Hi Dan, We have done integration times from 20ms upto a second. There are bursts that last for hours, minutes and a few ms to seconds as well.
We have not tried AGC on these bursts since we were aiming to study them only. In the 8 bit design, we had 3 bits for background and remaining 5 to accommodate bursts. The red pitaya can still be used if Colm can restrict the band to 20-80 mhz, because the ionosphere starts cutting of anything below 20mhz mostly(depending on the location of course). Then this can be down converted to fit into 0-62.5 mhz base band of the red pitaya. Thanks, Mugundhan On Wed, 5 Feb 2020, 22:23 Dan Werthimer, <d...@ssl.berkeley.edu> wrote: > > hi mugundhan, > > what's the time scale for these bursts? > rise and fall times? > can you use a AGC circuit (automatic gain control), > eg: computer controlled attenuator > to turn down the power going into the ADC during the bursts, > so you could keep the levels going into the ADC relatively constant? > if the rise and fall times are longer than 1ms (the integration time of > the spectrometer), > then you could adjust the power level for each spectrum, and write down > where > you set the attenuator for that spectrum, so you could still know the > absolute power. > > if not, there are some 14 bit 200 Msps ADC boards, and i think the new > RFSOC boards/chips have 14 bit ADC's, > but you'll have to write a casper yellow interface block for this ADC, > as we don't have a 14 bit 200 Msps ADC in the casper library. > > another possiblity is to multiplex your 80 MHz band, 40 MHz at a time into > a red pitaya board, > ping ponging back and forth between bands: 0 to 40 MHz for 1 ms, then 40 > to 80 MHz for the next ms. > > > best wishes, > > dan > > > > > On Wed, Feb 5, 2020 at 8:33 AM Mugundhan vijayaraghavan < > v.vaishnav151...@gmail.com> wrote: > >> 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. Kildare, Ireland. >>>> >>>> T: +353 1 708 3641 >>>> E: colm.brac...@mu.ie W: www.maynoothuniversity.ie >>>> >>>> Follow my work on https://nuim.academia.edu/ColmBracken >>>> >>>> >>>> >>>> And >>>> >>>> >>>> Research Associate >>>> >>>> Astronomy & Astrophysics Section >>>> School of Cosmic Physics >>>> Dublin Institute for Advanced Studies >>>> 31 Fitzwilliam Place >>>> Dublin 2, D02 XF86 >>>> >>>> >>>> >>>> T: +353 1 440 6656 ext 352 >>>> E: cbrac...@cp.dias.ie W: www.dias.ie/2017/06/22/dr-colm-bracken >>>> >>>> Follow my work on https://nuim.academia.edu/ColmBracken >>>> >>>> -- >>>> 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 view this discussion on the web visit >>>> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAEx9wh8jNxeUnPGaSvwwuAtPCRsnNoCbOFnhbpU9EDb%2BPKh-Bg%40mail.gmail.com >>>> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAEx9wh8jNxeUnPGaSvwwuAtPCRsnNoCbOFnhbpU9EDb%2BPKh-Bg%40mail.gmail.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>> -- >>> 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 view this discussion on the web visit >>> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAGHS_vH-6MvNUAxsZVs8KOW%2BUhOB5tUAZQdmu3_%3D9A24RL1Fqw%40mail.gmail.com >>> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAGHS_vH-6MvNUAxsZVs8KOW%2BUhOB5tUAZQdmu3_%3D9A24RL1Fqw%40mail.gmail.com?utm_medium=email&utm_source=footer> >>> . >>> >> -- >> 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 view this discussion on the web visit >> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAD560xkZtMmYT0huZPM-mR6z22Je00DVd7sSsEsDGwHP42KHGg%40mail.gmail.com >> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAD560xkZtMmYT0huZPM-mR6z22Je00DVd7sSsEsDGwHP42KHGg%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> > -- > 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 view this discussion on the web visit > https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAGHS_vHPmfPup6dY-CwvwdOnk62W0DobD62V5StCaOJyv3fJ0g%40mail.gmail.com > <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAGHS_vHPmfPup6dY-CwvwdOnk62W0DobD62V5StCaOJyv3fJ0g%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "casper@lists.berkeley.edu" group. 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