Stages of Superhetrodyne Radio Receiver
Superhetrodyne Radio Receiver- To understand this article properly you should also know about A.M. Radio Receivers.
Fig-1 shows the block figure of a superhetrodyne receiver.
It may be seen that R.F. amplifier stage, mixer stage and oscillator stage use tuned parallel circuits with variable capacitors.
capacitors are ganged together as shown by the dotted interconnecting lines. The gyration of the
common shaft contemporaneously changes the capacitance of these tuned circuits.
( i)R.F. amplifier stage
The R.F. amplifier stage uses a tuned parallel circuit L1C1 with a
variable capacitor C1.
The radio swells from varied broadcasting stations are interdict by the
taking upstanding and are couple to this stage.
This stage selects the asked radio surge and raises the
strength of the surge to the asked position.
(ii) Mixer stage
The amplified affair of R.F. amplifier is fed to the mixer stage where it is
combined with the affair of a original oscillator.
The two frequentness beat together and produce an intermediate Frequence( IF).
The intermediate frequence is the difference between oscillator frequence and radio frequence i.e.
I.F. = Oscillator frequence − Radio frequence
In asuper-hetrodyne receiver, the hetrodyne principle is use to produce an intermediate frequence.
Which is advance than that can be hear i.e., supersonic.
Superhetrodyne is short for supersonic hetrodyne.
The IF is always 455 kHz anyhow of the frequence to which the receiver is tune.
The reason why the mixer will always produce 455 kHz frequence above the radio frequence is that oscillator always produces a frequence 455 kHz
* above the elected radio frequence.
This is achieve by making C3 lower than C1 and C2.
By making C3 lower, oscillator will tune to a high frequence.
In practice, capacitance of C3 is designed to tune the oscillator to a frequence high than radio wave frequence by 455 kHz.
This frequence difference ( i.e. 455 kHz) will always be maintained because
when C1 and C2 are varied, C3 will also vary proportionally.
It may be note that in mixer stage, the carrier frequence is reduce.
The IF still contains the audio signal.
( iii)I.F. amplifier stage
The affair of mixer is always 455
kHz and is fed to fixed tuned I.F. amplifiers.
These amplifiers are
tuned to one frequence ( i.e. 455 kHz) and render nice amplification.
( iv) Sensor stage
The affair from the last IF amplifier stage
is coupled to the input of the sensor stage. Then, the audio signal is uproot from the IF affair.
Generally, diode sensor circuit is use because of its low deformation and excellent audio dedication.
(v)A.F. amplifier stage
The audio signal affair of sensor
stage is fed to a multistage audio amplifier. Then, the signal is amplified until it's sufficiently strong to drive the speaker.
converts the audio signal into sound swells corresponding to the original sound at the broadcasting station.
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