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Good afternoon.

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I'm Matthew Shuckman.

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I'm the founder of WarDrivingWorld.com and I'm here to talk to you about WarDriving hardware and how to build some if you want to WarDrive.

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Firstly, can I ask a question?

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How many of you have ever gone WarDriving?

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Can you raise your hands?

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Okay, so the rest of you are interested in WarDriving and the ones who have already gone WarDriving want to do some new things, so great.

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What?

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Mike?

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Better?

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Okay, that's better?

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Okay, sorry.

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Yeah, well, I'll be alright.

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Okay.

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What is WarDriving?

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To start off, for those of you who haven't done it, WarDriving is the sport, the name was coined by Peter Shipley, the act of driving around and looking with a laptop computer and locating access points for Wi-Fi networks.

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You don't necessarily need an antenna, you can use an internal Wi-Fi card on a laptop, but you can only go so far with that.

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There are a variety of pieces of software that have been shared by their authors or in the public domain, including packages like Morris Miller's NetStumbler, which allow you to record the access points that you find and record some information about them.

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And there are also packages like Kismet and that variety, which are crap Wi-Fi packets, and then to dissect them a bit and do little bits of surgery on them.

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First question, is it legal to WarDrive?

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Okay.

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Is it legal to WarDrive?

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It's a good question and it's one that I'm going to be covering more in tomorrow afternoon.

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There will be a session on the legal and ethical aspects of WarDriving.

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I'm the chair on that, and Frank Thornton will be there, Robert Hale and RenderMan, and the four of us will be having a panel discussion on some of the current legal issues and some of the ethical issues in terms of WarDriving.

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So I hope you can join us there.

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Yes.

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They've moved the time a few times, but I think it's at 1 p.m.

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tomorrow.

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I guess they'll let me know tomorrow.

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But look forward to seeing you there.

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Okay.

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Simply put, the construction of WarDriving tools is legal.

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And WarDriving is legal as long as you don't try to access a Wi-Fi signal that you don't have permission to access.

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Simply detecting the signal, so far, all the cases that have come forward have shown that at least accessing the signal is a problem, potentially.

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But simply detecting the signal is not.

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The problem comes in when you have a typical case of, let's say at home, I have a link-sys router.

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I pull the link-sys router out of the box, I configure some security there, and what do I use for an SSID that is the name on the router?

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Default.

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Okay?

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It seems unique.

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I now have my Windows XP laptop configured that when it sees default, it knows it's my home network and it links to it.

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While I drive around town, you're going to find a lot of link-sys routers configured with the name of default.

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And what does Windows do?

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And when linked up with link-sys, it simply goes and connects to the network, and it thinks it's yours.

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So, actively you haven't done anything.

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But the software and the hardware have combined, the software and the firmware have combined basically to allow you to have access to that network.

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So that's when the question becomes a little tricky.

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So we'll be discussing that more tomorrow.

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The original wardrivers were those IT folks who were asked to perform site surveys for the design of Wi-Fi systems.

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Their purpose was to see where the signal was emanating from, where it was strong, where it was weak, and where it needed to be changed.

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This is certainly a legal form of wardriving, because they're working with signals that they've been contracted to work with, or they're working with signals in their own company.

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Yes, there have been a few arrests of people for wardriving.

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Don't be scared.

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So far, there have been no cases of anyone arrested for wardriving that wasn't associated with some other nefarious activity.

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That is, they committed some other crime.

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Most of us, I think, would agree if you're using... I'll take questions later, thank you.

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Most of us would agree that if you're dropping in on somebody else's Wi-Fi signal and sending out child pornography as spam, that that's a crime, and that has nothing to do with the fact that they happen to be wardriving while doing it, or going up online on Wi-Fi and stealing people's credit card numbers that are coming across from a retail store.

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The crime really is not the wardriving, the crime was stealing the credit card numbers.

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So, so far, there have really been no yet recorded arrests for wardriving.

