|
NOTE: an audio version of the main topic
portion of my column is currently
offered in two formats: 1) Streaming for those with the
“RealPlayer” media-type program, and;
2) MP3 for “MS Media Player” or similar programs. Links are
provided for both below:
It's been several years since the last audio version of my column on the topic of the “antenneX mission.” In case you haven't heard that one in 2006, here it is:
Audio by Gary Nixon, WA6HZT |
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Radials Above and Below
INTRODUCTION
irst
and foremost, I wish everyone a happy, healthy, and prosperous New Year of
2012! In reflecting on the topics covered here in 2011, as in years past, we
saw the continued presence of “perennial” items such as radials. And, to
kick off this New Year, we will again revisit that subject, brought back to
the fore last month in the
antenneX
antenna discussion forum. I’ll start by highlighting the questions and
comments brought up in the forum, then we’ll look deeper into radials using
some materials we have found helpful in the past.
It all began with a question raised by Paul Clemens, DL4RAJ, as to whether
blank or bare metal radials were preferred over insulated ones. I’m not sure
if that question was ever fully answered, because a protracted discussion on
radials, radiation, and more quickly evolved and filled the forum for the
next several days.
At the
heart of it is how the current induced in the radials was getting there and
how it traveled on and near the radials themselves. As we have noted many
times in the past, even experts disagree, and that was quickly apparent. In
the end the participants agreed to disagree in essence, but that got me
thinking it was time to bring up radials again in this column since the
confusion prevails. The best way I know how to do that, is to bring you
quotes from the Master himself, my dear friend L. B. Cebik who passed away
in early 2008.
Of
note is this description of the book, as I saw it when it was added to
the Shopping Shack: “Throughout
the volume, Cebik takes a fairly unique view of the monopole. Instead of
looking at the antenna as an extension of a ¼-wavelength base-fed wire
against a perfectly conducting ground, he treats the monopole as half a
dipole with the ground-plane radial system acting as the completion of
the dipole structure.”
And, here’s what I wrote about the contents, or “notes” contained in the
book – looks like the perfect place to get some answers! “Over
the years, author Cebik has studied various aspects of both buried and
elevated ground planes, but his notes used a wide variety of
frequencies, often outside the amateur bands. Therefore, he started over
again, replicating and expanding his studies with special reference to
the amateur bands. Buried systems focus on the 160-, 80-, and 40meter
bands, while he also looked into elevated systems for the upper HF and
the VHF ranges. The sum of this work appears in this volume.”
And, there you have it — no significant difference. But in rereading
this collection of experiments and modeling, a number of other topics
presented themselves; topics that have been repeatedly brought up the
antenna discussion forum. A few of these are offered below with a short
answer summing up the long and very detailed answers found in
“Ground-Plane Notes.”
Q: How many radials must the ground plane use for adequate performance?
A: The short answer is: the more the better — to a point. Look at the chart below:
Based on modeling, it can be seen that more radials over very poor
ground makes the most difference. Over average to very good ground
the difference is far less. This chart is for the 160-Meter band,
but the information holds true for models done for 80 and 40 Meters,
as well. L. B. offers this summary:
“….I
have noted that for many purposes, 32 radials appear to mark a
threshold of performance stability in terms of gain and source
impedance…
However, above 32 radials, the amount of change per doubling of the
number of radials is small per step. Hence, any number of radials
from about 40 upward would likely be well within the region. Further
radials are not superfluous, but fields below the 30-radial level
may prove deficient for serious installations….”
On to the next…
Q: Does radial length make a significant difference to antenna performance?
A: Yes. Most of the changes that take place with various radial lengths happen between 0.01 to 0.25 wavelength, but there is still appreciable difference that can take place up to 0.5 wavelength. If choosing between fewer longer radials and several shorter ones, it is usually best to go with more short radials. But, shorter radials may also be questionable for average or very poor soils types, especially above 160 Meters.
And finally…
Q:
Does the depth of the radials make a significant difference to
antenna performance?
A:
I’ll let L. B. tackle this one personally: “For virtually any upper
MF or lower HF monopole installation, radial depth is unlikely to be
a major concern.”
There is so much more to this book than the small bits listed above.
