 This is Kent. Kent has been making antennas longer than I've been alive. He didn't bring a computer to DEF CON, so he's borrowing ours to give his presentation. But I don't actually know that he uses a computer anyway. He was telling me a bit about his antenna process. Windows 3.1 just wasn't compatible with ASCII. Yes, his Windows 3.1 computer just wasn't quite there, so we were loaning him one for now. So hopefully the slides all look good, but he can make antennas with his eyes closed. Sometimes he opens them just to make it a little more fun for everyone who's watching. I'm out of antenna jokes. Here's a guy who can show you which direction size matters most. I'm not quite sure how to respond to that introduction. With insults like that, I normally expect black fish net hose and a whip to be involved. I don't care what you wear. Okay, we're going to talk about some of the antennas that you can use with your various receivers and software-defined radios. There's some real problems with the SDRs. There's some pretty good ones out there. The fun key ones have to be one of the few that actually have filters built in with them. And you stick a little whip antenna like that, and it's good for listening to transmitters that are 10, 20, 30 feet away. But if you're trying to do some really serious work, and we're talking kilometers and miles, you're going to need something a lot better. Now you take your little software-defined radio and you put a serious antenna on it, and something happens. It stops working. A little closer? I get feedback. Okay, so you put a serious antenna on it, and things stop working. And I've seen this so many times. You guys put a nice big antenna on it, and they stop decoding. They stop receiving it. And I don't understand what the problem is because I've reloaded the software three times. Well, what your problem is, is this. This is looking at a spectrum analyzer from basically an AM broadcast band to one gigahertz. And you see all these monster signals. These added up together is enough to make most software-defined radios quit working. You have a first little transistor right there coming off the antenna. And if you hit that with enough signal, it goes non-linear. It stops working. This is an effect I'd like to describe as wearing a hearing aid to a rock concert. It just stops amplifying properly, and you no longer getting proper signals. Your biggest problem is that one over on the left. That's the FM broadcast band. Today, in most urban areas, there's more FM stations than there are TV stations now. And they run far more power. So if you're getting overloaded, it's probably in the FM broadcast band. One of the easiest things to do, it used to be get you a Radio Shack FM notch filter and notch out the FM band. No Radio Shacks, but there's a couple of these floating around. And another thing, don't be afraid of 75 ohms. When I connect a 50 ohm to a 75 ohm, I get about a 10% loss due to an impedance mismatch. But the 75 ohm coax has so much less loss, you're probably ahead in the long run. So don't be afraid of 75 ohm systems. Also, mini circuits makes entire families of filters. And it starts becoming important if you're doing some serious work to have filters that notch out everything except what you want to look at. Filters are very important. I also wouldn't rule out having some low power attenuators. It's quite often just putting a 1 or 2 dB attenuator in front of the antenna. I'm putting a radio is enough to suddenly start making it linear again. So some low value pads are very, very handy. Here's an antenna. Super secret design from the 1930s called a planar disc antenna. We got one running right here. An extremely broad band antenna, extremely. The lowest frequency is determined by how big the discs are. The highest frequency is determined by how close you can get those gaps together. And making these work over octave ranges is quite simple. We have a variety of them here. A few more. The one on the upper right is currently in orbit on a Canadian bird. And some other ones are going to be on some other satellites shortly. The one on the lower right goes from 700 megs to 26 gigahertz. It's pretty much a circular pattern at the low frequency. It becomes more of an ellipse as we go up. Radio Shack used to sell it as a universal cell phone antenna. And a different version. Get that gap real nice and close. But there's other alternatives. Go down to the dollar store and get you some 18 inch pizza pans. You don't want the aluminum ones. They're too hard to solder to. And mount them as close together as you can. And you now have a monitoring antenna that goes from about 150 megs up to about 2 gigahertz. Depending on how good your soldering job is. All the construction articles on these are available from my website. This is a winglet. Off of a long duration UAV that's designed for 11 day flights. Powered by a 9 horsepower diesel engine. Why diesel? Well, if you're in forward military areas, jet fuel is easier to find than gasoline. So it runs on diesel. This is