--- In digitalradio@yahoogroups.com, Peter Frenning <pe...@...> wrote: >
> The Signalink USB (which I recommend myself with the caveats on my > homepage), uses one of the same Cheap chips used by the low cost general > purpose adapters, in this case the "USB Audio Codec". As a class of > devices you are certainly correct in your assumption about the drivers, > but again, as a class of devices, they support all std. sampling rates > from 48000 and down, with one notable exception: 11025 (this became a de > facto std many years ago when it was the fastest rate these newfangled > devices (i think the first was a SoundBlaster 8-bit adapter) would do), > many many applications default to this, and for compatibility reasons > its being fudged in the Windows driver SW rather than aborting the > requesting application. Funny enough (or not as things may be) Linux > drivers don't do this and abort any application requesting 11.025 from > one of these devices! (this is the only case I know of where resampling > comes into play). > > Anyway, if your purpose isn't high quality HiFi or ultra high sampling > rate for SDR radios, i can recommend the cheaps sound cards - get real, > they have more than sufficient dynamic range, and you only need a > frequency response of some 500-2500 Hz anyway! > But there is more than frequency response and dynamic range required to preserve the information needed to decode digital modes. Your statement that the cheap devices do not support 11.025kHz sample rate may have something to do with why I found them so poor as that is the (fixed) rate used by the AGWPE soundcard packet modem. It is also the default rate used by MixW. As I said before, I could see the signal on the waterfall but it was just not being decoded. Really, if you want to be confident you have the best chance of decoding that weak signal it is better to be using a good quality device. After all, you spend hundreds if not thousands of pounds / dollars on the transceiver, why penny pinch on the sound card? Julian, G4ILO
