How to Make a Fractal Antenna for HDTV / DTV Plus More on the Cheap

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Introduction: How to Make a Fractal Antenna for HDTV / DTV Plus More on the Cheap

This instructable is from:

http://ruckman.net/archives.htm#FEATURED

and submitted by William Ruckman of http://ruckman.net

Showcased in the March 2015 issue of Popular Science Magazine:

http://www.popsci.com/learn-defy-cable-company-diy-hdtv-antenna

The first thing I would like to discuss is a little history, theory, and uses for fractal antennas.

Fractal antennas are a recent discovery. First discovered back in 1988 by Nathan Cohen and later published and patented in 1995. A fractal antenna has a few unique attributes as seen in this definition from Wikipedia:

"A fractal antenna is an antenna that uses a fractal, self-similar design to maximize the length, or increase the perimeter (on inside sections or the outer structure), of material that can receive or transmit electromagnetic signals within a given total surface area or volume."

What exactly does that mean? Well, you need to know what a fractal is. Also from Wikipedia:

"A fractal is generally a rough or fragmented geometric shape that can be split into parts, each of which is (at least approximately) a reduced-size copy of the whole,a property called self-similarity."

So basically, a fractal is a geometric shape that repeats and appears over and over no matter how far out or how far in you zoom magnification.

Source: Wikipedia and http://patimg2.uspto.gov/.piw?PageNum=6&docid=US007088965 Patent number: 7088965]

Fractal antennas have been found to be approximately 20% more efficient than normal antennas. Which could be useful. Especially if you want to make your own TV antenna to pick up over the air digital or high definition video, increase your cellular range, wifi range, FM or AM radio reception, and so on. Most cell phones already have built in fractal antennas. If you noticed in the past few years that cell phones no longer have antennas on the outside. That is because they have a internal fractal antenna etched on a circuit board which allows them to get better reception and pick up more frequencies such as bluetooth, cellular, and WIFI all from one antenna at the same time!

Wikipedia info:

"A fractal antenna's response differs markedly from traditional antenna designs, in that it is capable of operating with good-to-excellent performance at many different frequencies simultaneously. Normally standard antennas have to be "cut" for the frequency for which they are to be usedand thus the standard antennas only work well at that frequency. This makes the fractal antenna an excellent design for wideband and multiband applications."

The trick is to design your fractal antenna to resonate at what ever center frequency you wish to receive. Which means it will look different and be sized different depending on what you want to receive. A little math can be used to figure this out. (Or a online calculator)

In my example, I am going to make a simple one but you may want to make a more elaborate one. The more elaborate the better. I will use a spool of 18 Gauge solid core wire to make a antenna as an example but you could go as far as to etch your own circuit boards for aesthetic reasons, to make it smaller, or more elaborate with more resolution and resonance.

I am going to use the example of making a TV antenna for digital or high definition reception for over the air broadcasts. It is easier to work with these frequencies and they fall around half a foot to a few feet in length for half wavelengths of the signal. I am also going to base it off a common dipole antenna for simplicity and cheapness of parts for VHF. For UHF you may want to add a director or reflector which will also make it more direction dependent. VHF is direction dependent as well but instead of pointing directly at the TV station like UHF you want VHF rabbit ears (dipole antenna) to be perpendicular to the TV station. But there is a little more design to that. I want to keep this as simple as possible as it is already a very complex subject.

Basic supplies (cost me about $15):

Mounting surface such as the plastic project enclosure (8"x6"x3"). http://www.radioshack.com/product/index.jsp?productId=2062285
6 screws. I used steel self tapping sheet metal screws.
A impedance matching transformer 300 ohm to 75 ohm. http://www.radioshack.com/product/index.jsp?productId=2062049
Some 18 gauge solid hook up wire. http://www.radioshack.com/product/index.jsp?productId=2036274
RG-6 coaxial with terminators (and rubber jacket if mounting outside).
Aluminum if using a reflector. The enclosure above came with one.
A sharpie marker or equivalent preferably with a fine tip.
Two pairs of small needle nose pliers.
A ruler of at least 8 inches.
A protractor to measure angle.
A drill and drill bit that is smaller diameter than your screws.
Small wire cutter.
Screw driver or screw gun.

