To create a simple radio transmitter, what you want to do is create a rapidly changing electric current in a wire. You can do that by rapidly connecting and disconnecting a battery, like this:. A better way is to create a continuously varying electric current in a wire. The simplest and smoothest form of a continuously varying wave is a sine wave like the one shown below:.
How to Make FM Transmitter
By creating a sine wave and running it through a wire, you create a simple radio transmitter. It is extremely easy to create a sine wave with just a few electronic components -- a capacitor and an inductor can create the sine wave, and a couple of transistors can amplify the wave into a powerful signal see How Oscillators Work for details, and here is a simple transmitter schematic.
By sending that signal to an antenna, you can transmit the sine wave into space. How Walkie-talkies Work. How to Build a Radio. History of Radio Pictures. Prev NEXT. Simple Transmitters: Make Your Own.1W FM RF Amplifier Circuit (Boost Low Power Transmitters)
When you connect the battery, the voltage in the wire is 1. By connecting and disconnecting a battery quickly, you create a square wave that fluctuates between 0 and 1.
A sine wave fluctuates smoothly between, for example, 10 volts and volts. Related How Walkie-talkies Work.Electrical Academia. For a basic understanding of radio and television operations, we will first look at a simple radio receiver. This radio receiver consists of very few partsan antenna, a ground, a tank circuit, a diode, a filter, and a speaker or a set of headphones. In Figure 1there are three radio stations each broadcasting at a different wavelength. Each station is broadcasting a radio signal consisting of a carrier wave and an audio signal.
The radio waves of all three stations come in contact with the radio receiver antenna. The antenna converts the radio signals to alternating current, which is conducted up and down the antenna to the ground. The antenna circuit is coupled to the tank circuit by mutual induction. Figure 1. A simple crystal radio can receive AM radio signals and convert them to sound. Tank Circuit. The tank circuit consists of an inductor and a variable capacitor connected in parallel.
As we know that an inductor and capacitor connected in parallel will have a resonant frequency. By using a variable capacitor, you are able to vary the tank circuit resonant frequency until it matches the frequency of the desired station. For exampleif we wish to tune in station 1, the capacitor is varied until the resonant frequency of the tank circuit is equal to kHz. Receiving a frequency of kHz will cause the greatest voltage drop across the tank circuit.
The other frequencies station 3, and station 2 will not produce a large voltage drop across the tank circuit. The detector rectifies the radio signal to a pulsing dc signal. The filter capacitor smoothers the high frequency of the audio portion of the radio signal. The detector diode and filter capacitor are necessary to change the broadcast frequency and audio signal to a reproducible sound at the headphones.
The description above may sound simple, and that is because this is the simple operation of a radio receiver. The radio described is known as a crystal radio receiver. When constructed properly in the lab, you can actually receive and hear a few stations. Take special note of the fact that there is no battery or other conventional power supply for this radio.
First, we will discuss the power source for this radio. Radio Waves. A radio wave is an electromagnetic radiation produced from current alternating through an antenna. A transmitting antenna is surrounded by electromagnetic radiation. In the study of electromagnetism, we learned that a conductor carrying an electric current is surrounded by a magnetic field. In a magnetic field created by an alternating current, the field expands, collapses, and changes polarity in step with the frequency.
An oscillator can produce high-frequency alternating currents that produce a radio wave when connected to an antenna. In general, the radio wave is an electrostatic radiation of energy produced by an oscillator circuit. The electrostatic field is perpendicular to the electromagnetic field. Both travel away from the antenna. As a result, a radio wave is made up of electromagnetic and electrostatic fields. See Figure 2. The direction these waves radiate, in respect to the earth, is called polarization.
In Figure 3 the waves are radiated from a vertical antenna. Note that the electrostatic, or E waves, are in the same plane as the antenna, yet perpendicular to the direction of travel. The vertically polarized waves are perpendicular to the surface of the earth.There are many natural sources of radio waves. But in the later part of the 19th century, scientists figured out how to electronically generate radio waves using electric currents.
