What is a Tuned Radio Frequency Receiver || How to Construct a Tuned Radio Frequency Receiver

A tuned radio frequency receiver is a type of radio receiver, which utilizes multiple stages of tuned radio frequency amplifiers connected in series, which is followed by a detector to detect the audio from the radio signal. The audio signal is further amplified and it drives an earphone or a loudspeaker.

Working of a TRF Receiver
The input from the antenna is tuned to a specific frequency using a tuned circuit which tunes to an incoming radio signal. The signal goes to the next stage, which is a tuned radio frequency amplifier stage that tunes and amplifies it. There may be two or three stages of tuned RF amplifiers that further tunes and amplifies the radio signal.

When the required amplification is achieved, the signal is detected using an envelope detector or a product detector, which detects or extracts the audio signal from the radio frequency signal. The weak detected audio signal is then amplified using an audio power amplifier and fed through a loudspeaker.

Functioning of the TRF Receiver
The multiple tuned RF amplifier stages will amplify the weak signals and it also improves the selectivity of the receiver. The loosely coupled and narrowly tuned RF amplifier stages reduce the bandwidth and improve the selectivity of the receiver.

 

All tuned stages must be tuned to the same desired incoming signal to keep track of the signal and to improve the overall strength and selectivity. Adjacent radio frequency amplifier stages must be well isolated to prevent coupling of the output signal back to the input producing feedback and oscillations.

TRF Receiver Integrated Circuits
An earlier version of a TRF receiver was available in an IC chip, which could introduce sufficient sensitivity and selectivity to the radio.

The old Ferranti ZN414, ZN415 and ZN416 integrated chips had the TRF receiver circuit built into them. It could operate successfully in the medium wave band and around 1.6 MHz, and the maximum frequency limit was up to 5 MHz. Other similar replacement ICs are MK484, YS414, TA7642, UTC7642, LA1050 etc.

 

The TRF receiver is now largely replaced by the superheterodyne receiver, which helps to overcome many of its disadvantages.

Disadvantages of the TRF Receiver
1. Poor selectivity of the receiver. Selectivity becomes poor due to multiple tuned RF amplifier stages that can get off-tuned from the desired signal frequency.
2. Low sensitivity of the receiver. There is low sensitivity to weak signals despite the addition of multiple RF amplifier stages.
3. Bandwidth of the receiver increases with frequency. This requires high Q filters for tuning to higher frequencies. Maintaining constant bandwidth over the entire band is difficult to achieve.
4. Collectively tuning all the radio frequency tuned circuits to the same frequency is complicated. Aligning all the tuned circuits while tuning through the entire band is difficult.
5. There is chance for feedback if the gain exceeds the threshold limit for feedback.

Watch the Video: https://youtu.be/3yD3hrTPhG0

 

 

 

 

 

 

 

 

An AM/FM Receiver Using Sony CXA1691BS

This is a demonstration of a two band receiver based on Sony CXA1691BS. It has the MW and FM bands wired around this IC. It has good reception in the FM band.

Sony CXA1691BS with the connections made

 

Sony CXA1691BS AM/FM Receiver Board

The dual band receiver for the Sony CXA1691BS is not available now in India. If you would like to purchase an FM receiver only board you can visit these vendors below.
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Working of an FM, Bluetooth and MP3 Module and Connections

This is a multimedia player that plays from a variety of media sources such as FM, bluetooth, USB, TF card, aux-in etc. The FM section has a digital tuning and has a memory storage, which can store a number of stations. The FM tuning range is from 88 Mhz to 108 Mhz. It has an antenna input, which catches moderate to strong stations. An RF amplifier may be added in the front-end to help pick up distant FM stations.

If you would like to purchase this module at an affordable price in India from Amazon, please visit these top vendors below
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Amateur Radio Repeater Stations in Kerala

This is a dynamic map view of the repeater stations in the state of Kerala in India.

 Watch the Video: https://youtu.be/pogvPYRTcgM

                                                                                                                                                                                                   

 

 

 

 

 

 

 

CD1619CP Analogue FM radio module

This is an unboxing, description and demonstration video of CD1619CP Analogue FM radio module.

