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

[Brian Padalino]

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.

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.

> --
> Nos

Brian