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How I made an HDTV antenna so I could watch Jeopardy last night (blamcast.net)
263 points by chaosmachine on Feb 15, 2011 | hide | past | web | favorite | 68 comments

You'll get even better reception if you shape the wire in a fractal pattern, like this: http://www.instructables.com/image/FDXQQVBFP8NM7YF/Create-fr...

Nathan Cohen made this discovery after listening to a Mandelbrot talk on fractals: http://en.wikipedia.org/wiki/Fractal_antenna#Fractal_element...

"Nathan Cohen made this discovery..."

He's the reason you don't have a stubby antenna sticking out of your cell phone anymore. Really cool story.

"Nathan Cohen made this discovery..."

Surprisingly he does not have a wikipedia article. You'd think someone who made such an important discovery would have a rather long one.

I watched a Nova on fractals not too long ago, it covered this bit exactly. Definitely a cool story :) I don't 100% remember the title, but I think this was it: http://www.pbs.org/wgbh/nova/physics/hunting-hidden-dimensio...

I can't be the only person to notice that not every angle on the instructables example can be 60 degrees.

Thanks, I'm glad you took our comments to heart :)

Two questions:

1. What exactly is the purpose of the cardboard tube? I'm guessing the key point is that it's non-conductive, but would the same coil work without the cardboard? (not very knowledgable about antennae I admit)

2. How the hell does that connector even work? It looks so marvelously out of place ... does this mean the wire mesh around the normal coaxial cables is just shielding and doesn't actually do anything? If so, how come you don't need shielding?

Those were the two main questions that popped to mind, obviously I don't know anything about this stuff and I could probably look it up somewhere. But maybe someone here can provide a human-to-human good enough explanation.

Shielding is useful but not exactly required if the signal is strong enough and the cable is short enough. EX: You can use barbed wire to send 10 baseT. However, 1 gigabit has major issues without shielding.

PS: I once noticed my Sega genesis was producing a vary fuzzy picture, so I went to fiddle with the cable and noticed it was not even plugged in. At the time I really freaked out and to this day I still wish I had a picture.

I went to fiddle with the cable and noticed it was not even plugged in.

Back in college, we were watching a, umm, adult video on my roommate's VCR. The guy from the room next door walked past, and said "oh, you're watching the movie too?". It turns out that we'd mistakenly connected the VCR's RF output to the antenna, so the guy next door was watching our transmitted movie. (although his picture was poor)

The shell of coax (and what's in the space between it and the center conductor) also affects the impedance of the cable or antenna system. It's generally not that critical for a receiving antenna.

Sticking up almost any wire more than a few wavelengths long will collect a reasonable amount of a strong signal. A truly resonant antenna for the frequency you're interested is a lot better, but not that helpful for general HDTV viewing where the frequencies range all over VHF and UHF.

One of the amazing things I've learned from years of ham radio is how many unseen and unpredictable things affect radio signals. You can move your antenna twelve inches to the left and lose a signal completely, especially inside a structure. Or an airplane flying overhead can reflect enough "multipath" signal to wreck your TV viewing for 30 seconds. Of course your own body blocks a lot of signal and is capacitively coupled to the antenna system as you adjust it. So if you're playing with an HDTV antenna and are too young to remember the fun of constantly adjusting TV rabbit ears, just keep tweaking until you get a good signal.

"...too young to remember the fun of constantly adjusting TV rabbit ears..."

Too young, ha! I use rabbit ears on my HDTV (no cable, just netflix + locals is enough for me) and laugh when I go to Best Buy and see "state of the art high definition" antennas for anywhere from $20 to $100. The same laugh hits me when I go down the gold plated monster cable isle, but that's a different story.

I used to think Monster cables were a complete joke too until a musician friend pointed out that they have a lifetime warranty and very generous terms of exchange. One can essentially walk into any music store in the country and swap out the splinched cables for new ones, no questions asked.

It's an interesting pricing model, and the $20-$60 cables more than paid for themselves after a single tour. Probably not appropriate for casual use though.

Or you could go to Monoprice and order a baker's dozen for the same price or less.

You're not a big fan of packing light, are you?

This is like buying an expensive car for the lifetime warranty. I could buy a 300k supercar, or I could buy 20 economy cars and rent out all but 1.

Like with the cables, neither makes sense. I could just buy one cheap cable from a reputable brand and probably not need another for 30 years.

And if I do? I'll just buy another. Because they're cheap and work perfectly.

A place not to do this is with R/C helicopters. Best to buy them from Brookstone with the 1-year no-questions-asked warranty -- you WILL destroy them and you can go through your 3-6 choppers for the price of one.