The amount of time invested in researching and modeling so many
scenarios is staggering. Here is the Table of Contents contained in
the book:
-
Some Ground Grounding
-
Modeling Ground-Plane Antennas
-
A Matter of Perspective
-
Conductivity and Permittivity
-
Frequently Asked Questions
-
Elevated Radials
-
Parasitic and SCV Arrays
-
¼-λ to 5/8-λ Monopoles
-
Models Used in These Studies
You can find “Ground-Plane Notes” here:
http://antennex.com/Sshack/gplane/gplane.html
You can download it right now or order it on CD. I believe you will
find it is money well spent to help cut through the “mystery” of
radials — whether to use radials and how.
NEW SOFTWARE
And also, to start the New Year, we have some more new software in
the Shopping Shack from the ever-prolific Harold Kinsley, WA4GIB.
This time, he’s brewed up a brand new utility I think almost every
antenneX user can
appreciate — one that performs several calculations on VSWR (voltage
standing wave ratio).
Simply and appropriately called “VSWR Calc”, all you need to do is
put in a few parameters, push a button, and get instant results.
Here, in Harold’s own words, is what he has to say about “VSWR
Calc”: “Ever wonder how all
those units of measure such as return loss, percent reflected power,
VSWR and reflection coefficient are interrelated? Do you wonder
about the actual VSWR at the antenna when you measure it on the
ground (transmitter)? Are you curious about how line loss affects
the VSWR at the transmitter versus antenna and how much additional
loss the VSWR at the antenna causes on the line. This software
application can answer all these questions and more.”
The bottom line is you will find several commonly needed
calculations here in an easy-to-use piece of software.
It’s all very cleanly laid out and intuitive to use.
And, it’s available right now in the Shopping Shack.
We are pleased to add this new program to the Software
section of the Shopping Shack.
Click here to see more info.
You can find all of this item and more in the Shopping
Shack. Just check out the
Main Menu and sub-menus of categories
located there.
THE PURPOSE OF THIS JOURNAL
In my column for September 2006, “The antenneX Mission,” I wrote about
a subject close to my heart — the purpose of this journal. It had been quite
some time since I had reminded our readers of our original purpose when we set
out some 20 years ago.
More than anything else, this journal has always been a “labor of love” for me.
It is the reason I founded the antenneX magazine almost 20 years ago, knowing
that running a magazine is a tough business and especially so since I planned to
do it without the traditional revenue support from advertisers or outside
investors. I wanted this magazine to always be able to write about any issue
without concerns of losing the support from any of those type revenues. I am
pleased to say, we have never steered from that course one iota. And, as a
consequence, we have covered some very controversial developments throughout the
past two decades. In the process, we have provided valuable factual information
to more than 200 countries, even to the most remote regions of the globe. Hence,
our readers are much more informed about the truth about all of the “new”
devices as their stories unfolded in the antenna and antenna-related field. For
more details, you are encouraged to read my column from September 2006.
Additionally, we were pleased to receive and publish in the October 2006 issue, a very special editorial reaction to my column written by one of our long-term readers and contributors, Dr. Jef Verborgt. Those two articles are located by the following links below:
VISIT THE GUEST ROOMS
The relentless attacks on our web site by pirates and the like has made it
necessary to add more security to protect our material against such piracy. It's
only fair that we know who enters the House of antenneX, so our guests
will need to provide some minimal information in the process of obtaining a
login. This includes using your real active email address without which a login
cannot be received. Do not confuse this login with a paid subscription login.
They are not the same and your subscriber login will NOT work in the Guest Room
areas. Of course, you may choose to create your own login to the Guest Rooms
using the same login as your subscription, if the system will accept it.
Along with the continuing fight against spam/virii junk, protecting our material and valuable bandwidth against piracy takes up a great amount of our time—time we can't really spare. The Internet is simply not the friendly neighborhood it used to be in the "old days" and more and more security must be installed to counteract these intruders. Thus, we have made the access to the Guest Rooms as automatic as possible for you to manage your own login.
http://www.antennex.com/guests.html
http://www.antennex.com/guests.html
In view of the above, we have overhauled the numerous free and open-access sections that have always been wide open to all of our friends throughout the many years antenneX has been online. But, we must change with the times as the need dictates. I don't think the Internet will become more friendly in the near future and protected sites with logins are fast becoming the rule rather than the exception. To repeat, most would like to know who they invite into their house. The same applies at the House of antenneX. It's really worth the effort!
