TechStuff Gets on the Radar

curious about radar guns. But the technology is pretty simple once you know the the underlying principles. So I'm gonna lump them all together here. Plus I've talked a lot about radar recently, with topics on folks like Alfred Lee Loomis and his Loran navigation system, so a lot of that's going to tie in here as well. Now, to begin with, in order to understand radar and all the different principles behind it, we have to look back to the nineteenth century, all the way back in eighteen forty two.

And no, we weren't using radar in eighteen forty two. He didn't have a bunch of nineteenth century military officials trying to figure out where the next wooden boat was. But in eighteen forty two, an Austrian physicist and astronomer named Christian Johann Doppler published a paper on the determination of motion using the frequency of light in the study of the movement of stars, and this became known as

the Doppler principle. And here's what he was talking about. So, light is a type of electro magnetic radiation as part of the electromagnetic spectrum. You can measure light in waves, though light can also behave as a particle, but let's put that aside for an How we're specifically talking about light in its nature as a wave, and waves have a wave length. That is where you can measure from one point on a wave to the next point that is the exact same sort of point further down the wavelength.

That's the wavelength. So like the crest, if you go to the very peak and you measure to the next peak, that would be one wavelength of that wave. Visible light has a very very small wavelength. The visible light spectrum ranges from around three nine nanometers to seven hundred nanometers, and a nanometer is one billionth of a meter, so

very very tiny wavelengths. Now, do you remember your pneumonic device for the color spectrum, You know, the roy G BIV, which stands for red, orange, yellow, green, blue, indigo, violet. That's not just the spectrum, that's not just the colors of a rainbow. Those colors actually represent wavelengths of descending length. So red light has the longest wavelength invisible light, and

violet the shortest wavelength invisible light. All light travels at the same speed, which here you go, mind blowing fact. Here that's the speed of light. Now, keep in mind the speed of light actually changes somewhat depending upon the medium it passes through. When we typically say the speed of light, we usually mean through a vacuum, But speed of light through air is slightly slower because it's moving

through a different medium. When I say slightly slower, I mean incredibly incredibly tiny difference for us, Like, it's still wicked fast. So all light travels at that speed. Really, all electromagnetic radiation travels at that speed. But this also means that shorter wavelengths of light have a higher frequency, meaning you have more instances of a wave pass a specific point within a specific amount of time. Because the waves are shorter, but they're moving at the same speed

as the longer waves. Now, I used an analogy recently of a highway with cars on it. So just imagine you're standing on the side of this highway and all the cars are traveling at the same speed. Now, first, let's say that there are a there's a row of buses and they're just passing you, and they're all traveling at this particular speed, and for the purposes of this example,

we'll just say it's fifty miles per hour. They're equally spaced, just inches apart from each other, so it's incredibly dangerous, but they're all moving at this fifty miles per hour speed and they're passing you. Next, imagine that there is a row of tiny smart cars that are passing you. These are also inches apart from each other, so uh, they are very close together, and they're traveling at the same speed the buses were. Earlier, they're also traveling at

fifty miles per hour. You'll have more smart cars pass you by in that same amount of time because they're smaller. They're traveling at the same speed as the buses, but they have less lengths, so you get more of them. In in the same amount of time. Same thing is true with frequencies electromagnetic frequencies. Uh, light is the same thing.

All light is traveling at the same speed, but shorter wavelengths mean that you have a higher frequency, a higher number of waves passing through a certain point at a certain a certain amount of time. So what exactly was Doppler saying. Well, he was talking about how you could tell whether stars were moving toward or away from the viewer by the wavelength of light that you observed when

looking at the star. A body moving away from the viewer would have elongated waves, almost as if it were stretching out the light behind it, So it would be a red shift because you'd be shifting closer towards the red side of the spectrum. Uh, that's the side of the spectrum that has the longer wavelengths. So something moving away from you with these elongated wavelengths would be red shifted.

But if a star were moving toward you, then it would have compressed waves of light pushed ahead of it, so you would have the more of these wavelengths pushed towards you would be scrunched up. This would be blue shifted toward you. And we call this the Doppler effect, and it would become really important in radar, and it's also something that we can observe in our regular lives.

