> On low bands, the Q of resonant stubs is fairly low.
> Therefore, the effective common mode impedance of these
> baluns will not be extremely high.
I see a problem now!!!!
The only common mode issue would be if the center point of the elements,
which is the common shields, does not sum to zero volts.
Look at a 16.67 load at one element side, and 33.33 on the other, with 50
watts. The lines each force 1 amp into each side 180 out of phase, so shield
current from that is zero amperes. No problem.
Here's where the problem is. We have 16.67 volts across one cable (16.67
watts), and 33.33 volts across the other (33.33 watts). This places the
shield junction at 8.33 volts, in the phase direction of the low-Z element.
That means we have 8.33 volts driving the common mode impedance of the
shields, which will make the shields radiate and force the system out of
balance.
Correct me if I am wrong, but that is how I see it now at second look. It is
really only a balun when the load is balanced, or something makes CM
impedance high.
So to me, now at second look, it does not appear to be such a good balun.
Unless I'm missing something, it is only a good balun when the elements are
balanced.
73 Tom
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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