At 08:53 AM 9/9/2005, Al Williams wrote:
> >
> >----- Original Message -----
> >From: "Tim Makins" <tim.ei8ic@gmail.com>
>
> What does the terms 4:1, 16:1 etc. for baluns really mean?
It's basically the impedance ratio, but in reality, a better term might be
the squared turns ratio. This applies to all transformers (not just
baluns, balbals, ununs, etc.)
The reactive component is scaled the same as the resitive one.
Example..
I have a 2:1 turns ratio transformer.
I have a 1 ohm resistor on the "1 turn" winding...
I put 1 Volt into the "2 turn winding"
0.5 volts appears at the 1 turn winding (i.e. 1 * 1/2)
So, there's 0.5 amps flowing in the resistor (I=E/R)
Then, the current in the 2 turn winding is 0.25 amps (0.5 * 1/2)
So, to the source, it looks the same as if there was a 4 ohm resistor
connected (1 Volt, 0.25 Amps), so we call that a 4:1 transformer.
Makes no difference if the load happened to be a +1j ohms (except that the
currents would be imaginary)... it would look like +4j to the source.
If the turns ratio is "N", (that is, N turns on winding a and 1 turn on the
winding b)
Basic transformer equations...
Ea = N * Eb
Ia = 1/N * Ib
Za = Ea/Ia
Zb = Eb/Ib
Substituting:
Za = (N*Eb) / (1/N*Ib)
= N^2 * Eb/Ib
= N^2 * Zb
> Neither of
>these
> links and none of the books or articles that I have read (skimmed?) explain
> what happens to the reactance part of the impedance when a ratio balun is
> used! Most likely, all of the antennas that include a balun probably have
>a
> reactance part of their impedance which varies as the frequency changes so
>I
> would think that this is a valid question for understanding baluns?
It IS a good question...
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