We don't have to have a powerful telescope or a spectroscope to be able to do this because it works with lots of different kinds of waves, not just electro magnetic waves. It also works with sound waves. If you've ever heard a vehicle with a siren coming toward you, you might have noticed that it has a higher pitch sound as it approaches you, and then after it passes you, the pitch on the siren goes down as the vehicles

moving away. This is the Doppler effect, in which the sound waves are compressed as the vehicle is coming towards you, and they are elongated as the vehicles moving away from you. And the vehicle we're staying perfectly still, you would hear a pitch somewhere in between those two other pitches. Also, if you're going faster than the speed of sound, if you your vehicles traveling faster than sound itself can travel, you would create what's called a sonic boom. But that's

beside the point. So Smarty Pants Doppler observes this phenomena, which would allow future engineers a chance to determine if something was coming toward them or moving away from them based off of radar. It would take nearly a century

for that to pay off in that way. However, The next person I need to talk about briefly is Heinrich Hurtz, who was a German physicist who conducted numerous experiments in the late nineteenth century around the eighteen eighties, and Hurts has a familiar name if you have talked a lot about frequencies. Hurts, in turn was building off of theoretical work that was done by a Scottish physicist named James

Clerk Maxwell. So Maxwell had this idea. He had a theory that light and radio waves were all part of a larger spectrum of waves, so effectively this would be the electro magnetic spectrum, and that all of these waves would follow the same fundamental rules. Though the waves of cells would have a have very different wavelengths and frequencies, so the specific reactions will be a little different based upon the wavelengths and frequencies involved, but they would all

follow the same basic set of rules. Maxwell's work suggested that radio waves could be reflected off of metallic surfaces just as light. Could you know if you have a mirror, you can bounce light around. Well, he said, well, if that's the case, if light behaves this way, and if electromagnetic radiation also behaves in that way, then you would expect electromagnetic radiation to also bounce off these surfaces. We can't see it, but it should still happen because they

should still follow those rules. So Hurts set out to test that theory through experimentation, and he used radio waves that are frequency of about four hundred fifty five mega hurts, which meant the wavelengths were about sixty six centimeters in length. And he found in eight eight that Maxwell's theories held merit.

They did a seemed to follow those fundamental rules. So in nineteen o four we then have to talk about a German engineer named Christian Hulsmeyer who applied for a patent for a quote an obstacle detector and ship navigation device end quote based off of this principle. This would have been a very early form of radar, but at the time no one was terribly interested in it, as there was no real practical use for it, yet not in nineteen o four. Uh. It would later become extremely practical,

but no one could foresee that at the time. Skip ahead several decades after the development of radio, geniuses like Tesla and Marconi had advanced our understanding of radio waves and how to generate them, and by the nineteen thirties radio was widely deployed in many parts of the world. But engineers noticed something interesting. They saw that when you had transmitters posted across bodies of water, sometimes radio waves from one transmitter would bounce back to that source transmitter.

It corresponded with ups passing between the two transmitters. The engineers and scientists observing this theorized that what must be happening is that some of those radio waves were going out over the water, colliding with a shop, and then bouncing back to the source. They were noticing the same effects that Hurts had tested decades earlier. But how would they make it a practical technology. Well, many different nations explored the possibility of using radio to detect large objects.

In ninety two, in the United States, the United States Naval Research Laboratory in Washington, d C. Noted fluctuations in radio signal intensity between a transmitter on one side of the Potomac River and a receiver on the other side of the river. The fluctuations only occurred when a ship passed between the transmitter and the receiver on the river.

But the upper levels of the Navy weren't interested in the technology as it stood, and it was only after the development of monostatic radar and which you used the exact same antenna as a transmitter and a receiver, that the Navy began to fund serious research and development. And that wouldn't happen until nineteen thirty nine. Enter Sir Robert

Alexander Watson what a Scottish physicist. Now he is frequently credited as quote unquote the inventor of radar, but I need to say there were an awful lot of people, all working on similar ideas at the same time, so it's very difficult. In fact, it's impossible to say one person was the inventor of radar. One person tends to get the credit for it, but in fact this was happening all around the world simultaneously. So uh Watson what

was born in eighteen ninety two. He attended the University of St Andrews, and he had begun his scientific career as sort of a meteorologist uh timpting to develop technology that could detect and track thunderstorms. He had observed this phenomenon of radio waves reflected off of things like ships, and wrote a memorandum to the British government in nineteen

thirty five. It was his opinion that given a radio transmitter and a receiver, with sufficient power and radio waves in the proper frequency, you could potentially detect incoming aircraft, and such a device would be an incredibly powerful tool, not just in peace time, but also in war, and tensions were mounting in Europe in nineteen thirty five, so this was a high priority. Being able to detect an

incoming air attack could save thousands of lives. And I'll talk more about what he did in just a second, but first let's take a quick break to thank our sponsor Watson what began to experiment with a design for detecting aircraft in ninety five. He developed a transmitter and a receiver and was using it to locate any sort of aircraft from a distance of about ninety miles or His work inspired the British government to fund a project called chain Home, which was a system of radars that

