How a Car Radio Works
03-26-18, 03:44 PM
#1
Lexus Champion
Thread Starter
How a Car Radio Works
I took apart a Toyota radio to see what's inside and how it works. I made a short video on the simplified way it works, of course new radios are more complex:
The radio I took apart was a single DIN, AM/FM/CD radio:
Radio lid removed:
The main motherboard has a number of main components that make up the radio, including the antenna input, the demodulator, tuner, equalizer, micro-controller, amplifier, communication bus controller, human interface input/output, power distribution and CD ROM input:
Here's an overall system diagram of how things are laid out and work inside the radio:
Here's a closer look at the radio tuner (digital) and the demodulator:
If you remember physics class, AM stands for amplitude modulation, and FM stands for frequency modulation. Basically the amplitude or frequency of the radio waves are varied in order to carry a signal, which the demodulator turns into a voltage audio signal:
This is the back of the human interface board, including the LCD driver and buttons:
Moving on to the CD drive, there's 3 motors, one to turn the CD, one to load the tray, and one to move the laser head along the radius of the disk:
Closer look at the laser head:
Here's an overview of how it works, essentially light is reflected back based on the information burned onto the disk. A photo sensor pics up this light and turns that into usable information:
The last piece to a stereo is its output in the form of sound. This is done by repeatedly moving a paper cone back and forth at high frequency. This creates pressure waves in the air which we hear as sound.
The paper cone is controlled by an electromagnet:
And that's pretty much the very basics of how a car stereo works!
- Enjoy
The radio I took apart was a single DIN, AM/FM/CD radio:
Radio lid removed:
The main motherboard has a number of main components that make up the radio, including the antenna input, the demodulator, tuner, equalizer, micro-controller, amplifier, communication bus controller, human interface input/output, power distribution and CD ROM input:
Here's an overall system diagram of how things are laid out and work inside the radio:
Here's a closer look at the radio tuner (digital) and the demodulator:
If you remember physics class, AM stands for amplitude modulation, and FM stands for frequency modulation. Basically the amplitude or frequency of the radio waves are varied in order to carry a signal, which the demodulator turns into a voltage audio signal:
This is the back of the human interface board, including the LCD driver and buttons:
Moving on to the CD drive, there's 3 motors, one to turn the CD, one to load the tray, and one to move the laser head along the radius of the disk:
Closer look at the laser head:
Here's an overview of how it works, essentially light is reflected back based on the information burned onto the disk. A photo sensor pics up this light and turns that into usable information:
The last piece to a stereo is its output in the form of sound. This is done by repeatedly moving a paper cone back and forth at high frequency. This creates pressure waves in the air which we hear as sound.
The paper cone is controlled by an electromagnet:
And that's pretty much the very basics of how a car stereo works!
- Enjoy
03-26-18, 04:33 PM
#2
Lexus Fanatic
Nice post as usual. 
I don't know why AM is still included in today's car-radios.
Almost no one actually listens to it anymore. FM stereo took over decades ago, and, of course, more recently, Sirus/XM satellite radio. AM signals DO have the advantage of traveling further than FM signals, especially over and around obstacles (known as "Line-of-Sight" distance), although they usually are tinny-sounding, are less-clear in sound-clarity, and often have static, especially near lightning flashes in a storm (years ago, that was one way of telling if there were thunderstorms in the area that you couldn't physically see or hear yet). And, some of the added advantage of AM signals in distance is nullified by FCC regulations that force some radio stations to cut back their transmitting-power at night.
Perhaps the biggest advance in car radios, though (as with some other electronic devices), came back in the 1950s and early 60s, when the old vacuum-tubes inside the radios were replaced by more modern transistors. That meant instant-on and instant-off for the radios, without having to wait for the hot-running tubes to warm up when the set was turned on or cool off when turned off. Transistors, besides being far more efficient, also produced much less heat, so they didn't have to be periodically replaced like burnt-out tubes.
Car radios, at one time, were all more or less a standard size, and slipped in and out more or less standard-sized rectangular holes in the dash, which generally made it easy to change or upgrade one's unit (it also made them quite easy to steal). Newer units, of course, not only vary all over the place in size/shape/design, but are often permanantly-integrated into the dash's video-screen and wiring.
I don't know why AM is still included in today's car-radios.
