[evlatests] Broken/Malfunctioning Switched Power -- A summary

[Rick Perley]

Answers, below:

Michael Rupen wrote:
>>    1) Global problem:  ea17 in LCP was providing extremely noisy data.
>> The PDif values vary over a ratio of nearly 2:1 at all bands, and in
>> both IFs B and D.  The same variations are seen in PSum, but they are
>> proportionally much smaller -- so the derived Tsys also varies by nearly
>> a factor of two.  The character of the variations is pure noise -- there
>> is no trend on any timescale.
>
>
> I assume this is NOT present in the visibilities?

    You assume correctly. 
>
>
>>    2) Band-dependent problems:
>>
>>    a)  ea28 in LCP at L-band.  The system works well for about half the
>> time.  For the other half, the values are many times higher, with
>> enormous variations in power.  The system stays in each state for
>> typically an hour or two, then reverts to the other state.  *** This
>> situation has never changed since the switched power system was
>> installed on this antenna***.
>
> Again, I assume this is NOT present in the visibilities?
>
    Again, correctly. 
>
> Have you played any games with applying the switched power from one
> subband to another?  This might help avoid the RFI problems you
> mention.  Or does out-of-band RFI affect *all* subbands equally? (which
> would be surprising)
>
    This is my standard procedure, and works well.  There is a scale 
offset in the visibilities, but that is a small price to pay for getting 
reliable gain correction.  We need to investigate the WIDAR option of 
placement of the non-correlating subband into a 'safe' RFI zone.  This 
is a major issue for L and S bands, especially for those experiments 
which are not utilizing 'wide-band' mode. 


>              -- Michael