Speaker 1: Get in text with technology with tech Stuff from how
Speaker 1: stuff Works dot com. Hey there, and welcome to tech Stuff.
Speaker 1: I'm your host, Jonathan Strickland. I'm an executive producer at
Speaker 1: how Stuff Works in a love all things tech, and
Speaker 1: today we're going to talk about radar, the history of radar,
Speaker 1: how it works, that kind of stuff. This comes to
Speaker 1: us courtesy of some listener requests. Actually two different listeners,
Speaker 1: Scott and Doug both asked about this. Doug specifically was
Speaker 1: curious about radar guns. But the technology is pretty simple
Speaker 1: once you know the the underlying principles. So I'm gonna
Speaker 1: lump them all together here. Plus I've talked a lot
Speaker 1: about radar recently, with topics on folks like Alfred Lee
Speaker 1: Loomis and his Loran navigation system, so a lot of
Speaker 1: that's going to tie in here as well. Now, to
Speaker 1: begin with, in order to understand radar and all the
Speaker 1: different principles behind it, we have to look back to
Speaker 1: the nineteenth century, all the way back in eighteen forty two.
Speaker 1: And no, we weren't using radar in eighteen forty two.
Speaker 1: He didn't have a bunch of nineteenth century military officials
Speaker 1: trying to figure out where the next wooden boat was.
Speaker 1: But in eighteen forty two, an Austrian physicist and astronomer
Speaker 1: named Christian Johann Doppler published a paper on the determination
Speaker 1: of motion using the frequency of light in the study
Speaker 1: of the movement of stars, and this became known as
Speaker 1: the Doppler principle. And here's what he was talking about. So,
Speaker 1: light is a type of electro magnetic radiation as part
Speaker 1: of the electromagnetic spectrum. You can measure light in waves,
Speaker 1: though light can also behave as a particle, but let's
Speaker 1: put that aside for an How we're specifically talking about
Speaker 1: light in its nature as a wave, and waves have
Speaker 1: a wave length. That is where you can measure from
Speaker 1: one point on a wave to the next point that
Speaker 1: is the exact same sort of point further down the wavelength.
Speaker 1: That's the wavelength. So like the crest, if you go
Speaker 1: to the very peak and you measure to the next peak,
Speaker 1: that would be one wavelength of that wave. Visible light
Speaker 1: has a very very small wavelength. The visible light spectrum
Speaker 1: ranges from around three nine nanometers to seven hundred nanometers,
Speaker 1: and a nanometer is one billionth of a meter, so
Speaker 1: very very tiny wavelengths. Now, do you remember your pneumonic
Speaker 1: device for the color spectrum, You know, the roy G BIV,
Speaker 1: which stands for red, orange, yellow, green, blue, indigo, violet.
Speaker 1: That's not just the spectrum, that's not just the colors
Speaker 1: of a rainbow. Those colors actually represent wavelengths of descending length.
Speaker 1: So red light has the longest wavelength invisible light, and
Speaker 1: violet the shortest wavelength invisible light. All light travels at
Speaker 1: the same speed, which here you go, mind blowing fact.
Speaker 1: Here that's the speed of light. Now, keep in mind
Speaker 1: the speed of light actually changes somewhat depending upon the
Speaker 1: medium it passes through. When we typically say the speed
Speaker 1: of light, we usually mean through a vacuum, But speed
Speaker 1: of light through air is slightly slower because it's moving
Speaker 1: through a different medium. When I say slightly slower, I
Speaker 1: mean incredibly incredibly tiny difference for us, Like, it's still
Speaker 1: wicked fast. So all light travels at that speed. Really,
Speaker 1: all electromagnetic radiation travels at that speed. But this also
Speaker 1: means that shorter wavelengths of light have a higher frequency,
Speaker 1: meaning you have more instances of a wave pass a
Speaker 1: specific point within a specific amount of time. Because the
Speaker 1: waves are shorter, but they're moving at the same speed
Speaker 1: as the longer waves. Now, I used an analogy recently
Speaker 1: of a highway with cars on it. So just imagine
Speaker 1: you're standing on the side of this highway and all
Speaker 1: the cars are traveling at the same speed. Now, first,
Speaker 1: let's say that there are a there's a row of
Speaker 1: buses and they're just passing you, and they're all traveling
Speaker 1: at this particular speed, and for the purposes of this example,
Speaker 1: we'll just say it's fifty miles per hour. They're equally spaced,
Speaker 1: just inches apart from each other, so it's incredibly dangerous,
Speaker 1: but they're all moving at this fifty miles per hour
Speaker 1: speed and they're passing you. Next, imagine that there is
Speaker 1: a row of tiny smart cars that are passing you.