NOTE: The bottom of the antenna is to the right of this picture where the transformer sticks out.

Step 1: Adding the Reflector

Assemble the enclosure with the reflector under the plastic cover.

Step 2: Drill Holes and Add Mounting Points

Drill small tap holes on the opposite side from the reflector in the following positions and place a conductive screw.

Step 3: Measure, Cut, and Strip Wire

Cut four 8" pieces of the solid core wire and strip it bare.

Step 4: Measure and Mark Wire

Use a marker and mark every 1" on the wire. (This is where we are going to make the bends)

Step 5: Create Fractals

You will repeat this step for each wire. Each bend on the wire will be 60 degrees exactly as we will be making equilateral triangles with this fractal. I used two pairs of pliers and a protractor. Each bend will be made at the 1 marks. Make sure you visualize the direction of each bend first before making it! Use the diagram below to help.

Step 6: Create Dipoles

Cut 2 more pieces of wire at least 6 inches long and strip them. Bend these wires around the top and bottom screws going longways and contact the center screws. So all three are contacted. Use the wire cutter and trim unneeded wire.

Step 7: Mount Dipoles and Mount Transformer

Place and screw down each of your fractals to the corner screws.

Attach the impedance matching transformer across the two center screws and tighten them down.

BUILD COMPLETE! Test and enjoy!

Step 8: Testing Verses Store Bought Antenna

To see the results of the tests I ran click the link below:

http://ruckman.net/archives.htm#DTV

ENJOY!

Step 9: More Iterations / Experimentation

I have made some new elements using a paper template I made in Gimp (photo editor). I used small solid core wire from telephone wire and it was solid enough, small enough, and malleable enough to bend into the intricate shape required at the selected center frequency (554Mhz - as this is the mean of the digital UHF over the air TV channels in my area) and iteration of the chosen fractal design. Which is repeated triangles.

Photo attached. It may be hard to see with the photo taken in low light, the color of the cardboard, and the color of the copper with tape over it to hold it in place. But you get the idea.

At that size the elements are pretty fragile, so they have to be handled carefully.

I have also attached the template in png format. For it to print the proper size, you have to open it in a photo editor like Gimp. The template isn't perfect as i made it by hand with a mouse, but it is close enough for human hands and a needle nose for bending of the elements.

Enjoy.

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Hi,
I built this and am trying to test the performance using a RF Vector Analyzer. I am getting very poor results. Does this antenna need to be grounded? I'm not sure how I would go about doing that. Any input would be greatly appreciated!

Thank you.

316 Comments

I have made some new elements using a paper template I made in Gimp (photo editor). I used small solid core wire from telephone wire and it was solid enough, small enough, and malleable enough to bend into the intricate shape required at the selected center frequency (554Mhz - as this is the mean of the digital UHF over the air TV channels in my area) and iteration of the chosen fractal design. Which is repeated triangles.

Photo attached. It may be hard to see with the photo taken in low light, the color of the cardboard, and the color of the copper with tape over it to hold it in place. But you get the idea.

At that size the elements are pretty fragile, so they have to be handled carefully.

I have also attached the template in png format. For it to print the proper size, you have to open it in a photo editor like Gimp. The template isn't perfect as i made it by hand with a mouse, but it is close enough for human hands and a needle nose for bending of the elements.

