Hi Dan, Usually quiet sun doesn't show such abrupt changes, but bursts do (easily 40-50dB or more) for bright bursts. We have built 8 bit spectrometers in 40-80Mhz, but have found then when the burst is pretty strong, saturation effects starts kicking in.
Thanks, Mugundhan On Wed, 5 Feb 2020, 21:52 Dan Werthimer, <d...@ssl.berkeley.edu> wrote: > > hi colm, > > regarding dynamic range > --------------------------------- > for your solar spectrometer, do you need 14 bits of ADC dynamic range? > it's very unusual in radio astronomy to need that much instantaneous > dynamic range on the input. > does the sun vary on short time scales in the radio band by factor of 1000 > in voltage (1,000,000 in power) ? > or do you have very strong bursting RFI that is 1000 times the average > noise voltage (1M in power) in the whole band? > > as you probably know, you'll have lots more dynamic range in the output > power spectrum than the dynamic range of the ADC: > if you are building a 1024 channel spectrometer with 1 ms integration, > you'll get about 8 bits more bits of dynamic range above your ADC dynamic > range in frequency domain voltage, > which is 16 bits more of dynamic range above your ADC dynamic range in > power spectra. > so you'll have about 20 bits of spectral dynamic range if you use an 8 bit > ADC, > (power spectrum dynamic range of about 1 million in 1 ms with an 8 bit > ADC, setting noise at 3 bit RMS). > and 24 bits of spectrral dynamic range for a 10 bit ADC, 28 bits for 12 > bit ADC, and 32 bits for for 14 bit ADC). > > regarding boards for your spectrometer > --------------------------------------------------- > > 1) as adam pointed out, the red pitaya is cheap, but sample rate and > bandwidth don't quite get the specs you need. > > 2) another possibility is to use a snap board, which costs more, but can > sample 3 inputs at 950 Msps, > or 6 inputs at 500 Msps, or 12 inputs at 250 Msps with 8 bit ADC's. most > people populate the snap board with 8 bit ADCs, > but a few people have populated it with 12 bit ADC's, although the sample > rate goes down by 8/12. > > 3) another possibility is to use a xilinx RFSOC board. the first gen has > a bank of 12 bit ADC's (8 inputs at 4 Gsps, or 16 inputs at 2 Gsps), > but i think the new generation has 14 bit ADC's ? the RFSOC boards cost > more than snaps, but RFSOC was designed > in dublin, so you can probably get one from xilinx dublin.... the ZCU111 > board has not been fully casperized yet though. > > best wishes, > > dan > > > > > > Dan Werthimer > Marilyn and Watson Alberts Chair > Astronomy Dept and Space Sciences Lab > University of California, Berkeley > > > On Wed, Feb 5, 2020 at 5:06 AM Colm Bracken <colmbrac...@gmail.com> wrote: > >> Hello CASPER people, >> >> We are looking to build a spectrometer with not too demanding >> requirements. >> Based on the specs below, would the Red Pitaya be up to the job do you >> think? >> Or, is there another, better suited (but similarly affordable) solution? >> >> Chanel widths: ~< 100 kHz >> Time sampling: ~< millisecond >> Polarisation: 2 channels >> Antenna freq range: 10-85 MHz (total bandwidth of 75 MHz) >> Digitisation: 14 bit >> >> Any advice on this would be great! >> >> Thanks in advance, >> Colm >> -- >> >> *Dr Colm Bracken* >> Lecturer >> Maynooth University Experimental Physics >> >> >> Maynooth University, Maynooth, Co. 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