John Miles wrote: >> Most, but not all, sound cards have a low frequency cutoff of 20Hz or so. >> Some (but not all) sound card ADCs can dc coupled. >> A high resolution dc coupled ADC may be more effective for frequencies >> below 20Hz. >> > > True; I'm assuming that anyone using a sound card for these purposes is > either going to bypass the coupling capacitor in front of the ADC, or > calibrate out the highpass response by adding an inverse function. (A QEX > article gave an example of the latter technique not too long ago.) > > I'm still hoping to get a 24-bit, 2.5-MSPS ADC chip hooked up via USB 2.0 > fairly soon. That will solve a multitude of problems, eliminating the need > for both a sound card and an HF analyzer. I have C code on the PC that's > talking to the FPGA, but haven't yet tried to bring the ADC up with it. > > >> Sound card support appears to be something of a minefield, baudline >> thinks my 16 bit 48kHz motherboard sound system is a 24 bit 192kHz system. >> This probably means that the frequency scale and consequently FFT filter >> noise bandwidths are unreliable. >> However with a low frequency noise calibration source and set of marker >> harmonics derived from a crystal these calibration issues can be resolved. >> Windows software fares little better and some crashes when set to sample >> at 192kHz (the windows machine has a sound system with a 192kHz 20 bit >> ADC system). >> > > Yeah, I think it'd be better not to even use the sound-card drivers if > possible. At 10 million bytes per second (32 bits/sample at 2.5 MSPS) they > won't be an option for the hardware I'm looking at. > > That would be the AD7760 then? >> A dual mixer time difference system can have a lower noise floor than a >> single mixer system. >> > > I wonder if those are still covered by patents in various corners of the > world, the way the TSC's dual-ADC architecture appears to be... > > -- john, KE5FX > > John
Unlikely, the dual mixer time difference technique has been around so long that most patents like: United States Patent 5128909 (issued 7 July 1992, expired on 7 July 2004). which is an extension of the technique to multiple channels, have expired. Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
