Topband: Inverted L SWR Jumps ???

[DAVID CUTHBERT]

W8JI solved another problem and saved someone much time and frustration.

I'd like to thank Tom for the great help and knowledge he has imparted in
me and many, many others over the years.

In my expert opinion as an engineer he is one of just a very small number
of "super engineers" I know.

Dave WX7G
 On Nov 28, 2012 11:57 AM, "Jim Brown" <jim at audiosystemsgroup.com> wrote:

> On 11/28/2012 10:14 AM, Ashton Lee wrote:
>
>> I rebuilt the antenna from new wire, built a two insulator termination at
>> the end of the horizontal section where the high voltage is,
>>
>
> One thing I observed here several years ago with a dipole with an end
> touching tree branches is arcing to the branch, accompanied by scorching of
> the wire insulation (white THHN).
>
> Also, a common mode choke whose choking impedance is too low can overheat
> if the common mode voltage is high enough.  That voltage depends on the
> degree of imbalance, which, as Tom observes, is highly dependent on the
> antenna system, INCLUDING the feedline and the radial system (and/or
> counterpoise). Tom's analysis of Guy's folded counterpoise design showed it
> to have significant imbalance, which fried common mode chokes, but was at
> least partially corrected by the stray Z of an isolation transformer.
>
> Overheating in a common mode choke wound on a lossy ferrite core shows up
> in the wire itself (the coax shield) and can melt the dielectric, allowing
> it to either short, arc, or change spacing. I've done some experiments
> purposely intended to observe what happens when the choking Z is inadequate.
>
> 73, Jim K9YC
>
> ______________________________**_________________
> Topband reflector - topband at contesting.com
>