[evlatests] Phases on antennas 14 and 24

[Rick Perley]

    Certainly worth the change. 

    To answer Rob's questions:  The jumps are the same on both IFs, and 
they occur at every band tested (L, C, and X). 

    Rick

BTW -- my statement about the jumps occuring exactly on 10-second ticks 
was not correct.  The L-band data taken Friday showed the jumps 
occurring 'on the 5's -- i.e., at 15, 25, 35, 45, ... seconds.  All the 
rest of the information remains correct. 


Jim Jackson wrote:
> 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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>
>