2007-12-18
Receiver Boxed Up
I finally got around to putting the PA2OHH-style Reflexing-Regenerative Receiver circuit into a more permanent form. The tuning was arranged to cover 31 metres, spread nicely across the dial. It is no longer touchy to use and tunes slowly through the band. There is a slight body capacitance effect on the spot on the box nearest the coil, but it is hardly noticable unless you are using the receiver oscillating. For using a plastic box (a cheap Jaycar potting box) it is surprisingly stable. I chose this box so as to keep the guts accessible for tinkering and show-and-tell purposes.
A very simple audio amplifier was built into the radio to make it self-contained, driving standard 32 Ohm headphones in series. Its fidelity isn't wonderful, but its a reasonable match for the quality of the detector. There is a common-mode choke in the headphone lead to prevent any stray RF getting into the audio amplifier (which isn't especially well designed to reject RFI). The choke was added after experiencing some minor problems with FM and TV stations breaking into the AF-side of the radio.
The dial has not been calibrated yet, and probably won't be. There is no front-end at all, the antenna is directly coupled to the resonator, so this is really only a toy radio, but it is quite usable for shortwave listening. I don't think it is too bad for 3 transistors and only a few mA of draw. The huge knob is all I had which wasn't for fluted shafts, but its large size is useful for smooth tuning, so I may keep it that way if I'm not going to calibrate the dial.
The circuit diagram.
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Attachments
| title | type | size |
|---|---|---|
| Circuit Diagram Source | application/postscript | 18.217 kbytes |
Parent article: Regenenerative-Reflexive Receiver.