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64900	75180	Good afternoon. I'm Matthew Shuckman. I'm the founder of WarDrivingWorld.com and I'm
75180	81880	here to talk to you about WarDriving hardware and how to build some if you want to WarDrive.
82180	86740	Firstly, can I ask a question? How many of you have ever gone WarDriving? Can you raise
86740	95900	your hands? Okay, so the rest of you are interested in WarDriving and the ones who have already
95900	110980	gone WarDriving want to do some new things, so great. What? Mike? Better? Okay, that's
110980	122440	better? Okay, sorry. Yeah, well, I'll be alright. Okay. What is WarDriving? To start off, for
122440	126900	those of you who haven't done it, WarDriving is the sport, the name was coined by Peter
126900	134920	Shipley, the act of driving around and looking with a laptop computer and locating access
134920	142080	points for Wi-Fi networks. You don't necessarily need an antenna, you can use an internal Wi-Fi
142080	149340	card on a laptop, but you can only go so far with that. There are a variety of pieces of
149340	155420	software that have been shared by their authors or in the public domain, including packages
155420	162740	like Morris Miller's NetStumbler, which allow you to record the access points that you find
163420	168600	and record some information about them. And there are also packages like Kismet and that
168600	176860	variety, which are crap Wi-Fi packets, and then to dissect them a bit and do little bits
176860	193380	of surgery on them. First question, is it legal to WarDrive? Okay. Is it legal to WarDrive?
193820	200800	It's a good question and it's one that I'm going to be covering more in tomorrow afternoon.
200800	208500	There will be a session on the legal and ethical aspects of WarDriving. I'm the chair on that,
209020	216360	and Frank Thornton will be there, Robert Hale and RenderMan, and the four of us will be
216360	221360	having a panel discussion on some of the current legal issues and some of the ethical issues
221360	230300	in terms of WarDriving. So I hope you can join us there. Yes. They've moved the time
230420	234440	a few times, but I think it's at 1 p.m. tomorrow. I guess they'll let me know tomorrow. But
235420	241600	look forward to seeing you there. Okay. Simply put, the construction of WarDriving tools
242640	248720	is legal. And WarDriving is legal as long as you don't try to access a Wi-Fi signal
248720	254840	that you don't have permission to access. Simply detecting the signal, so far, all the
254840	260920	cases that have come forward have shown that at least accessing the signal is a problem,
260920	267320	potentially. But simply detecting the signal is not. The problem comes in when you have
267460	273300	a typical case of, let's say at home, I have a link-sys router. I pull the link-sys router
273300	279420	out of the box, I configure some security there, and what do I use for an SSID that
279420	287480	is the name on the router? Default. Okay? It seems unique. I now have my Windows XP
287480	291840	laptop configured that when it sees default, it knows it's my home network and it links
291840	296580	to it. While I drive around town, you're going to find a lot of link-sys routers configured
296580	303580	with the name of default. And what does Windows do? And when linked up with link-sys, it simply
303580	310200	goes and connects to the network, and it thinks it's yours. So, actively you haven't
310200	317320	done anything. But the software and the hardware have combined, the software and the firmware
317320	322460	have combined basically to allow you to have access to that network. So that's when the
322460	326820	question becomes a little tricky. So we'll be discussing that more tomorrow.
334100	340640	The original wardrivers were those IT folks who were asked to perform site surveys for
340640	346960	the design of Wi-Fi systems. Their purpose was to see where the signal was emanating
346960	353100	from, where it was strong, where it was weak, and where it needed to be changed. This is
353100	357480	certainly a legal form of wardriving, because they're working with signals that they've
357480	363560	been contracted to work with, or they're working with signals in their own company. Yes, there
363560	371180	have been a few arrests of people for wardriving. Don't be scared. So far, there have been no
371180	377040	cases of anyone arrested for wardriving that wasn't associated with some other nefarious
377040	382880	activity. That is, they committed some other crime. Most of us, I think, would agree if
382880	387800	you're using... I'll take questions later, thank you. Most of us would agree that if
387800	393200	you're dropping in on somebody else's Wi-Fi signal and sending out child pornography as
393200	397520	spam, that that's a crime, and that has nothing to do with the fact that they happen to be
397520	403160	wardriving while doing it, or going up online on Wi-Fi and stealing people's credit card
403160	407660	numbers that are coming across from a retail store. The crime really is not the wardriving,
407660	412320	the crime was stealing the credit card numbers. So, so far, there have really been no yet
412320	420660	recorded arrests for wardriving. So, to start doing wardriving and performing Wi-Fi site
420660	426340	surveys, what do you need? As I said, if you already have a laptop with built-in Wi-Fi,
426340	431980	that's all you need. You can drive around with that, and a piece of software like NetStumbler,
431980	437000	and you can detect networks. The first time I went wardriving, I lived in South Florida.
