Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Recommend 1 Antenna Construction Handbook  (Read 703 times)
KC2NLT
Member

Posts: 92




Ignore
« on: November 09, 2017, 02:12:50 AM »

Of all the dozens of antenna books and handbooks that advertize as “practical” antenna guides, is there one and only one that is the holy grail for antennas, a guide that everyone and their uncle swears by?

Please note that I’m only interested in 50 Mhz and above.
Logged
KM1H
Member

Posts: 2508




Ignore
« Reply #1 on: November 09, 2017, 07:10:48 AM »

Nope unless it is a vertical or dipole.

VHF and up horizontal gain antennas have made substantial improvements over the past decade.

A good software package is also an advantage if you have specific pattern needs such as a superb F/R pattern; most commercial offerings seriously lack in this area unless you start investing more money than I consider them worth.  Any yagi can be improved with a little effort and almost no money Grin

My 8el 6M yagi started as a well used 6 el Cushcraft 617B Boomer of 1970's era design and resulted in a repeatable 38-40 dB F/R over the lower 500 kHz and a real 13 dBi of gain. I had localized arc welding, computer, and power line noises that impacted DX and other weak signal chasing.

Carl
Logged
WB6BYU
Member

Posts: 17072




Ignore
« Reply #2 on: November 09, 2017, 09:40:31 AM »

No, there isn't.  Mostly because there are too many options to fit in one book.

The state of the art is continually advancing, and there are a number of antenna designers who
are continually coming up with new products.

In practice there are at least 3 different aspects to antenna designs:

* The electrical design, which determines the gain and pattern.

* The matching method, which determines the feedpoint impedance and SWR.

* The mechanical construction, which determines cost, reliability, ruggedness, materials required, etc.


There are, of course, some interactions:  changing the diameter of the elements for strength requires
changes in the element lengths to implement the same electrical design, for example.

But one problem with a lot of books (and magazine articles) is that they are written as if there is only
one way to build the antenna - exactly duplicating the one shown in the article.  True, many hams
want someone to tell them the "right" way to build it, but this rigidity of thinking isn't very useful.

Let's take a 3-element 2m yagi as an example.  A typical VHF antenna book may include one design,
perhaps a second if it was for a specific application.  But I have a collection of over 50 such designs
that I've modeled, using various element lengths, diameters, and spacings, and different boom lengths.
Why?  Because different applications may require a different choice of SWR, front/back ratio, size, gain,
side lobes, construction method, frequency coverage, materials, etc.

The late W4RNL wrote an article titled, "So You Want to Build a Yagi" that discussed 4 different 3-element
yagi designs for 10m:  three different boom lengths, which affected the gain among other factors, plus
one that was designed for a wide-band 50 ohm match, but with somewhat reduced gain.  Which is the
best design?  Depends on your needs.  Later he developed a spreadsheet that calculated yagi dimensions
for 3 different 3-element yagis:  one optimized for high gain, one for wide bandwidth, and one for a very
deep rear null.

And many of those models don't address matching or construction methods.  Some of my yagis use
1/8" aluminum wire stuck through PVC pipe, which is cheap, light, and great for portable or temporary use.
For a more permanent installation I might use 1/4" rod or 1/2" tubing, depending on what I have handy
and how much wind it needs to survive.  With a metal boom the element lengths need to be adjusted,
depending on how the element is mounted.  I also use steel tape measure for the elements of yagis that
I use while running through the woods, though I'm also experimenting fiberglass rods covered with wire
or copper braid.  Such antennas are usually no more than 24" long for ease of handling in the brush,
though I've also designed a longer 37" yagi for more accurate bearings.

A few of these have 50 ohm feedpoint impedances, but many are closer to 15 or 28 ohms, or wherever
they happen to end up.  Some use quarter wave transmission lines for matching, some use a folded driven
element, or a transformer in the boom, or a beta match, or something more exotic.  In many cases for
modeled yagis  don't even bother designing the match:  I'm mostly concerned with the radiation pattern
and the physical dimensions, and will figure out to match it when I get around to building one.


And that is all just for a 3-element 2m yagi.  Imagine how many options you have as you add more
elements and more bands...


Oh, and did I mention scaling antenna designs for other bands?  For example, G0KSC has some very good
quad designs for 6m that I've adapted for 20m and 15m for Field Day.


So you really need something that helps you choose a good design and shows the many different ways
that antennas can be built physically, and methods for matching impedances.  That allows you to choose
a combination that best meets your needs for your particular application and the materials
you have on hand and/or are comfortable working with.


A good place to start is GM3SEK's Long Yagi Workshop, then follow some of his links.
Logged
KC2NLT
Member

Posts: 92




Ignore
« Reply #3 on: November 09, 2017, 02:25:05 PM »

Thank you for that very detailed and helpful information. I appreciate that.

If commercial software is lacking in many areas, what would be a good way to determine if designs I play around with or a design I build is efficient?

Is an antenna analyzer the answer? Will that be the best tool to use?

Logged
N1CZ
Member

Posts: 24




Ignore
« Reply #4 on: November 09, 2017, 03:25:41 PM »

I recommend a less expensive to construct antenna to build of your possible interests. I think the details that you want are where the tire the meets the road. Get some experience in other words and your mileage *will* vary based on your own skills and how you interpret the cookbook.

