[evlatests] P-band status

[Dan Mertely]

Hi Rick.  Fernando & I got time this Maint day to check out
5 of the 10 EVLA antennas where you reported > 10% cross-pol.
All that we checked out were sequentially at the end of the
west arm (for our convenience).  The results were:

ea18:
o Alignment almost perfect (referenced to the quad legs).
o Both dipoles were straight.
o The elements were 180 deg out from "normal".  ie: When
   the antenna is at EL < 90, the vertical dipole element
   that connects to the coax center is on top.  (We finally
   found one!)

ea22:
o Alignment almost perfect (referenced to the quad legs).
o Both dipoles were straight.
o The elements were oriented "normal" (shield side up
   for the V dipole).

ea03:
o Alignment almost perfect (referenced to the quad legs).
o The vertical dipole elements were straight, but the
   horizontal were not in alignment--1 side off by maybe
   1.5 degrees, while the other side pointed directly at
   the center of its quad leg.
o The elements were oriented "normal" (shield side up
   for the V dipole).

ea16:
o Alignment almost perfect (referenced to the quad legs).
o Both dipoles were straight.
o The elements were oriented "normal" (shield side up
   for the V dipole).

ea19:
o Alignment almost perfect (referenced to the quad legs).
o Both dipoles were *not* straight.  For both the H & V
   sides, 1 element leg would be off by maybe 1.5 degrees,
   while the other side of the same dipole pointed directly
   at the center of its quad leg.
o The elements were oriented "normal" (shield side up
   for the V dipole).

So, I'm not sure what caused your cross-pol results.  Perhaps
the linearity of the dipole elements is showing up, but then
why would ea18, ea22, & ea16 show bad?  They were straight.
(As noted by my email "Re: ea26 & ea24 P-band dipole orientation
check" of 20170912, your reference antenna, ea24, also has a
linearity problem with one of the 2 dipoles.  Could the reference
antenna's imperfections be transferring to the antennas
under test?  Still, the 1/4 wavelength element that was crooked
on ea24 was only off by around 1.5 to 2 degrees.  ??.)
-Mert


On 9/22/2017 11:00 AM, Frank Schinzel wrote:
>
>
> On 09/22/2017 10:55 AM, Rick Perley wrote:
>>     Some P-band data were taken earlier this week. Frank asked me to
>> check on the quality:
>>
>>     I extracted the four scans of 3C147, and used five spectral
>> windows (5 through 9).  I find:
>>
>>     1) Antenna 28 was in the barn, and antennas 13 and 14 were both
>> out of service during these observations.
>>
>>     2) Antenna 23 was in a peculiar state -- the 'Y' channel
>> oscillated in delay on a fast (few seconds) timescale.  The 'X'
>> channel also had irregular delays, but only for the first two
>> calibrator scans -- it seemed fine for the last two (two hours later).
>>
> This is probably a DTS issue. It has been doing funny things.
>>
>>     3) Requantizers seemed to be working (meaning, they changed level
>> between the second and third calibrator observation).
>>
>>     4) CALIB gains (after applying the RQ correction) showed a wide
>> range of antenna correlated power -- a factor of four between highest
>> and lowest for a given SPW.
>>
>>     5) The 3 MHz bandpass ripple is strong on:  7X (2dB, pk-pk in
>> power), and 17X (2 dB).  All others are less than 1dB.
>>
>>     6) With respect to 'golden antenna 24', the cross-polarization is
>> high (above 10%) on:  ea03, ea10, ea14, ea16, ea17, ea18, ea19, ea21,
>> ea22, ea27.  These are likely to to dipole orientation.  A
>> confirmation check would be useful.
>>
> Note ea24 DTS was flaky when the data was taken, if you don't see
> anything crazy in the phases or delays then it might have been ok.
>>
>>     Rick
>>
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