hi gerry, my number of frequency channel estimates assume the correlator always has a total bandwidth of 125 MHz (250 Msps), but the number of frequency channels across the 125 MHz varies.
the number of frequency channels and number of analog signal inputs is limited by memory on the fpga: (memory usage is roughly proportional to Nsignals * Nfrequencychannels) hong thinks my estimates are likely too conservative by a factor of two - so you might be able to get twice the number of frequency channels (or twice the number of analog inputs) on a roach II. best wishes, dan On Fri, Aug 24, 2012 at 7:07 PM, Gerry Harp <[email protected]> wrote: > Hi Dan > > Your numbers look somehow backwards. > > Did you mean: > 32 inputs at 8K > 16 at 4K > 8 at 2K > 4 at 1K? > > Presumably, by narrowing the input bandwidth could permit proportionally > smaller channels at the output? So at 2.5 MHz input one could do 1 Hz > channels? > > Trying and compiling is the right thing to do. Hopefully we can arrange to > do this pretty soon. > > Gerry > > On 8/24/2012 8:55 AM, Dan Werthimer wrote: > > > hi john, > > to get a real number, it would be best to compile the design . > you can re-compile zaki's octal F engine designed for roach I > (8 inputs at 250 Msps), or Hong's F engine (32 inputs at 250 Msps, > designed for roach II). > > rough guess: you can get 32 analog inputs at 1K channels, > or 16 analog inputs at 2K channels, or 8 analog inputs at 4K channels, > or 4 analog inputs at 8K channels. > > best wishes, > > dan > > > On Fri, Aug 24, 2012 at 7:54 AM, Jon Richards <[email protected]> wrote: > >> All, >> >> I need some advice. We are looking into developing an FX correlator using >> the Roach2 s as the "F" and GPUs as the "X". >> >> We will have 4 inputs to the Roach2 ADCs, at 250Msamples/sec, 8Gb/sec >> flowing out to the X boards. How many channels should the Roach2 be able to >> process? How would I guestimate that? >> >> Any ideas appreciated! >> >> Thanks, >> Jon Richards >> >> [image: Drawing showing 4(intputs) x 250M samples/sec x 8bits/sample >> (4r/4i) = 8Gb/sec] >> > > > -- > ---------------------- > Gerald R. Harp, Ph.D. > Director, Center for SETI Research > SETI Institute > >
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