[evlatests] P-band status

[Rob Long]

Some comments below.

Rob


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. We looked 
>> carefully at these two antennas and found that the ripple problem 
>> exists mostly at the higher end of the band (and somewhat at the 
>> lower end.) When we terminated the receiver inputs with a 50 ohm 
>> load, bandpass was flat across the entire range. We also replaced the 
>> dipole to receiver cables on ea17 as the semi-rigid had broken solder 
>> joints. However, VSWR on the dipoles show good return loss in the 
>> narrow region around 327 but terrible VSWR above about 350 MHz. Maybe 
>> we need to pull these dipoles and have a closer look, but their 
>> performance is fairly similar to other antennas in the array.
>>
>>     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. I have noticed that the P-band 
>> dipoles move around a bit during sub-reflector movement. I would be 
>> interested in knowing if cross-pol is higher or lower depending on if 
>> the sub is moved into position from CW or CCW movement or any other 
>> sub movement. It just seems that we have a large number of antennas 
>> with high cross-pol.
>>
> 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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