Almost no one actually listens to it anymore. FM stereo took over decades ago, and, of course, more recently, Sirus/XM satellite radio. AM signals DO have the advantage of traveling further than FM signals, especially over and around obstacles (known as "Line-of-Sight" distance), although they usually are tinny-sounding, are less-clear in sound-clarity, and often have static, especially near lightning flashes in a storm (years ago, that was one way of telling if there were thunderstorms in the area that you couldn't physically see or hear yet). And, some of the added advantage of AM signals in distance is nullified by FCC regulations that force some radio stations to cut back their transmitting-power at night.Perhaps the biggest advance in car radios, though (as with some other electronic devices), came back in the 1950s and early 60s, when the old vacuum-tubes inside the radios were replaced by more modern transistors. That meant instant-on and instant-off for the radios, without having to wait for the hot-running tubes to warm up when the set was turned on or cool off when turned off. Transistors, besides being far more efficient, also produced much less heat, so they didn't have to be periodically replaced like burnt-out tubes.
Car radios, at one time, were all more or less a standard size, and slipped in and out more or less standard-sized rectangular holes in the dash, which generally made it easy to change or upgrade one's unit (it also made them quite easy to steal). Newer units, of course, not only vary all over the place in size/shape/design, but are often permanantly-integrated into the dash's video-screen and wiring.
Last edited by mmarshall; 03-26-18 at 04:47 PM.
03-26-18, 05:03 PM
#3
Lexus Fanatic
iTrader: (20)
03-26-18, 05:20 PM
#4
Lexus Fanatic
I don't listen to it but at least until i last did there was more dedicate sports broadcasting and all talk stations on a.m. than f.m. But now sirius for those who subscribe has tons of all that and of course works driving coast to coast which is great. It is irritating though when you're stuck under and overlass and the signal goes out.
Sirius XM radio, IMO, is somewhat overpriced, but, at least, is dependable (I've never lost service), crystal-clear in sound, not range-limited, and offers a lot of programming variety. I spend a lot of time on it listening to NPR, FOX News, Catholic/Christian programming/music, and local weather/news. GM, at one time, like it did with OnStar, gave you a year of XM free with a new vehicle.....then it was six months, now it's down to three.
Last edited by mmarshall; 03-26-18 at 05:23 PM.
03-27-18, 10:13 PM
#5
AM still has some good stuff on it, WSM 650 is a lot of fun if you're into the oldies country music, bluegrass, americana etc. WSM is the original channel that still broadcasts the Grand Ole Opry from Nashville. On a clear night with a decent antenna I'm pretty sure it still broadcasts for a good 800-1000 miles from Nashville.
There's also a good bit of conservative talk radio on the AM band around where I live, but I can't listen to that crap for more than a couple minutes before I start yelling at the people who can't hear me lol.
What I find interesting about car stereos, is how much this stuff has come down in price. I mean in 1983, a good Alpine cassette deck was like $400 not adjusted for inflation. Now days you can buy a good single DIN reciever that bluetooths your calls, music, USB and aux inputs, CD player, more adjustments than you can shake a stick at for about $100. I think the main problem back in the day was its hard to make stuff small, even harder to make it small and cheap. I mean we still have home hi-fi gear from the 60's/70's/80's people collect/still use because it sounded that good and was that well made, but car stereos from that era, its all crap compared to newer gear IMO.
There's also a good bit of conservative talk radio on the AM band around where I live, but I can't listen to that crap for more than a couple minutes before I start yelling at the people who can't hear me lol.
What I find interesting about car stereos, is how much this stuff has come down in price. I mean in 1983, a good Alpine cassette deck was like $400 not adjusted for inflation. Now days you can buy a good single DIN reciever that bluetooths your calls, music, USB and aux inputs, CD player, more adjustments than you can shake a stick at for about $100. I think the main problem back in the day was its hard to make stuff small, even harder to make it small and cheap. I mean we still have home hi-fi gear from the 60's/70's/80's people collect/still use because it sounded that good and was that well made, but car stereos from that era, its all crap compared to newer gear IMO.
Last edited by Aron9000; 03-27-18 at 10:18 PM.
03-28-18, 06:12 AM
#6
Lexus Fanatic
That's one of the few compromises you have to make with the higher-quality signals you get from FM and satellite. AM signals are more flexible over and under obstacles, but often sound like crap and have static.
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03-29-18, 06:45 PM
#8
Lexus Champion
Thread Starter
Thanks, I'm just a normal Mechanical Engineer who likes to take things apart and learn the practical way. We didn't learn this in school, as you are learning from my videos, I'm learning along the way myself. Of course, some background research helps before hand. And yes, I try to cover a wide range of automotive topics because I find it interesting.
03-29-18, 10:00 PM
#9
Racer
Great write up, speedkar9! Very interesting and informative. I was already familiar with the internal workings of ROM drives and disc media, but didn't know about the radio transmission part. Thank you again for sharing and taking the time to put the information together in an easily digestible format. It is not easy teaching others like you have done. It reminds me of an old adage along the lines of "if you truly want to test your knowledge, then try to teach". You have a good grasp of technical details and teach it well.
