ve2pid wrote:
Hi to all..

How does a 4:1 or 1:1 balun affects reactance? For example, what would
be the new value Z=a +/-Jb of, say, Z=3000 - J4500 Ohms after
transformation by the 4:1 or 1:1 balun ?

Thanks de Pierre VE2PID

The impedance that your transmitter or matching network has to deal with
is the differential impedance, that is, the impedance between the two
conductors. A properly designed, constructed, and applied 1:1 balun will
effect no transformation at all of the differential impedance. A 4:1
balun will make it either four times greater or four times less. Both
types of baluns, again if properly designed, constructed, and applied,
will greatly increase the common mode impedance, that is, the impedance
you'd see if you connected the two feedline conductors together and
measured the impedance to ground.

In reality, any transformer will usually behave reasonably well only
when terminated in an impedance near its design impedance. For example,
a 4:1 balun or transformer designed to transform 200 to 50 ohms will
work well only if the high-Z end is connected to around 200 + j0 ohms.
(Such a transformer might have a high-Z winding impedance of 1000 - 2000
ohms, and it might well be resistive as well as reactive.) If you get
very far from 200 + j0, you'll find that the transformation ratio
changes and the transformer adds reactance and sometimes resistance. The
error can get dramatic with even moderate excursions from the design Z,
depending on the transformer design. It would be a difficult job to make
a transformer other than air core with a resonant winding which would do
a decent job of transforming the impedance you quote. So the short
answer is that it's anyone's guess what a 4:1 balun would do to that
impedance. A 1:1 current balun can be made from a section of
transmission line made into a coil, wound on a core, or with cores put
around it. The impedance will be transformed according to well known
transmission line effects, which depend on the length and Z0 of the line
used for making the balun.

Roy Lewallen, W7EL