operated on frequencies ranging from twenty two to fifty mega hurts. Now, visible light is in the four dred thirty to seven seventy terror hurts range. So how long were the wavelengths that Watson What was working with? While they ranged from about six meters or nineteen point seven ft to thirteen point six meters or forty four point seven feet, So these were waves that were on many orders of magnitude longer than the nanometer scale wavelengths of visible light. They

were huge in comparison. Watson What said that the use of such long wavelengths followed a philosophy he called the cult of the imperfect. He defined this as quote, give them the third best to go on with, the second best comes too late, the best never comes end quote. So in other words, he says, yeah, we could have tried to generate smaller wavelengths, which would have solved a lot of problems. One, it would have given you better resolution to It would have cut down on noise and interference,

but it also would have taken longer to develop. If you want something that you can deploy, you go with an easier solution, you have to set that goal lower than what you want in order to deliver on time if timeliness is more important than resolution. For example, the chain home system went online in September night as a

twenty four hour detection system. The system helped England detect incoming bombing runs from the Germans and melt a limited air defense with their own capabilities, and without that system, the damage and losses from German attacks would have been much greater than what they were. Other nations such as the Soviet Union, Germany, Japan, the United States, and many others were all working on similar radar technologies around this time,

primarily for use during the war. German systems operated at three five mega hurts and five hundred sixty egga hurts, which gave them superior resolution and accuracy, and it also meant German systems had less noise to deal with. So why is all this Well, remember that higher frequencies correspond with shorter wavelengths. Shorter wavelengths are more narrow and thus you can get a better picture of where something is when you're using them. So remember that radar is essentially echolocation.

If you send out a very long wavelength and the very long wavelength returns to you. You know the wavelength encountered something that it reflected off of, but it's harder to figure out exactly where that object is because the wavelength is literally covering more space. You can tell how far away the object is, and the way you do that is you measure the amount of time it took the radio wave to leave the transmitter and then return

to the receiver. You know that radio waves are traveling at the speed of light, so you take the amount of time it took for the radio wave to go out and back. Then you take half of that number, and you multiply at times the speed of light, and you get the sense of the object. You have the number because otherwise you have the round trip. Right, that's just the full distance between you and the target object doubled,

so you have to take one half of that. Further, by looking for any changes in wavelength, you can determine if the object is moving towards you or away from you. This again is that Doppler effect. If the returning wavelengths are the same as the ones you sent out, the object you detected is sitting still relative to your position. If the wavelengths are shorter than the object is moving toward you, And if the wavelengths are longer than what you sent out, then the object is moving away from you.

But if the wavelengths are already pretty long, you don't have a lot of accuracy when you're looking at the feedback. A narrower beam will give you a better idea of exactly where in the sky the object is. This is clearly more helpful in both military and peacetime operations. So Germany was way ahead of everyone else in terms of radar when World World War two began. The country had deployed radar on ships and on ground defense stations. They

were using shorter wavelengths than just about anybody else. The country continued to develop the technology until about nineteen forty. So why did they stop Well, German leaders were confident that the war would soon be over and Germany would be victorious, so they stopped work on radar to concentrate on the war effort. Meanwhile, the UK and the US were stepping up their efforts accelerating the evolution of the technology.

By the time Germany determined that the end of the war was still years away, it was too late the country was hopelessly left behind in terms of radar tech. And now we touch on the part of the story that I've mentioned in recent episodes about Alfred Loomis and the Loran system. Scientists at the University of Birmingham developed a cavity magnatron oscillator to produce waves in the microwave frequency, and I'm talking about Birmingham in the UK hunt Alabama.

These devices used electric and magnetic fields to stimulate microwave generation and chambers called cavities within a vacuum tube like device. Microwaves can have a wavelength of between one meter all the way down to one millimeter, and that gives them frequencies of between three hundred megahurts to three hundred giga hurts.

