That's true; I did assume a reasonably good ground plane, to the extent that
the unbalanced assumption would be accurate.
Still - it's a component that can be removed - at least temporarily - to see if
it is contributing to the problem.
Here's another thought: connect a dummy load out at the antenna end of the
feedline and run up to full power. This will effectively determine whether
it's something in the feel line/balun/lightning arrestor. If all is well to
that point then the problem is in the antenna itself, perhaps the arc-over to
the tree that others have reported.
73
-Jeff
>________________________________
> From: Tom W8JI <w8ji@w8ji.com>
>To: Jeff Woods <jmwooods@yahoo.com>; Ashton Lee <Ashton.R.Lee@hotmail.com>;
>topband@contesting.com
>Sent: Wednesday, November 28, 2012 11:30 AM
>Subject: Re: Topband: Inverted L SWR Jumps ???
>
>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
>
>
>
>
>
>
_______________________________________________
Topband reflector - topband@contesting.com
|