[evlatests] System Temperature, switched power

[Rick Perley]

    From the same 8-band test taken Monday evening, we review the system 
monitoring of power and temperature:

    1)  X-Band.  At this band, the monitor data (PDif, PSum) all behave 
well -- good evidence the synchronous mechanism is functioning as 
expected.  But we have high *claimed* system temperatures for antennas 
20, 21, 22 and 26, for which values of 80K or higher are claimed.  
('Claimed' is in quotes, because an incorrect value of Tcal will give an 
incorrect calculation of Tsys). 

    2) Ku-Band:  All seven equipped antennas give good values, typically 
20 to 25K in system temperature. 

    3) K-Band:  Something is amiss with antenna 13, in RCP only.  IFs A 
and B give no fringes, and no useful switched power, while LCP (IFs C 
and D) are both fine.  (This is a correction to the summary given last 
night, which claimed both polarizations were affected). 
           Tsys for antenna 11 is claimed to be about 150K.

    4) Ka-Band.  All is normal with Tsys, including the two antennas 
which gave no fringes (7 and 22).  Antenna 13 has no receiver. 

    5) Q-Band:  Antenna 13 behaves the same here as at K-band.  Antenna 
22, which gave no, or vanishingly weak fringes, provides good switched 
power.
       Antenna 17 is very special:  Tsys drops continuously and smoothly 
by a factor of nearly 50% (i.e., from 90 to 60K) through the 45 second 
observation, reaching a stable value about 5 seconds before the end of 
the scan.  This matches the behavior of the fringe power.  Although the 
Tsys profile looks like a primary beam, pointing cannot be the cause, as 
the antenna temperature provided by the source is nowhere near this.  
This behavior was identical on all three observations.  This behavior is 
seen *only* at this band. 

    6) C-band.  Many -- even most -- of the receivers are giving very 
large values for PSum and PDif -- typically a factor of 10 larger than 
other bands.  But this is a simple scale factor -- Tsys is normal.  Many 
abnormalities are seen:
           ea 14, LCP:  PDif is random about zero. 
           ea 19, LCP:  PDif oscillates between two values, a factor of 
1.5 apart. 
           ea 12, RCP:  Both PDif and PSum changed gains, midway through 
each of the three scans.  The ratio of the scale factor is about a 
factor of 100!  But no such effect was seen in the fringe power.  Tsys 
looks o.k. 
           ea 15: claimed Tsys is 250 in RCP, 1100 in LCP! 

    7) S-band:  Various problems:
           ea 06, RCP:  PDif (and hence Tsys) is oscillatory, about a 5 
second period, with 50% amplitude). 
           ea 12, both RCP and LCP:  PDif is all noise, centered at 
zero.  PSum o.k.  (acts like no switched power). 
           ea 07:  Claimed Tsys is 100K! 
           ea 27:  Tsys noisy in LCP only (but value is o.k.) -- this is 
due to very low PDif (less than 1 count). 

    8) L-band:  Various problems:
             ea 09, both polarizations:  PDif is all noise, zero mean.  
(like there's no switched power). 
             ea28, LCP only:  PDif very wild values, but not with zero 
mean.  Tsys values average out o.k., but are also very wild.  PSum looks 
o.k. 
             ea15, both polarizations:  Tsys above 100K.  This antenna 
is marked 'out for repair' -- clearly it's in place, but certainly 
deserves repair!  :)