[RFI] Linksys Router Birdies

[Christopher E. Brown]

On Thu, 11 Mar 2010, Tony wrote:

> All,
>
> What is the best method of getting rid of router birdies? I have a Cisco
> Linksys router with both wireless and wired connections. There's a long
> run (50ft) of unshielded CAT 5 cable going to the shack which I'll be
> replacing with shielded cable. I'm told the wallwart can be a source of
> RFI as well.
>
> Is there a particular brand of Ethernet cable that's shielded better
> than others?
>
> Thanks,
>
> Tony -K2MO
>


Using STP requires a STP supporting device.  It will have a metal contact 
fingers around the inside rim of the RJ45 port made to contact the metal 
body of the RJ45 STP connector.


This is not normally found in consumer devices.  Even when it is, you tend 
to end up with device internal RF on the outside of the shield.


2.4 inch Type 31 toroids, on the power and on each ethernet cable leaving 
the device.  For a long run put one on each end of the ethernet cable.

Consult Jims paper for the proper # of turns for max supression on the 
freqs the birdies are bothering you.



That and using *quality* cabling will get you more than STP.


These devices like to put lots of internal clock noise onto the cables in 
common mode, the toroids reduce that.  Low cost devices and poor cabling 
tend to be les than perfectly balanced.  Any unbalance leads to signaling 
ending up as common mode on the cable.