Speaker 1: These are also inches apart from each other, so uh,
Speaker 1: they are very close together, and they're traveling at the
Speaker 1: same speed the buses were. Earlier, they're also traveling at
Speaker 1: fifty miles per hour. You'll have more smart cars pass
Speaker 1: you by in that same amount of time because they're smaller.
Speaker 1: They're traveling at the same speed as the buses, but
Speaker 1: they have less lengths, so you get more of them.
Speaker 1: In in the same amount of time. Same thing is
Speaker 1: true with frequencies electromagnetic frequencies. Uh, light is the same thing.
Speaker 1: All light is traveling at the same speed, but shorter
Speaker 1: wavelengths mean that you have a higher frequency, a higher
Speaker 1: number of waves passing through a certain point at a
Speaker 1: certain a certain amount of time. So what exactly was
Speaker 1: Doppler saying. Well, he was talking about how you could
Speaker 1: tell whether stars were moving toward or away from the
Speaker 1: viewer by the wavelength of light that you observed when
Speaker 1: looking at the star. A body moving away from the
Speaker 1: viewer would have elongated waves, almost as if it were
Speaker 1: stretching out the light behind it, So it would be
Speaker 1: a red shift because you'd be shifting closer towards the
Speaker 1: red side of the spectrum. Uh, that's the side of
Speaker 1: the spectrum that has the longer wavelengths. So something moving
Speaker 1: away from you with these elongated wavelengths would be red shifted.
Speaker 1: But if a star were moving toward you, then it
Speaker 1: would have compressed waves of light pushed ahead of it,
Speaker 1: so you would have the more of these wavelengths pushed
Speaker 1: towards you would be scrunched up. This would be blue
Speaker 1: shifted toward you. And we call this the Doppler effect,
Speaker 1: and it would become really important in radar, and it's
Speaker 1: also something that we can observe in our regular lives.
Speaker 1: We don't have to have a powerful telescope or a
Speaker 1: spectroscope to be able to do this because it works
Speaker 1: with lots of different kinds of waves, not just electro
Speaker 1: magnetic waves. It also works with sound waves. If you've
Speaker 1: ever heard a vehicle with a siren coming toward you,
Speaker 1: you might have noticed that it has a higher pitch
Speaker 1: sound as it approaches you, and then after it passes you,
Speaker 1: the pitch on the siren goes down as the vehicles
Speaker 1: moving away. This is the Doppler effect, in which the
Speaker 1: sound waves are compressed as the vehicle is coming towards you,
Speaker 1: and they are elongated as the vehicles moving away from you.
