[evlatests] P-Band Characteristics, (cont.)

[Rick Perley]

    Ken observed in P-band again, this time with a subband width of 64 
MHz, with 1 MHz channel separation, 2 IFpairs set to the same frequency 
(center of 320 MHz), and full polarization.  He observed 3C84 for a few 
minutes -- (not the best choice, the source has a large halo which is 
spectacularly visible to D configuration).    27 antennas were in the 
array, and gave correlator data. 

    Essential results are:

    1) 13 antennas fringe, more or less:  2, 8, 11, 13, 15, 17, 18, 19, 
21, 23, 25, 26 and 28.  Antenna 15 in RCP (IFs A and B) is weak by -10 
dB in power, antenna 28 in IF 'B' is also weak by the same factor.  All 
others antennas/IFs fringed at about the same amplitude. 

    2) Delays are fairly large, up to 50 nsec. 

    3) Bandpasses look surprisingly good, showing that (as advertised) 
the -3dB response runs from 300 to 340 MHz, and the -10dB response from 
about 295 to 345 MHz.   Unsurprisingly, there is quite a lot of 
'frequency structure' in the individual bandpasses, doubtless due to 
visibility changes, solar emission, and whatever else there is out there 
which is beating with the astronomical signal. 

    4) There are only two identifiable sources of man-made RFI: 
         a) A very strong signal at 300 MHz, which was on for a short 
period of time (perhaps 20 seconds, at most). 
         b) A weak signal at 333 MHz -- I think this is from the Abq. 
airport. 
       Note that with 1 MHz channelwidth, our sensitivity to RFI is 
rather low.  Should we repeat this observation with appropriately narrow 
widths, we'll doubtless see a lot more 'stuff'. 

    5) Phase stability looked fine, except on antenna 13 which changed 
slowly and continously throughout, by many tens of degrees.  This cannot 
be ionosphere, since no other antennas showed anything like this.