3955 - 4455 kHz local oscillator (VFO)

This 2 transistor based covers the whole 80m bandwidth (frequencies between 3500 and 4000 kHz).

This Basic Colpitts LC oscillator designed for 80-meter receiver with 455-kHz IF uses zener in supply line to minimize frequency drift. Emitter-follower buffer contributes to stability by isolating oscillator from mixer.
Low-pass filter C13-L2-C14 attenuates harmonics developed in Q3 and Q4.
L1 is Miller 4503 1.7-2.7 uH variable inductor.
L2 is 48 turns No.30 enamel closewound on 1/4-inch wood dowel or polystyrene rod.
Main tuning capacitor C10 can be 365-pF unit with six of rear rotor plates removed.


Q3 and Q4 - 2N4124

D. DeMaw and L. McCoy, Learning to Work with Semiconductors, QST, June 1974, p 18-22 and 72


Reference: www.seekic.com

No comments:

Post a Comment