437420	445220	I drove in a four-mile square, four miles on each side around my house, on major roads.
445220	454600	I detected 83 access points. Approximately 15% had some form of protection. All of the
454600	461040	others were naked. The SSIDs, that is the name given to the networks that were naked,
461040	467440	included a local hospital, two law firms, one of which was named Law Firm, and the other
467440	472020	one which was named by the name of the law firm, so certainly they weren't trying to
472020	480720	hide, and one bank and one local city agency. Obviously there's a lot of people that are
480720	486780	unprotected out there, but enough said about the vulnerability of Wi-Fi. One of the reasons,
486780	491320	in a sense, that we all appreciate wardriving is that we are trying to improve the security
491320	497720	that exists within Wi-Fi. But again, I don't like to place the blame on the consumers who
497720	502580	purchase the equipment which accesses it, or the consumers who have the equipment in
502580	507440	their offices. I think that something is up to the, responsibility should be in part with
507440	511260	those who design the operating systems and those who design the hardware. They want to
511260	516980	make it so easy to use, they make the lack of security a default, rather than security
519320	525020	a default. There are different cards to use for Wi-Fi for different purposes. Internal
525020	530520	Wi-Fi cards. People come up to me, one of the most common emails we get is, I bought
530680	536380	a new Dell 8600, it has great internal Wi-Fi, what do I need to hook up your antenna to
536380	542780	it? And I say, it's not going to help you at all. These type of laptops, their Wi-Fi
542780	547080	is not upgradable unless you want to open up the screen, solder in a connector, that's
547080	550480	going to void your warranty, and I don't want to sell the parts for it because I don't want
550480	557100	to get involved in the problems. So, I suggest to them, what you need, generally, is an external
557100	563260	Wi-Fi card that you plug in, which has an external connector, which allows you to hook
563260	570640	up a variety of antennas. They're more power hungry than the internal card, they are going
570640	576320	to draw power, but most people's batteries are in pretty good shape these days. Not all
576320	582060	Wi-Fi, external Wi-Fi cards, PCMCIA or Cardbus, that have external antenna connectors are
582060	589680	created equal. They run the full gamut. But there is no one Wi-Fi card which is the best.
590060	595700	Some people prefer, the two chipsets that are most commonly used are the ones based
595700	601780	on the Hermes or the Orinoco Classic Gold, and the other one is the ones based on the
601780	608740	Prism chipset. Again, they are both different cards. The Orinoco Gold Classic was manufactured
608740	615080	by Orinoco. It was related to when it was part of Lucent. And when it was made, it was
615080	620540	not only manufactured for Lucent as an Orinoco card, it was manufactured under private label
620540	631420	for Anterasys, 2Wire, Deltru Mobile, Compaq, Toshiba. At one point, just about every Wi-Fi
631420	640340	card you picked up was really an Orinoco. And it was a very nice design. Proxim bought
640340	647540	the hardware licenses from Orinoco, and a company called Ageri bought the software licenses.
647620	652320	So when you use a Gold Classic card these days, most of the time you are ending up putting
652480	657340	a card in, if it is a new one, it is manufactured by Proxim, and the software still comes from
657340	663100	Ageri. So people often ask me, when they get a card, here is a real Orinoco. Is there any
663100	668100	difference between this and the Compaq? There are about 2 bytes of difference. But on a
668100	674420	performance basis, there is no difference. And they will both run the same drivers.
