May 25, 2011 • 38 mins
Radios are fascinating -- but how do they work? In this podcast, Jonathan and Chris tackle some of the fundamental processes of radio. Tune in to learn more about radio waves, radio stations and more.
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Speaker 1 (00:00):
Brought to you by the reinvented two thousand twelve camera.
It's ready. Are you get in touch with technology with
tech Stuff from how stuff works dot com. Hello again, everyone,
Welcome to tech stuff. My name is Chris Pollett, and
(00:20):
I'm an editor here at how stuff works dot Com.
Broadcasting from the seat across from me, as usual, is
senior writer Jonathan Striffland. You gave them all those old
time stars through wars of worlds invaded by Mars. You
made him laugh, you made him cry, you made us
feel like we could fly. Just remember video killed the
(00:42):
radio stars. But for now, we're still going to talk
about radio. Yeah, and you guys might remember not that
long ago, we did a podcast about who invented the
radio and we came up with a conclusion of I
don't know, although actually Chris and I both agreed that
if if gun were held to our heads, we would
(01:02):
we would claim that Tesla was the the inventor of
the radio. It's just that he did not He was
not able to implement it in the same sort of
scale as Marconi, whose implementation depended somewhat on Tesla's work.
But yeah, but it had gone on for some time
there were a number of people as and and this
happens a lot in science that uh, you know, their
(01:26):
contributions made radio possible. They were it was sort of
invented in increments really. Um. And of course Tesla was
a very prolific inventor. He had his fingers and lots
of different pies. I'm sorry, I had to watch Jonathan's
high clay everyone, and um, I'm having a little moment here.
(01:46):
And Marconi was was really a radio guy. He really
was interested in radio. So it's it's really kind of
no surprise that he really pushed radio very hard, harder
than Tesla did, and so he got a lot of
the credit for it. But um, we were going to
talk today about the invention itself, how radio itself actually works,
(02:08):
and to really talk about this first we have to
understand a little bit about radio frequencies, radio waves, and
uh so let's talk about radio waves first. Now, waves
are this is a complicated issue because there are different
types of waves, right. There's there are mechanical waves, which
(02:29):
are the waves that we can observe with our own
eyes through various means. Like there's you know, if you
look at a notion and you see the waves coming across.
Those are mechanical waves. Due, yes, they are, in fact
gnarly During an earthquake, the earth moves in mechanical waves, yes,
and sound travels through mechanical waves. But yeah, now you
(02:50):
may not think of sound as a mechanical wave because
it's not something that you can typically see. Although if
there is a sound loud enough, it can create a
mechanical wave powerful enough to vibrate uh an objects. So
you can see that, right, Well, you could see um
if you've ever watched videos of explosions, especially when a
video shot from overhead, you can see the shock wave, yeah,
(03:14):
traveling outward from that, which is you watch any Michael
bay movie, the moment where the two heroes running away
from the explosion leap into air and are propelled fifty
feet that is kind of what Chris is talking about. Okay,
that was an even better description than the one I
had Michael Bays solves. Anyway, So yeah, so these waves
(03:35):
they move, they move, and uh there's a crest and
then there's a trough, right, the crest being the highest point,
the trough being the lowest point. And you consider the
point from the top of one crest to the top
of the next crest, the wave length of that wave, right,
all right, So these these mechanical waves, they have to have, uh,
some sort of of medium to move through. They require that.
(03:58):
Even sound, which is why if you were to be
in outer space and you were to take off your
space helmet and shout to your buddy across the way, Uh,
your buddy would not hear you, because there is no
medium there spaces of vacuum. More or less. There are
particles in space, but they're so far there's there's so little,
(04:19):
there's no contact. Right. The particles in space are are
so far apart from one another that there's no way
to to propagate a mechanical wave through space. I think
we understand the lack of gravity in this situation, thank you.
So yeah, nature of hors a vacuum, so do I.
That's why I only sweep vacuum. So anyway, Yeah, you
need a medium for a mechanical wave to to move through.
(04:41):
But electromagnetic waves are different. They do not require that.
They can they can propagate through a vacuum. They can
move through the vacuum space and in fact, they will
continue to move once generated forever. Really Um, so the
radio waves that we generated way back when we were
first figuring this out, they are now, oh well, let's see,
(05:04):
more than around a hundred light years away, because radio
waves travel at the speed of light. And then you know,
the invention of the radio really dates back a century.
So anything around there, anything generated at that time, would
now be traveling a hundred light years away. It's kind
of cool. Yeah, yeah, because it travels the speed of light. Okay,
(05:25):
so all those all those broadcasts in the forties and
fifties of the radio cereals, those are now forty fifty
light years away. Cereal. Um yeah, it's Chris's weakness was
cereal is like my weakness with pie. So don't don't
get me wrong. I like the pie. So yeah, I
mean light and and radio waves are both forms of
electromagnetic radiation. Um, and it's I had something I was
(05:48):
gonna say there, I've got something here. So when we
say electromagnetic that's really important. Now, when you're talking about
a mechanical wave, you're talking about a wave and a
particular our alignment. Let's let's say vertical, you know, like
waves you would see on a notion. Electromagnetic waves are
actually a pair of waves. There's an electric field wave
(06:11):
and a magnetic field wave. Now you've heard us talk
a lot about the relationship between electricity and magnetism and
how there is this interesting connection between the two. As
it turns out, if you were to generate an electromagnetic wave,
you would then have a an electric field wave and
a magnetic field wave moving at the same time, and
(06:32):
each one replenishes the other. The electric field, because it's
changing over time, generates a magnetic field. The magnetic field,
as it changes over time, regenerates the electric field, and
that's why it can continue at infinitum out into the
forest reaches of space until it hits the end of
the universe. Or we started getting reruns of I Love
(06:52):
Lucy from you know, a billion light years away. Yeah.
I remember hearing as a kid that the shows that
we watched we're going to be available out in space,
like people in Mars with the right equipment. Of course,
theoretically there aren't any people on Mars. I don't think
there are. Um, I wouldn't call them people, yeah, exactly. Um,
(07:16):
but yeah, if you had a TV and you were
you know, at that point they said, if you're watching
from Mars right now you would be catching reruns of
I Love Lucy. This was years ago, but I was going,
really seriously, that's that's very cool. So, uh, you know,
I hadn't realized that they would they would do that.
But on the same by the same token, if you
think about the giant radio telescopes that they use UM
(07:37):
to search for extraterrestrial life, some sign that other people
are using radio frequencies. Basically they're just listening to space
to see if there is something. I mean, there's there's lots,
there's noise. Besides, there's something that is generated in a
in a meaningful way as opposed to UM, because lots
of stuff produces radio waves, lots and lots of stuff. Uh.
(08:00):
And really, like I was saying, so, the the was
talking about electric field and the magnetic fields that that
are traveling in this electromagnetic wave. UM. The electric fields
they exert forces on electric charges, magnetic fields exert forces
on magnetic polls. So these waves can do work because
they can exert force upon particular things. In the case
(08:24):
of the electric field, of course, is the electrically charged particles.
That's the important part for radios. Without that, without the
the ability to do work. Radios wouldn't work at all.
We wouldn't be able to pick these things up. And
uh so that's really a fundamental element that you have
to understand before we can get into the mechanical and
(08:44):
technological elements of radio. Uh and uh so let's talk
a little bit about how how we get a radio
signal from a transmitter to a receiver. Alright, so you've
got a radio station and the radio station you are recording,
or you're you're trying to broadcast some sort of sound signal.
(09:07):
You are using a microphone, let's say. So let's say
this is a talk radio. So there's a guy talking
into a microphone. Uh. The I can't picture that, right, Yeah,
it's so hard to understand when you're facing someone doing it. Uh.
