Joe Joe Gwinn wrote: > Bruce, > > At 3:54 AM +0000 12/19/08, [email protected] wrote: > >> Message: 6 >> Date: Fri, 19 Dec 2008 16:54:12 +1300 >> From: Bruce Griffiths <[email protected]> >> Subject: Re: [time-nuts] Sub Pico Second Phase logger >> To: Discussion of precise time and frequency measurement >> <[email protected]> >> >> Joe >> Joe Gwinn wrote: >> >>> This is from home. I'll not be at work until next year. >>> >>> At 11:48 PM +0000 12/18/08, [email protected] wrote: >>> >>> >>>> Message: 4 >>>> Date: Fri, 19 Dec 2008 12:17:33 +1300 >>>> From: Bruce Griffiths <[email protected]> >>>> Subject: Re: [time-nuts] Sub Pico Second Phase logger >>>> To: Discussion of precise time and frequency measurement >>>> >> >> <[email protected]> >> >> >> >>>> Joe >>>> >>>> >>>> >>> >>>> >> >> >> [snip] >> >> >> Sources: >> >>>> >>>> >>>>>> 1) Wien bridge or equivalent (eg state variable oscillator with soft >>>>>> clamping) relatively low distortion oscillator. >>>>>> >>>>>> 2) Buffered low pass filtered output of binary divider driven by a >>>>>> crystal oscillator >>>>>> >>>>>> >>>>>> >>>> > RC oscillator sounds far simpler and more flexible. >>>> >>>> A Wien bridge using a lamp is perhaps the simplest. >>>> I'll create a circuit schematics for this using an OPA2134 (dual lowish >>>> noise JFET opamp). >>>> One opamp for the oscillator one to drive the sound card (attenuation of >>>> the oscillator output will be required for some sound cards and it is >>>> desirable to have a low output impedance driver). >>>> >>>> >>> Jim Williams of Linear Technology had a very good low-distortion AGC >>> controlled Wein Bridge oscillator. If I recall, he used a photo-FET >>> or the like as the servoed resistor in the bridge. There may be an >>> application note on the LT website, but I saw it in a chapter of a >>> book on analog circuitry, the chapter author being Jim W. >>> >>> >>> >>> >> I have the application note. >> > > LT App Note 43 is what JW mentions. Figure 47 is the key. (He also > mentions App Note 5.) > > These cites are from the refs of "Max Wien, Mr. Hewlett, and a Rainy > Sunday Afternoon", Jim Williams, Chapter 7 in "Analog Circuit Design > -- Art, Science, and Personalities, edited by Jim Williams, > Butterworth-Heinemann 1991. The relevant section of App Note 43 > seems to be shared with this chapter. > > It wasn't a photo-FET he used, it was a Vactec model VTL5C10 > optically (LED) driven CdS photocell. > > Note for those (in Australia, NZ and Europe) who may want to replicate that oscillator: The VTL5C10 device is obtainable locally from RS Components. > Most of it is here (what's missing is some history and the refs): > <http://books.google.com/books?id=Il4xxTTyhbEC&pg=PA43&lpg=PA43&dq=Max+Wien,+Mr.+Hewlett,+and+a+Rainy+Sunday+Afternoon&source=bl&ots=jnHNItJrOF&sig=ZL_CB_yIdT0ZbsD7Ieu_CjVYJHk&hl=en&sa=X&oi=book_result&resnum=1&ct=result#PPA53,M1>. > > > >> >> For an AP192 the directly (without sample rate interpolation) available >> >>>> output sample rates are: >>>> >>>> 192, 96, 64, 48, 32, 8 KSPS. >>>> >>>> >>> OK. I would start with 8 ksps. We will end up decimating below that >>> anyway, except for 1 KHz test signals. >>> >>> >>> Joe >>> >>> >>> >> I'll breadboard an oscillator over the holidays and take some samples. >> > > A rainy-day activity for sure. In the Boston area, the issue is > snow - a noreaster is just now starting, with a foot of snow expected. > > Joe > > AFAIK it has never snowed here. It does snow on the central NI Plateau but not usually in December. I'll start with a diode limited (soft clamps - resistance in series with diodes) oscillator and move to a lower distortion one if necessary.
Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