Speaker 1: And the vehicle we're staying perfectly still, you would hear
Speaker 1: a pitch somewhere in between those two other pitches. Also,
Speaker 1: if you're going faster than the speed of sound, if
Speaker 1: you your vehicles traveling faster than sound itself can travel,
Speaker 1: you would create what's called a sonic boom. But that's
Speaker 1: beside the point. So Smarty Pants Doppler observes this phenomena,
Speaker 1: which would allow future engineers a chance to determine if
Speaker 1: something was coming toward them or moving away from them
Speaker 1: based off of radar. It would take nearly a century
Speaker 1: for that to pay off in that way. However, The
Speaker 1: next person I need to talk about briefly is Heinrich Hurtz,
Speaker 1: who was a German physicist who conducted numerous experiments in
Speaker 1: the late nineteenth century around the eighteen eighties, and Hurts
Speaker 1: has a familiar name if you have talked a lot
Speaker 1: about frequencies. Hurts, in turn was building off of theoretical
Speaker 1: work that was done by a Scottish physicist named James
Speaker 1: Clerk Maxwell. So Maxwell had this idea. He had a
Speaker 1: theory that light and radio waves were all part of
Speaker 1: a larger spectrum of waves, so effectively this would be
Speaker 1: the electro magnetic spectrum, and that all of these waves
Speaker 1: would follow the same fundamental rules. Though the waves of
Speaker 1: cells would have a have very different wavelengths and frequencies,
Speaker 1: so the specific reactions will be a little different based
Speaker 1: upon the wavelengths and frequencies involved, but they would all
Speaker 1: follow the same basic set of rules. Maxwell's work suggested
Speaker 1: that radio waves could be reflected off of metallic surfaces
Speaker 1: just as light. Could you know if you have a mirror,
Speaker 1: you can bounce light around. Well, he said, well, if
Speaker 1: that's the case, if light behaves this way, and if
Speaker 1: electromagnetic radiation also behaves in that way, then you would
Speaker 1: expect electromagnetic radiation to also bounce off these surfaces. We
Speaker 1: can't see it, but it should still happen because they
Speaker 1: should still follow those rules. So Hurts set out to
Speaker 1: test that theory through experimentation, and he used radio waves
Speaker 1: that are frequency of about four hundred fifty five mega hurts,
Speaker 1: which meant the wavelengths were about sixty six centimeters in length.
Speaker 1: And he found in eight eight that Maxwell's theories held merit.
Speaker 1: They did a seemed to follow those fundamental rules. So
Speaker 1: in nineteen o four we then have to talk about
Speaker 1: a German engineer named Christian Hulsmeyer who applied for a
Speaker 1: patent for a quote an obstacle detector and ship navigation
Speaker 1: device end quote based off of this principle. This would
Speaker 1: have been a very early form of radar, but at
Speaker 1: the time no one was terribly interested in it, as
Speaker 1: there was no real practical use for it, yet not
Speaker 1: in nineteen o four. Uh. It would later become extremely practical,
Speaker 1: but no one could foresee that at the time. Skip
Speaker 1: ahead several decades after the development of radio, geniuses like
Speaker 1: Tesla and Marconi had advanced our understanding of radio waves
Speaker 1: and how to generate them, and by the nineteen thirties
Speaker 1: radio was widely deployed in many parts of the world.
Speaker 1: But engineers noticed something interesting. They saw that when you
Speaker 1: had transmitters posted across bodies of water, sometimes radio waves
Speaker 1: from one transmitter would bounce back to that source transmitter.
Speaker 1: It corresponded with ups passing between the two transmitters. The
Speaker 1: engineers and scientists observing this theorized that what must be
Speaker 1: happening is that some of those radio waves were going
Speaker 1: out over the water, colliding with a shop, and then
Speaker 1: bouncing back to the source. They were noticing the same
Speaker 1: effects that Hurts had tested decades earlier. But how would
Speaker 1: they make it a practical technology. Well, many different nations
Speaker 1: explored the possibility of using radio to detect large objects.
Speaker 1: In ninety two, in the United States, the United States
Speaker 1: Naval Research Laboratory in Washington, d C. Noted fluctuations in
Speaker 1: radio signal intensity between a transmitter on one side of
Speaker 1: the Potomac River and a receiver on the other side
Speaker 1: of the river. The fluctuations only occurred when a ship
Speaker 1: passed between the transmitter and the receiver on the river.
