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Fractal Antenna anyone?

myu701

myu701

Vintage futurist
A saw an episode of Nova on PBS that covered the subject of fractals. Very interesting program. In part of it, there was mention of a fractal antenna that tests showed about a 20%* improvement in reception over a conventional antenna.

Interestingly enough, cellular phones now have fractal antennas inside them, which is why you do not see any of them using external antennas any longer.

Most of the DIY examples I've seen, like this one, mention the use for DTV (or HDTV). I'm wondering if this would work well for FM reception, given the proper size ratios.

Has anyone here ever tried a home built fractal antenna for FM reception?

(* figure of 20% was mentioned elsewhere)
 
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I saw that episode. Looks like the big benefit is it picks up a wide frequency band. Not something that is needed for just FM use.
 
^ thanks. Yeah, I'm thinking the square antenna is the way to go for FM, based on the research done and testimonies given.
 
Built one, and am going to do another twice as large just for fun. I use it with my Sony HD receiver. Works just fine for my local HD2/3 stations (all three bars).

Recommend you cut the 8" sections at 9" to allow some slack for the bends. Then trim the excess after.
 
Voltron said:
Built one, and am going to do another twice as large just for fun. I use it with my Sony HD receiver. Works just fine for my local HD2/3 stations (all three bars).

Recommend you cut the 8" sections at 9" to allow some slack for the bends. Then trim the excess after.
Click to expand...

Got pictures?
 
Here ya go. Chrome grid is just plastic from a scrap elevator ceiling light diffuser.
 

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Voltron said:
Here ya go. Chrome grid is just plastic from a scrap elevator ceiling light diffuser.
Click to expand...

Out of curiousity, is the chrome grid anything necessary, or just cosmetic?. May have to look into building one of these, seem pretty compact, and i'd love to have better reception than the rabbit ears.

Who knew geometric patterns could be so usefull:yes:
 
Chrome grid may have magical properties, but was selected using the "appropriate junk" criteria.

Build one.
 
Voltron, thanks for showing us your handiwork. :) Have you used this strictly for HD radio reception or have you tried analog FM as well? If so, how'd it stack up to what you've used before?
 
First fractal

myu701 said:
Voltron, thanks for showing us your handiwork. :) Have you used this strictly for HD radio reception or have you tried analog FM as well? If so, how'd it stack up to what you've used before?
Click to expand...

Myu,
First of all, thank you very much for the thread.
I did build one (please see attachment) using an old modem base which is too small. The use of an old 30/60/90 drafting triangle as a mandrel made the job easier.
Nevertheless, I tried it on a mid fi receiver and the Magnum Dynalab FT101.
I was and continue to be amazed with the sound quality and strength of signal of analog FM.
Interestingly, signal strength was astonishing when I was touching the copper vanes. And performance was greatly improved when the panel is postioned vertically.
Next steps:
  1. Build 3 more Fractals
  2. List 3 Terks and 1 Parsec in Barter town ;)
picture.php
 
For my FM in the bedroom, I am using a Sansui 2000x as my amp with a Sansui TU-0301i tuner.

Clearly superior!

Rabbit ears to dumpster.
 
Voltron said:
For my FM in the bedroom, I am using a Sansui 2000x as my amp with a Sansui TU-0301i tuner.

Clearly superior!

Rabbit ears to dumpster.
Click to expand...

Sounds like a plan(the rabbit ears thing). Did you use one of the print-out plans/layouts available on the site linked above, or actually calculate what pattern was needed?...or, a more accurate question, it's meant for tv use, does anything need to be altered for better fm reception?.

Gotta be honest, I can work through electronic stuff/equations alright but as soon as airwaves talk comes up it's a brickwall:scratch2:

...i'll have to find something cool to mount this too, no chrome stuff around, may have to go with a colored record or something.
 
You can use just about any non metallic material, I built a second one using two pieces of wood. One piece for the mounting panel, the other for a small base to stand it on. I have not built one with a reflector, so someone needs to file a report.

For some reason it works well under the bed.

I have not tried this with my DTV. I have an outdoor antenna for that.
 
Just a note, I used 12 gauge wire. Just happened to have a roll l discovered on a scrap run some time ago.
 
Quick couple of questions;

1) How exact do the bends need to be?. I'm using the paper print out and lining it up using that, but the bends can't be exact. If you wire is not exactly flat, but is in roughly equal segments and almost exact angles, it should work fine, right?

2) Reading the matching transformer, since i'm using this for FM on my receiver, I don't need a coaxial plug, how should I terminate the outputs?, would just using spade connectors work, if I ran it at the 300ohm tap, or should I get a transformer and use the 75ohm tap?

Using 12 gauge wire, since we have a large bundle of house wire in the basement:yes:
 
For my first effort, I laid out the bend pattern on a 1/2" thick piece of junk plywood using a 30/60 drafting triangle and a T square. At the bend points I drilled a shallow hole and inserted some small finishing nails. These were the fulcrums for the bends. As your bending proceeds, simply move the nails as appropriate.

Square the result and trim to size. Stack the four bent pieces and adjust for uniformity.

As far as connections to the antenna, I used simple spade connectors.

Connecting the antenna to your tuner depends on what type of connections it has. You may need to use a transformer depending on what the tuner expects. I got away with an rg-6 to spade adapter and a barrel connector to the rg-6/spade wire from my tuner.
 
Thanks for the assistance, i'm going to have to find some spade plugs tomorrow. Wish I had thought of finishing nails, I was going at it with pliers and brute force. Got it looking pretty close to the design, and everything is about even. Have it mounted on wood, and to try it out, used some lamp cord between it and the receiver.

Not sure how much better it is than rabbit ears, but it picked up stations nicely, and is really compact. I have a feeling with a proper cord it may do even better. It picked up 88.1 fairly well, which is the hardest one to get in my area, that I listen to (it's a college station quite a ways away). Despite it being a far away station, I was reading 4/5 in signal strength. The tuner in the 727 doesn't like to fine tune in that area though, keep getting a small woosh noise as I move the dial, but just while moving:scratch2:

I'll try to get spade connectors and a picture tomorrow. This thing really is great for the size:yes:
 
Voltron said:
Here ya go. Chrome grid is just plastic from a scrap elevator ceiling light diffuser.
Click to expand...

I wouldn't necessarily call that a fractal antenna. It's really an array of two virtual bow-ties with meandering elements. Meandering is a way to make the antenna physically smaller. Generally, the way to increasing gain is to increase the antenna's capture area or aperture.


-Gregory
 
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