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

From: Brian Padalino
Subject: Re: [Discuss-gnuradio] Re: PCIe know-how?
Date: Sun, 4 Mar 2007 17:47:36 -0500

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

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.



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