Speaker 1: But the upper levels of the Navy weren't interested in
Speaker 1: the technology as it stood, and it was only after
Speaker 1: the development of monostatic radar and which you used the
Speaker 1: exact same antenna as a transmitter and a receiver, that
Speaker 1: the Navy began to fund serious research and development. And
Speaker 1: that wouldn't happen until nineteen thirty nine. Enter Sir Robert
Speaker 1: Alexander Watson what a Scottish physicist. Now he is frequently
Speaker 1: credited as quote unquote the inventor of radar, but I
Speaker 1: need to say there were an awful lot of people,
Speaker 1: all working on similar ideas at the same time, so
Speaker 1: it's very difficult. In fact, it's impossible to say one
Speaker 1: person was the inventor of radar. One person tends to
Speaker 1: get the credit for it, but in fact this was
Speaker 1: happening all around the world simultaneously. So uh Watson what
Speaker 1: was born in eighteen ninety two. He attended the University
Speaker 1: of St Andrews, and he had begun his scientific career
Speaker 1: as sort of a meteorologist uh timpting to develop technology
Speaker 1: that could detect and track thunderstorms. He had observed this
Speaker 1: phenomenon of radio waves reflected off of things like ships,
Speaker 1: and wrote a memorandum to the British government in nineteen
Speaker 1: thirty five. It was his opinion that given a radio
Speaker 1: transmitter and a receiver, with sufficient power and radio waves
Speaker 1: in the proper frequency, you could potentially detect incoming aircraft,
Speaker 1: and such a device would be an incredibly powerful tool,
Speaker 1: not just in peace time, but also in war, and
Speaker 1: tensions were mounting in Europe in nineteen thirty five, so
Speaker 1: this was a high priority. Being able to detect an
Speaker 1: incoming air attack could save thousands of lives. And I'll
Speaker 1: talk more about what he did in just a second,
Speaker 1: but first let's take a quick break to thank our
Speaker 1: sponsor Watson what began to experiment with a design for
Speaker 1: detecting aircraft in ninety five. He developed a transmitter and
Speaker 1: a receiver and was using it to locate any sort
Speaker 1: of aircraft from a distance of about ninety miles or
Speaker 1: His work inspired the British government to fund a project
Speaker 1: called chain Home, which was a system of radars that
Speaker 1: operated on frequencies ranging from twenty two to fifty mega hurts. Now,
Speaker 1: visible light is in the four dred thirty to seven
Speaker 1: seventy terror hurts range. So how long were the wavelengths
Speaker 1: that Watson What was working with? While they ranged from
Speaker 1: about six meters or nineteen point seven ft to thirteen
Speaker 1: point six meters or forty four point seven feet, So
Speaker 1: these were waves that were on many orders of magnitude
Speaker 1: longer than the nanometer scale wavelengths of visible light. They
Speaker 1: were huge in comparison. Watson What said that the use
Speaker 1: of such long wavelengths followed a philosophy he called the
Speaker 1: cult of the imperfect. He defined this as quote, give
Speaker 1: them the third best to go on with, the second
Speaker 1: best comes too late, the best never comes end quote.
Speaker 1: So in other words, he says, yeah, we could have
Speaker 1: tried to generate smaller wavelengths, which would have solved a
Speaker 1: lot of problems. One, it would have given you better
Speaker 1: resolution to It would have cut down on noise and interference,
Speaker 1: but it also would have taken longer to develop. If
Speaker 1: you want something that you can deploy, you go with
Speaker 1: an easier solution, you have to set that goal lower
Speaker 1: than what you want in order to deliver on time
Speaker 1: if timeliness is more important than resolution. For example, the
Speaker 1: chain home system went online in September night as a
Speaker 1: twenty four hour detection system. The system helped England detect
Speaker 1: incoming bombing runs from the Germans and melt a limited
Speaker 1: air defense with their own capabilities, and without that system,
Speaker 1: the damage and losses from German attacks would have been
Speaker 1: much greater than what they were. Other nations such as
Speaker 1: the Soviet Union, Germany, Japan, the United States, and many
Speaker 1: others were all working on similar radar technologies around this time,
Speaker 1: primarily for use during the war. German systems operated at
Speaker 1: three five mega hurts and five hundred sixty egga hurts,
Speaker 1: which gave them superior resolution and accuracy, and it also
Speaker 1: meant German systems had less noise to deal with. So
Speaker 1: why is all this Well, remember that higher frequencies correspond
Speaker 1: with shorter wavelengths. Shorter wavelengths are more narrow and thus
Speaker 1: you can get a better picture of where something is
Speaker 1: when you're using them. So remember that radar is essentially echolocation.
