[Antennas] Multiple dipole spacing

2002年8月14日 13:08:18 -0400

Dear George, 'Yellow Rose', I'm hard of hearing!!! That tells you how
much the toroidal balun hurts at 30:1 VSWR with balanced feeders on 75
meters.
The MFJ balun is mounted right outside the window in the shack. I'm
about three or four feet from it. So, I can actually hear it hum on
voice peaks AND high power on 75 phone. 
Seriously, the real issue becomes one of transmitting spurious signals
from the toroidal balun non-linearities.
In a toroidal balun there are two components of the current in the
circuit: first, the magnetizing current which is typically <1% of input
current. This component has high harmonic content. If the toroid is
overdriven from the 'linear' region into saturation then much higher
harmonic components are created. 
Secondly, the input/output transformed currents. These currents use the
magnetic permeability to 'balance' the currents in two windings. The
'permeability' curve is not linear as a function of excitation, it's
close but not perfect, so, some harmonic energy is caused to flow in the
system.
Air wound baluns avoid both problems.
Having written this, I guess I'm committed to winding a new air wound
balun.
DD, W1MCE
____________________________
"George, W5YR" wrote:
>> Wish I had your ears!
>