[QCWA] Baluns part 4

[Jeffrey D Angus]

A short refresher course on transmission line theory.

Remember the magic 1/4 wave matching section?

Transmitter -> any length of 50 Ohm coax -> 1/4 wave
length of 75 ohm coax -> 112.5 load.

I mention this because how having a different impedance
transmission line in series between the source and the load
is going to change what the load sees.

(See told you it was short)

4:1 current balun

(1)-uuu-(2)
(3)-uuu-(4)

(5)-uuu-(6)
(7)-uuu-(8)

Here we have two individual 1:1 current baluns.
We can connect them to make a 4:1 impedance
transformation at the same time as the balun
operation.

Connect (1) and (5) to the coax center. (3) and (7)
to the shield. (inputs are in parallel)
Connect the balanced load to (2) and (8) and tie
(4) and (6) together. (outputs are in series.)

For this to work properly, both of the transmission
lines have to be the correct impedance. In this case,
100 Ohm line.

100  / 2 = 50 (the inputs in parallel) and 100 * 2 =
200 (the outputs in series).

A pair of #16 AWG enameled wires spaced about
0.006" apart gives you a 100 ohm balanced line.

Jeff-1.0
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