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From: "Peter O. Brackett"
Subject: Re: 2 way Splitter
Date: Wed, 18 Dec 2002 10:06:49 -0500
Organization: MindSpring Enterprises
X-Server-Date: 18 Dec 2002 15:06:50 GMT
X-Newsreader: Microsoft Outlook Express 5.00.2919.6600
> It really ISN'T that easy to make a good inductive splitter. Especially
> one that works at 350 kHz AND 50 MHz.
That's a matter of opinion.
It's not at all difficult if you understand wire winding layups and the
extremely simple physics of inter and intra winding capacitance.
Of course they don't teach that stuff anywhere anymore! Especially
in the new Computer Engineering schools. Heh, heh...
I have not seen this discussed in "regular" Engineering school curricula
since at least the 1950's.
Today if you have common mode problems ya gotta hire a consultant
[I'm always available!], go figure it out yourself or, read "old" books.
> Common-mode rejection? In an unbalanced system?
> Regards, John Woodgate, OOO - Own Opinions Only.
John, your statement implies that you might be suffering from a common
Common mode rejection has nothing to do with whether a system is "balanced"
"unbalanced". Either system can and often do have common mode "problems".
In any transmission system there are two conductors, one "go" and one
These conductors may be coaxial (unbalanced) or not (balanced). In either
case, if the voltages
at corresponding points on the two transmission conductors are denoted V1
and V2, then a
common mode can be induced either by a variety of intra or extra system
effects. The common
mode voltage [a.k.a. longitudinal voltage] with respect to the "common" is
Vcm = (V1 + V2)/2.
Similarily the differential mode voltage [a.k.a. metallic or transverse
voltage] is Vdif = (V2 - V1).
There are corresponding definitions for/of the longitudinal and transverse
currents. Of course one
must be aware of what and where "the common" is in a particular case. In
the transversal currents and voltages which are the intended causes and
results of interest, and the
longitudinal or common mode currents and voltages which often cause
interference and many other
kinds of problems e.g. inadvertent overloading, or incorrect biasing, etc.
In coaxial transmission systems it is often mistakenly believed that
currents exist only on the
outer surface of the inner conductor and on the inner surface of the outer
is simply not true, often current [The common mode current.] also flows on
of the outer [coaxial] conductor. It gets there because of poor common mode
This phenomena is well known to RF and Video System Engineers who often have
take precautions and design their systems to ensure that common modes do not
even on coaxial cables!
Applications in hostile common mode environments *need* to be designed for
common mode [longitudinal signal] rejection.
The rejection of common mode signals is inherent in well designed
systems. Appropriately designed transformers and/or common mode chokes will
eliminate most common mode effects and artifacts. This protection may be
needed whether the
transmission system is balanced or unbalanced. Often just winding a coaxial
a few turns, with or without a ferrite core, will help immensely. If you
understand why an unbalanced system may need common mode rejection, then you
simply have not yet had to design systems for difficult common mode
television studio work, high RF fields, etc...
Indialantic By-the-Sea, FL
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