[evlatests] Huge RFI in Ku-band

[Dan Mertely]

Hi Rick.  Kleid & I performed another Ku RFI search this
morning on ea16 & EA01.  Today we saw booming signals on
both antennas, both via the bandpass plotter (attached plot
for ea16), and with a spectrum analyzer at the FE outputs
in the Vertex Rooms.

By turning the Low Band Receiver (LBR) FE off/on, off/on, we
verified that the LBR was the source of the RFI on this
antenna as well.  That makes it 4 for 4:

ea19 a few weeks ago (already repaired),
ea06 (Verified last week to be LBR caused), and
ea01 & ea16 (Verified today to be LBR caused).

The FE group has supplied 2 clean LBR FE's to use as replacements,
but a sleet and rain storm has started here in the past 1/2
hour, preventing any apex work for now.
-Mert

On 3/23/2017 2:35 PM, Rick Perley wrote:
>     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
>>>
>>> _______________________________________________
>>> evlatests mailing list
>>> evlatests at listmgr.nrao.edu
>>> https://listmgr.nrao.edu/mailman/listinfo/evlatests
>>
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