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 ----- Original Message ----- From: "Tayloe Dan-P26412" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Tuesday, January 09, 2007 15:16 Subject: [Flexradio] Higher sampling rates yeilds improved sensitivity? >I was thinking about the coding gain that we are currently using when we > sample at 48K samples per second, but only use a 500 Hz bandwidth. This > reduction in bandwidth results in (I think) ~ 20 db of gain, which is > essentially a sensitivity improvement. > > The question that I was wondering was if increasing the sampling rate > from 48K to 192K gives me another 6 db of sound card sensitivity > improvement. Moving to 4x more over sampling of the desired signal (48K > -> 192K) is should give the same result as adding bits to the A/D > converter. This is the basis that Phil is using in his very fast RF A/D > converter receiver. The effective 15 bits of his A/D converter gives 90 > db of dynamic range (20*log(2^15)), while moving from a sampling rate of > 65 (?) MHz down to 3 KHz gives a coding gain of 43 db > (10*log(65e6/3000)). For a total of 133 db of dynamic range. I guess > that since there needs to be at least two samples for the highest > frequency, the coding gain is really 3 db less (10*log((65e6/2)/3000)) > for 130 db of gain. > > Has anyone noticed this sensitivity gain on your faster sound cards? > With the sound card connected to your SDR receiver, but with the SDR > receiver hardware turned off, you ought to be able to measure the noise > floor of your sound card and see if that noise floor decreases as the > sampling rate is increased from 48K to 96K to 192K. > > I have not seen anyone comment on this, so I was wondering if any of you > see it happen in practice. I know that as the sampling rate of an A/D > converter is raised, the internally generated digital noise also > increases, and that this effect can offset the gains to some degree. > > If true, it seems like another good excuse to go to a faster converter. > > - Dan, N7VE > > _______________________________________________ > 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/ _______________________________________________ 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/