The mechanical waves from the sound of the voice go
into the microphone. They hit a little diaphragm which then
(09:28):
uh manipulates an electric charge, creating a frequency within that
electric charge, which then goes to a I'm simplifying here,
but but it goes to a transmitter, which then changes
this electric charge into one of two different um uh
kinds of radio signals. You've probably heard of a M
(09:49):
and FM. Yes, well it's not just two, but those
are the two weeks, those are the two years for broadcast. Yeah,
for for broadcast radio. Yes, yes, I'm I'm specifically talking
about the kind of radios where you tune in to
listen to music or or or talk or whatever. It's
not I'm not talking citizens band, I'm not talking any
of the other other kind of UM. Yeah, So, uh,
(10:13):
the way you you transmit information across those radio waves
depends on whether you're using a M or FM radio. Right,
you have to have a carrier wave, which is a
frequent a radio frequency wave that is able to hold
information and take it from the transmitter to the receiver. UM.
And basically it sort of depends on the frequency and amplitude.
(10:37):
That's that's exactly what a M and FM are. Its
amplitude modulation and frequency modulation. So with amplitude modulation, you
remember we were talking about a wave. You know, you
have the crests the trough, and the from crest to
crest is wavelength. Well, the the height I guess you
could say the height of the crests or the depth
of the trough, which are equivalent in the case of
(11:00):
these waves. UM. That is the amplitude, right. The bigger
the amplitude, the the taller those those waves are going
to look when you look at them as a wavelength. UM.
So with amplitude modulation, it's exactly what sounds like. You
you modify the amplitude to contain the uh, the information
that you're transmitting. When that information is received by a radio,
(11:23):
I'm gonna skip a little bit here. We're gonna go
back to the middle section in a minute. But when
your radio receives an A M signal, it's going to
detect it's going to detect the the height of those waves.
And as the height changes over time, that's going to
give the speaker in your radio the signal to move
in or out, and your speaker cone technically your speaker
(11:45):
cone in the speaker. As the speaker cone in your
speaker moves in and out, that's what generates the sound
you hear. So as those waves go up and uh
down in in amplitude uh, and they're gonna be doing
this uh thousands of of times per second because along
with the the crest trough and wavelength, you have the frequency.
(12:06):
The frequency is how many uh, how many cycles, how
many wavelengths you go through within a second. We call
that like, if you were to do one cycle a
second would be one hurts, right, so it kill hurts
is one thousand cycles in a second. A mega hurts
would be a million cycles in a second, a giga
hurts would be a billion cycles in a second. So
(12:27):
that's a lot. So you're at home. The radio has
detected the signal and it's detecting the difference in that amplitude,
and as that amplitude changes over time, that's what tells
the speaker how to uh to move in and out
and generate the sound that you hear. Frequency modulation is different.
The amplitude remains the same, it remains steady h So
(12:48):
you don't change the amplitude. That's not what tells the
speaker what the how to interpret that's that's signal to
turn it into sound. Instead, you you change the frequency
itself of the transmission, which is a little tricky because
to tune a radio you have to tune it into
a specific frequency to to really pick up a good signal. UH.
(13:10):
So it really generates it keeps it within a fairly
tight set of parameters. It can't go far beyond that,
or else you would no longer be able to pick
up the radio station. But by changing the frequency, that
is the the number of cycles that UM wavelength goes
through in a second, that's what tells the speaker how
(13:32):
to move in and out and generate the sound you hear.
Now we have to tackle the magical bit in the middle. Okay,
you know, so we've got you know, you've generated the
sound and you've heard the sound. But what's happening between
those two moments and there's some fascinating stuff here, and
we're gonna get into some science. Uh So, some apologies
to uh to Robert and Julie who would normally tackle
(13:55):
this kind of thing, but we're gonna do it. Um. So,
when you generate that signal at the transmitter, you actually
create an electric charge that moves up and down your
transmitter antenna. All right. So antenna are used for two
main purposes, to transmit signals and to receive signals. Yep.
And it's true too that, uh the type of frequency
(14:19):
you're using requires a different type of antenna. For example,
if you're broadcasting AM versus FM, it requires a different
antenna length because that has a lot to do with it.
And and if you've always wondered why, uh, you know,
I have a clock radio and it's got it basically
has an internal AM antenna, but it's got an external
FM antenna. And I didn't understand why until I you know,
(14:41):
I just really didn't care to look until we were
deciding to do this. And yeah, it has a lot
to do with the exactly what we were just talking
about or what you were just talking about, which is, uh,
the ways in which they and the carrier wave is
transmitted in these different technologies, so you know, you need
a different kind of antenna to transmit and to receive
(15:02):
those signals depending on what you're trying to do. And
in general, a general rule of thumb is the best
antenna to receive a signal is one quarter of the
length of the radio waves wavelength. But here's the thing.
AM radio that gets big. I mean AM radio can
be uh so big. That's larger than a football field.
(15:25):
And so having an AM radio antenna receiver antenna that's
a quarter the size of a football field is not
really on most people's list of home improvement UM projects.
So there are ways around that, but that's the ideal
length for a reception antenna. Now, when you when you
(15:48):
create this electric charge that's going up and down the
the antenna, you're actually you're using an oscillator to change
the charge. So you're you're essentially switching the charge. You're
you're switching voltage on and off up and down this
this antenna, and that electric charge has it changes over
time up and down the antenna. That's what creates the
electromagnetic wave that propagates out from the the transmitter antenna.
(16:13):
You know, I've watched a lot of movies where um uh,
you know you've got your giant radio antenna and these
little electrical things come out the top. You mean that's
not exactly right. No, you're thinking of our ko Ka
the old arcade. Yeah, no, you can't see them, although
it was. Although here's Here's the interesting thing though, is
that you can pick up you can receive electricity this way,
(16:36):
although it's a minuscule amount. In fact, that's that's the
basis of why this ends up working. So you you
pump lots and lots of electricity into this antenna. We're
talking about thousands of watts for for an a m station,
and you are using an oscillator to to move that
that electric charge up and down the antenna at a
(16:57):
certain rate. And UH, at that rate depends upon what
the FCC in the United States has designated as your
broadcast range. You broadcast your signal that way. Now, let's
say you want to pick that signal up. The electromagnetic waves, UH,
move out from that antenna, their directional, they move out
in every direction really from the antenna. Uh. And then
(17:20):
you are a certain distance away. You have your radio,
You've got your antenna extended up. As the electromagnetic waves
move towards your antenna, your antenna actually can we'll pick
up a little electrical charge because you've got you know,
the antenna. That's the whole reason why the radio works
is that electric field is able to enact the work
(17:44):
on an electric charge. You've got a little electric charge
inside that antenna. It alters. But due to this radio wave,
and assuming that you have your radio tune to the
right station, UH, what's gonna happen is the electric charge
in your antenna, your receptor antenna is going to move
up and down a certain frequency. If you have tuned
(18:05):
your radio properly, it's going to be at the circuit
in your radio is gonna be at a resonant frequency
with that charge that's moving up and down in your antenna. Now,
if you've heard about resonant frequencies, that's when you can
uh make something essentially vibrate at uh an ideal frequency
for stuff to go crazy like we we've seen. You know,
(18:29):
you might have seen a MythBusters episode where they started
talking about resonant frequencies. Yes, the idea being that us
should wind blow across a bridge at a particular frequency
of a particular speed. It would create this uh, this
sort of uh vicious cycle that feeds into itself where
the bridge itself starts to shake apart. Well, resonant frequencies
(18:51):
are a real thing, and if you do generate uh
the right resonant frequency, you can create a larger and
larger um uh vibrations in a medium. So think of
it kind of like you've got a kid on a
swing and you're pushing the kid on the swing. If
you push the kid at just the right time, the
kid's gonna go up higher each on each swing, Right,
(19:14):
You're you're adding more energy into it, and it's and
uh you see the output as the kid goes up higher.
