This
was a regular and popular monthly column by L.B. Cebik, W4RNL (SK)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, 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
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!
The
author of the monthly column Antenna Design & Use
is Justin Johnson, G0KSC who does in fact design and install antennas in
many parts of the world. He�s a real hands-on expert with years of
experience in this field. Following this column will be helpful
especially to those pondering a new antenna project. Examples of how to
model the designs will appear at times as well. There is something here
for just about everyone wishing to know more about how antennas are
created, tested and used.
FEATURE ARTICLES THIS MONTH IN THE LIBRARY Subscription Required to View Click to
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A Reference
Dipole by Grant Bingeman, KM5KG
I imagine many amateur radio
enthusiasts choose a simple horizontal dipole as their first
shortwave antenna. Therefore it is natural for them to compare
any subsequent antennas with that trusty dipole. Physicists and
antenna engineers tend to compare all antennas to an isotropic
radiator, which is a fictional beast that creates a spherical
radiation pattern. That is, the RF signal level is the same in
all directions. But since none of us has actually operated an
isotropic radiator, we never developed a gut sense for its
behavior. Instead, we are more familiar with a backyard dipole,
even though few of us can describe its 3D pattern in detail.
Practical Antennas: Part 5.07 By
Marcel H. De Canck, ON5AU
Many times the
use of a balun is recommended for proper performance of an
antenna system. Within the amateur radio community baluns have
three main functions.
o First, they convert an antenna
feedpoint or a parallel transmission line from a balanced
circuit to a single-ended unbalanced configuration. The
single-ended unbalanced configuration is necessary for cables
and equipment using coaxial connectors in which the outer
conductor is connected to ground somewhere in the system.
o Second, often we employ baluns to attenuate or avoid
common-mode currents to keep them out of equipment and off the
surface of coaxial cable sheaths.
o Third, we employ some
baluns to transform load impedance values to an alternative
value. There are many designs for baluns capable for various
impedance ratios from 1:1 upward, whereas the most usual
impedance ratio is 4:1. But depending on the need and
circumstances, other transformation ratios are available such as
6:1 and 9:1.
More than often baluns are also described as
a choke, current or voltage type. Some explanation is needed
here to see the forest from the trees. First of all, what is a
balun? The name balun is short for Balanced to Unbalanced and
each part is pronounced the same way as in the separated words
and not as balloon more than often heard. A balun is a
device which somehow connects a balanced load to an unbalanced
transmission line. This article explains.
NewcomerNotes: Special Propagation
Conditions By Robert Gulley, AK3Q
This month I want to examine special propagation conditions
which bring about unusual openings on bands which might
otherwise be closed, and I want to discuss solar activity and
its impact on communications in general.
Last time I discussed some basics
concerning propagation, including the components of the
ionosphere which allow signals to be reflected around the earth,
seasonal variations, and variable band conditions. These topics
form a basis for understanding propagation because they are
relatively constant. The ionosphere reacts predictably most of
the time, seasonal variations follow similar paths each year,
and band characteristics remain fairly consistent, again in the
most general of terms.
Relationship
of Vertical Height vs Optimum Radial Length By Rudy Severns N6LF
The suggestion the length of radials in a vertical ground system
is related to the height of the vertical has long been part of
amateur antenna lore. The idea is that with a 1/4-wave antenna
you use 1/4- wave radials and with an 1/8-wave vertical 1/8-wave
radials, etc. While you can make arguments why this might be, I
thought it would be interesting to conduct a modeling study
using NEC (EZNEC Pro 5.0 w/NEC 4) to see if I could find any
support for this idea.
Hidden Momentum in a Coaxial Cable
By Kirk T. McDonald Joseph Henry Laboratories, Princeton
University
Here we calculate the electromagnetic
momentum and identify the "hidden" mechanical momentum in a
coaxial cable of length L, inner radius a,
outer radius b, when a battery of voltage V is
connected to one end and a load resistor R0
is connected to the other. The current may be taken as uniformly
distributed over the inner conductor, which has resistivity
p. The outer conductor has negligible resistivity, and the
current flows on it in a thin sheet at radius b. The
battery shows negligible internal resistance.
Then, we
shall deduce the charge per unit length on the outer surface of
the inner conductor. Then, suppose the battery can be turned off
in such a way the current in the cable falls to zero with some
time dependence I(t). We calculate the impulse on the
charge on the surface of the inner conductor due to the electric
field induced by the transient current.
Intermediate-sized loop Antennas By
David J. Jefferies, PhD
A loop antenna
has a continuous conducting path leading from one conductor of a
two-wire transmission line, "the feed", to the other conductor.
You may think of it as a "coil that radiates". The coil may have
only a single turn. It may have arbitrary shaped perimeter, but
the essence of a coil is that the defining wire encloses an
area. Thus, a folded dipole is not a loop antenna in this sense,
since the area inside the conductor path is vanishingly small.
In a loop antenna, the magnetic field (generated by the loop
current) threads the area of the loop and this provides the loop
with inductance.
?need a compact
antenna
?have
signal problems either transmitting or receiving ? can't choose between a vertical or horizontal antenna
? want
to learn about antenna modeling
? just
want to know more about propagation
? want to design an antenna, but don't
want to redo the wheel
? need
a program for antenna design and antenna plotting
? don't
know what antenna is best for hamsats or others
? have
a busy mobile signal on all bands
? need
an inexpensive directional antenna for 10 meters
? need
a low-noise antenna for 160 meters
? want
to know if someone else has solved your problem
? need
a disguised mobile antenna for the vehicle
? just
want to know more about antennas
This
was a regular and popular monthly column by L.B. Cebik, W4RNL (SK)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??
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
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!
