Built $9 Fractal Antennna, 21 Digital Channels

[PX4sc40sw]

Gosh, I just noticed that I have not much recollection of those curves either. Time to go back to teaching.

Not the type of curves I pay much attention to either...

 

[ziggy29]

Since I'm 25 - 40 miles away, I think I'll stick with my big @ss antenna up in the attic.

I'm more like 60 miles away. Needed some pretty serious hardware mounted to the side of the garage to above the roofline, but it all works...

 

[BunsGettingFirm]

Guess the question for you Al, do you think you will ever become a cave man? To the point that widely publicized information has escaped notice.

Like, "Dewey has now been declared the loser".

I quit watching TV about 30 years ago and I mean "QUIT", have not owned a TV for more than 1 year of the last 30. I have seen adverts, etc, but I have no idea what a "reality show" is. And I feel OK with myself. Although others let out an audible, "gah" when I reveal that.

That happens all the time. I was at salsa class 3 weeks ago, and the people there were talking about that celebrity dancing show, and I had the gall to ask what night the show is on. Doesn't take a lot to be out of tune with popular culture.

 

[calmloki]

I've had good luck with this :

YouTube - Coat Hanger HDTV Antenna!

Built this today and sprung for the $2.99 75-300 ohm resistor and hooked it up to the cable side of the tv card in the gal's Vista machine and got....nothing. Bummer. Lcd monitor so i figured sure it would work, but guess we're just too far from a signal...

 

[PX4sc40sw]

The design has almost ZERO gain, I doubt it would be too effective at any more than 2-3 miles from the x-mitter.

The fractal is probably good up to 15 miles.

BTW, cell phones use tiny (1" fractal antennas and can pickup signals much weaker than TV transmission at 15 miles.

Built this today and sprung for the $2.99 75-300 ohm resistor and hooked it up to the cable side of the tv card in the gal's Vista machine and got....nothing. Bummer. Lcd monitor so i figured sure it would work, but guess we're just too far from a signal...

 

[donheff]

Well, I built the fractal antenna with mixed results. In DC, channels 7 and 9 (ABC and CBS) were broadcasting their digital signals on UHF channels prior to the switch. I set-up a few old folks' digital TVs and they got those stations perfectly. After the switch, 7 and 9 moved their digital transmission down into the old VHF slots and they disappeared from view. This was not just a re-scanning issue, the stations new signals were simply too weak to tune in. Today's Washington Post confirms that the change has screwed up viewers all over the area but particularly in the center city (us) - apparently VHF works well in hilly areas but UHF is better in crowded buildings. I built (or sorta built - I am not a skilled handiman) a fractal antenna using the instructions posted here and on the linked website and took it over to a digital conversion victim's house. On his new digital TV in the downstairs kitchen it got all the stations his old rabbit ears pick up but like the rabbit ears it didn't get 7 and 9. On his old upstairs TV with a converter box I was able to get channel 9 (an improvement) but still no 7. The Post says the stations may have to boost their signals to improve the situation -- here's hoping they do.

 

[ziggy29]

It sounds like a lot of people in DC had trouble with 7 and 9. In fact, having trouble with stations that just moved back to VHF seems to be a common problem nationwide.

 

[PX4sc40sw]

The fractal has to have very precise alignment with the Star of David shape. Exact 1" segments and very accurate 60 deg angles, or it will lose a lot of it's gain.

The beauty of this fractal is that it will replace the big contraptions like rabbit ears and the need for a huge roof antenna.

Sounds like the major issue is that the ABC and CBS people had several years to get this right and failed miserably.

Well, I built the fractal antenna with mixed results. In DC, channels 7 and 9 (ABC and CBS) were broadcasting their digital signals on UHF channels prior to the switch. I set-up a few old folks' digital TVs and they got those stations perfectly. After the switch, 7 and 9 moved their digital transmission down into the old VHF slots and they disappeared from view. This was not just a re-scanning issue, the stations new signals were simply too weak to tune in. Today's Washington Post confirms that the change has screwed up viewers all over the area but particularly in the center city (us) - apparently VHF works well in hilly areas but UHF is better in crowded buildings. I built (or sorta built - I am not a skilled handiman) a fractal antenna using the instructions posted here and on the linked website and took it over to a digital conversion victim's house. On his new digital TV in the downstairs kitchen it got all the stations his old rabbit ears pick up but like the rabbit ears it didn't get 7 and 9. On his old upstairs TV with a converter box I was able to get channel 9 (an improvement) but still no 7. The Post says the stations may have to boost their signals to improve the situation -- here's hoping they do.

 

[donheff]

The fractal has to have very precise alignment with the Star of David shape. Exact 1" segments and very accurate 60 deg angles, or it will lose a lot of it's gain.

The beauty of this fractal is that it will replace the big contraptions like rabbit ears and the need for a huge roof antenna.