If you push it the wrong time, the kid just
ends up drinking around and falling off the swing set
and crying like like I did. Thanks Dad. Anyway, uh So,
the the circuit in your radio, when you tune it,
(19:35):
you actually alter the circuit a little bit so that
it will resonate at a different frequency once it hits
the right frequency for the radio wave that's hitting your antenna.
Those little uh the electric charge is going up and
down your your antenna will cause a larger reaction within
the circuit in your radio, which is what you're is
picked up by the amplifier and then converted into um
(19:58):
sound through your speaker. Yeah. Yeah, So should we get
into some of the other cool stuff? Yeah, like hit
me with stereo. Oh man, I didn't even go into stereo.
I was. I was so concentrated on I want to
make sure I can explain the science of how this
radio wave moves across. Um. It's actually really fascinating stuff.
(20:19):
And all, you know what we should do before we
talk about stereo. Crystal radio. Okay, that's the simplest kind
of radio I can think of. As a matter of fact. Um,
when I was a kid, I had I probably still
do in the box somewhere a crystal radio kit. UM.
And yeah, when I was when I was doing a
little research. UM, one of the things that really lead
(20:40):
to radio being functional was UM the ability to when
they discovered the ability to tune a radio. It's like
I I don't want to just search for whatever. I
want to be able to lock it in to to
detect a specific UH signal. And and when they developed
the ability to tune a radio, that basically made UM
(21:02):
what is what is now the radio industry possible because
you can tune into a specific UH station and leave
it there and it's not going anywhere. UM. Of course,
you have to be very careful, especially if you're the
the licensing group. UM. Here in Atlanta there are tons
and tons of radio stations. And I had this problem
with UM. UM. I had an iPod with a broadcaster
(21:26):
that I used to use trying to play through my
radio rather than you know, hooking it up in some
way physically with a tape adapter or a plug or
something like that. And UH, you know, you have to
have a certain distance between stations for the signal not
to for the carrier waves not to bleed over and
and basically muddle the information in between. And I had
(21:47):
as I would drive around Atlanta, I would have to
change the station that my iPod broadcaster was broadcasting on
because um, you know, I would start to enter another
station more powerful signal would start to interfere with it,
and I would have to to do that. UM. So yeah,
this the crystal set that's really really basic. UM. In fact,
(22:09):
the one I got from radio Shack was basically, uh,
it was already hooked up, so to speak. It had
It was one of those that has the springs and
you you connect the wires using the springs. And if
you haven't seen these kits, um, you know, basic electronics
type kits. There's a h the board is wired underneath
and there are very tight, tightly coiled springs installed in
(22:31):
the top. And to make a connection from one point
to the other to finish your kit build the radio.
In this case, UM, you have wires that are um
uh not insulated on the very ends and you bend
the spring stick the end of the metal end of
the wire and let go and the spring holds it
into place. UM. And with that, you know, and I
had a long wire that I would use to pick
(22:52):
up a M signals. That would be your antenna. The antenna.
But yeah, if you're you know, if you don't know
what's going on, it looks sort of a lot the
other wires in the kit, but you know, you'd have
to extend it away, and and a small knob that
you would use to tune that. But it also had
a coil of metal. It looked like electromagnet. Yeah, I
can actually talk a little bit about that. There are
(23:13):
four basic components of a crystal radio. These are These
are literally the only four things you need to make
the most basic a M radio. You need an antenna,
so some sort of wire to act as an antenna.
That you need a tank circuit, which is what looked
like the electro magnet to you, I'm guessing, yes, you
(23:34):
need a diode, and and then you need an earphone
of some sort. In this case it was hardwired in
was one of those petty color uh you know, yeah,
and the and the and you don't need a battery.
And the reason you don't need a batteries because, like
I said, when you have the antenna, the electromagnetic field
(23:55):
will cause an electric charge to move up and down
that antenna on its own, it don't. You don't need
a battery to create that electricity from the start. Now,
the signal you're going to receive will be very weak,
even unless well the closer you get to the to
the radio station, the more powerful the signal will be,
but still be pretty weak. And but you're the human
ear is remarkably sensitive, so you'll be able to hear
(24:15):
the transmission even if the signal itself is weak. By
the way, Uh, this the fact that you are able
to to collect in a way, or that you're able
to receive electricity over the air this way, that was
one that was one thing that Tesla was obsessed about
the idea of broadcasting electricity and too, you're gonna find
if you do a search online, you'll find some um wow,
(24:41):
to call them Charlottean's might be too strong a word,
but you'll find some people who claim that they have
created a way to generate electricity through or transmit electricity
through through broadcast using this method. Well, it's true that
you can get electricity this way, but it's on such
a tiny amount that you would need a receptor antenna
(25:01):
that would be enormous in order to generate to receive
enough electricity for it to be enough to power a
light bulb even yeah, be basically a trickle. Yeah. So
so it's it's it's more likely than not if you
see someone who says that they have this new free
energy type thing where you're just gonna be pulling in
radio waves and changing that into electricity. And since since
(25:24):
so many things out in the universe create radio waves,
therefore it's almost free energy, be on alert because that's
not exactly true. I mean, you will get electricity that way,
but it won't be enough to do any real significant
work anyway. So you've got those four basic UH components.
So so the antenna UH projects up. It collects the
(25:45):
electromagnetic or into the electromagnetic fields that's passing by UM,
and then that creates the difference in charge up and
down the antenna. And then you've got the tank circuit,
which is it's a coil of wire and it's connected
at each end to the two ends of a capacitor.
So you've got a capacitor and UH and a coil
of wire. That's what a tank circuit is. And generally
(26:05):
the way you tune a radio is that you either
alter the coil, or you alter the capacitor, one of
the two most radios they work on. You know you
you are are changing one of those two elements in
order to tune the radio. Um. The diode is an
interesting electrical component. I'm not sure that we may have
(26:25):
talked about it in our Basics of Electronics podcast, but
I can't remember exactly I want to say we did.
But a diode it kind of a it's it's something
that allows electricity to flow one direction but not the
other way. It's like a it's like a one way
street in a way, and using that connected to the
tank circuit, and then you have the earphone connected through there.
(26:48):
That's what allows you to have have the right electric
signals sent to the earphone that then oscillates at the
right frequency to create the sound, and then you can
hear it. Although again it's gonna be very very faint.
It's not gonna be like, you know, hey, is that
freedom rockman? Will turn it up? Man? Do you remember
those commercials our listeners don't anyway for them? Yeah, you're
(27:13):
better off for it, but uh so, yes, so that
that I just wanted to talk about that since it's
the most basic and our listeners. If you're interested, you
can actually go out and find components and build one
of these yourselves. Uh. There's some places that sell the
kits um. Depending upon the electronics stores that maybe in
your area, you might even be able to buy the
(27:34):
the individual components and and build your own AM radio
from scratch that way. Now, keep in mind again this
is a very uh primitive and therefore um limited piece
of technology, and your your experience with it will depend
heavily on how close you are to the nearest a
UM transmitters, because the further way you are, the weaker
(27:58):
that signal is going to be, and it may get
to the point where you just can't get enough of
a signal to be able to hear the transmission. UM.