Enjoy.

fractal.pngfractal.jpg

A fractal pattern, as mentioned elsewhere in this article, is a pattern that looks the same up close as it does from a distance, "Fern leaves and Romanesco broccoli are two examples from nature" (Benoit Mandelbrot 1924-2010, the discoverer of fractals). A practical application of this can be found in antenna design. In my case, I seek to view roughly eight OTA channels, covering the basic ABC, CBS, NBC, Fox and PBS. Fair enough, except the frequencies range from a low of 186 MHz to a high of 602 MHz. As we know, an antenna works because its length must correspond to the wavelength, such that it will resonate. We also know that a wire used in the antenna will not only resonate at a length equal to the wavelength, 'full wave', but other fractions of the wavelength as well, 'quarter wave' in the example I will use. Using the online converter found here: http://www.csgnetwork.com/freqwavelengthcalc.html or doing the calculation by hand using v=fλ, where v=the speed of light (983,571,056 ft/sec), and f=the frequency I wish to capture, I can calculate λ=the wavelength I need to cut my wire to. Choosing my lowest frequency, 186 MHz (186,000,000 cycles/sec), performing the division yields the full wavelength of one cycle equal to 5.29 feet, or 63.5 inches. I could build an antenna with a wire of that length, but can also use a quarter of that length, 15.8 inches, which is more practical and will resonate as a quarter wave antenna.Repeating the calculation for my highest frequency, 602 MHz, gives a quarter wavelength of .4 feet, or 4.9 inches. So I need an antenna that spans from roughly 15 inches to resonate at 186 MHz, to roughly 5 inches to resonate at 602 MHz. By comparison, our hearing works by the same principle, tiny hairs in our ear are arranged like the teeth on a comb, ranging from very short, to resonate at the short wavelengths (high frequencies), and increasing in length to resonate at longer and longer wavelengths (lower and lower frequencies), which gives us a hearing range of 20 Hz to 20 KHz.In the case of our antenna design, unlike that of the ear, we do not have the luxury of using the range of wires needed to cover the 186 to 602 MHz range, so a compromise has to be made. If I then take a 15 inch piece of wire and bend it three times every 5 inches, I have a 'fractal' pattern, the 5 inch sections will resonate at the 602 MHz frequency, and the sum of the three sections will give me the 15 inches I need to resonate at the 186MHz frequency. As I mentioned above, a compromise will have to be made, and the intermediate frequencies will have to find a way to resonate.As well, two 5 inch pieces will resonate at an intermediate frequency that corresponds to the 10 inch wavelength, so I am covered at both ends of the spectrum I need, and the center as well. Therefore, using a 30 inch piece of wire, bending it in half and making two 15 inch pieces of 5 inches per section gives me a design comparable to the designs seen in this article.I have made and used the 'cats whisker' design, from 16 inch pieces of coat hanger bent in half to make two 8 inch sections, a total of 8 whiskers, 4 per side, based on the excellent youtube video that got me launched down this road to begin with, and am getting between 31 and 35 channels depending upon the orientation of the antenna. I am 60 miles southeast of Washington DC/Baltimore, those are the closest stations,and the antenna is working beautifully, but depending on the orientation I can only get 3 of the 4 majors, sometimes all but NBC, sometimes all but CBS and so on. I didn't realize till I got started on this quest a week ago (Jan 2018, late in the game compared to most of the posts), that the frequency range was so radical, hard to make an antenna that will cover that much of a range. So I will build this one and get back. The one variable I am not too sure about is the diameter of the wire, intuitively it seems the thinner wire would resonate more easily, and thinking back to my school days thicker wire can set up reflections, but that would take some experimentation which unfortunately I do not have time for. Having said that, I was liking the antenna posted by SpeakerBoy back in March of 2013 that used foil tape, beautiful and seems to have worked, tape in lieu of wire, might have to try that. Thank you for the wonderful article.

A few more things to note that will help:
1. I like to use PVC pipe in my builds. The reason being is it's cheap, it can be bent if needed by a heat gun or even a hair dryer in a pinch, and is non conductive.
2. A hot glue gun is a nice to have when putting things together. I believe screws that hold down aerials change the way the signal is captured for it adds metal to the shape of the aerial. In my last build I used the hot glue gun to glue my connections together. This worked really well. I did an experimental build with cardboard to see how this would work and I was really pleased with the results.
3. Line of site is best when positioning your antenna.
4. Use high quality coax and pick the best for the job. Look here on what to select:

http://forums.solidsignal.com/showthread.php/505-C...

