RFI from 3-8 MHz

On kiwisdr.w1euj.com, I've got this blanket of pulsing noise over these frequencies. I'm looking for the most effective ways to figure out the source.

Location: KiwiSDR setup is located in the barn, which is 100 feet from the house (buried power line to it) and 200 feet from the house and horse barn on the adjacent properties. This is the only thing in the barn that is powered.

Kiwi: The Kiwi is in a metal trashcan, with the power, Ethernet and antenna cables running out the rim. The antenna input has a Mini-Circuits SMA LPF for 30 MHz.

Antenna: A large wire Vertical Delta loop in the trees behind the barn (about 30 feet away) with 50 foot apex, feedpoint at the bottom corner. 4:1 balun at the feedpoint, running to LMR style cable along the ground for 30 feet to the entry point on the barn. Runs through a grounded Polyphaser arrestor, then the wall, then inside for 5 feet to an Array Solutions reciever protector, then 1 foot of cable to the inside of the trashcan.

Power: A linear power supply (2-prong AC connection and inside a plastic box), with the DC lines then wrapped (10 turns) on a large ferrite ring before then running a very short distance into the trashcan.

Ethernet: This is unique. I an running a pair of Ubiquiti Bullet M5 radios to link the barn to the house. They are connected to small yagi antennas mounted on the corner of the barn closest to the house - about 20 feet away from the Kiwi and connected to it via the CAT6 cable. The Bullet in the barn is powered from a linear power supply. Both the power and Ethernet lines are wrapped through several ferrite rings. 


  • Please post a picture with spectrum at a couple zoom levels.
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  • edited January 10
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  • In AM, it sounds like a higher pitched version of driving over rumble strips.
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  • Hi

    Remember that the Ubiquiti Bullet M5 have a buildin switchmode psu :-)


  • I have to think that the quickest experiment is to shut down the house for a moment, bring my IC-706 on a battery and see what 40 meters (the worst affected band) sounds like. If its the same then sucks to be me. If not then I've got some chance to locate and fix the issue.

  • Hi,

    We used some Ubiquiti kit at another WEB SDR site some time ago and had similar problems.

    From memory the Ubiquiti is powered over the Ethernet cable via a PoE adaptor. It does use internal DC-DC switching convertors, but they were fairly well screened.

    I think both the head unit and PoE adaptor had got RJ45 sockets with a metal screen connection. So you can use foil screened CAT5 cable if you are not already doing so. If not, try swapping over to it so that there is an electrical bond between the Head unit and PoE adaptor.

    The next problem was that the PoE adaptor didn't have a separate ground connection, so if your PSU is 'floating' (no third pin on the mains connector or no connection between the DC connector and a mains ground) there is no electrical bond between the PoE adaptor and ground. 

    It may be worth trying an electrical bond between the Ubiquiti kit and the antenna ground on your KiWi. This may (or may not) improve things so you may need to experiment a bit to get the best results.

    Ferrite chokes can work well, but they do need to be optimised for the frequency range in use. The type of ferrite and number of turns makes a huge difference to the level of performance you may be able to obtain.  Steve G3TXQ has a good guide to this on his website - http://www.karinya.net/g3txq/chokes/


    Martin - G8JNJ

  • I took a screenshot starting around 200 kHz (see below). The interrupted carriers spaced about 7 kHz apart look very similar to ones shown in the last image of the thread where someone had RFI from using Ethernet-over-powerline: http://valentfx.com/vanilla/discussion/902/dealing-with-excessive-noise-solved-ethernet-over-power-caused-noise#latest

    The RFI with the horizontal streaks sort of looks like what this guy had with a bad streetlight: http://valentfx.com/vanilla/discussion/951/wideband-pulsing-noise-noise-blanker-absence-i-m-in-trouble-nb-added-in-v1-152#latest

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  • Thanks for the feedback. I've been running the Bullet POE using a lab power supply - I noticed a lot of issues with the noise with the original POE injector.

    I'm going to run a long cable out to the barn to eliminate the Bullets and see what changes.
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