Sounds like the major issue is that the ABC and CBS people had several years to get this right and failed miserably.

Well, with my poor skills I think I may have blown the alignment. I found some brass rods at the hardware store that seemed about right but it was difficult to get a precise bend with them. The website calls for 18 gauge hookup wire. I think my rods may be more like 12 gauge. I may try another version with thinner wires.

 

[PX4sc40sw]

Donheff,
same issue with mine, I got the rod stock and it was difficult to bend, went back and got a second piece but thinner and it worked pretty nicely.

Good luck, I know you are trying to help some others get good reception so I hope it works out.

Here is how mine looks. Awesome quality picture.

Well, with my poor skills I think I may have blown the alignment. I found some brass rods at the hardware store that seemed about right but it was difficult to get a precise bend with them. The website calls for 18 gauge hookup wire. I think my rods may be more like 12 gauge. I may try another version with thinner wires.

 

[ERD50]

.... . In DC, channels 7 and 9 (ABC and CBS) were broadcasting their digital signals on UHF channels prior to the switch.

....

After the switch, 7 and 9 moved their digital transmission down into the old VHF slots and they disappeared from view.

Sounds like the major issue is that the ABC and CBS people had several years to get this right and failed miserably.

I don't see how you can say that "the ABC and CBS people had several years to get this right and failed miserably"?

They could not move until the switch was complete, as others were in their spectrum until they moved. It's not their "fault". They were stuck - it happened to a few channels, others were "lucky" and have been simulcasting on their new turf for a long time. These stations did not have that luxury.

Maybe they could have got better info out there, like "if you have trouble picking up channels x,y,z now, you may have trouble getting us after we move". That's a guess on my part, I don't know if any TV channels were broadcasting near their final frequencies to use as a test.

-ERD50

 

[ziggy29]

They could not move until the switch was complete, as others were in their spectrum until they moved. It's not their "fault". They were stuck - it happened to a few channels, others were "lucky" and have been simulcasting on their new turf for a long time. These stations did not have that luxury.

In some cases, I agree -- those who had been broadcasting digitally on channels above 51 had to change. But there were a lot of stations broadcasting digitally on UHF channels 14-51 which didn't *have* to move, but did so anyway -- to VHF (usually channels 7-13). The reasons for changing are obvious; it takes at least 20x as much power to transmit UHF for the same coverage area. But this is still a conscious choice which requires them to perform work after the transition to get a decent signal.

Our Fox affiliate in Austin is an example. Of course, in their case they had to move because they were digital on a frequency being vacated (channel 56), but they chose to go back to channel 7 (where their analog was). But to do so means they are now broadcasting on a weak, low-mounted temporary antenna which many people can't even pick up in Austin proper. It will be a few weeks until they get their final setup in place.

 

[toofrugalformycat]

Did you tell the box to RESCAN?

Some stations moved their frequencies as part of the switch. They couldn't do it before, because they had to wait for others to free up the spectrum. IF they moved, you need to rescan to get them. Also, if they moved to a different part of the band, it's possible that the antenna isn't sensitive in that range, but rescan first - if that's the issue no amount of antenna tweaking will 'fix' it.


-ERD50

Thanks, ERD50. Yes, we've tried RESCAN, and also trying for the exact frequency NBC is broadcasting on - there is just a tiny faint signal there. I just got back down from the roof, re-aiming the antenna. We get all the stations better now, most are usable, except for NBC.
So now I'll contact the local station directly and see what they have to say for themselves.

 

[skyline]

I believe the problem with the VHF signals is that the wavelengths are much bigger than UHF signals. I don't believe most small antenna designs will ever pickup the lower portion of the high VHF band (ch 7 & ch 9) with any strength. They're just physically too small to deliver much gain.

BTW, for those of you shopping for a new antenna because you lost ch 7 (seems to be the most common issue), remember that most of the reviews out there were posted before the cutover - so those glowing reviews you see are really only about UHF performance. Wait a little while before you see reviews on high VHF performance before buying anything (or buy a hi-VHF/UHF rated antenna).

 

[ERD50]

I believe the problem with the VHF signals is that the wavelengths are much bigger than UHF signals. I don't believe most small antenna designs will ever pickup the lower portion of the high VHF band (ch 7 & ch 9) with any strength. They're just physically too small to deliver much gain.

True, but (as I understand it), that is what the Fractal Antenna design is all about - it "looks" large electrically, but is physically small. See the wiki entry for more....

BTW, for those of you shopping for a new antenna because you lost ch 7 (seems to be the most common issue), remember that most of the reviews out there were posted before the cutover - so those glowing reviews you see are really only about UHF performance. Wait a little while before you see reviews on high VHF performance before buying anything (or buy a hi-VHF/UHF rated antenna).

Good point.

-ERD50

 

[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]

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]

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]

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]

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]

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?