Fractal Antenna for DTV Over-the-Airheads

[ahhaa]

I was watching NOVA on Fractals and they mentioned in passing about the astounding results you get with even tiny fractal antennas- like have completely replaced whip antennas in cell phones and such.

I'm in the boonies and have a long boom on a rotator; it works by being very dirctional, which doesn't work too well with the scanner in the digital tuner. Rescanning is necessary whenever the antenna is rotated, and fine tuning is nearly impossible as the picture doesn't get snowier- it just disappears entirely.

The advantages of a fractal designed antenna include broadband reception too.

Anybody wanna bend some coathangers?

[nic2k4]

Check this forum, there is talk of it as well as software and designs:

http://www.digitalhome.ca/forum/showthread.php?t=83772

[williamruckman]

I have a walkthrough here:

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

"How to make a fractal antenna for HDTV / DTV plus more on the cheap"

[edDV]

While this is an interesting topic for urban multipath reception, I see no claims yet for deep fringe reception.

Although I have cable, for OTA I suffer local terrestrial blockage, trees in the yard and weak distant ATSC stations out 60-99 miles. I'm going to experiment with ATSC tuners and antennas as a hobby after these stations go to full power on 17 feb.

[redwudz]

Years ago when I used a long boom antenna and a rotator, the control box I used had presets on it and I would just move it to the mark for the station of choice. I rarely had to adjust for best picture.

[ahhaa]

I have a walkthrough here: http://ruckman.net/blog/news.php?item.21.4

McGyver! I mean William! Excellent!

I think you really put a great info package together for experimenters.
Highly recommend you polish your article for Scientific American or even one of PBS's kid shows...
http://pbskids.org/dragonflytv/scifair/index.html

I'd read the fractal antenna impedance was zero, so I didn't know how to handle coupling, if that's the word, to physical cable, twinlead or single or coax or what...
I liked your reflector, most would have just called it a lid! 8)
I'm still unsure about orientation, if its more like the rabbitears magic dance or more like waves under a pier.
---
I wound up buying a commercial unit from Malmart: a supposed RCA ANT 1450, self-rated as between Excellent and Superior.
(if folks don't know, the once omnipotent RCA is now nothing but a rebadging of Audiovox's chinese imports. It was originally taken over and spayed by multinational GE, something like what happened to IBM. )

It's a white plastic 'tray', mebbe 1"x10"x12" that costs about $30; slightly amusing is they managed to mis-spell digital on the box. I liked the design because the amp is optional and attaches inline as opposed to directly on the antenna itself- allowing extending the cable.

I can't say I've had good luck with it, but we've had blizzard alternating with monsoon conditions here until just lately.

From what I've read, it is the only kind of antenna that could work in the woods without rotation, 'reticulation' & size being the only signal strength factors. If I'm understanding right!

&... Happy New Year All!

[SingSing]

How do people test these antenna?

Emit on a omni direction antenna with a known power, then measure the received power ?

[ahhaa]

Good question, as traditional antennae tend to get gain by being directional and frequency tuned. These fractal puppies seem to partake of the same somewhat reversed magic as the difraction grating wavicle demos (where a photon fired thru a slit winds up in more than one place...)

Also, now, antennas can be beautiful too!

[usually_quiet]

Also, now, antennas can be beautiful too!

If they can be small, or at least unobtrusive as well, even better.

[edDV]

Also, now, antennas can be beautiful too!

If they can be small, or at least unobtrusive as well, even better.

The higher the frequency, the smaller the antenna needs to be, but also the more it needs to be line of sight.

[misterbill]

There are no magic antennas, this one (Fractal) is a good example of that.
A full size, resonant frequency, multi-element is best. After that compromise comes in and efficiency goes out.

Read somewhere:

"Disadvantages of a fractal antenna:
gain loss.
complexity.
the benefits begin to diminish after the first few iterations."

Antennas, religions and politics. Some heated discussions are sure to take place.

[ahhaa]

well, there's an easy one called a Mandelbrot H-tree (which is actually used in CPUs for timing pulses) which looks like a plumber's antenna

UCLA photos : http://www.antlab.ee.ucla.edu/~johng/fractal.html

the real milspec skinny is here: http://www.fractenna.com/

[williamruckman]

The fractal antenna I made is only a 2nd iteration fractal. I am going to try a 3rd iteration to see if there is any difference but I will need to get myself some finer tools :P

It is more complex as stated above which is a downside when building it.

