
> power where the attenuators in the T304 can't compensate,

When checking the T304 LOIF screen on low band, I have seen 10-12dB 
differences in attenuator settings between LCP and RCP.  However, I've 
never seen anything much more than about 25-30dB total attenuation 
applied, or about half the attenuation range (on Ch. 1).

> or it means a really screwed up bandpass (or birdies) in the 1 GHz
> bandpass that the detector in the T304 sees.

The problem I have noted on occasion with large differences in LCP-RCP 
attenuator settings is particularly strong RFI or other power in one 
polarization over the other in the 1GHz bandpass of the Ch. 1 power 
detectors.  Since P-band is only about 25% of the 1GHz power detector 
range, attenuator settings are not determined entirely or heavily 
influenced by P-band power alone when other power or RFI is present.

For example, integrating sky power while stowed can show large 
differences between LCP and RCP due to RFI, but pointing to the sun, 
attenuators are usually within a few dB of each other with plenty of 
headroom to go (i.e., still linear).  On the sun, unwanted powers are 
pretty much swamped by the sun (a 15-20dB increase on the sun over cold 
sky), allowing powers and attenuator settings to be very close channel 
to channel and antenna to antenna on the sun.

Has anyone tried to check the low band power differences by manually 
setting the attenuators to the same fixed values to get true receiver 
and IF system power differences?



Paul