Internet Junction Box Causing Serious RF Interference


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So after a couple years of running a CB radio base station in my house to chat with the locals, I've finally discovered the cause of some serious interference I've had on some channels.  It's weird because you can hear it on several frequencies spread out across the 11 meter CB band (27 Mhz) but the channels aren't necessarily next to each other.  For example I hear it on channel 4 (27.005 Mhz), but not 5 or 6, and the channels are only 10 khz apart.  I can hear it REALLY loud on channel 16 (27.155 Mhz).

 

I found the culprit by just turning up the volume on my radio and flipping to channel 16, then I started killing breakers in the house until the noise stopped.  After I found the breaker, I kicked it on and off slowly a few more times to make sure it wasn't just a coincidence.  Then I grabbed my hand-held radio and started walking around the kitchen (the breaker in question) trying to find where the noise was loudest.  The fridge wasn't running, the microwave wasn't going, the lights were all off, strangely enough it seemed to be emanating from the hood over the oven, but there was nothing turned on so I decided to keep looking for other sources.  I walked outside and the noise got much much louder, and as I held the radio up to the plastic internet/phone junction box next to the house, I realized that was the source of the noise.  All static disappeared and all I could hear was a sort of digital whine.  I went inside and started a file download running and went back outside and held the radio up and sure enough the occasional, almost rhythmic pop I heard in the midst of the whine before had turned into a roar of activity.  After stopping the download, the noise went back to a steady whine with only the occasional pop.  It's not my computer, because when I killed the noise by flipping breakers, the computer was running.

 

It's dark outside for now, but here's my idea, and I'm wondering if you guys have any other suggestions.  The box around the device is plastic, and has the lid bolted on.  My first idea is just to check the grounding rod and make sure it's properly grounded.  If that doesn't help, my 2nd idea was to call the phone company and see if I can get a metal box since, from what I understand, plastic is RF transparent, and metal should help contain it.  If they don't have any, I figured I could find or construct a large metal box to hang over top of the post that the device is on.  This isn't an end of the world situation because 99% of the people I actually talk to are on channels not affected, but it would be nice to rectify the issue.

 

You guys have any other suggestions?

 

Here's audio of the noise recorded from my base station in the house.  The coax is shielded, so most if not all of this interference is coming in through the antenna from about 50 feet away.  In the middle of the video I started a download for a few seconds and then stopped it, and you can hear how it just turns into a roar when internet activity picks up.

 

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How accessible is the inside of the box? Could lining it with tin foil be an easier option?

At least try covering the outside of it first, to see how effective that may be.

Is there something wrong with it that needs repairing, rather than masking?

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If you were in the UK, Virgin Media (One of the largest ISP's) have a dedicated team to deal with this exact problem. I was speaking to the guys and they seem to keep getting busier. They track down interference from Pirate Radio Stations etc . 

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Update: This post is incorrect, but I'm leaving it in place for those interested to follow my investigation.

 

So it appears to be my wireless router and not the junction box outside, it's just backfeeding along the ethernet wire to the junction box.  I'm down at 27 Mhz on the CB radio, and my wireless router is running at 2.4 Ghz, which makes it weird that it would produce this much interference.  I would blame it on dirty electrical power, but I'd think that would dissipate pretty quickly.

 

I'll have to try a different router and see if it exhibits the same problem.

 

For those curious it's a Linksys E800 router.  Interference is loudest on 16 AM (27.155 Mhz).  Channel width on the router is set to automatic, channel is set to automatic, and changing the channel on the router manually doesn't seem to help.

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The issue appears to be the CATV cabling.  None of the cabling is shielded, and my desktop computer with a CATV cable is sitting literally 2 feet from my CB radio.  When I un-plug the ethernet wires from the router, the noise goes out, even though the router is still powered on and broadcasting a wireless signal.  I think I've got some shielded CATVI laying around somewhere, I'll try replacing my unshielded CATV with that and see how it goes.


Weird that unshielded CATV would produce this much interference.  I mean I can stand in the middle of my kitchen 10 feet from any networking cables with the hand-held radio and hear it loud and clear.  Unplug those ethernet wires and the noise stops.

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I would suggest investing in either Ferrite RF chokers for your existing Cat5 or invest in quality full shielded Cat5, Cat5 by design should be double insulated to stop RF interference, sounds like you have cheap Chinese cabling.

 

http://electronicdesign.com/components/how-determine-when-shielded-network-cabling-required

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I would suggest investing in either Ferrite RF chokers for your existing Cat5 or invest in quality full shielded Cat5, Cat5 by design should be double insulated to stop RF interference, sounds like you have cheap Chinese cabling.

 

http://electronicdesign.com/components/how-determine-when-shielded-network-cabling-required

Yeah I've got some shielded Cat 6 cable I'm supposed to go pick up; let a friend use some of it a year or so ago but he only used like 50 feet off a 300 foot roll.

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Yeah I've got some shielded Cat 6 cable I'm supposed to go pick up; let a friend use some of it a year or so ago but he only used like 50 feet off a 300 foot roll.

 

You'll likely need to terminate it correctly to metal STP CAT6 RJ45 connectors and grounded Ethernet ports to stop the interference completely.

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You'll likely need to terminate it correctly to metal STP CAT6 RJ45 connectors and grounded Ethernet ports to stop the interference completely.

Aren't most ethernet ports grounded by virtue of being mounted to the PCB?  If not, I guess it'd be as easy as running a wire from the outside edge of the ethernet port to a common ground or some exposed metal on the case, correct?

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Aren't most ethernet ports grounded by virtue of being mounted to the PCB?  If not, I guess it'd be as easy as running a wire from the outside edge of the ethernet port to a common ground or some exposed metal on the case, correct?

 

Depends on the manufacturer really. Equipment without a 3-pin plug should have a grounding screw to attach your own ground source. The rack mountable stuff should also have this regardless.

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