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So, to start doing wardriving and performing Wi-Fi site surveys, what do you need?

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As I said, if you already have a laptop with built-in Wi-Fi, that's all you need.

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You can drive around with that, and a piece of software like NetStumbler, and you can detect networks.

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The first time I went wardriving, I lived in South Florida.

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I drove in a four-mile square, four miles on each side around my house, on major roads.

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I detected 83 access points.

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Approximately 15% had some form of protection.

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All of the others were naked.

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The SSIDs, that is the name given to the networks that were naked, included a local hospital, two law firms, one of which was named Law Firm, and the other one which was named by the name of the law firm, so certainly they weren't trying to hide, and one bank and one local city agency.

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Obviously there's a lot of people that are unprotected out there, but enough said about the vulnerability of Wi-Fi.

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One of the reasons, in a sense, that we all appreciate wardriving is that we are trying to improve the security that exists within Wi-Fi.

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But again, I don't like to place the blame on the consumers who purchase the equipment which accesses it, or the consumers who have the equipment in their offices.

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I think that something is up to the, responsibility should be in part with those who design the operating systems and those who design the hardware.

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They want to make it so easy to use, they make the lack of security a default, rather than security a default.

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There are different cards to use for Wi-Fi for different purposes.

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Internal Wi-Fi cards.

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People come up to me, one of the most common emails we get is, I bought a new Dell 8600, it has great internal Wi-Fi, what do I need to hook up your antenna to it?

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And I say, it's not going to help you at all.

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These type of laptops, their Wi-Fi is not upgradable unless you want to open up the screen, solder in a connector, that's going to void your warranty, and I don't want to sell the parts for it because I don't want to get involved in the problems.

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So, I suggest to them, what you need, generally, is an external Wi-Fi card that you plug in, which has an external connector, which allows you to hook up a variety of antennas.

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They're more power hungry than the internal card, they are going to draw power, but most people's batteries are in pretty good shape these days.

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Not all Wi-Fi, external Wi-Fi cards, PCMCIA or Cardbus, that have external antenna connectors are created equal.

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They run the full gamut.

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But there is no one Wi-Fi card which is the best.

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Some people prefer, the two chipsets that are most commonly used are the ones based on the Hermes or the Orinoco Classic Gold, and the other one is the ones based on the Prism chipset.

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Again, they are both different cards.

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The Orinoco Gold Classic was manufactured by Orinoco.

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It was related to when it was part of Lucent.

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And when it was made, it was not only manufactured for Lucent as an Orinoco card, it was manufactured under private label for Anterasys, 2Wire, Deltru Mobile, Compaq, Toshiba.

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At one point, just about every Wi-Fi card you picked up was really an Orinoco.

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And it was a very nice design.

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Proxim bought the hardware licenses from Orinoco, and a company called Ageri bought the software licenses.

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So when you use a Gold Classic card these days, most of the time you are ending up putting a card in, if it is a new one, it is manufactured by Proxim, and the software still comes from Ageri.

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So people often ask me, when they get a card, here is a real Orinoco.

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Is there any difference between this and the Compaq?

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There are about 2 bytes of difference.

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But on a performance basis, there is no difference.

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And they will both run the same drivers.

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The Proxim 2 based cards come in a variety of packages.

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Many Linux users prefer it.

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In particular, there is a Cisco version, which is a 100 mW card.

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The Orinoco cards are only running at about 35 mW.

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There is also an SMC version, which is at 200 mW, and I think they have now come out with a 300 mW version.

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So if you want power, the Proxim is a good card to go to.

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But if you try pumping out 200 mW on a continuous basis, you will certainly drain your batteries quite quickly.

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One of the important issues when working with a card, and you want to do serious war driving, and serious war driving would involve accepting some packets and examining their contents.

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This is what we would call promiscuous mode.

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Promiscuous mode is not as naughty as it sounds.

