K4SAV wrote:
> The balun is an unusual design. It's a combo 22 to 50 ohm unun plus a
> common mode choke. Most people say that won't work. However if you
> look at what they did it almost makes sense. The unun part is tri-filar
> wound which produces very little core flux. They only used about half
> the core for this. So if it produces little core flux then it shouldn't
> affect the other part of the core. So they took the the coax that hooks
> to the unun and used the other part of the core to wind a choke. That
> is the part that is questionable in my mind. The choke will produce
> core flux. So shouldn't that couple back the the unun? Apparently this
> arrangement works or so they claim. I just don't know how well it
> works. I was hoping you had measured it.
>
> Jerry, K4SAV
It's that old gag: it depends on what you mean by "works".
It will work in terms of operating the SteppIR whether it is a voltage
balun or a current balun. So that fact that it works for that
purpose doesn't shed any light on whether it will work for top loading
a shunt fed tower.
I don't agree with some of your analysis. The unun certainly produces
core flux at the lower frequencies. Below 7 MHz, the MonstIR balun
goes south due to insufficient magnetizing inductance, according
to my measurements. On 160 meters, the capacitive reactance of
a 40 meter element as a top hat is about 300 ohms (measured). For
a SteppIR 20 meter element, double this. Even if the SteppIR balun
acted as a common mode choke on 20 meters and up, it would have
relatively low impedance on 160 meters, and shouldn't amount to
much in series with 600 ohms.
I can't measure this now because all 3 of my SteppIR band antennas
are on the tops of towers :-).
Rick N6RK
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