Marco Thanks for a very understandable reply. I would also like to thank other people for adding their knowledge and opinions.
This is certainly an interesting thread... Wayne --- In soft_radio@yahoogroups.com, Marco IK1ODO -2 <ik1...@...> wrote: > > At 10:31 13-05-10, you wrote: > > > > > >Alberto > > > >Thanks for a great reply. I'm familiar with the analysis that you > >detailed. I should have mentioned that I'm interested in SSB and PSK. > > > >You mentioned that 86 db might not be enough for HF. What drives the > >quest for dynamic range? Is it the ability to dig out a weak station > >next to a powerful one? > > Hello Waine, > > your receiver ADC gets all the signals that are present at his input. > That may be the antenna, or the output of a preselection filter if > there is one between antenna and ADC. > You want to have a receiver sensitive enough to hear the band noise; > that requires a noise figure in the order of 10 dB in HF. That means > approx. -129 dBm of input power in 3 kHz BW. > On the other side, the ADC has to handle the strongest signals that > reach the input. If you listen to 40m by the evening in EU, you get > up to +10 dBm peak (1 V pk, measured...) due to BC signals close to > the amateur bands. > So the required dynamic range is of the order of 139 dB in 3 kHz. > Since it is currently unreachable, you need a preselector to limit > the signals that the ADC sees, and an attenuator to work on low bands > (where the band noise is higher and a loss of sensitivity is acceptable). > To have 139 dB of dynamic range one needs a 100 MS/s ADC with 16 bits > of ENOB, or 94 dB dynamic range ... current 16 bit ADCs have far > less, at the point that there is a very little difference in dynamic > range between 14 and 16 bit converters. > > 73 - Marco IK1ODO / AI4YF >
