Topband: Inverted L SWR Jumps ???

[Jeff Woods]

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 at w8ji.com>
>To: Jeff Woods <jmwooods at yahoo.com>; Ashton Lee <Ashton.R.Lee at hotmail.com>; topband at 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.
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>MOST antennas are in a "neither" world of being neither perfectly balanced nor perfectly unbalanced.
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>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.
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>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.
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>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.
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>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
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