The scientists at the University of Birmingham had created a cavity magnetron capable of producing microwaves that were about ten centimeters in wavelength, meaning they were very close to three giga hurts and frequency. If used with radar, this would make a system capable of unprecedented accuracy and resolution. But the scientists needed help, and so they traveled to America to meet with experts at M i T Now to avoid suspicion, Taffy Bowen, a British scientist, traveled to the

United States under the pretense of going on holiday. He made the trip aboard a cruise ship called the Duchess of Richmond, which is not a bad way to deliver top secret technology to allies across the ocean. The scientists collaborated together and they created the newly formed rad Lab at m I T to develop microwave radar technology. The United States Navy was the actual entity to name the technology radar, and originally that was an acronym that stood

for radio detection and ranging. These days, it's just a regular noun. We just call it radar. You don't have to capitalize it either. One other thing to note about this time. On December seven, ninety one, and Army radar site picked up a signal that indicated more than a hundred aircraft were on approach to Hawaii. George Elliott, one of the two operators of the radar site, passed this information up the chain of command, but no one acted

upon it. According to Elliott, he and his co operator, Joe Lockard were to run the station only between the hours of four and seven a m. But Elliott wanted to get in a bit more experience. He was brand new to operating radars, so he wanted to practice for a while, so he kept the system running for a few minutes after seven am, and it was seven oh two when he saw the large reading. It was actually larger than any other reading they had previously seen at

that station. After calling in the report, he was told that it was likely a group of US bombers heading towards San Francisco. But then the Japanese forces unleashed a devastating attack on Pearl Harbor, which would pull the United States into World War Two. The microwave radar technology began to get a rapid deployment in the early nineteen forties as part of a top secret effort to gain an

advantage in the war. The Axis forces had learned how to jam earlier radar systems like the SCR TO six eight, which used longer radio waves, and that was from the United States and it operated on a much lower frequency than the microwave radar stations they were, so the Germans were unprepared for the high precision of the new microwave systems that were represented in the s c R five

eight four radar designation. The new radar had a parabolic reflector antenna that measured two meters or about six point six feet in diameter, and it was first used in combat in nineteen forty four in Italy to great effect. Many different versions of radar were developed and deployed during the war, including radar systems aboard aircraft and those on

naval vessels. On May nine, a German warship called the Bismarck sunk a British ship called the h MS Hood, but a British aircraft carrier called the Arc Royal used shipborn radar to detect and track the Bismarck, and that allowed Allied forces to converge and attack the ship, ultimately sinking it. After World War Two ended, Winston Churchill would say that while the atomic bomb may have ended the war,

radar was the technology that won the war. Now I have a little bit more to say about radar, but first let's take another quick break to thank our sponsor. Towards the end of World War Two, the UK and the US had both worked with radar to aid with landing aircraft to guide them into landing strips safely. And that use of radar quickly expanded to civil oberations, and

that would become the basis of air traffic control. And at first they would use this just for the purposes of guiding aircraft to land at landing strips or to take off, and then ultimately to become more of a holistic air traffic control system that could be handed off from one control tower to another to maintain contact with pilots as they traveled across vast distances. Advances in radar

also helped fuel more study in radio astronomy. Radio astronomy uses large arrays of radio antenna to detect extra terrestrial radio signals, And by that I don't necessarily mean we're listening to the equivalent of alien television rerun ones. In fact, I don't mean that at all, because lots of stuff emits radio waves. So we're talking about studying signals from various celestial phenomenas just stars, galaxies, quasars, pulsars, and more. Another use of radar that grew out of military use

was for meteorology. During the war, radar operators noted that many times they detected excess noise or clutter when they directed radar transmissions towards weather elements like precipitation. After the war, engineers and scientists began to adapt radar to track storms, Specifically, special radar systems that could detect precipitation, including how intense that precipitation was, began to help meteorologists track weather patterns and adjust forecasts. So you may have heard of Doppler

radar on your local weather forecast. That's what's talking about. Their using radar to detect things like precipitation and the movement of these thunderstorms and weather patterns. Other advances include pull Doppler radar, and it's pretty much what sounds like. It sends out signals and pulses and then that is very useful. It helps limit the amount of noise that comes back when you are detecting the returning radio waves.

So the way this would work, if you wanted to, I don't know, create a radar speed gun like the police use. This was part of the request. You would have a velocity threshold and this would essentially tell the system ignore anything below a certain threshold as far as velocity goes. So if it detects that an object is traveling slower than the velocity threshold, it ignores it, which is really useful if you're doing something like using a

radar gun to detect speed. If you're pointing it down the street and a car passes by and it's well below the threshold, then it shouldn't even activate the warning. Or if your radar is picking up something apart from just a car, if it's below that threshold, it doesn't come back as a false hit. Otherwise you could end up getting signals bounced off of all sorts of different surfaces, and the radar gun would be confused as to which

one's meant what. You would pick up these signals, some of which would indicate that there were objects moving, some of which said that there's not objects moving. And this is where we get to that noise and clutter and UH problems. So clutter is the the return signals you get from a radar transmitter that aren't related to whatever your target is. So it's very easy to understand with a radar gun, your target is a car. You're pointing a radar gun at a car. You're getting some signals

