[RTTY] A Question for Chen... Soundcards?

[Michael Haack]

Thanks, Chen. Thanks, Ed.

The question more to the point, And Ed you got there before I did...
Is the higher DSP and processing capabilities of the external soundcards 
an advantage for RTTY Dxing, Or is it not really necessary?

Chen, I thought I recalled you had done some piece on the subject but 
wasn't sure.

Thanks Guys.





On 2016-03-24 4:06 PM, Kok Chen wrote:
> On Mar 24, 2016, at 1:36 PM, Michael Haack via RTTY wrote:
>
>> Is there a decided advantage to using a high powered external sound card vs the internal card for RTTY/MMTTY/2tone use?
> I am not sure what you mean by a "high powered" sound card.  Sound card works with millivolts to hundreds of millivolts, and very high input impedances.  Very little power involved.
>
> If you mean the dynamic range of the sound card, I think I have already addressed that in an earlier posting.
>
> You can measure your own sound card by using free spectrum analyzer programs that exists in all the OS platforms that I know. (On Mac OS X, you can use my Amici spectrum analyzer/tracking generator program.)
>
> With the radio tuned to atmospheric noise (no signal), measure the difference between the noise floor and the full scale (clipping level).
>
> If you are running 48000 samples/second, there is another 27 dB or so of available dynamic range from the processing gain from a good modem.  If you use 24000, samples per second, you have 3 dB less (24 dB processing gain).
>
> Add the processing gain to what you measured earlier, and you pretty much have the dynamic range of your modem.
>
> If this number is greater than your receiver's dynamic range, the sound card is adequate.  If this number is worse than your receiver, you will either need to use a better sound card, or ride the gain of the sound card so that a signal is always higher than the noise floor, but is not clipping.
>
> If you are using a wideband system (e.g., for a skimmer or a wideband RTTY demodulator), you will also need to measure the intermodulation distortion and the harmonic distortion of the sound card.
>
> 73
> Chen, W7AY
>
>