The Physics of an AM Radio

The Physics of an AM Radio

Length: 1738 words (5 double-spaced pages)

Rating: Excellent

Open Document

Essay Preview

More ↓
The Physics of an AM Radio

It’s was a beautiful sunny morning and Bill just kissed his wife goodbye and headed out the door on his way to work. As Bill got into his car he realized that he missed the Utah Jazz game the night before because of a late business meeting and fell asleep before the news came on so he couldn’t catch the highlights or even the score. He remembered that he could catch the rundown on AM frequency 930 (Sports News Radio).

Many people enjoy listening to AM radio because of how convenient it is to listen and catch up on the sports, weather or just enjoy the entertainment of listen to Rush or Dr. Laura, but are much like Bill and don’t have any idea how the signal that carries these programs is sent or even received. In an attempt to understand this process, Bill confronts a part time employee who is currently studying electronics and has a basic knowledge of how the AM radio found his car or even his home works.

Almost all AM radios work under the same basic design. There are two very simple yet very important things that make AM radio possible. What are these things? A transmitter(the station) and a receiver(the radio).


Each radio station that desires to have a frequency(signal) on AM radio must notify the FCC and are assigned a frequency that they can use to send their information out on. The very first part of the transmitter is a quartz crystal. This is used because it is very stable and efficient which is important because there are certain laws and guidelines that the stations must abide by. They cannot go over or below the assigned frequency by more than 5K hertz, making a bandwidth of 10K hertz. After the quartz crystal, is an oscillator where the actual physics of the transmitter comes in. The oscillator is made up of a variety of electronics components including an operational amplifier and a combination of resistors and capacitors.

Resistors are defined as-The impedance to the flow of electric current. The resistance is equal to the voltage across the object divided by the current through it. Measured in volts per ampere, or ohms.(Physics, A World View 513)

Current is defined as-A flow of electric charge. Measured in amperes. (Physics, A World View 513)

A combination of a resistor and capacitor in series or parallel is called a filter.

How to Cite this Page

MLA Citation:
"The Physics of an AM Radio." 24 Sep 2018

Need Writing Help?

Get feedback on grammar, clarity, concision and logic instantly.

Check your paper »

The Physics of an AM Radio Receiver Essay

- The Physics of an AM Radio Receiver The AM Radio has been around for a long time. When the AM radio was first invented, it was not meant to be used to broadcast music. That is why today most music radio stations are on the FM band. Instead, the AM band was used to carry voice frequencies, thus, all the AM talk radio stations. Due to new technology, music is broadcast over the AM band but does not have the same sound quality as the FM band. According to the FCC regulations at, the AM broadcasters are only allowed 5 KHz each side of their carrier frequency for their side bands....   [tags: Radio Technology Electronics Essays]

Free Essays
1268 words (3.6 pages)

Radio Waves Essay

- Radiowaves are the oscillations of magnetic waves by varying the modulation to generate different signals which can be converted into information such as sound, video, or digital communication. As these waves pass through a conductor, an alternating current is generated and this can be converted into usable information. As one could see from the picture above, radio waves are the the electromagnetic waves with wave lengthes between 1mm and 10 Mm. This converts to a frequency range of 300Ghz to 30Hz, respectively....   [tags: physics radio wave]

Free Essays
363 words (1 pages)

Questions and Answers on Ernest Rutherford Essay

- ... Ernest did a lot of work before he discovered the atomic theoryanx made a big name for himself. Ernest went to England in 1907 to become Langworthy Professor of Physics in the University of Manchester. In 1919 he accepted an invitation to succeed Sir Joseph Thomson as Cavendish Professor of Physics at Cambridge. He also became Chairman of the Advisory Council, H.M. Government, Department of Scientific and Industrial Research He became the Professor of Natural Philosophy, Royal Institution, London; and the director of the Royal Society Mond Laboratory, Cambridge....   [tags: nuclear physics, radio active materials]

Research Papers
683 words (2 pages)

The Physics of Sound Essay

- Introduction Produced sound from speakers has become so common and integrated in our daily lives it is often taken for granted. Living with inventions such as televisions, phones and radios, chances are you rarely ever have days with nothing but natural sounds. Yet, few people know the physics involved in the technology that allows us to listen to music in our living room although the band is miles away. This article will investigate and explain the physics and mechanism behind loudspeakers – both electromagnetic and electrostatic....   [tags: tv, radio, phones]

Research Papers
1419 words (4.1 pages)

Physics of the Theremin Musical Instrument Essay

- The theremin is an electronic musical instrument that is played using electrical fields. When it was first introduced, people were shocked to see this instrument that could be played without even touching it. The theremin unsually is tuned so that it has a range of three and a half octaves. The theremin's operation is based on the theory of beat frequencies. Two antennas stick out on each side. Usually a vertical antenna is located on the right which controls the pitch. The closer the players hand is, the higher the pitch....   [tags: physics theremin]

