Post on 21-Jun-2015
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RADIO RECEIVERS
ContentsIntroductionHistoryTypes Of Radio ReceiverSensitivity and SelectivityFrequency range
IntroductionA radio receiver is an electronic device that
receives radio waves and converts the information carried by them to a usable form.
HistoryAlexander Stepanovich Popov First radio receiver in 1896.It was based on electromagnetic waves, which were proven to exist by James Clerk
Maxwell only a few years earlier in 1887.
Types Of Radio ReceiverCrystal radio receiverTuned radio frequency receiverSuperheterodyne Receiver
Crystal radioA crystal radio is the simplest kind of radioIt needs no battery or power sourceIt gets all of its power only from the radio
wave.
Components of Crystal RadioAntennaTunerCoilGround wireDetectorCapacitorDiode
Working
Tuned radio frequency receiver one or more tuned radio frequency (RF) individually tuned to the station's frequency
Tuned Radio Frequency ReceiverA tuned radio frequency receiver (or TRF
receiver) is a type of radio receiver that is usually composed of one or more tuned radio frequency (RF) amplifier stages followed by a detector (demodulator) circuit to extract the audio signal and an audio frequency amplifier. Popular in the 1920s, it could be tedious to operate because each stage must be individually tuned to the station's frequency. By the mid 1930s it was replaced by the superheterodyne receiver invented by Edwin Armstrong.
How it worksThe classic TRF receivers of the 1920s and 30s
consisted of three sections:One or more tuned RF amplifier stages. These
amplify the signal of the desired station to a level sufficient to drive the detector, while rejecting all other signals picked up by the antenna
a detector, which extracts the audio (modulation) signal from the radio carrier signal by rectifying it
optionally, but almost always included, one or more audio amplifier stages which increase the power of the audio signal.
Advantages and disadvantagesDisadvantage.Since they used inductor and capacitor as
tunning the element, the circuit is bulky and costly.
They are not suitable to amplify audio frequencies
If the band of the frequency is increased, design become complex.
Advantages and disadvantagesAdvantagesThey amplify defined frequency.
Signal to noise ratio at output is good.
They are well suited for radio transmitters and receiver.
The band of frequency over which amplification is required can be varied.
Superheterodyne Receiver Antenna RF(Radio Frequency) Mixer Local Oscillator(LO) IF(Intermediate Frequency) Detector Audio amplifier Power amplifier Speaker
Architecture of Superheterodyne ReceiverAntennaThe antenna pick up all radiated signal and feeds them into the RF(Amplifier) .These signal are very small (usually only a few microvolts).
RF(Amplifier)This circuit can be adjusted (tuned) to select and amplify
any carries frequency within the AM Broad cost band . Only the selected frequency and its two side bands pass through the amplifier.(Some AM Receiver don’t have a Separate RF amplifier stage.)
Local OscillatorThis circuit generates a steady sine
wave at a frequency 455 khz above the selected RF
MixerIntermediate Frequency
fIF = fRF ± fLO
RF=1000Khz
LO=1455Khz
fIF=2455, fIF=455
IF AmplifierIncrease the level of the signal .
DemodulationThe received signal is now processed by the demodulator stage where the audio signal (or other baseband signal) is recovered and then further amplified.
Audio AmplifierThis circuit amplifies the detected audio signal and drive the speaker to drive sound
Sensitivity and SelectivitySensitivity
Weak signalnoise
SelectivityBand width filter1% of RC Frequency
How radio waves travel.Although radio waves are sometimes colloquially referred to as
"airwaves", they do not require air or any other medium in which to travel and can travel through a vacuum.
Like light waves, radio waves travel in straight lines unless something reflects or refracts them. Like light waves, radio waves may be obstructed by obstacles, which can cast a radio "shadow". Although radio waves can pass through many non-conductive material without much loss, they do suffer some loss when passing through walls, floors and roofs. This loss depends upon the building materials used and increases at higher frequencies. Metal, water, ground and other electrically conductive materials cause large losses to radio waves passing through them and in some cases no usable signal may pass through.
Frequency rangeA radio receiver may be designed to tune to a fixed
frequency, MF AM broadcast band, 535 kHz - 1605 kHzGeneral coverage MF/HF communications receiver 100 kHz -
30 MHzVHF FM broadcast band, 88 - 108 MHzUHF TV broadcast band (analogue or digital) 470 - 860 MHzScanning receiver 0.5 MHz - 1300 MHzGSM 900, GSM1800 or 3G mobile phone bandsWireless LAN band 2400 - 2483.5 MHz
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