674420	682900	The Proxim 2 based cards come in a variety of packages. Many Linux users prefer it. In
682900	688080	particular, there is a Cisco version, which is a 100 mW card. The Orinoco cards are only
688080	695120	running at about 35 mW. There is also an SMC version, which is at 200 mW, and I think they
695120	699840	have now come out with a 300 mW version. So if you want power, the Proxim is a good card
699840	704640	to go to. But if you try pumping out 200 mW on a continuous basis, you will certainly
704640	713590	drain your batteries quite quickly. One of the important issues when working with a card,
713590	719890	and you want to do serious war driving, and serious war driving would involve accepting
719890	727330	some packets and examining their contents. This is what we would call promiscuous mode.
728070	736830	Promiscuous mode is not as naughty as it sounds. It relates to networking, where you have a
736830	742690	Wi-Fi card, which is able to recognize and accept all the network traffic which comes
742690	750450	along, passively. So it's basically somewhat stealthy, and it's just sitting there and
750450	756890	listening. And generally you not only need a promiscuous mode card that will do it, you
756890	763050	also need a driver that will allow you to do it. I put it this way, if you want to listen
763050	768530	to the music of Wi-Fi, and you want to look at the notes that are being played, you need
768530	777310	to become promiscuous. One of the important factors in terms of choosing a card is receive
777310	785370	sensitivity. Receive sensitivity indicates how faint an RF signal is that can be successfully
785370	792250	be received by your card. The lower power level that a card can receive, the better
792250	799090	the receive sensitivity. In Wi-Fi equipment, receive sensitivity is generally stated as
799210	806330	a function of network speed. It will generally tell you at what speed your sensitivity is.
807350	813290	For any given receiver, the higher the data rate, the less sensitive will be the receiver,
813290	818070	because the more power that is required to support that higher data rate. So people often
818070	823270	ask me, I'm at a distance, it's dropping down to two megabits. Yes, that's what's going
823270	827470	to happen. That's why you put an antenna in, to increase the amount of signal that you're
827470	830610	getting, even though you're not increasing the amount of receive sensitivity, so then
830610	842340	you can boost up your speed again. I'm not going to do too much math here, just briefly.
842380	847940	Receive sensitivity is frequently a confusing issue for people. That is because it's expressed
847940	853340	in decibels. It's not generally a unit that most of you are familiar with if you're not
853900	860860	working in RF or you're not working in acoustics. A decibel is a ratio expressed on a logarithmic
860860	868840	exponential scale. So a 10 to 1 ratio is 10 dB, a 2 to 1 ratio is 3, and a 1 to 1 ratio
868840	876220	is 0 dB. While ratios of less than 1 to 1 are expressed as negative numbers, for example
876360	884220	a 1 to 2 ratio equals minus 3 dB. Receive sensitivity, when you look at a card and the
884220	889840	specifications, is expressed using a version of decibel employed in measurements of radio
889840	899460	power, the dBm scale. 0 dBm equals 1 milliwatt. That's what I have on the scale. A power of
899460	909300	100 milliwatts equals 20 dBm. And 1000 milliwatts equals 30 dBm. Power levels below 1 milliwatt
909300	913520	are expressed as a negative number. That's just what happens when you're looking at something
913520	919320	logarithmically. But when you need to compare the receive sensitivity, for example, 0.01
919320	926120	milliwatts would be minus 20 dBm. And so when taking a look at it, what you really have
926120	933760	to look at is the absolute value. What I mean by that is a signal of minus 98 dBm.
934900	940260	Sensitivity is much better than sensitivity at minus 95 dBm.