This list pertains to those sections with free access now in our new Guest Rooms we have built and fully operating:
• Antenna Science
• Preview Articles
• Software Download
• Antenna Modeling
• From the Shack
• Propagation
• Ham WorkShop
• Stone's Throw!
• Discussion Forums
• Patents (new room under construction)
We have activated a new login system for access to the above guest rooms — and, the login can be totally managed by our guests. Above is a graphic of what you see as a login page to the new consolidated area, "antenneX Guest Rooms." This new page for logins is at this location now and available for your use:
Get your login all setup now at this URL:
http://www.antennex.com/guests.html
We've really tried to make it easy while still fending off the bad guys, i.e., pirates!
As a result of this new programming, you will be able to obtain your own login, change it to update your info, change your password and delete membership if & when you desire without our help. Of course, the bottom link on the new page provides help if you still need it.
If you still need help or
have questions about our login areas, check this page first:
http://www.antennex.com/help/need_help.html
The new Antenna Discussion List is a infinite fountain of ideas making it a great "watering hole" for exchange of ideas, questions and answers on a wide range of antenna-related subjects. You will be in good company along with some of the brightest minds available. Were else would you have such free access to this level of expert advice? To participate or just read along on some very interesting subjects each month with 2000+ members from all around the globe, you are welcome to join us:
You are encouraged to contribute your thoughts on various subjects to a worldwide audience.
AN INVITATION TO CONTRIBUTORS
antenneX
thrives on the contributions of antenna experimenters, ranging from the informal
home shop construction project to the theoretical investigation of basic
antenna, feedline, and propagation phenomena. Over the years, we have published
articles on the use of new or newly adapted materials, known antennas adapted to
new circumstances, modifications of antenna structures, basic explorations of
both common and unusual antennas, antenna modeling exercises, design
improvements, antenna matching techniques from both a physical and mathematical
perspective, evaluations of mini-antennas and their underlying theory of
operation, new and patentable designs, propagation tutorials, and.... The list
goes on, since no antenna-related topic is irrelevant to the readers of
antenneX.
At the same time, antenneX has experienced continuous growth in its
readership—for which we are appreciative. However, all readers can help us do
even better. How? By submitting an article every now and then based on your
current antenna work that may be useful at any level to other readers.
Among the engineering and researching readers, there are
undoubtedly a number of unclassified and non-proprietary findings that
antenneX readers would like to know. Among the practical antenna designers,
there are ideas, tests, and numerous other practical findings to benefit our
readers. Antenna builders very likely have some techniques to share with other
readers. Besides the regular articles, we always have the home work shop column
for shorter practical ideas and we always have the invited news and editorial
column for information about new technologies, future advances, lost old but
good ideas, and personal views on the good to bad things that are happening in
the world of antennas and propagation.
If you are uncertain about whether your ideas merit an article, please feel free
to send an outline to the general editor/publishers at
manuscripts at antennex.com
. Do not feel that you must be ready to be a regular submitter to write for
antenneX, because we welcome the individual contribution as much as monthly
articles. As well, do not believe that the slots in each issue are already
spoken for—we shall always make room for a worthy article.
To see details of our writing guidelines, please look at: Writing for antenneX
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Keep the issues coming and stay on the leading edge of antenna technology!
~ BE SURE TO VISIT THE SHOPPING
SHACK ~
Shipments worldwide ~ plus instant downloads
| Subscription |
Books |
Software |
Antennas |
Components |
IN THIS ISSUE
We again include many fine articles by our great writing team from around the globe. Now, allow me to introduce this month's line-up of content:
OUR MONTHLY COLUMNS (plus this one you are reading):
- Antenna
Modeling By L. B. Cebik, W4RNL
(SK)
This column has ended subject to replacement.
-
From the Shack
By Neal Arundale - M1CHS
A Coax Switch
This article shows how to make an inexpensive homemade antenna selection switch. If you question the use of a cheap slide switch and SO239 coax sockets, read on. Measurements in a physics lab showed there to be practically no reflection on HF and even on 70 cm the SWR was below 1.3 : 1! That is explained here.
