This is from home. I'll not be at work until next year. At 11:48 PM +0000 12/18/08, time-nuts-requ...@febo.com wrote: >Message: 4 >Date: Fri, 19 Dec 2008 12:17:33 +1300 >From: Bruce Griffiths <bruce.griffi...@xtra.co.nz> >Subject: Re: [time-nuts] Sub Pico Second Phase logger >To: Discussion of precise time and frequency measurement > <time-nuts@febo.com> >Message-ID: <494ada0d.3060...@xtra.co.nz> >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. > >> 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 _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.