[TenTec] Strange FD RFI

[Jim Brown]

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