Built $9 Fractal Antennna, 21 Digital Channels

[PX4sc40sw]

It it key to realize that a Fractal antenna should not work, at all, based on what the "known facts" are. But more imaginative minds would not accept that antennas could only work at 1/2 wavelenth or more.

So we carry cell phones with fractal antennas and not the 1.25 foot dipole antenna sticking up.

AverMedia RF Antenna for TV Tuner

It is about 4.5" long and 14 guage, and against all laws of physics, it works very well.

Here is a good paper on fractals and right now I think I'm close to getting n=4 version for UHF, so standby. It will be about 1.5" square or so.
http://www.hep.princeton.edu/~mcdonald/examples/fractal_antenna.pdf

We are trying to use a programmable sewing machine and very fine copper wire, about 3 mil diameter.

[donheff]

Quote:

Originally Posted by PX4sc40sw Here is a good paper on fractals and right now I think I'm close to getting n=4 version for UHF, so standby. It will be about 1.5" square or so. http://www.hep.princeton.edu/~mcdonald/examples/fractal_antenna.pdf We are trying to use a programmable sewing machine and very fine copper wire, about 3 mil diameter.

That sounds cool By the way, my new, slightly better built, fractal antenna works pretty good but still has problems with 7 and 9 unless it is up on the 2nd or 3rd floor in most Capitol Hill houses. Hopefully ABC and CBS will boost their signals soon.

[ziggy29]

Quote:

Originally Posted by donheff That sounds cool By the way, my new, slightly better built, fractal antenna works pretty good but still has problems with 7 and 9 unless it is up on the 2nd or 3rd floor in most Capitol Hill houses. Hopefully ABC and CBS will boost their signals soon.

Lots of problems with the VHF frequencies out there; so many of them are on temporary facilities with reduced power. One station (WHDH in Boston) had it so bad they had to petition the FCC for an emergency temporary authority to simulcast their programming on UHF channel 42 in addition to channel 7 until they can figure out how to improve the reception on channel 7.

Another big problem (which many expected) is WPVI (channel 6) in Philly, not just using VHF but a LOW VHF frequency (channels 2-6). Many people don't have any equipment to receive low VHF and very few stations are using it. And these are a lot harder to pick up with desktop rabbit ears than UHF or even the higher VHF channels. Sounds like they want to increase power about fourfold, but in reality what they need is to get off channel 6.

[ERD50]

Quote:

Originally Posted by PX4sc40sw Here is a good paper on fractals and right now I think I'm close to getting n=4 version for UHF, so standby. It will be about 1.5" square or so. http://www.hep.princeton.edu/~mcdonald/examples/fractal_antenna.pdf We are trying to use a programmable sewing machine and very fine copper wire, about 3 mil diameter.

I wonder if someone could make one by either etching a copper-clad PC board, or using one of those sign-making machines (similar to a CAD-router) to remover the "waste" areas?

I'm assuming that since the dimensions are so much smaller than a wavelength, that they are all fairly critical. Probably affects the impedence matching too. So accuracy might improve the reception a lot.

I used to work in close proximity to some antenna guys. I didn't pick up much by osmosis. There always seemed to be a fair amount of "voodoo" thrown in with the science and calculations, there are a lot of physical characteristics and parasitics and tolerances and interactions that are tough to model. Start there and tweak until it works.

I might get around to trying one of these - one TV is just on rabbit ears, we get most, but not all channels on it. The rest are tapped into a good size antenna in the attic, they get everything.

-ERD50

[FUEGO]

Did these fractal antenna designs come about by some genetic algorithm tests of random antenna designs? I seem to recall something about an antenna design for a satellite that was extremely tiny but effective, yet it had no order or symmetry to it. They just kept trying different random combinations of lengths, angles, and branches and retained the more optimal designs while discarding the suboptimal designs, slowly building up the performance of the antenna.

[samclem]

Quote:

Originally Posted by travelover I've had good luck with this : YouTube - Coat Hanger HDTV Antenna!

I built the same antenna yesterday, it works great. I had some copper wire, so I used it instead of coathangers. For those who want the written plans instead of a video, they can be found here (and there's another video there, too.) I didn't put any reflectors on it--I don't need them.

I'm about 20 miles from the stations. Before I built this we were using a bowtie antenna. One channel was coming in weak (signal strength of 48 arbitrary units according to my DTV box) and we'd get pixelation sometimes. With the new rig in the same spot, everything comes in at 90+ signal strength. For those who need more signal strength, a reflector might do the trick.

This design excels at UHF frequencies. We're fortunate that all digital TV in Dayton is UHF. For the VHF frequencies, I might need a differnt setup (fractal, a big 'ol yagi, etc).

[Westernskies]

Quote:

Originally Posted by samclem I built the same antenna yesterday, it works great. I had some copper wire, so I used it instead of coathangers. For those who want the written plans instead of a video, they can be found here (and there's another video there, too.) I didn't put any reflectors on it--I don't need them. I'm about 20 miles from the stations. Before I built this we were using a bowtie antenna. One channel was coming in weak (signal strength of 48 arbitrary units according to my DTV box) and we'd get pixelation sometimes. With the new rig in the same spot, everything comes in at 90+ signal strength. For those who need more signal strength, a reflector might do the trick. This design excels at UHF frequencies. We're fortunate that all digital TV in Dayton is UHF. For the VHF frequencies, I might need a differnt setup (fractal, a big 'ol yagi, etc).

I built one of these when I was waiting for the local cable company to grace us with an appearance. Picked up 39-49 channels (every scan was diffferent; I tried moving the antenna around and was finally able to get 43 channels with it hanging down behind the entertainment center, out of sight.) The local HD channels come in better than the cable signal.

If it wasn't for the DIY network, Discover, History, TLC, pay-per-view movies, etc. I would cancel cable in a minute...

[FUEGO]

This thread reminded me that I forgot to watch over the air tv for over four months. I guess you get busy sometimes and forget to focus on your priorities?