[DTV Student]

Hi Folks,

Has anybody tracked down any information about the design of "fractal antenna" beyond the lead that Autofils mentioned last spring?

Thank you,
DTV Student

 

[DTV Student]

I would like to learn about fractal antennas that an average do it yourself experimenter with nothing more than 12 gauge copper wire, pliers and other simple tool could build.

Your comments are appreciated,
DTV Student

 

[DTV Student]

Fractals - 4nec2 - Re-Think

Hi Folks,

300ohm... I took your advice and installed 4nec2. I browsed through "A Beginners Guide to Modeling with NEC" by L. B. Cebik. His explanation was pretty understandable. So, I jumped right into the fractal examples that were installed with the 4nec2 software. Very interesting. I have no idea how to re-scale the examples for use in the 470 MHz to 700 MHz range.

Actually, I think I am getting way ahead of myself. I better learn how to use 4nec2 to model something like a simple dipole first. LOL... Somethings in life are humbling.

Have a Great Day,
DTV Student

 

[DTV Student]

Hi Folks,

I am not sure where I found "A Beginners Guide to Modeling with NEC" by L. B. Cebik. Perhaps it was in some of the extras I found at Arnie Voors' website (http://home.ict.nl/~arivoors/). I am not a member of ARRL. I bet they have lots of great background information too.

I found the _GetStarted.txt file and have just started reading it. It looks like it will take some serious time to work through this tutorial. I am sure I will have lots of questions.

Thanks for the information and encouragement.
DTV Student

 

[DTV Student]

Getting Started with 4NEC2

Hi Folks,

I finally made it through the _GetStarted.txt file. WOW! The first half was not so bad. I was able to work through the examples and I even had a vague idea of what the plots were trying to tell me. I really liked exploring the 3D far field plots. LOL... then I got to the Smith Charts. Yikes!!! Time to do some back tracking on Wikipedia.

I have found many references to L. B. Cebik's website and a huge number of articles he wrote on antenna designs and modeling. I remember looking at some of his work last year when I first started reading about basic antenna design. Mr. Cebik, W4RNL, was still writing articles for antennaX at that time. It is my understanding that Mr. Cebik passed away in April 2008. He will be greatly missed.

Many of his articles are no longer freely available. I guess antennaX has to make a buck too.

Are there other antenna modeling tutorials out there written at the same level and style of Mr. Cebik?

Thank you,
DTV Student

 

[DTV Student]

4NEC2 - A Very Cool Tool

Hi Folks,

I have been busy exploring 4NEC2. I wish I understood one hundredth of what this software package is all about. I am very impressed!

It takes some serious time playing around with the graphical editor to get used to all of its features. I keep stumbling into new features. Very nice indeed.

Being able to switch back and forth between the FOUR editors is also very helpful especially when one want to apply a "voltage source" to one's latest antenna idea. LOL... I think I finally figured out how to work around that problem by looking at the EX record or "card" in a few of the models provided with the software.

I have worked through the phasing harness problem for the vertically stacked 4 bay bowtie designed I mentioned in another thread. I first drew the four bowtie stack. Then I added the parallel and equal length harness. I learned a lot about the editor just by building that harness. I saved that file, copied it, renamed it and edited the new file to add a crossover harness like the CM4221. I also did a third design one similar to the second but with no crossover. LOL... I had heard that bowties in this sort of configuration cancel each other out. Sure enough 4NEC2 predicted this design to be a failure. It is nice to know theory matches up with others' experiences.

A little later on, I added a large relector grid. The first 4 or 5 grids had to many segments for the software to process. I kept reducing the number of vertical and horizontal elements in the grid until the software stopped complaining. I would have been better off to have used a series of horizontal rods instead of the built-in reflector grid. The reflector, of course, made a big difference in performance. The reflector grid increased the processing time beyond belief. One can get a good idea of how something like the harness problem might work by leaving off the reflector grid and comparing the two designs by looking at the horizontal gain patterns and/or the forward gain chart from 470 to 700 MHz. Frequency scans are so cool !!!

Maybe I will clean up these three examples and post them for comments. I am still a little confused about the "Source/Load" concept(s).

Have a Great Day,
DTV Student

 

[DTV Student]

4NEC2 - Struggling with Concepts

I have worked through the phasing harness problem for the vertically stacked 4 bay bowtie designed I mentioned in another thread. I first drew the four bowtie stack. Then I added the parallel and equal length harness. I learned a lot about the editor just by building that harness. I saved that file, copied it, renamed it and edited the new file to add a crossover harness like the CM4221. I also did a third design one similar to the second but with no crossover. LOL... I had heard that bowties in this sort of configuration cancel each other out. Sure enough 4NEC2 predicted this design to be a failure. It is nice to know theory matches up with others' experiences.

Hi Folks,

Clearly, I am getting way ahead of myself. I got so involved with exploring the graphical editor, generating the far field patterns and drooling over the 3D viewer results, especially the "Total Gain and Multi-Color" mode, that I totally missed what the Azimuth and Elevation angles were all about. LOL... Back to basics.

Scratch my earlier comments about the 4 bay bowtie with no crossover in the phasing harness. Appearently, I was looking at some part of the Total Gain Pattern that had a circular shape and a value less than 0 dBi. Who knows? When I came back to it later, it looked very different than I had remembered.

I better take a short course in what Azimuth and Elevation angles are all about. Your comments and/or explanations are greatly appreciated.

Thanks,
DTV Student

 

[DTV Student]

Spherical Coordinate System

Hi Folks,

ericball... Thank you!

I also found a good explanation of the Spherical Coordinate System at:

http://en.wikipedia.org/wiki/Spherical_coordinate_system

Testing Fonts:
Phi = Φ
Theta = Θ
How about that!

Have a Great Day,
DTV Student

 

[DTV Student]

File Attachments ???

Hi Folks,

I am new to the "Digital Forum". I have only made 9 posts so far. So... maybe that is the problem?

On other forums similar to this one, I have been able to attach files containing examples of the subject being discussed. I don't see any way to attach a file using this "Reply to Thread" editor. I must be missing something. LOL... but what is it?

Your comments are appreciated.

