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26th January 2011 14:42
Haskell,
Not really. It takes time for the oscillations to grow from the noise/weak signal level up to macroscopic levels which alter the bias of the blocking oscillator (or are otherwise detectable and can trigger some kind of gating).
You most definitely can super-regenerate at lower frequencies, but the ramp-time becomes very large in human time scales. This would make it more of a "clicking" rather than a tone dipper, and it would become very frustrating to use.
A more usable approach is probably conventional dipping, but if you wanted a read-out as an audio tone you might arrange a current of voltage controlled audio oscillator to drive the speaker and give you an audio read-out.
Alternatively a bridge-balance technique is very general and can be applied to just about any frequency as long as you can make coupling into the circuits in question. Basically you use a pair of identical inductors in a Wheatstone bridge arrangement, driven by a variable RF generator. One inductor is coupled to the circuit under test, the other is not (or at least not as strongly), when the resonant circuit absorbs energy from the coupled coil the large change in reflected impedance will noticeably unbalance the bridge. The detector can drive any kind of read-out device you like and it can be made extremely sensitive, especially with logarithmic detectors. Another possibility is a return-loss bridge measuring the RL of a single small coupling loop. It lacks the beauty of the symmetry of the direct RF bridge but is easier to make work over several octaves of frequency. Demands more of the bridge and detector system though.
Regards,
Alan
17th January 2011 12:35
Could your tone dipper be built for VLF/ELF, say 1000-30,000 Hz?
14th December 2010 03:05
Hi, Just came across your site searching for RFID info. Some bells rang from way back in the past ref the superegenerative circuits. On the jfet version, might be able to adapt as a 'squegging oscillator' which when presented with a heavy rf load will prevent oscillation until the load is removed. Must be very low power when not oscillating. (To warn when items near by are moved). Good site....Regards.
23rd April 2013 20:44
qrp.gaijin wrote...