the winglet. And as you can see, it's not quite three feet long. They sent it to me for testing. Because if you hold it up to the sun, you can see what we have inside the wing layout. Long periodics. And then the antenna going back to the 1950s. Another extremely broad band antenna. Directional, about 6 dB gain. Unless you're talking to the marketing departments of some other ones that sell them. Very broad range again. The one in the very middle goes from 300 megs to 11 gigahertz. And I make that for a spook in the UK. He sweeps offices for a living. Every so often people ask me, how do you stack log periodics? Usually not recommended. Your biggest problem is finding a power divider that works over that broad range of frequency. But the stacking distance needs to be a certain amount of a wavelength. So as you get to lower wavelengths, they need to be further apart. So if you do insist on stacking them, that's how you have to do it. Yes, I tried making some. They looked really good on the computer as a Gerber file. But after I got them back from the PCB house, I never figured out how to attach coax. Here's another technique. This is a log periodic to a Yagi. I've stopped figuring out how to blow on that. You can't add additional reflector elements, but you can add additional director elements. So this was used for basically a 2 to 6 gig log periodic. And they've added director elements at 6 gig. So that gives it a little more gain, a little more directionality up at the 6 gig area. And allowing for losses in the coax, you probably come out about even. Log periodics also make cute little dish feeds. I've had one up for about 20 years now. Not every 10 years I have to replace it. But now your dish works in this case from 2 gigs to 10 gigs. I've yet to understand the fascination of Helix and Tetas. Krause's originally formula for them were shall we be polite, optimistic? I have had perhaps a hundred of these on the antenna range. About one in 10 are circularly polarized. Just because it's a curly queue, it is not circularly polarized. The signal goes down to Helix, hits the end, reflects, comes back and cancels itself. So you can sit there and snip little tiny pieces off the tip and make it circularly polarized. There's another major problem. If I have just a wire in free space, signal travels down the wire at about 95% the speed of light. When I put a dielectric material, plastic, fiberglass, anything else around it, the speed of light is slower. So now the signal is going down that wire at about 60% the speed of light, not 95%. This is the way NASA makes Helix and Tetas. Fiberglass center, tiny small spokes touching it. Other material is negligible. So now when I start wrapping that around what have I done to my turns ratio? It ain't what that little calculator calculated. I'm not saying you can't allow for this. I can get out my simulation packages, spend about three weeks letting it go through, but I have no problem. What's the dielectric constant of that plastic? Go down to Home Depot and ask the guy in the plumbing department what the die. Oh, I'm going to be smarter than that. I'm going to look it up on the internet. That is standard for... That calculating that is measured at 1 kilohertz, not 2.4 gigahertz. And the dielectric constant changes with frequency. I'm not saying you can't build it. I'm not saying you can't allow for it, but you're going to need a lot of tools. I will talk about some patch antennas. Here we have just one simple patch antenna. I've done a few. In total I've done about 1,200 different antennas. The bottom one is kind of fun. That's a Bluetooth antenna. This was done for a project where we set them up and shot Bluetooth across the interstate highway and tried to do a Bluetooth acquisition with every card that went by. This was a few years ago. We got a 15% hit rate. Then they went down the road, passed a bunch of intersections and clover leaves and set up a bunch more. How they knew how many cards went this way, how many cards went that way, and what the transit times was. The computing system was trying to read and remember every license plate. This was a little simple. Here's another way of doing a patch antenna. By trimming the corners, you see just a little bit of taking off the corners, you get the two sides out of phase. And if you get it just right, it now puts out a circular wave. So by putting it just the right place, I generate circular polarization. I got two attach points. Attach it one place, it goes out right, attach it to the other place, it goes out left. So now you end up with sort of a MIMO antenna. This is what you would call a sector antenna. Very commonly used in the cell phone industry. I've got a whole bunch vertically set up, so I end up with a pattern that's very narrow with the horizon, about 120 degrees wide left and right. Now we set up three of them, and we have the three sectors covered for cell phone use. Here's another trick. This is a way of going for direction finding. Most of the guys try and have the antennas find a peak, look