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It relates to networking, where you have a Wi -Fi card, which is able to recognize and accept all the network traffic which comes along, passively.

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So it's basically somewhat stealthy, and it's just sitting there and listening.

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And generally you not only need a promiscuous mode card that will do it, you also need a driver that will allow you to do it.

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I put it this way, if you want to listen to the music of Wi-Fi, and you want to look at the notes that are being played, you need to become promiscuous.

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One of the important factors in terms of choosing a card is receive sensitivity.

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Receive sensitivity indicates how faint an RF signal is that can be successfully be received by your card.

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The lower power level that a card can receive, the better the receive sensitivity.

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In Wi-Fi equipment, receive sensitivity is generally stated as a function of network speed.

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It will generally tell you at what speed your sensitivity is.

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For any given receiver, the higher the data rate, the less sensitive will be the receiver, because the more power that is required to support that higher data rate.

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So people often ask me, I'm at a distance, it's dropping down to two megabits.

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Yes, that's what's going to happen.

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That's why you put an antenna in, to increase the amount of signal that you're getting, even though you're not increasing the amount of receive sensitivity, so then you can boost up your speed again.

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I'm not going to do too much math here, just briefly.

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Receive sensitivity is frequently a confusing issue for people.

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That is because it's expressed in decibels.

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It's not generally a unit that most of you are familiar with if you're not working in RF or you're not working in acoustics.

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A decibel is a ratio expressed on a logarithmic exponential scale.

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So a 10 to 1 ratio is 10 dB, a 2 to 1 ratio is 3, and a 1 to 1 ratio is 0 dB.

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While ratios of less than 1 to 1 are expressed as negative numbers, for example a 1 to 2 ratio equals minus 3 dB.

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Receive sensitivity, when you look at a card and the specifications, is expressed using a version of decibel employed in measurements of radio power, the dBm scale.

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0 dBm equals 1 milliwatt.

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That's what I have on the scale.

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A power of 100 milliwatts equals 20 dBm.

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And 1000 milliwatts equals 30 dBm.

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Power levels below 1 milliwatt are expressed as a negative number.

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That's just what happens when you're looking at something logarithmically.

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But when you need to compare the receive sensitivity, for example, 0.01 milliwatts would be minus 20 dBm.

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And so when taking a look at it, what you really have to look at is the absolute value.

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What I mean by that is a signal of minus 98 dBm.

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Sensitivity is much better than sensitivity at minus 95 dBm.

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Let's take a look at antennas for a moment.

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The simplest antenna, and what I'm going to tell you, if any of you came to the booth in the vendor area this week, everybody wants the biggest antenna.

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It's an American tradition.

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Bigger is always better.

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In war driving, bigger is not always better.

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And many of you I encourage to buy a lower gain antenna.

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Why?

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The radiation pattern of a theoretically perfect omnidirectional antenna is a sphere.

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That's called an isotropic antenna.

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However, that only exists in theory.

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A real antenna cannot have an isotropic, a perfect radiation pattern.

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The field propagates in a direction perpendicular to the radiating wire.

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So for a vertical antenna, the field isn't going to propagate up and down as much as it is sideways.

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That means that a 5 dB antenna is going to go to a certain range, but it will also go up, let's say, to the 15th or the 20th floor if you're in an urban area.

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If you suddenly go up to a 7 dB or an 8 dB gain antenna, you will get the additional range this way, but you will suddenly maybe not be able to retrieve a signal above the 10th floor or the 8th floor.

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So, that's why if you're in an urban area, bigger is not always better.

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Directional antennas.

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The two I'm going to talk about are the Cantena and the Yagi.

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The antenna we're looking at here on the top is a Yagi.

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Using a variety of elements that collect, reflect, or radiate the signal, antennas can be constructed so the transmission and reception isn't always equal in all directions.

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The definition of what a directional antenna is.

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The first antenna we're going to consider here is the top one.

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It's called a Yagi-Uda antenna.

