Hi Ross, I'm not working with Colm on this. So I don't know about the resources available to him.
What you're saying is true. Doing it with a single stage may be problematic as with 20 MHz LO, the there will be overlap of the side bands. So, minimally, we need to have two stages. where the 20-80 MHz can be up-converted to outside the band and then down-converted into the base band of 0-60 MHz. Sorry for not being clear earlier. But anyway, for the RedPitaya, due to the sampling restrictions, 20-80 MHz band has to be got into 0-60 MHz for getting the full band with the board. Thank you, Mugundhan On Mon, Feb 10, 2020 at 2:32 PM Ross Martin <ross.mar...@ieee.org> wrote: > Hi Mugundhan, > > Could you say a little more about how you're downconverting 20-80MHz to > 0-60MHz? My understanding is that this is not easy to do while retaining > signal quality. The band overlap of the input and output bands means > simple conversion methods with normal mixers don't work. > > Ross > > > On Mon, Feb 10, 2020, 1:09 AM Mugundhan vijayaraghavan < > v.vaishnav151...@gmail.com> wrote: > >> Hi jishnu, >> >> With red pitaya, you have to down convert 20-80 to 0-60 baseband to use >> the band fully. As such, it has a cutoff at 65MHz. >> >> Thanks, >> Mugundhan >> >> On Mon, 10 Feb 2020, 13:30 Jishnu Nambissan T, <jis...@rri.res.in> wrote: >> >>> Hi Mugundhan, >>> >>> With red pitaya, can you sample 20-80 MHz without downconversion ? And >>> if analog down conversion is required, wouldn't that restrict the usable >>> dynamic range (unless a high level mixer is used) ? >>> >>> Jishnu >>> >>> ------------------------------ >>> *From: *"Mugundhan vijayaraghavan" <v.vaishnav151...@gmail.com> >>> *To: *"casper" <casper@lists.berkeley.edu> >>> *Sent: *Thursday, February 6, 2020 1:06:09 AM >>> *Subject: *Re: [casper] Solar Spectrometer Channeliser >>> >>> 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 >>>>>>> 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<https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAD560xm_P9M%3DaWWxuW47ZexoX4URR6as9egJaoL9%2BMK55_HJVA%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/CAG4nf71Ft-GeapgVxDLqhbkLC0cwkjy9KYna1zmbcDwSg_ZGRQ%40mail.gmail.com > <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAG4nf71Ft-GeapgVxDLqhbkLC0cwkjy9KYna1zmbcDwSg_ZGRQ%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- V. 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