> You don't have to replace the wiring. Get yourself an old AC brut force
> line filter from one of the surplus electronic warehouses or buy a new
> one from Arcade electronics.
> Eric Rosenberg wrote:
>
> > In trying to calm down the telephone RFI problem in my old house, the
> > K-COM folks suggested I replace the old, solid, 4-conductor wire with
CAT
> > 3 cable.
Virtually all the time the problem is common mode excitation, and the type
of wire changes that very little if at all.
As for beads, people just throw a few beads at the problem and assume they
are making some profound change in the system. Actually most beads, like
most cables, have little effect on the system. You might remove medium
amounts of RFI, but won't likely make any large canges.
I use 100uH to 1mH RF chokes, one in series with each wire of the line,
depending on how severe the problem is. A .005uF 500v or higher disc acoss
the line also helps a great deal on the telco device side of the chokes if
you have any differential mode issues.
While there are many good reasons to change wire, like networking or adding
pairs, I'd NEVER rewire a house to cure RFI. I think that is a very
ill-advised step when a few bucks in parts would make a huge difference.
By the way, it takes a huge number of beads (dozens or more) to generate the
same common mode rejection as a $1.00 RF choke. I tested a bunch of commonly
available beads last week, and the 50 ohm common mode rejection was in the
order of a couple dB per bead. One popular type sold at a national chain had
a fraction of a dB per bead at 7MHz!!! You really need at least a 73 or 77
material bead, and even that material would provide in the order of a few
dozen ohms impedance per inch of linear length. It really gets much worse
when you use incorrect materials!
73 Tom
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