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

From: eenjrgi
Subject: Re: [Discuss-gnuradio] Re: PCIe know-how?
Date: Mon, 5 Mar 2007 13:22:20 +0000
User-agent: Internet Messaging Program (IMP) 4.0-cvs

just to stick my oar in...

Quoting Brian Padalino <address@hidden> on Sun 04 Mar 2007 22:47:36 GMT:

> On 3/4/07, address@hidden <address@hidden> wrote:
> > 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.
> Just wondering - any reason why you want 16-bits of resolution?  That
> gives you ~96dB of dynamic range which is great, but do you really
> need it?  12-bits should actually give you a really good amount of
> dynamic range while keeping everything within budget.  Even a 10-bit
> solution would probably give you enough to be really good while
> keeping everything on the cheap.  I believe even those really
> expensive Agilent or Tektronix oscilloscopes just use 8-bit
> converters.

this is a good idea, you will probably find that the analogue receive chain
introduces so to much noise to make anything over 6 or 7 bits resolution  (at
best) meaningful anyway

> Maxim has a pretty decent selection of high speed ADCs.  Which ones
> did you have in mind that you were looking at?
> > 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.
> Those ADCs probably have a really wide analog bandwidth and allow for
> "high IF" sampling - where the desired signal is located somewhere
> higher than your sample rate, but the bandwidth of the signal is much
> lower than your actual sampling rate.  You then sample at a lower rate
> than the IF and get an "image" of that actual signal - exploiting the
> aliasing instead of trying to filter it out.

you said earlier that this is a home project, do you mean you have no intention
of (low volume) production?  for a single board $100 is a very ambitious target.
 BGA packages usually need multilayer to escape the signals, and PCIe needs
controlled impedance.  you might find that the PCB tooling costs alone exceed
your budget

> > --
> > Nos
> Brian

if you can reduce your data rate so that gigE will do, it's probably worth
having a look for FPGA gigE development boards with an versatile i/o header,
then designing a single layer (cheap) daughter board for the ADC.  otherwise
you're probably best to wait for the gigE usrp.

(you might have to offer to do someones washing/cooking/cleaning to get them to
sell it to you for $100 :)


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