Free Essays
781 words (2.2 pages)

Physics of a Car Essay

- Physics of a Car The average driver doesn’t think about what keeps their car moving or what keeps them on the road, but that’s because they don’t have to. The average driver doesn’t have to worry about having enough downforce to keep them on the road or if they will reach the adhesive limit of their car’s tires around a turn. These are the things are the car designers, professional drivers, racing pit crews, serious sports car owners, and physicist think about. Physics are an important part of every sports and racing car design....   [tags: Physics Car Driving machine Essays]

Research Papers
1540 words (4.4 pages)

Physics of the Acoustic Guitar Essays

- Stringed instruments are most likely the oldest type of musical instruments. The acoustic guitar has been around since the 1500's, and is the most common stringed instrument used today. The guitar is one of the most versatile instruments in existence, being used in virtually every style of music. It can produce a wide range of sounds depending upon the style of the guitar and the type of strings used on it. The two main styles of acoustic guitars are the nylon-stringed and the steel-stringed....   [tags: physics guitars]

Research Papers
1810 words (5.2 pages)

Essay on Physics of Toilets

- Throughout the ages we have seen timeless inventions to numerous to name. We have seen everythingfrom the inventio of the radio to the engine to the atomic bomb. But there is one invention that goes onunappreciated, even looked down upon. The toilet. The toilet is an amazingly simple invention which,without it, the world would be a very different place. Without toilets there would be waste in our housesas well as in the streets that would have to be manually taken care of. Without the flush toilet there is nopossible way that the world could survive as populated as it is....   [tags: physics toilet toilets]

Free Essays
808 words (2.3 pages)

Essay on Physics of Electric Guitars

- Introduction More than any other instrument, the electric guitar has shaped and redefined music in the last century. Although popular culture did not pay much attention to it when it was first introduced in the 1930s, it has since become equated with the very essence of rock and roll music. On an international level, the electric guitar is by far "the most famous instrument to come out of the United States" ( Background Inventors have been playing with the idea of electrically powered musical instruments since the 1800s, but "the first attempts at an amplified instrument did not come until the development of electrical amplification by the radio industry in the 1...   [tags: physics electric guitar]

Research Papers
1313 words (3.8 pages)

Essay about Radio

- Radio: Making Waves in America Radio-wave technology is one of the most important technologies used by man. It has forever changed the United States and the world, and will continue to do so in the future. Radio has been a communications medium, a recreational device, and many other things to us. When British physicist James Clerk Maxwell published his theory of electromagnetic waves in 1873, he probably never could have envisioned the sorts of things that would come of such a principle. His theory mainly had to do with light waves, but fifteen years later, a German physicist named Heinrich Hertz was able to electrically generate MaxwellÕs ÒraysÓ in his lab....   [tags: essays research papers fc]

Free Essays
1500 words (4.3 pages)

Related Searches

This is key in an oscillator because the frequencies that are not desired must be filtered out by this combination of components. Inside the operational amplifier is a series of three amplifiers a differential amplifier, a voltage amplifier, and a power amplifier

Capacitors have an internal resistance called an impedance. This impedance is found by the formula = XC(impedance) = The inverse of 2 X pi X freq X the capacitance of the capacitor. The combination of the resistor and capacitor forms an impedance together and this is defined by R(resistance)+j(cap impedance) in rectangle form.(Practical Circuit Analysis Mcdonald 25) The purpose of this oscillator is to filter out the unwanted frequency so only the frequency that the particular radio station operates on will be amplified and transmitted.

The next step in the transmitter is what’s called a frequency multiplier. Generally the frequency that is spoken on the air is only between 100 hertz and 5K hertz and the assigned frequency will be between 540K hertz and 1600K hertz. These are the frequencies found on the dial of an AM radio. The function of the frequency multiplier is to multiply this 100 hertz to 5K hertz signal to that of the transmission frequency.

The next step that must be taken is to build a voltage driver. This driver is what drives or forces the signal into the air. Much has been said about resistance and capacitance but very little about voltage. The voltage in a circuit is defined
by the resistance in a particular circuit multiplied by the current. This idea or principle is known as Ohm’s Law. The Ohm’s Law formulas are V(voltage)=I(current)R(resistance) and likewise I(current)=V(voltage)\R(resistance) and R(resistance)=V(voltage)\I(current). Using this simple principal the voltage, resistance and current of a particular circuit can be found. (Physics A World View 504)

Last of all the intelligence (signal) that is desired to be sent goes through a power amplifier so the signal will have enough strength to be broadcast out to the receivers.
(your radio) The power of a circuit is defined by the voltage of a particular circuit multiplied by the current. The formula looks like this-P(power)=V(voltage)I(current) and P(power)=I(current)squared X R(resistance) and P(power) = V(voltage)squared\R (resistance) (Physics A World View 510). So the amplifier is designed so that the power the transmitter expends is amplified so it will with the voltage driver adequately force the signal to the receivers.

