Joe - AB1DO wrote: > Dan, > > just out of curiosity I performed the following experiment: > Using PowerSDR1.9.0 SVN821 > Scound card is a Delta-44 > Disconnected the Delta-44 cable at the break-out box, thus disconnecting the > hardware > Preamp set to Med > Measured the noise floor in a 500Hz filter. To stabilize the digital signal > meter, I set it to average over a period of 3 seconds. > > Result: > At a sample rate of 48kB/s, the noise floor measured -130.5dBm > At a sample rate of 96kB/s the noise floor measured -132.5dBm > > That would indicate an improvement of around 2dB in sensitivity, though not > quite the 3dB you predicted. I cannot test 192kB/s (yet). > > Hope this helps, > 73 de Joe - AB1DO > You might not be measuring what you think you are measuring. The results you get are a result of the fft algorithm. The fft algorithm indicates power present in each bin. At 48kHz, lets say you get noise power in the 500Hz bin with 10 units of noise (bogus scale just to demonstrate a point) At 96kHz, this bin gets broken into 2. One of these bins will have the 500Hz signal, the other will not. So, on average, the 500Hz bin will now have 5 units of noise, with the other 5 units in the next door bin. One therefore has the apparent reduction in noise at 96kHz over 48kHz.
As the sample rate increases, each bin has a narrower bandwidth. Oversampling does improve the result a bit, but one gets diminishing returns, so 60Mbits/s sampling at 16bit, is unlikely to give 26bit accurate samples at 48Khz. One does not spontaneously improve the dynamic range of the front end just by oversampling. James _______________________________________________ FlexRadio mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Homepage: http://www.flex-radio.com/ FlexRadio Knowledge Base: http://kb.flex-radio.com/
