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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.
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! |
FEATURE ARTICLES THIS MONTH IN THE LIBRARY
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The
Practical Lindenblad Stack
By L. B. Cebik, W4RNL
(A Posthumous
Publication) |
|
Our examination of basic
Lindenblad array theory and practice in the preceding issue of
antenneX showed us the underpinnings of N. E. Lindenblad's 1942
development of an omni-directional antenna capable of circular
polarization in the X-Y plane (that is, parallel to the surface of
the ground). The advantage of the antenna system is that it
communicates well on a point-to-point basis with either vertically
or horizontally polarized antennas. I adapted the system to 6-meter
and 2-meter antennas that provided full-band coverage. Such antennas
are useful to anyone who wishes to use a single antenna for the
diverse services that we find on those bands, ranging from
horizontally polarized CW, digital, and SSB at the low end of the
bands to vertically polarized FM in most of the upper part of the
bands.
In typical amateur radio fashion, I began to wonder: if one antenna
is good, might two be better? From that thought arose the idea of
stacking Lindenblads vertically to increase omni-directional gain.
This article will tackle the new question in some detail after
redesigning the Lindenblad for that kind of service. Stacking is not
a casual practice of simply setting two antennas in vertical
alignment and then feeding them in phase. |
|
"Hidden" Momentum in a Coaxial Cable
By Kirk T. McDonald, PhD
Joseph Henry
Laboratories, Princeton University |
|
The objective here
is to 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 resister R0
is connected to the other. The current may be taken as uniformly
distributed over the inner conductor, which has the sensitivity p.
The outer conductor has negligible resistivity, and the current
flows on it in a thin sheet at radius b. The battery has
negligible internal resistance.
Then to 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). Next, calculate the impulse on the charge on
the surface of the inner conductor due to the electric field induced
by the transient current. |
|
Yagi Antenna Q Factor
By
Dragoslav
Dobričić, YU1AW |
In one of my previous
articles, in the April 2008 Issue of antenneX, I proposed use
of the antenna SWR working bandwidth as contributor in evaluation of
Yagi antenna figure of merit. Antenna VSWR bandwidth is important as
relative measure of antenna Q factor and overall antenna
reproducibility and sensitivity to presence of other objects in its
near field. Because of that, VSWR bandwidth or Q factor contribute
to overall characteristics of antenna.
The VSWR bandwidth is relative measure of antenna Q factor and it is
very important factor for any evaluation of overall Yagi antenna
quality. In this article I want to show how we can calculate antenna
Q factor for use in antenna quality evaluation instead of previously
proposed use of VSWR bandwidth. |
|
Basic Operating Needs of the Radio
Shack
By L.
B. Cebik, W4RNL
(A Posthumous
Publication) |
|
Looking
at the shack as a place, we can begin the process of
transforming it into a center of activity. Amateur radio is a very
broad name for many activities. To sort out what may be most
relevant to each of us as individual hams, we must go back to
basics. In this article, we will look at the basics from a
perspective which differs somewhat from our usual view of Hamming:
one of being deeply involved in one or another part of it. Perhaps
the most fundamental aspect of amateur radio is communications,
so let's start there in this series of
articles. |
|
Bicycle Mobile, Direct Feed 146MHz
J-Pole: II
By Ed Lawrence, WA5SWD |
|
This is an
original design to address problems encountered with other bicycle
antenna designs available. Concerns addressed included good RF
behavior, effectiveness, safety, size, durability and ease of
construction and use. Compromise was necessary in some areas to meet
the overall objective. Further development efforts are continuing
but the basic concept seems sound.
Few simple antennas outperform a simple ground plane but, for a
bicycle mobile, radials are not acceptable due to safety concerns. A
stub-matched half-wave design looked promising but excessive RF
coupling to the shield made the coax ‘hot’ for RF and it was ruled
out.
Any antenna that requires a good ground plane such as the bicycle
frame will either be mounted too low for maximum signal or not have
a good ground or both. No other antenna designs were found that did
the job as well as a J-Pole described in this article. |
|
Coaxial Cable Current
By Jacques Audet, VE2AZX |
In this paper I
analyze and measure coaxial lines when subjected to currents on the
outer shield. The analysis may be done with simple models, no black
magic being necessary. A lab grade VNA is used to precisely measure
SWR and attenuation.
The first case deals with measurements done with the split 25 Ω – 25
Ω termination. This case was modeled at both low RF and higher
frequencies, up to a coax length of two wavelengths.
Measurements and modeling results show that this method does not
generate large shield currents as compared to feeding a half wave
dipole with a coaxial cable.
Possible transformer action of a short length of semi-rigid coax was
also investigated, by forcing current to flow longitudinally along
the shield. It shows that only skin effect coupling can be detected
below 5 MHz, using a very sensitive detector. |
|
|
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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? have
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? want
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Last modified:
June 02, 2008
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