Tuning display system for FM receiver - applies IF signal to input of amplifier containing resistor FET controlled by frequency discriminator

摘要

The tuning display system uses the d.c. output of a frequency discriminator with S-shaped characteristics to control the display of the amplitude of the IF signal. The latter is applied to the base of the input transistor (Q1) of an amplifier (Q1,Q2) for the display. The base is connected via a first resistor (6) to ground and via a second resistor (R2) to the current supply. The first resistor is an FET whose gate is connected to the dc output of the frequency discriminator (4). The demodulator and display unit (7) is connected to the collector of the input transistor. The FET may alternatively be connected between ground and the base of the output transistor (Q2) of the amplifier.