[TowerTalk] QST on drugs (was: 2006 Top Ten Chutzpah ...)
hwardsil at gmail.com
Thu Aug 24 16:01:17 EDT 2006
> 1. On p. 21 is something called a "fractal antenna" which appears to be a
> weird 12 sided wood table top with a hole in the middle, hanging somehow
> from something out of the picture. What appear to be two legs of
> undeterminable material protrude down from above. The text says this is a
> 600 foot long loop. Maybe it's a joke?
Actually, there has been quite a bit of work done on fractal antennas over
the past ten years or so. (numerous IEEE Antenna society articles) Your
mobile phone or 802.11 equipment may use a fractal or near-fractal antenna.
The antenna pictured apparently makes use of one of the more common fractal
generators (algorithm) known as "Koch's Snowflake" to fold the loop in a
repetitive way. While the actual length of wire in the loop remains more or
less the same as a full-sized antenna, the total area occupied by the loop
is greatly reduced. Unfortunately, the antenna's effectiveness is also
reduced. Some fractal generators do produce modest area reductions with a
tolerable reduction in performance, but not in this rather extreme case.
The poor performance is noted in the photo's caption, by the way. Fields
radiated by folded antennas are generally not as strong as those by a
straight-line element because the fields from all the various segments tend
to cancel and from other effects.
2. In Hints and Kinks on p. 55, someone has submitted what can only be
> considered a Kink: Use a plastic Budwig open wire feedline holder as a
> mechanical means of effecting a transfer from unbalanced cable, to window
> line. No balun, no Z transformation of any type is in evidence.
There are a number of ways to use a direct coax-to-parallel line connection,
such as the G5RV antenna. I would use some kind of a choke balun (beads,
most likely) to keep the outside of the braid from becoming part of the
antenna, but this is probably just a demo photo. As far as the impedance
discontinuity from the connector itself, the total electrical distance
involved is a very small fraction of an HF wavelength, so the width of the
Budwig is a non-issue.
Neither of these appear to be worth the irritation they apparently caused.
Try decaf, maybe?
73, Ward N0AX
More information about the TowerTalk