Thank you,
DTV Student

 

[DTV Student]

4NEC2 Editor Examples (Part 1 of 4)

Hi Folks,

I am learning how to use the geometric editor in 4NEC2 Version 4.7.3. I want to follow the conventions suggested by the late L. B. Cebik in his 4 part series titled "A Beginners Guide to Modeling with NEC".

Eventually, I would like to compare the effects of several slightly different phasing harnesses on a vertically stacked four bay bowtie array. But first, I have to learn how to layout the various antenna elements and build a proper NEC file.

I used the geometric editor and notepad to create three example files. To keep things simple, I made each bowtie whisker about 10 inches long. The bowtie assemblies were stacked vertically 10 inches apart center to center. I did not include a reflector. The same set of bowtie assemblies are used in each example.

The differences are all about how the bowtie assemblies are connected together. In the simplest example, I connected the bays together with a parallel structure which looks like railroad tracks. The next example is very similar to the first case, except the leads going to the top and bottom bays are crossed but not touching in a manner similar to the CM4221. The last example is a little more complex. The runs from the center feed point to the center of each bay are all equal lengths. This harness is sort of like a tree turned on its side. I have heard tree structures are the best way to avoid phasing problems common in a wide band width vertical and/or horizontal stack designs.

Since I have not figured out how to attach my NEC files to this post, I will list the three files separately in the next few posts. Hopefully, you will be able to cut and paste the listings to individual Notepad text files. Then you can rename the text files from something like TREE.TXT to TREE.NEC. If you do not change the file extension from ".TXT" to ".NEC", 4NEC2 can still open it. Run 4NEC2 and click the file open button. The "Open File" common dialog form will appear. Be sure to set the "Files of Type" drop down list box near the bottom of this from to "*.TXT files (*.TXT)" or to "All files (*.*)" and then select the file of interest. I am sure there are dozens of ways to do the same thing.

I would like to hear your thoughts and suggestions concerning the geometric layout of these examples. Am I making any obvious mistakes? Am I following common antenna layout conventions?

Your comments are appreciated,
DTV Student

 

[DTV Student]

4NEC2 Editor Examples (Part 2 of 4)

Hi Folks,

Below is the listing of my bt-4bvs-10w10ctc-railroad.nec file:

CM Bowtie, 4 Bays Vertically Stacked, 10 inch Whiskers with 10 inch center to center spacing
CM Phasing Harness is a Parallel Structure like Railroad Tracks
CM No Reflector Grid (add one to improve preformance)
CE
GW 1 3 0 -0.5 0 0 0.5 0 0.04040404
GW 2 17 0 0.5 15 0 10 18.5 0.04040404
GW 3 17 0 0.5 15 0 10 11.5 0.04040404
GW 4 17 0 -0.5 15 0 -10 11.5 0.04040404
GW 5 17 0 -0.5 15 0 -10 18.5 0.04040404
GW 6 17 0 0.5 5 0 10 8.5 0.04040404
GW 7 17 0 0.5 5 0 10 1.5 0.04040404
GW 8 17 0 -0.5 5 0 -10 1.5 0.04040404
GW 9 17 0 -0.5 5 0 -10 8.5 0.04040404
GW 10 17 0 0.5 -5 0 10 -1.5 0.04040404
GW 11 17 0 0.5 -5 0 10 -8.5 0.04040404
GW 12 17 0 -0.5 -5 0 -10 -8.5 0.04040404
GW 13 17 0 -0.5 -5 0 -10 -1.5 0.04040404
GW 14 17 0 0.5 -15 0 10 -11.5 0.04040404
GW 15 17 0 0.5 -15 0 10 -18.5 0.04040404
GW 16 17 0 -0.5 -15 0 -10 -18.5 0.04040404
GW 17 17 0 -0.5 -15 0 -10 -11.5 0.04040404
GW 18 21 0 0.5 15 0 0.5 5 0.04040404
GW 19 11 0 0.5 5 0 0.5 0 0.04040404
GW 20 11 0 0.5 0 0 0.5 -5 0.04040404
GW 21 21 0 0.5 -5 0 0.5 -15 0.04040404
GW 22 21 0 -0.5 -15 0 -0.5 -5 0.04040404
GW 23 11 0 -0.5 -5 0 -0.5 0 0.04040404
GW 24 11 0 -0.5 0 0 -0.5 5 0.04040404
GW 25 21 0 -0.5 5 0 -0.5 15 0.04040404
GS 0 0 0.0254 ' All in in.
GE 0
EX 0 1 2 0 1 0
GN -1
FR 0 1 0 0 585 0

 

[DTV Student]

4NEC2 Editor Example (Part 3 of 4)

Hi Folks,

Below is the listing of my bt-4bvs-10w10ctc-crossover.nec file:

CM Bowtie, 4 Bays Vertically Stacked, 10 inch Whiskers with 10 inch center to center spacing
CM Phasing Harness is a Crossover style like the CM4221
CM No Reflector Grid (add one to improve preformance)
CE
GW 1 3 0 -0.5 0 0 0.5 0 0.04040404
GW 2 17 0 0.5 15 0 10 18.5 0.04040404
GW 3 17 0 0.5 15 0 10 11.5 0.04040404
GW 4 17 0 -0.5 15 0 -10 11.5 0.04040404
GW 5 17 0 -0.5 15 0 -10 18.5 0.04040404
GW 6 17 0 0.5 5 0 10 8.5 0.04040404
GW 7 17 0 0.5 5 0 10 1.5 0.04040404
GW 8 17 0 -0.5 5 0 -10 1.5 0.04040404
GW 9 17 0 -0.5 5 0 -10 8.5 0.04040404
GW 10 17 0 0.5 -5 0 10 -1.5 0.04040404
GW 11 17 0 0.5 -5 0 10 -8.5 0.04040404
GW 12 17 0 -0.5 -5 0 -10 -8.5 0.04040404
GW 13 17 0 -0.5 -5 0 -10 -1.5 0.04040404
GW 14 17 0 0.5 -15 0 10 -11.5 0.04040404
GW 15 17 0 0.5 -15 0 10 -18.5 0.04040404
GW 16 17 0 -0.5 -15 0 -10 -18.5 0.04040404
GW 17 17 0 -0.5 -15 0 -10 -11.5 0.04040404
GW 18 5 0 0.5 15 -0.5 0 12.5 0.04040404
GW 19 5 -0.5 0 12.5 0 -0.5 10 0.04040404
GW 20 9 0 -0.5 5 0 -0.5 10 0.04040404
GW 21 5 0 -0.5 15 0.5 0 12.5 0.04040404
GW 22 5 0.5 0 12.5 0 0.5 10 0.04040404
GW 23 9 0 0.5 5 0 0.5 10 0.04040404
GW 24 9 0 -0.5 -5 0 -0.5 -10 0.04040404
GW 25 5 0 0.5 -15 -0.5 0 -12.5 0.04040404
GW 26 5 -0.5 0 -12.5 0 -0.5 -10 0.04040404
GW 27 9 0 0.5 -5 0 0.5 -10 0.04040404
GW 28 5 0 -0.5 -15 0.5 0 -12.5 0.04040404
GW 29 5 0.5 0 -12.5 0 0.5 -10 0.04040404
GW 30 9 0 -0.5 5 0 -0.5 0 0.04040404
GW 31 9 0 -0.5 0 0 -0.5 -5 0.04040404
GW 32 9 0 0.5 5 0 0.5 0 0.04040404
GW 33 9 0 0.5 0 0 0.5 -5 0.04040404
GS 0 0 0.0254 ' All in in.
GE 0
EK
EX 0 1 2 0 1 0
GN -1
FR 0 1 0 0 585 0

