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]> >> Message-ID: <[email protected]> >> Content-Type: text/plain; charset=ISO-8859-1 >> >> Joe >> >> >> >>> >> >>>> [BG] Proposed test setup: >>>> (preliminary to be refined) >>>> >>>> Drive 2 sound card inputs in parallel with the same source. >>>> >>>> Source amplitude: >>>> Max sound card input -3dB >>>> >>>> >>> What kind of dB? >>> >>> >>> >> Peak input signal voltage = 70% of sound card maximum peak input voltage. >> Just to leave some margin for gain tolerances. >> > > OK. > > > >> >> 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. >> >> Test frequencies: >> >>>> 100Hz >>>> >>>> 1kHz >>>> >>>> >>> Why no 10 Hz? (Well, 20 Hz.) >>> >>> >>> >> No particular reason other than some complications if a lamp stabilised >> oscillator is used. >> A diode soft (series R) clamped RC oscillator is more flexible in this >> regard. >> I'll also produce a circuit schematic for one of these oscillators. >> > > Jim Williams' circuit would handle 10 Hz if I recall. > > > >> >> Sound card sample rate: >> >>>> ~24KSPS >>>> >>>> >>> I assume that this is the lowest rate supported, and certainly is overkill >>> for 1 KHz. >>> >>> >>> >> It varies with the sound card. >> I just suggested that for a starting point in the discussion. >> >> 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.
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.
