[evlatests] Phases on antennas 14 and 24

[Jim Jackson]

I think Ken may be right about the cable length issue with this one.  I
think we fixed this before by lengthening or shortening the 128MHz
reference cable to the offending L302.  Some of the L302's have been moved
around and/or reprogrammed lately so we may have to try experimenting with
this.

Jim




 The antenna 14 B/D issue certainly looks like it may be hardware
> related.  If the phases in both IFs jump the same, is the magnitude
> identical from band to band?  What bands did you see this effect in and
> was X-band doing this also?
>
> Rob
>
> Rick Perley wrote:
>>     I reported yesterday on phase changes seen on two EVLA antennas
>> during the 'modcomp-free' tests last Friday.
>>
>>     To Recap:
>>
>>     14B and D showed two alternating phase states, separated by about 40
>> degrees.
>>     24, all IFs, showed multiple phase states.
>>
>>     For both antennas, phases are stable within any phase state.  The
>> transitions are abrupt, but always are such that an intermediate phase,
>> exactly halfway between the two, is seen.  Hence, the cause must be
>> linked to the fundamental integration time -- 0.417 seconds.
>>
>>     Vivek reported that likelihood that antenna 24's behavior was likely
>> due to a misbehaving RT phase.  Ken disabled this meter.
>>
>>     Data taken today, with Modcomps in control, show:
>>
>>     Antenna 24 now has stable phase.
>>
>>     Antenna 14, IFs B and D are behaving as reported above.
>>
>>     Upon review, the following additional characteristics are seen on 14
>> B and 14 D:
>>
>>     The transition always takes place following a 10-second 'tic'.  The
>> duration of the alternate phase is always 10.0, or in rare
>> circumstances, 20.0 seconds.  The two IFs always jump together, by equal
>> amounts.
>>
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