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It's an antenna in which the gain of a single dipole element is enhanced by putting a reflector behind it,

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a reflector behind it, and then directional elements in front of it, so that you can take a signal and push it forward, have a gain from all the reflected power, and keep it directed on a narrow path.

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This antenna was invented in 1926 by H.

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Yagi and S.

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Uda.

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Uda's name dropped out along the way, but from what I heard from someone, he's the one who got the original patents.

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But a Yagi-Uda antenna is a long-time favorite.

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Any of you who are ham radio enthusiasts, any of you who remember what an old TV antenna looks like?

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Anybody ever see a TV antenna the days before cable?

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Right.

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Those were Yagis, okay?

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And they were very directional, and that's why you frequently put a rotator on them to rotate it in the direction of the signal.

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The next antenna we're going to show you is a Cantena.

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This is the original Heathkit Cantena.

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This is not an antenna.

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I only show this to you because some people ask me, how did it get the name Cantena?

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In the 70s and 80s, this is a product, which is basically a one-gallon paint can that was filled with oil that was used to test radio transmitters.

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It would dissipate the power up to 1,000 watts.

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So you put a transmitter on it, and you dissipated the power so that you wouldn't blow out a transmitter if you didn't have an antenna on it.

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That name came along, and what happened was in about 2001, Andy Clapp presented a novel design for a very simple antenna based on a Pringles can.

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Many of you have heard of it.

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The Pringles antenna showed a great potential for a simple, low-cost, less than $10, high-gain directional Wi-Fi antenna.

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At this point, the other high-gain Wi-Fi antennas that were anywhere near it were several hundred dollars apiece.

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I don't exactly know who to credit, but along the way, someone simplified the design and came up with what we have for a current tin can waveguide antenna, or cantena.

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Since it was much easier to build, the cantena became very popular.

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This is an example of a commercial cantena.

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Here's what a cantena looks like inside.

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Essentially, a cantena is constructed out of a can that can range from about 3 to 5 inches.

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You can go lower, you can go higher, but if you want reasonable gain, stay within that range in diameter.

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The most popular one uses a total can length of approximately 12 inches, which on a 3, 3.5 inch cantena results in a gain of about 12 dB, and a beam width of roughly 30 degrees.

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You can build a cantena yourself, and that's the whole basis for this talk.

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There are professionally manufactured cantenas, we sell them, there are plenty of them available on eBay and online.

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But you can very simply build your own cantena, and that's how I started off in this sport, so I want to share that information with you.

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The tin can waveguide antenna basically acts as a collector, and the closed end on the back here acts as a reflector.

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What happens is that the 2400 MHz signal that's coming in is reflected off the back, and it intersects with the waveforms that are coming in.

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As these incoming signals and these reflecting signals meet, there are certain points where there are troughs, and there are certain points where you have a maximum signal.

199
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The trick is that if you place the collector at about a 1 quarter wavelength position from the rear of the can, you're on one of the tops.

200
00:22:06,760 --> 00:22:09,220
You get the maximum signal collection.

201
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At the very closed end of it, you get a zero signal.

202
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Anywhere along in the middle, you're going to get a different signal.

203
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The optimal position is about 1 quarter wavelength along the way.

204
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I'm going to diverge momentarily off the cantenna, because you can't really use a cantenna very well without a pigtail, and I want to explain a little bit about pigtails briefly.

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Firstly, you don't need a pigtail to use a cantenna.

206
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Simply by having a cantenna in proximity to a Wi-Fi card, since it's tuned at the same frequency, there's a certain amount of signal strength that will radiate over, and you will get an increase.

207
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But it's minimal, and going through the air, you lose a lot of that signal.

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So although you don't need a cable to connect the two, I strongly recommend it.

209
00:23:06,000 --> 00:23:07,060
What's a pigtail?

210
00:23:07,060 --> 00:23:08,080
What's a cable?

