[Elecraft] Re: PC Scope

[n1al at cds1.net]

It's true that with a 40 msps sample rate you can only view NON-REPETITIVE
signals up to 20 MHz bandwidth.  For a repetitive waveform, the
oscilloscope can combine multiple sweeps.  Assuming each sweep samples at
a different time offset in the waveform, the additional samples occur in
between the original samples, resulting in a much higher effective sample
rate.

I Have an HP54600 digital oscilloscope that does just that.  The bandwidth
is 100 MHz but the sample rate (each channel) is only 20 MHz.  It works
just fine on repetitive signals up to 100 MHz, but for single-shot events
the bandwidth must be less than 10 MHz.  I find that nearly all the
signals I want to look at, both digital and analog, are repetitive.

Regarding the 8-bit analog-digital converter (ADC), remember that the 8 x
6 = 48 dB dynamic range is for the entire bandwidth, single-shot.  For
slow sweeps,  you are only seeing a much smaller bandwidth, so the
effective noise is lower.  That's because each display point is actually
an average of many ADC samples. When doing an FFT, each display point is
only a small fraction of the total bandwidth, so the dynamic range is much
greater than 48 dB with an 8-bit ADC.

By the way, I really like the HP54600 because it is a true digital
oscilloscope with a user interface that looks and feels just like an
analog scope.  There is a separate front-panel control for each major
feature so you don't have to keep diving deep into a menu tree to make it
do what you want.

Al N1AL



> My concern, if I have read the spec correctly, is the 40M sample/sec.
>
> I assume that is the max rate (ie not 2x 40Ms in dual mode) because the
> usual aim is to make the spec look good!
>
> So, even in single channel mode, that is a display bandwith a bit under
> 20MHz.  Not entirely surprised, very fast sampling costs.
>
> Also note it is 8 bit.  Fine in scope mode but if planning to use an FFT
> and consider spectrum analysis, 8 bits is not that high a dynamic range.
>
> A very careful 'what do I want this for' is appropriate.
>
> Regards  73   Alan  G0HIQ
>
> --- On Sat, 13/9/08, elecraft-request at mailman.qth.net
> <elecraft-request at mailman.qth.net> wrote:
>
> Message: 26
> Date: Sat, 13 Sep 2008 12:05:55 +1000
> From: "Mike Walkington" <mike.walkington at gmail.com>
> Subject: [Elecraft] OT - PC Oscilliscope Performance
>
> All,
> Just found this PC based oscilloscope
> http://www.bitscope.com/product/BS310/
> and wonder what you think of it. Yes you are limited by needing a PC, but
> the  waveform generator, spectrum analyser and logic analyser
> functionality
> seem to be most versatile.
> Mike
> VK1KCK
>
>
>
>
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