Yes, you're right. We transmit 2-bits per sample and use channel bw's of 32-MHz but perhaps as low as 8-MHz to avoid S-band RFI. I also like the 2*ASIAA + ROACH2 option. I proposed it to the group but as you suspected there are several ROACH1's out there. How difficult is the migration from ROACH1 to ROACH2? Thanks, -Bill.
________________________________ From: Jonathan Weintroub <[email protected]> To: Bill Petrachenko <[email protected]> Sent: Thursday, May 31, 2012 12:00:13 PM Subject: Re: [casper] 1-2 GHz sampler Hi Bill, Thanks, I was a bit mixed up and this does clarify. One other question, as is typical in VLBI back ends, you're just storing 2-bits per sample, is that right? And probably 16 Gb/s, using something like the Mark6 data recorders? I'd probably advocate for the ASIAA boards--you could then bring in both polarizations with one ADC board, and with both ZDOKs loaded, you could process two dual polarization IFs or 4 GHz of total bandwidth (16 Gb/s) with a single ROACH2. You need the ROACH2, technically, to support the data rate across ZDOK. Is there an installed base of ROACH1 hardware (RDBEs) which you want to conserve? I may say a little more on the general thread when I have a chance. Cheers, Jonathan On May 30, 2012, at 10:04 PM, Bill Petrachenko wrote: > Yes, the application is geodetic VLBI in collaboration with Haystack > Observatory. What we would like to do is sample a band starting at 1024 and > ending at 2048-MHz in two polarizations. This would require two digitizers > each clocking at an effective Nyquist rate of 2048-MHz, which could be > interleaved at 1024-MHz or direct sampling at 2048-MHz. > > Hope this is clearer, > -Bill. > > From: Jonathan Weintroub <[email protected]> > To: Bill Petrachenko <[email protected]> > Cc: casper <[email protected]> > Sent: Wednesday, May 30, 2012 10:57:05 AM > Subject: Re: [casper] 1-2 GHz sampler > > Hi Bill, > > Can you clarify: when you say you need an ADC "clocked at 2048 MHz" do you > mean a sampling rate of 4096 MS/s or 2048 MS/s? (The ADC sample rate for > some parts is twice the clock rate.) I'm a bit confused as to what you are > after, looking back at your original framing of your problem, and some of the > responses to it. > > You said: > > I need to sample two Nyquist zones at 1024-2048 MHz. > > Can you clarify which two Nyquist zones you mean? > > May have some more to say depending on your clarification. This application > has a VLBI-recorder-like look . . . > > (apologies to all for spamming multiple copies on my last response will try > not to do it again). > > Jonathan > > > On May 30, 2012, at 9:18 AM, Francois Kapp wrote: > > > Hi Bill, > > > > Not quite yet, but we are working on a board that could do 2.2 GSPS > > non-interleaved. It is called the adc1x2200-10 which indicates 1 channel, > > 10 bits, 2200 MSPS. It is based on the e2v AT84AS008 part with associated > > DMUX and the status is that we have a PCB design, PCB's and components > > ordered and assembly booked. If all goes well we should be able to get > > some measurement results out within the next two months. > > > > This may be an option depending on your schedule? > > > > Regards, > > Francois > > > > On Wed, May 30, 2012 at 2:57 PM, Bill Petrachenko <[email protected]> wrote: > > OK, so it looks like I'll need to pay more attention to interleaving than I > > had hoped. I assume there are no ROACH-compatible boards that use chips > > that clock at 2048-MHz but without interleaving. > > > > Also, we're using a flexible down-converter to select 1-GHz bands anywhere > > in the 2-14-GHz range. At many sites RFI at S-band will be a problem so > > dynamic range is an issue. The chips on the ASIAA, ADC1x3000, and Kat-ADC > > all seem to drop to about ENOB = 6-bits at 2-GHz which is less than ideal. > > Using a 10- or 12-bit sampler would