[RFI] ARRL to FCC...

[Jim Brown]

On 3/25/2014 12:56 PM, Hare, Ed W1RFI wrote:
> Hi, Jim,
>
> What I am suspecting is that we may need to install the following filters:
>
> Differntial-mode AC filter
> Common-mode choke on AC mains
> Common-mode choke on incoming coaxial cable
> Common-mode choke on any other long leads to the TV screen

Two problems with commercial line filters are 1) that what they call 
common mode is the voltage between neutral and the green wire, which is 
not common mode as we would define it. 2) the green wire goes straight 
through the filter, and the green wire is often what's carrying the RF 
current because the green wire is not properly tied to the shielding 
enclosure (chassis) within the noise source. Instead, there's a "Pin 
One-Like Problem" with termination of the green wire. I've long 
suspected a similar mechanism for coupling RF noise onto coax.  Problem 
#2 happens either because of circuit layout or because the intended 
connection is insulated from the chassis by paint.  I've seen this, for 
example, in three Astron power supplies that I've looked at. The green 
wire goes to the mounting terminal of an old fashioned terminal strip, 
and there's paint between it and the chassis.

> Jim, is your choke cookbook on line?

Yes. It's part of k9yc.com/RFI-Ham.pdf   Chapter 8, I think. Appendix 
One has the raw measured data for single turns of small wire on 2.4-in 
o.d. toroids. Measured data for larger wire, and for 1-in i.d. clamps 
precedes the "Cookbook."

I need to expand the cookbook to include recommendations for smaller 
clamps on smaller cables. Our last group purchase was for Fair-Rite 
0431173551, which is 0.75-in. i.d. and a bit more than an inch long. We 
bought 7 boxes at a per-unit price of $2.28, as compared to $9.08 each 
for the much larger (and longer) 1-in i.d. clamps in 144 quantity. These 
smaller clamps are equally effective on smaller cables if you wind 
enough turns to move the resonance down to where you need it.  Even 
smaller clamps work fine too, if you can get the required number of 
turns through them.

> I want to make sure that ARRL links to it, on a number of our pages, actually. :-)

My main publications page is k9yc.com/publish.htm   It has lots of other 
stuff of use to hams. Thanks for the interest.

Someone else to talk to about plasma sets is W1HIS. He's got one that he 
has figured out is magentically coupling to plumbing pipes below the 
set, which in turn couple to his antenna(s). He's trying to choke the 
plumbing pipes with big #31 clamps. While he may be right about the 
coupling, I don't expect he can get enough resistive choking Z to get 
useful suppression at HF, but perhaps you could measure his set.

73, Jim K9YC