Constructing an antenna is exciting, incredibly rewarding, and more expensive than you imagine .. contingent on your innovation to devise the necessary constructs.
Logged
WB6BYU
Member

Posts: 17072




Ignore
« Reply #5 on: November 09, 2017, 03:30:22 PM »

Many of the designs from DK7YB, W4RNL, G0KSC, etc. (as linked on the previously referenced
page) should be quite reliable and reproducible if you follow their directions.  Read the instructions
and descriptions from each designer.  Hopefully those sites (along with the WA5VJB "Cheap Yagis")
will give you enough options that you can find one that meets your needs.  Note that some European
designs will be optimized only for 144 - 146 MHz on 2m, because that is the extent of the band in
ITU Region 1.  That should be fine for CW/SSB or other weak signal work at the bottom of the band,
but the SWR will be higher at the top of the band if you are using FM to 148 MHz.  Pay attention to
bandwidth curves and matching details.

The more changes you make in things like element diameter and mounting method, the more it
can affect performance.  Not just gain, but sidelobes, F/B ratio, SWR curve, matching, etc.  Using
3/8" tubing rather than 1/4" rod isn't the end of the world, especially for simple designs, but in a
highly-optimized long yagi a significant change in diameter or mounting can negate the addition
of the last element or two.  This may not be a big deal if you are trying to hit a distant repeater,
but more critical if you are building an array for moonbounce.

It isn't necessarily that the antenna will have poor efficiency, however.  Usually what happens is
that the beamwidth is wider, or there are additional side lobes that mean less power is concentrated
in your main lobe.  Even if you don't have a certified antenna range for testing, a quick check on
a distant signal should show whether your pattern is similar to the original.  Significant changes will
also often show up in the feedpoint impedance:  the SWR will be higher than expected.  (You really
don't need an antenna analyzer to measure it:  a simple SWR meter should be adequate, as long as
it is designed for that frequency range.)

If you do want to branch out on your own and modify some of the existing designs, there is free
software that can help.  W9CF has a yagi modeling applet that used to run in your browser, but
with the newer Java versions you have to load it on your computer.  4NEC2 is a free modeling
package with lots of features, including a built-in optimizer.  Otherwise, if you get stuck and
want some help, post your design here on eHam and there are a number of Elmers who can
model it for you.  And if you have a particular application or constraints in mind, someone might
already have a design that fits.
Logged
VK6HP
Member

Posts: 155




Ignore
« Reply #6 on: November 09, 2017, 07:25:21 PM »

Great that you're approaching the challenge with interest and an open mind.  You have some good comments from Dale and Carl, among others.  One point I want to pick up is the value of becoming familiar with basic modelling tools, including a package like EZNEC.  I think you may have over-interpreted Carl's (correct) comment about the ultimate limitations of some software when the application gets demanding.  It's important to realize that you're currently some way from hitting most of those limits and that using readily available tools, in conjunction with a good dose of reading the types of design material recommended in previous posts, will help you develop insight and gain a feel for what you're doing.  I'll add a bit to the previous suggestions and recommend that you try reverse engineering some of the better-documented designs in (e.g.) EZNEC.  That's also a good way of progressing your expectations of what you can expect in the real world, along with building your own antennas, of course.

Your choice of a VHF start has both good and bad aspects.  On the positive side, it's easy to prototype and relatively easy to test.  The downside is that when antennas become "structural" (significantly 3D in wavelength terms), as they start to be in the VHF ham bands, some of the modelling limitations become more apparent.  An example is in fact the calculation of efficiency, where some approaches do quite badly at estimating apparently simple things, like dissipative losses.  In applications where we're extremely concerned with optimizations around efficiency (such as in radio astronomy), packages like FEKO do significantly better.  There are still applications, involving any number of other optimizations, where customized computational electromagnetics software is needed but progress in the last decade has fed my pragmatism/laziness; there's not much that can't be done with FEKO on a good processor cluster given enough cups of coffee while waiting Smiley  

By the way, some of the design tools for specific antenna types (like VHF yagis) incorporate first-order corrections to simple assumptions.  That's often fine in a practical sense but take the time to appreciate the nature and approximate magnitude of the tweaks.

Becoming familiar with modelling, and combining it with experiment and data, will certainly allow you to understand the value of approximation, grow your antenna interest and allow thoughtful interactions with the folks here and elsewhere.  It allows you to bring something to the table in the discussion and avoids what I've begun to see as the "serial pest" syndrome, where book-learnin' (and indeed most other learnin') is first deprecated, then pages written about minor variations around a highly specific, often fairly randomly chosen, part of a design/solution space - the sort of thing the poster could sort out themselves with 5 minutes in front of a PC and reference book.

Regarding the antenna analyser question, it's a very useful thing to have, especially if you take the time to learn about measurement techniques that work best, especially at VHF.  You want one that will last you a while, but without paying a fortune.  Have a look for one that covers the frequency range of interest and, these days, I'd go for a model that shows you the sign of the reactance directly.  There are a few current and recent threads from which you might get some ideas.

73, and good luck,
Peter.

« Last Edit: November 09, 2017, 07:40:23 PM by VK6HP » Logged
KM1H
Member

Posts: 2508




Ignore
« Reply #7 on: November 10, 2017, 12:11:39 PM »

The only real efficiency software I am aware of is the old K6STI YO (Yagi Optimizer) It keeps a running account against a theoretical algorithm as you make changes or let the computer do most of it. All mine from 40M to 70cm were designed with it.

His AO (Antenna Optimizer) works with all sorts of wire arrays and verticals, but has the usual NEC/Mininec inaccuracies with on ground radials.

Both are no longer being sold but copies do exist.

Carl
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!