944300	953820	Let's take a look at antennas for a moment. The simplest antenna, and what I'm going to
953820	960980	tell you, if any of you came to the booth in the vendor area this week, everybody wants
960980	967600	the biggest antenna. It's an American tradition. Bigger is always better. In war driving, bigger
967600	975920	is not always better. And many of you I encourage to buy a lower gain antenna. Why? The radiation
975920	982340	pattern of a theoretically perfect omnidirectional antenna is a sphere. That's called an isotropic
982340	990900	antenna. However, that only exists in theory. A real antenna cannot have an isotropic, a
990980	997800	perfect radiation pattern. The field propagates in a direction perpendicular to the radiating
997800	1003960	wire. So for a vertical antenna, the field isn't going to propagate up and down as much
1003960	1010860	as it is sideways. That means that a 5 dB antenna is going to go to a certain range,
1010860	1015340	but it will also go up, let's say, to the 15th or the 20th floor if you're in an urban
1015340	1021760	area. If you suddenly go up to a 7 dB or an 8 dB gain antenna, you will get the additional
1021760	1026220	range this way, but you will suddenly maybe not be able to retrieve a signal above the
1026220	1031720	10th floor or the 8th floor. So, that's why if you're in an urban area, bigger is not
1031720	1041100	always better. Directional antennas. The two I'm going to talk about are the Cantena and
1041100	1053150	the Yagi. The antenna we're looking at here on the top is a Yagi. Using a variety of elements
1053150	1059950	that collect, reflect, or radiate the signal, antennas can be constructed so the transmission
1059950	1067710	and reception isn't always equal in all directions. The definition of what a directional antenna
1067710	1074110	is. The first antenna we're going to consider here is the top one. It's called a Yagi-Uda
1074110	1080770	antenna. It's an antenna in which the gain of a single dipole element is enhanced by
1080770	1090440	putting a reflector behind it, a reflector behind it, and then directional elements in
1090440	1098520	front of it, so that you can take a signal and push it forward, have a gain from all
1098520	1104420	the reflected power, and keep it directed on a narrow path. This antenna was invented
1104420	1111240	in 1926 by H. Yagi and S. Uda. Uda's name dropped out along the way, but from what I
1111240	1116180	heard from someone, he's the one who got the original patents. But a Yagi-Uda antenna is
1116300	1119780	a long-time favorite. Any of you who are ham radio enthusiasts, any of you who remember
1119780	1124720	what an old TV antenna looks like? Anybody ever see a TV antenna the days before cable?
1124720	1130360	Right. Those were Yagis, okay? And they were very directional, and that's why you frequently
1130360	1137080	put a rotator on them to rotate it in the direction of the signal. The next antenna
1137080	1147420	we're going to show you is a Cantena. This is the original Heathkit Cantena. This is
1147420	1151900	not an antenna. I only show this to you because some people ask me, how did it get the name
1151900	1159460	Cantena? In the 70s and 80s, this is a product, which is basically a one-gallon paint can
1159460	1164700	that was filled with oil that was used to test radio transmitters. It would dissipate
1164700	1171560	the power up to 1,000 watts. So you put a transmitter on it, and you dissipated the
1171560	1176080	power so that you wouldn't blow out a transmitter if you didn't have an antenna on it. That
1176080	1185380	name came along, and what happened was in about 2001, Andy Clapp presented a novel design
1185380	1192420	for a very simple antenna based on a Pringles can. Many of you have heard of it. The Pringles
1192420	1198700	antenna showed a great potential for a simple, low-cost, less than $10, high-gain directional
1198700	1203960	Wi-Fi antenna. At this point, the other high-gain Wi-Fi antennas that were anywhere near it
1203960	1209400	were several hundred dollars apiece. I don't exactly know who to credit, but along the
1209400	1216040	way, someone simplified the design and came up with what we have for a current tin can
1216040	1222500	waveguide antenna, or cantena. Since it was much easier to build, the cantena became very
1222500	1233570	popular. This is an example of a commercial cantena. Here's what a cantena looks like
1233570	1239670	inside. Essentially, a cantena is constructed out of a can that can range from about 3 to
1239670	1244230	5 inches. You can go lower, you can go higher, but if you want reasonable gain, stay within
1244230	1250330	that range in diameter. The most popular one uses a total can length of approximately 12
1250330	1259490	inches, which on a 3, 3.5 inch cantena results in a gain of about 12 dB, and a beam width
1259490	1268000	of roughly 30 degrees. You can build a cantena yourself, and that's the whole basis for
1268000	1274640	this talk. There are professionally manufactured cantenas, we sell them, there are plenty of
1274640	1279320	them available on eBay and online. But you can very simply build your own cantena, and
1279320	1284240	that's how I started off in this sport, so I want to share that information with you.
1284960	1290720	The tin can waveguide antenna basically acts as a collector, and the closed end on the
1290720	1298840	back here acts as a reflector. What happens is that the 2400 MHz signal that's coming
1298840	1306240	in is reflected off the back, and it intersects with the waveforms that are coming in. As
1306240	1311640	these incoming signals and these reflecting signals meet, there are certain points where
1311640	1317780	there are troughs, and there are certain points where you have a maximum signal. The trick
1317780	1323940	is that if you place the collector at about a 1 quarter wavelength position from the rear
1323940	1330220	of the can, you're on one of the tops. You get the maximum signal collection. At the
1330220	1335780	very closed end of it, you get a zero signal. Anywhere along in the middle, you're going
1335780	1341680	to get a different signal. The optimal position is about 1 quarter wavelength along the way.