5. Signal strength monitor - I have a USB digital TV adapter for my laptop. There is software you can use with them to measure signal strength. For example this one:

http://www.hauppauge.com/site/support/support_digi...

6. if you have old RG-59 coax and you have a mess of wires in the back of your TV, this will cause a loss of signal due to noise the other wires generate.
7. Dimmer switches that are on the same circuit as the TV are big causes of signal noise and can cause a lose of signal for the antenna.
8. When hooking up the impedance matching transformer to your antenna, it is best to have it at a 90 degree angle to the vertical plane of the antenna (put it in horizontal, having it go straight back ) so that when the coax cable is connected to it the coax is well away from the aerials. Otherwise you run the risk of the coax interfering with the aerials capturing the broadcast signal. You will see this setup on pretty much every store bought antenna.
9. As I said in my other post - you can combine antennas just as long as the coax from each antenna to the junction point is the same length. If you need to build several directional antennas to capture weak signals from distance towers - make sure the antennas are at least 2 feet apart when it comes to the reflector on the antenna. You may be able to put them closer but at the time of this writing I have not tested this. I plan to see if I can build a long range antenna to test. Should be fun.
10. The coax will require a 7/16 wrench. Make sure you have two wrenches.
11. Before hooking to the TV, look to see if the coax plug on the TV has a capture nut on it. If yes, make sure it is snug but DO NOT OVER TIGHTEN. You will break the plug if you over tighten. If you break it you may be able to solder a replacement connection but most likely you will have to replace the board the connector is soldered to inside the TV. (Been there, got the t-shirt - did it on my booster)
12. If you are a old gamer like me you may have a NES. The NES coax connector will cause a lose of signal. I even tried a booster to get around that. Nope. You have to hook up the NES using the RCA connectors.
13. I tried using a jig to bend the wire when making an aerial. I found it made for round corners that needed to be tweaked and it made the straight sections not so straight.
14. Some folks will let the aerials be free standing in that they are only connected at the joining wire point. You "can" do this but be warned - if the angles of the bends in the aerials change at all you WILL lose signal. In my builds I like to draw the pattern on the backing material that the aerial is attached to and use my glue gun to make sure the aerial is exactly in the right place. This makes a huge difference in my opinion in signal gain.
15. Aerial stack - in some long rang antennas I've seen a stack of small aerials in front of a reflector. I plan to use this concept in a future build to see if a fractal setup in a stack in front of a reflector would bring in weak signals better without a booster.

I've been reading everything in this thread and I've learned a few things that will help:

1. When making the bends in the wire for the aerials - the corners need to be sharp as possible. Rounded bends in the fractal aerial reduce signal.
2. In between each bend for the wire for the aerials - the wire needs to be as straight as possible. - this increases signal.
3. You CAN combine several antennas together to increase signal. The things to remember is the wires coming from the different antennas need to be the same length to the junction point. Otherwise you get ghosting. I have a 4 antenna setup for my living room TV that works perfectly using this principle.
4. The cable length from the antenna should NOT have bends in it if at all possible. Any bends cause a loss of signal.
5. The cable length from the antenna to the TV should be as short as possible. Longer cable equals more signal loss.
6. It is possible to make a fractal aerial setup omni-directional. In a 4 pair fractal setup - I took and pivoted each pair in the stack by 15 degrees. I then combined several antennas together so I had fractal pairs pointing in every direction. This setup worked extremely well.
7. The higher the antenna, the more signal you get but only to a point and then only diminishing returns on any further gains.
8. If you use a antenna that is outside - it is critical the antenna is grounded and has a surge protector to protect from lightening strikes.
9. Home run (one continuous line) the line from the antenna to the TV if possible. Each additional junction, even a barrel connector will cause a loss of signal.
10. Elbow connectors - they cause a loss of signal. I've tried a couple of brands and they all caused a loss of signal.
11. Anything metal usually deflects and reflects signal. Things in your home like wires in the walls, appliances, duct work - they all will change the way the signal reaches the antenna or block it.
12. Don't use cardboard in making an antenna. It will seem to work well at first but the cardboard is really just paper and sooner or later - the cardboard will warp. I discovered this with an antenna I made and put in my attic. It was warped something terrible after only a few days.
13. Spend the money on quality coax connectors. The cheap ones are simply that cheap and you lose signal. Harbor freight sells a crimper for the quality coax connectors that is around 20$. That may seem a lot but I've seen them go for much more. They also throw in a few coax connectors in the box and they normally got for about a dollar a piece.
14. Do the math on figuring out the best type of fractal antenna will work for you. Look at the channels you should get, and how far away they are from you. The links on this thread on doing this are very helpful.
15. For the wires that link the Fractal aerials and if they cross (in a 4 pair setup for example) - there HAS to be a 1/2 gap where the wires cross. Put in a spacer so the wires stay apart. You will notice on the impedance matching transformer 300 ohm to 75 ohm the two wires coming out of it have a gap between them. That is there for a reason. If they get closer together - you lose signal.


