[evlatests] Two Remarkable Characteristics

[Dan Mertely]

Hi Rick.  I think you were on the right track on considering
RFI to be the culprit.  If you notice from the attached
Google Earth plot, all the antennas mentioned as having
serious problems are toward the center of the east and
west arms.  As you noted, the Mangus Mtn to Gray Hill
C-band links are at 6123.100 & 6152.750 MHz, 30 MHz wide
each.  The path of the link runs directly over the middle
of the east and west arms (see map, wide yellow line).

Note that there are now 2, bi-directional links between
Gray Hill & Mangus Mtn at C-band.  You were seeing the
lower frequency, Mangus to Gray Hill links.  The Gray Hill
to Mangus side of the link is at 6375.140 & 6404.790 MHz,
which is above your highest frequency of observation (this
time!).

(And no, I've had no success with WNMT in getting these
links moved.  Instead, they've added the 2nd link pair
just this year.  Sigh!)

-Mert


Rick Perley wrote:
>     I've been reducing some 'ECSO' data, taken in July and August.  
> There were three runs, each of about 4 hours long, at C-band.  No 
> frequency or band retunings.  We observed in 'extended OSRO' mode, 16 
> adjacent subbands, extending from 4.2 through 6.25 GHz. 
>     In general, the data were outstanding!  Calibration and imaging are 
> completed, and we reached the thermal noise. 
>    
>     But in the course of the calibration, two curious characteristics 
> were found, one good, and on bad. 
> 
>     1) Good 
> 
>     We are all familiar with the 'subband 0' rolloff, of still 
> mysterious origin (although I understand there's a good chance this 
> originates in the station board?) 
>     In determining the bandpass, I reviewed the bandpass solutions.  The 
> 'rolloff' is completely absent in two antennas -- ea19 and ea21, on IF 
> 'B' only!  Subband '0', on those two antennas on that IF is beautifully 
> sharp and flat, except for the sharp drop due to the anti-aliasing filter. 
>     A number of other antennas show a dramatically smaller 'rolloff' on 
> various IFs -- but none are flat like ea19 and ea21 on IF 'B'.  This 
> bandpass was identical on all three runs. 
>     Keith has been informed, and reviewed the T304 data for those 
> antennas -- nothing unusual.  It's gotta have something to do with the 
> station board.  (Can we make all the others like these two?)
> 
>     2) Bad
> 
>     The antenna stabilities were all very good ('good' defined as +/- 5% 
> or so) in all subbands *except* one -- subband 16 showed huge (up to 
> factors of 2) variations in fringe amplitude on timescales of minutes, 
> in all four IFs, **** on some antennas only****.  The bad antennas were 
> the same in all three runs (which were distributed over more than a 
> month in time):  2, 7, 11, 14, 15, 17, 18, 19.  Some others were less 
> variable, but still well outside the norm:  27 and 28.  All other 
> antennas were as 'good as gold'. 
>     There is no spatial relations of the listed antennas.  They behaved 
> correctly in all other subbands. 
>     Now, subband 16 does contain moderate RFI -- in the lower 64 MHz:  
> 6100 to 6165 MHz.  But it's hard to see how this could cause such 
> instability in some antennas, but not in others... 
> 
>    
> _______________________________________________
> evlatests mailing list
> evlatests at listmgr.cv.nrao.edu
> http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Mangus2GrayHill.pdf
Type: application/pdf
Size: 236124 bytes
Desc: not available
URL: <http://listmgr.nrao.edu/pipermail/evlatests/attachments/20110826/b863924a/attachment.pdf>