[evlatests] P-band checkup: ea01 pol prob

[Dan Mertely]

Hi Rick.  No, I don't know how this mis-alignment may have happened.
The locking bolts on the antenna jam-nut mount were very tight.  Once
I loosened them I found that I could tighten the jam nut a bit before
it sucked the antenna up into the mount tightly, but the locking bolts
should have done that already.  I must admit that I didn't inspect the
"clam-shell"/dual-half-moon slip-clamp at the top.  It has 6 thin but
long screws in it the prevent the whole central assembly from
rotating.  I suppose it could be loose, but I don't think the slots
can provide the 20-30 degrees of slip we saw.  We should probably
inspect it though.  Mike Romero has an improved version that we will
be installing on future retrofits.  It can also be swapped-out in the
field.  -Mert

On 7/15/2016 8:59 AM, Gene Cole wrote:
> It is possible that the lockdown clamps which hold the rotary joint to the subreflector tube have loosen enough to cause the dipole move out of alignment.
>
> --Gene
>
> -----Original Message-----
> From: evlatests [mailto:evlatests-bounces at listmgr.nrao.edu] On Behalf Of Rick Perley
> Sent: Friday, July 15, 2016 8:19 AM
> To: evlatests at listmgr.nrao.edu
> Subject: Re: [evlatests] P-band checkup
>
>
>
>       Thanks to Paul and crew for attending to these issues so quickly.
>
>       Regarding the polarization of ea01.  It's good that the cause was easily found and corrected.  Misaligned dipoles is the most obvious -- but not the only -- way to get high cross-polarization. This is one of the antennas which has the modified mounting system -- so I think it's important to understand how it got misaligned by ~30 degrees.  Any ideas?
>
>       For ea08, we'll need to run another on-sky test to see if the connector correction has made the polarization better.  Probably best to wait until the switched power issue for ea01 is resolved -- next week?
>
>       Rick
>
> On 07/14/2016 06:21 PM, Paul Harden wrote:
>> Made some low band progress at the site on Thursday.
>>
>> On 7/11/2016 7:49 PM, Rick Perley wrote:
>>> 1) All antennas *except* ea08Y worked well.  The sensitivity of this
>>> polarization channel is less than half of the others.
>>
>> We fixed this low band antenna.  A bad connector-adapter gobbling up
>> the power on the RCP side.  Bandpass plots shows all IF's now at
>> proper power and passbands.
>>
>>> 4) Very large cross-polarizations are seen on some antennas.
>>>
>>>           a) The worst (by far) are:  ea01,ea06, ea08, ea17, ea27.
>>> (ea01 is nearly 50% cross-polarized!!!).
>> EA08 alignment looks pretty good.  Nothing really to realign.
>> EA01 indeed was misaligned by about 30 deg.  Dan Mertely and Brandon
>> got it realigned and reported the mounting hardware was all tight with
>> the new mounting collar and no real explanation on why it had moved so
>> far.  We'll see what happens over the next few months.  At the moment
>> anyway, it is properly aligned to the quadrapod legs.
>>
>> We didn't get a chance to check P-band dipole alignments on EA06, 17
>> or 27.  Will catch next maintenance day.
>>
>> Also worked on the no CAL switching on EA01.  Problem is the CAL term
>> from the F318 to the low band system is switching at 20Hz vs. 10Hz.
>> Put in a new F318, no change, so obviously an input problem somewhere.
>> Jim Jackson thinks he knows what the problem might be in the fiber
>> interface, so will likely be fixed very soon.
>>
>> Paul, Sandra, Dan, and Brandon
>> The Low Band Brigade, San Augustin Chapter
>>
>>
>>
>>
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