1344440	1349840	I'm going to diverge momentarily off the cantenna, because you can't really use a cantenna very
1349840	1357360	well without a pigtail, and I want to explain a little bit about pigtails briefly. Firstly,
1357360	1364720	you don't need a pigtail to use a cantenna. Simply by having a cantenna in proximity to
1365580	1370500	a Wi-Fi card, since it's tuned at the same frequency, there's a certain amount of signal
1370500	1376560	strength that will radiate over, and you will get an increase. But it's minimal, and going
1376560	1382100	through the air, you lose a lot of that signal. So although you don't need a cable to connect
1382100	1389160	the two, I strongly recommend it. What's a pigtail? What's a cable? An extension cable
1389160	1393860	is simply a cable which has two of the same connectors, one at each end. A pigtail is
1393860	1398880	one which has two different connectors. That's the only distinction. The nomenclature isn't
1398880	1403920	that firm, but that's at least how most of us use it. Why are there so many varieties
1403920	1410400	of connectors? We've shown three up here. One, not all connectors are designed to operate
1410400	1416280	efficiently at microwave frequencies. 2.4 gigahertz, which is Wi-Fi, is microwave. It's
1416280	1420360	the same frequency approximately that your microwave oven operates on, except that's
1420360	1428860	running at 4, 5, 800 watts, and we're talking here about milliwatts. One, manufacturers
1428880	1434240	want you to purchase their accessories for their product, so they use a custom connector,
1434240	1440400	and you're forced to use their antennas with their Wi-Fi devices. But it also originated
1440400	1447300	with the FCC. Part 15 of the FCC code says that the frequency we're working in at around
1447300	1454480	2,400 megahertz is in public domain. However, you're limited to an effective radiated power
1454480	1461660	of about 4 watts. The way the FCC managed to limit manufacturers was to say that if
1461660	1468080	you had a D-Link antenna and you had a D-Link router, D-Link had to go and submit approval
1468440	1479440	for the antenna and the router in combination together. And until last year, 2004, the FCC
1479440	1484280	came out with a new ruling which said you could mix and match. Technically, before that
1484280	1489760	summer ruling, if you took an antenna and put it on a Linksys router, you were doing
1489760	1494960	something not permitted by FCC Rule 15, because you might have increased the power above the
1494960	1503500	limit that they wanted to. To comply with the FCC, each manufacturer came up with somewhat
1503500	1510140	of a custom connector and got it approved by the FCC. Some took the popular SMA connector
1510720	1516140	and they reversed the ground and the signal, and you came up with an RP, which is a reverse
1516140	1523840	polarity SMA cable. Others came up with a custom connector called the MC, which is what
1523840	1529200	Orinoco uses. It's somewhat of a fragile connector, but again, we didn't design it. They came
1529200	1535480	up with it, so it was customized for them. Samsung took the SMA connector and reversed
1535480	1541920	the threads on the connector, and you have something called an RT-SMA. So, one thing
1541920	1545860	is, when you get to the point at which you're looking for pigtails, be very careful which
1545860	1552180	pigtail you're looking for. An SMA is not an RP-SMA, it's not an RT-SMA. Look carefully,
1552180	1556060	talk to people you know, go up online, there are some tables for each one of the types
1556060	1562360	of equipment, so that you can find out which type of cable you're going to use. The other
1562360	1567720	important thing to keep in mind with connectors is, people say to me, I'm a CB enthusiast,
1567720	1574060	I have a PL259 connector. It looks about like an N connector. It does. It, however, was
1574060	1579840	never made to operate at microwave frequencies, so you're going to see a lot of loss. Choose
1580200	1589640	a connector, preferably an N, that is efficient at microwave frequencies. Cables. What makes
1589760	1593480	a good cable? People are always calling me up and saying, I want a really, really low
1593480	1599040	loss cable. A really, really low loss cable is about three quarters of an inch in diameter.