bouncing back. Some of them are bouncing back from the car. Some of them are bouncing back from other vehicles on the road. Some of them may be bouncing back from just the surface of the ground, and you want to be able to make sure you're looking specifically at the signals that are related to the target. Everything else is clutter, it's distracting, and it could give you a false uh

information seat of information about whatever your target is. So that's why you have to have something like a velocity threshold to help eliminate a lot of that uh. There's also the possibility that you would get noise from other sources of radio waves. This is interference, so this is not coming from your radar antenna. This is coming from other sources and could also give false positives or clutter

up your information. So you want to have a device that can very easily find the signal through all the noise. On top of that, there is the concept of radar jamming, and this is a very real thing. If you know what frequency a radar system is using, and then you broadcast that same frequency toward the radar. Let's say you've

got line of sight on the radar antenna. You could broadcast that same frequency of radio waves at the antenna and you're essentially overwhelming it it can't detect the returning signals because it's getting blasted by the exact frequency continuously. So it's just it's like it's continuously getting a hit, and so it never knows when there's a real hit. So radar jamming is an actual thing. And not only that, but to make matters worse, you don't even need a

particularly powerful transmitter to jam radar. And the reason for that is that radar radio signals they decrease in strength as they travel. So if you're sending out a radar signal from the transmitter, it's probably a very powerful signal, but once it gets to wherever it's going, let's say it's trying to detect aircraft, and then once those signals

return back to the receiver, they're pretty weak. So the receiver has to be very sensitive to pick up those signals, which means that if you have a transmitter of even modest power, you could probably fool the receiver into thinking it's picking up those signals all the time. So jammers do not have to be as strong as radar transmitters in order to still be a fact active, but you

do kind of have to have line of sight. You can get a little bit off to one side or the other, and then you can have what is called a side lobe radar jammer, but that's not nearly as effective as having a direct line of sight on on the radar. Radars also these days tend to work as both an antenna and a receiver. I mentioned that earlier this idea of monostatic radar. In order to do that, you have to have something called a duplex or a duplex er is sort of the switch. It switches the

radar between transmit mode and receive mode. And typically the way these work is that a radar will transmit for just a few thousandths of a second, so a fraction of a fraction of a second, it sends out blast of radio signals, and then it listens for a while, and then it will do the same thing again and again and again, so every second it does it's only transmitting for thousands of a second and the rest of

the time it's listening. This is the case for lots of different radar systems up there, that including things like CT where you're you're you're sending out signals briefly, but you're really spending most of your time listening and so the same is true with all radar systems really that that rely on this monostatic approach. That is, then there's some other related technologies that are not specifically radar, but they work on a similar principle. So one of those

would be lidar. Lidar, as you might guess from the name, it relies on light, infrared light and UH to be specific, and infrared light. Light guns have largely replaced radar guns for the police. And UH light is you know again, it's it's signals are even shorter than things in the microwave realm, so you can get even higher accuracy with a more narrow beam, and it can cut down on noise even more assuming you don't have an infrared generator

just blasting back at the light gun. So light guns have largely replaced radar guns, although we have plenty of uses for radar itself, not just not just in radar guns these days. And then there's sonar that's the sound,

navigation and arranging. We use sonar for underwater applications. Things like submarines use sonar to detect obstacles and navigate because, as it turns out, electromagnetic waves don't travel all that well through dense seawater, so we rely on these sonic based systems for detecting objects underwater rather than using electromagnetic waves because they're just not very effective once you get

below a certain depth. So most submarines have both radar and so in our systems, but the radar systems are used when the submarine has surfaced, and typically you would use it if you were navigating into port, for example, and whenever you're underwater you would use the sonar system. So that kind of wraps up this discussion of radar.

There a lot of other particular as We could talk about specific variations on radar, things like phase shifting, that sort of stuff, but it gets really technical, and honestly, it's just variations on what I've already talked about using different elements of the physics of radio waves. And while it's fascinating, it's also again hard to describe without the use of visual aids. But I hope that this was an interesting episode for you guys. I love looking into

technologies like this. If there's a technology you would like me to cover in a future episode of Tech Stuff, or maybe there's someone you would like me to talk about or two. You should send me a message and let me know. The email address for the show is tech Stuff at how stuff Works dot com, or drop me a line on Facebook for Twitter, they handle it both of those is tech Stuff H. S W. Don't forget to follow us on Instagram and I'll talk to you again really soon for more on this and fathoms

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