Larkin's Oscillator Explained
in [Design]
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From: Baron on 16 Jun 2010 16:06 John Larkin Inscribed thus: > On Wed, 16 Jun 2010 08:39:19 -0700 (PDT), George Herold > <gherold(a)teachspin.com> wrote: > >>On Jun 15, 11:22 pm, Phil Hobbs >><pcdhSpamMeSensel...(a)electrooptical.net> wrote: >>> George Herold wrote: >>> > On Jun 15, 5:32 pm, Phil Hobbs >>> > <pcdhSpamMeSensel...(a)electrooptical.net> wrote: >>> >> George Herold wrote: >>> >>> On Jun 15, 2:54 pm, Phil Hobbs >>> >>> <pcdhSpamMeSensel...(a)electrooptical.net> wrote: >>> >>>> baron wrote: >>> >>>>> George Herold Inscribed thus: >>> >>>>>> On Jun 14, 3:29 pm, John Larkin >>> >>>>>> <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>>>>> On Mon, 14 Jun 2010 12:12:17 -0700 (PDT), George Herold >>> >>>>>>> <gher...(a)teachspin.com> wrote: >>> >>>>>>>> Could someone tell me what squegging is? A google search >>> >>>>>>>> gives hints of something like motor-boating, but different? >>> >>>>>>> We're referring to an oscillator that oscillates in bursts, >>> >>>>>>> rather than continuously. A resonator connected to a >>> >>>>>>> negative resistance doesn't squegg, but on the other hand >>> >>>>>>> its amplitude builds to infinite (for certain values of >>> >>>>>>> infinite) at a rate determined by Q.. You can think of an LC >>> >>>>>>> resonator as having a 1st order response, measuring >>> >>>>>>> oscillation envelope versus drive. Oscillators squegg when >>> >>>>>>> some amplitude limiting mechanism adds additional time >>> >>>>>>> delays or memory, more poles in the control loop, like the >>> >>>>>>> capacitor in the base of my circuit. A bigger cap reduces >>> >>>>>>> the tendency to squegg. A superregen receiver is a >>> >>>>>>> squegging-on-purpose RF oscillator. That's a fascinating >>> >>>>>>> circuit. John >>> >>>>>> Hmm, OK something like motorboating gone to the extreme.. >>> >>>>>> enough amplitude modultaion to shut the oscillator off for >>> >>>>>> some time. (?) Does the squegg rate stay constant in a >>> >>>>>> sugerregen receiver? I'm not real sure what a superregen >>> >>>>>> reciever is, anything like a marginal oscillator? >>> >>>>>> George H. >>> >>>>> Its a technique by which an amplifier is held on the verge of >>> >>>>> oscillation by positive feedback, at which point the gain is >>> >>>>> very high. By causing the oscillation to be quenched at the >>> >>>>> instant it starts is where the "Super" bit comes from in >>> >>>>> "Superregenerative". Commonly used in radio receivers where a >>> >>>>> single active device is used to both amplify the incoming RF, >>> >>>>> demodulate it and amplify the resultant AF, often driving >>> >>>>> headphones directly. Often frowned upon because of the >>> >>>>> interference that can be caused by radiated RF. >>> >>>> I think you're confusing it with a Q-multiplier, which is a >>> >>>> marginally-stable positive feedback gizmo used to sharpen up >>> >>>> crummy RF tank circuits in HF radios. (They're noisy as can >>> >>>> be, but you don't care at HF.) >>> >>>> A superregen is an oscillator that gets quenched (i.e. turned >>> >>>> on and off) at some more or less fixed ultrasonic frequency >>> >>>> like 50 kHz. Quench can be internal (due to squegging or >>> >>>> blocking), or can be applied externally. >>> >>>> Since oscillation has to build up from noise, even a small >>> >>>> input signal changes the average output level dramatically. >>> >>>> The build-up is exponential, so an input signal e times the >>> >>>> thermal noise speeds up the build-up by one whole time >>> >>>> constant. >>> >>> Excellent! I was reading a few web things about it and this is >>> >>> the critical point that I did not see mentioned. >>> >>> Hmm, seems like you might be able to measure changes in noise >>> >>> with a super-regen too. (I'm not sure how you would calibrate >>> >>> it.) George H. >>> >> The rushing sound from the speaker is amplified thermal noise. >>> >>> >> Cheers >>> >>> >> Phil Hobbs >>> >>> >> -- >>> >> Dr Philip C D Hobbs >>> >> Principal >>> >> ElectroOptical Innovations >>> >> 55 Orchard Rd >>> >> Briarcliff Manor NY 10510 >>> >> 845-480-2058 >>> >> hobbs at electrooptical dot nethttp://electrooptical.net-Hide >>> >> quoted text - >>> >>> >> - Show quoted text - >>> >>> > I've never heard it... sigh. The noise only 'sets' the size of >>> > the first oscillation (or so). Ever 50kHz 'squegg' gets a >>> > different seed. (I'm probably using squeeg wrong.) The noise in >>> > the noise will go like the squegg freq over the carrier. Seems >>> > like I'm going to have to try and build one. My son and I can >>> > listen to AM radio. >>> >>> > George H. >>> >>> Or even FM. Of course due to the logarithmic response the AM is >>> sort of distorted. You can also run a superregen in linear mode, by >>> speeding up the quench so that the oscillation never quite reaches >>> its final amplitude. That's quite a bit tweakier, though. >>> >>> Cheers >>> >>> Phil Hobbs >>> >>> -- >>> Dr Philip C D Hobbs >>> Principal >>> ElectroOptical Innovations >>> 55 Orchard Rd >>> Briarcliff Manor NY 10510 >>> 845-480-2058 >>> hobbs at electrooptical dot nethttp://electrooptical.net- Hide >>> quoted text - >>> >>> - Show quoted text - >> >>I don't quite 'see' how it works with FM, but that's OK. I guess AM >>at 1MHz just sounded easier than FM at 100MHz. Oh I was thinking of a >>linear mode... tweaky, gives you something to do. It's really pretty >>neat that with one amp you can from noise levels up to volts. >> >>George H. > > A superregen makes a decent noise generator. > > John At the right frequency can really annoy the neighbors. :-) -- Best Regards: Baron. |