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 <[email protected]> >To: Jeff Woods <[email protected]>; Ashton Lee <[email protected]>; >[email protected] >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 - [email protected]