 

[DTV Student]

4NEC2 Editor Example (Part 4 of 4)

Hi Folks,

Below is the listing of my bt-4bvs-10w10ctc-tree.nec file:

CM Bowtie, 4 Bays Vertically Stacked, 10 inch Whiskers with 10 inch center to center spacing
CM Phasing Harness is an Equal Length Tree Structure
CM No Reflector Grid (add one to improve preformance)
CE
GW 1 3 -1 -0.5 0 -1 0.5 0 0.04040404
GW 2 17 0 0.5 15 0 10 18.5 0.04040404
GW 3 17 0 0.5 15 0 10 11.5 0.04040404
GW 4 17 0 -0.5 15 0 -10 11.5 0.04040404
GW 5 17 0 -0.5 15 0 -10 18.5 0.04040404
GW 6 17 0 0.5 5 0 10 8.5 0.04040404
GW 7 17 0 0.5 5 0 10 1.5 0.04040404
GW 8 17 0 -0.5 5 0 -10 1.5 0.04040404
GW 9 17 0 -0.5 5 0 -10 8.5 0.04040404
GW 10 17 0 0.5 -5 0 10 -1.5 0.04040404
GW 11 17 0 0.5 -5 0 10 -8.5 0.04040404
GW 12 17 0 -0.5 -5 0 -10 -8.5 0.04040404
GW 13 17 0 -0.5 -5 0 -10 -1.5 0.04040404
GW 14 17 0 0.5 -15 0 10 -11.5 0.04040404
GW 15 17 0 0.5 -15 0 10 -18.5 0.04040404
GW 16 17 0 -0.5 -15 0 -10 -18.5 0.04040404
GW 17 17 0 -0.5 -15 0 -10 -11.5 0.04040404
GW 18 21 0 0.5 15 0 0.5 10 0.04040404
GW 19 21 0 0.5 5 0 0.5 10 0.04040404
GW 20 21 0 -0.5 5 0 -0.5 10 0.04040404
GW 21 21 0 -0.5 15 0 -0.5 10 0.04040404
GW 22 21 0 0.5 -5 0 0.5 -10 0.04040404
GW 23 21 0 0.5 -15 0 0.5 -10 0.04040404
GW 24 21 0 -0.5 -15 0 -0.5 -10 0.04040404
GW 25 21 0 -0.5 -5 0 -0.5 -10 0.04040404
GW 26 3 0 0.5 10 -1 0.5 10 0.04040404
GW 27 3 0 0.5 -10 -1 0.5 -10 0.04040404
GW 28 3 0 -0.5 -10 -1 -0.5 -10 0.04040404
GW 29 3 -1 -0.5 10 0 -0.5 10 0.04040404
GW 30 36 -1 0.5 0 -1 0.5 10 0.04040404
GW 31 36 -1 0.5 -10 -1 0.5 0 0.04040404
GW 32 36 -1 -0.5 0 -1 -0.5 -10 0.04040404
GW 33 36 -1 -0.5 10 -1 -0.5 0 0.04040404
GS 0 0 0.0254 ' All in in.
GE 0
EX 0 1 2 0 1 0
GN -1
FR 0 1 0 0 585 0

 

[DTV Student]

Gray Hoverman Threads

Hi Folks,

Yeah, I took a look at both treads last month. It took a lot of time just to scan all of that material. Clearly, the thread leaders have put in a lot of hard work supporting Gray Hoverman design and improving it. Bravo!!!

I was impressed with level of detailed design drawings, practical implementation suggestions and the mathematical modeling that so many contributors have provided. Triple Bravo!!!

After reading through these threads, I started thinking that maybe I should spend a little time learning about antenna modeling instead of just cutting and bending coat hangers into all sorts of exotic shapes. LOL... Besides, I am running out of coat hangers, not to mention all my old copper tubing and electrical wiring left overs. So began my interest in the 4NEC2 freeware by Arie Voors.

I have been playing with 4NEC2 for a few weeks now. While I have learned alot, I still have a lot more to learn about the package and theory of antennas before I could ever think of contributing in a meanful way to the Gray Hoverman Threads.

Currently, I am back tracking through all of the experimental antennas I have hanging from the rafters of my garrage. I am trying to model them with the 4NEC2 software and to understand their performance issues. I gotta start somewhere. I will also re-read the posts about modeling the Gray Hoverman antenna and try to apply the suggestions to my own understanding of the 4NEC2 software. I just gotta stop chopping up coat hangers without any idea of what I am doing or where I am going. I see antenna modeling as a way of experimenting with an idea before committing it to real hardware.

Sooner or later, I will build one of the second generation Gray Hoverman designs.

