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Re: [Discuss-gnuradio] Re: PCIe know-how?

From: ceriel
Subject: Re: [Discuss-gnuradio] Re: PCIe know-how?
Date: Mon, 5 Mar 2007 00:24:37 +0200

On 3/4/07, Eric Blossom <address@hidden> wrote:
On Sun, Mar 04, 2007 at 10:16:21PM +0200, address@hidden wrote:
> On 3/4/07, Eric Blossom <address@hidden> wrote:
> >>
> >> Hm. Looks like I got my mailing lists crossed. This was intended for
> >> the Open Graphics list, but at least you know what I'm trying to do
> >> now... Anyone interested?
> >
> >Sure, I'm interested.
> >
> >We've got tons of signal processing code that could be useful, and of
> >course you are free to reuse it all under the terms of the GPL.
> >
> >Keep us posted regarding your project, and feel free to discuss
> >both the h/w and s/w here.  The more the merrier.
> >
> >Eric
> Thank you for your reply, Eric.
> The general idea behind the project is that since squeezing the
> signals over USB requires a whole lot of effort and hardware, if I
> could refrain from the squeezing I'd save a whole lot of cash in
> buying new hardware. However, this does means that the CPU will have
> to handle the data instead. It'll be about 200MBps, and I'm still
> unsure about how doable that is. If I could use the FPGA to do some
> pre-processing of the data, I might be able to lower the hardware
> requirements a bit... Most of us geeks aren't lacking in the CPU cycle
> dept, but I'd like this to be affordable to as many people as
> possible.
> I don't know Verilog, never written that complex C-code before, and
> never designed a PCB, so I have a lot to learn before I can truly get
> started. Lucky for me I love learning things that are of use! =)
> You had a $300 version of the USRP that you showed in that recent
> video where you presented the project... Are the design files for that
> available anywhere so I don't go reinventing a whole lot of wheels?

Matt Ettus sells the USRP.  Lot of folks are using them.  See http://ettus.com

Why do you think you need 200MB/s for this project?
That would imply that you have an RF front end that had an IF that was
about 50MHz wide.  Is that the case?

There will be an version of the USRP available later this year that
has a gigabit ethernet interface.  I'm hoping to be able to get
100MB/s through that.


Oh yes! Sorry, forgot to mention that part.
I'd like to have an ADC with 65 to 105 Msps at 16 bits. This should
allow me to sample up to 30 or 50MHz respectively. I was inspired to
this from the Mercury project of the HPSDR, but that project relies on
a whole lot of other hardware, running at a total cost of some $500,
and it still relies on USB for the interface.

0 to 30MHz would allow me to sample the entire shortwave band and
below simultaneously, so I could for example have code in place to
automatically decode and display every data transmission taking place,
if my CPU is up for it. Tuning would be instant; I could automagically
jump to new transmissions in the amateur bands, or click and drag on a
waterfall display to tune. If I can code that...

The ADCs I've been looking at can apparently somehow sample
frequencies above their sampling rate aswell. I'm not really sure how
this works, but I don't think it's an issue I must bother with right
now. Added value for later, I think. Right now I'm only interested in
shortwave transmissions, but the bandwidth of the ADC could surely be
used for other things aswell.


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