Two components are required for radio communication: a transmitter and a receiver. A radio transmitter consists of several elements that work together to generate radio waves that contain useful information such as audio, video, or digital data. Power supply: Provides the necessary electrical power to operate the transmitter.
Oscillator: Creates alternating current at the frequency on which the transmitter will transmit. The oscillator usually generates a sine wave, which is referred to as a carrier wave. Modulator: Adds useful information to the carrier wave. There are two main ways to add this information. The first, called amplitude modulation or AM, makes slight increases or decreases to the intensity of the carrier wave. The second, called frequency modulation or FM, makes slight increases or decreases the frequency of the carrier wave.
Amplifier: Amplifies the modulated carrier wave to increase its power. The more powerful the amplifier, the more powerful the broadcast. A radio receiver is the opposite of a radio transmitter. It uses an antenna to capture radio waves, processes those waves to extract only those waves that are vibrating at the desired frequency, extracts the audio signals that were added to those waves, amplifies the audio signals, and finally plays them on a speaker.
Antenna: Captures the radio waves. Typically, the antenna is simply a length of wire. When this wire is exposed to radio waves, the waves induce a very small alternating current in the antenna. RF amplifier: A sensitive amplifier that amplifies the very weak radio frequency RF signal from the antenna so that the signal can be processed by the tuner. Tuner: A circuit that can extract signals of a particular frequency from a mix of signals of different frequencies. On its own, the antenna captures radio waves of all frequencies and sends them to the RF amplifier, which dutifully amplifies them all.
Unless you want to listen to every radio channel at the same time, you need a circuit that can pick out just the signals for the channel you want to hear. The tuner usually employs the combination of an inductor for example, a coil and a capacitor to form a circuit that resonates at a particular frequency.
This frequency, called the resonant frequency, is determined by the values chosen for the coil and the capacitor. This type of circuit tends to block any AC signals at a frequency above or below the resonant frequency. You can adjust the resonant frequency by varying the amount of inductance in the coil or the capacitance of the capacitor.
In simple radio receiver circuits, the tuning is adjusted by varying the number of turns of wire in the coil. More sophisticated tuners use a variable capacitor also called a tuning capacitor to vary the frequency. Detector: Responsible for separating the audio information from the carrier wave. For AM signals, this can be done with a diode that just rectifies the alternating current signal. For FM signals, the detector circuit is a little more complicated.
This can be done using a simple transistor amplifier circuit. Of course, there are many variations on this basic radio receiver design.
Many receivers include additional filtering and tuning circuits to better lock on to the intended frequency — or to produce better-quality audio output — and exclude other signals. Still, these basic elements are found in most receiver circuits.
Radio Electronics: Transmitters and Receivers.A short range FM transmitter is a low-power FM radio transmitter that broadcasts a signal from a portable audio device such as an MP3 player to a standard FM radio. Most of these transmitters plug into the device's headphone jack and then broadcast the signal over an FM broadcast band frequency, so that it can be picked up by any nearby radio. This allows portable audio devices to make use of the louder or better sound quality of a home audio system or car stereo without requiring a wired connection.
Being low-powered, most transmitters typically have a short range of — feet 30— metersdepending on the quality of the receiver, obstructions and elevation.
Typically they broadcast on any FM frequency from In this project we design the circuit in such a way that ,the circuit will collect the input through aux cable and broadcast with in FM frequency range.
The broadcasted output can be collected with a FM radio. If you want how to make fm receiver click here for tutorial. For more projects subscribe my youtube channel [ Click Here ].
Did you use this instructable in your classroom? Add a Teacher Note to share how you incorporated it into your lesson. Resistors [ Banggood ]. Capacitors [ Banggood ]. If you uses mic ,it senses the audio and broadcast to near by fm radio.
It can also be used as spy bug. Now the time to tune the transmitter, which is very hard and time taken process. Be patience while tuning.
