VFO circut

Posted on Feb 6, 2014

Building VFOs in 2011 might seem an irrelevant exercise given the move to and evolution of digital signal generators laden with bells and whistles like memories and audio or video frequency displays. A successful L-C VFO requires skill, patience and some good parts to pull off ” else, a `drift monster` may result. Despite their limitations, it`s

VFO circut
Click here to download the full size of the above Circuit.

possible to build L-C VFOs with low frequency drift, distortion and phase noise; our typical VFO performance markers. L-C VFOs don`t require programming skills or equipment to encode a microprocessor ” making them a good choice for people who don`t build or can`t afford kit oscillators. Most of all, they kindle creativity, problem solving and pride when your oscillator actually works as planned. Junk box radio; my passion. This material reflects lots of empiricism; not pure science. It`s really your VFO design odyssey; a chance to think creatively and critically to sort out what works and what`s folly. Countless web pages discuss VFO design and I encourage you to search for and read them. Wes` EMRFD oscillator and temperature compensation notes = essential reading. Only your first 25 VFOs will prove difficult ” it gets easier after that. Building an oscillator that stays on frequency purports our greatest challenge and goal in L-C VFO design. Since drifting VFOs pose a source of frustration, I cover some topics that may help your VFO stay on frequency ” do they help I`m uncertain, for after warm-up, I`ve measured kits that drifted 50-150 Hertz per hour, built L-C VFOs that drifted under 20 Hz per hour and every once and a while, build a drift monster VFO that sweeps upward at 2 - 8 hertz per minute! Likely under 20 Hertz per hour after warm up = a gold standard to compare against. You should be able to listen to a 10-20...

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