[RFI] Cable Modem Interference

Phil Duff na4m@arrl.net
Thu, 29 Nov 2001 00:02:03 +0000

At 10:51 11/28/01 -0500, Peter D. Vouvounas wrote:
>Now that so many hams have cable modem I'd like to ask for feedback
>regarding experiences with noise generation into the HF bands.  Particularly
>3.5 - 4 MHz.

Yep - I get crud off my cable modem also - especially noticeable on the low 
Mine is provided by Cox Communication and is a "Terayon" unit.  I feed my 
PC card directly from the modem - no hub, etc.

>  If I remove power from the cable modem the same major drop in
>noise. Tried wrapping the modem in aluminum foil and grounding with little
>or no effect.
>I've tried ferrites on the cables to no avail.  Should I move the cable
>modem from the Ham/Office location it would only bring it closer to the
>antenna systems on the roof.

I've tried similar remedies all to no avail.  Ferrites on power supply 
input/output cords, cable modem coax, etc.
  My cable modem is located in the radio shack and the only effective thing 
I've found with mine
is to unplug the modem power supply.

It's possible these things meet FCC specs but can still generate enough 
noise to cause
interference in closeby sensitive HF radios?

73 Phil NA4M

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Phil Duff NA4M     na4m@arrl.net   Georgetown, Texas