Then slowly vary in that area, when transmitter and receiver frequency matches you can get the clear output from radio. Good little project. Have you worked with timers? I have built a timer Radio transmitter that can travel feet min. With powerful transformers between the coil it may be able to trasmit farther than 60 feet.
It was an amazing project to do. Reply 2 months ago. Reply 10 months ago.
I was only able to find a male jack with 4 rings. Would it be okay to connect left, right, and mic to the signal line? What do you think would be the best connection to make? Reply 2 years ago.
I wanted to make a switch using this circuit for my room lights so if I just replace the mic with a push button then will it work or there is something else that I would have to do? Could you please send me the formula you used for calculating the inductance of the coil, my wires have other diameters.
Reply 3 years ago. More by the author:. About: HI! I am much interested in inventing something new yet from my childhood.Engineered to meet the needs of the most demanding network operators and stations, it combines reliable performance, highest efficiency, and state-of-the-art innovations.
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More details on the Tech Note : What Happens if…? Figures given in this chapter may vary depending on the transmitter power level and version. Craft Your Own Amazing Sound. Read more about 5 Band Sound Processor. Learn more about SmartFM. No other FM Transmitter Manufacturer even comes close to that commitment or confidence! We can offer the 10 Year Warranty with confidence thanks to:. It sends the user regular reports on the status of key parameters such as temperatures, currents and voltages, plus information on the performance and lifespan of components such as the fan and power supply of the transmitter.
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WorldCast Systems supports Ecreso users in reducing energy costs Mar 30, Here we are building a wireless FM transmitter which uses RF communication to transmit the medium or low power FM signal. The maximum range of transmission is around 2 km. FM transmission is done by the process of audio pre amplification, modulation and then transmission. Here we have adapted the same formula by first amplifying the audio signal, generating a carrier signal using an oscillating and then modulating the carrier signal with the amplified audio signal.
The amplification is done by an amplifier, whereas the modulation and carrier signal generation is done by an variable frequency oscillator circuit. The power of the FM signal from the oscillator is then amplified using a power amplifier to produce a low impedance output, matching that with the antenna.
FM Transmitter Circuit
Here we are designing a simple single stage common emitter amplifier as the pre-amplifier. Let us assume this value to be about 1mA. The collector voltage needs to be about half of Vcc. We select a 5K resistor for better operation. The bias current is approximated to be 10 times the base current.
Now base current, Ib is equal to the collector current divided by the current gain, h fe. This gives the value of Ib to be 0.
The bias current is thus 0. The voltage across the base, Vb is assumed to be 0. This gives Vb to be 1. Here we select a 22K resistor. Here we select a 90K resistor. Here we select a Ohms resistor. It serves the purpose of bypassing the emitter current. A large value indicates low frequency basswhereas a lesser value increases treble higher frequency. Here we select a value of 5 uF. Let us assume the current through microphone to be 0.The antenna present at the end of transmitter section, transmits the modulated wave.
In this chapter, let us discuss about AM and FM transmitters. AM transmitter takes the audio signal as an input and delivers amplitude modulated wave to the antenna as an output to be transmitted. The block diagram of AM transmitter is shown in the following figure. The audio signal from the output of the microphone is sent to the pre-amplifier, which boosts the level of the modulating signal.
Power amplifier is used to increase the power levels of AM wave. This wave is finally passed to the antenna to be transmitted. FM transmitter is the whole unit, which takes the audio signal as an input and delivers FM wave to the antenna as an output to be transmitted.
The block diagram of FM transmitter is shown in the following figure. This signal is then passed to high pass filter, which acts as a pre-emphasis network to filter out the noise and improve the signal to noise ratio. The oscillator circuit generates a high frequency carrier, which is sent to the modulator along with the modulating signal. Several stages of frequency multiplier are used to increase the operating frequency.
Even then, the power of the signal is not enough to transmit. Hence, a RF power amplifier is used at the end to increase the power of the modulated signal. This FM modulated output is finally passed to the antenna to be transmitted. Analog Communication - Transmitters Advertisements. Previous Page. Next Page. Previous Page Print Page.