Indeed second Nyquist zone before decimation. My thought was 143.05 MHz -> transpose by 100 MHz using the DDC (NCO at 100 MHz considering the 200 MHz sampling rate) to reach 43.05, and after transposition, decimating to reach 8 MS/s (I do have Epcos B3607 SAW filters 140+/-3 MHz frontend to select only the signal I am interested in). It is in the decimation process that I was thinking of being in the third Nyquist zone after decimation, which is incorrect because 8 MS/s is -4 to +4, so that 43.05 is in the 6th Nyquist zone after decimation (\in[36:44] MHz).
Thanks, JM -- JM Friedt, FEMTO-ST Time & Frequency/SENSeOR, 26 rue de l'Epitaphe, 25000 Besancon, France July 20, 2020 5:20 PM, "Marcus D. Leech" <patchvonbr...@gmail.com> wrote: > On 07/20/2020 07:37 AM, jean-michel.fri...@femto-st.fr wrote: > >> I'd like to analyze a higher Nyquist zone with a X310 fitted with a BasicRX: >> trying to listen at 143.5 MHz (GRAVES), I can transpose by 100 MHz but am >> still >> far from the ~8 MS/s sampling I can use on the Gb Ethernet interface. Since >> the >> signal is only in the third Nyquist zone, I'd like to tell the BasicRX/DDC >> *not* >> to anti-alias (CIC filter ?) the received signal. It tried playing with the >> Bandwidth parameter of the USRP Sink but no improvement there. >> >> Is there a way to alias on purpose the signal with X310+BasicRX ? >> >> Thanks, JM >> >> -- >> JM Friedt, FEMTO-ST Time & Frequency/SENSeOR, 26 rue de l'Epitaphe, >> 25000 Besancon, France > > The X310 has a 200MHz ADC clock by default, so 143.5MHz would be in the 2nd > Nyquist zone, would it > not?
