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
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