[RFI] Internet Modem / Router Cable Length and RFI

[Jim Brown]

Think of EVERY cable connected to digital electronics as an antenna 
radiating trash. That includes the router's coax or telco cable, and all 
the power supply cables.

Guidelines.  Shorter cables are better, ALL with common mode chokes.If 
cables are longer than about 1/10 wavelength at frequencies you care 
about, choke both ends. Make maximum use of WiFi for routing.

Replace all switch-mode power supplies with linear ones that you have 
scrounged or saved or bought at hamfests or second hand stores.  My 
router and cable modem run from a vintage lead-acid battery that is 
float charged by a linear wall wart. No noise from the PSU, and it's 
also a UPS for that gear. My internet doesn't die in a power failure 
until the cable company's batteries run down (they're good for about 6 
hours, our outages here in the mountains can get a lot longer).

For conceptual discussion and lots of specifics, see k9yc.com/RFI-Ham.pdf

73, Jim K9YC

On Sun,5/31/2015 9:53 PM, Tony wrote:
> All:
>
> I'm about to relocate the wireless router in my home which currently 
> sits next to my internet modem connected with a short run of CAT5. 
> Relocating the router will lengthen the CAT cable by 40 feet so I'm a 
> bit concerned about RFI birdies, noise etc.
>
> That said, I was wondering if it's better to relocate both cable modem 
> and the router to the same location to keep the CAT cable short. I 
> would then have to lengthen the coax cable for the modem instead of 
> the CAT cable.
>
> The question is: which setup has more potential for RFI?