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Intermediate Frequency Amplifier - How does a radio receiver work .. Electronics

Intermediate Frequency Amplifier

The intermediate frequency amplification stage (153) consists of the intermediate frequency transformer MTM 1, which is permanently tuned to the intermediate frequency on which the device is designed. After that, the signals pass to the transformer MTM? after being amplified by transistor 1, then take their way to the other transistor TR 2. It is noted that the bases of the two transistors are fed from points S and S.

It is always taken into account in transformers used to connect valves, transistors and other circuits that they have two separate coils as in Figure (154),

153 - Intermediate Frequency Amplifier
154 - Intermediate Frequency Transformer

It is also taken into account that each of these transformers is permanently tuned to the required frequency by a fixed capacitor S. In most cases, the diode transformer coils (MTM 3, Figure 153) are not tuned. Some secondary coils of transformers are not tuned in some receivers and transistors may be used in demodulation processes (155). In this case, audio signals are taken through capacitor S. As for the thermoelectric valves such as the diode and triode, they are used to detect signals in demodulation. It should be noted that the semiconductor diode is commonly used.

Figure (156) shows a schematic diagram of the different stages contained in the receiver, where the frequency converter converts all incoming signals, regardless of their frequency, into a signal with a fixed frequency, which is the middle frequency of the device. The process of tuning the circuits of the amplifier of the middle frequency signals is useful in eliminating interference that may occur as a result of capturing some other signals, and it is also useful in increasing the intensity of the desired signal.

The detection stage requires separating the signal with the audible frequency from the carrier signal. Therefore, it passes to the stage of amplifying the audio signals. The last stage, which is the output stage or the final amplification stage, works to strengthen the intensity of the audio signal and raise its level to the point that it can operate the loudspeaker. It is obvious that the stages used in transistor devices and how they are sequenced are the same as those used in devices that use valves.

155 - Transistor detector.
156 - Schematic diagram of the receiver stages actually above the contrast.