[evlatests] New RFI in Antenna 14!

[Jim Jackson]

We are waiting on new nut plates for these covers.  The old ones were 
too thin and kept stripping out.  Jim Ruff is working on it.  At 
least one of the covers is also out for chromate plating.

Jim


At 12:30 PM 8/31/2007, Dan Mertely wrote:
>The network LAN stuff in that enclosure is quite noisy,
>although I haven't tested it to the freq resolution you mention.
>My test of last spring found significant spikes all the
>way into X-band, with various spacings--commonly 6 & 12 MHz.
>We used an RBW of 100 KHz, and 800 points in 1000 MHz.
>
>I have attached the 1-2 GHz plot, and a 1.4 - 1.45 GHz
>close-up.  The plots were labeled as "IP Phone LAN System", but the
>LAN switches are the same ones used for all antenna LAN
>communications.
>
>The detrimental threshold line on these 2 plots was plotted
>for the use of these LAN switch boxes as if used in the vertex
>room without shielding, so I appears that only a reasonable
>amount of shielding (20 - 30 dB) will drop the emissions
>below the detrimental threshold.  The digital hash continues
>beyond 5 GHz, and is especially dense between 3 and 3.5 GHz.
>
>Clearly, we should be buttoning-up all these enclosures when
>the LAN stuff is not being worked on, but then, we all already
>knew that, didn't we?
>
>-Mert
>
>
>Rick Perley wrote:
>>     I ran a 12-hour RFI check of antenna 14 last night 
>> (Wednesday/Thursday), using the 'FFT Spectral Scanner' of Mike's 
>> and Walter's.  The goal was to monitor the DME spectrum, to see if 
>> (as anticipated) the 1.05 -- 1.15 GHz spectrum opens up late at night.
>>     8192-channel spectra (resolution of 250 kHz) spectra were 
>> taken every minute.  The results show a remarkable comb on RFI, 
>> *** which was not present in that antenna a few months ago ***:
>>     There is a comb of strong, steady interfering tones, with 
>> spacing 62.5 MHz, starting at 1000.0 MHz, and extending all the 
>> way to 1940 MHz.
>>     I was in that antenna today (as part of a tour), and noted -- 
>> with some surprise -- that the cover plate of the utility box was 
>> not attached!  I suspect that the comb I saw (plus a lot of other 
>> steady RFI in the spectrum) was emanating out of that gaping hole, 
>> from the considerable digital stuff located within.
>>     Is this spectrum of RFI expected from the hardware within?
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>
>
>
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