[evlatests] Huge RFI in Ku-band

[Rick Perley]

     We got more holography data at Ku band last night -- I looked for 
these birdies.

     I found two:

     1) The strongest by far was on ea06:  155600 MHz. Interestingly, it 
rose by 6 MHz between the beginning and end of the run (3.5 hour span in 
the evening).   This is strong enough that it is seen in cross-power on 
all the nearby antennas.

     2) A much weaker birdie on ea01, at 15412 MHz.

     3) The previously-reported birdie on ea16 was not seen in 
cross-power in this run, but is visible in autocorrelations.



On 03/22/2017 03:04 PM, Dan Mertely wrote:
> Hi Rick.  Kleid & I went out to each of the 3 antennas today
> to search for the source.  We found a very strong bi-stable
> source on ea06 which was coming from the Low Band Receiver (LBR).
> We could not find any Ku band RFI for ea01 or ea16.
>
> The Details:
> Following the same technique as we did to find the source of
> the 15.5 GHz Ku band RFI reported a month ago on ea19, we set
> the 3 antennas up for Ku band & starting with ea16, connected
> a spectrum analyzer to the receiver LCP output to search for
> the RFI.  We made sure that the Low Band Receiver (the source
> of the February "15.5 GHz" RFI) was cal switching, since that
> RFI source was tracked-down by the FE Group to  the LBR noise
> source.
>
> After verifying excess noise (to insure we were seeing the Ku
> bandpass), we searched for the reported 15450 MHz CW by
> sweeping from:
> 14-16 GHz with 1 KHz RBW (noise floor -110 dBm): no detections.
> 15.4-15.6 GHz with 100 Hz RBW (noise floor -120 dBm): no detections.
> 15.2-15.4 GHz with 100 Hz RBW (noise floor -120 dBm): no detections.
> We tried peak hold, 10 sweep averaging (to beat down the noise),
> fast, narrow sweeps, slow, wide sweeps, and both polarizations ...
> no detections.
>
> We also swept the full 12-18 GHz bandpass (although at 100 KHz RBW
> in order to reduce the sweep time ... no detections.
>
> We ran similar sweeps on ea01... no detections.
>
> ea06 was found to have a strong RFI signal (40 dB SNR!), which
> rapidly changed frequency from 15555 to 15556 MHz.  When we turned-
> off the LBR the signal went away, when we turned the power to the
> LBR back on, the signal re-appeared, still bi-stable in frequency,
> but at a slightly higher frequency, slowly drifting back down to
> the original 2 frequencies.
>
> Either the RFI is intermittent on ea16 & ea01, or they were picking
> up the signal from ea06 during Rick's test.  But if so, why not other
> closer antennas as well?
> -Mert
>
>
> On 3/16/2017 9:24 AM, Rick Perley wrote:
>>     A holography test was done last night, using Ku-band.
>>
>>     Three enormous RFI spikes have been found:
>>
>>     on ea01, at 15418 MHz. (Maint form C139733)
>>
>>     on ea06, at 15566 MHz. (Maint form C139734)
>>
>>     on ea16 at  15450 MHz. (Maint form C139735)
>>
>>     All appear to be CW.  None is a multiple of 128 MHz.  All appear to
>> be on during the whole of the run.
>>
>>     What's going on?
>>
>>
>>     Rick
>>
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