[evlatests] Curiosity in PDif and PSum at S-band

[Rick Perley]

    I continue to exercise the PDif/PSum data...

    At S-band, I have noted on some antennas/IFs, a perfectly regular 
'pulsation' in the PSum and PDif values.  Two notable exceptions are 
attached showing the PSum and PDif values for both polarizations for two 
antennas, 7 and 23.  (These are postscript files.  In each are two 
plots, the first showing PSsum for (top) RCP and (bottom) LCP.  The 
second shows PDif for the same two polarizations.  ea23 shows the effect 
more clearly ...
   
    In words:

    A very few antennas are showing a 5-second period 'pulse' in the 
PSum values.   Once every 5 seconds, the 'PSum' value jumps upwards by a 
small, but easily measureable value.  On the PDif values, we see a 
similar effect, *except that* the PDif difference is itself sinusoidally 
modulated on a period of about 1 minute!  (You have to see the plots!). 

    This is absolutely not external interference.  The affected 
antenna-IFs are:  7A, 26A, 23C, and (weakly) 21B.  The 'AC' frequencies 
are centered at 2550 MHz (BW = 128 MHz), the BDs at 3520 MHz.  The fact 
that the perturbations are different between PSum and PDif tells us that 
this is not a gain effect. 

    Any idea of what is happening here?


-------------- next part --------------
A non-text attachment was scrubbed...
Name: 7A-S
Type: application/postscript
Size: 65045 bytes
Desc: not available
URL: <http://listmgr.nrao.edu/pipermail/evlatests/attachments/20111110/517505b8/attachment.ai>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 23C-S
Type: application/postscript
Size: 64350 bytes
Desc: not available
URL: <http://listmgr.nrao.edu/pipermail/evlatests/attachments/20111110/517505b8/attachment-0001.ai>