211
00:23:08,140 --> 00:23:12,720
An extension cable is simply a cable which has two of the same connectors, one at each end.

212
00:23:13,040 --> 00:23:15,920
A pigtail is one which has two different connectors.

213
00:23:16,160 --> 00:23:17,700
That's the only distinction.

214
00:23:17,960 --> 00:23:21,720
The nomenclature isn't that firm, but that's at least how most of us use it.

215
00:23:22,360 --> 00:23:24,740
Why are there so many varieties of connectors?

216
00:23:24,740 --> 00:23:26,260
We've shown three up here.

217
00:23:26,340 --> 00:23:32,440
One, not all connectors are designed to operate efficiently at microwave frequencies.

218
00:23:32,440 --> 00:23:35,760
2.4 gigahertz, which is Wi-Fi, is microwave.

219
00:23:35,920 --> 00:23:44,800
It's the same frequency approximately that your microwave oven operates on, except that's running at 4, 5, 800 watts, and we're talking here about milliwatts.

220
00:23:47,380 --> 00:23:58,620
One, manufacturers want you to purchase their accessories for their product, so they use a custom connector, and you're forced to use their antennas with their Wi-Fi devices.

221
00:23:59,000 --> 00:24:01,800
But it also originated with the FCC.

222
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Part 15 of the FCC code says that the frequency we're working in at around 2,400 megahertz is in public domain.

223
00:24:11,200 --> 00:24:16,140
However, you're limited to an effective radiated power of about 4 watts.

224
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The way the FCC managed to limit manufacturers was to say that if you had a D-Link antenna and you had a D-Link router, D-Link had to go and submit approval for the antenna and the router in combination together.

225
00:24:33,560 --> 00:24:43,120
And until last year, 2004, the FCC came out with a new ruling which said you could mix and match.

226
00:24:43,220 --> 00:24:56,420
Technically, before that summer ruling, if you took an antenna and put it on a Linksys router, you were doing something not permitted by FCC Rule 15, because you might have increased the power above the limit that they wanted to.

227
00:24:59,540 --> 00:25:06,500
To comply with the FCC, each manufacturer came up with somewhat of a custom connector and got it approved by the FCC.

228
00:25:07,260 --> 00:25:18,100
Some took the popular SMA connector and they reversed the ground and the signal, and you came up with an RP, which is a reverse polarity SMA cable.

229
00:25:18,480 --> 00:25:25,320
Others came up with a custom connector called the MC, which is what Orinoco uses.

230
00:25:25,440 --> 00:25:28,760
It's somewhat of a fragile connector, but again, we didn't design it.

231
00:25:28,760 --> 00:25:31,500
They came up with it, so it was customized for them.

232
00:25:32,440 --> 00:25:39,760
Samsung took the SMA connector and reversed the threads on the connector, and you have something called an RT-SMA.

233
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So, one thing is, when you get to the point at which you're looking for pigtails, be very careful which pigtail you're looking for.

234
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An SMA is not an RP-SMA, it's not an RT-SMA.

235
00:25:51,100 --> 00:26:00,200
Look carefully, talk to people you know, go up online, there are some tables for each one of the types of equipment, so that you can find out which type of cable you're going to use.

236
00:26:01,720 --> 00:26:10,060
The other important thing to keep in mind with connectors is, people say to me, I'm a CB enthusiast, I have a PL259 connector.

237
00:26:10,080 --> 00:26:12,020
It looks about like an N connector.

238
00:26:12,020 --> 00:26:13,040
It does.

239
00:26:13,260 --> 00:26:19,240
It, however, was never made to operate at microwave frequencies, so you're going to see a lot of loss.

240
00:26:19,400 --> 00:26:25,540
Choose a connector, preferably an N, that is efficient at microwave frequencies.

241
00:26:27,000 --> 00:26:27,960
Cables.

242
00:26:28,920 --> 00:26:30,720
What makes a good cable?

