IF Amplifier

INTRODUCTION:

In this instructables, I am going to make a two stages IF (Intermediate Frequency) Amplifier for MW(Medium Wave a) and SW(Short Wave) Receivers. IF amplifiers are used in Superhetrodyne radio receivers to amplify inter mediate frequency or IF. So, Let's get Started!

AMPLIFIER:

An amplifier is an electronic circuit or device that is used to amplify electrical signals (voltage and current). The amplifier is a most popular and useful circuit in electronics and electrical engineering. Almost every analog electronic circuits consists at least one amplifier in order to amplify signals(voltage or current). Amplifiers can be classified on the basis of Frequency, operating point or class, Configuration, stage, coupling and power.

ON THE BASIS OF FREQUENCY:

On the basis of frequency amplifiers are of 5 (five) types-

1. Audio Frequency Amplifier
2. Video Frequency Amplifier
3. Radio Frequency (RF) Amplifier
4. Intermediate Frequency (IF Amplifiers)

ON THE BASIS OF COUPLING:

On the basis of coupling amplifiers are of four types-

1. RC (Resistance Capacitor ) coupled amplifier
2. Transformer Coupled Amplifier
3. LC ( Inductor Capacitor) coupled Amplifier
4. Direct Coupled (DC) Amplifier

ON THE BASIS OF POWER:

1. Low Power Amplifier
2. High Power Amplifier

ON THE BASIS OF OPERATING POINT:

On the basis of position of operating point, amplifiers are of four types-

1. Class A Amplifier
2. Class B Amplifier
3. Class AB Amplifier
4. Class C Amplifier
5. Class D Amplifier

ON THE BASIS OF TRANSISTOR CONFIGURATION:

On the basis of Transistor configurations Amplifiers are of three types-

1. Common Emitter(CE) Amplifier
2. Common Base(CB) Amplifier
3. Common Collector(CC) Amplifier

ON THE BASIS OF USED STAGES:

On the basis of number of used stages amplifiers are of three types-

1. Single stage Amplifier
2. Two stage Amplifier
3. Multistage Amplifier

now you will surely familiar with all kinds of amplifiers used in Electronics. Here I shall discuss about Intermediate Frequency Amplifier only because explaining all the amplifiers given above is not possible here.

INTERMEDIATE FREQUENCY

In superhetrodyne radio receivers, IF amplifiers are widely used. Superhetrodyne Radio receivers uses the principle of superhetrodyne so they are known as superhetrodyne radio receivers. Superhetrodyne principle was discovered or invented by an American electrical Engineer Sir. Edwin Howard Armstrong(December 18, 1890 - February 1, 1954) in1918. Intermediate frequency in AM Radio receivers is 455KHZ or 465KHz and In FM Radio receivers it is 10.7MHZ.

PRINCIPLE OF SUPERHETRODYNE:

This is a principle that is used in communication engineering and this principle was invented by an American Engineer Edwin H. Armstrong in 1918. Now a days all radios and Television receivers use the principle of superhetrodyne.

according to superhetrodyne principle " The RF signal received by the antenna is mixed with a local oscillator signal and mixer produces a signal whose frequency is either the sum of RF signal and Local oscillator signal or the difference of RF signal and local oscillator signal and this signal given by the mixer is called Intermediate frequency also known as IF

IF AMPLIFIER

IF or Intermediate frequency amplifier is a transformer coupled amplifier that is used in superhetrodyne radio receivers to amplify intermediate frequency. AM radio receivers uses 455KHz as intermediate frequency while FM receivers uses 10.7MHz as intermediate frequency the IF frequency of a radio receiver can be calculated by the following formula-

1. IF = F(lo) - F(rf)
2. F(lo) = F(rf) + IF

Parameters:

IF = intermediate frequency. F(rf) = frequency of received RF signal. F(lo) = frequency of local oscillator. here I shall discuss about about the IF amplifier that is used in AM Superhetrodyne Radio Receivers to amplify 455KHz IF signal. The circuit diagram of a single stage IF amplifier is given below.

SINGLE STAGE IF AMPLIFIER:

The circuit diagram of single stage IF amplifier has been shown below. The circuit consists of following components-

1. BF495 Transistors
2. R1,R2 Resistors
3. T1,T2 IF Transformers
4. C1,C2 Capacitors

I have used fixed bias circuit to provide the dc bias to the transistor because the calculation and design of fixed bias amplifier is not as complicated as other transistor bias circuit. IF amplifiers use transformer coupling to couple two, three or more IF stages. IF amplifier is a fixed frequency amplifier because it only amplifies the input signal that have a frequency equal to the input IF transformer In am radio receivers all IF stages are tuned at 455KHz frequency. So for a good reception of any signal all the if transformers must be tuned at 455KHz frequency