Clay, Just in rough numbers, you get a 1/2-bit for every divide-by-two decimation you do. If you are looking at dynamic range in a 500Hz bandwidth (this is what we typically do). The math I generally use to get there is log(f1/f2)/log(2)/2. I just think this way as a programmer (do everything in base 2). So if you take log(245.76E6/500)/log(2)/2 you get 9.4 extra bits when added to the 16 gives you 25.5 bits (152.7dB dynamic range). This assumes all 16-bits of the ADC are "good" which is probably not a good assumption. I'd have to pull out the notes and look at the data sheet again, but this should give you a rough idea. Hopefully I haven't made an additional "duh" today myself!
Bottom line -- there's plenty of dynamic range. Also, if you are interested, we are using Xilinx DSP48E1 blocks which use an 18x25 multiplier and so Xilinx tools generate the on-board DDS as a 25-bit DDS by default --- again to preserve the SFDR of the receiver. We could add extra bits, but 25 are fine for the same reason. Steve Stephen Hicks, N5AC, AAR6AM VP Engineering FlexRadio Systems™ 4616 W Howard Ln Ste 1-150 Austin, TX 78728 Phone: 512-535-4713 x205 Email: st...@flexradio.com Web: www.flexradio.com *Tune In Excitement™* PowerSDR™ is a trademark of FlexRadio Systems On Fri, May 18, 2012 at 6:33 PM, Clay W7CE <w...@curtiss.net> wrote: > Hi Bob, > If it's OK with everyone, I'd like to count this as my "oh duh" moment for > today (my target is no more than one per day). I wasn't thinking about > decimation. However, assuming a bandwidth of 192 kHz and a sample rate of > 245 MHz, doesn't that only give an extra 5 bits or so of effective > resolution? That still leaves us 3 bits short of the 5000A ADC, which > still means 18 dB less dynamic range. > > Maybe I missed it in the PDF file, but I didn't see a dynamic range spec. > > 73, > Clay W7CE > > > > On 5/18/2012 3:44 PM, Robert McGwier wrote: > >> >> Clay : >> >> The difference is more than made up in the the fact that the new AD >> operates at 245 MHz and the old AD is 200 kHz and you get huge processing >> gain in the downsample and filter process greatly increases the dynamic >> range. >> >> Bob >> >> On May 18, 2012 4:46 PM, "Clay W7CE" <w...@curtiss.net <mailto: >> w...@curtiss.net>> wrote: >> >> Did anyone else notice that the receivers on the 6500 and 6700 use >> a 16-bit ADC rather than 24-bit like the 5000A? That reduces the >> dynamic range by up to 48 dB (same dynamic range as the 1500). >> That will probably be fine on HF, but I already have occasional >> problems with ADC saturation on 6M when locals (within 25 miles) >> running 1500 watts are transmitting in the 96 or 192kHz bandpass >> of my current frequency. Of course, I can eliminate the >> saturation by turning off my preamp, but then I can't hear the >> weak station I was trying to work. >> >> 73, >> Clay W7CE >> >> ______________________________**_________________ >> FlexRadio Systems Mailing List >> FlexRadio@flex-radio.biz >> <mailto:FlexRadio@flex-radio.**biz<FlexRadio@flex-radio.biz> >> > >> >> http://mail.flex-radio.biz/**mailman/listinfo/flexradio_** >> flex-radio.biz<http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz> >> Archives: >> http://www.mail-archive.com/**flexradio%40flex-radio.biz/<http://www.mail-archive.com/flexradio%40flex-radio.biz/> >> Knowledge Base: http://kc.flexradio.com/ Homepage: >> http://www.flexradio.com/ >> >> No virus found in this message. >> Checked by AVG - www.avg.com <http://www.avg.com> >> Version: 2012.0.2176 / Virus Database: 2425/5007 - Release Date: 05/18/12 >> >> > ______________________________**_________________ > FlexRadio Systems Mailing List > FlexRadio@flex-radio.biz > http://mail.flex-radio.biz/**mailman/listinfo/flexradio_**flex-radio.biz<http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz> > Archives: > http://www.mail-archive.com/**flexradio%40flex-radio.biz/<http://www.mail-archive.com/flexradio%40flex-radio.biz/> > Knowledge Base: http://kc.flexradio.com/ Homepage: > http://www.flexradio.com/ > _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
