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spurious emissions from kiwisdr on 144,010

i notice strong emissions on multiple frequencies from the kiwisdr or the attached beglebone green. The emissions are realy strong.
The most anoying frequency is in the 2m ham Band on 144,010. Has anyone else noticed this?

Best regards
Robert, db1jj


  • @rjschneider, dumb question, but how are you receiving anything at 144 MHz when the KiwiSDR is a 0-30 MHz receiver?  Even with harmonics, I don't see how anything from the 2m band could 'get in' to the 0-30 MHz of usable bandwidth.  

    Could you post screenshots?
  • i receive this emmissions not with the kiwisdr. I never said this.  I receive them with other equipment, for example a airspy, or with my icom R7000 receiver. I can post a screenshot later
  • We've had a couple reports of this issue. But it is difficult because it's not necessarily a simple problem with the Kiwi but rather a more complex systems problem with cabling conduction and re-radiation issues.

    Your Kiwi might use a coax antenna cable that goes up to the roof near your other V/UHF antennas. The Kiwi cable might even travel in the same bundle of cables or at least parallel to the cables of your other antennas. Digital noise from the Kiwi or your Ethernet-based network can easily be conducted along the cables unless they are decoupled or proper grounding is in place. A perfect example of this is the Kiwi self-interference observed when an E-field probe (Mini-whip) fed with coax is used (there was just a thread about this topic). The digital noise rides up the other braid of the coax and is received by the Mini-whip.

    It would be very interesting to know how the 2m interference differs when changes are made to the Kiwi cabling and operation of the server software. First, try logging into the Beagle and typing "cdp" and "mst" to stop the Kiwi server from running. Does the interference decrease? Then it is related to the network traffic on the Ethernet or level of digital activity on the Kiwi FPGA or Beagle. Does it decrease then the Ethernet cable is disconnected? Then it is likely noise being coupled into the Kiwi system from your network in general: add toroid decoupling to the Ethernet cable attaching to the Kiwi.

    How does the interference change when the Kiwi antenna (and/or GPS antenna) is removed? This would tell you if Kiwi noise is being coupled into the power supply or Ethernet cables and re-radiated.

    How is the Kiwi grounded? Does your 5V power supply to the Kiwi provide a ground path to the power mains ground pin? If you also then ground to another source like an external ground rod or ground at another location then you are creating a huge ground loop that can cause re-radiation problems.

  • I tried several things.
    1. I added a clip-on-ferrite and some ferrite cores to the 5 V power cord. 
    2. I added a common mode choke  to the ethernet cable
    3. I disconnected the gps
    4. I disconnected the Antenna
    I opened a client session with Firefox on the kiwisdr. On my Airspy with sdr-console (first screenshot)
    Then i close Firefox. after about 30 to 60 sec the noisespectrum changes. (second screenshot)
    Then i log in the thw kiwisdr via ssh and enter cdp and then mst (you see the effect of cdp and mst on the third screenshot

    In a last try i started the kiwisdr, with only ethernet and power connected. opened one client via Firefox and then removed the ethernet cable. And even then with no possible ground loop ( becaus kiwisdrs only connection is power), i get the noise peak. (last screenshot, you see when i unplugged ethernet)

  • jksjks
    edited December 2016
    Are you saying with only a decoupled 5V power cable to the Kiwi you get the 2m noise? (no other BB/Kiwi cables attached). Is this with the Kiwi server stopped?

    If so, there is a test I'd like you to do. It's a pain but if you could remove the Kiwi board and run the Beagle alone with only power connected I'd like to know the result. Be very careful when removing the Kiwi board gently rock the Kiwi board along its long length a little at a time unit the spring tension of the Beagle headers releases. If you bend the Kiwi board too much the ball joints of the FPGA will break and then all is lost.

    When re-attaching the Kiwi board be absolutely certain to put pin #1 of the Kiwi pins at the far end of the Beagle header. If you're off by one pin the wrong voltages will be applied and the FPGA will be destroyed. Look here if there are any questions:

  • This is a list of all integer sub-multiples of 144.010 MHz and the known direct and derived clocks of the Beagle and Kiwi.
    So it looks like 3x the USB or SPI clocks could be near 144.010 or 6x the Beagle CPU main clock of 24 MHz. These are only some possibilities of course.

    sub-multiple MHz
    source, continuous unless otherwise noted

    BB derived: HDMI?
    1 144.010

    BB derived: Ethernet
    2 72.005000

    Kiwi oscillator: ADC/FPGA
    3 48.003333

    BB derived: USB

    Kiwi/BB derived: SPI clock (only when SPI active)
    4 36.002500

    5 28.802000

    BB crystal: Ethernet PHY

    BB crystal: HDMI, should be disabled
    6 24.001667

    BB crystal: CPU clock
    7 20.572857

    8 18.001250

    Kiwi oscillator: GPS clock
    9 16.001111

    10 14.401000

    11 13.091818

    12 12.000833

    13 11.077692

    14 10.286429

    15 9.600667

    16 9.000625

    17 8.471176

    18 8.000556

    19 7.579474

    20 7.200500

    21 6.857619

    22 6.545909

    23 6.261304

    24 6.000417

    25 5.760400

    26 5.538846

    27 5.333704

    28 5.143214

    29 4.965862

    30 4.800333

    31 4.645484

    32 4.500313

    33 4.363939

    34 4.235588

    35 4.114571

    36 4.000278

    37 3.892162

    38 3.789737

    39 3.692564

    40 3.600250

  • jksjks
    edited December 2016
    Sorry about the formatting of that last message. Not sure what happened.

    Anyway, I've had a third report now of strong 2m interference saying that it only happens when an Internet connection is made to the Kiwi.
    I'm beginning to wonder if the couple of centimeters of the 48 MHz SPI clock line that goes on the header between the Beagle and FPGA is a problem. That frequency can be changed with software, with some loss of performance. Also I think the strength of the drivers of the SPI signals can be lowered to decrease the slew rate and maybe attenuate any harmonics. I'll try some of these things out.

    I just bought a near-field antenna probe kit I can attach to my spectrum analyzer so I can go do some EMI hunting. It will take a little while to be delivered.

  • Yes i noticed that too, now as you say it. I bootet the kiwi up, and the interference got really strong at just the time i connected to kiwi the first time.
    I try this again later. If this is the case, does the BB standalone test make sense?
    I think the driver strenth and measurement with the near field probe is a good starting point.

    I also have a beaglebone black (the one with hdmi ) lying around. Perhaps it has something to do with the layout of the bb-green.

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