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| Antenna Modeling |
From The Shack |
 This
is a regular and popular monthly column by L.B. Cebik, W4RNL Because
computerized antenna modeling has become widespread, and its popularity as a design tool
continues to increase, this series is devoted to helping readers get the most from the
design software used. The articles focus upon the use of NEC and MININEC, along with
useful adjunct software as well.
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This column is primarily for "Guest
Editorials" to provide a podium for our readers to voice their opinions to the rest
of the world too. This is a chance for readers to get on their "soapbox" and
speak about antenna and radio-related subjects. Don't miss these interesting views about
anything and everything about radio and antenna systems! Now, what have YOU to say?? |
Ham WorkShop |
Stone's
Throw! |
|
Ham WorkShop, is also another
regular monthly column filled with a variety of "RADIO-STUFF" of value to
almost everyone in amateur radio from Novice to Extra and those just beginning to take up
this special hobby. This includes subjects, but not limited to: VHF, choosing the right
antenna, coax cable, small to mid-scale construction projects in a practical manner, use of test
equipment, etc. It is also meant to help readers become more familiar with the technical
jargon and the fun side of radio.
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 Stone' Throw! a
monthly column by antenneX publisher,
Jack L. Stone, among other things, is to keep
the readers informed about our progress, new developments, plans for the future, and to
introduce the authors and their subjects each month. Also, our main slogan around here is
"we aim to please", so this serves as a place for the readers to tell the
publisher what is wanted or at least make suggestions. Just remember, the publisher is
only a Stone's Throw away! Go in for a visit and read this month's column.
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Propagation |
 Propagation
another monthly column by Marcel H. De Canck, ON5AU of Belgium. Signal propagation
is a subject that is one of the most basic ingredients of radio and is something everyone
in radio should know about in order to maximize communications in the most effective way.
It’s not enough to have the best equipment and the best antenna if you are trying to
send out a signal against a brick wall. Conversely, one may possess a very crude rig,
running low power, but yet transmit/receive a signal to great distances with ease, simply
by making use of a thorough knowledge about how signal propagation works within the
environment. Follow this column and learn more about propagation!
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FEATURE ARTICLES THIS MONTH IN THE LIBRARY
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A Tale of
Three LPAs:
Some Notes on Zig-Zag Log-Periodic Arrays
3. The X or Saw Tooth Zig-Zag LPA
By L. B. Cebik, W4RNL
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The trapezoid (discussed
last month) was not the only solid-surface element shape to have a
wire-outline analog in the development of LPAs. Performing similarly
to the trapezoid was the saw tooth shape. Like the trapezoid,
solid-surface forms used a central boom composed of a line that grew
wider as the distance from the vertex increased. The wire-outline
version reduced the central line to the diameter of the wire itself.
Folding two bays together produced a directional beam. The pattern
of elements formed the series of Xs that yields the casual array
name.
In the early 1960s, J. W. Carr discovered that he could remove the
central boom and still have a useful beam. Therefore, we shall have
to see whether boomless X LPAs are more or less successful than
boomless trapezoidal arrays. Finally, we shall look at two amateur
examples of X LPAs using far less stringent design criteria than the
ones we shall employ in our main comparative study.
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The Force on an Antenna Array
By Kirk T. McDonald, PhD
Joseph Henry
Laboratories, Princeton University
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Antennas
radiate (vector) momentum as well as energy, but if the radiation
pattern is symmetric, the total radiated momentum is zero. Consider
a simple antenna array that consists of two short linear dipole
antennas whose centers are λ/4 apart and whose
conductors point along the line of centers of the antennas. If the
two antennas are excited with a 90-degree phase difference, deduce
the asymmetric radiation pattern and the time-average rate of
momentum dáPñ/dt,
that is radiated. The antenna experiences a time-average reaction
force áFñ
= dáPñ/dt.
The solution is explained in this paper.
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My Antenna System
and the AIM 4170
By Fred M. Griffee, N4FG (EE Retired)
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The AIM 4170
impedance-measuring device is used here to measure the needed data
since its accuracy is much higher than any other available
instrumentation I have used to date. Comparisons with matching
network theory and measured data will be used and my antenna system
will be the source of measurement data.
The common mode current must be addressed and it is essential to
eliminate it to prevent unwanted errors. A one-foot length of
RG-8X/U coaxial cable covered with 50 Amidon FB-73-2401 ferrite
beads is used at the balanced pi-network tuner input. The
characteristics of the coaxial bead choke are included through the
use of the AIM 4170 instrument. A table of comparison data are
presented for analysis purposes.
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The modified Sperrtopf Antenna
for the 88-108 MHz Broadcast Band
By Mike Tobin, Systems Engineer
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This article describes
modifications to the antenna as posted on the web at the antenneX
free download site at
sperrtof.pdf for operation on the FM broadcast band 88 108
MHz. Radio KLFM has a split service area.
To cover this split area, KLFM uses 2 frequencies, 96.5 MHz at an
elevated site (480m ASL) just south of Mandurang and 106.3 MHz as a
translator service to cover the Castlemaine area. Castlemaine is a
regional town with a population of about 20,000 that sit in the
floor of a valley and is surrounded on three sides by hills 400 to
450 metres high hence direct coverage from Bendigo is not possible.
The original service for both areas was transmitted via side mount
dipoles whilst these antennae are broadband they suffer from 2
deficiencies for which a solution is presented in this article.
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A Practical Short Dipole
By Dave
Cuthbert, WX7G
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Have you
ever wondered just how short a dipole can be and still give good
performance? The answer depends on several factors such as the
desired radiation efficiency, bandwidth, and the type of
construction. Tradeoffs must be made between size, efficiency, and
bandwidth. Ultimately the following rule applies:
1. Short length
2. High efficiency
3. Wide bandwidth
One may choose any two.
In this article we will go through the design of a short yet useful
dipole for the 20-meter amateur band. We explore the many tradeoffs
and finish with a paper design; this antenna has not been built and
tested yet. In the 2nd part of this article we will go through the
construction and extensive testing and see how well theory matches
the real antenna.
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AMOS
Antenna with Semicircular
Radiation Diagram for 2.4 GHz
By
Dragoslav
Dobričić, YU1AW
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In WiFi
communications, antennas with semicircular radiation diagram in the
horizontal plane are often needed. Antennas with circular radiation
diagrams may have gain values as high as it is possible to narrow
its vertical radiation diagram. That's where antennas with radiating
dipoles aligned vertically are used. When a circular diagram is
needed, and vertical polarization is used, the alignment of
half-wave dipoles can be carried out according to the principle of
the famous Franklin's antenna.
An open half-wave dipole fed in the middle is extended on both sides
with one continuous conductor, which is, every half wavelength
folded into a quarter-wave short-circuited part of symmetrical
two-wire line. In this way, proper phasing of the half wave dipoles
is performed. This kind of wire antenna has been used, mainly in
horizontal polarization, from the very beginnings of radio on medium
and short waves and is known as Franklins antenna, after its
author.
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ARCHIVES Volume I, II, III, IV, V, VI,
VII, VIII & IX available!
Go
Here to See List of Articles
|
? need a compact
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Last modified:
December 30, 2006
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