> Go to yccc.org. Find W1HIS's white paper on common mode
> chokes.
> It talks about antennas...but wind one for the power line
> instead.
> You can make them out of half inch clip-ons and not have
> to cut
> the power wire. You can get half inch clip-ons from
> RadioWorks.
> (radioworks.com). This would be my first line of attack.
> Might
> help. Won't cost too much.
Common mode chokes are FAR oversold and overused, and poorly
understood.
The function of a common mode choke is to reduce current
flowing through an unwanted path. The effectiveness of the
common mode choke depends on the series impedance of the
system at the point where it is installed, and the shunt
impedance at either end of the choke providing a bypass path
for the unwanted current.
If I add a common mode choke and it makes a little change,
adding a second one of the same value will have
significantly less effect.
Some equipment already has significant common mode impedance
between terminals. That means adding an additional impedance
from a choke doesn't do much. The same is true if the common
mode source impedance of the line supplying the common mode
current is high.
This is why I virtually never use common mode chokes on
things like TV sets and VCR's. The very first thing I do is
provide a low impedance bypass for current around the
affected device and everything connected to it. 99% of the
time the problem is eliminated, and the side benefit is
lightning protection is improved. As a matter of fact if we
properly cure the susceptibility to lightning damage the RFI
generally goes away with the problem.
If you are hung up on using chokes and if one or two good
common mode chokes don't cure a problem, it is hundreds of
times more effective to add a bypass rather than more
chokes. It's simple circuit behavior.
73 Tom
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