So yeah, I had a number of other related things
that I had been curious about. UM. One of them
was stereo, although not as much together. And stereo is
actually fairly simple um because basically you have the two
(28:20):
you have two microphones you absolutely uh well this will
be obvious really when you think about it. The stereo
signal has two separate channels, you know, one for the
left one for the right. UM. So that means you
would need more than one microphone, and uh, the trick
is that you have to you know, it essentially works
the same way that you have two feeds going into
the box and you know they go from the box
(28:42):
to the tower and through the air and back to
the thing. The thing is you have to make sure
that the wave is able to carrier wave is able
to handle that. And for a long time that was
only possible through frequency modulation UM just because it has
more capacity UM than AM UM. And you know, we
really didn't talk about the frequencies used. That's true. We
(29:05):
talked about in our CB radio I think I remember
we did talk about the electromagnetic spectrum and we talked
about which parts of the spectrum were allowed for H
for radio use. Yeah yeah, and that was years ago.
Yeah yeah, but yeah, you need that. That's one of
the reasons why. And I know that they were able
they promoted AM stereo some years ago. UM. But basically
(29:28):
the difference being that the frequency modulation signal is able
to carry more information. Therefore you can UH, you can
do that, but you have to UH to make it
possible and then carrier wave to carry a stereo signal
with more than one UH channel of information. Um, you
want to talk about the ionosphere any I was gonna
(29:49):
just mention that the ion a sphere. Uh. You might
wonder why at night you can hear radio stations much
further away, or at least in the evening, late evening
at dusk you can hear radio stations much further away
than normal, and that that does have to do with
the ionosphere. And uh, the ionosphere has its own sort
(30:12):
of Uh. Well, it's it's like an electric mirror in
a way. If if radio waves of a particular uh
frequency and and wavelength hit the ionosphere, they could be
reflected back down toward the Earth. And you can actually
bounce a radio signal off the ionosphere and back towards
the surface of the planet, and therefore it will travel
(30:33):
much further than it would just through line of sight. Yeah,
they discovered that in two Um. There were there were
a couple of people who were involved with that. Arthur
Edwin Kennelly who was an electrical electrical engineer in the
United States, and Oliver Heaviside from UH from England, was
a mathematician. Um. Again one of those situations. Uh, there
(30:54):
seems to be a lot of that in radio where
people sort of simultaneously discovered this UM and I got
lot of information from the article about radio and Britannica.
This is where I picked this particular bit up. But yeah,
they were the ones who u Ino had figured out
that UM you could basically transmit towards the sky and
the iono sphere would refract them back towards Earth and
(31:18):
that would help you extend the range of your transmitting. Yeah,
it's it's interesting because and during the daytime, the ionosphere,
the the electrically charged particles in the ionosphere, they don't
act as a very good electrical conductor. Uh. It's only
really once you hit UH in the early evening that's
when the conductivity actually improves. And we don't the ionosphere,
(31:41):
the magnetosphere, these elements of the the Earth's uh hesitate
to use the word ecosystem, but the these elements connected
to Earth are still things that we are learning about today.
So we don't have all the information on it because
scientists are still really building on the knowledge that we
already have. You gotta keep in mind that until until
(32:03):
a little over a hundred years ago, we didn't even
know these things existed, at least not in the way
we do now, and not in the level of detail, right.
I mean, we knew that compass has worked, but there
was you know, our our level of knowledge about the
magnetosphere was limited. We didn't know anything of the geomagnetic
storms and uh and how the Sun can affect our
(32:25):
own magnetosphere. So this is information that we're still building
on today. But yeah, so and in the evening, the
conductivity improves. That's what allows the the A M waves
to to bounce off the ionosphere and back on the Earth.
FM waves. By the way, the uh, the wavelength is
too small and the frequencies too high, they actually just
passed right through the atmosphere. They don't they don't bounce
(32:47):
back down. So that's why FM stations you aren't. You
aren't going to get that same effect. It's not like
at night you're gonna start picking up the FM station
from the city, you know, a hundred miles away, when
normally you'd have to be on top of the city
to pick it up. It's just not gonna happen. Yeah,
and um, I mean there are there are a lot
of differences too. I mean, you don't notice that the
(33:08):
changes um at nighttime with FM, so in such a
pronounced fashion. Le's not in my experience as you do
with AM. UM. There are a lot of things that
you can detect. AM is a lot more finicky. Also,
some radio gets dirtier at night. I noticed that, not
the programming. Oh sorry, I was thinking about all the
(33:28):
songs that I hear once, you know, once the primetime. Okay,
I'm clearly I'm off off base here, so but uh
but yeah. And also that the direction. You know, there
were in the United States clear channel stations that were
given more range, you know, to to go ahead and
keep broadcasting full strength at night, UM, whereas other stations
were asked to back off at certain times of the day. UM.
(33:52):
And something else I wanted to I know, we're getting
towards the end of our time, but something else I
wanted to, uh to point out was if you've ever
been in a car are like mine, for example, where
you want to tune into an AM station and it's
just a pain in the neck because you get a
lot of static. Well with that FIM stations you don't
have the interference from all kinds of things like for example,
(34:15):
UM power lines or lightning or lightning or in some
cases UM I would assume it's the rebar and overpasses
and stuff like that. Um, you know that are interfering
with your signal. You'll go under something and you get it,
you know sort of thing. Maybe they're electrical wires in
there that I didn't notice. But also spark plugs. My
(34:37):
spark plugs interfere with the AM signal. You know, if
you are in an area that has a lot of antenna,
you can actually get interference because the antenna, as the
electrical charge moves up and down the antenna while you're
receiving it, it's being it's being created by the electromagnetic field.
That means your antenna is also creating an electromagnetic field.
It's much it's a much lower powered electromagnetic field, but
(34:58):
there are enough antenna packed into a small enough space
that can create interference, uh for him, especially for AM transmissions. Yeah,
but but I have a station that I try to
listen to on a m every once in a while
and um, you know, catch the game from the local
sports team. And uh apparently yeah, um, apparently the the
(35:21):
spark plug in your car will when it fires, it
creates interference in a very high frequency range, which is
the thirty mega hurts range, and that's just at the
right frequency to seriously irritate the the AM signal and
cause problems. You know what's that that one right there?
(35:45):
Sorry everybody, I just blew up our listeners ears that
in the sixty cycle. Hum, Hey, Casey, can you lower
that a little bit so that they don't they don't
all write to me and complain thanks, You can just
uh if if the answer is yes, lower it a
little the answer is no, I'll direct all emails to Casey. Alright.
So there's a lot more to radio. There's tons more
(36:07):
and then and it gets into quite a bit of detail. Yeah,
but like I said, we we kind of gave the
the bird's eye view of the science on this. So
but it's really fascinating stuff. We do have an article
on the site about how radio works. Um, there are
plenty of other sites out there that that discuss radio
and the technology behind it, the science behind it. Uh.
(36:28):
There's a Center for Cosmological Physics has a a great
summary on it. It was it was for a summer program, uh,
the Yerkey's Summer Institute two thousand two program. But they
have a a PDF document that's available online. So if
you do a search for uh cosmological physics radio wave basics,
(36:49):
it'll tell you not just the radio wave basics the
science behind it, but also the actual basics behind radios themselves.
So that's a that's a helpful guide, and it was
it was made for science classes who were going out
and actually doing creating their own radios and kind of
explaining the science behind it. So I recommend a read
(37:09):
of that if if you want to get a little
more information. And of course, like I said, there's tons
of of of references out there on the web that
you can use. So we're gonna wrap this discussion up.
If you guys have any suggestions for topics that we
should tackle, let us know on Twitter and Facebook are handled.
There is tech Stuff hs W, or you can send
us an email and that address is text stuff at
(37:32):
how stuff works dot com. Chris and I will talk
to you again really soon. Be sure to check out
our new video podcast, Stuff from the Future. Join how
Stuff Work staff as we explore the most promising and
perplexing possibilities of tomorrow. The How Stuff Works iPhone app
has arrived. Download it today on iTunes. Brought to you
(37:58):
by the reinvented two thousand and twelve camera. It's ready,
Are you
Brought to you by the reinvented two thousand twelve camera.
