A recent article on eHam.net by Alan Applegate, K0BG "In
Search of 'The Perfect Mobile Antenna'" on Aug. 5, 2003 and
posted comments, created some controversy and heated exchange between
myself and the "well respected engineer" (according to
Aaron, NN6O) Tom Rauch, W8JI. This article had some flaws and was
far from approaching "perfect" mobile antenna. To which
"By using a flawed and seriously over-simplified
model, the results are totally misleading when applied to conventional
antennas. Repeating misleading information in article after article
does NOT make it correct. It certainly does not make our community
more skilled or better informed about how things work."
"While I appreciate all your (K0BG) efforts, it
is important that readers and writers fully understand why and
how something works before reaching conclusions. Otherwise this
all just wastes bandwidth, and people learn incorrect information.
The goal of E-Ham and Internet should be to INCREASE technical
skills through mass peer review and learning, not to repeat misinformation.
In view of
the above and in order to "INCREASE technical skills through mass peer review and learning"
I have summarized in my posting
the most important items contributing to high efficiency of mobile
or shortened antennas. W8JI commented that I was wrong about
the current distribution in the antenna loading coils, where I
"4. Loading coils. Should be mounted as high as possible
in the antenna mast to increase the current radiating portion
of the whip. Wire or tubing should be rated to carry the power
without melting the coil. Q of the coil is not that important,
coil in this situation is the part of the radiating element, most
of the current is at the base of the coil and surprisingly Q or
form factor is not THAT important as measured and verified experimentally
by W9UCW. Loading coils at the base or autotuners are the worst.
Bugcatchers, single coils with no shorting, spider mounts for
multiple coils are very efficient."
To which W8JI replied:
current is high in only the start of a coil is not correct.
Model an antenna with EZnec, and look at the load. Model a coil
in any software, and look at current. Read any textbook, even
beginner's textbooks, and see what they say. Measure a real antenna
are like to call names, insult people, and argue rather than take
the time to learn basic electronics. This is in any book, including
the ARRL Handbook. If you look at HOW an inductor works, the current
flowing in one terminal ALWAYS equals the current flowing out
the other terminal. "
rest of the exchange can be seen at eHam.net following the K0BG
article at http://www.eham.net/articles/5998)
was quite an accusation and a challenge to reality and my knowledge.
This was not the first time that W8JI "challenged" me
and was proved wrong. Knowing what was the reality (uneven current
distribution, coil gets hotter at the bottom) and what Barry Boothe,
W9UCW measured, I was curious what was the source of W8JI misinformation. I ordered 19th edition
of ARRL Antenna Book and followed chain of references that
led to information on page 16-7 and Fig. 9 and 10. (see
at those two pictures, we can see that the current across the
radiator was "linearized" to be a nice straight line
instead of actual cosine curve. Also, Fig. 10 is missing the important
cross-hatched area, the current across the coil is shown as a
"nice" linear current over h2 and coil apparently has
zero physical length. This passage in the Antenna Book is written
by Bruce Brown, W6TWW "Optimum Design of Short Coil-Loaded
High-Frequency Mobile Antennas" first published in ARRL
Antenna Compendium, Volume 1, page