1599500	1607340	It takes two people to carry it down the street, okay? But yes, it works. The thicker the central
1607340	1613480	conductor on a coax cable, the stronger the shield, there's almost this direct correlation,
1613480	1619420	the lower the loss of the signal along the cable. However, the thicker the cable, the
1619420	1626360	less flexible. The cables you're generally going to run into are an LMR400, and that's
1626360	1631320	about three quarters of an inch, sometimes almost an inch thick. It's very heavy, it's
1631320	1637180	very bulky, but if I'm running a 50 foot span up to the roof, and I know I'm only going
1637180	1646080	to lose 6cb over 100 feet, here's a piece of LMR400, okay? This is not the type of
1646080	1655860	thing you want to plug into your little laptop, okay? This is what we call equivalent to about
1655860	1661580	an LMR200 cable. It's a lot lighter weight, it's a lot more flexible. If you're going
1661580	1667340	to do a run of 20 feet or less, this is a great cable to use. They call it LMR240, they
1667340	1676260	call it LMR200, they call it low loss 200, it's a great cable to work with. This is an
1677300	1683880	LMR100 cable. Very thin. On the other hand, if I'm trying to connect this into a card
1684560	1690600	that I plugged into my laptop, I certainly couldn't plug in that LMR400 into it. One,
1690600	1694520	there's no place to put the connector. Two, the weight of it would break the connector.
1694920	1705580	So we use pigtails to connect from one size of a connector up to another. Just be careful
1705580	1709620	in a sense, when you're looking for a cable, you have to decide how long it's going to
1709620	1720380	be. Now that you know a little bit about cables, and you know a little bit about connectors,
1720860	1725480	the next step is, you want to build a tin can waveguide antenna. That's what you all
1725480	1732520	came to hear. What are the parts and tools you're going to need? You're going to need
1732640	1739040	a tin can, you're going to need an end connector, you could use another microwave connector,
1739040	1744460	I'm going to use my example using an end connector, the example stays the same. You're going to
1744460	1748700	need a drill or a device to make a hole in the can, you're going to need a short piece
1748700	1754020	of wire, you only need about one and a quarter inches, but I would say start off with about
1754020	1758680	six inches so you can make a few mistakes. You're going to need a soldering iron and
1758680	1764720	solder, a little flux doesn't hurt. My partner here, King Tuna Makes, and he says if you've
1764720	1770680	soldered, put a little flux on it, it's going to make life a lot easier. And most importantly,
1771180	1779900	you're going to need a ruler. Don't do it by line of sight. I'm sorry, by sight. Choosing
1780120	1793840	a can. You can choose many different types of cans. Yes. Um, yes. King Tuna says I build
1793840	1802180	better canned tuna's when I've had a shot of Jack, but we, uh, we've used coffee cans work,
1802180	1807720	um, you can eat beans, baked beans cans work great, particularly anybody, anybody here from
1807720	1813460	England? The baked bean cans are a lot wider there and they're much better for a cantenna.
1813840	1818880	Or you can use or drink scotch at holiday time and it comes in a nice little metal commemorative
1818880	1825540	can, which happens to be almost perfect for a great cantenna. Stoli also provides them.
1828310	1834970	You can download plans for many of the cantennas. We're going to distribute one plan here off of
1834970	1841990	the internet. Some of them will have very exact measurements of how to build it. Relax,
1841990	1848750	you don't have to be that exact. You can be within 10% and still make a good cantenna.
1851410	1857950	There are some dimensions which are important. You start off by having an end connector. This
1857950	1863430	is an end connector. You're going to take this end connector, it has a female end on one end,
1863430	1868390	and it'll have a little stub on the other side. You're going to be soldering a piece of copper
1868390	1874870	wire to that. We have, in my business, we happen to use a little brass tube that we have pre-soldered.
