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

[Paul Harden]

On 9/16/2014 2:38 PM, Huib Intema (NRAO) wrote:

> * Antenna power levels (determined from gain calibration):
> Most antennas have similar (healthy) power levels, within ~30 percent of
> the median, except:
> - EA04 RCP: P = 0.05
> - EA04 LCP: P = 0.40
> - EA14 RCP: P = 0.35
> - EA16 RCP: P = 0.35
> - EA18 RCP: P = 0.45
> - EA19 RCP: P = 0.45
> (P = power level relative to median)

I want to ensure I understand this correctly.  For example, on EA16 
P=.35, this means the power is 35% lower than your mean/median?  That 
would equate to about 4.5dB less than the median (probably marginally OK 
- see below).  On EA04 P=.05 would be -13dB (clearly bad).

Specs for most of the modules calls for LCP and RCP powers to be within 
2dB of each other.  I know the low band receiver output powers never 
exceed 2dB with 1-1.5dB typical (when they leave the lab).  However, 
this 1-2dB LCP-RCP difference is also probably typical of the T301 4/P 
Converter and the T302 LSC Converter.  If the LCP channels (for example) 
in these modules are all low by 1-2dB, this could easily accumulate to 
4-5dB difference by the time it gets to the T304s ... but shouldn't the 
T304 automatic leveling make up for that?  (WIDAR path, not VLITE). 
Thus, I would think 4-5dB accumulative difference might be the norm, and 
within the EVLA system specs.

On some of the reported low antennas, Dan and I can check the power as 
it trickles through the IF system (once it stops raining) to see where 
this difference is originating, or if an accumulative effect.

Bottom line: What would be the maximum power difference between LCP and 
RCP in the system you'd like to see?  Then, we can try to figure out how 
to equalize the powers if ~ 4dB difference is not acceptable.  Might 
require adding coaxial attenuators between modules to equalize the power 
(at the expense of a few dB loss of sensitivity in one channel).

Paul