On 3/19/2012 9:29 PM, Larry Benko wrote:
> Ferrites alone were not
> adequate to eliminate the RF interference.
Thanks for documenting and sharing your work on this. One red flag that
I see in at least some of the photos is that the Green Wire bypasses the
common mode choke. It has been my experience that the Green Wire is
often (usually) part of the common mode circuit, and must pass with the
other conductors through the choke.
As an example of this issue, a few years ago I fitted very good
conventional line filters into boxes and connectorized them (very short
leads) for use with some Honda generators for Field Day and California
QSO Party county expeditions that are noisy on 20M-10M. The filters
didn't work at all, because the trash was radiated on the Green Wire. I
lengthened the line (portable 20A cordage) between the generator and the
filter enough to wind about six turns through two #31 toroids and that
killed the noise.
Note that W4EF shows exactly that solution on the following page for
noise on his Honda generator. Mike is an EE at JPL.
BTW -- the REASON that the Green Wire is part of the problem is a "Pin
One Problem-like" error in the connection of the Green Wire at the noise
source. The same sort of error also couples RF trash out of TV sets
onto coaxial wiring that we THINK is bonded to the chassis but is not.
Notice also that both Mike and I were working on noise in the 14-28 MHz
range, so we both settled on chokes resonant in that range. He used #43
because that's what he had, and also because it's the best choice above
about 20 MHz. I used #31 because that's what I had, and because it's
almost as good in that range. We would both use more turns for noise on
the lower HF bands.
Another BTW -- what a Power System engineer calls common mode is current
that is equal on phase and neutral. But from an RFI point of view, all
three conductors are part of the antenna, and if the Green wire and
internal bonding are not proper, we must choke all three conductors (or
four in a 240V system with a neutral).
73, Jim Brown K9YC
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