Topband: Inverted L SWR Jumps ???

[Tom W8JI]

Remove the balun. It's not doing anything for your and is a potential source 
of loss and problems. Coaxial cable is unbalanced, as is a ground-fed 
inverted L. No need for a balun. >>>

Unfortunately, that is not a universally true statement.

MOST antennas are in a "neither" world of being neither perfectly balanced 
nor perfectly unbalanced.

Perfectly balanced would be equal and opposite currents entering and leaving 
each conductor at each end of a balanced line, with equal voltages to the 
world around the line from each conductor.

Perfectly unbalanced  would be the same equal and opposite currents entering 
and leaving each conductor (shield and center) at each line end, and zero 
voltage from the shield to the outside world around the line.

Very few antenna systems meet that criteria, although Marconi systems with 
many radials are close enough to be nearly perfectly unbalanced. Significant 
departure from UNbalanced occurs when radial systems are sparse, or 
truncated, or the feedline exits above the plane of the radials. There isn't 
any clear boundary, but a slow system dependent transition from the perfect 
case (feedline exits below the radial plane and an infinite full size radial 
system) to the worse case (a single radial of any design). Even four 1/4 
wave radials have significant voltage to "ground" at the common point.

Choking impedance required varies with the number, configuration, and length 
of radials and how the feeder is routed and grounded, and in nearly all 
cases a few hundred ohms is enough. An exception might be if the ground 
system common point has abnormally high voltages to earth (for example, a 
single truncated radial) or if the coax is elevated and coupled to the 
antenna.

73 Tom