be preferred but it seems no > > ROACH-compatible sampler boards have been designed with 10- or 12-bit > > capability and the interface won't handle the extra bits anyway. Having > > said that though I seem to recall that you implied in your initial email > > that the ASIAA card could be used in the dual sampler mode (assuming a > > 1-GHz bandwidth) if interaced to the ROACH2 and yet the ZDOK connection for > > both ROACH1 and ROACH2 both use a 40 differential pair interface. How do > > you get the extra bandwith with the ROACH2? > > > > Yes, I did pick up that we would need the higher bandwidth filter. However, > > I also noticed that there were some plans to implement shields and heat > > sinks for the Kat-ADC. Has this come to pass or has it become apparent that > > neither are required? > > > > Many thanks, > > -Bill. > > > > From: Dan Werthimer <[email protected]> > > To: Bill Petrachenko <[email protected]> > > Sent: Monday, May 28, 2012 11:21:40 PM > > Subject: Re: [casper] 1-2 GHz sampler > > > > the kat-adc has two different front end fiilter options. > > make sure to order the filter option for high frequency. > > > > dan > > > > On Mon, May 28, 2012 at 7:19 PM, Bill Petrachenko <[email protected]> wrote: > > > Thanks Dan. It sounds like the Kat-ADC is probably best for us. > > > > > > -Bill. > > > > > > ________________________________ > > > From: Dan Werthimer <[email protected]> > > > To: Bill Petrachenko <[email protected]> > > > Cc: Casper <[email protected]> > > > Sent: Monday, May 28, 2012 8:47:45 PM > > > Subject: Re: [casper] 1-2 GHz sampler > > > > > > > > hi bill, > > > > > > i think all the boards you mention have analog bandwidth out to 2 GHz, > > > so they should work well for your 1-2 GHz band. > > > > > > the asiaa board is the least expensive, but this board does not have > > > programmable > > > attenuators like the Kat-ADC. the asiaa board can be used as a single > > > 5 Gsps ADC, or as a dual 2.5 GHz ADC. > > > we have used the asiaa board as a single 5 gsps adc, and it works quite > > > well. > > > but we have never tested it as a dual adc - perhaps others reading > > > this email can > > > give you advice about using it in dual mode. if you are using roach > > > I, you can't > > > get the 8 bit version of the asiaa board working at the full 5 gsps. > > > if you are using > > > roach II, you can use it at 5 Gsps. > > > > > > best wishes, > > > > > > dan > > > > > > > > > > > > > > > On Thu, May 24, 2012 at 11:30 AM, Bill Petrachenko <[email protected]> > > > wrote: > > >> I'm designing a digital data acquisition system using a ROACH1 board. I > > >> need > > >> to sample two Nyquist zones at 1024-2048 MHz. It appears that in the > > >> Casper > > >> group of products, a pair of ASIAA, ADC1x3000-8, or KatADC boards would > > >> work > > >> well and nicely interfaced to a single ROACH1 board (although the ASIAA > > >> board is not mention explicitly on the web-site). Is there any reason to > > >> choose one board over another? The gain adjustment stage is attractive on > > >> the KatADC but the performance of the ADC1x3000-8 chip seems marginally > > >> better at 2-GHz input frequency. The e2v chip seems less established than > > >> the National chips. Is interleaving or calibration an issue for any of > > >> the > > >> chips? > > >> > > >> I'd be grateful for any opinions on this. > > >> Thanks, -Bill. > > > > > > > > > > > > > > > > > > -- > > Francois Kapp > > > > Sub-system Manager > > Digital Back End > > meerKAT > > > > SKA South Africa > > Third Floor > > The Park > > Park Road (off Alexandra Road) > > Pinelands > > 7405 > > Western Cape > > South Africa > > > > Latitude: -33.94329 (South); Longitude: 18.48945 (East). > > > > (p) +27 (0)21 506 7300 > > (p) +27 (0)21 506 7360 (direct) > > (f) +27 (0)21 506 7375 > > (m) +27 (0)82 787 8407 > > >