Thanks for the suggestions and encouragement,
DTV Student

 

[DTV Student]

GH Driver Array - Modeling Experiment - Part 1

Hi Folks,

I am a newbie to the world of antenna modeling. I have been playing with Arie Voors' 4NEC2 modeling software for about a month. I have developed some skill using the geometric editor. I can layout three dimensional wire structures that resemble basic antenna shapes. My lack of understanding of antenna design and the use of Arie's software is profound. I would appreciate your suggestions and comments as I blunder through my first modeling experiment.

I plan to go back to the beginning of the great work done by autofils, 300ohm and others on the Gray Hoverman design. I want to systematically explore the basic parts of this design. I hope to build some understanding of the modeling process and to obtain some insight into the major components of the Gray Hoverman antenna and how they interact with each other. I will build one of the models, so I will use only English measurements, simple tools and materials found in my garage.

I will begin by exploring the driver array of the Gray Hoverman design. Later, I will add a simple reflector and model how it enhances performance. The structure of the driver array can be though of in terms of the lengths of all straight wire elements and the angles between them. I will preserve the original angles between all of the elements and the symmetry of the design. I will only change the lengths of straight wire elements. With these constraints in mind, I think the driver array can be reduced to three length variables: 1) the feedpoint gap, 2) the 12 zig zag elements and 3) the 4 stubs.

For my next post, I hope to have a few plots of the total horizontal gain vs. channel number that might help me to visualize what is happening as I systematically change one of these three variables at a time.

Your comments and suggestions are always appreciated.

Thank you,
DTV Student

 

[DTV Student]

GH Driver Array - Modeling Experiment - Part 2

Hi Folks,

Experiment #1

Purpose of Experiment:

To observe what happens to the Total Horizontal Forward Gain vs. Channel Number curves as the feedpoint gap distance is changed from 0.5 inches to 3.0 inches in steps of 0.5 inches for several families of the Gray Hoverman Driver Array Assembly.

Figure 1: The Gray Hoverman Driver Array Assembly

In Figure 1, the length of wire number 17 corresponds to the feedpoint gap distance; wire numbers 2 through 7 and 10 through 15 represent the zigzag elements; and wire numbers 1, 8, 9 and 16 make up the stub elements.


Methods and Materials:

At http://www.digitalhome.ca/forum/showthread.php?t=81982&page=19, Post 284, I found a drawing by Elvis Gump of the First Generation Gray Hoverman Antenna developed by Autofils and others. This seemed like a great place to start since it is a real working and well optimized antenna. The feedpoint gap is 1.77 inches. The length of each zigzag element is 7.07 inches. The length of each stub is 5.59 inches.

In this experiment, I planned to let the gap distances vary from 0.5 inches to 3.0 inches in steps of 0.5 inches and the stub lengths vary from 2.0 inches to 6.0 inches in steps of 1.0 inch. I decided to fix the zigzag element lengths at 7.07 inches in order to keep the total number of antenna modeling files down to a modest count. The next job was to construct all of these models and to save the resulting NEC input files.

The 4nec2 software provides access to four different NEC input file editors. Each has its uses. The most primitive is “Notepad Edit” (Ctrl+F1). Using Notepad to prepare an NEC input file is equivalent to sitting down in front of an old IBM Hollerith Card Keypunch Machine with a deck of blank cards.

The original Numerical Electromagnetics Code (NEC) program was developed in the 1970s for the US Navy at the Lawrence Livermore Laboratory. The software evolved over the next few years. In January 1981, a three part manual was published detailing the NEC2 program description and theory, program listing, and user’s guide. The187 page User’s Guide speaks mostly of preparing an NEC input card deck. Each card type and its associated fields are thoroughly described.

The second editor, called “NEC Editor” (Ctrl+F2), is a much more user friendly interface than Notepad and the 187 page User’s Guide. It knows about each card type and it fields. The user can insert a card into the deck by selecting an appropriate card type and filling in the well labeled fields.

The third editor is called “Geometry edit” (Ctrl+F3). An in depth knowledge of card types and their fields is not required to model an antenna. Instead, one can focus on laying out an antenna’s elements in a three dimensional coordinate system, XYZ space. The geometric editor has buttons to switch from 3D space to the two dimensional XZ, YZ and XY planes. For flat, two dimensional, designs like in this experiment, one can work exclusively in the YZ plane. The geometric editor features a “drag and drop” drawing style for creating straight wire elements. A graph paper like grid is provided in the two dimensional planes for drawing individual straight wire elements. In the “Select object mode”, the properties of any wire can be displayed and/or edited by left clicking on the object of interest. The ends of wires can be easily connected by taking advantage of the “Snap to grid” and “Snap to wire” functions. Beware of “Keep connected” function. When adjusting a wire, there are times to turn it on and times to turn it off. The “Edit/Undo Move” function found on the standard menubar is critical, especially after accidentally making a mess of things.

“NEC editor (new)” (Ctrl+4) is the forth editor. It is a logical extension of the second “NEC editor”. The user interface has subject tabs for “Symbols”, “Geometry”, “Source/Load”, “Frequency/Ground”, “Other” and “Comment”. Most of the tabs provide a spreadsheet like grid for data entry and editing. In some future experiment, I hope to become familiar with using the elegant “Symbols” method for modeling an antenna”. But for now, I will move ahead using the “Brute Force” technique.

I used 4nec2’s geometric editor to build the NEC model files. The stubs were very easy to draw. I was a little worried about the 7.07 inch zigzag elements. The snap to grid and the snap to wire functions made drawing the zigzag elements much easier than I first thought. The strange 7.07 inch length turns out to be the hypotenuse of a right triangle with two 5.0 inch sides on either side of the 90 degree angle. The two 5.0 inch sides neatly correspond to the graph paper like horizontal and vertical grid lines. In the add wire mode, it became a matter of left clicking the mouse to anchor one end of a new wire then dragging 5.0 inches horizontally and 5.0 inches vertically (or the equivalent diagonally in just one step) and releasing the mouse button.

Adjusting the feed point gaps was difficult in the beginning. Then, I read the help file and discovered a drag and drop technique for moving and rotating groups of wires. It goes something like this. While in the geometric editor’s 2D select object mode, left click a wire that will shortly become the “dragging handle”. Move the cursor to an empty spot on the grid. Next, left click and immediately drag and drop diagonally over the group of wires to become a temporary unit. A rectangle will appear showing you what you are about to include. When you let up on the mouse button all of the wires with both ends inside the rectangle will be selected and will turn red. One of the wires will appear thicker than the others. This is the "dragging handle". You can left click and then drag and drop the unit to its new location. It takes a little time to get used to it, but it is very effective. Try it, you will like it.

