Design Diary: Varactor-Tuned Regen Receiver

[QRP Gaijin] likes to build regenerative receivers. If you’ve ever built a serious one, you know there are (at least) two problems: One is you need a variable capacitor (hard to find these days). The other annoyance is that if you cover a wide frequency range, you probably need more than one coil.

[QRP Gaijin’s] latest radio design doesn’t have either of these problems. He uses a coil with a single pole double throw switch to bandswitch a single coil. There is no traditional main tuning capacitor. Instead a 1SV149 varactor provides the radio’s main tuning capacity (the diode tunes between 35 to 500 pF).

The post provides a nice design and a neat looking build in a Tupperware container (well… the outside is neat, at least; the inside is… best left inside the Tupperware). Better still, [QRP Gaijin’s] post details how he got to the final design, starting with the idea, and detailing the original design and the changes he made along the way. He also used data from an earlier build to limit how much the regeneration control has to be changed over wide frequencies and details how that changed the design. The prototype actually lacks the planned bandswitch, but will cover 3 to 30 MHz with the right coil.

There are certainly simpler regenerative receivers out there. However, the sophistication of this design along with the details of the designer’s thought processes makes this an interesting intermediate weekend project.

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WiFi streaming radio update

Since our last post about his WiFi Streaming Radio Project, [Jeff] has been hard at work to release part 8 of the project where he adds tuning control to the radio. Interestingly enough, the addition of the tuning control only requires a potentiometer and the completed AVR LCD board from part 7. After wiring the potentiometer to the analog to digital converter on the AVR and adding a few lines of code, the radio can now be tuned quickly and easily. In addition to thoroughly explaining the hardware changes, [Jeff] details the configuration changes required to the OpenWRT framework so that bidirectional communication between the router and AVR is possible, allowing the tuner to function properly. Be sure to check out the video above to see the tuner in action.