Transmitter: Radio Transmitters and Receivers
This article covers information that is required for understanding and learning about transmitters, receivers, and analog communication.
What is communication?
Communication is the process of transferring data and information from transmitter to the receiver by means of the channel which can be a wired channel or wireless channel. Just like you talk to your friend by phone, emailing documents, the songs and news that you listen on radio extra are simple examples of the process of communication.
What is the modulation?
Modulation may be defined as a process by which some characteristics of a signal known as the carrier is varied according to the instantaneous value of another signal known as modulating signal. The signal containing information to be transmitted is called a modulating signal or baseband signal. The signal which results from the process of modulation is known as the modulated signal.
Elements of communication system:
Information source: the communication system communicates the message. The message can be in the form of voice, pictures, data, code, music extra. The information can be one dimensional or multidimensional.
Transducers: the transducer converts physical or analog signals into electrical signals.
Transmitters: transmitter modifies the baseband signal for efficient transmission. It consists of various subsystems such as analog to digital converters, an encoder, and modulators.
Receivers: A receiver consists of digital to analog converter, decoders, and demodulators.
Channel: the channel is a medium that conveys the electrical signal from the transmitter to the receiver. It may be a wired channel or wireless channel.
Output transducer: these transducers convert’ electrical signals back to its physical form.
A transmitter is a device used electronics and telecommunication for the production of radio signals and waves. The main function is to send and receive information and data. A radio frequency alternating current is applied to the antenna and the signal is broadcasted. There are various types of transmitters depending upon the requirements and standard, some examples are Wi-Fi, Bluetooth, and cellular extra.
The basic design of the transmitter includes various parts which are discussed below:
Supply: the source used to power up the device and initiate the broadcasting process.
Oscillators: electronic oscillators are used for the generation of the wave where information is superimposed on the carrier.
Modulators: modulators are used for the modulation process and there are various schemes that can be used.
Amplifiers: amplifiers are used for powering up the signal in order to increase the range of broadcasting.
Impedance matching circuit: These circuits are used matching the impedance of the transmitter and the antenna in order to transfer the power to the antenna efficiently and prevent the standing wave problem.
Radio transmitter and receiver:
In this carrier signal is modulated by message signal and then amplified by a power amplifier and radiated through antenna.
Power amplification can be done in several stages.
Impedance matching is necessary when the output of one stage is given as input to another stage. A class ‘c’ amplifier is used as a power amplifier. The output of the power amplifier is distorted which can be corrected by an LC tuned circuit.
The teta factor of the LC tuned circuit is an important parameter that is defined as the ratio of resonating frequency to its bandwidth. Too high teta will clip the sideband of the modulated signal; with too low teta will distort the signal.
There are two types of radio receivers:
TRF receivers are used for medium wave frequencies. Their responses become poor at high frequencies. The performance is improved by introducing the principle of heterodyning and a receiver based on this is called superheterodyne receivers.
The performance of the TRF receiver is judged by its selectivity, sensitivity, fidelity.
Features of the receiver:
Sensitivity: the ability of the receiver to detect the weakest possible signal is known as the sensitivity of the receiver.
Selectivity: it is a receiver’s ability to distinguish between two adjacent carrier frequencies.
Fidelity: it is the ability of the receiver to reproduce faithfully all the frequency components present in the baseband signal. It mainly depends upon the bandwidth of audio amplifiers.
Advantage of TRF receiver:
TRF receiver are cheaper than superheterodyne receiver also they do not have a problem such as an image signal rejection or tracking and alignment that arises in superheterodyne receivers.
It gives better performance than the ‘TRF’ receiver. The main feature of this receiver is that all incoming radio frequencies are converted to a single intermediate frequency by the heterodyning process. In this the incoming carrier and a locally generated signal are mixed in a mixer, also referred to as the first detector. The mixer generates the sum and difference of frequencies at the output. The difference is selected by a properly tuned circuit. The intermediate frequency in a commercial radio receiver is fixed at 455 kHz.
The detector stage of a superheterodyne receiver operates at a fixed frequency and hence it can be designed to detect entire baseband without introducing much distortion.
Advantage of the superheterodyne receiver:
All the incoming carrier frequencies are connected into a fixed IF frequency of 455 kHz, therefore, all succeeding stage has to operate on a fixed IF frequency, hence the circuit design becomes simple with improved performance.
IF signals are amplified by IF amplifiers. The sensitivity of the superheterodyne receiver depends upon IF amplifiers. A high gain IF amplifier provides better sensitivity than the TRF receiver. In TRF receiver the sensitivity is decided by RF amplifier which amplifies the entire band of medium and short waves rather than a fixed IF frequency.