hi xavier, we use 8 bit wideband digitizers at arecibo and parkes where the RFI is fairly strong. do you think you might be able to get away with 8 bits ? :
perhaps you know all this adc and dsp dynamic range stuff already, but here are some thoughts: an 8 bit digitizer usually works well if the total power of the RFI doesn't exceed about 10 times the total power from the noise from the whole band. (eg: RFI can be incredibly strong if it's confined to a relatively narrow band compared to the total band). although this general rule doesn't apply if the RFI is impulsive (see below). have you studied the adc histogram from an 8 bit ADC at your site? how often does the ADC saturate? eg: if you set the signal level so the ADC RMS is around 5 (on a scale from -128 to +127), how often do you get -128 or +127? if you have strong impulsive RFI that occasionally saturate the ADC. there are some casper blocks that can excise these low duty cycle events. if the total power from the RFI is significantly stronger than the noise power from the total band, then you might consider using an 8 bit ADC, but only using the sign bit from the ADC. (use the ADC as a one bit digitzer, that outputs only +1 or -1). you'll loose some SNR with a one bit digitizer (see thompson/moran/swenson), and you'll need to apply the van vleck correction to measure strong signals accurately, but you won't have a dynamic range problem with a one bit digitizer. spectrometers and correlators can have 64 bits or more of dynamic range with 8 bit or 1 bit digitizers. (the digital part of your design can have lots of dynamic range, independent of the ADC range). but if the ADC saturates, and you don't handle the saturation appropriately, then you'll get spectral contamination no matter how many bits you use in the post-adc signal processing). best wishes, dan On Thu, Dec 7, 2017 at 2:10 PM, Xavier Bosch <bruixa.aburrid...@gmail.com> wrote: > Hi CASPERites, > > > > We are developing a wideband spectrometer (~1.6 GHz ) in a band that has a > lot of RFI. Currently we are using the 8-bit 5-GSPS ASIAA ADC board and the > ROACH2, and the ADC resolution appears to be inadequate for our extreme RFI > environment. > > > > We would like to move over to a higher resolution ADC (12 to 14 bits), > probably with a JESD204B interface, and a Xilinx development kit. We are > considering something like this evaluation board KCU105 > <https://www.xilinx.com/products/boards-and-kits/kcu105.html#hardware>and > something like FMC217 > <https://www.vadatech.com/product.php?product=528&catid_prev=0&catid_now=0> > as a digitizer. > > > Has anyone been in a similar situation dealing with RFI? > > Has anyone ported CASPER library to Xilinx development kits and JESD204B > ADCs? > > > Thank you, > > XB > > -- > You received this message because you are subscribed to the Google Groups " > casper@lists.berkeley.edu" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to casper+unsubscr...@lists.berkeley.edu. > To post to this group, send email to casper@lists.berkeley.edu. > -- You received this message because you are subscribed to the Google Groups "casper@lists.berkeley.edu" group. To unsubscribe from this group and stop receiving emails from it, send an email to casper+unsubscr...@lists.berkeley.edu. To post to this group, send email to casper@lists.berkeley.edu.
