[LAU] Jack sample-rate

[Adam Sampson]

Will Godfrey <willgodfrey at musically.me.uk> writes:

>> Not for audio, but having JACK run at 96000 Hz is quite useful for
>> low-cost software-defined radio...
> Explain.... please.

A common architecture for an SDR receiver uses a quadrature sampling
detector: you mix the incoming radio signal with a pair of clocks 90
degrees apart, and sample the two resulting signals (I/Q).  Some DSP
then allows you to "tune in" any signal within the bandwidth that you've
sampled -- if my detector's clock is running at 7 MHz and I'm sampling
I/Q at 48 kHz, my SDR receiver can demodulate any signals between 6.976
MHz and 7.024 MHz (and can receive several signals simultaneously
provided they're within that range of frequencies).

So the advantage of sampling at a higher rate is that you can receive a
wider chunk of the radio spectrum without having to retune. High-end SDR
receivers have a dedicated ADC that can run at a high sampling rate, but
cheap radios like the SoftRock kits (http://wb5rvz.com/sdr/) use a
regular soundcard.

I'm using a SoftRock RXTX with dttsp (and sdr-shell/softrig/fldigi),
which uses JACK for audio IO. Running JACK at 96 kHz for this means that
I can see most of the 30m amateur band at the same time...

Cheers,

-- 
Adam Sampson <ats at offog.org>                         <http://offog.org/>