On 6/26/2012 6:30 AM, Frederick Mott wrote:
I think that a good line filter such as the Corcom EMI F3482 / F3482X just
might be the solution.
The very popular (and very nice) Honda EU2000i generator puts out some
hash that I've mostly heard on 20M and 15M. It may be on other bands,
but we always start out on those bands and it gets fixed before we get
to 40 or 80 later.
Conventional AC line filters do NOT make a dent in this RFI because it
is conducted out of the generator as a common mode signal on the AC
power line. There IS an easy solution though -- simply add a multi-turn
ferrite choke right at the generator by winding turns of the AC cable
through several #43 or #31 toroids, or a suitably sized clamp-on of the
same material. Use the guidelines in my Choke Cookbook --
http://audiosystemsgroup.com/RFI-Ham.pdf -- for coax that is about the
same size as the AC cable you're winding through the toroids.
Remember that the AVERAGE current draw for a 100W station with computer
and small lamp is typically no more than 4-5A, so while you certainly DO
want big cable (#12 or larger) for the long run between the generator
and the station, it's perfectly OK to use a short length of #14 (or even
#16) AC cable to wind the choke. This makes it easier to fit enough
turns into the ferrite core(s).
BTW -- while the specs for good AC line filters like Corcom and Delta
SAY that they filter common mode, they really don't, because what THEY
call common mode is not what WE call common mode. When THEY talk about
common mode noise they're talking about noise between neutral and green,
or between the combination of phase/neutral and green. When WE talk
about common mode, we're talking about current that is in phase on all
three conductors, and no voltage between conductors. So their specs are
lying, they're simply talking about something entirely different.
73, Jim Brown K9YC
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