[RFI] Balanced-line antennas and couplers

[Jim Brown]

On Fri,8/5/2016 10:20 AM, Rob Atkinson wrote:
>   You can construct one
> and use a dual trace oscilloscope to adjust the network taps so the
> sides are 180 degrees out of phase if this bothers you.

But phase is an important part of "equal and opposite." The fields 
around the conductors cancel ONLY if they are equalin magnitudeand 
opposite in phase. Danny is exactly right -- a measurement that ignores 
phase or gets it wrong is a bad measurement.

I agree with Roy's papers on voltage and current "baluns." What we often 
call a "current balun" is fundamentally a common mode choke. It does NOT 
attempt to force balance -- it works by adding a high resistive 
impedance in series with the common mode circuit, which in turn reduces 
common mode current. When placed at/near the feedpoint of an antenna, it 
essentially removes the feedline from the equivalent circuit of the 
antenna. That is, the feedline is no longer PART OF the antenna, but 
only provides power to it.

And, of course, even this is an oversimplification -- if the feedline 
does not run exactly parallel to the antenna it shows up in the antenna 
circuit as a conductor grounded at the bottom end and open circuit at 
the top end, and acts as a parasitic element, causing imbalance in the 
antenna circuit.

73, Jim K9YC