This module is no longer available in the market in India. If you would like to purchase the Sony CXA1691BS FM radio FM receiver board, you can visit these vendors below.
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 Watch the Video: https://youtu.be/1jCDF_1jlEQ

 

Sony CXA1691BS FM Radio Receiver

This is an unboxing, description and demonstration video of Sony CXA1691BS radio IC board and its FM radio section performance. The sensitivity of the receiver is excellent. Selectivity is good. It only has a mono mode in FM operation.

If you would like to purchase this FM receiver board in India, you can visit these vendors below.
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Watch the Video: https://youtu.be/i0PvXWdXIls

 

 

 

 

 

 

 

 

 

 

What is a Tuned Collector Oscillator | How to Construct a Tuned Collector Oscillator

A Tuned Collector Oscillator is another widely used as a local oscillator as well as beat frequency oscillator in radios. A tuned collector oscillator consists of a parallel combination of L and C placed at the collector of the transistor tuned to a specific frequency. The tuned collector oscillator produces oscillations at a frequency determined by this resonant tuned circuit.

 

Tuned Collector Oscillator Circuit

The amplifier device used here is a BJT transistor Q1. The L1 and C1 forms the LC tank circuit. L1 forms the primary winding of the transformer and L2 the secondary. The resistors R1 and R2 form the biasing resistors of the transistor. The emitter resistor Re forms the current limiting resistor and provides stability. The capacitors C2 and Ce are the bypass capacitors. The winding of the primary and the secondary of the transformer provides 180 degree phase shift. The common emitter configuration of the transistor provides another 180 degree of phase shift between the input and the output. This gives a total of 360 degree phase shift which is needed for sustained oscillations.

Operation of a Tuned Collector Oscillator
A tuned collector oscillator consists of a parallel combination of L and C placed at the collector of the transistor. The tuned collector oscillator produces oscillations at a frequency determined by the resonant tank circuit. When the circuit is powered on, the transistor begins to conduct and the capacitor C1 starts charging. The charge is stored in the capacitor as an electrostatic field between the plates. When the capacitor is fully charged, it tries to discharge through the primary coil L1 of the transformer. The capacitor C1 then discharges into the L1 and the charge is stored in the coil L1 as an electromagnetic field.

As the voltage across C1 decreases, the coil L1 produces a back EMF that opposes the decrease in current flow. This back EMF charges the capacitor C1 and the capacitor gets charged again by the stored charge in the coil L1. These back and forth charging and discharging cycles are repeated to form a series of oscillations in the tank circuit.

The oscillation at the primary winding L1 of the transformer is coupled to the secondary winding L2 through inductive coupling. A signal is induced in the secondary winding of the transformer. The output of the secondary coil L2 is coupled to the input of the transistor Q1. The secondary winding of the transformer produces a 180 degree phase shift with the primary. The common emitter amplifier produces another 180 degree phase shift and thus a total of 360 degree phase shift is produced. This 360 degree phase shift is necessary for the positive feedback and sustenance of oscillations. The amount of feedback is adjusted by the number of turns of the secondary coil L2 of the transformer.

The energy lost in the tank circuit due to damped oscillation is overcome by the amplified signal at the collector. The frequency of oscillations can be varied by changing the parallel capacitor or the inductor.

The frequency of oscillations of the tank circuit is determined by the equation

F = 1/2π√ [(L1C1)]

Where F is the frequency of oscillation, L1 is the inductance of the primary coil of the transformer and C1 is the parallel capacitor across L1.

Applications of a Tuned Collector Oscillator
1. It is used in radio as a local oscillator.
2. It is used in radios as a beat frequency oscillator for resolving SSB signals.
3. It is used as a signal generator.
4. It is used as an RF oscillator.

Watch the Video: https://youtu.be/kSDRhl2mm6s

Crystal Radio Working on Medium Wave and Shortwave Bands

 

This is a demonstration of a crystal radio that works on different radio bands from the medium wave band up to the higher short wave bands. The ground is connected to a ground rod outside the house or to a metal water pipe. The antenna is a long wire about 20 meters long in the open space. The bands are changed by replacing the coils with another coil set needed for the required band. The tuning is done using the two sections connected together of a 2J gang capacitor, used in earlier radios. The antenna coupling may be adjusted by putting the required value of C1 or by utilizing adequate number of turns in the primary winding in the coil.

 Watch the Video: https://youtu.be/EUd2PhyUZ6A