[Antennas] Broadbanding an antenna...

[Rick Karlquist]

This is pretty much that same technique that has been used with
screwdriver antennas since their inception.  You will notice
that certain screwdriver models have a base that cleverly has
a helical groove cut into it, forming a fairly low value shunt
inductor.  If your screwdriver doesn't have this, you can attach
your own coil, which is what I did for my Hi-Q screwdriver.
I haven't seen any articles describing this approach either,
but considered it "common knowledge" or something that any
serious investigator would eventually figure out on his own.
Fairly obvious how it works once you see it.

Anyway, it is a really nice technique that is applicable over
much more bandwidth than just the 160 meter band.  In a screwdriver
application, it is good from 160 up to 17 meters, using a
102 inch CB whip on top of the 4 foot screwdriver base.

I don't know who invented this, but I suspect it was someone
involved in the early history of screwdriver antennas.

Notice that this technique only tracks the resistive portion of
the antenna impedance.  The reactance cannot be "tracked" by
any fixed component configuration, hence the need for the motor
driven inductor in the screwdriver.

Rick N6RK


Ray wrote:
> Charles Michaels, W7XC, (someone else has this call now), designed and
> built an interesting network to successfully broadband his short 160
> meter vertical.  He called it a "Load Tracking Network".   It was
> published in the April issue, 1992, QST.
>
> I've not seen any other reference materials or articles on his
> approach.  It involved designing a series inductance plus a shunt "L-C"
> network.   The shunt network resonated at about 3.4 Mhz thus had the
> reverse reactance characteristic of what occurred as he tuned off of his
> optimum frequency.   It seems like a valuable approach to broadbanding
> and antenna.
>
> Has anyone else has expanded or written on such a "Load Tracking
> Network" that it could be more easily utilized in other narrow banded
> applications such as HF mobile antennas or other bands?
>
> Thanks for your attention.
> 73,
> Ray, W4BYG
> ______________________________________________________________