Nice tip. I've always wanted to get one of the R/C helicopters and was always planning on getting it from one of the aisle mall shops - but this advice is helpful.

That's a case where there's real immediate risk of something breaking, so paying more for the warranty is justifiable.

And I know what I'm doing next time I'm at the mall.

What you said may be true, but their main justification for the cost is the supposed supreme quality over cheaper cables that has been disproven time and again, and some of their cables cost much much more than $60. That's not to mention their litigation practices. They are truly a horrible company.

I used to think Monster cables were a complete joke too until a musician friend pointed out that they have a lifetime warranty and very generous terms of exchange. One can essentially walk into any music store in the country and swap out the splinched cables for new ones, no questions asked.

Is he doing it right? Should the cables fail after every show? Shouldn't he just get better cables?

Chaotic environment; hookup and unhooking frequently stresses connectors; people trip over them.

1. Basically, I just wanted something I could wind a length of wire around and stick in my window. The tube did the trick. After the show, I tried a few other things, like wrapping the tube with tinfoil, but the basic wire around the tube design performed best.

2. The shielding is there to keep signal interference out, which is useful if you have a clean source to start with (ie: Cable TV or a properly designed antenna). In my case, I just wanted to pick up as much signal as possible, and this is what I had to work with.

very Interesting attempt. I would like to give a try. Btw, did u do some math in arriving at length of cable or the number of winds? Did u try increasing number of winds etc?

1. Structure. The wire he's using isn't strong enough to just stay up standing by itself. It would fold over on itself. Also, it probably does need to be non conductive or you need to use coated wire.

2. It's not shielded because the entire thing is the antenna. I guess he could shield it between the TV and the actual wrapped tube part but this is sow low-tech it wouldn't make a difference. Your standard roof mounted antenna is shielded between the antenna and the tv because you don't want interference between the two points.

>Your standard roof mounted antenna is shielded between the antenna and the tv because you don't want interference between the two points.

To clarify this, with a roof mounted antenna the wire needs shielding because it is typically running down the middle of the house and thus would be subject to interference from the many electronic devices therein.

With this guy's solution, the wire just runs out of his window, and therefore as long as he doesn't have any ageing analogue equipment (speakers, cordless phones etc) near his TV or his window the issue of interference is minimal.

My HDTV antenna is a paperclip stuck into the back of a TiVo. I get solid HD reception, no artifacts or other problems. It is all about how close you are to the broadcast towers. I have line of sight to towers that are about 12 miles away.

Which city are you in? I'm in downtown Ottawa and with a store-bought HDTV antenna I get only 2 stations. Maybe I'll have to go buy a spool of wire!

Go to tvfool.com and put in your addresses. From what I can find they have Canada data in their DB too. The first step to understand how to get good reception is to learn where all the towers are located and what band they broadcast on.

South end of Ottawa :)

Well that settles it. I'm buying a spool tonight. Thanks!

I had the same experience in Vanier (Ottawa East..). I actually brought back the antenna to the store because I thought it was broken.

You can use http://www.tvfool.com/ to chart the strength of nearby TV signals based on your location. It includes both US and Canadian broadcast towers.

I'd be interested to know the strength of the signals you're able to receive with your paper-towel-tube antenna design.

If you are smack in a city where the signals are literally washing over you I guess just a wire will work.

The coathanger antenna works best for me though, I'm too far away from most stations for just a wire.

Your design might work best for VHF stations while the coathanger method is best for UHF

Canada still has analog stations?

Just made one of these, really really half-assed.

I had to strip a coaxe cable with a pair of scissors and my hands. That took at least 20 mins.

But here we are


I have to remember to take that down before someone gets cut in half running down the stairs

If you're more lazy and don't mind watching someone watch the show, this worked at 7 PM Eastern yesterday: http://www.ustream.tv/channel/final-jeopardy-man-vs-machine

Ive been looking for an excuse to do this: http://www.re-nest.com/re-nest/how-to/how-to-make-a-string-t... Thanks!

Gray Hoverman antennae do a good job for longer distances: http://www.digitalhome.ca/ota/superantenna/

If you search a little more through the http://www.digitalhome.ca/ forums, you can find newer generations of the design. Various folks have been using genetic algorithms to find more efficient modifications to the original design. http://www.digitalhome.ca/forum/showthread.php?t=119489

My antenna is currently a coaxial cable screwed into the back of my TV and extended up to my curtain rod. It looks like I'm getting curtain-rod cable.

I have an antenna from RCA that is "enhanced". When I plug it in, it definitely helps in solidifying the picture.


