Re: KFS reception quality - IMD and other (internal?) noise sources...


Rob Robinett
 

I have just returned from 5 hours at KFS and have time for only a brief report:

1) I removed the Nooelec AMB BF and 6/9 dB pads which were between the Qbit LNA outputs and the Kiwi RF inputs.  
    There are 2 Mhz HPF out at the antennas and I have muted the whole of the AM band, so no user can tune there on a Kiwi.  
    So the Omni Kiwis have additional 6 dB gain and the others an additional 9 dB gain.  I will monitor WD's overload log to verify those changes don't result in significant overload events.
2) I confirmed that the NW feed from the primary multicoupler is suffering from severe AM IMD in the 2-4 Mhz region, so this IMB is generated in that multicoupler or more likely by the LNA out at the antenna
    Omni A and B also show that IMD but to much lesser extent.  Fixing these will require help from ARINC
3) Thanks to Glenn's AA and the tinySA, I tracked down the source of the every 40 Khz switcher RFI:  it is a vertically polarized signal generated at the cell phone equipment shed at the base of the cell phone tower shared with the NW antenna.  Again, ARINC is going to have to get  that fixed if they care about it.  That same RFI can be heard on the Omni which is the other antenna closest to the cell phone shed (about 100M away).  The SE and SW antennas are about 200+M away from that shed and so that RFI is barely noticable on those antennas.
4)  I see other switcher RFIs, so I'm sure there are many other bugs to squash, but the signals we see on the Kiwis are pretty much what the portable Kiwi sees when connected to the primary multicouplers.  So all indications are the problems are outside the building. 
4) Glen''s AA + the portable Kiwi showed a very clean spectrum when I got 300M away from the cell shed and main building.  There is very good wifi coverage out in the fields, so I think deploying a solar powered AA + Kiwi as far as possible (e.g 400M)  from the cell shed would result in a very clean full spectrum.

I now understand the location of all the antennas and can see why the NW and Omni will always be impaired by the cell shed.

Rob


On Thu, Jun 10, 2021 at 12:33 PM ON5KQ <ON5KQ@...> wrote:
In the meantime, I must correct my report from above. There are indeed also during the night severe man-made noise sources, which I believe are produced somewhere in the signal distribution system.,,,,more detailed reports I have sent to Rob, to help to find a solution and support kfs...



--
Rob Robinett
AI6VN
mobile: +1 650 218 8896

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