There are many different ways to design the fractals and many different antenna designs to incorporate the fractals into. Not sure which ones will give the best reception as this is the first one I have designed but it worked out well and was cheap.

If you have any improvements or suggestions I am always open. Just shoot me a line from my contact form on my website. ( http://ruckman.net ).

It is easy to make a antenna more compact this way but it would be great to mount it in a picture frame and call it art!

[SingSing]

well, there's an easy one called a Mandelbrot H-tree (which is actually used in CPUs for timing pulses) which looks like a plumber's antenna

H-tree is a very primitive, and simple scheme. I have not seem it in any text books. It only get mentioned in beginner physical digital design once in a while.

[ahhaa]

H-tree is a very primitive

Yeah, I think it actually goes back to Pythagorus or so...

[ahhaa]

It is easy to make a antenna more compact this way but it would be great to mount it in a picture frame and call it art!

A couple fabrication ideas:

the Koch triangle could be done by spraygluing foil to something, cutting away with your vintage T-square & an Xacto, and then covering with a laminate sheet...

Radio Shack used to carry the stuff for making circuit boards; I tried it and its very similar to amateur chemical photography. The resist can be wax, paint, vinyl, or a silkscreen type coating.

Walmart carries a computerized hobbist automatic vinyl cutter (for letters), there are ma&pa computer-controlled laser cutters around for etching those wood and aluminum signs, and for the really bold- the sheet metal guys have CAD controlled plasma cutters! (They are so cool! 8) )

[MysticE]

The fractal antenna I made is only a 2nd iteration fractal. I am going to try a 3rd iteration to see if there is any difference but I will need to get myself some finer tools :P

It is more complex as stated above which is a downside when building it.

There are many different ways to design the fractals and many different antenna designs to incorporate the fractals into. Not sure which ones will give the best reception as this is the first one I have designed but it worked out well and was cheap.

If you have any improvements or suggestions I am always open. Just shoot me a line from my contact form on my website. ( http://ruckman.net ).

It is easy to make a antenna more compact this way but it would be great to mount it in a picture frame and call it art!

I noticed all talk was about UHF, in Chicago 2 channels will be VHF.

[ray.casey]

ruck man... this is just a post to tell ya this is the coolest post i have stumbled into on the iternet . Great work... i am so looking forward to hearing more...

Rayc

[SingSing]

The fractal antenna I made is only a 2nd iteration fractal. I am going to try a 3rd iteration to see if there is any difference but I will need to get myself some finer tools :P

I know that Phillips amplified antenna, because I got one.

Did you feed your fractal antenna thru the Phillips RF amplifier? Or your passive antenna can beat the Phillips hand down ?

What gauge wire did you used ? Look like AWG20.

[williamruckman]

It was AWG18 wire.

[xmellman]

Sorry if this is the wrong forum. I have been trying to get an answer for this and can't seem to get a definitive one. I live south of Portland, OR. I have a nice Radio Shack VHF/UHF antenna in my attic. I get pretty decent reception of the main VHF channels in my area and don't really watch any UHF. I've got my converter boxes for my old-school TVs and I am ready for the switch in June or whenever our omniscient Congress decides we are ready for the switch (Lord knows I can't possibly think for myself, but this is for another topic on another forum!). Now the problem - I get next to NOTHING with my digital box - only 4 channels, and they are channels I don't care about. Someone told me that I am behind a hill blocking me from receiving the UHF signal that all of the channels are now being broadcast over. The questions are: will the "main" alphabet networks switch their digital signals over to the VHF spectrum come Feb. 17 (or June!), or am I going to be without TV (save the 4 weird channels I am getting)? Second, is there anything I can do, other than becoming a slave of my cable company, to receive the signals better, given the apparent issue with my location? Would a fractal antenna work better? Thanks in advance for your insight.

[usually_quiet]

@xmellman: There's no way to tell if a fractal antenna will help you. They are only experimental for TV reception.

www.tvfool.com and www.antennaweb.org can tell you what kind of conventional antenna you need. I found www.tvfool.com to be very good at predicting what I would get pre-transition, and it can also predict what post-transition reception will be like. You should also be able to see which stations, if any, will be VHF.

http://www.rabbitears.info/termlist.php has a list of stations that will teminate analog transmissions early.

Your digital converter box's tuner may be worse than average. Which one is it?

[SingSing]

Would a fractal antenna work better? Thanks in advance for your insight.

