> I now have one small binocular core transformer, made from two small
> toroids, that gives me a 1.2:1 match at 2 MHz when terminated with a
> 910 ohm resistor. Then I wound a separate 1:1 transmission-line balun
> on another small core and connected it to the 50-ohm side of the
> transformer. I still get 1.2:1 through the balun, so I think I'll
> stop there.
> The balun presents about 500 ohms reactance at 2 MHz, so should be
> plenty adequate to decouple the transformer from the feedline.
(You may want to crosspost this the the Flag group.)
We have to be very careful adding reactances in series with the
common-mode impedance of a system to reduce unwanted current. In many
cases, we can make the system worse by adding reactance.
The rule-of-thumb that claims using a balun with an impedance several
times the feedline impedance actually is not a good rule. As a matter
of fact, it really has almost no relationship to what happens in the
It leads to misconceptions, like the common misconception that claims
moving a balun to the input of a floating tuner will improve balance
or the other common misconception that several hundred ohms of balun
reactance is enough for a choke balun.
To improve balance, a choke balun must increase the common-mode
impedance of the system significantly. If the antenna and feedline
junction has a capacitive common-mode reactance, like a Flag or
Pennant presents, and we connect an inductance (choke balun) in
series with the feedline, it will actually make balance WORSE...not
That is why almost everyone recommends using an isolation transformer
with loose coupling, because like-sign series reactances add
(increase) while opposite series reactances would decrease the
opposition to common mode currents.
You have to look at each individual system type, and determine what
type of balun will work. If not, adding a balun can make things
73, Tom W8JI