Introduction: Indoors Fractal HDTV Antenna
This antenna design grew out of my attempts to build an indoor HDTV antenna using fractal patterns after I had watched a TV show and had read a magazine article on the use of fractal patterns in cell phone antennas, My goal was to design an antenna that not only worked well, but one that was easy to build and could be built from easiliy obtainable materials.
The result is an antenna that is somewhat omnidirectional, and performs well receiving digital TV signals at my home from the low end of the VHF high-band (i.e Channel 7 at 174 MHZ) to the high end of the 600 MHz UHF band. (There are no channels in the 700 MHz band in my area, but Channel 51 at 692 MHz is one of the strongest signals here.)
This antenna can be used at a maximum line-of-site distance from the broadcast tower of about 50 miles for high power stations, and somewhat less for low power stations. I'm sorry that I can't be more definite about these distances, but a lot depends upon the type of construction used in the building and the location of the antenna within the building (e.g. downstairs living room vs. second story bedroom or attic).
So, with all that in mind, let's get started.
Step 1: Gather Needed Materials
- A 150mm X 400 mm ( 6 inch X 15 3/4 inch) piece of poster board. This is the stuff from which cake boxes and the gift boxes for shirts and blouses are made. A 24 inch X 28 inch sheet of it can be bought at hobby stores and other places for less than a dollar.
- The pattern for the antenna. Download the PDF file at the bottom of this page.
- Some cellophane tape.
- Map pin or other sharp pointy object for punching holes in poster board.
- 3.2 meters (~10.5 feet) of small diameter (24 - 20 AWG) copper or aluminum wire. This can be salavaged from an old discarded electric motor or purchased from a hobby or hardware store.
- Crimp connectors and crimping tool or a soldering iron and solder for connecting lead-in wire to antenna.
- A length (let your situation be your guide as to the length) of 300 Ohm twin lead antenna lead-in wire and a 300 Ohm to 75 Ohm matching transformer. The matching transformer can be purchased from Radio Shack, Wal-Mart, Target, on-line, or at any number of hardware stores. Best prices are found on-line, you just have to wait a few days for delivery.
- A length of 75 Ohm coax and a in-line 300 Ohm to 75 Ohm matching transformer can be used instead of the 300 Ohm twin lead antenna wire listed above as Item 8. It's getting harder to find the good old fashion 300 Ohm twin lead antenna wire, and all the TVs manufactured in recent times have antenna connections for 75 Ohm coaxial cable.
- A craft knife or other knife with a small sharp blade for cutting Slots A & B in antenna form.
Step 2: Print Pattern and Prepare Antenna Form
When you have a printed copy of both pages:
- Cut the trailing end off of the first sheet.
- Lay the first sheet on top of the second sheet and align the pattern and big "plus sign" registration marks on top of each other.
- Tape the two sheets together.
- Use the scissors to trim the excess paper from the edges of the pattern leaving only a 150 mm X 400 mm rectangle.
- Tape the pattern to a piece of poster board and trim the poster board along the edges of the pattern.
- Tape the pattern to the poster board, use a couple of layers of shipping carton card board as padding, and use the map pin or other sharp pointy tool to punch hole at every point in the pattern marked with a dot.
- Use a craft knife or other small sharp blade to cut Slots A & B into the poster board.
Step 3: "Lace" the Wire Onto Antenna Form
Use a 1.6 meter length of wire for each side of the antenna form, and starting at the hole marked "Start" lace the wire back and forth from one side of the poster board to the other following the pattern. Keep the wire as straight as possible between the holes and be careful to not kink the wire when pulling it through the holes. Leave about 1/2 inch of wire on the back side of the poster board at the end of each wire to be used for connecting the lead-in wire.
The best way to connect the lead-in wire or in-line matching transformer to the antenna is to twist together the stripped wires of the lead-in/matching transformer with the end wires of the antenna and solder both connections. If you don't have a soldering iron and solder, the next best connection is made using crimp connectors and a crimping tool or pliers.
After the lead-in/matching transformer is connected to the antenna, it's a good idea to punch a hole through the poster board on both sides of the lead-in wire or in-line matching transformer and tie the wire to the poster board using a small cable tie or tristy from a loaf of bread.
Step 4: Finishing Up
After the lead-in has been connected to the antenna, all that is left to do is to form the antenna into a cyclindical shape and insert Tabs A & B into Slots A & B. (A little cellophane tape along the seam works wonders in maintaining the shape of the antenna.)
The antenna is now ready to be connected to the "Antenna In" connector on your TV or converter box. The antenna works best if set on a window sill or taped to a window pane, but you should experiment with the placement and orientation of the antenna to find what works best for you.
Step 5: Adding a Decorative Touch
The antenna will fit into various empty clear plastic containers and can be used to display family photos or sports pictures.