THE RECEIVER:The receiver of an AM radio is made of three basic parts, the antenna, the mixer and the oscillator. The antenna is obviously a very important part of the receiver. This is where the signal enters the radio. The frequency passing through the antenna creates a small voltage (V=IR) which drives the circuit. Within the receiver the radio wave at the antenna is amplified and then mixed with the local oscillator to produce the Intermediate Frequency which is the next stage. The mixer\oscillator stage contains a transistor which is a key component in amplification. This transistor not only amplifies the signal but simultaneously oscillates at a frequency 455K Hz above the desired radio station frequency. So to calculate the frequency the oscillator operates at the frequency of 455K Hz can be added to the frequency of radio station seen on the dial of the radio. The following formula defines this: Fo(Freq. of oscillator) + Fi(Freq. of Intelligence). The frequency of the intelligence is the frequency that is transmitted by the radio station. The antenna and the oscillator coils have resonant circuits that change when the radio is tuned for different stations. Again these resonant circuits act as filters to filter out and pass the desired frequency and reject the frequencies of the other stations.

The next stage of the receiver is the first of two If(Intermediate frequency) amplifiers. The gain of the first If amplifier decreases after the Automatic Gain Control threshold is passed to keep the audio output constant at the detector and prevent overload of the second If amplifier. This is made possible by making the base voltage of the transistor in this stage lower as the signal strength increases. Transistors have three pins or leads that make this amplification possible a base pin, collector pin, and emitter pin. So this drop in voltage on the base pin causes a drop in voltage on the emitter pin. Since the output of this emitter pin is coupled to the next stage of the receiver, this is what causes a decrease in gain.

The stage following the first If amplifier is the second If amplifier. The purpose of this second If amplifier is to increase the amplitude of the intermediate frequency (If) and at the same time provide Selectivity. Selectivity is the ability to “pick out” one radio station while rejecting others.(Omnitron Electronics 19) This second If amplifier at the same time acts as a bandpass filter, passing the desired frequency while rejecting the unwanted signals.

The next to last stage consists of an AM Detector and an automatic gain control stage. The purpose of the detector is to change the amplitude modulated If signal back to an audio signal. This is obviously important because this is what enables the
intelligence frequency to be heard. A process called detection is what makes this possible. The amplitude modulated If signal is applied to a diode in such a way as to leave only the negative portion of that signal. This diode serves a purpose of something called rectification. Rectification is when the negative half of the sine wave the Intelligence frequency rides on is cut off. This acts like an electronic check valve that only lets current pass in the same direction as the anode on the diode points. A diode has a positive lead and a negative lead. The positive lead is called the anode and the negative lead is called the cathode. In this situation, the positive lead or anode is pointing toward the direction the current is passing. When the diode is on (in conduction) it will cause the capacitors in the circuit to charge to approximately the same voltage at the negative peak of the If signal. When the diode is off the capacitors discharge through the resistors in this stage of the receiver. The automatic gain control circuit is simply to maintain a constant audio level at the detector regardless of the strength of the incoming signal. This makes it possible to listen to all signals at the same volume. Without the ACG the volume would have to be adjusted for each station (Omnitron Electronics 16).

The last and final stage is the audio amplifier. The audio amplifiers purpose is to increase the audio power to a level sufficient to drive an 8 ohm speaker.(all speakers have an internal resistance) To do this, the DC(direct current) from the battery if in a car or a battery driven radio into an AC(alternating current) in the speaker. This is partially what the diode is responsible for. In this circuit there is a couple of transistors that work together amplify the small voltage produced by the antenna to large enough signal that the speaker will turn on and operate so the signal transmitted by the station is amplified to an actual audible audio signal heard through the speaker.

In conclusion, there is an outstanding amount of physics that goes into the process of transmitting a signal carrying the desired intelligence to receiving the AM signal with an AM radio. A basic AM radio combines basic electronics knowledge (Ohm’s Law) and some more in depth electronics such as amplification and rectification. So hopefully after a brief explanation of how an AM radio works, Bill will take more thought as to how the signal he is listening to is received and transmitted. The physics behind how an AM radio works is very interesting to me and something I understand fairly well that’s why I chose this topic.

Works Cited:

1.Physics A World View; Kirkpatrick and Wheeler

2.Practical Circuit Analysis; Lorne MacDonald

3.Omnitron Electronics Superhet AM-550TK
Return to