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  1. #1
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,750

    Default DYI HDTV Fractal antenna

    I have a rooftop antenna that powers about 8 devices in my house, but it requires an amplifier to work. I'm about 30 miles from most of the stations I tune to. It will power one device only without the amplifier but splitter losses overcome it when multiple devices are hooked up.

    Anyway, got the wife a new antenna for the upstairs bedroom. No more spots left on the rooftop so I tried "rabbit ears". Even with an amplifier, it didn't work. Found this on the net and made one. Works like a champ on one device, don't think it will do two devices though, signal strength appears to be just adequate for one device.

    http://ruckman.net/blog/news.php?item.21.4

    Instead of buying the project box, I made a box from scrap wood, one 12x12" piece of 1/8" lauan plywood and some 1x4 for edges. Used a piece of aluminum foil across the back (open side of the box) for a reflector and mounted the antenna elements on the face of the box. Used 18 ga copper wire to make the elements.

    This is a single iteration fractal. Tried to make a larger 2 iteration version, didn't work. As with most things in electronics, only odd numbered iterations work and a 3rd iteration would take way too long to make. I might try making another one iteration with 1.5" legs instead of 1", I think that would probably work better, I'll let you know if I do and if it does. 2" legs might even work better as it would be closer in size to the Grey Hoverman design that works well in fringe areas.

    http://www.digitalhome.ca/ota/superantenna/design.htm

  2. #2
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,750

    Default Re: DYI HDTV Fractal antenna

    Well I made a fractile with 1.5" segments. I looked up the frequencies for the stations in my area, calculated the wave length, divided by 4. The fractile with 1.5" segments covered the entire spectrum. Still using the same reflector, which may be a problem. Anyway, some channels came in clearer, some worse. Unfortunately the ones my wife likes to watch were in the worse class. Bear in mind that no other indoor antenna works at all without an amplifier, and this one works better that the rabbet ears with an amp.

    I'm thinking about trying the square type fractile but I have ordered a dual output Blonder Tongue Vaulter III amplifier from solidsignal.com to hook up to my outdoor antenna in the attic. This will be my final solution but I do like to experiment from time to time.

  3. #3
    Join Date
    Jan 2008
    Posts
    2,118

    Default Re: DYI HDTV Fractal antenna

    Fractal is a new and interesting approach to antennas, and the first new one in about 100 years that actually works. Of course it was invented by another Ham It still has one issue that is insurmountable in it's tiny size. Sometimes in weak signal areas you need to 'capture" more RF in the air which requires more metal. Another issue to consider in self-designed antennas is the velocity factor of the metal itself. Since the metal's electrical resistance slows the flow of electrons passing through it, a tuned antenna is actually a bit shorter than free-space frequency calculations show it to be, thus compensating for the wavelength time factor. Also everything in a near-field RF environment affects an antenna, including sections tuned for other frequencies. Multi-frequency Fractals look simple but are actually designed with some very heavy calculation going on, and even just 20 years ago that much computing capability wasn't readily available to average people.

    I'll pass on an old Ham trick- use it at your own risk with copyrighted designs like the Fractal! Simply obtain a sample of a working device and make as exact a copy of it as you can. If you know what you're about, you can change things to work with any different materials you are going to use so that it stays tuned where you want it to. One of these days, this old antenna nut is going to delve as deeply into Fractals as I have conventional antennas when I have the time.

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