at the RSSI, and try and find a 1DV change or something. That's not the way the guys, big guys do it. In fact, we're looking at the same technique as used during World War II to DF onto German submarines. We had three large direction finding systems along the East Coast, and when the submarine communicated back to Berlin, we knew their latitude and longitude usually to higher accuracy than their navigator. When I have the two antennas side by... Well, let's go to the next step. Here we have two antennas side by side. As I get the antennas further apart, I get a narrower beam towards the middle. So you have a little bit. I've got a narrow beam further. The problem is... I think we went with the wrong one. Okay, this is the pattern of the single patch. So this is what you see when we just have a single patch out there. When we go to the two patches, we start getting like this, and that gets worse as we go up in frequency. And that's what happens when we really start getting them far apart. Try looking for the peak on that using our SSI. So now we have one where the bottom one, the two patches are out of phase. There's got to be a better way of doing this. Where the two are out of phase. And when I have them out of phase, you end up with a null right in the middle. So I have a peak on the left, a peak on the right, and a 40 dB null one degree wide down the middle. And most of the direction finding systems are based on peaking on that null. All those are techniques where I could switch back and forth between the two antennas. So I go peak null, peak null. Now I have a one degree wide 40 dB change. Not a few points in our SSI. Good old Yagis. Named after Dr. Yagi, who developed them at the University of Tokyo in 1926. Although his graduate student Uta actually did most of the work. The center element, you can see the copper one is where you collect the signal. The one in the back is a little longer, so it acts like a mirror. The ones in front are a little smaller. They tend to act like a lens. And this is what I like to consider to be the optical equivalent of a Yagi antenna. So you have a light bulb, a mirror, and a lens. You can't add another mirror, but you can add more lenses. So you can add additional elements out front to gain more directionality. My personal record is 80 elements. And they can be made on the friend at circuit board. There are quite a few different variations of those. Here we have a little 400 meg 3 element Yagi. It's built on a ground plane. So you only have half of the Yagi. The other half is part of the mirror image. This was a 400 megs. It was part of a radar system to determine when it was at exactly 1,800 feet. I've always enjoyed the irony that in 1945 we returned the Yagi antenna to Japan. Usually that gets a few giggles. Okay, we'll talk about log spirals. This is another extremely broadband antenna. Frequency ranges as much as 40 to 1 are possible. How fine you can do the little artwork in the very center determines the upper frequency. Total diameter determines the lowest frequency. Here's a couple I use on the antenna range that I've made myself. By flipping one over, I have one which is left hand circular, one that's right hand circular, so I can test a test antenna to see what's coming out. Historically, I found that when engineers design circular polarized antennas, they're left and right to have about a 50% chance of being correct. Ah, this is one I do for the Navy. This is a monopulse radar decoy. Aim 120 missiles, love it. So every time the Navy has a live fire exercise off the coast of California, I lose two antennas. They like to shoot down the drones. Breckage, burning jet fuel, this is fun, but it's expensive. So the Navy is now taking the drones and they put a stealth kit on it and remove about 90% of the radar echo, take a long wire, and you can see it shackled down at the bottom, hook a long wire to this, and the drone tows this, and the missiles go for this instead of the drone. On radar, this looks almost identical to a Boeing 727, and the missiles love it. Another extremely broadband antenna, Vivaldi. I had some rather interesting arguments as to whether it was designed in Italy or it was designed by an English engineer who just liked Vivaldi as the composer. We picked the wrong one, but this will work. The lowest frequency is determined by the width of the opening. The highest frequency is determined by how fine you can make that gap. These antennas run around 6-8 dB gain and easily operate over 10-1 frequency ranges. The big brass one is currently being mounted at the focus of a dish on some P3 Orion Elant aircraft. The smaller ones have a lot of other uses. If you've ever been around any EMI work, you've seen ridged horns. I like to think of Vivaldi's as a ridged horn without the horn, and they make cute little dish feeds. Everybody asks what simulation program do you use? I use the one by Rodin Swartz and Hewlett Packard. I have three families of antennas that HFSS cannot deal with. Oh, it gives you an answer to 12 dB places, but