On Sat, 22 May 2010 21:00:47 +0100, Steve Hunt wrote:
>Jim,
>Sorry, but I'm still going to disagree ;)
>Tom (W8JI) and Owen (VK1OD) have both shown that you can't create a 4:1
>current balun by combining the two 1:1's on a common magnetic circuit.
>Two of the examples I quoted earlier show exactly the same thing because
>they require different voltages across the windings of the two baluns -
>obviously that's not possible if they have the same number of turns and
>are wound on the same core.
That's right, and it's what I said. No disagreement.
>My point is a different one. Depending on the degree of balance of the
>load, one or both of the 1:1 baluns has a minimum of half, and in some
>cases much more, of the differential-mode voltage across it. The flux in
>those 1:1 baluns will be no different than the flux in a voltage
>transformer with the same core, same number of turns, and the same
>voltage across the windings. They both obey Faraday's Law just the same.
That's true if we're comparing flux due to common mode current to flux in
the same core, same turns, single wire and NO power coupled to another
winding.
BUT -- the flux is proportional to the common mode current, and thanks to
the 5K resistance coupled from the core (the #31 or #43 core around its
broad resonance), there is very little common mode current, and thus very
little flux. There IS differential current in both windings -- that's how
power is coupled to the load -- but the differential component of current
produces no flux.
73,
Jim Brown K9YC
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