[evlatests] 'Holography' phase jumps, continued.

[Jim Jackson]

Just a note - the last L302 with old DDS and MIB firmware (Ant 14BD) was 
changed out yesterday. As of this point all of the 10 second phase jump 
issues associated with L302 DDS firmware should (theoretically) be gone.

The only issue still remaining should be the timing problem we've been 
correcting by changing the length of the 128MHz cable to the module. I 
haven't heard any comments about this recently - has anyone noticed 
symptoms of this on any L302's?

Jim

At 04:57 PM 10/24/2006, Rick Perley wrote:
>     The dataset referenced in the previous message shows interesting
>phase behavior.
>
>     The three BW/Fluke setups were:
>
>     BW = 50, Flukes = 100, 200.
>
>     BW = 25, Flukes = 112.5, 212.5
>
>     BW = 12.5, Flukes = 118.75, 218.75.
>
>     The results for phase stability are:
>
>     1) For BW = 50, there were no phase jumps of any kind.
>
>     2) For BW = 25, there was a single *global* phase jump, affecting
>all EVLA antennas (using a VLA antenna as reference), and all IFs
>equally.  The jump was 125 degrees for all IFs.  The jumps was
>effectively instantaneous -- duration less than 0.4 seconds.
>
>     3) For BW = 12.5, we had three *global* phase jumps, affecting all
>EVLA antennas equally in all IFs.  But in this case, the jumps were all
>by *precisely* 180 degrees.   Again, all jumps were effectively
>instantaneous -- much shorter than the 0.417 second integration time.
>
>     It is noteworthy that there were *no* 10-second style phase jumps,
>that plagued us last summer.
>
>     There is no way to tell from these data whether the jumps were in
>the VLA, or the EVLA.
>
>     Question:  Can we do holography yet with an EVLA reference antenna?
>If we have only these global jumps, I can proceed with holography, using
>an EVLA reference.
>
>
>_______________________________________________
>evlatests mailing list
>evlatests at listmgr.cv.nrao.edu
>http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests