4-ANALOG RECEIVERS AND NOISE Flashcards
Superheterodyne
The superheterodyne is a common architecture used in radio receivers. It works by mixing the incoming radio frequency (RF) signal with a local oscillator frequency to produce an intermediate frequency (IF) signal. This IF signal is easier to process and filter than the original RF signal, making it a fundamental part of most modern radio receivers . It allows for better selectivity, sensitivity, and signal processing in radios.
Transmission
The radio transmitter consists of a transducer which converts speech or intelligence
into audio frequency electrical signals. These amplified AF signals modulate the radio frequency
carrier. The modulator performs the task of modulation. The modulated RF carrier is then amplified
and transmitted through an antenna.
Reception
The radio receiver consists of an antenna connected to a tuning circuit. The received
modulated RF carrier is amplified and then passed through the demodulator to extract the AF
signals. The AF signal is then amplified and fed to transducer which converts it into speech or
intelligence.
Requirements of a Receiver
- It should be cost-effective.
- It should receive the corresponding modulated waves.
- The receiver should be able to tune and amplify the desired station.
- It should have an ability to reject the unwanted stations.
- Demodulation has to be done to all the station signals, irrespective of the carrier signal
frequency.
AM Receiver (Receiver Operation)
The process of receiving a radio signal can be broken down into a series of five steps. Not
every receiver will perform every step, but most do.
* Signal Acquisition:
* Signal Selection:
* RF Amplification
* Information Recover
* Recovered Information Processing
Important receiver characteristics ( parameters)
Selectivity, Fidelity, Sensitivity, Noise,
Bandwidth Improvement Factor, Dynamic Range, Insertion Loss and Double Spotting
Types of Receiver
There are two basic types of radio receivers: coherent and noncoherent.
Heterodyning
Necessity of heterodyning:
The necessity of heterodyning action is due to the following reasons.
1. It is difficult to design a RF amplifier with high gain and high band width.
2. It is relatively easier to design a high gain IF amplifier having uniform gain over a narrow band
of comparatively lower intermediate frequencies (IF).
3. Hence it is necessary to convert the Radio frequencies to Intermediate Frequencies for efficient
processing.
Heterodyning action:
Heterodyning action is a process of combining two ac signals of
different frequencies in-order to obtain signals of new frequencies. A circuit called mixer or
converter is used for heterodyning two signals. If f1 and f2 are the two frequencies combined, then
heterodyning results in two components
1. The sum component with frequency f1+f2 which is filtered out using a bandpass filter.
2. The difference component with frequency f1- f2 is retained and processed
there are five sections to a superheterodyne receiver
the RF section, the
mixer/converter section, the IF section audio detector section, and the audio amplifier section.
FM Receiver
A radio or FM receiver is an electronic device that receives radio waves and converts the
information carried by them to a usable form. An antenna is used to catch the desired frequency
waves
FM frequency ranges
Frequency modulation is used in a radio broadcast in the 88-108MHz VHF band. The FM radio transmitter has a 200kHz wide
channel. The maximum audio frequency transmitted in FM is 15 kHz as compared to 4.5 kHz in
AM.
Stereo VHF FM Broadcast
Stereo VHF FM Broadcast combines the use of VHF frequencies and FM modulation to deliver high-quality stereo audio signals for radio broadcasting.
Comparison Stereo amplifier with Mono amplifier
Stereo Amplifier Mono Amplifier
1 As the name suggest, the basic
stereophonic system has two separate
channels after the pre amplifier stage.
1There is only one channel after pre amplifier
stage.
2 Stereophoic sound is created by two
independent audio channels to provide
sense of direction
2 Sense of direction is not pronounced as in
stereophonic amplifier.
3 Consists of two preamplifiers power
amplifiers and loud speakers
3 Consists of one preamplifiers tone and
volume controls, power amplifier.
4 Stereophony creates the impression of
sound heard from various directions as
in natural hearing
4 In monophonic or ‘mono’ sound, the audio is
in the form of one channel, often centered in
the sound field.
5 Less signal to noise ratio.
5 Better than 50 dB is the S/N ratio.
6 Non-linear distortion occurs.
6.Non-linear distortion not more than
input/output.
7 Equalizers are not used. 7 Contains equalizer circuit.
8 Two-way cross-over network with gain
control exist.
8 Three-way cross-over network exist.
STEREO SIGNAL GENERATOR (Transmitter)
A stereo signal generator, often referred to as a stereo transmitter, is a device used to transmit stereo audio signals wirelessly. It’s commonly found in FM radio stations.
