[RTTY] Sound card for RTTY/MMTTY

[Kok Chen]

On Jan 16, 2011, at 11:46 AM, Jim Reisert AD1C wrote:

> According to NewEgg:
> 
>    SIIG IC-510012-S2 : Signal/Noise ratio = 68.5 dB
>    SIIG IC-710012-S2 : Signal/Noise ratio = 92.0 dB
> 
> How relevant are those S/N ratios for for RTTY?

It depends.

If you are using narrow I.F. filters, the answer is probably that you will see no difference whatsoever.  If you use a good rig and wideband (waterfall) modes, then you will see some difference between those two.

I have measured the very best 16 bit sound card used in amateur radio (a pair of different microHAM keyers) to come in within a couple of dB of the limit of a 16 bit converter (98 dB dynamic range).  OM7ZZ obviously takes great care with the noise floor of his designs.  

With a narrow I.F. filter that lets only one signal through, I don't think you ever need more than 60 dB of dynamic range to take care of all conditions (even when there is selective fading, where one RTTY tone can be significantly below the other tone).

When you use wideband receiving, it is a different story.  You can only see and copy signals that are above the noise, relative to the loudest signal in the passband.  For that, you really would like the dynamic range to be better than 80 dB.  The more the better.

73
Chen, W7AY