With all the things above and if you are careful - you will build an antenna that will give you a much higher signal than one that is poorly made. I've made about a dozen antennas now and I'm finding doing all these little things add up in getting more channels, more stable signal, and less messing with having to do things like rotating the antenna to pick up the channel you want.
Happy building!

will it work if I connect the transformer to a 50 ohm coax?

Made this antenna 1st try was able to get 4 stations reliably. Did a search for the following had an example I tried to follow.

How do you determine the length of an antenna and the size of a fractal antenna?

Found my frequencies for my area averaged the used the above search result converted to inch

Made a 2nd set of fractals using 4-5/16" wire instead of 8" much smaller but picked up 2 more stations. Now have main network stations OTA.

Thanks for the info, plan to make 2 more for sons who view TV online Hulu and Netflix

Hi,

Sorry, I have dug up this old post. I am interested in making a Antenna for my new TV to receive digital TV signal.

I have some questions on the material:

1) What will the different effect of I use different material, say, steel, copper, and aluminum?

2) What will be the effect of width/thickness of the wire?

3) Must the wire in the antenna be bare? Can I let it in the insulator?

4) Can I use stranded wire? What is the effect?

5) I have an old "V" shaped antenna (rabbit ear?), can I just use the matching transformer here?

6) I have another old flexible antenna (I cannot remember the name for this), can I make it into a Fractal Antnna?

7) What do you think of the effect of this antenna:

http://lifehacker.com/5919128/build-your-own-paper...

Attached are the 2 antennas that I mentioned in (5) and (6).

20151026_010409[1].jpg20151026_010453[1].jpg

I recently built a 4 DP "whisker" antenna and it works better than expected, I can reach about 30 mi with it. It does currently get ch 10 (192 mhz) which is the local channel for us so I need to be able to get it. Now my question is this- the whiskers are 10" long so each wire is cut at 20" and bent to give me about 4" between each whisker tip. When I design my fractal antenna would I still cut the wires at 20" and bend them or does the fractal design create a longer wavelength because of all the bends? Also would I keep the closest points of the fractal antenna 4" apart? I tried using the antenna analyzing tool MMANA-GAL but as I am new to this I don't know how to use it properly

Hello Everyone! I just wanted to drop in and let you all know a few things that happened with the project recently. I have attached a picture of a build I did on Plexiglas which is one more iteration smaller.

Also, this antenna was showcased in the March 2015 issue of Popular Science:

http://www.popsci.com/learn-defy-cable-company-diy...

There are some more things in the making, but i will hit you with them when it is a reality!

Let's keep the wonderful collaboration going! I can't wait to see more of your designs!

CAM00012.jpg

OK I'll try this again.

