Magnus Danielson wrote: > From: "Pete" <[EMAIL PROTECTED]> > Subject: Re: [time-nuts] Fast frequency counting question > Date: Sun, 4 May 2008 16:07:02 -0600 > Message-ID: <[EMAIL PROTECTED]> > > Pete, > > >> I may be out in left field (again), but isn't this >> a textbook measurement for a fast sampling >> 'scope? I think most of the recent devices in >> this category have 500MHz to 10+GHz >> sampling rate, with plenty of memory depth. >> They can output a time record via GPIB, >> USB or whatever. >> >> The time record can be post-processed to >> yield actual zero crossings. You also get all >> the amplitude data, which should help with >> analysis. >> >> Some of the newer 'scopes have the post- >> processing software built in & there is at >> least one source of PC based timing >> analysis available. >> > > I still think it will be hard to acheive the required resolution that way. > But yes, modern scopes have moved considerably in the right direction lately. > > I also somewhat question the importance of this initial time. It should not be > the make or break of the application as being claimed. > > One interesting thing one can do is to hook a spectrum analyser to the > oscillator output and see how the spectrum changes over the first initial > time. > It should be an interesting experience trying to figure out what is happening > and why... :) > > Cheers, > Magnus > > The quickest and easiest way to achieve the required resolution is to buy a high speed (~100MHz) sampling ADC evaluation kit from Analog Devices, Linear Technology etc, use a low phase noise crystal oscillator (eg Wenzel ULN or equivalent performance device) or equivalent bandpass filter the output and use as the sampling clock source. Then either:
1) Sample the 40MHz signal directly (possibly after some bandpass filtering) then post process the raw data. 2) Use a mixer to produce a ~1MHz output bandpass filter it and sample this signal (amplifying if necessary) with the ADC then post process the raw data. This will achieve lower noise. However the mixer LO has to have very low phase noise. High speed ADC evaluation kits are readily available (at least from Linear) and considerably cheaper than a timer counter with equivalent resolution and noise f such an instrument is available at all. The LTC evaluation kits include a board with local sample storage and a USB interface to a PC. The sampling clock frequency need not be exactly 100MHz as long as its frequency is known. 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.
