[RFI] RF getting into 4-port wirelss router.

[Jim Brown]

On Mon,1/12/2015 8:49 PM, KD7JYK DM09 wrote:
> Wrap a half-dozen turns around
> your hand in a loop four to five inches across and secure with plastic ties.
> See what happens, try a few more or few less turns if the problem persists.

That is NOT a choke, it is an inductor, which can resonate with a cable 
whose length makes it capacitive. An effective choke must cause the 
common mode circuit to have a high common mode Z at the frequency(ies) 
of the interference. The only practical way to do that is with 
multi-turn choke wound around a lossy ferrite core, placing the broad, 
low Q (typically 0.4) in the center of range where suppression is 
needed. That is EXACTLY how #43 clamp-ons work with a single turn at VHF 
-- their resonance is centered around 150 MHz.

Further, the choke must raise the common mode Z enough that the common 
mode current falls by enough to eliminate the interference. If the 
common mode Z is 500 ohms without the choke, we must raise it to at 
least 1,000 ohms to get 6 dB of suppression. What if we add a 500 ohm 
inductor and the cable is 500 ohms capacitive? Now the common mode 
circuit is series resonant, and interference gets much worse!

Study k9yc.com/RFI-Ham.pdf

73, Jim K9YC