243
00:26:30,780 --> 00:26:34,600
People are always calling me up and saying, I want a really, really low loss cable.

244
00:26:34,920 --> 00:26:39,040
A really, really low loss cable is about three quarters of an inch in diameter.

245
00:26:39,500 --> 00:26:42,920
It takes two people to carry it down the street, okay?

246
00:26:42,920 --> 00:26:44,560
But yes, it works.

247
00:26:45,520 --> 00:26:56,740
The thicker the central conductor on a coax cable, the stronger the shield, there's almost this direct correlation, the lower the loss of the signal along the cable.

248
00:26:57,140 --> 00:27:00,620
However, the thicker the cable, the less flexible.

249
00:27:00,920 --> 00:27:09,440
The cables you're generally going to run into are an LMR400, and that's about three quarters of an inch, sometimes almost an inch thick.

250
00:27:09,540 --> 00:27:24,960
It's very heavy, it's very bulky, but if I'm running a 50 foot span up to the roof, and I know I'm only going to lose 6cb over 100 feet, here's a piece of LMR400, okay?

251
00:27:25,180 --> 00:27:30,580
This is not the type of thing you want to plug into your little laptop, okay?

252
00:27:32,100 --> 00:27:37,880
This is what we call equivalent to about an LMR200 cable.

253
00:27:37,900 --> 00:27:40,740
It's a lot lighter weight, it's a lot more flexible.

254
00:27:41,100 --> 00:27:45,380
If you're going to do a run of 20 feet or less, this is a great cable to use.

255
00:27:45,660 --> 00:27:52,280
They call it LMR240, they call it LMR200, they call it low loss 200, it's a great cable to work with.

256
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This is an LMR100 cable.

257
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Very thin.

258
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On the other hand, if I'm trying to connect this into a card that I plugged into my laptop, I certainly couldn't plug in that LMR400 into it.

259
00:28:10,300 --> 00:28:12,140
One, there's no place to put the connector.

260
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Two, the weight of it would break the connector.

261
00:28:14,920 --> 00:28:24,280
So we use pigtails to connect from one size of a connector up to another.

262
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Just be careful in a sense, when you're looking for a cable, you have to decide how long it's going to be.

263
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Now that you know a little bit about cables, and you know a little bit about connectors, the next step is, you want to build a tin can waveguide antenna.

264
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That's what you all came to hear.

265
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What are the parts and tools you're going to need?

266
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You're going to need a tin can, you're going to need an end connector, you could use another microwave connector, I'm going to use my example using an end connector, the example stays the same.

267
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You're going to need a drill or a device to make a hole in the can, you're going to need a short piece of wire, you only need about one and a quarter inches, but I would say start off with about six inches so you can make a few mistakes.

268
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You're going to need a soldering iron and solder, a little flux doesn't hurt.

269
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My partner here, King Tuna Makes, and he says if you've soldered, put a little flux on it, it's going to make life a lot easier.

270
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And most importantly, you're going to need a ruler.

271
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Don't do it by line of sight.

272
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I'm sorry, by sight.

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Choosing a can.

274
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You can choose many different types of cans.

275
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Yes.

276
00:29:50,760 --> 00:29:52,600
Um, yes.

277
00:29:52,980 --> 00:30:08,400
King Tuna says I build better canned tuna's when I've had a shot of Jack, but we, uh, we've used coffee cans work, um, you can eat beans, baked beans cans work great, particularly anybody, anybody here from England?

278
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The baked bean cans are a lot wider there and they're much better for a cantenna.

279
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Or you can use or drink scotch at holiday time and it comes in a nice little metal commemorative can, which happens to be almost perfect for a great cantenna.

280
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Stoli also provides them.

281
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You can download plans for many of the cantennas.

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We're going to distribute one plan here off of the internet.

283
00:30:36,670 --> 00:30:41,130
Some of them will have very exact measurements of how to build it.

284
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Relax, you don't have to be that exact.