-
Antenna Design & Use
By
Justin Johnson, G0KSC
An introduction to the OP-DES Yagi
In this article we take a look at the OP-DES (Opposing Phase Driven Element System) Yagi and explore the potential benefits it possesses over and above the traditional split dipole fed Yagi.
Since the early influences of YU7EF I have looked to achieve the best possible performance from a 50-Ohm direct feed Yagi. There are a number of reasons for doing this: First relates to bandwidth and stability as it has always been the case that 50-Ohm dipole fed Yagis tend to be able to achieve far wider bandwidths with flatter SWR curved that low impedance types. This means that such designs can be ‘more forgiving’ to the home builder as small errors will not have an impact on the performance of the antenna and no matching device is required either. The disadvantage is performance within split dipole 50-Ohm Yagis tends to be a little down on lower impedance types, in particular, the levels of front to back ratio (F/B) that can be achieved.
FEATURE ARTICLES IN THE LIBRARY:
|
A Power divider
/ splitter |
|
As an alternative to a phasing harness, it's possible to build a 2-way splitter which is a more precise way of matching two 50-Ohm antennas. Also, they can be bought commercially. Justin, G0KSC identified the sizes of box section and tubing to use but I thought it worthwhile checking the size suggestions and this article explains the details of that and construction. |
|
Practical Antennas: Part 5.03 |
|
Every transmission line will have some inherent loss, partly of the resistance of the conductors, partly because power is consumed in the dielectric used for insulating the conductors and partly because in many cases a small amount of power escapes from the line by radiation. As transmission lines are made larger by using thicker conductors, the resistance is reduced and as the dielectric material gets closer to low-loss air, the losses are reduced. The skin effect causes current to travel nearer to the surface of the conductors at higher frequencies. Therefore, the effective loss increases as the frequency is increased. |
|
NewcomerNotes ~ It's a New Year! |
|
2011 was an interesting, fun, and frustrating year for me and radio.
Interesting because I had the opportunity to experiment with some
new antennas, radios, and modes. Fun because (see above!) and
because I passed a personal milestone of 100+ DX amateur radio
countries. Frustrating because I didn’t get to spend as much time on
the air as I wanted (do we ever?!), and because I had some storm
damage to antennas which were working quite well before Mother
Nature got involved. Maybe I have equally described your 2011 experiences too (hopefully without the damage!), and like me you are looking forward to 2012. I have a number of projects in mind (always more than I can get to), all of them poised to enhance my enjoyment of this wonderful hobby. I frankly don’t understand people who get bored with radio considering the massive number of things one can hear and do with even a modest setup. No insult intended to those who are finding their interest in radio dwindling; it’s just that I always seem to find new things to challenge me and “old” things to re-discover and thus, new to me. |
|
What is the Role
of the Arms of a Linear Broadcast Antenna? |
| A broadcast antenna is a transducer of energy from a voltage source into the energy of distanct electromagnetic fields. In its simplest form the antenna should consist of a compact voltage source located in the gap between two linear conductors (the "arms") as shown in a sketch within this paper. We go on to discuss the configuration is substantial detail. |
|
The Self- Resonant Ferrite Rod Antenna
- Part 2 |
|
A reduction in the length of resonant wire antennas has previously
been achieved by placing ferrite beads over the wire. However it is
shown here that the ferrite is used more effectively if the wire is
wound around the ferrite |
|
The DK7ZB-Match for Yagis |
|
It is a well known
phenomenon that the radiators resistance in a Yagi-structure drops
down by adding parasitic elements to a dipole as a radiating
element. For the VHF-Bands (50-50.5MHz, 144-146MHz, 430-440MHz) a
radiation resistance of 25-35Ohm has the best balance for gain, back
and side-lobes, bandwidth and SWR at tenable losses in a Yagi. The classic match for that resistance/impedance is the Gamma-Match. The Beta-Match is a good choice as well, but realisation on VHF is difficult for a homebrew. For that reason a new simple, easy to build match was developed in 1995 for Yagis with resistive loads of 12.5, 18 and 28 Ohms. We present my version in this article. |
Well, there you have it, folks—thanks for
listening and remember, the reading lamp is always on for you in the reading
rooms. If I can be of further help, I'm just a
Stone's Throw! away.
-30-
Jack L. Stone,
Publisher
January 2012 antenneX Online
Issue #177