[evlatests] 4band, interference and ea14

[Gregory Taylor]

Hi Frazer,

     The emission at 55.25 MHz is the video carrier for TV channel 2.
We see this quite strongly with LWA1. At 60 MHz we see a moderately
strong source to the North of LWA1 (see plot).  We might be seeing a VLA
antenna.  The extended source in the  NE is from power-lines.  They are better
following some mitigation earlier this month, but still obvious.
Ciao,
                             - Greg


[cid:50266521-6F65-4B8D-9860-0749349F0653 at phys.unm.edu]

On Jun 23, 2014, at 9:40 AM, Frazer Owen <fowen at nrao.edu<mailto:fowen at nrao.edu>>
 wrote:


    We made a successful test of the the new 4band MJP dipoles using
antennas 12, 14, and 19. 14 is important for interference tests because
it has the new ACU.  The autocorrelations on 12 and 19 show the 5MHz
clock comb that is thought to come from the old ACU. 60 MHz is
particularly strong and variable for test to test. The autocorrelations
for antenna 14 do not show the 5MHz comb. This seems to confirm that
that the 5 MHz comb is from the old ACU

     Antenna 14 also does not show interference at 64MHz, which I
understood was a possible frequency from the new ACU. It does show a
fairly strong spike at 55.25, much stronger than any else in the 54-86
MHz band. The very narrow spike is clearly different from the 55MHz
spike on 12 and 19, which is part of the 5MHz comb. 12 and 19 don't show
a spike at 55.25.

    Interestingly the 5MHz comb frequencies correlate on baselines to
14 (as they do on 12-19). Since the 5MHz clock is supposed to be
incoherent from antenna to antenna, there must be a general source of
the comb frequencies, especially 60MHz, which is being broadcast around
the site. Could this be one very bad antenna ?

---Frazer
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