285
00:30:44,190 --> 00:30:48,750
You can be within 10% and still make a good cantenna.

286
00:30:51,410 --> 00:30:54,130
There are some dimensions which are important.

287
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You start off by having an end connector.

288
00:30:57,650 --> 00:30:59,150
This is an end connector.

289
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You're going to take this end connector, it has a female end on one end, and it'll have a little stub on the other side.

290
00:31:06,330 --> 00:31:09,750
You're going to be soldering a piece of copper wire to that.

291
00:31:09,990 --> 00:31:14,870
We have, in my business, we happen to use a little brass tube that we have pre-soldered.

292
00:31:14,870 --> 00:31:18,930
You can use a brass tube, you can use copper, you can use a copper piece of wire.

293
00:31:18,930 --> 00:31:20,590
They'll all work about the same.

294
00:31:23,110 --> 00:31:28,390
You need 1.21 inches for a radiator to be effective.

295
00:31:29,150 --> 00:31:29,810
Why?

296
00:31:30,590 --> 00:31:32,030
Let's go to the next slide, please.

297
00:31:32,570 --> 00:31:33,210
Okay.

298
00:31:33,230 --> 00:31:39,290
Now, they've just told me I only have 10 minutes because we started a little late, so I'm going to try to go briefly.

299
00:31:40,510 --> 00:31:50,710
The first thing to determine is based on the width of the can, the diameter of the can that you have, will determine what the length is for a wavelength.

300
00:31:50,750 --> 00:31:55,570
You need to position the collector one quarter wavelength from the end.

301
00:31:55,870 --> 00:31:57,770
That's the optimal point.

302
00:31:58,110 --> 00:32:00,990
That is the distance that you have to be careful on.

303
00:32:00,990 --> 00:32:06,730
Anywhere a little further, a little less, the antenna will still work, but you'll get lower gain.

304
00:32:07,290 --> 00:32:16,830
The other important measurement is what we call L over 4 here, which is the length of the radiator which is going to collect the signal.

305
00:32:16,830 --> 00:32:20,670
That should be as close to 1.21 inches as you can.

306
00:32:21,670 --> 00:32:29,250
Using a ruler to make an antenna, here's an example of one that my partner King Tuna made.

307
00:32:29,250 --> 00:32:31,770
It took him about 15 minutes this afternoon.

308
00:32:32,630 --> 00:32:37,430
This is made from a 13 inch coffee can, 13 ounce coffee can.

309
00:32:38,090 --> 00:32:42,430
It's not the optimal can to do it, but it shows you can do it with any can.

310
00:32:43,450 --> 00:32:44,850
At CVS we bought it.

311
00:32:45,530 --> 00:32:59,450
You take this can, we've got some plans, you can go up and there's some calculators that we'll give you that are on the internet, which based on the diameter of the can, will tell you the distance out from here that is one quarter wavelength.

312
00:33:00,590 --> 00:33:07,850
Cut a hole, in this case we just used a screwdriver and a mallet to cut a hole that's about 5 1⁄8 inches around.

313
00:33:08,570 --> 00:33:21,610
You take the radiator that you've constructed, which looks like an end connector, with a 1.21 inch piece of copper wire or brass rod, insert it, screw it down.

314
00:33:21,790 --> 00:33:24,370
You don't need for it to be a round connector.

315
00:33:24,370 --> 00:33:29,070
If you've got a square connector you can use that, you can screw it in place, you can glue it in place.

316
00:33:29,710 --> 00:33:32,710
The other dimensions are not going to be that important.

317
00:33:32,930 --> 00:33:41,070
For an optimal cantenna, you want this length to be approximately at least three quarters of a wavelength.

318
00:33:41,270 --> 00:33:49,630
For this particular can, which is four inches across, three quarters of a wavelength works out to be 5.15 inches.

319
00:33:49,830 --> 00:33:52,270
This happens to be 5.25 inches.

