This project is a 7MHz vfo that uses a 3.58MHz ceramic resonator. The oscillator output is fed to a frequency doubler but the output of the stage contains full of harmonics. To clean the output waveform, a double tuned band pass filter is added. Each filter resonates at 7MHz and the passband is quite sharp which effectively attenuate the unwanted harmonics.
The output level is at 3volts peak to peak and has a 60Hz per hour drift after some warm-up. Using 1N4007 as varactor, i was able to tune +/- 0.200MHz from the center frequency of the oscillator. 73 de du1vss
