[evlatests] P-Band system report ...

[Sandra Wroblewski]

OK, I made a mistake and hurriedly came to an incorrect conclusion 
yesterday.  After taking a  look at the IF C & D, I see 3 really strong 
ripple in P-Band.  That is usually due to a bad cable or connector.  
After reviewing my notes from Paul, the badness is probably around the 
trombone.  I will go out during next week maintenance day and trouble 
shoot and hopefully correct the problem.

Sorry for the first incorrect conclusion.

--Sandy

On 12/8/2016 3:39 PM, Rick Perley wrote:
> Frank asked me to check up on the P-band performance.
>
>     I took some data on 3C286, and a nearby blank field, early in the 
> afternoon.
>
>     Antennas 15 and 23 were out of the array.
>
>     Problems found:
>
>     1) ea14 has *very* low sensitivity -- by a factor of 2 to 4 in the 
> center part of the band to very much worse at the lower frequencies.  
> The bandpass is also odd, particularly in phase.
>     All other antennas have nominal sensitivity.
>
>     2) ea28X has a much larger 3 MHz ripple than any other antenna -- 
> 2 dB in power (pk -- pk).  All others are less than 1 dB.  (The 
> frequency structure indicates a reflection of equivalent free-space 
> length of 50 meters).
>
>     3) Cross polarization is very low on a set of antennas, and very 
> high on others:
>
>     a) Very low: (< 5%)  ea01, 3, 7, 14, 16, 22, 25 and 26.
>     b) Very high: (> 40%) ea02, 06, 17, 19, and 27.
>
>     The oddity is:  the list of low - polarization antennas have very 
> little correlation with the list of antennas whose P-band dipoles have 
> been stabilized.  These are:  ea01, 8, 10, 14, 20, 22, and 24.  (ea 
> 01,14 and 22 are the only ones common to both).
>
>     When observing an unpolarized source (which all our standard 
> calibrators are at P-band), the major source of cross polarization 
> must be misaligned dipoles.  (The only alternative is very poor 
> isolation between the two electronics channels).
>
>     Thus:
>     a) the dipoles in the list given in 3(b) must all be *seriously* 
> out of alignment with those listed in 3(a).
>     b) the dipoles in list 3(a) should all be close to parallel.
>     c) The dipoles in the stabilized antennas:  ea08, 10, 20, and 24 
> are not properly aligned with those in ea01, 14, and 22.
>
>     Reminder:  Keeping the cross-polarization below 5% (the same limit 
> imposed at the high frequency bands) requires the dipoles to be 
> aligned to ~ 2.5 degrees.
>