320
00:33:52,270 --> 00:33:55,350
With a 13 ounce coffee can it just happens to work well.

321
00:33:55,890 --> 00:34:01,390
Put it in, screw it down, that's all there is to building a cantenna.

322
00:34:01,790 --> 00:34:06,610
Essentially the only part that you're gonna have a problem finding is the end connector.

323
00:34:06,690 --> 00:34:13,230
You can get it from radio supply houses, we may even have a few left at our booth, there are plenty of places to buy them on the internet.

324
00:34:13,370 --> 00:34:20,490
That, a 1.21 inch radiator, and a good tin can.

325
00:34:22,630 --> 00:34:27,710
Take that, this particular one is four inches, 100 millimeters.

326
00:34:28,270 --> 00:34:28,470
I

327
00:34:33,580 --> 00:34:42,160
could go over the math but basically the distance that you're going to measure from here to there is going to change based on the diameter of the can.

328
00:34:45,570 --> 00:34:54,010
If you want, you put a pigtail on, you can then connect it up to your card.

329
00:34:54,570 --> 00:35:01,910
A simple cantenna like this, which took about 20 minutes to build, will give you about somewhere between 8 to 10 dB gain.

330
00:35:01,910 --> 00:35:03,690
We haven't fully measured this.

331
00:35:03,790 --> 00:35:12,250
If you're a lot more careful about the calculations, if you're a lot more careful about the length of the can, you can probably get 12 to 14 dB gain.

332
00:35:12,530 --> 00:35:20,790
If we make this shorter, we will get less gain, but then again we'll get a wider signal coming out of it.

333
00:35:21,290 --> 00:35:26,810
Some people have made them about four inches or so, and they get about a 50 degree signal breadth.

334
00:35:27,030 --> 00:35:32,910
If you make it about 12 inches long, you're going to drop down to about a 25 or a 30 degree signal breadth.

335
00:35:33,170 --> 00:35:59,610
We find it very useful to go to Home Depot, pick up a little tripod, threads a 1.25 by 20 inch, 1.25 by 20 threaded bolt, put it on there, screw it in, and now you don't have to take your coffee cup and try to measure it to get it off and left to focus it.

336
00:35:59,610 --> 00:36:01,550
You can put it on any camera tripod.

337
00:36:02,370 --> 00:36:04,950
It's really very simple to build a cantenna.

338
00:36:04,950 --> 00:36:07,490
Again, two calculations necessary.

339
00:36:07,770 --> 00:36:16,570
The length of this is 1.21, and go and find, either use the plans that we've got for working with a simple coffee can or go on the web.

340
00:36:16,570 --> 00:36:22,450
We've got a website where you can go to a calculator and measure this out to this 1.25 wavelength.

341
00:36:23,590 --> 00:36:25,050
Any questions?

342
00:36:33,950 --> 00:36:45,110
The optimal radiator is a trapezoid, actually a cone, but it's pretty hard to make a cone like that.

343
00:36:45,250 --> 00:36:49,750
So by making a rod, we end up trying to get in the middle channel.

344
00:36:54,640 --> 00:36:56,260
See me afterwards.

345
00:36:56,260 --> 00:37:04,700
What you want is a trapezoid, I think it's six millimeters at the bottom and one millimeter at the top.

346
00:37:04,700 --> 00:37:07,020
Again, 1.21 across.

347
00:37:07,020 --> 00:37:08,000
That's optimal.

348
00:37:08,000 --> 00:37:08,700
Yes?

349
00:37:12,460 --> 00:37:13,420
No.

350
00:37:14,480 --> 00:37:19,260
We tried it with copper, we tried it with bronze, we even tried it with aluminum.

351
00:37:19,260 --> 00:37:20,680
They all work well.

352
00:37:20,980 --> 00:37:23,180
We didn't see a significant difference.

353
00:37:24,120 --> 00:37:24,860
Yes.

354
00:37:41,450 --> 00:37:42,930
Thank you very much.