Maximum frequency and sampling rate supported by 3.5mm audio port with 128kbps driver

Hey guys,

I'm designing a amateur radar system that uses a laptop for signal processing. I'm trying to figure out the maximum sampling rate of the audio port of my computer. The driver indicates that the sampling bit rate is 128kbps. If I'm sampling at the nyquist rate, does this imply that the maximum frequency of the analog signal I can sample is 64kHz?

There will be an anti aliasing filter somewhere in the works, at a high enough frequency to work with audio signals only, 20Khz cut off if your are lucky. Therefore you may just end up sampling at 44KHz, anything other than that and you are just oversampling more. The lower sampling rate might help as far as the processing speed is concerned. The higher sampling rates mean less problems with the antialiasing filter, since its cutoff is not brickwall, frequency foldback and noise issues may improve. Probably difficult to get information on the filter.
You may need to plug an audio signal into the port and see what happens, you should be just as concerned about S/N, the audio input ADC may look good on paper, but there is a lot of digital hash floating around the innards of a pc. Are you are using a doppler system?
Another thing to consider is that the PC would have to keep up with the data rate if you wish to process in real time, which may end up being the limiting factor, so you need to look at the execution time of your major code loops.
Cheers,
Richard

Hey Richard,

Yes we're planning on using doppler to resolve the speed and maybe stfft in combination with triangle wave frequency modulation to resolve range. It would nice to have beat frequencies for doppler up to 100khz, so I was thinking maybe I could use a sample and hold circuit before the audio port to reduce the frequency?

Oh man I didn't even think about the code keeping up with the sampling... Might have to scrap that.

Yeah before I do anything I think I've got to run some tests on the audio port so I understand what the limits are. Thanks so much for your help!!