[evlatests] total power measurements and antenna 16

[Robert Hayward]

According to Mert's Voltage vs. Temperature spreadsheet, 5.51V is about 
11K, so the receiver seems to be nice and cold.

-Bob


Ken Sowinski wrote:
> I was at the VLA today to take care of a Modcomp problem and
> took advantage of that to measure the deflection in TP due
> to 3C273 for the two EVLA antennas at all bands.
> 
> General comments.  I turned off the backend ALC at the T5 and
> tried to measure TP on and off 3C273.  Except at K band the
> deflections were large and it was easy to get a five to ten
> percent result.  14 did not seem to be very stable at X band.
> In general 14D was behaving funny: I can easily see the sudden
> jumps that Rick and Bob reported seing at the downconverter
> output.  The SD voltage is still negative for antenna 16.  The
> ACU in antenna 14 behaved impeccably.
> 
> I express the deflection as (on-off)/off averaged over IFs and
> in some cases over two trials; the error is an eyeball RMS of
> the deflection estimated from the variation amon IFs.  No idea
> why the result is so large for L band.
> Antenna    14                 16
> L   0.39  +/- 0.04      0.31  +/- 0.06
> C   0.11  +/- 0.003     0.026 +/- 0.002
> X   0.082 +/- 0.07      0.10  +/- 0.003
> K   too unreliable to report
> 
> This is consistent with my report of interferometrically derived G/T 
> for antenna 16 at all bands on Sept 20.  At that time C band was 
> about 1/4th as good as X band.  I leave it to someone else to look
> up the flux of 3C273 and say what these numbers mean in an absolute
> sense.
> 
> This rules out LO purity and alisasing to explain the poor performance
> at C band.  The only likely suspects are pointing, antenna optics, and
> system temperature.  If we were pointed at a sidelobe power would be down
> by at least 10 dB; we only see about 6 dB compared to X band.  An optics
> problem would probably be seen in beam cuts; we should try this next week.
> Unlike the other receivers the C band cryo temperatures are not monitored
> There is a readout on the side of the receiver which I am told indicates
> cryo temperature.  I am told that it has been reading 5.51 lately, but
> I have no idea what that means.
> 
> The two things to do next week are to measure system temperature and
> try beam cuts.  We have enough test time that it should be easy to find
> time for the latter.
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