Using your antenna, how could I go about amplifying the reach in an attempt to pick up more channels and/or increase the display quality of current channels?

Going through common antenna design compromises...

Depends on your location, of course, but the most effective thing I could do is get out of this valley. Next, I'd straighten the antenna wire and move the antenna outdoors (with a 75Ω coax line connecting it to the TV). You could also adjust the length so it's resonant at a particular frequency, but that will weaken the signal you receive on other channels. Alternatively, cutting it way longer than the minimum resonant length (like an order of magnitude or so) seems to make for a pretty forgiving frequency response. Then again, commercial broadcast transmitters are probably running enough output power that unobstructed line of sight makes more of a difference than anything else can.

I've gotten pretty good reception with a UHF loop antenna like catalog # 46-200 pictured here:


I use a matching-transformer to connect it to the coax plug.

Heres plans for an antenna I built. http://www.tvantennaplans.com/

I like the simplicity and potential of your design though. I want to try an array of tubes and wiring, and see how well that works.

I got the same plans via Make and have been using mine for 2+ years. It works awesome. Before dtv I could get 1-2 stations of mostly fuzz. Now I get 7 channels in full HD.


Tried some shielding on the back and it did not make any difference.

same here... I receive over 30+ channels now, most are HD (LA) area. With this and a computer hooked up to my TV would never consider going back to cable.

Note that 4-bay may be overkill depending on how far out you are.

I can get all the stations possible in my area with just 2-bay.

So build with 2-bay first and test maybe to save time/money.

I also did not need the reflector, in fact it made things worse.

I was looking at that design yesterday. I decided I didn't have the time to buy the materials and build it in the 30 minutes I had before the game started, so I ended up watching on Youtube. I plan on building this antenna in the future though.

Google Chrome is warning me that soccergoalplans.com is including content from an external website known for malware.

Does this work in the US? I've been under the assumption that with the recent switch from analog to digital signal (and the need for a digital converter box), connecting an antenna straight to a TV no longer works.


The frequencies are the same, and since they're not doing anything freaky with the signal (just broadcast) the same kind of antenna ought to work. In fact, you should get a better signal, because ATSC has much better multipath resistance than NTSC did.

Mine is just a copper wire, no fancy cardboard tubes or coils.

I'm in a place that's hilly and the towers are far away. Maybe I'd get something with a 75 foot tower, maybe.

For me it's ivi.tv

>Maybe I'd get something with a 75 foot tower

    1) Attach 75-foot wire to TV
    2) Attach other end to weather balloon
    3) Inflate balloon
    4) Watch Jeopardy
Maybe tie some brightly coloured threads onto the wire at intervals to stop birds flying into it.

Note: there are probably many other reasons why you shouldn't do this. Make sure to let us know when you find out what they are.

Enjoy the pyrotechnics during the next thunderstorm.

Also, static electricity will build up on a wire like that unless you bleed the charge off to ground with something like a nice high-ohm resistor.

This article is excellent! And thank you, chaosmachine, for providing instructions for replication.

It's my strong opinion that everything here is ethically sound. This sort of "hacker" culture is the meat and potatoes of what drives innovation in the United States today, and whether this specific incident results in a new product or simply higher security by cable providers, progress has been made.

What do cable providers have anything to do with this?

He built his own antenna to receive local channels that are broadcast over the air. These are broadcast specifically so that people with antennas can receive them.

Why doesn't the outside part of the coax port have to also touch the wire?

Because no signal is transmitted on the outside part, that is just used to secure the cable to the port. If you look at a coax cable, you will see it is essentially a copper wire wrapped in shielding wrapped in a vinyl(?) casing and the end is terminated with a connector that feeds the copper into the port and secures the connection.

I think that DirecTV setups transmit power and control signal through the shield. A given wavelength carries two polarized signals and the control signal tells the LNB which polarization to watch for. (or maybe I've got it all wrong, but this is what I've gathered from setting up and troubleshooting my own)

You are right, though satellite transponder frequencies with different polarizations do not typically share the same wavelength. With alternating polarization they are offset by (presumably) half the frequency separation needed for identically polarized signals.

I don't think coaxs have a 'return' on the actual cable. The outside part of a coax is just a screw for holding the cable in place. It could be made with plastic for all it matters.

Nah, it's to ground the shield. Shields work marginally better when grounded, but the difference is minor.

dont you need the outside to ground two devices together?

Private Justin.tv broadcast anyone?

What size is the cardboard tube?

whoa; that's too kool; congratulations!!!

can we see how it was put in the window?

lol whut. THATS TOO EASY!

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