Several observations in pursuit of my ongoing war on using words to
describe things that get in the way of understanding how things work.
(And not intended to be critical of Steve.)
Phase is a continuously valued function and is measured in degrees. It
has meaning ONLY for signals of precisely the same frequency. For any
system where time is a factor, phase is a linear function of frequency
and of time.
What is being discussed in this thread is NOT phase, it is POLARITY.
Polarity is the definition of which wire in a signal pair is positive.
Changing it requires the inversion of an entire waveform, either by
going through an electrical gain stage, or through a transformer, or by
reversing a pair of wires carrying the signal. Polarity is independent
of frequency (within the limits of the perfection of the circuit
carrying the signal).
The word "balun" is carelessly used to describe nearly a dozen very
different physical objects. One such object is a common mode choke.
Common mode chokes are continuous from one end to the other, so their
polarity can be determined with an Ohmeter. The polarity of a common
mode choke made with coax is obvious. :)
ALL common mode chokes add phase shift, because they are part of the
transmission line.
The method that Steve described is a good one for some other types of
"baluns."
73, Jim K9YC
On Fri,3/17/2017 10:13 AM, Steve London wrote:
If you have two identical baluns, you can match the phasing this way:
- Connect a signal generator to a tee-connector. Connect each side of
the tee to the input of each balun.
- Connect the outputs of the two baluns in series, leaving you with
two wires - one connected to balun "A" and the other to balun "B".
- Connect the 2 wires to an oscilloscope or RF voltmeter. Measure the
voltage.
- Swap the wires on one of the baluns. Measure the voltage.
One of the voltage measurements will be much higher than the other.
The higher voltage will be when the two baluns are in phase with each
other.
73,
Steve, N2IC
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