[evlatests] Changing P-band Dipole orientations

[Ephraim Ford]

I did a quick climb up on EA11 and EA23 since they were close enough to allow a lone-worker visit. Attached are photos of the dipole positions. EA11’s 10.3* rotation was clearly more noticeable than EA23’s 5.2* rotation.

Ephraim

From: evlatests <evlatests-bounces at listmgr.nrao.edu> On Behalf Of Rob Long via evlatests
Sent: Wednesday, September 11, 2024 3:44 PM
To: Rick Perley <rperley at nrao.edu>; evlatests <evlatests at nrao.edu>
Cc: Clarke, Tracy E CIV USN NRL WASHINGTON DC (USA) <tracy.e.clarke2.civ at us.navy.mil>
Subject: Re: [evlatests] Changing P-band Dipole orientations


What Rick mentioned is correct. Unfortunately, it is difficult to keep the dipole aligned "perfectly", dependent on which direction the sub-reflector was last rotating. There are nylon guide blocks at the apex of the antenna trombone assembly which do loosen/wear over time and allow more slop in the dipole orientation. CCW vs CW rotation of the sub-reflector can leave the dipole in slightly different positions. Usually, this is within a couple of degrees.



Rob


On 9/11/2024 10:12 AM, Rick Perley via evlatests wrote:
I noted yesterday some discrepant dipole orientations, and noted that I had the impression these were worse than at earlier times.

By happenstance, I'm calibrating some old (2019) P-band data for Tracy Clarke, which allows me to judge the correctness of that statement.

The statement is wrong.   Misorientations were worse in 2019 than now.

Tracy's data were taken twice – in March and in September of 2019.  The distribution of orientations were in fact worse than now, and also were very different.  Antennas misoriented now were better (or worse) in 2019.  Indeed, the correlation between the two 2019 observations is not very strong.

I believe these conclusions are not surprising, as the dipoles are known to be subject to rotation caused by the rotating subreflector.  Perhaps Rob Long can confirm this statment.

Rick



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