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Permeability Tuned Oscillator (PTO) Working Nicely

My last entry described my accidental discovery of the PTO for QRP purposes. I breadboarded it and was amazed at the results! I went ahead and built this carefully in an enclosure and the output is wonderful. It’s strong, it’s stable, and it tunes effortlessly over the same range it did before (about 1MHz). The video describes details of the action, and demonstrates the stability of the oscillator by letting you hear it audibly on a nearby receiver.

The fundamental concept and hardware is straightforward. Two nuts are soldered into an Altoids tin providing much-needed grounding for the screw (reduces shift when it’s touched). Also the wire soldered over the screw is pinched firmly at the base to apply constant pressure to the screw to make it hard to turn and therefore more stable while turning. The inductor is a bunch of turns (no idea how many, about a meter of magnet wire) around a McDonalds straw.

Alltogether it’s a simple colpitts oscillator with a MPF102 JFET at its heart, using a 74hc240 CMOS buffer as an amplifier. There’s a voltage regulator in there too.DSCN1356

The result? Pretty darn stable (by CW QSO standards).  That’s without any regard to thermal isolation or temperature compensation. I’m quite pleased!  I look forward to MUCH more experimentation now that I’m starting to feel good about designing and building simple, tunable, stable oscillators. It’s always hard to nail all 3 in a single device!

About the author

Scott W Harden

Scott Harden has had a lifelong passion for computer programming and electrical engineering, and recently has become interested in its relationship with biomolecular sciences. He has run a personal website since he was 15, which has changed names from HardenTechnologies.com, to KnightHacker.com, to ScottIsHot.com, to its current SWHarden.com. Scott has been in college for 10 years, with 3 more years to go. He has an AA in Biology (Valencia College), BS in Cell Biology (Union University), MS in Molecular Biology and Microbiology (University of Central Florida), and is currently in a combined DMD (doctor of dental medicine) / PhD (neuroscience) program through the collaboration of the College of Dentistry and College of Medicine (Interdisciplinary Program in Biomedical Science, IDP) at the University of Florida in Gainesville, Florida. In his spare time Scott builds small electrical devices (with an emphasis on radio frequency) and enjoys writing cross-platform open-source software.

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