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Tuned radio frequency receiver
one or more tuned radio frequency (RF)
individually tuned to the station's frequency
Tuned Radio Frequency Receiver
A 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
How it works
The 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
Advantages and disadvantages
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
Advantages and disadvantages
They 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.
The antenna pick up all radiated signal and feeds them into
the RF(Amplifier) .These signal are very small (usually only
a few microvolts).
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.)
This circuit generates a steady sine
wave at a frequency 455 khz above
the selected RF
Increase the level of the signal .
The received signal is now processed by
the demodulator stage where the audio signal (or
other baseband signal) is recovered and then further
This circuit amplifies the detected audio signal and
drive the speaker to drive sound
Sensitivity and Selectivity
Band width filter
1% 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
A radio receiver may be designed to tune to a fixed frequency,
MF AM broadcast band, 535 kHz - 1605 kHz
General coverage MF/HF communications receiver 100 kHz -
VHF FM broadcast band, 88 - 108 MHz
UHF TV broadcast band (analogue or digital) 470 - 860 MHz
Scanning receiver 0.5 MHz - 1300 MHz
GSM 900, GSM1800 or 3G mobile phone bands
Wireless LAN band 2400 - 2483.5 MHz