It's ready. Are you get in touch with technology with
tech Stuff from how stuff works dot com. Hello again, everyone,
Welcome to tech stuff. My name is Chris Pollett, and
(00:20):
I'm an editor here at how stuff works dot Com.
Broadcasting from the seat across from me, as usual, is
senior writer Jonathan Striffland. You gave them all those old
time stars through wars of worlds invaded by Mars. You
made him laugh, you made him cry, you made us
feel like we could fly. Just remember video killed the
(00:42):
radio stars. But for now, we're still going to talk
about radio. Yeah, and you guys might remember not that
long ago, we did a podcast about who invented the
radio and we came up with a conclusion of I
don't know, although actually Chris and I both agreed that
if if gun were held to our heads, we would
(01:02):
we would claim that Tesla was the the inventor of
the radio. It's just that he did not He was
not able to implement it in the same sort of
scale as Marconi, whose implementation depended somewhat on Tesla's work.
But yeah, but it had gone on for some time
there were a number of people as and and this
happens a lot in science that uh, you know, their
(01:26):
contributions made radio possible. They were it was sort of
invented in increments really. Um. And of course Tesla was
a very prolific inventor. He had his fingers and lots
of different pies. I'm sorry, I had to watch Jonathan's
high clay everyone, and um, I'm having a little moment here.
(01:46):
And Marconi was was really a radio guy. He really
was interested in radio. So it's it's really kind of
no surprise that he really pushed radio very hard, harder
than Tesla did, and so he got a lot of
the credit for it. But um, we were going to
talk today about the invention itself, how radio itself actually works,
(02:08):
and to really talk about this first we have to
understand a little bit about radio frequencies, radio waves, and
uh so let's talk about radio waves first. Now, waves
are this is a complicated issue because there are different
types of waves, right. There's there are mechanical waves, which
(02:29):
are the waves that we can observe with our own
eyes through various means. Like there's you know, if you
look at a notion and you see the waves coming across.
Those are mechanical waves. Due, yes, they are, in fact
gnarly During an earthquake, the earth moves in mechanical waves, yes,
and sound travels through mechanical waves. But yeah, now you
(02:50):
may not think of sound as a mechanical wave because
it's not something that you can typically see. Although if
there is a sound loud enough, it can create a
mechanical wave powerful enough to vibrate uh an objects. So
you can see that, right, Well, you could see um
if you've ever watched videos of explosions, especially when a
video shot from overhead, you can see the shock wave, yeah,
(03:14):
traveling outward from that, which is you watch any Michael
bay movie, the moment where the two heroes running away
from the explosion leap into air and are propelled fifty
feet that is kind of what Chris is talking about. Okay,
that was an even better description than the one I
had Michael Bays solves. Anyway, So yeah, so these waves
(03:35):
they move, they move, and uh there's a crest and
then there's a trough, right, the crest being the highest point,
the trough being the lowest point. And you consider the
point from the top of one crest to the top
of the next crest, the wave length of that wave, right,
all right, So these these mechanical waves, they have to have, uh,
some sort of of medium to move through. They require that.
(03:58):
Even sound, which is why if you were to be
in outer space and you were to take off your
space helmet and shout to your buddy across the way, Uh,
your buddy would not hear you, because there is no
medium there spaces of vacuum. More or less. There are
particles in space, but they're so far there's there's so little,
(04:19):
there's no contact. Right. The particles in space are are
so far apart from one another that there's no way
to to propagate a mechanical wave through space. I think
we understand the lack of gravity in this situation, thank you.
So yeah, nature of hors a vacuum, so do I.
That's why I only sweep vacuum. So anyway, Yeah, you
need a medium for a mechanical wave to to move through.
(04:41):
But electromagnetic waves are different. They do not require that.
They can they can propagate through a vacuum. They can
move through the vacuum space and in fact, they will
continue to move once generated forever. Really Um, so the
radio waves that we generated way back when we were
first figuring this out, they are now, oh well, let's see,
(05:04):
more than around a hundred light years away, because radio
waves travel at the speed of light. And then you know,
the invention of the radio really dates back a century.
So anything around there, anything generated at that time, would
now be traveling a hundred light years away. It's kind
of cool. Yeah, yeah, because it travels the speed of light. Okay,
(05:25):
so all those all those broadcasts in the forties and
fifties of the radio cereals, those are now forty fifty
light years away. Cereal. Um yeah, it's Chris's weakness was
cereal is like my weakness with pie. So don't don't
get me wrong. I like the pie. So yeah, I
mean light and and radio waves are both forms of
electromagnetic radiation. Um, and it's I had something I was
(05:48):
gonna say there, I've got something here. So when we
say electromagnetic that's really important. Now, when you're talking about
a mechanical wave, you're talking about a wave and a
particular our alignment. Let's let's say vertical, you know, like
waves you would see on a notion. Electromagnetic waves are
actually a pair of waves. There's an electric field wave
(06:11):
and a magnetic field wave. Now you've heard us talk
a lot about the relationship between electricity and magnetism and
how there is this interesting connection between the two. As
it turns out, if you were to generate an electromagnetic wave,
you would then have a an electric field wave and
a magnetic field wave moving at the same time, and
(06:32):
each one replenishes the other. The electric field, because it's
changing over time, generates a magnetic field. The magnetic field,
as it changes over time, regenerates the electric field, and
that's why it can continue at infinitum out into the
forest reaches of space until it hits the end of
the universe. Or we started getting reruns of I Love
(06:52):
Lucy from you know, a billion light years away. Yeah.
I remember hearing as a kid that the shows that
we watched we're going to be available out in space,
like people in Mars with the right equipment. Of course,
theoretically there aren't any people on Mars. I don't think
there are. Um, I wouldn't call them people, yeah, exactly. Um,
(07:16):
but yeah, if you had a TV and you were
you know, at that point they said, if you're watching
from Mars right now you would be catching reruns of
I Love Lucy. This was years ago, but I was going,
really seriously, that's that's very cool. So, uh, you know,
I hadn't realized that they would they would do that.
But on the same by the same token, if you
think about the giant radio telescopes that they use UM
(07:37):
to search for extraterrestrial life, some sign that other people
are using radio frequencies. Basically they're just listening to space
to see if there is something. I mean, there's there's lots,
there's noise. Besides, there's something that is generated in a
in a meaningful way as opposed to UM, because lots
of stuff produces radio waves, lots and lots of stuff. Uh.
(08:00):
And really, like I was saying, so, the the was
talking about electric field and the magnetic fields that that
are traveling in this electromagnetic wave. UM. The electric fields
they exert forces on electric charges, magnetic fields exert forces
on magnetic polls. So these waves can do work because
they can exert force upon particular things. In the case
(08:24):
of the electric field, of course, is the electrically charged particles.
That's the important part for radios. Without that, without the
the ability to do work. Radios wouldn't work at all.
We wouldn't be able to pick these things up. And
uh so that's really a fundamental element that you have
to understand before we can get into the mechanical and
(08:44):
technological elements of radio. Uh and uh so let's talk
a little bit about how how we get a radio
signal from a transmitter to a receiver. Alright, so you've
got a radio station and the radio station you are recording,
or you're you're trying to broadcast some sort of sound signal.
(09:07):
You are using a microphone, let's say. So let's say
this is a talk radio. So there's a guy talking
into a microphone. Uh. The I can't picture that, right, Yeah,
it's so hard to understand when you're facing someone doing it. Uh.