I am watching DTV now, with the amplified Phillips Antenna. You can get one from Walmart, if that did not help, you rteturn it. if that help, then update to fractal antenna.

[ahhaa]

X-man:
Check this forum
http://www.digitalhome.ca/forum/forumdisplay.php?f=81
there are a lot of advanced OTA posters there from your northwest area, posting signal strength maps pinpointing the new broadcast towers etc.

Your problem will be that UHF doesn't bend into shadow areas as well as VHF. Antenna altitude may make all the difference- a few feet or much more... the reason that fractal antennas might help you are: they are omnidirectional - no rotator needed which helps tuning too; they are small, the Ruckman Mark #1 is about the size of a comic book; they are lightweight and offer little wind resistance, making them easy to mount high inconspicuously; you can make your own out of household scrap for free.
Also, your neighbors should have the same problem, mebbe there is a mutual solution?
'nuff said?

[xmellman]

Thanks for the info. I have a Digitalstream converter box. Good, or not? It looked like it was picking up everything fine in the Radio Shack store with just simple rabbit ears - they are not in the shadow like I apparently am. Maybe I can mount an antenna on the top of the street light pole on my street . Sounds like I might be SOL come the 17th...

[lacywest]

Interesting

[edDV]

Sorry if this is the wrong forum. I have been trying to get an answer for this and can't seem to get a definitive one. I live south of Portland, OR. I have a nice Radio Shack VHF/UHF antenna in my attic. I get pretty decent reception of the main VHF channels in my area and don't really watch any UHF. I've got my converter boxes for my old-school TVs and I am ready for the switch in June or whenever our omniscient Congress decides we are ready for the switch (Lord knows I can't possibly think for myself, but this is for another topic on another forum!). Now the problem - I get next to NOTHING with my digital box - only 4 channels, and they are channels I don't care about. Someone told me that I am behind a hill blocking me from receiving the UHF signal that all of the channels are now being broadcast over. The questions are: will the "main" alphabet networks switch their digital signals over to the VHF spectrum come Feb. 17 (or June!), or am I going to be without TV (save the 4 weird channels I am getting)? Second, is there anything I can do, other than becoming a slave of my cable company, to receive the signals better, given the apparent issue with my location? Would a fractal antenna work better? Thanks in advance for your insight.

When the dust settles your channels will look like this

2 KATU ABC --> 43
6 KOIN CBS --> 40
8 KGW NBC --> 08
10 KOAP PBS --> 10
12 KPTV FOX --> 12
22 KPXG ION --> 22
32 KRCW CW --> 33
49 KPDX MY -->30

So you better look for a good UHF antenna.
Put your address in this page to get a predicted signal level.
http://www.tvfool.com

[usually_quiet]

Thanks for the info. I have a Digitalstream converter box. Good, or not? It looked like it was picking up everything fine in the Radio Shack store with just simple rabbit ears - they are not in the shadow like I apparently am. Maybe I can mount an antenna on the top of the street light pole on my street :). Sounds like I might be SOL come the 17th...

The Digital Stream CECBs reportedly have better-than-average tunners, so that is probably not contributing to your problem.

That being said, if you need to get another converter box at some point, some user reviews state that the Channel Master CM-7000 and Zenith DTT901A are more sensitive or do better where there is a problem with multipath reception from reflected signals. There's no guarantee that they will be any better for you, but they would be good choices if you want to try something different next time.

You may still have analog reception for some channels after February 17th. On February 4, the date was for which analog shutoff is mandatory was pushed back until June 12, although some stations will be allowed to discontinue analog on February 17. Under the new FCC rules announced yesterday, they must notify the FCC by February 9, and if the FCC does not have a problem with it, they can go ahead. It is still uncertain at this point whether all those who notified the FCC before yesterday will be granted permission.

[xmellman]

Does that tvfool.com site take into account the actual topography of my location? Does it "know" that I am in a "shadow?" I have attached the report. It looks much better than what I am seeing. I have my antenna pointed to approx. 335 degrees (I just took a small compass up to my attic and eyeballed it).

The one channel I am getting (four channels) is 22 - loud and clear.

[usually_quiet]

tvfool does take terrain into account and "knows" you are behind a ridge. They have links to terrain maps as well that show reception over the entire area served by each station. If you used your street address. you might try entering the exact latitude and longitude for your house, in case tvfool made a mistake using your address .