[evlatests] 4band, interference and ea14

[Frazer Owen]

On 06/23/2014 02:35 PM, Gregory Taylor wrote:
> 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
     I had noticed the coincidence with 55.25 and channel 2. The problem 
is that we don't see that signal, at least anywhere near as strong, on 
the other two 4band antennas, just ea14. Unless ea14's location at E8 
allows it to see a channel 2 while the others are blocked, then I don't 
understand why we just see 55.25 on ea14. That signal is much stronger 
than anything else we see, including the other TV channels. For the 
other antennas channel 5 is by far the strongest of the clearly external 
signals.

     Not sure where 60 MHz is coming from. We should find out.
>
>
>
> 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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