The mechanical waves from the sound of the voice go
into the microphone. They hit a little diaphragm which then
(09:28):
uh manipulates an electric charge, creating a frequency within that
electric charge, which then goes to a I'm simplifying here,
but but it goes to a transmitter, which then changes
this electric charge into one of two different um uh
kinds of radio signals. You've probably heard of a M
(09:49):
and FM. Yes, well it's not just two, but those
are the two weeks, those are the two years for broadcast. Yeah,
for for broadcast radio. Yes, yes, I'm I'm specifically talking
about the kind of radios where you tune in to
listen to music or or or talk or whatever. It's
not I'm not talking citizens band, I'm not talking any
of the other other kind of UM. Yeah, So, uh,
(10:13):
the way you you transmit information across those radio waves
depends on whether you're using a M or FM radio. Right,
you have to have a carrier wave, which is a
frequent a radio frequency wave that is able to hold
information and take it from the transmitter to the receiver. UM.
And basically it sort of depends on the frequency and amplitude.
(10:37):
That's that's exactly what a M and FM are. Its
amplitude modulation and frequency modulation. So with amplitude modulation, you
remember we were talking about a wave. You know, you
have the crests the trough, and the from crest to
crest is wavelength. Well, the the height I guess you
could say the height of the crests or the depth
of the trough, which are equivalent in the case of
(11:00):
these waves. UM. That is the amplitude, right. The bigger
the amplitude, the the taller those those waves are going
to look when you look at them as a wavelength. UM.
So with amplitude modulation, it's exactly what sounds like. You
you modify the amplitude to contain the uh, the information
that you're transmitting. When that information is received by a radio,
(11:23):
I'm gonna skip a little bit here. We're gonna go
back to the middle section in a minute. But when
your radio receives an A M signal, it's going to
detect it's going to detect the the height of those waves.
And as the height changes over time, that's going to
give the speaker in your radio the signal to move
in or out, and your speaker cone technically your speaker
(11:45):
cone in the speaker. As the speaker cone in your
speaker moves in and out, that's what generates the sound
you hear. So as those waves go up and uh
down in in amplitude uh, and they're gonna be doing
this uh thousands of of times per second because along
with the the crest trough and wavelength, you have the frequency.
(12:06):
The frequency is how many uh, how many cycles, how
many wavelengths you go through within a second. We call
that like, if you were to do one cycle a
second would be one hurts, right, so it kill hurts
is one thousand cycles in a second. A mega hurts
would be a million cycles in a second, a giga
hurts would be a billion cycles in a second. So
(12:27):
that's a lot. So you're at home. The radio has
detected the signal and it's detecting the difference in that amplitude,
and as that amplitude changes over time, that's what tells
the speaker how to uh to move in and out
and generate the sound that you hear. Frequency modulation is different.
The amplitude remains the same, it remains steady h So
(12:48):
you don't change the amplitude. That's not what tells the
speaker what the how to interpret that's that's signal to
turn it into sound. Instead, you you change the frequency
itself of the transmission, which is a little tricky because
to tune a radio you have to tune it into
a specific frequency to to really pick up a good signal. UH.
(13:10):
So it really generates it keeps it within a fairly
tight set of parameters. It can't go far beyond that,
or else you would no longer be able to pick
up the radio station. But by changing the frequency, that
is the the number of cycles that UM wavelength goes
through in a second, that's what tells the speaker how
(13:32):
to move in and out and generate the sound you hear.
Now we have to tackle the magical bit in the middle. Okay,
you know, so we've got you know, you've generated the
sound and you've heard the sound. But what's happening between
those two moments and there's some fascinating stuff here, and
we're gonna get into some science. Uh So, some apologies
to uh to Robert and Julie who would normally tackle
(13:55):
this kind of thing, but we're gonna do it. Um. So,
when you generate that signal at the transmitter, you actually
create an electric charge that moves up and down your
transmitter antenna. All right. So antenna are used for two
main purposes, to transmit signals and to receive signals. Yep.
And it's true too that, uh the type of frequency
(14:19):
you're using requires a different type of antenna. For example,
if you're broadcasting AM versus FM, it requires a different
antenna length because that has a lot to do with it.
And and if you've always wondered why, uh, you know,
I have a clock radio and it's got it basically
has an internal AM antenna, but it's got an external
FM antenna. And I didn't understand why until I you know,
(14:41):
I just really didn't care to look until we were
deciding to do this. And yeah, it has a lot
to do with the exactly what we were just talking
about or what you were just talking about, which is, uh,
the ways in which they and the carrier wave is
transmitted in these different technologies, so you know, you need
a different kind of antenna to transmit and to receive
(15:02):
those signals depending on what you're trying to do. And
in general, a general rule of thumb is the best
antenna to receive a signal is one quarter of the
length of the radio waves wavelength. But here's the thing.
AM radio that gets big. I mean AM radio can
be uh so big. That's larger than a football field.
(15:25):
And so having an AM radio antenna receiver antenna that's
a quarter the size of a football field is not
really on most people's list of home improvement UM projects.
So there are ways around that, but that's the ideal
length for a reception antenna. Now, when you when you
(15:48):
create this electric charge that's going up and down the
the antenna, you're actually you're using an oscillator to change
the charge. So you're you're essentially switching the charge. You're
you're switching voltage on and off up and down this
this antenna, and that electric charge has it changes over
time up and down the antenna. That's what creates the
electromagnetic wave that propagates out from the the transmitter antenna.
(16:13):
You know, I've watched a lot of movies where um uh,
you know you've got your giant radio antenna and these
little electrical things come out the top. You mean that's
not exactly right. No, you're thinking of our ko Ka
the old arcade. Yeah, no, you can't see them, although
it was. Although here's Here's the interesting thing though, is
that you can pick up you can receive electricity this way,
(16:36):
although it's a minuscule amount. In fact, that's that's the
basis of why this ends up working. So you you
pump lots and lots of electricity into this antenna. We're
talking about thousands of watts for for an a m station,
and you are using an oscillator to to move that
that electric charge up and down the antenna at a
(16:57):
certain rate. And UH, at that rate depends upon what
the FCC in the United States has designated as your
broadcast range. You broadcast your signal that way. Now, let's
say you want to pick that signal up. The electromagnetic waves, UH,
move out from that antenna, their directional, they move out
in every direction really from the antenna. Uh. And then
(17:20):
you are a certain distance away. You have your radio,
You've got your antenna extended up. As the electromagnetic waves
move towards your antenna, your antenna actually can we'll pick
up a little electrical charge because you've got you know,
the antenna. That's the whole reason why the radio works
is that electric field is able to enact the work
(17:44):
on an electric charge. You've got a little electric charge
inside that antenna. It alters. But due to this radio wave,
and assuming that you have your radio tune to the
right station, UH, what's gonna happen is the electric charge
in your antenna, your receptor antenna is going to move
up and down a certain frequency. If you have tuned
(18:05):
your radio properly, it's going to be at the circuit
in your radio is gonna be at a resonant frequency
with that charge that's moving up and down in your antenna. Now,
if you've heard about resonant frequencies, that's when you can
uh make something essentially vibrate at uh an ideal frequency
for stuff to go crazy like we we've seen. You know,
(18:29):
you might have seen a MythBusters episode where they started
talking about resonant frequencies. Yes, the idea being that us
should wind blow across a bridge at a particular frequency
of a particular speed. It would create this uh, this
sort of uh vicious cycle that feeds into itself where
the bridge itself starts to shake apart. Well, resonant frequencies
(18:51):
are a real thing, and if you do generate uh
the right resonant frequency, you can create a larger and
larger um uh vibrations in a medium. So think of
it kind of like you've got a kid on a
swing and you're pushing the kid on the swing. If
you push the kid at just the right time, the
kid's gonna go up higher each on each swing, Right,
(19:14):
You're you're adding more energy into it, and it's and
uh you see the output as the kid goes up higher.
