[evlatests] L-Band sensitivity on 13, 14 and 16

[Walter Brisken]

On Tue, 25 Apr 2006, Rick Perley wrote:

>   We really do have a serious sensitivity problem at L-band on these 
> antennas.

>   So where is the problem?   Bob Hayward and I did efficiency and Tsys
> tests at the front end on antenna 13 which clearly showed that G/T should
> be about the same as VLA -- perhaps at most reduced by 10%.
>   I list some possible explanations:  a) High Tsys.  b) Low efficiency.
>   c) Bad pointing.  d) Defocussed.  e) Subreflector seriously out of 
> position.

I'd add to the list two other possibilities consistent with having a good 
receiver: f) out-of-subband power (RFI or internal) either causing 
clipping or inappropriate level setting, and g) low or unstable LO power 
at chosen tuning.  Could g have an affect in the LSC converter that would 
not show up at C band?

Next time you do L-band tests let me know and I'll capture some voltages 
to peek at the 1GHz spectrum.

-Walter