[evlatests] antenna 24 AC

[Jim Jackson]

Rob and Mike are going to change out the L302-1 in Antenna 24 with a spare 
today. Hopefully, this will improve Antenna 24AC.  Per Ken's request, they 
will look at the SD variations before and after.

This will also result in a swap of the L302-1 in Antenna 13 to get the 
proper revision B synthesizer back into it. The revision C spare needed for 
24 is currently running in 13 with an adapter cable for the power. We 
wanted to get that swapped back anyway so this is as good a time as any to 
do it.

Jim

At 10:18 AM 1/10/2007, Ken Sowinski wrote:
>Antenna 24 has not been a very good pointer.  In examining
>the pointing run from last night I found that many trials
>were rejected because the estimated beam width was narrower
>than all other antennas by about 8 percent.  This has happened
>in previous pointing runs as well.
>
>Focus seems OK, in any case it should only make a broader beam.
>However in examining focus I saw that the AC amplitudes are
>not very stable.  There are changes of about 5 percent from
>record to record in AC while BD is stable.  There are similar
>variations in the IF A synch detector, but less clearly in IF C.
>Again, both B and D synch detectors are stable.
>
>I don't see how to consistently make a narrower beam from this
>behavior, but it certainly can make the pointing unreliable.
>Given the symptoms: only A and C and at X band, it just about
>has to be the AC L302.  If I had to guess, it might be related
>to phase switching.
>
>If the SD variations are indeed linked to the amplitude
>variations than it should be easy to see in real time whether
>swapping L302s helps, even if we can't see correlated data.
>
>Further information might be gleaned by:
>1.  Using 0.4 sec integration time to see the temporal behavior.
>2.  Turn off phase switching.
>3.  Convince the pointing solver to only use BD data.
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