Here it is shown how to make a universal crystal oscillator that outputs signal with frequency 1 to 20MHz. It is a fundamental mode crystal oscillator as opposed to harmonic crystal oscillator. Fundamental mode crystal oscillator are crystal oscillator which outputs signal with fundamental frequency which is same as the crystal frequency. This oscillator is useful to testing and alignment of FM signal at the receiver.
The following shows circuit diagram of crystal oscillator.
The oscillator is in Colpitts oscillator topology. The capacitor C1 and C2 forms the capacitive feedback network. The value of the capacitors are selected such that ratio of these capacitors C1/C2 provides tradeoff between output amplitude level and stability of the oscillator. Silver mica or NPO disk ceramic capacitors should be used for these capacitors. The resistors R1 and RE provides the necessary biasing of the transistor. The transistor 2N3904 is used here but one can also use the 2N2222 transistor. The capacitor C5 connected between collector and ground and which has value between 0.01uF to 0.1uF is used to as bypass capacitor. For ac signal this bypass capacitor keeps the ac signal to ground and for dc signal it keeps the dc power voltage between 9V to 12V.
The following video demonstrates how the universal crystal oscillator works.