Speaker 1: If you send out a very long wavelength and the
Speaker 1: very long wavelength returns to you. You know the wavelength
Speaker 1: encountered something that it reflected off of, but it's harder
Speaker 1: to figure out exactly where that object is because the
Speaker 1: wavelength is literally covering more space. You can tell how
Speaker 1: far away the object is, and the way you do
Speaker 1: that is you measure the amount of time it took
Speaker 1: the radio wave to leave the transmitter and then return
Speaker 1: to the receiver. You know that radio waves are traveling
Speaker 1: at the speed of light, so you take the amount
Speaker 1: of time it took for the radio wave to go
Speaker 1: out and back. Then you take half of that number,
Speaker 1: and you multiply at times the speed of light, and
Speaker 1: you get the sense of the object. You have the
Speaker 1: number because otherwise you have the round trip. Right, that's
Speaker 1: just the full distance between you and the target object doubled,
Speaker 1: so you have to take one half of that. Further,
Speaker 1: by looking for any changes in wavelength, you can determine
Speaker 1: if the object is moving towards you or away from you.
Speaker 1: This again is that Doppler effect. If the returning wavelengths
Speaker 1: are the same as the ones you sent out, the
Speaker 1: object you detected is sitting still relative to your position.
Speaker 1: If the wavelengths are shorter than the object is moving
Speaker 1: toward you, And if the wavelengths are longer than what
Speaker 1: you sent out, then the object is moving away from you.
Speaker 1: But if the wavelengths are already pretty long, you don't
Speaker 1: have a lot of accuracy when you're looking at the feedback.
Speaker 1: A narrower beam will give you a better idea of
Speaker 1: exactly where in the sky the object is. This is
Speaker 1: clearly more helpful in both military and peacetime operations. So
Speaker 1: Germany was way ahead of everyone else in terms of
Speaker 1: radar when World World War two began. The country had
Speaker 1: deployed radar on ships and on ground defense stations. They
Speaker 1: were using shorter wavelengths than just about anybody else. The
Speaker 1: country continued to develop the technology until about nineteen forty.
Speaker 1: So why did they stop Well, German leaders were confident
Speaker 1: that the war would soon be over and Germany would
Speaker 1: be victorious, so they stopped work on radar to concentrate
Speaker 1: on the war effort. Meanwhile, the UK and the US
Speaker 1: were stepping up their efforts accelerating the evolution of the technology.
Speaker 1: By the time Germany determined that the end of the
Speaker 1: war was still years away, it was too late the
Speaker 1: country was hopelessly left behind in terms of radar tech.
Speaker 1: And now we touch on the part of the story
Speaker 1: that I've mentioned in recent episodes about Alfred Loomis and
Speaker 1: the Loran system. Scientists at the University of Birmingham developed
Speaker 1: a cavity magnatron oscillator to produce waves in the microwave frequency,
Speaker 1: and I'm talking about Birmingham in the UK hunt Alabama.
Speaker 1: These devices used electric and magnetic fields to stimulate microwave
Speaker 1: generation and chambers called cavities within a vacuum tube like device.
Speaker 1: Microwaves can have a wavelength of between one meter all
Speaker 1: the way down to one millimeter, and that gives them
Speaker 1: frequencies of between three hundred megahurts to three hundred giga hurts.
Speaker 1: The scientists at the University of Birmingham had created a
Speaker 1: cavity magnetron capable of producing microwaves that were about ten
Speaker 1: centimeters in wavelength, meaning they were very close to three
Speaker 1: giga hurts and frequency. If used with radar, this would
Speaker 1: make a system capable of unprecedented accuracy and resolution. But
Speaker 1: the scientists needed help, and so they traveled to America
Speaker 1: to meet with experts at M i T Now to
Speaker 1: avoid suspicion, Taffy Bowen, a British scientist, traveled to the
Speaker 1: United States under the pretense of going on holiday. He
Speaker 1: made the trip aboard a cruise ship called the Duchess
Speaker 1: of Richmond, which is not a bad way to deliver
Speaker 1: top secret technology to allies across the ocean. The scientists
Speaker 1: collaborated together and they created the newly formed rad Lab
Speaker 1: at m I T to develop microwave radar technology. The
Speaker 1: United States Navy was the actual entity to name the
Speaker 1: technology radar, and originally that was an acronym that stood
Speaker 1: for radio detection and ranging. These days, it's just a
Speaker 1: regular noun. We just call it radar. You don't have
Speaker 1: to capitalize it either. One other thing to note about
