2008-04-18
Tone Dipper Update
Patrick Egloff TK5EP asked me to redraw the circuit diagram to make it more clear. This is a great idea, and I took the opportunity to correct some errors as well. Follow the link above and take a look at Patrick's site, he is quite an accomplished photographer and I love his Return Loss/VSWR calculator wheel!
Anyway, here is the updated circuit diagram:
A Single JFET Version
I have since built a single JFET version which is somewhat harder to get working across broad frequency ranges, but performs well to upper VHF frequencies. I just tacked it together on a piece of PCB to keep the strays low, making it capable of operating into UHF with changes to the feedback topology.
And here is the prototype, which while just a hack on a fragment of PCB is quite useful for fixed-tune dipping. Just set it against the signal generator in absorption mode then lay it on the desk and couple a tank to it while you tune for a tone frequency change. This is very useful for measuring small inductances with a test jig comprising a calibrated trimmer and a clamp which holds the two together.
Obviously with no AF amplifier this is a little quiet, but it is more than loud enough for bench work.
Some Notes
For making different coils for other bands I have brought out both gangs of the polyvaricon to the DIN plug. This isn't strictly needed, and the current coils only use the "A" gang, which is the larger of the two with a better capacitance range.
If you only need a small amount of capacitance then you can add a series capacitor, estimated with my VFO calculator. The large device capacitances of the emitter coupled oscillator will make such calculations estimates as best, but it is useful to get you in the ballpark. It is quite easy to reduce the range of tuning to cover just a band, but in dipper service you probably want at least a few MHz per coil. That said there is nothing to stop you from making coils for special purposes, I do when I need to.
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Attachments
| title | type | size |
|---|---|---|
| Circuit Diagram Source | application/postscript | 17.060 kbytes |
| JFET Version Source | application/postscript | 15.216 kbytes |
Parent article: Super-Regenerative Tone Dipper.