From: Claudio Pozzi <smtp01@email.it>
To: rsgb_lf_group@blacksheep.org
Date: Thu, 24 Feb 2005 12:23:37 +0100
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Subject: Re: LF: Re: Off Topic  Ft101zd
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On Thursday 24 February 2005 02:18, Alexander S. Yurkov wrote:
> Dear Alberto,
>
> On Wed, 23 Feb 2005, Alberto di Bene wrote:
> > Do really exist A/D converters capable of 24-bit resolution at 30
> > MHz bandwidth ?
>
> Why one need 24-bit? Though 16 bit is adequate for most SW,MW,LW
> recievers. 16 bit yelds abt 90 dB dynamic range (every bit exept
> sign bit yelds 6dB).

This means that 1 bit give a sufficient MDS? The recovered audio is 
ON/OFF tone?
 
> But this is dynamic range if there is no 
> filtering. When you make banwidth narrow by DSP then dynamic range
> will be improved because noise decreases. If frontend sampling rate
> is, say 100 MHz (there is such an ADC) and bandwidth of DSP filter
> is about, say 10 kHz this yelds 40 dB of noise decreasing. Thus RX
> dynamic range to be about 90+40=130 dB!   Realy DD is not 130 dB of
> cose. But it much less due to analog (!) effects in ADC absolutely
> similary as in conventional analog RX. This is not digital effect!

But without a single channel roofing filter a 130 dB outband signal 
make the AD converter overload, despite any sampling rate. Or not?

I have some unanswered question:

1- How many bits are needed for a good audio reproduction, i.e. a S/N 
ratio of 10 dB with some voice dynamics? Telephone signals usually 
are sampled 8 kHz 8 bits for a telephonic quality (with no 
compression). May be that 4 bits are sufficient but 1 bit I don't 
think.

2- Those bits are to be taken in account for calculating the dynamic 
range? i.e. 16 - 4 = 12 bits =72 dB dynamic range.

73 de Claudio, ik2pii

- 
Claudio Pozzi  -  Happy Linux User  -  http://www.qsl.net/ik2pii

 

 

 

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