Speaker 1: this time. On December seven, ninety one, and Army radar
Speaker 1: site picked up a signal that indicated more than a
Speaker 1: hundred aircraft were on approach to Hawaii. George Elliott, one
Speaker 1: of the two operators of the radar site, passed this
Speaker 1: information up the chain of command, but no one acted
Speaker 1: upon it. According to Elliott, he and his co operator,
Speaker 1: Joe Lockard were to run the station only between the
Speaker 1: hours of four and seven a m. But Elliott wanted
Speaker 1: to get in a bit more experience. He was brand
Speaker 1: new to operating radars, so he wanted to practice for
Speaker 1: a while, so he kept the system running for a
Speaker 1: few minutes after seven am, and it was seven oh
Speaker 1: two when he saw the large reading. It was actually
Speaker 1: larger than any other reading they had previously seen at
Speaker 1: that station. After calling in the report, he was told
Speaker 1: that it was likely a group of US bombers heading
Speaker 1: towards San Francisco. But then the Japanese forces unleashed a
Speaker 1: devastating attack on Pearl Harbor, which would pull the United
Speaker 1: States into World War Two. The microwave radar technology began
Speaker 1: to get a rapid deployment in the early nineteen forties
Speaker 1: as part of a top secret effort to gain an
Speaker 1: advantage in the war. The Axis forces had learned how
Speaker 1: to jam earlier radar systems like the SCR TO six eight,
Speaker 1: which used longer radio waves, and that was from the
Speaker 1: United States and it operated on a much lower frequency
Speaker 1: than the microwave radar stations they were, so the Germans
Speaker 1: were unprepared for the high precision of the new microwave
Speaker 1: systems that were represented in the s c R five
Speaker 1: eight four radar designation. The new radar had a parabolic
Speaker 1: reflector antenna that measured two meters or about six point
Speaker 1: six feet in diameter, and it was first used in
Speaker 1: combat in nineteen forty four in Italy to great effect.
Speaker 1: Many different versions of radar were developed and deployed during
Speaker 1: the war, including radar systems aboard aircraft and those on
Speaker 1: naval vessels. On May nine, a German warship called the
Speaker 1: Bismarck sunk a British ship called the h MS Hood,
Speaker 1: but a British aircraft carrier called the Arc Royal used
Speaker 1: shipborn radar to detect and track the Bismarck, and that
Speaker 1: allowed Allied forces to converge and attack the ship, ultimately
Speaker 1: sinking it. After World War Two ended, Winston Churchill would
Speaker 1: say that while the atomic bomb may have ended the war,
Speaker 1: radar was the technology that won the war. Now I
Speaker 1: have a little bit more to say about radar, but
Speaker 1: first let's take another quick break to thank our sponsor.
Speaker 1: Towards the end of World War Two, the UK and
Speaker 1: the US had both worked with radar to aid with
Speaker 1: landing aircraft to guide them into landing strips safely. And
Speaker 1: that use of radar quickly expanded to civil oberations, and
Speaker 1: that would become the basis of air traffic control. And
Speaker 1: at first they would use this just for the purposes
Speaker 1: of guiding aircraft to land at landing strips or to
Speaker 1: take off, and then ultimately to become more of a
Speaker 1: holistic air traffic control system that could be handed off
Speaker 1: from one control tower to another to maintain contact with
Speaker 1: pilots as they traveled across vast distances. Advances in radar
Speaker 1: also helped fuel more study in radio astronomy. Radio astronomy
Speaker 1: uses large arrays of radio antenna to detect extra terrestrial
Speaker 1: radio signals, And by that I don't necessarily mean we're
Speaker 1: listening to the equivalent of alien television rerun ones. In fact,
Speaker 1: I don't mean that at all, because lots of stuff
Speaker 1: emits radio waves. So we're talking about studying signals from
Speaker 1: various celestial phenomenas just stars, galaxies, quasars, pulsars, and more.
Speaker 1: Another use of radar that grew out of military use
Speaker 1: was for meteorology. During the war, radar operators noted that
Speaker 1: many times they detected excess noise or clutter when they
Speaker 1: directed radar transmissions towards weather elements like precipitation. After the war,
Speaker 1: engineers and scientists began to adapt radar to track storms, Specifically,
Speaker 1: special radar systems that could detect precipitation, including how intense
Speaker 1: that precipitation was, began to help meteorologists track weather patterns
Speaker 1: and adjust forecasts. So you may have heard of Doppler
Speaker 1: radar on your local weather forecast. That's what's talking about.