Uh, I don't know about the crystal clear sound, mmarshall. I just cancelled my SiriusXM trial subscription early because most of the channels are mediocre and the satellite sound quality is especially bad. It was as if everything is transmitted at 96 kbps or something. Every other source input in the LS 460 beats out SiriusXM in sound quality. I agree that the service is over-priced, especially for the subpar sound quality.
Sirius XM radio, IMO, is somewhat overpriced, but, at least, is dependable (I've never lost service), crystal-clear in sound, not range-limited, and offers a lot of programming variety. I spend a lot of time on it listening to NPR, FOX News, Catholic/Christian programming/music, and local weather/news. GM, at one time, like it did with OnStar, gave you a year of XM free with a new vehicle.....then it was six months, now it's down to three.
03-30-18, 05:24 PM
#10
Lexus Fanatic
Great write up, speedkar9! Very interesting and informative. I was already familiar with the internal workings of ROM drives and disc media, but didn't know about the radio transmission part. Thank you again for sharing and taking the time to put the information together in an easily digestible format. It is not easy teaching others like you have done. It reminds me of an old adage along the lines of "if you truly want to test your knowledge, then try to teach". You have a good grasp of technical details and teach it well.
Uh, I don't know about the crystal clear sound, mmarshall. I just cancelled my SiriusXM trial subscription early because most of the channels are mediocre and the satellite sound quality is especially bad. It was as if everything is transmitted at 96 kbps or something. Every other source input in the LS 460 beats out SiriusXM in sound quality. I agree that the service is over-priced, especially for the subpar sound quality.
Uh, I don't know about the crystal clear sound, mmarshall. I just cancelled my SiriusXM trial subscription early because most of the channels are mediocre and the satellite sound quality is especially bad. It was as if everything is transmitted at 96 kbps or something. Every other source input in the LS 460 beats out SiriusXM in sound quality. I agree that the service is over-priced, especially for the subpar sound quality.
My experience with Sirius XM reception, which has been mostly in Buicks, has been very good. If you have an LS460, especially with the Mark Levinson unit, you have what is (arguably) the best automotive stereo on the market. If I can get good satellite reception in Buicks, and you can't in an LS, then I just don't know what to say.
Perhaps you and I have different ear-tuning, or different opinions on what is considered good stereo sound. Or, maybe you live and drive regularly near or under large obstacles and tunnels that can mask the satellite signals. Unlike AM signals, which are crappy-sounding but can go over obstacles for great distances, FM and satellite signals depend on an obstacle-free environment....which, with satellites being constantly overhead, is usually the case, but not always.
03-30-18, 05:58 PM
#11
Racer
My experience with Sirius XM reception, which has been mostly in Buicks, has been very good. If you have an LS460, especially with the Mark Levinson unit, you have what is (arguably) the best automotive stereo on the market. If I can get good satellite reception in Buicks, and you can't in an LS, then I just don't know what to say. Perhaps you and I have different ear-tuning, or different opinions on what is considered good stereo sound. Or, maybe you live and drive regularly near or under large obstacles and tunnels that can mask the satellite signals. Unlike AM signals, which are crappy-sounding but can go over obstacles for great distances, FM and satellite signals depend on an obstacle-free environment....which, with satellites being constantly overhead, is usually the case, but not always.
Perhaps you and I have different ear-tuning, or different opinions on what is considered good stereo sound. Or, maybe you live and drive regularly near or under large obstacles and tunnels that can mask the satellite signals. Unlike AM signals, which are crappy-sounding but can go over obstacles for great distances, FM and satellite signals depend on an obstacle-free environment....which, with satellites being constantly overhead, is usually the case, but not always.I listened to the SiriusXM trial for three weeks while driving all around town and I would equate the quality to regular FM when I'm not receiving an HD FM signal. I suppose that isn't as terrible as I make it out to be, but in the LS it sure does sound poor. Faced with so many other options I just don't see a compelling reason for SiriusXM. Glad you're enjoying the service.
04-03-18, 06:50 PM
#13
Lexus Champion
Thread Starter
Great write up, speedkar9! Very interesting and informative. I was already familiar with the internal workings of ROM drives and disc media, but didn't know about the radio transmission part. Thank you again for sharing and taking the time to put the information together in an easily digestible format. It is not easy teaching others like you have done. It reminds me of an old adage along the lines of "if you truly want to test your knowledge, then try to teach". You have a good grasp of technical details and teach it well.
04-06-18, 06:21 PM
#14