If you push it the wrong time, the kid just
ends up drinking around and falling off the swing set
and crying like like I did. Thanks Dad. Anyway, uh So,
the the circuit in your radio, when you tune it,
(19:35):
you actually alter the circuit a little bit so that
it will resonate at a different frequency once it hits
the right frequency for the radio wave that's hitting your antenna.
Those little uh the electric charge is going up and
down your your antenna will cause a larger reaction within
the circuit in your radio, which is what you're is
picked up by the amplifier and then converted into um
(19:58):
sound through your speaker. Yeah. Yeah, So should we get
into some of the other cool stuff? Yeah, like hit
me with stereo. Oh man, I didn't even go into stereo.
I was. I was so concentrated on I want to
make sure I can explain the science of how this
radio wave moves across. Um. It's actually really fascinating stuff.
(20:19):
And all, you know what we should do before we
talk about stereo. Crystal radio. Okay, that's the simplest kind
of radio I can think of. As a matter of fact. Um,
when I was a kid, I had I probably still
do in the box somewhere a crystal radio kit. UM.
And yeah, when I was when I was doing a
little research. UM, one of the things that really lead
(20:40):
to radio being functional was UM the ability to when
they discovered the ability to tune a radio. It's like
I I don't want to just search for whatever. I
want to be able to lock it in to to
detect a specific UH signal. And and when they developed
the ability to tune a radio, that basically made UM
(21:02):
what is what is now the radio industry possible because
you can tune into a specific UH station and leave
it there and it's not going anywhere. UM. Of course,
you have to be very careful, especially if you're the
the licensing group. UM. Here in Atlanta there are tons
and tons of radio stations. And I had this problem
with UM. UM. I had an iPod with a broadcaster
(21:26):
that I used to use trying to play through my
radio rather than you know, hooking it up in some
way physically with a tape adapter or a plug or
something like that. And UH, you know, you have to
have a certain distance between stations for the signal not
to for the carrier waves not to bleed over and
and basically muddle the information in between. And I had
(21:47):
as I would drive around Atlanta, I would have to
change the station that my iPod broadcaster was broadcasting on
because um, you know, I would start to enter another
station more powerful signal would start to interfere with it,
and I would have to to do that. UM. So yeah,
this the crystal set that's really really basic. UM. In fact,
(22:09):
the one I got from radio Shack was basically, uh,
it was already hooked up, so to speak. It had
It was one of those that has the springs and
you you connect the wires using the springs. And if
you haven't seen these kits, um, you know, basic electronics
type kits. There's a h the board is wired underneath
and there are very tight, tightly coiled springs installed in
(22:31):
the top. And to make a connection from one point
to the other to finish your kit build the radio.
In this case, UM, you have wires that are um
uh not insulated on the very ends and you bend
the spring stick the end of the metal end of
the wire and let go and the spring holds it
into place. UM. And with that, you know, and I
had a long wire that I would use to pick
(22:52):
up a M signals. That would be your antenna. The antenna.
But yeah, if you're you know, if you don't know
what's going on, it looks sort of a lot the
other wires in the kit, but you know, you'd have
to extend it away, and and a small knob that
you would use to tune that. But it also had
a coil of metal. It looked like electromagnet. Yeah, I
can actually talk a little bit about that. There are
(23:13):
four basic components of a crystal radio. These are These
are literally the only four things you need to make
the most basic a M radio. You need an antenna,
so some sort of wire to act as an antenna.
That you need a tank circuit, which is what looked
like the electro magnet to you, I'm guessing, yes, you
(23:34):
need a diode, and and then you need an earphone
of some sort. In this case it was hardwired in
was one of those petty color uh you know, yeah,
and the and the and you don't need a battery.
And the reason you don't need a batteries because, like
I said, when you have the antenna, the electromagnetic field
(23:55):
will cause an electric charge to move up and down
that antenna on its own, it don't. You don't need
a battery to create that electricity from the start. Now,
the signal you're going to receive will be very weak,
even unless well the closer you get to the to
the radio station, the more powerful the signal will be,
but still be pretty weak. And but you're the human
ear is remarkably sensitive, so you'll be able to hear
(24:15):
the transmission even if the signal itself is weak. By
the way, Uh, this the fact that you are able
to to collect in a way, or that you're able
to receive electricity over the air this way, that was
one that was one thing that Tesla was obsessed about
the idea of broadcasting electricity and too, you're gonna find
if you do a search online, you'll find some um wow,
(24:41):
to call them Charlottean's might be too strong a word,
but you'll find some people who claim that they have
created a way to generate electricity through or transmit electricity
through through broadcast using this method. Well, it's true that
you can get electricity this way, but it's on such
a tiny amount that you would need a receptor antenna
(25:01):
that would be enormous in order to generate to receive
enough electricity for it to be enough to power a
light bulb even yeah, be basically a trickle. Yeah. So
so it's it's it's more likely than not if you
see someone who says that they have this new free
energy type thing where you're just gonna be pulling in
radio waves and changing that into electricity. And since since
(25:24):
so many things out in the universe create radio waves,
therefore it's almost free energy, be on alert because that's
not exactly true. I mean, you will get electricity that way,
but it won't be enough to do any real significant
work anyway. So you've got those four basic UH components.
So so the antenna UH projects up. It collects the
(25:45):
electromagnetic or into the electromagnetic fields that's passing by UM,
and then that creates the difference in charge up and
down the antenna. And then you've got the tank circuit,
which is it's a coil of wire and it's connected
at each end to the two ends of a capacitor.
So you've got a capacitor and UH and a coil
of wire. That's what a tank circuit is. And generally
(26:05):
the way you tune a radio is that you either
alter the coil, or you alter the capacitor, one of
the two most radios they work on. You know you
you are are changing one of those two elements in
order to tune the radio. Um. The diode is an
interesting electrical component. I'm not sure that we may have
(26:25):
talked about it in our Basics of Electronics podcast, but
I can't remember exactly I want to say we did.
But a diode it kind of a it's it's something
that allows electricity to flow one direction but not the
other way. It's like a it's like a one way
street in a way, and using that connected to the
tank circuit, and then you have the earphone connected through there.
(26:48):
That's what allows you to have have the right electric
signals sent to the earphone that then oscillates at the
right frequency to create the sound, and then you can
hear it. Although again it's gonna be very very faint.
It's not gonna be like, you know, hey, is that
freedom rockman? Will turn it up? Man? Do you remember
those commercials our listeners don't anyway for them? Yeah, you're
(27:13):
better off for it, but uh so, yes, so that
that I just wanted to talk about that since it's
the most basic and our listeners. If you're interested, you
can actually go out and find components and build one
of these yourselves. Uh. There's some places that sell the
kits um. Depending upon the electronics stores that maybe in
your area, you might even be able to buy the
(27:34):
the individual components and and build your own AM radio
from scratch that way. Now, keep in mind again this
is a very uh primitive and therefore um limited piece
of technology, and your your experience with it will depend
heavily on how close you are to the nearest a
UM transmitters, because the further way you are, the weaker
(27:58):
that signal is going to be, and it may get
to the point where you just can't get enough of
a signal to be able to hear the transmission. UM.