Altogether, thirty NEC files were created and separated into the following five family groupings:

H01 - 7.07in ZigZags - 2in Stubs - 0.5in Gap.nec
H02 - 7.07in ZigZags - 2in Stubs - 1.0in Gap.nec
H03 - 7.07in ZigZags - 2in Stubs - 1.5in Gap.nec
H04 - 7.07in ZigZags - 2in Stubs - 2.0in Gap.nec
H05 - 7.07in ZigZags - 2in Stubs - 2.5in Gap.nec
H06 - 7.07in ZigZags - 2in Stubs - 3.0in Gap.nec

H07 - 7.07in ZigZags - 3in Stubs - 0.5in Gap.nec
H08 - 7.07in ZigZags - 3in Stubs - 1.0in Gap.nec
H09 - 7.07in ZigZags - 3in Stubs - 1.5in Gap.nec
H10 - 7.07in ZigZags - 3in Stubs - 2.0in Gap.nec
H11 - 7.07in ZigZags - 3in Stubs - 2.5in Gap.nec
H12 - 7.07in ZigZags - 3in Stubs - 3.0in Gap.nec

H13 - 7.07in ZigZags - 4in Stubs - 0.5in Gap.nec
H14 - 7.07in ZigZags - 4in Stubs - 1.0in Gap.nec
H15 - 7.07in ZigZags - 4in Stubs - 1.5in Gap.nec
H16 - 7.07in ZigZags - 4in Stubs - 2.0in Gap.nec
H17 - 7.07in ZigZags - 4in Stubs - 2.5in Gap.nec
H18 - 7.07in ZigZags - 4in Stubs - 3.0in Gap.nec

H19 - 7.07in ZigZags - 5in Stubs - 0.5in Gap.nec
H20 - 7.07in ZigZags - 5in Stubs - 1.0in Gap.nec
H21 - 7.07in ZigZags - 5in Stubs - 1.5in Gap.nec
H22 - 7.07in ZigZags - 5in Stubs - 2.0in Gap.nec
H23 - 7.07in ZigZags - 5in Stubs - 2.5in Gap.nec
H24 - 7.07in ZigZags - 5in Stubs - 3.0in Gap.nec

H25 - 7.07in ZigZags - 6in Stubs - 0.5in Gap.nec
H26 - 7.07in ZigZags - 6in Stubs - 1.0in Gap.nec
H27 - 7.07in ZigZags - 6in Stubs - 1.5in Gap.nec
H28 - 7.07in ZigZags - 6in Stubs - 2.0in Gap.nec
H29 - 7.07in ZigZags - 6in Stubs - 2.5in Gap.nec
H30 - 7.07in ZigZags - 6in Stubs - 3.0in Gap.nec

These Gray Hoverman Driver Array files can be found in the Yahoo Group named AntennaModelingExperiments under Hobbies and Crafts.

A horizontal frequency sweep was produced for each of the above NEC files using 4nec2’s Generate (F7) function. The following parameters were used: Resolution: 5 degrees; Frequency Start: 455 MHz; Frequency Stop: 715 MHz; Frequency Step: 6 MHz; Forward Theta: 90 degrees; Forward Phi: 0 degrees; Forward delta-Phi: 5 degrees; Backward Theta: 90 degrees; Backward Phi: 180 degrees; and Backward delta-Phi: 5 degrees. A 455 to 715 MHz range with steps of 6 MHz was selected to produce points which fell in the center frequencies of each UHF channel from 14 through 51 with three extra points on either side of this channel range.

As the Total Horizontal Forward Gain data were generated for each NEC file, it was immediately transferred to an Excel spreadsheet for later plotting. See http://www.digitalhome.ca/forum/showthread.php?t=85987&page=14, Post 208 for 300ohm’s method of transferring output data from 4nec2 to a spreadsheet.


Results and Conclusions:

The Total Horizontal Forward Gain vs. Channel plots are shown below. The first family of gain curves shows the Gray Hoverman Driver Array which is most similar to Elvis Gump’s drawing without a reflector.

For this family, 7.07 inch zigzag elements and 6.0 inch stub elements, there appears to be very little practical difference between the Total Horizontal Forward Gain curves with feedpoint gaps distances ranging from 0.5 inches to 3.0 inches.

As the stub element lengths become shorter and shorter, the effect of the feedpoint gap distance slowly begins to appear.

**********************************************************
Experiment #1 Continued in GH Driver Array - Modeling Experiment - Part 3
Due to an Image Limit of 4 per Post
**********************************************************

 

[DTV Student]

GH Driver Array - Modeling Experiments - Part 3

Hi Folks,

Experiment #1 Continued...

For a Gray Hoverman Driver Array with zigzag element lengths in the 7 inch neighborhood and stub element lengths in the 6 to 3 inch range, feedpoint gap distances appear to be of little or no importance in terms of the Total Horizontal Forward Gain curves across the UHF DTV channels. Feedpoint gap distances become increasing more important for channels below 28 as the stub element lengths become shorter than 3 inches.

For a future experiment, it seem worthwhile to repeat this experiment except using a fixed feedpoint gap distance of say 1.0 inch and to vary the zigzag element lengths and stub element lengths.

This would generate several different families of the Gray Hoverman Driver Array Assembly and their Total Horizontal Forward Gain vs. Channel Number curves. Perhaps, other interesting observations and generalities would be revealed.

Your comments and suggestions are always appreciated.

Thank you,
DTV Student

 

[DTV Student]

GH Driver Array - Experiment 1 - Additional Notes

Hi Folks,

The 30 NEC files for Experiment 1 are in a zipfile called "Exp 01 - Antenna Geometry Files.ZIP" under a Yahoo group I recently created call "AntennaModelingExperiments". Yeah, that's all one word, sort of Pascal style. The URL for the folder is http://groups.yahoo.com/group/Anten...Designs/Experiment 01/Antenna Geometry Files/.

