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AR15.COM
7/18/2010 4:21:05 PM EDT
My Arris cable modem is causing bad interference on HF, mostly around 40 meter band and lower. I have put ferrite cores on every cable going into it and it helped very little. The only way I can get the interference to go away is to unplug power to it. Any ideas on how to fix this?
7/18/2010 4:59:32 PM EDT
[#1]
It sounds like you have a leak somewhere in the cable system, either in your home or nearby in the outside plant.

I'm sure Jazz will be along shortly with a more drawn out explanation.
7/18/2010 5:54:16 PM EDT
[#2]
It may be the modem, or the wall wart.  

D-Link and others had a problem with the wall wart switching power supplies for a while.

7/18/2010 6:24:46 PM EDT
[#3]
Quoted:
It sounds like you have a leak somewhere in the cable system, either in your home or nearby in the outside plant.


If it was a cable "leak", the problem would still remain when his modem was unplugged (due to "leakage" from other modems connected to the cable).

As A_Free_Man mentioned, wall warts that use switching power supplies are notorious RFI generators. If you could temporarily power the modem with a linear power supply of some sort instead, it would positively identify (or rule out) the switching wall wart as the cause of your RFI problems.
7/18/2010 6:39:39 PM EDT
[#4]
Don't know how crafty you are, but find out how many volts DC the wall wart is putting out. You could make up a battery back and power cable to power you modem (temporarly off battery power. That will also rule out the wall wart!
7/18/2010 7:35:56 PM EDT
[#5]
No wall wart. Power supply is built into the modem.
7/19/2010 3:12:20 AM EDT
[#6]
Replace the modem. Make sure the new one is Docsis 3.0 compliant.
7/19/2010 8:13:26 AM EDT
[#7]
Modems are built with very little shielding. It's likely an unshielded circuit board mounted in a molded plastic enclosure.
Nothing to attenuate the rich harmonics generated by the CPU.
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