[Antennas] Broadbanding an antenna...

[Rick Karlquist]

Andy wrote:
> I have seen this technique applied to VHF whip antennas, with an L/C
> impedance compensating network built into the antenna mount.  I've
> forgotten now who the vendor was (they made commercial antennas, not
> just for the ham bands).  I think they were able to more or less
> double, maybe as much as triple, the usable bandwidth of the antenna
> this way.  I haven't done the math myself, but this leads me to
> believe that the tracking is rather less than ideal.
>
> They didn't have anything written about the technique in publicly
> available articles or sales brochures.  But you could clearly see the
> components in their close-up photos.
>
> Andy
> ______________________________________________________________

The technique cited only works with a variable inductor.

There are techniques for broadbanding with a fixed network, however,
they work on different principles.  In those cases, the network
converts a match that is excellent over a narrow bandwidth to a match
that is mediocre over a wider bandwidth.  There is a theoretical
limit to what you can do known as the Fano limit.  There were a
handful of articles in Technical Correspondence in QST in the 1980's
IIRC that discussed this.

Rick N6RK