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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. |
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. |
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. |
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.
Its 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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Notes on 2-Band (2-M, 70-CM) LPDAs
Part 1. Narrow-Band LPDAs
By L. B. Cebik, W4RNL
(A Posthumous
Publication) |
|
The amateur 2-meter and
70-centimeter bands have an approximate 3:1 frequency ratio. On both
bands, FM repeaters use the upper portion of the bands, so the ratio
is more exact. For example, the 3rd harmonic of 146.7 MHz is about
440 MHz. FM repeater services use vertically polarized antennas on
both bands. Therefore, the idea of a single antenna to cover the FM
repeater portions of both bands naturally arises.
It is possible to use a ½-λ dipole element in the 3/2-λ mode to
provide dual band coverage. The advantage of this strategy is that
the impedance on both frequencies will be relatively low. However,
as we increase the mode of use, the self-resonant impedance does
increase. As well, because a 3/2-λ center-fed element has only two
ends—and hence, only two end-effect regions—the ratio of
self-resonant frequencies tends to be slightly higher than 3:1.
One way to overcome these potential limitations is to use one or
another form of wide-band technology. The most common form is to
create a log-periodic dipole array (LPDA) for the lower frequency
region and then to operate the array on the upper band as well.
These notes examine the practice as commonly implemented and then
with improvements. In this part, we shall look at a minimalist
design intended to cover only the amateur band at 2 meters and the
FM portion of the 70-cm band. |
|
Momentum in a DC Circuit
By Kirk T. McDonald, PhD
Joseph Henry
Laboratories, Princeton University |
|
We discuss the
electromagnetic and mechanical momentum in a DC current loop of
resistance R that is powered by battery of voltage V.
Because the loop is at rest in the laboratory, its total momentum
should be zero. However, a DC current loop is a dynamical system and
that its electrical resistance R causes dissipation of power
at the rate V2/R= VI = I2R, where the
DC current I is, of course, I = V/R. This
power flows from the battery to the loop in a manner first well
described by Poynting. As shown in a diagram by Poynting in this
article, the power does not flow down the wire of the loop, but
rather it flows through the air/vacuum and enters the wire at right
angles to its surface. |
|
Performances of Wet Yagi Antennas
By
Dragoslav
Dobričić, YU1AW |
In a previous
article, now in the antenneX Archive 9, I conducted some small
research about performance of antennas when they become wet. The
antenna gain and input SWR were two parameters monitored in the
antenna simulation while the antenna elements were covered with
water coating of different thickness. This simulation shows that
different antennas have very different sensitivity to moisture. Some
antennas become completely unusable with very thin water coating on
elements, while others are working still very satisfactory with much
thicker water coating.
Some correlation between the input resistances, which are for
VHF/UHF antennas mainly consisted of the antenna radiation
resistances due to very low loss resistances, and sensitivity to
moisture were established. The radiation resistance is important in
antenna Q factor value determination. Hence, there is dependence of
the antenna sensitivity to moisture on the antenna Q factor. |
|
Reviewing the TAK-tenna: Part 1
By
Dave Cuthbert, WX7G |
|
In this Part 1 of my review, we’ll explore the
theoretical aspects of this antenna and small dipoles in general. In
Part 2, we’ll fire up the TAK-tenna and see how it performs on the
air, how to get the most out of it, and how to multiband it, and
most importantly of all, how it works. |
|
The Double Slit Puzzle
Quantum or Classical?
By William C. Miller, KT4YE |
|
Charles Augusta Young1 (1834-1908), professor of astronomy at
Princeton University (1877-1905), first accomplished the Double Slit
experiment in the first decade of the 19th century. It was inspired
by earlier experiments using water to investigate wave performance.
His experiment was designed to test whether light was composed of
waves or particles. The results were similar to those obtained with
water, and showed that light is a wave phenomenon. Later tests
showed that the Double Slit experiment also opened the door to a
remarkable puzzle. A solution to this puzzle led us to the enigmatic
world of Quantum Mechanics.
At first glance, this physics experiment seems to have nothing at
all to do with antennas. However, as we shall see, there is a
possibility that a well-known antenna configuration — the slot
antenna — explains the puzzle without the need for Quantum
Mechanics! |
|
Magnetic loop automatic tuner
By Anselmo Stiffan |
The
magnetic loop antennas are highly appreciated for their very low
noise, reasonable efficiency despite the very small size, ability to
work close to ground and tunable across a very wide range of
frequencies. All these qualities are often not sufficient to make it
popular because of few drawbacks: it needs a very high voltage
variable capacitor (usually a vacuum type) and needs to be retuned
when moving the frequency by few KHz.
While I suggest the reader to review past antenneX articles to
minimize the first inconvenience, I tackled the second issue by
designing an automatic tuner specific for this type of antennas.
The design objectives were:
1. Low cost
2. Ability to work at 100W power level
3. Single supply of 12V
4. Possibility to operate close to the TX
5. Minimum number of control wires to the antenna |
|
|

ARCHIVES Volume I, II, III, IV, V, VI,
VII, VIII, IX & X available!
Go
Here to See List of Articles



|
? need a compact
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Last modified:
June 02, 2008
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