[evlatests] Huge RFI in Ku-band

[Dan Mertely]

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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