[Elecraft] odds and ends...

[Joe Subich, W4TV]

 > A single channel of adc samples at 48ks/s can only display VALID
 > unique frequency data up to 24 kHz before the spectrum "folds over".
 > Since both I and Q can be used, they effectively double the sample
 > rate, as if you were sampling at 96k.  Not exactly correct, but close
 > enough.

Correct ... I was recalling the bandwidth from the built-in sound
device on one of my systems and thinking (incorrectly as it turns
out) that it was sampling at 48 KHz when it actually has 96KHz
drivers.

73,

    ... Joe, W4TV


On 8/19/2012 11:51 PM, WB4JFI wrote:
> "Reputable" companies also sell oxygen-depleted cables to
> audiophiles.
>
> You can't cheat mother nature, no matter how hard you try.  I don't
> doubt that they can display whatever they want, but as to actual,
> significant data displayed thereon, that's a different matter.
>
> A single channel of adc samples at 48ks/s can only display VALID
> unique frequency data up to 24 kHz before the spectrum "folds over".
> Since both I and Q can be used, they effectively double the sample
> rate, as if you were sampling at 96k.  Not exactly correct, but close
> enough.
>
> Nyquist -who is still valid in the real world - theory says that you
> can only recover signals whose freq is up to one-half the sample
> rate.  Again, I am generalizing, but close enough.  So, one-half of
> 96k is 48k, not 96k.  Factoring not involved.  48k total bandwidth
> before the spectrum folds over.  Doesn't matter what the display
> says.  Try it on Rocky, Powersdr, hdsdr, winrad, etc.
>
> I'm not saying that Joe or Larry are doing anything wrong, just that
> if your sound card (or DDC or other device) is providing I/Q samples
> at 48ks/s per I/Q pair, th best you can get is a total of 48k of
> valid, unique, and correct spectrum data points.  That usually
> results in plus and minus 24khz being displayed around center
> frequency.
>
> To say that you can display 96k of unique, correct spectrum data from
> a 48ks/s rate I/Q pair is, well, not accurate (wrong).  It's like
> depleting too much oxygen from your speaker cables.  You end up with
> a hollow sound, like taking the oxygen away left too much room for
> the electrons to bounce around in.  If you like fuzzy bass, that's
> ok.
>
> But, I've been wrong before. Sent from tfox iPad
>
>