[RFI] Bonding to a PC

[Jim Brown]

On 2/28/2019 3:39 PM, David Huff wrote:
> Note that many people have installed clamp on ferrites or torroids on the AC power cord, just to keep the RF noise generated in the PC from being coupled back into the house 120V system.

There's a lot of science about this that is specific to the suppression 
of noise at HF and MF that is VERY different from VHF and UHF.  A single 
turn through a suitable ferrite core may be useful at VHF and UHF, but 
it is unlikely to do much at MF or HF. Multiple turns must be wound 
through the "right" ferrite core to move the choking impedance down in 
frequency to the HF spectrum, and to multiply the impedance coupled from 
the core by the square of the turns ratio.

There are several tutorials on my website that address this. 
k9yc.com/RFI-Ham.pdf  k9yc.com/  is the "from the ground up" tutorial on 
RFI, and http://k9yc.com/KillingReceiveNoise.pdf  is a step by step 
applications note on identifying, locating, and killing RF noise. While 
the fundamentals apply to LF through UHF, the emphasis of both is MF and 
HF.

> Bonding might be good, but you should also experiment with RF suppression ferrites or torroids on the power cords, and anything else (USB, mouse, keyboard, etc.) routed from the PC out to the rest of the radio system.

Bonding is quite important, but the primary reasons for bonding are 
lightning protection and minimizing the coupling of power line leakage 
currents into systems with unbalanced interconnections. Here are slides 
for a tutorial talk I've done at Pacificon and Visalia conventions. Most 
of the concepts were incorporated into N0AX's recent ARRL book on the 
topic. http://k9yc.com/GroundingAndAudio.pdf   A connection to earth is 
rarely part of a cure for RF noise.

> Your PC is a tremendous source of RF noise, and keeping that noise out of other systems may entail grounding and bonding, or it might entail isolation.

Most RF noise is conducted onto cables as common mode current and 
radiates by simple antenna action. The most common mechanism by which 
the noise gets onto the cable is failure to terminate the cable shield 
(or the Green Wire of the power cord) to the shielding enclosure AT THE 
POINT OF ENTRY. This was first identified in 1994 by the late Neil 
Muncy, a ham working in the world of Pro Audio, and he called it "The 
Pin One Problem," because Pin 1 of the XL-3 connector widely used in pro 
audio, is the shield contact.  (and NOT to the connector shell, for good 
reasons related to their use in broadcasting and large entertainment, 
sports, and worship spaces).  He published this work in a classic AES 
paper that year, and in the Journal of the AES in June 1995.

Because these connections are part of a passive network, the couple RF 
in both directions.

73, Jim K9YC