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Author Topic: Clear Explanation of Antenna Information  (Read 271 times)
K6ATT
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Posts: 42




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« on: February 24, 2007, 11:09:28 AM »

I have no engineering or technical background, and that means that the ARRL Antenna Book and similar books on the subject of antennas are hard to understand. And the web sites I have seen on this subject are also rather technical.  Are there books or other sources (web sites perhaps) that explain antenna concepts more simply?  I do not understand feedline impedance and other concepts as well as I'd like to.  I also wonder how many other hams out there would benefit from simplified, yet accurate, information in this and other areas of this hobby.
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K0BG
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« Reply #1 on: February 24, 2007, 12:23:51 PM »

Jeff, by the vary nature of the beast, antenna theory is difficult at best. At its core is a need to understand what makes up impedance, and for that you need to start a the bottom end. That is to say, you need to have a good understanding of how inductors (L) and capacitors (C) react with respect to frequency. All of the information you need to start with, is in the first 5 or 6 chapters of the ARRL Handbook.

The next step is what happens when you put the two together (L & C) along with some resistance. In other words, a network. Once you're there, then a good portion of the information about antennas starts to make sense.

For sure, people spend their whole lives studying antennas, and still don't know it all. One of the foremost experts in the field is the good Dr. Maxwell, W2DU, and I'd bet even he would admit to not knowing it all.

Alan, KØBG
www.k0bg.com
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N6AJR
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« Reply #2 on: February 24, 2007, 01:29:12 PM »

ARRL has a vidieo on antennas where a fellow uses a 3 GHZ platform and shows you antenna pattersns and such with the mini antennas needed for 3 ghz. interesting tape.  lots of info there.

bottom line is you really need a little backround to get an idea on how antennas work. and why different types of antennas do what.

for instance a dipole will put out a figure 8 signal path perpindicular to the wire if it is high enough above ground,  too close to ground and it becomes almost onmnidirectional, a verticle with no radials is broad banded, but not very efficient, adding a ton of ground  radials makes it mo=re efficient, but the BW is decreased.

just grab a book and read the explainations. talk to friends and keep at it.  some times you can do rule of thumbs and get by with an antenna.

good luck, it is an interesting aspect of ham radio, but maybe something like ham radio for dummies would be a good starting place.
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W5DXP
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« Reply #3 on: February 24, 2007, 02:10:26 PM »

Antennas may be easier to understand from a quantum electrodynamics (QED) standpoint than from a conventional fields and waves standpoint. The free electrons in the copper or aluminum antenna elements absorb or emit photons at the carrier frequency depending upon whether they are decelerating or accelerating. The photons that escape the grasp of the free electrons are the photons that are radiated by the antenna. IMO, quantum particle physics is actually easier to understand than fields, waves, and Maxwell's equations.
--
73, Cecil, w5dxp.com
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
KB9CRY
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« Reply #4 on: February 24, 2007, 04:31:55 PM »

Join a local club or get a local elmer to steer you in the right direction.
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KB4QAA
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« Reply #5 on: February 25, 2007, 09:37:49 AM »

You can spend a life time in Ham radio playing with and learning about antennas.   Don't get frustrated, it is one of those things that provide some of the greatest interest and satisfaction with the hobby.

73, bill.
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VA7CPC
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« Reply #6 on: February 25, 2007, 10:26:13 AM »

>> I also wonder how many other hams out there would benefit from simplified, yet accurate, information in this and other areas of this hobby.
<<

Take your choice -- it can be simplified, or it can be accurate, but not both.  

The ARRL Handbook is a good place to start.  Take a look at the "Tales and Technicals" section of
   www.cebik.com  .  

It's not simple, but Cebik's explanations are clearer than most.

    Charles
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N3OX
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« Reply #7 on: February 25, 2007, 10:40:57 AM »

"Take your choice -- it can be simplified, or it can be accurate, but not both"

I'm not sure simplified is what's necessary.  I think "written in lay language" is more like it.

