[Elecraft] USB sound dongle

[Rick Johnson]

Has anyone ever used a NewQ Gold DSP in conjunction with
digital ops?  
I was given one and don't really know if it usable for digital.
 
73,
Rick W3BI

 

> Date: Tue, 21 Aug 2012 14:28:10 -0400
> From: lists at subich.com
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] USB sound dongle
> 
> 
> On 8/21/2012 11:18 AM, Jim Brown wrote:
> > On 8/21/2012 7:48 AM, Barry LaZar wrote:
> >> However, 24 bits of quantization will get you a better dynamic
> >> range.
> >
> > Not if the dynamic range of the analog electronics limits it, which
> > is what Joe has pointed out. Often those extra bits are "advertising
> > bits" -- they fool those who don't know any better into believing
> > that more bits is better.
> 
> There are two issues here -
> 
> First most amateurs run their digital software from "line out" or the
> demodulated audio from the transceiver. The demodulated audio has
> generally been through at least one A to D to A cycle and the noise
> floor is simply too high to take advantage of even the theoretical 96
> dB dynamic range of a 16 bit sound card.
> 
> Now, if one is looking at the "raw" I/Q RF/IF or direct downconversion
> audio 24 bits "might" be usable *IF* the noise floor is low enough (a
> real *IF* with off the air signals) and any mixers and amplifiers are
> really linear through the theoretical 138 dB dynamic range *without* AGC.
> 
> None of this addresses the noise floor and dynamic range of any preamp
> in the sound card ... it only looks at the theoretical dynamic range
> of the analog to digital converter.
> 
> Then there is an additional consideration pointed out by Chen in a
> private e-mail - properly designed software can achieve dynamic range
> (sensitivity) *better than* the A to D converter (that is, it can
> "receive into the noise") by applying proper lowpass filtering and
> decimation. I know Chen uses decimation even with 16 bit cards in
> cocoaModem but it does not appear that any of the Windows centric
> digital software does so since many are based on 11025 or 12000 Hz
> sample rates and effectively throw away the potential processing gain
> by not performing any lowpass filtering in the 44100/48000 to 11025
> or 12000 sample rate downconversion.
> 
> 73,
> 
> ... Joe, W4TV
> 
> 
> On 8/21/2012 11:18 AM, Jim Brown wrote:
> > On 8/21/2012 7:48 AM, Barry LaZar wrote:
> >> However, 24 bits of
> >> quantization will get you a better dynamic range.
> >
> > Not if the dynamic range of the analog electronics limits it, which is
> > what Joe has pointed out. Often those extra bits are "advertising bits"
> > -- they fool those who don't know any better into believing that more
> > bits is better. Actually, it's far more important to optimize the
> > signal level that the A/D converter sees. That's why I like the Tascam
> > USB interface better than the Numark -- it has a much greater range of
> > gain adjustment and a clip light on the front panel. That allows me to
> > easily optimize the 90 dB or so of dynamic range that its 16 bits provides.
> >
> > Besides -- the 90 dB dynamic range provided by a decent 16-bit A/D is
> > probably more than most hams will ever see at the audio output of their
> > radios. While the radio itself has much greater dynamic range, the
> > WORKING dynamic range is limited by noise received by the antenna that
> > is often 30-50 dB greater than the electrical noise levels inside the
> > radio.
> >
> > 73, Jim K9YC
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