So yeah, I had a number of other related things
that I had been curious about. UM. One of them
was stereo, although not as much together. And stereo is
actually fairly simple um because basically you have the two
(28:20):
you have two microphones you absolutely uh well this will
be obvious really when you think about it. The stereo
signal has two separate channels, you know, one for the
left one for the right. UM. So that means you
would need more than one microphone, and uh, the trick
is that you have to you know, it essentially works
the same way that you have two feeds going into
the box and you know they go from the box
(28:42):
to the tower and through the air and back to
the thing. The thing is you have to make sure
that the wave is able to carrier wave is able
to handle that. And for a long time that was
only possible through frequency modulation UM just because it has
more capacity UM than AM UM. And you know, we
really didn't talk about the frequencies used. That's true. We
(29:05):
talked about in our CB radio I think I remember
we did talk about the electromagnetic spectrum and we talked
about which parts of the spectrum were allowed for H
for radio use. Yeah yeah, and that was years ago.
Yeah yeah, but yeah, you need that. That's one of
the reasons why. And I know that they were able
they promoted AM stereo some years ago. UM. But basically
(29:28):
the difference being that the frequency modulation signal is able
to carry more information. Therefore you can UH, you can
do that, but you have to UH to make it
possible and then carrier wave to carry a stereo signal
with more than one UH channel of information. Um, you
want to talk about the ionosphere any I was gonna
(29:49):
just mention that the ion a sphere. Uh. You might
wonder why at night you can hear radio stations much
further away, or at least in the evening, late evening
at dusk you can hear radio stations much further away
than normal, and that that does have to do with
the ionosphere. And uh, the ionosphere has its own sort
(30:12):
of Uh. Well, it's it's like an electric mirror in
a way. If if radio waves of a particular uh
frequency and and wavelength hit the ionosphere, they could be
reflected back down toward the Earth. And you can actually
bounce a radio signal off the ionosphere and back towards
the surface of the planet, and therefore it will travel
(30:33):
much further than it would just through line of sight. Yeah,
they discovered that in two Um. There were there were
a couple of people who were involved with that. Arthur
Edwin Kennelly who was an electrical electrical engineer in the
United States, and Oliver Heaviside from UH from England, was
a mathematician. Um. Again one of those situations. Uh, there
(30:54):
seems to be a lot of that in radio where
people sort of simultaneously discovered this UM and I got
lot of information from the article about radio and Britannica.
This is where I picked this particular bit up. But yeah,
they were the ones who u Ino had figured out
that UM you could basically transmit towards the sky and
the iono sphere would refract them back towards Earth and
(31:18):
that would help you extend the range of your transmitting. Yeah,
it's it's interesting because and during the daytime, the ionosphere,
the the electrically charged particles in the ionosphere, they don't
act as a very good electrical conductor. Uh. It's only
really once you hit UH in the early evening that's
when the conductivity actually improves. And we don't the ionosphere,
(31:41):
the magnetosphere, these elements of the the Earth's uh hesitate
to use the word ecosystem, but the these elements connected
to Earth are still things that we are learning about today.
So we don't have all the information on it because
scientists are still really building on the knowledge that we
already have. You gotta keep in mind that until until
(32:03):
a little over a hundred years ago, we didn't even
know these things existed, at least not in the way
we do now, and not in the level of detail, right.
I mean, we knew that compass has worked, but there
was you know, our our level of knowledge about the
magnetosphere was limited. We didn't know anything of the geomagnetic
storms and uh and how the Sun can affect our
(32:25):
own magnetosphere. So this is information that we're still building
on today. But yeah, so and in the evening, the
conductivity improves. That's what allows the the A M waves
to to bounce off the ionosphere and back on the Earth.
FM waves. By the way, the uh, the wavelength is
too small and the frequencies too high, they actually just
passed right through the atmosphere. They don't they don't bounce
(32:47):
back down. So that's why FM stations you aren't. You
aren't going to get that same effect. It's not like
at night you're gonna start picking up the FM station
from the city, you know, a hundred miles away, when
normally you'd have to be on top of the city
to pick it up. It's just not gonna happen. Yeah,
and um, I mean there are there are a lot
of differences too. I mean, you don't notice that the
(33:08):
changes um at nighttime with FM, so in such a
pronounced fashion. Le's not in my experience as you do
with AM. UM. There are a lot of things that
you can detect. AM is a lot more finicky. Also,
some radio gets dirtier at night. I noticed that, not
the programming. Oh sorry, I was thinking about all the
(33:28):
songs that I hear once, you know, once the primetime. Okay,
I'm clearly I'm off off base here, so but uh
but yeah. And also that the direction. You know, there
were in the United States clear channel stations that were
given more range, you know, to to go ahead and
keep broadcasting full strength at night, UM, whereas other stations
were asked to back off at certain times of the day. UM.
(33:52):
And something else I wanted to I know, we're getting
towards the end of our time, but something else I
wanted to, uh to point out was if you've ever
been in a car are like mine, for example, where
you want to tune into an AM station and it's
just a pain in the neck because you get a
lot of static. Well with that FIM stations you don't
have the interference from all kinds of things like for example,
(34:15):
UM power lines or lightning or lightning or in some
cases UM I would assume it's the rebar and overpasses
and stuff like that. Um, you know that are interfering
with your signal. You'll go under something and you get it,
you know sort of thing. Maybe they're electrical wires in
there that I didn't notice. But also spark plugs. My
(34:37):
spark plugs interfere with the AM signal. You know, if
you are in an area that has a lot of antenna,
you can actually get interference because the antenna, as the
electrical charge moves up and down the antenna while you're
receiving it, it's being it's being created by the electromagnetic field.
That means your antenna is also creating an electromagnetic field.
It's much it's a much lower powered electromagnetic field, but
(34:58):
there are enough antenna packed into a small enough space
that can create interference, uh for him, especially for AM transmissions. Yeah,
but but I have a station that I try to
listen to on a m every once in a while
and um, you know, catch the game from the local
sports team. And uh apparently yeah, um, apparently the the
(35:21):
spark plug in your car will when it fires, it
creates interference in a very high frequency range, which is
the thirty mega hurts range, and that's just at the
right frequency to seriously irritate the the AM signal and
cause problems. You know what's that that one right there?
(35:45):
Sorry everybody, I just blew up our listeners ears that
in the sixty cycle. Hum, Hey, Casey, can you lower
that a little bit so that they don't they don't
all write to me and complain thanks, You can just
uh if if the answer is yes, lower it a
little the answer is no, I'll direct all emails to Casey. Alright.
So there's a lot more to radio. There's tons more
(36:07):
and then and it gets into quite a bit of detail. Yeah,
but like I said, we we kind of gave the
the bird's eye view of the science on this. So
but it's really fascinating stuff. We do have an article
on the site about how radio works. Um, there are
plenty of other sites out there that that discuss radio
and the technology behind it, the science behind it. Uh.
(36:28):
There's a Center for Cosmological Physics has a a great
summary on it. It was it was for a summer program, uh,
the Yerkey's Summer Institute two thousand two program. But they
have a a PDF document that's available online. So if
you do a search for uh cosmological physics radio wave basics,
(36:49):
it'll tell you not just the radio wave basics the
science behind it, but also the actual basics behind radios themselves.
So that's a that's a helpful guide, and it was
it was made for science classes who were going out
and actually doing creating their own radios and kind of
explaining the science behind it. So I recommend a read
(37:09):
of that if if you want to get a little
more information. And of course, like I said, there's tons
of of of references out there on the web that
you can use. So we're gonna wrap this discussion up.
If you guys have any suggestions for topics that we
should tackle, let us know on Twitter and Facebook are handled.
There is tech Stuff hs W, or you can send
us an email and that address is text stuff at
(37:32):
how stuff works dot com. Chris and I will talk
to you again really soon. Be sure to check out
our new video podcast, Stuff from the Future. Join how
Stuff Work staff as we explore the most promising and
perplexing possibilities of tomorrow. The How Stuff Works iPhone app
has arrived. Download it today on iTunes. Brought to you
(37:58):
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