90-125 Mhz Crystal RF Oscillator

This is a circuit of 90-125 MHz Crystal which is very useful for VHF/UHF converters. This circuit provide 5 to 15 mW output. High-quality fifth- or seventh-over-tone crystal type can be used in this circuit. Undesired oscillation never reach above 500 MHz because of Ferrite bead FB. Using regulated power supply and allowing crystal to operate at its natural series-resonant frequency, will give best stability. Here is the schematic diagram of the circuit:

The C1 is a 10pF mica. For C2, use as high value as possible such as 20 to 60pF mica. A 20 pF miniature trimmer or piston is used for C3. The value of L1 is 8 turns no 24(0.5mm) on amidon T37-12 toroid core, tapped 3 turns fro cold end. For Q1, we can uses 2N5179, 2N2857,2N3563m 2N918 or equivalent but fairchild 2N5179 is recommended. The value of The RFC is 0.39µH which resonate with crystal holder capacitance. The maximum length of Y1 is 6mm or 1/4″. The value of Y1 is 90 to 125 MHz, 5th or 7th overtone, series-resonant, HC-18/U crystal. [Circuit’s schematic diagram source: J. Reisert, VHF/UHF Techniques, Ham Radio, March 1976, p 44-48]