1874870	1879270	You can use a brass tube, you can use copper, you can use a copper piece of wire. They'll all
1879270	1891070	work about the same. You need 1.21 inches for a radiator to be effective. Why? Let's go to the
1891070	1896950	next slide, please. Okay. Now, they've just told me I only have 10 minutes because we started a
1896950	1903370	little late, so I'm going to try to go briefly. The first thing to determine is based on the
1903370	1909730	width of the can, the diameter of the can that you have, will determine what the length is for
1909950	1916370	a wavelength. You need to position the collector one quarter wavelength from the end. That's the
1916370	1922370	optimal point. That is the distance that you have to be careful on. Anywhere a little further,
1922470	1928430	a little less, the antenna will still work, but you'll get lower gain. The other important
1928430	1935450	measurement is what we call L over 4 here, which is the length of the radiator which is going to
1935450	1943290	collect the signal. That should be as close to 1.21 inches as you can. Using a ruler to make
1943290	1950370	an antenna, here's an example of one that my partner King Tuna made. It took him about 15
1950370	1958550	minutes this afternoon. This is made from a 13 inch coffee can, 13 ounce coffee can. It's not
1958550	1966190	the optimal can to do it, but it shows you can do it with any can. At CVS we bought it. You take
1966190	1971530	this can, we've got some plans, you can go up and there's some calculators that we'll give you that
1971530	1977030	are on the internet, which based on the diameter of the can, will tell you the distance out from
1977030	1984310	here that is one quarter wavelength. Cut a hole, in this case we just used a screwdriver and a
1984310	1991950	mallet to cut a hole that's about 5 1⁄8 inches around. You take the radiator that you've
1991950	1998930	constructed, which looks like an end connector, with a 1.21 inch piece of copper wire or brass
1998930	2005090	rod, insert it, screw it down. You don't need for it to be a round connector. If you've got a square
2005090	2010390	connector you can use that, you can screw it in place, you can glue it in place. The other
2010390	2016910	dimensions are not going to be that important. For an optimal cantenna, you want this length to be
2016910	2023350	approximately at least three quarters of a wavelength. For this particular can, which is
2023350	2030670	four inches across, three quarters of a wavelength works out to be 5.15 inches. This happens to be
2030670	2039150	5.25 inches. With a 13 ounce coffee can it just happens to work well. Put it in, screw it down,
2039150	2043490	that's all there is to building a cantenna. Essentially the only part that you're gonna
2043490	2049450	have a problem finding is the end connector. You can get it from radio supply houses, we may even
2049450	2054330	have a few left at our booth, there are plenty of places to buy them on the internet. That,
2054490	2060490	a 1.21 inch radiator, and a good tin can.
2062630	2075560	Take that, this particular one is four inches, 100 millimeters. I could go over the math but
2075560	2080200	basically the distance that you're going to measure from here to there is going to change
2080200	2089250	based on the diameter of the can. If you want, you put a pigtail on,
2090910	2097150	you can then connect it up to your card. A simple cantenna like this, which took about 20 minutes
2097150	2103690	to build, will give you about somewhere between 8 to 10 dB gain. We haven't fully measured this.
2103790	2108430	If you're a lot more careful about the calculations, if you're a lot more careful about the length of
2108430	2117710	the can, you can probably get 12 to 14 dB gain. If we make this shorter, we will get less gain,
2117710	2123370	but then again we'll get a wider signal coming out of it. Some people have made them about four
2123370	2129090	inches or so, and they get about a 50 degree signal breadth. If you make it about 12 inches long,
2129090	2132910	you're going to drop down to about a 25 or a 30 degree signal breadth.
2133170	2146050	We find it very useful to go to Home Depot, pick up a little tripod, threads a 1.25 by 20 inch,
2146050	2155770	1.25 by 20 threaded bolt, put it on there, screw it in, and now you don't have to take your coffee
2155770	2161550	cup and try to measure it to get it off and left to focus it. You can put it on any camera tripod.
2162370	2168390	It's really very simple to build a cantenna. Again, two calculations necessary. The length of
2168390	2174230	this is 1.21, and go and find, either use the plans that we've got for working with a simple
2174230	2180190	coffee can or go on the web. We've got a website where you can go to a calculator and measure this
2180190	2202630	out to this 1.25 wavelength. Any questions? The optimal radiator is a trapezoid, actually a cone,
2202630	2208490	but it's pretty hard to make a cone like that. So by making a rod, we end up trying to get in
2208490	2222440	the middle channel. See me afterwards. What you want is a trapezoid, I think it's six millimeters
2222440	2233420	at the bottom and one millimeter at the top. Again, 1.21 across. That's optimal. Yes? No.
2234480	2239880	We tried it with copper, we tried it with bronze, we even tried it with aluminum. They all work
2239880	2262930	well. We didn't see a significant difference. Yes. Thank you very much.