Elvis Gump's drawing has a feedpoint gap of 1.77 inches, a zigzag element length of 7.07 inches and a stub element length of 5.59 inches. The model that I created nearest Elvis Gump's drawing has a feedpoint gap of 2.0 inches, a zigzag element length of 7.07 inches and a stub element length of 6.0 inches. It is very typical of the other 29 files and follows:

CM Driver Assemblies for a Gray Hoverman Antenna (6 Gage Wire)
CM 2" Feed Point Gap, 7.07" Zig Zags, 6" Stubs
CM Reflector Not Included
CE
GW 1 13 0 6 15 0 12 15 0.08101138
GW 2 15 0 6 15 0 1 10 0.08101138
GW 3 15 0 1 10 0 6 5 0.08101138
GW 4 15 0 6 5 0 1 0 0.08101138
GW 5 15 0 1 0 0 6 -5 0.08101138
GW 6 15 0 6 -5 0 1 -10 0.08101138
GW 7 15 0 1 -10 0 6 -15 0.08101138
GW 8 13 0 6 -15 0 12 -15 0.08101138
GW 9 13 0 -6 15 0 -12 15 0.08101138
GW 10 15 0 -6 15 0 -1 10 0.08101138
GW 11 15 0 -1 10 0 -6 5 0.08101138
GW 12 15 0 -6 5 0 -1 0 0.08101138
GW 13 15 0 -1 0 0 -6 -5 0.08101138
GW 14 15 0 -6 -5 0 -1 -10 0.08101138
GW 15 15 0 -1 -10 0 -6 -15 0.08101138
GW 16 13 0 -6 -15 0 -12 -15 0.08101138
GW 17 5 0 -1 0 0 1 0 0.08101138
GS 0 0 0.0254 ' All in in.
GE 0
EK
EX 0 17 3 0 1 0
GN -1
FR 0 1 0 0 585 0


Autofils...

At this point in time, I am operating in the "Brut Force" mode. I have not explored the Symbols (SY) card yet. I barely have the discipline to stay away from it. LOL... I am just getting comfortable with the geometric editor and some of the other very basic 4nec2 operations. There are many concepts I need to get a better understanding of, such as, "Raw Gain, Net Gain, and Standing Wave Ratios". My lack of understanding in the world of electronics and antennas is indeed profound! Math was once one of my favorite subjects about 45 years ago. So you see, I can hardly wait to begin exploring parameter based designs and playing with the optimizer.

I went back to the beginning of this thread and pulled up one of your comments to ericball:

From ericball... http://www.digitalhome.ca/forum/showthread.php?t=83772&page=4 Post 46

Calculating Net Gain

I have 4nec2 installed and I've been playing around with it and a parameterized SBGH model. I'd like to throw it at the genetic optimizer, but I'm wary of gain/SWR versus net gain. (I'm assuming the gain values aren't net gain.) What's the translation? Or should I just assume that as long as the SWR is close to the un-optimized version that everything is okay?




From Autofils... http://www.digitalhome.ca/forum/showthread.php?t=83772&page=4 Post 47

RE: Calculating Net Gain

Ericball,

I sent you a PM, but I didn't get a reply, so I guess you haven't visited the forum for a while.

Here is a method to calculate Net Gain:

NetGain = RawGain+10*log(Feed-pointGain)
where Feed-point Gain = 4*Zr*Zo/((Zr+Zo)^2+Zi^2)

The [10*log(base10)]" converts to decibels, and Feed-point Gain is less than 1, since there is a loss.

Zo = characteristic Impedance for the transmission line connected to the antenna ( Zo=300 for the GH)
Zr = real part of antenna's complex impedance at a specific frequency
Zi = imaginary part of antenna's complex impedance at a specific frequency
RawGain = Gain output given by 4nec2 at the specific frequency

If you have any programming skills, I would dearly love to obtain an executable that can parse the 4nec2 F8 output file for the RawGain. and Antenna's complex impedance (real and imaginary parts) for each frequency that is stepped in the frequency sweep at the appropriate Phi and Theta values of 90 and 0 degrees.

Yes... the NEC output file is a serious piece of work. I guess I should be looking at it a little more closely. So far, I am still trying to make heads and tails out of the frequency sweep charts (F5). The only one I thought I had a warm fuzzy feeling about was the "Forward Gain" plot. LOL... I guess not.

I think you and ericball were saying the data presented in 4nec2's "Forward Gain" chart is really "Raw Gain" data. It is not necessarily the effective gain delivered by the antenna. There are additional factors (SWR, etc, etc) that could heavily influence what a very nearby tuner sees. I think you are saying, "Net Gain" vs Frequency plots are the proper modeling method to compare different antenna geometries.

Your comments and suggestions are always appreciated.

Thank you,
DTV Student

 

[DTV Student]

"Net Gain" Frequency Sweep Procedure

Hi Folks,

In http://www.digitalhome.ca/forum/showthread.php?t=83772&page=4 Post 47, I found Autofils' method for calculating the Net Gain. I don't have to understand where the formulas came from, but I would like to be able to pull the right data out of the 4NEC2 frequency sweep plots and to execute the calculations properly. So, I have worked up a little example. I would appreciate it if y'all would walk through this example to verify whether I got it right or not.

In http://www.digitalhome.ca/forum/showthread.php?t=81982&page=19, Post 284, I found a drawing by Elvis Gump of the First Generation Gray Hoverman Antenna developed by Autofils and others. I entered the measurements in inches from this drawing into 4NEC2's geometric editor and save the file as GH12.NEC. The content of this file follows:

CM Active Driver Assemblies for a Gray Hoverman Antenna (6 Gage Wire)
CM Measurements Taken from a Drawing by Elvis Gump
CM Including 12 Element Co-Linear Reflector
CE
GW 1 13 0 5.885 15 0 11.475 15 0.08101138
GW 2 15 0 5.885 15 0 0.885 10 0.08101138
GW 3 15 0 0.885 10 0 5.885 5 0.08101138
GW 4 15 0 5.885 5 0 0.885 0 0.08101138
GW 5 15 0 0.885 0 0 5.885 -5 0.08101138
GW 6 15 0 5.885 -5 0 0.885 -10 0.08101138
GW 7 15 0 0.885 -10 0 5.885 -15 0.08101138
GW 8 13 0 5.885 -15 0 11.475 -15 0.08101138
GW 9 13 0 -5.885 15 0 -11.48 15 0.08101138
GW 10 15 0 -5.885 15 0 -0.885 10 0.08101138
GW 11 15 0 -0.885 10 0 -5.885 5 0.08101138
GW 12 15 0 -5.885 5 0 -0.885 0 0.08101138
GW 13 15 0 -0.885 0 0 -5.885 -5 0.08101138
GW 14 15 0 -5.885 -5 0 -0.885 -10 0.08101138
GW 15 15 0 -0.885 -10 0 -5.885 -15 0.08101138
GW 16 13 0 -5.885 -15 0 -11.48 -15 0.08101138
GW 17 5 0 -0.885 0 0 0.885 0 0.08101138
GW 18 25 -3.94 -12.5 15 -3.94 -0.3935 15 0.08101138
GW 19 25 -3.94 0.3935 15 -3.94 12.5 15 0.08101138
GW 20 25 -3.94 -12.5 7.5 -3.94 -0.3935 7.5 0.08101138
GW 21 25 -3.94 0.3935 7.5 -3.94 12.5 7.5 0.08101138
GW 22 25 -3.94 -12 2.5 -3.94 -0.3935 2.5 0.08101138
GW 23 25 -3.94 0.3935 2.5 -3.94 12 2.5 0.08101138
GW 24 25 -3.94 -12 -2.5 -3.94 -0.3935 -2.5 0.08101138
GW 25 25 -3.94 0.3935 -2.5 -3.94 12 -2.5 0.08101138
GW 26 25 -3.94 -12.5 -7.5 -3.94 -0.3935 -7.5 0.08101138
GW 27 25 -3.94 0.3935 -7.5 -3.94 12.5 -7.5 0.08101138
GW 28 25 -3.94 -12.5 -15 -3.94 -0.3935 -15 0.08101138
GW 29 25 -3.94 0.3935 -15 -3.94 12.5 -15 0.08101138
GS 0 0 0.0254 ' All in in.
GE 0
EK
EX 0 17 3 0 1 0
GN -1
FR 0 1 0 0 585 0


Then, I brought up 4NEC2's Generate (F7) screen. I set the first group of radio buttons to "Far Field pattern". The Frequency was set to 585 MHz. The third group of radio buttons was set to "Full". The resolution was set to 5 degrees. I checked the "Run Average Gain Test" and clicked the "Generate" button. After a short time, the "AGT results" were displayed on the Main (F2) screen as "1.02 (0.08 dB)". I think this is trying to tell me that the "Raw Gain" estimated at 585 MHz might be in error by as much a 0.08 dB. In my book that is very small error. If the error had been a lot larger, I would have increased the number of segments in each wire and tried again. I remember reading something about the "Convergence Test" but I have not tried it yet. Anyhow... the "Average Gain Test" looks pretty good. So, I take it that the output data can be trusted.

Next, I brought up the 4NEC2's Generate (F7) screen again. I set the first group of radio buttons to "Frequency sweep". The third group of radio buttons was set to "Hor.". The resolution was set to 5 degrees. The Starting Frequency was set to 473 MHz, the Stop Frequency was set to 695 MHz and the Step size was set to 6 MHz. The Forward Theta was set to 90 degrees. The Forward Phi was set to 0 degrees. The Backward Theta was set to 90 degrees. The Backward Phi was set to 180 degrees. Both “d-Phi”s were set to 5 degrees. Finally, I clicked the "Generate" button. After a little while, the DOS screen and the "Status" screen disappeared to be replaced with the "Pattern (F4)" and "Imp. / SWR / Gain (F5)" screens.

On the main menubar of the "Imp. / SWR / Gain (F5)" screen, I selected "Show/Forward gain", to see if the Total Forward Gain curve for the 473 to 695 MHz UHF band was about what I expected. There were no surprises. It was a pretty flat gain curve. The lowest gain of 12.5 dBi occurred at 473 MHz and the highest gain of 14.1 dBi occurred at 665 MHz. It was really nice. Until very recently, I thought this gain curve was the most important characteristic of a modeled antenna and that it provided an excellent way to compare different antenna geometries. Now, I hear this curve is really the "Raw Gain" curve and perhaps it could be adjusted using a few other estimates available in the 4NEC2 output to build a "Net Gain" curve. Using the “Net Gain” curve should provide even more realistic comparisons. Is that true?

Next, I started Excel on top of 4NEC2 and opened an empty spreadsheet. I labeled a few columns with the following titles: Frequency, Channel, Raw Gain, Zo, Zr, Zi, FP Gain, Net Gain and Delta. I switched back to 4NEC2's "Imp. / SWR / Gain (F5)" screen and selected "Plot/Forw-gain" from the main menubar. An information box appeared to tell me that "wGnuPlot.exe was not found... ". I clicked the OK button to acknowledge the message. 4NEC2 scheduled Notepad to show me all the beautiful data it had copied into the Plot.txt file for the wGnuPlot application. I closed Notepad.

The Plot.txt file structure is very simple and can be easily imported into an Excel spreadsheet. On my computer, the Plot.txt file lives in the C:\4nec2\plot folder.

I switched back to Excel and imported the Plot.txt into a new spreadsheet. I copied the numbers in the Frequency column and paste them to my first spreadsheet just under the Frequency column label. I repeated the process for the Total Gain numbers and pasted them just under the "Raw Gain" column label. I closed the Plot.txt spreadsheet. I switched back to 4NEC2's "Imp. / SWR / Gain (F5)" screen and selected "Plot/R-in (real)" from the main menubar. 4NEC2 overwrote the Plot.txt file with this new data and complained as before when it could not schedule wGnuPlot.exe. I think the "R-in (real)" data corresponds to the real part of antenna's complex impedance (Zr). So as above, I imported it into a new spreadsheet, copied the data in "Real-in (real)" column and pasted it just under the Zr label in my first spreadsheet. I switched back to 4NEC2's "Imp. / SWR / Gain (F5)" screen and selected "Plot/X-in (imag)" from the main menubar. 4NEC2 overwrote the Plot.txt file with this new data and complained as before when it could not schedule wGnuPlot.exe. I think the "X-in (imag)" data corresponds to the imaginary part of antenna's complex impedance (Zi). So again, I imported it into a new spreadsheet, copied the data in the "X-in (imag)" column and pasted it just under the Zi label in my first spreadsheet. I populated the Channel and Zo columns. I built the "FP Gain" and "Net Gain" formulas based on Autofils’ suggestion to ericball and populated those two columns. I built a Delta Gain column which is nothing more than the difference between the "Net Gain" and the "Raw Gain". Finally, I added some documentation above the table and cleaned things up a bit. The spreadsheet text follows:


"Net Gain" Calculations for the Gray Hoverman 12 Antenna

Frequency (MHz) vs. Total Net Horizontal Gain Estimates (dBi)

Geometric Design Data Taken from Elvis Gump's Drawing (6 Gage Wire)
Data extracted from 4nec2's plot files using 300ohm's cut and paste method
"Net Gain" calculated using Autofils' method outlined below

NetGain = RawGain+10*log(Feed-pointGain)
where Feed-point Gain = 4*Zr*Zo/((Zr+Zo)^2+Zi^2)

The [10*log(base10)] converts to decibels, and Feed-point Gain is less than 1, since there is a loss.

Zo = characteristic Impedance for the transmission line connected to the antenna ( Zo=300 for the GH)
Zr = real part of antenna's complex impedance at a specific frequency
Zi = imaginary part of antenna's complex impedance at a specific frequency
RawGain = Gain output given by 4nec2 at the specific frequency
Delta = Net Gain - Raw Gain

Freq Ch Raw Zo Zr Zi FP Net Delta
(MHz) No. Gain Ohms Ohms Ohms Gain Gain Gain
473 14 12.58 300 116.705 -204.150 0.650 10.71 -1.87
479 15 12.72 300 116.756 -168.820 0.693 11.13 -1.59
485 16 12.83 300 119.062 -138.807 0.733 11.48 -1.35
491 17 12.94 300 123.117 -112.943 0.770 11.81 -1.13
497 18 13.03 300 128.585 -90.478 0.804 12.08 -0.95
503 19 13.11 300 135.215 -70.918 0.834 12.32 -0.79
509 20 13.18 300 142.789 -53.934 0.861 12.53 -0.65
515 21 13.24 300 151.099 -39.297 0.884 12.71 -0.53
521 22 13.30 300 159.936 -26.830 0.904 12.86 -0.44
527 23 13.35 300 169.089 -16.379 0.921 12.99 -0.36
533 24 13.40 300 178.348 -7.788 0.935 13.11 -0.29
539 25 13.44 300 187.516 -0.888 0.947 13.20 -0.24
545 26 13.49 300 196.420 4.509 0.956 13.30 -0.19
551 27 13.53 300 204.926 8.608 0.964 13.37 -0.16
557 28 13.57 300 212.940 11.629 0.971 13.44 -0.13
563 29 13.61 300 220.422 13.786 0.976 13.50 -0.11
569 30 13.65 300 227.380 15.287 0.980 13.56 -0.09
575 31 13.69 300 233.868 16.314 0.984 13.62 -0.07
581 32 13.73 300 239.981 17.015 0.987 13.67 -0.06
587 33 13.77 300 245.844 17.500 0.989 13.72 -0.05
593 34 13.82 300 251.610 17.836 0.991 13.78 -0.04
599 35 13.86 300 257.444 18.033 0.993 13.83 -0.03
605 36 13.91 300 263.528 18.057 0.995 13.89 -0.02
611 37 13.95 300 270.041 17.805 0.996 13.93 -0.02
617 38 14.00 300 277.158 17.103 0.998 13.99 -0.01
623 39 14.05 300 285.040 15.702 0.999 14.04 -0.01
629 40 14.09 300 293.803 13.242 0.999 14.09 0.00
635 41 14.14 300 303.492 9.244 1.000 14.14 0.00
641 42 14.18 300 314.013 3.089 0.999 14.18 0.00
647 43 14.21 300 325.039 -5.986 0.998 14.20 -0.01


Please take a look at this procedure and please run a few spot checks of the "Net Gain" calculations. I need to know how to work through a problem by hand before I can automate the process.

Yikes!!! The editor stripped out all of the tabs in the spreadsheet table. That's not nice. Stuff Happens... LOL... Just Stay Out of the Stuff Storms!!!

Thank you,
DTV Student

 

[DTV Student]

Another Question about "Net Gain"

Hi Folks,

I am re-doing Experiment 1 and trying to apply Autofils' suggestions. Its a whole lot of work to calculate the "Net Gain". LOL... now I understand why Autofils wanted somebody to step up and write some code to parse 4NEC2's frequency sweep output files.

The other day, I outlined a procedure as I understand it to take the 4NEC2 "Raw Gain" data and a few other data items to calculate "Net Gain" data:

Autofils in an earlier post wrote:

NetGain = RawGain+10*log(Feed-pointGain)
where Feed-point Gain = 4*Zr*Zo/((Zr+Zo)^2+Zi^2)

The [10*log(base10)] converts to decibels, and Feed-point Gain is less than 1, since there is a loss.

Zo = characteristic Impedance for the transmission line connected to the antenna ( Zo=300 for the GH)
Zr = real part of antenna's complex impedance at a specific frequency
Zi = imaginary part of antenna's complex impedance at a specific frequency
RawGain = Gain output given by 4nec2 at the specific frequency

I forgot to ask about the Characteristic Impedance or Zo term. Autofils said, "Zo = characteristic Impedance for the transmission line connected to the antenna ( Zo=300 for the GH)". I remember the old flat 300 ohm twin lead in wire. Today, the usual practice is to connect a 300 ohm to 75 ohm "Balum" transformer immediately to the antenna and run 75 ohm coax cable down to the TV tuner.

Also somewhere in my readings, I believe I remember a basic dipole antenna has a Characteristic Impedance of about 72 ohms, a basic bowtie antenna has a Characteristic Impedance of about 75 ohms and a basic folded dipole has Characteristic Impedance of about 300 ohms. Where did thing this Characteristic Impedance thing come from and why does a Gray Hoverman design have a Characteristic Impedance of 300 ohms? Why isn't it say 100 or 200 ohms?

Thanks,
DTV Student