Even Cebik's writings (that I'd really recommend as a good read) don't have a section that explains what the impedance of a transmission line really is (the ratio of voltage to current if you're feeding power into the end of a semi-infinite line).

The trouble is that all decriptions have to start somewhere, and a lot of antenna descriptions that I could find, at least online, assume you know electronics already...

K6ATT, I think the solution might be to go to the library and check out all the books you can find on electronics and antennas and sort of do a survey of what makes sense to you to give you a starting point.  Basically, try to look up the stuff that you don't understand from the Antenna book.

I don't know of a good web resource for this, but digging around Wikipedia on each particular topic you want to know about might be pretty fruitful.  Wikipedia articles tend to be geared a little more toward those with no particular background in the subject.

Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
WB6BYU
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« Reply #8 on: February 26, 2007, 07:06:45 PM »

All of us had to start somewhere learning about antennas, and mostly
without a formal technical education in the subject.  Here is what has
worked for me over the years:

(1)  We start with the simple, easily-memorized rules.  The formula for
the length of a dipole, for example.  These give us general guidelines
to work with, even though we discover later that they are wrong.

(2) Read whatever you can find on the subject.  True, much of this may
be hard to understand, but try to extract one or two glimmers of
enlightenment out of each article.

(3) Experiment.  Try building antennas using your understanding.  Wire
antennas are cheap and you can reuse the same materials.  Sometimes
the results won't be what you expected - the dipole may have a high
SWR even though it is cut to the calculated length, or your fancy new
antenna may not work as well as a simple dipole.

(4) Think about what you learned in step (3).  What concepts do you
need to understand better?  Find some more articles and go back to
step (3).  Over time the various concepts start to sink in.

(5) Don't be afraid to discover that the general rules you learned in step (1)
were wrong.  Or to find that you've gained  better understanding of how
things work than popular writers on the subject.  After a while you will
find that you can judge a writer's level of understanding, and whether
their advice can be trusted.  The truth is that there is a lot of garbage
and bad advice floating around based on a flawed or incomplete
understanding of the subject.  Find writers who are both clear and
technically competent and use them as your guide.

(6) www.cebik.com/radio.html is a good place to start.

(7) If you aren't making mistakes, you aren't learning anything.
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K8GU
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« Reply #9 on: February 28, 2007, 07:08:06 AM »

I'm going to weigh in a little late on this.  You've been given good advice on how to get the information.  But, I'm going to try to shed some light on the subject as briefly as possible.  

There is an article in the Nov 1992 QST which is reproduced on the ARRL TIS website called "Why an Antenna Radiates."  It's a pretty accessible introduction to the language of antennas and electromagnetics.  (There is hardly any math involved.  However, if you find mathematics distasteful, you will forever be disadvantaged in learning more about antennas.)

The concept of impedance links the world of circuits to the world of electromagnetics.  Just as Z = V/I in circuits, Z = E/H in electromagnetics.  You should immediately recognize the analog between voltage and the electric field and current and the magnetic field.  Basically, the characteristic impedance forces the relationship between voltage and current waves on the line.  The physical configuration of materials in the transmission line dictate which wave 'modes' the line can support.  A mode is a solution to Maxwell's equations in the transmission line that specifies a certain unique configuration (essentially, a wave) of magnetic and electric fields (currents and voltages) that is valid for that structure.

Most amateur transmission lines take advantage of two 'TEM mode' waves, one travelling in the forward and the other in the backward direction along the line.  At any point on the line, the observed voltage and current is the sum of the voltage or current from the forward- and backward-going waves.  If the load is "matched", that is, equal to the characteristic impedance, the magnitude of the reflected voltage and current waves are zero.  Therefore, everywhere in the line, the ratio of the observed voltage and current (the observed impedance) is equal to the characteristic impedance.  

So, there's a lot more to it than this...but, I hope you get a chance to wrap your mind around it.  W5DXP's suggestion to start with QED is also quite elegant.  The idea that radiation occurs from points of "current acceleration" is very helpful even to practicing engineers!
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