[evlatests] Some low-band issues

[Barry Clark]

The P band receivers, unlike all the other bands, do not identify
themselves.  I have therefore been reluctant to put Tcals into the
database until the system stabilizes enough that receivers are no
longer getting swapped in or out, lest they do so without my
noticing.  Since P and 4 bands are sort of unified as the LowBand
system, the Tcals for those two receivers need to be entered as a
pair.  I don't think the system is stable enough now, but maybe
fairly soon.

There are some old Tcal values in the system, left over from the
old receivers, which I've not done anything about.

On 03/07/2013 03:33 PM, Rick Perley wrote:
>      Paul:
>
>      Thanks for the reply.
>
>      So, it seems that  ea01 and ea03 should show fringes, but don't.
> (In fact, ea01 was fringing, but the SNR was so low I had to leave it
> out when making a bandpass calibration).
>
>      Perhaps Ken or Barry can update the parameters database with the Cal
> values.
>
>      As for the F14s -- we'll try find out how to make sure these are on,
> when needed.
>
>      Rick
>
>
>
>
> Paul Harden wrote:
>>
>>
>> Rick Perley wrote:
>>   >      1) No astronomical signals came from ea03, ea08, ea26 or ea27
>> -- all
>>> of which are claimed (on the Coordination Meeting Summary) to have
>>> low-band receivers.
>>
>> The antennas WITHOUT low band receivers since 1 MAR are:
>> 07, 08, 10, 12, 14, 16, 21 and 27
>>
>> Low band receivers (LBR) will be installed in EA07 and 14 next week.
>> EA15 and 19 have known cable problems which should be repaired shortly.
>>
>> A map showing which antennas have and have not LBR receivers is at:
>> http://www.aoc.nrao.edu/~pharden/LBR/lbr.htm
>> I update this web page upon every low band installation.
>>
>>>      2) Zero-mean PDif values (or values so small they are not
>>> meaningful) were found in ea01, ea04, ea11, ea13, and ea25.   For all
>>> these, the PSum values look normal, so it appears the noise diode is
>>> not switching.
>>
>> No CAL switching is a continual complaint.  I have been to every LBR
>> antenna with a spectrum analyzer, where I can clearly see the CAL
>> switching on 74MHz, even without the dipoles.  TCAL on P-band is too
>> small to see.  The LBR gets the CAL switching signal from the old F14s
>> driving the old card cages.  In many cases upon entering the Vertex
>> Room, CAL switching on the F14s is turned off.  I don't know why they
>> are getting turned off.  Regardless, on a low-band run, have the VLA
>> operator issue the command that turns on the CAL switching to the
>> F14s.   It doesn't seem to be in whatever script you use.  Trust me -
>> it works when the CAL/SOLAR CAL command is sent to the F14s.
>>
>>>      3) Clearly incorrect system temperature values (typically, 10K)
>>> were derived on ea13, ea22, ea23, ea24, and ea28.  The reason is
>>> simple:  These antennas have not had their Tcal values entered into
>>> the database.  (For these, and for ea01, ea04, ea05 and ea25 the
>>> value is 1.0 -- the default. )
>>
>> On the above linked web page, there is a table showing all EVLA
>> antennas and those with receivers installed.  The Tcal values for both
>> 4- and P-bands on each installed receiver are also shown on that
>> table.  I can provide Trx and other hot/cold test data if you need.
>>
>> Paul Harden
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