If you are looking for a constant frequency generator that easy and inexpensive. Here are the transistor crystal oscillator circuit ideas. They may help you works finish. Since 30 years ago, I used this oscillator circuit to AM radio station. I use it as a radio frequency carrier with 639kHZ Crystal. The below circuit works perfectly.
- C1 is trimmer 2-30pF
- You can use any crystal, for example, 100kHz to 10MHz.
- The output is sine waveform about 0.3-0.5Vp-p.
- The power supply volatage is 3V to 12V regulated supply.
I will show you full article of AM carrier frequency later.
Also, Others transistor oscillator circuit ideas for you. Though very ancient and easiest, they still have many uses.
Oscillator astable multi-vibrator with Crystal controller
An oscillator circuit of this nature. Often used as a clock circuit. This circuit uses a million crystal frequency control with stability. And a circuit that does not use the capacitor or Inductor all.
Each transistor to work, the amplifier with feedback. The Q2 transistors(2N834) to circuits with a gain equal to 1. The gain of the transistor Q1(2N834), as a function of the resistance of the crystal, while the resonance.
By default, the resistance will be less than 22K.This is the feedback resistance of the circuit. Therefore, the gain of the circuit Q1, it is higher than one.
Output from a square wave circuit.The size of the signal depends on the voltage input to the circuit.This circuit can oscillate from birth 3 KHz up to 10MHz.
On the long time ago I’ve used this product on a standard radio frequency AM 639KHZ can work well. The output signal is a sine Very low distortion. But temperature should be careful stable.
Low voltage crystal oscillator Circuit using FET
We can easily use FET and Crystal to generate the frequency as Low voltage crystal oscillator Circuit, 1.5V-10V supply. It can operate at a supply voltage to 1.5 volts only and at crystal frequency 100 KHz to 10 MHz.
The crystal is connected to between the drain and gate of FET-T1 BF256. It runs in resonance mode in parallel coil form. The inductor L1 makes better frequency stability and can use crystal in the wide frequency range, Although the crystal is not appropriate, it also works.
The capacitor C1 is connected with the crystal to act as “padding” for the return phase 180 degrees, to the input of FET. The output will be buffer by T2. This designed circuit is tested to operate at frequencies 100 Khz, 1 MHz, 4 MHz, 8 MHz and 10 MHz at lowest 1.5 volts only.
Parts you will need
T1: BF256 FET transistors
T2: BC147 NPN Transistors
C1: 1nF 50V (0.001uF) Ceramic capacitors
C2: 22nF 50V (0.022uF) Ceramic capacitors
X’t: 100K-10MHz Crystal
R1: 4.7M 0.25W resistors
R2: 220 ohms 0.25W resistors
Symmetrical Harmonic Oscillator circuit
Here is another one of transistor crystal oscillator circuit idea. This is the Symmetrical Harmonic Oscillator circuit. It generates 3rd harmonic frequency using crystal. This special circuit is without tuning circuit. Because these type circuits always use a tuning circuit.
How it works
In the circuit diagram below is Astable multivibrator Oscillator circuit. There is the crystal across between both emitter lead of transistors Q1 and Q2. Which The 40pF trimmer capacitor-C5 connects with crystal to adjust the fundamental frequency to get 3rd harmonic frequency as you want.
This circuit is designed for the crystal that uses the fundamental frequency of 6-20 MHz. The output frequency of the circuit is between 18MHz to 60 MHz.
You can use the normal RF transistors can in this circuit. The output has signal about 500mVp-p. That is enough for the common usage.
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