Speaker 1: Their using radar to detect things like precipitation and the
Speaker 1: movement of these thunderstorms and weather patterns. Other advances include
Speaker 1: pull Doppler radar, and it's pretty much what sounds like.
Speaker 1: It sends out signals and pulses and then that is
Speaker 1: very useful. It helps limit the amount of noise that
Speaker 1: comes back when you are detecting the returning radio waves.
Speaker 1: So the way this would work, if you wanted to,
Speaker 1: I don't know, create a radar speed gun like the
Speaker 1: police use. This was part of the request. You would
Speaker 1: have a velocity threshold and this would essentially tell the
Speaker 1: system ignore anything below a certain threshold as far as
Speaker 1: velocity goes. So if it detects that an object is
Speaker 1: traveling slower than the velocity threshold, it ignores it, which
Speaker 1: is really useful if you're doing something like using a
Speaker 1: radar gun to detect speed. If you're pointing it down
Speaker 1: the street and a car passes by and it's well
Speaker 1: below the threshold, then it shouldn't even activate the warning.
Speaker 1: Or if your radar is picking up something apart from
Speaker 1: just a car, if it's below that threshold, it doesn't
Speaker 1: come back as a false hit. Otherwise you could end
Speaker 1: up getting signals bounced off of all sorts of different surfaces,
Speaker 1: and the radar gun would be confused as to which
Speaker 1: one's meant what. You would pick up these signals, some
Speaker 1: of which would indicate that there were objects moving, some
Speaker 1: of which said that there's not objects moving. And this
Speaker 1: is where we get to that noise and clutter and
Speaker 1: UH problems. So clutter is the the return signals you
Speaker 1: get from a radar transmitter that aren't related to whatever
Speaker 1: your target is. So it's very easy to understand with
Speaker 1: a radar gun, your target is a car. You're pointing
Speaker 1: a radar gun at a car. You're getting some signals
Speaker 1: bouncing back. Some of them are bouncing back from the car.
Speaker 1: Some of them are bouncing back from other vehicles on
Speaker 1: the road. Some of them may be bouncing back from
Speaker 1: just the surface of the ground, and you want to
Speaker 1: be able to make sure you're looking specifically at the
Speaker 1: signals that are related to the target. Everything else is clutter,
Speaker 1: it's distracting, and it could give you a false uh
Speaker 1: information seat of information about whatever your target is. So
Speaker 1: that's why you have to have something like a velocity
Speaker 1: threshold to help eliminate a lot of that uh. There's
Speaker 1: also the possibility that you would get noise from other
Speaker 1: sources of radio waves. This is interference, so this is
Speaker 1: not coming from your radar antenna. This is coming from
Speaker 1: other sources and could also give false positives or clutter
Speaker 1: up your information. So you want to have a device
Speaker 1: that can very easily find the signal through all the noise.
Speaker 1: On top of that, there is the concept of radar jamming,
Speaker 1: and this is a very real thing. If you know
Speaker 1: what frequency a radar system is using, and then you
Speaker 1: broadcast that same frequency toward the radar. Let's say you've
Speaker 1: got line of sight on the radar antenna. You could
Speaker 1: broadcast that same frequency of radio waves at the antenna
Speaker 1: and you're essentially overwhelming it it can't detect the returning
Speaker 1: signals because it's getting blasted by the exact frequency continuously.
Speaker 1: So it's just it's like it's continuously getting a hit,
Speaker 1: and so it never knows when there's a real hit.
