[evlatests] EVLA tests, Aug 8, 2005

[Jim Jackson]

I'm taking the IF-A DTS module and a new L302 out to antenna 16 
tomorrow.  Unfortunately the new L305 is not working yet so I can't take 
that out.

 From your comments on timing, it sounds like the 19.2 Hz may be 
inverted.  I'm not sure if it's been that way all along or just happened 
last week.  That's the only hardware explanation I can think of that would 
result in things happening in the middle of the waveguide cycle while the 
9.6Hz switched power is correctly synchronized.

For an easy test, I think I can send the L305 19.2Hz optical signal back by 
simply substituting it for the optical 9.6Hz feeding the noise diodes.  In 
the control building I should be able to see that 19.2 Hz out of the T5 and 
verify it is correctly lined up with the master 19.2Hz.  Once I determine 
that, I can compare it to the differential timing signals in the antenna to 
see if we have any of them connected in their inverted state.

Jim

At 05:20 PM 8/8/2005, Ken Sowinski wrote:
>                        EVLA Tests, August 8 2005
>
>It has been a week since we tried anything semi-serious so the goal
>today was to see what state antenna 16 is in now.  When I began the
>day last week IF C was the only broken IF; today IF C was the only
>working IF.
>
>L302-2 did not lock at any of the bands tried.  Jim proposed to take
>up a replacement module on Tuesday.  IF A did not work because there
>is no DTS module.
>
>That leaves IFC.  I was able to make it work at L and C bands, but not
>at X band.  Delays were far off because IF C was not working last time
>delays were adjusted.  I fixed that and looked at the phase switching
>problem which had not magically fixed itself since last week.
>
>The phase in IF C was stable at L and X band.  It is conceivable
>that it was winding so fast at X band that the antenna looked
>incoherent.  That is supported by the large RMS seen on D10 while
>looking for X band fringes.
>
>The fact that phase switching does not work suggests a timing error.
>The intent today was to try to estimate that timing error.  Phase
>switching was turned off at the correlator, a simple square wave
>pattern (seed=32; 32 on, 32 off) was used in the L302 and the
>integration time was set to 8 WG cycles allowing 4 integrations in
>each state.  If timing were correct we would see a pattern that is
>eight records long, 4 with direct phase and 4 with the phase offset
>by 180 degrees; all of the same amplitude.  What was seen was that
>the first record of each phase state had the amplitude degraded by
>about 1/8th.  I offset the timing by one WG cycle (to -(32sec + 1 WG
>cycle) and the degraded record changed to the last record of each
>phase state and again by about 1/8th.  This behavior suggests that
>the phase switching events are occurring in the middle of a WG cycle.
>The 12.5 per cent amplitude reduction is consistent with a shift of
>half a WG cycle when the integration time is eight WG cycles.
>
>offset    ampl   ampl at phase transition
>======    ====   ========================
>-32+1WGC  .24      .15
>-32       .24      .21
>-32-1WGC  .24      .21
>-32-2WGC  .24      .15
>
>Either we have something very subtle wrong in the L302 or the phase
>offsets are being strobed into the DDS in the middle of a WG cycle.
>If there really is something wrong it is hard to see how it would
>I asked the L305 to resynchronize and that did not help (or hurt)
>matters.
>
>
>It seemed to me that the T304 power level setting command is not working
>right.  I discussed this with Pete and he demonstrated that the MIB does
>the right thing when commanded by hand.  I was able to demonstrate that
>the executor sets the target correctly, at least at X band.  Is it possible
>that it does not work at other bands, or that the target command arrives
>before power levels have stablilized after a band switch?
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