it's useless. There are big holes in those simulation packages, and because the guys are simulating and rarely build the antennas, they don't know there's holes in them, and when they do build them and they don't work, well, you didn't build it right. So I use simulations, but not very often. For those of you who've actually played with HFSS, I can build and test one in less time than you can set up your HFSS boundary conditions. I've also got an antenna range, and I can go out to 100 meters. I'm pretty continuous out to 30 gigs and spotty up to 100 gigs. I do a lot of TV antennas. We can go into Best Buy, Circuit City, Walmart, and I can show you some of myself hanging on the wall. This was a confusion factor. If you take the calculations for a horn antenna, this cannot work. It cannot work. No signal below 3 gigahertz can go in the opening. It cannot work. So we got the original sour cream and onion used in the original paper, built some of these up, and they did not work. But wait a minute. They're saying how great this is. Well, we made one as though we didn't know how to make one, and if you accidentally turn that coax connector ever so slightly and you don't have it tight, you now damage aluminum foil-coated cardboard. And if you turn it and you tear the aluminum foil close, you now have this fat monopole extended telescoping thing, not a horn antenna. Yes, I've been known to work on antennas of all sizes. I'm the little guy. The other one's the director of engineering of Daystar Network. He's got about 60 guys working for him, and only one actually came up with him and wouldn't get out of the elevator. He called me up and I just asked if he was buying lunch. So there's my shoes. How many of you have known this guy, assuming you're not this guy? I put in seven gallons of gas. I drove 200 miles. I got 28.5714. Somebody needs to take his scientific calculator, crush it, and slap him upside at the head with a slide roll. Here you go onto these guys who do these antenna programs that you can download. This one is now doing calculations in 10 billionths of an inch. How about this one? He likes to do it in hundreds of a millimeter. Ed may know how to do little calculators to put on a website, but he doesn't know very much about antennas. Let's see. Well, I had some others I was going to go over, but apparently they're not in this talk. This was an earlier version. This should look a little further. Any questions? Snydery marks? Insults? Yes. All antennas have reciprocity. What they do on transmit, they do on receive. The log periodics at the lower frequencies have run 100 watts through them without any issues. The little itty-bitty tiny one at about 7 watts at 10 gig, it does change color. If you can generate 7 watts at 10 gigahertz. Yes. Let's do here. I figure I'll make this thing come down. It was in there somewhere, wasn't it? That's right, it was right after the test equipment. You can see the top half of it. Okay, I use the older style. I have a signal generator that's modulated with 1,000 hertz. Then I have a receiver. It's just a crystal diode that goes down to an audit, a DC voltmeter, which is tuned to 1,000 hertz and calibrated in dB. So everything is done by looking at a 1,000 hertz tone. Any other direct current, DC current carriers out there or video carriers are not at 1,000 hertz. And I then put up my reference antenna, measure the signal level, put up the new antenna, and tell you how many dB difference there is between. It is a grant. The source antenna is placed on the ground, which then makes the ground part of it. I back up and find an area where the signal level is consistent. If I'm working up in the many gigahertz, then I'll elevate the source, have a high gain antenna on the source, and no energy ever really hits the ground. My lot's 550 feet long. I also pack it up and take it to various conferences and we test antennas at conferences. I was at the demo lab two hours ago. I brought a small antenna range. However, American Airlines bagging channelers had been a little difficult audit and the modulator did not survive. But I've got quite a collection of reference antennas. Most of my reference antennas are hordes because horn antennas are very predictable, very consistent. Aperture area is easy to calculate. Just need a yardstick. Yes, filters. Notch filters. And your option is what? How is the switch going to help you? You would have to somehow switch faster than the sample rate of the SDR and that's going to be quite a switch to switch at that speed. Well, if you know exactly what the high power is and knowing your services in the area is very important, look at a high-pass filter or perhaps a low-pass filter and those do not have as much loss as your passband filters. And if you know what it is, it's usually not that difficult to make a notch filter and then a notch filter will have almost no loss on your primary signal. Questions? Cygremarks? Insults? I don't want to wake him up. Any other questions? How do I return control of this menagerie to these guys? Okay.