Speaker 1: So radar jamming is an actual thing. And not only that,
Speaker 1: but to make matters worse, you don't even need a
Speaker 1: particularly powerful transmitter to jam radar. And the reason for
Speaker 1: that is that radar radio signals they decrease in strength
Speaker 1: as they travel. So if you're sending out a radar
Speaker 1: signal from the transmitter, it's probably a very powerful signal,
Speaker 1: but once it gets to wherever it's going, let's say
Speaker 1: it's trying to detect aircraft, and then once those signals
Speaker 1: return back to the receiver, they're pretty weak. So the
Speaker 1: receiver has to be very sensitive to pick up those signals,
Speaker 1: which means that if you have a transmitter of even
Speaker 1: modest power, you could probably fool the receiver into thinking
Speaker 1: it's picking up those signals all the time. So jammers
Speaker 1: do not have to be as strong as radar transmitters
Speaker 1: in order to still be a fact active, but you
Speaker 1: do kind of have to have line of sight. You
Speaker 1: can get a little bit off to one side or
Speaker 1: the other, and then you can have what is called
Speaker 1: a side lobe radar jammer, but that's not nearly as
Speaker 1: effective as having a direct line of sight on on
Speaker 1: the radar. Radars also these days tend to work as
Speaker 1: both an antenna and a receiver. I mentioned that earlier
Speaker 1: this idea of monostatic radar. In order to do that,
Speaker 1: you have to have something called a duplex or a
Speaker 1: duplex er is sort of the switch. It switches the
Speaker 1: radar between transmit mode and receive mode. And typically the
Speaker 1: way these work is that a radar will transmit for
Speaker 1: just a few thousandths of a second, so a fraction
Speaker 1: of a fraction of a second, it sends out blast
Speaker 1: of radio signals, and then it listens for a while,
Speaker 1: and then it will do the same thing again and
Speaker 1: again and again, so every second it does it's only
Speaker 1: transmitting for thousands of a second and the rest of
Speaker 1: the time it's listening. This is the case for lots
Speaker 1: of different radar systems up there, that including things like
Speaker 1: CT where you're you're you're sending out signals briefly, but
Speaker 1: you're really spending most of your time listening and so
Speaker 1: the same is true with all radar systems really that
Speaker 1: that rely on this monostatic approach. That is, then there's
Speaker 1: some other related technologies that are not specifically radar, but
Speaker 1: they work on a similar principle. So one of those
Speaker 1: would be lidar. Lidar, as you might guess from the name,
Speaker 1: it relies on light, infrared light and UH to be specific,
Speaker 1: and infrared light. Light guns have largely replaced radar guns
Speaker 1: for the police. And UH light is you know again,
Speaker 1: it's it's signals are even shorter than things in the
Speaker 1: microwave realm, so you can get even higher accuracy with
Speaker 1: a more narrow beam, and it can cut down on
Speaker 1: noise even more assuming you don't have an infrared generator
Speaker 1: just blasting back at the light gun. So light guns
Speaker 1: have largely replaced radar guns, although we have plenty of
Speaker 1: uses for radar itself, not just not just in radar
Speaker 1: guns these days. And then there's sonar that's the sound,
Speaker 1: navigation and arranging. We use sonar for underwater applications. Things
Speaker 1: like submarines use sonar to detect obstacles and navigate because,
Speaker 1: as it turns out, electromagnetic waves don't travel all that
Speaker 1: well through dense seawater, so we rely on these sonic
Speaker 1: based systems for detecting objects underwater rather than using electromagnetic
Speaker 1: waves because they're just not very effective once you get
Speaker 1: below a certain depth. So most submarines have both radar
Speaker 1: and so in our systems, but the radar systems are
Speaker 1: used when the submarine has surfaced, and typically you would
Speaker 1: use it if you were navigating into port, for example,
Speaker 1: and whenever you're underwater you would use the sonar system.
Speaker 1: So that kind of wraps up this discussion of radar.
Speaker 1: There a lot of other particular as We could talk
Speaker 1: about specific variations on radar, things like phase shifting, that
Speaker 1: sort of stuff, but it gets really technical, and honestly,
Speaker 1: it's just variations on what I've already talked about using
Speaker 1: different elements of the physics of radio waves. And while
Speaker 1: it's fascinating, it's also again hard to describe without the
Speaker 1: use of visual aids. But I hope that this was
Speaker 1: an interesting episode for you guys. I love looking into
Speaker 1: technologies like this. If there's a technology you would like
Speaker 1: me to cover in a future episode of Tech Stuff,
Speaker 1: or maybe there's someone you would like me to talk
Speaker 1: about or two. You should send me a message and
Speaker 1: let me know. The email address for the show is
Speaker 1: tech Stuff at how stuff Works dot com, or drop
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Speaker 1: have their topics. Is that how stuff works dot com