I built the fractal antenna shown in the attached picture. Works great. I am 35 miles south of Milwaukee, WI and I receive 20 - 30 stations clearly. I can get Chicago stations but I must rotate the antenna.

Please comment on the circular design that I plan to build. Will it work if there are 20 fractals on the large diameter and only 11 on the small diameter. The large circle is 20 inches in diameter. The small circle is 18 inches in diameter. The fractals are approximately 3 inches tall.

Thanks for posting you instructions for the fractal antenna. Much better than my V shaped coat hanger design.

Sorry if I get multiple images. ??????

Antenna 002.JPGIMGP0566.JPGAntenna 002.JPGIMGP0566.JPG
6 replies
user

You want to design Antennas, I suggest you use a program like, MMANA-GAL to simulate it before you build it. http://hamsoft.ca/pages/mmana-gal.php
A couple of observations on your idea.
1. You have to be careful with the feedpoint impedance. Your TV equipment uses 75 Ohms. Most antennas, like the fractal and loop antenna I posted above will have a 300 Ohm feedpoint. This is the reason we use the adapter. More specifically a BalUn. In this case a 4:1 BalUn to convert 300 to 75.
2. Your design assumes that the feedpoint will be 75 Ohms, I guarantee it will not be. This is why you have to simulate it before you build it.
3. Antennas want to be balanced (in most cases), your design will be imbalanced so the feed point will have to be moved to achieve balance or a suitable feedpoint impedance.
If there is an impedance mismatch (antenna to receiver) the amount of signal present at the TV will be much lower.
For example if you connect the 75 Ohm coax directly to the feedpoint of the fractal antenna I posted (which has a 300 ohm impedance) you would experience 4.087 db loss. Every 3 dbs of loss is a halfing of the signal. Therefore, you would loose more than half your signal.
I hope this helps.

Your statements are correct, but your math is wrong.

75 vs 300 ohms gives a SWR of 4 and a miss match loss of ~1.9 dB.

A SWR of 8 gives the ~4 dB loss you stated.

A point you didn't cover is that SWR of greater than 3 can interfere with the tuners ability to decode the digital symbols and resulting in a much higher apparent signal loss (signal quality ).

You are absolutely right about modeling and simulations.

Hello,

I was wondering if you could help me out with a few doubts I have.

1. Is the design (like for example the one in this instructable) dependent on the location (city/country/continent)?

2. If it is, what details do I need to find out in order to design an efficient "HD" antenna (transmitted frequencies or other stuff maybe)? If so, any suggestions on how to look them up?

3. Do I need a BalUn regardless of the design of the fractal/antenna I make or is the design dictating if I really need it? I ask cause I found a "box" design in youtube where they basically just stapled the narrow end of the antenna to the coaxial, no balun, but then you mentioned that most antennas will need it.

Thank in advance for your help! :D

Thanks for your comments. I have moved on from the circular design. It did not work as well as the rectangular design. I built a larger (More Fractals) antenna which worked quite well but it was large and not very attractive.

user

Gerry, I am a HAM radio Extra class operator, and have studied antenna design a lot. My hobby relies on it very much. One thing that is not mentioned in this instructable, partly because it is out of the scope of it, is that even number of elements tend to work better. Keep that in mind when creating antennas. Also when you have stacked elements it is a good idea to have half of them out of phase to the others.
What this means is that if you call one wire A and the other B, have A going to the left side of two elements and then to the right side of the other 2 elements. You can see this in the design I posted a few days ago in this forum. Good luck and have fun experimenting. That is what it is all about!

The circular fractal antenna that you have showing in a diagram - did you make it yet? How did that work out?

Can't you paint this shape using liquid conductive paste?

1 reply
user

You could, but it would be very thin. The thiness might limit the antennas bandwidth (frequency range). This antenna needs to receive from (470-698 Mhz) which is pretty wide.

hi friends,

Am going to do research in fractal antenna can anybody say what recent problem in fractal antenna? and how to find recent problems in fractal microstrip patch antenna?

Very nice instructable, clear and concise.