455kHz intermediate frequency signal generator ----- 455kHz Signal Generator

Keywords: 455kHz signal generating circuit The oscillator can generate 455 kHz amplitude modulation signals, which can be used as a frequency calibration in the ultraformation modulation radio. Signal is sent to the first neutral (after the mixer), with the correction operation of the calibration, the output of the signal generator is subtractively decreased to prevent the radio AGC (Automatic Gain Control) circuit. . Figure 1 is a oscillator circuit, divided into two parts. The first portion is a multi-harmonic oscillator composed of two transistors (Q1 and Q2), producing a square wave of about 500 Hz, and the second portion is connected between the transistor (Q3) collector and the reference, a ceramic resonator (X1), constitutes The phase shifting oscillator is usually called the Piedz oscillator. R7 (22kΩ) is connected to the end of the voltage resistors R4 and R5 as the node of the voltage divisor resistors R4 and R5, and the q2 is driven, so that the current of 455 kHz oscillator is used to realize amplitude modulation of 455 kHz signal. . The multi-harmonic oscillator generating a rectangular wave or square wave is only one transistor conduction, and the other transistor is turned off, and the conversion frequency is determined by R2 and R3 and C1 and C2, and the frequency of square waves is calculated by the following formula. F = 1 / [0.693 (R2C1 + R3C2)] With the value of Fig. 1, the theoretical value is derived from 465 Hz. Due to the difference in the actual value of resistance capacitance. The frequency is slightly changed, while R2C1 and R3C2 are not absolute, and the duty ratio is not accurate to 50%. The modulation signal is coupled to a wire as antenna output with capacitor C6. The printed plate R is 72 mm × 31mm, and Fig. 2 is a component arrangement. The instrument's test work is very simple, and the LED is lit after the power is turned on. The circuit will output. 455kHz modulated signal. With the modem radio to 910kHz or 1365kHz (quadratic and triple filtering), the sound of the antenna should be heard from the sound of about 500 Hz. The oscilloscope can detect that the Q1 and Q2 collectors have a square wave of about 500 Hz, and the Q3 collector should have a sine wave of 455 kHz, which is fluctuated.

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