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Introduction:

Cordless Communication Circuit will demonstrate how a radio wave is transmitted and received using a very simple tuned radio frequency design. (TRF).

Radio signals:

A radio wave is a complex signal that contains the carrier frequency and the audio output of the microphone or audio amplifier source. It begins with the RF oscillator circuit, which is in affect a signal generator that is tuned to the precise operating frequency of that particular station. The generator output is applied to the final output stage of the transmitter, made up of several tuned tank circuits.

Transmitter:

The function of  the  Transmitter  is  to    modulate  the   audio  signals  and   to   transmit.It consists of oscillator and tank circuits that are connected to the antenna where the signal is radiated into the atmosphere over long distances. Before it is transmitted, the audio signal is modulated with the RF carrier so that it becomes part of the transmitted signal. In AM transmission, this is done by changing the amplitude of the RF carrier signal with a circuit called the MODULATOR. A modulator is a circuit that combines two signals together to form one signal, but the characteristics of both are retained. This means that a modulated radio wave contains the carrier frequency and the audio signal when it is transmitted. The transmitted signal can than travel over thousands of miles to a radio receiver, depending on the design.  

Receiver:

The function of the Receiver is to recover the audio signal that was modulated onto the RF carrier at the radio station, and apply it to the speaker, reproducing the sounds of the announcer. The source of the radio signal starts at the receiver antenna, which is a length of wire exposed to the atmosphere. When the RF energy passes by the wire, a small voltage and current will be induced that will change in step with the RF energy striking it. RF energy will induce voltage and current in any kind of conductor that gets in its path the other end of the antenna is connected to a tank circuit and it is tuned to only one resonance frequency. Even though there are hundreds of frequencies transmitting signals at the same time and they are all hitting the antenna inducing currents, only one of them will cause enough current to be of any use. The tank circuit used in this circuit is a series connected tank, which means the current will be maximum at the resonance frequency. If we make one of the reactance's variable, we can select or tune Any frequency passing by the antenna wire by adjusting the  reactance to a new Resonant frequency.