[RFI] Internet Modem / Router Cable Length and RFI

[N1BUG]

Tony,

My experience has been that long CAT5/6 cables do radiate and cause 
RFI. Mostly it is carriers on numerous HF and VHF frequencies. Any 
broadband noise has generally turned out to be a "bad" power supply 
or specific device such as a router or access point.

In order to minimize the problem I keep my modem and router/in-house 
access point at the same location, connecting them with a one foot 
CAT5 cable. I do, however, have one 225 foot run of CAT6 going up a 
tower right into the midst of my antenna farm! It is for a tower 
mounted access point for a 5.8 mile link to a repeater site. This 
cable was a major problem. It now has multiple common mode chokes at 
both ends - some optimized for VHF, some for upper HF, some or lower 
HF. All other cables (power, internet, etc.) connected to the 
network are similarly fitted with chokes. This does not completely 
eliminate the problem but brings it down to a level I can live with 
considering the benefit of the extended LAN link to my repeater 
site. I got rid of all the switch mode wall warts that came with 
network devices. The modem, router, and passive PoE injector for the 
tower mounted access point are all fed 13.8VDC from an Astron linear 
supply.

73, Paul



On 06/01/2015 12:53 AM, 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?
>
> Thanks
>
> 73, Tony


-- 
Paul Kelley, N1BUG
RFI Committee chair,
Piscataquis Amateur Radio Club
http://www.k1pq.org