am-fm radio receivers
TRANSCRIPT
SUPERHETRODYNE
A radio receiver receives the radio waves from different broadcasting stations. The desired radio waves is selected by the radio frequency amplifier, in addition to this radio receiver performs the following functions as:
Intercept the radio waves coming from various transmitting stations arrive at the antenna. These radio waves contain electrical energy in the form of an electromagnetic wave.
Pick up the desired modulated radio frequency signal from all other unwanted signals.
Select the desired station. Amplify the weal signals. Demodulate or detect the carrier signal. Reproduce the audio signal.
A radio is an electronic circuit that picks up a desired modulated radio frequency signal, from all other unwanted signals, amplifying, demodulating it an finally producing it in the desired manner which is usable for the consumer, such as sound, pictures, etc.
Following are the two types of radio receivers:
Tuned radio frequency receiver, and Super-heterodyne radio receiver.Out of theses two, tuned Radio Frequency
(TFR) receiver is the oldest one. But it has lots of shortcoming. The super-Heterodyne radio receiver is most popular and being widely used today due to many of its advantages, over TRF receiver.
Tuned radio frequency (TRF) receiver are also called ‘ simple or straight radio receiver’. These were introduced before World War II as improvement over crystal and regenerative receivers existing that time. In these receivers, two or more R.F. amplifiers (tuned together) are employed to select and amplify the incoming frequency and rejecting all others. After this, the A.F. signal is detected and amplified suitably.
The major advantages of TRF receiver are as follows:
The TRF receivers have high sensitivity. They are comparatively cheap i.e. low cost.But the receiver suffers from poor selectivity,
instability in gain variation of band width over the band. The receiver works satisfactorily at low and medium frequencies but at higher frequencies it has poor reception of no reception. The receiver also suffers from a variation in the Q factor and the band with of the tuned circuit employed in RF amplifier at different frequencies of band.
The TRF receivers suffer from following drawback This is a variation in its Band Width(B.W.) over
the tuning rang. It has inability to achieve sufficient selectivity
at higher frequencies because of the use of large number of single tuned circuits. It is not feasible to use double tuned RF amplifies in TRF receivers due to the difficulty of making several double tuned amplifiers, tuned in unison.
RF amplifier Mixer and local oscillator IF amplifier Detector AF and power amplifierADVANTAGES OF SUPERHETERODYNE RADIO RECIEVER: It reduces the signal from very high frequency sources where
ordinary components wouldn’t work (like in a radar receiver) The bandwidth remains constant over entire operating
range. It allows many components to operate at a fixed frequency
and therefore they can be optimized or made more inexpensively.
It can be used to improve signal isolation by arithmetic selectivity.
High sensitivity and selectivity