[hpsdr] General question - sampling rate vs bits on ADC

[Dr. David Kirkby]

On 05/18/11 05:01 AM, Glenn Thomas wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> There is an issue with using a PC sound card that has not yet been
> mentioned. That is the fact that one winds up with a really bad level of
> system integration. All of the extra cables between the RF hardware and
> the PC give many additional opportunities for interface failures
> (connector corrosion, wear) and provides additional paths for RF feedback.
>
> If you want to find out with a fairly good SDR (better than the Soft
> rock IMHO), see if you can find a Flex SDR-1000. That's very close to
> the best example of a full-featured SDR that uses a PC sound card
> (albeit a very high quality card - just any card isn't good enough, for
> reasons described by Steve Bunch). Later Flex hardware uses the same
> Tayloe mixer as the '1000 but include an integrated ADC/DAC - much
> better system integration than the '1000 but the overall system isn't as
> flexible or as high performance as HPSDR.
>
> 73 de Glenn WB6W

Thank you. A friend and I were going to build an SDR radio, but with the PC 
components integrated into the same box as the RF circuitry, which would address 
some of the issues you describe.

The sound card is a reasonably good Asus one

http://www.asus.com/Multimedia/Audio_Cards/Xonar_D2X/#specifications

with 24 bits (only 19.6 of which are valid based on the 118 dB S/N spec), 192 
kHz sampling rate. The 3 dB bandwidth is <10 Hz to 46 KHz. It is RF shielded. My 
only concern was the fact there are no Linux drivers. (My friend chose this, and 
looking at it, I can't see why he did not get one for which there are Linux 
drivers).

There seems to be a lot of criticism of the FM performance of the Flex radios. 
It's interesting that the top end rigs from ICOM and Yaesu use an FM 
discriminator chip for the FM demodulation despite using a DSP for AM, CW and SSB.

-- 
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?

 1305694709.0