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Re: [Discuss-gnuradio] Welcome and brief update

From: Daniel Rogers
Subject: Re: [Discuss-gnuradio] Welcome and brief update
Date: Fri, 10 Jan 2003 10:47:10 -0800
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.2) Gecko/20021202

(1) RF Hardware design: to make GNU radio more accessable for those
without high speed A/D hardware, we'd like one of you RF guys to
design a simple RF front end that could be directly hooked to one of
the "HiFi" 96 KHz sampling rate sound cards.  Please make it simple
and buildable out of things that anybody can order from mini-circuits,
digikey, etc.  The idea is not to build the greatest piece of RF
hardware ever, but to build something minimalist that actually works.
Perhaps a basic 2M or 70cm downconverter.
If you've got other ideas, please jump in.

I was thinking about this as well. My idea was that I could use a single chip ADC and connect it to an existing hardware link (such as PCI, or Firewire-2, or Ethernet). There are tons of single chip ADC solutions out there. One I stumbled upon is this one from Texas Instruments:
ADS800, 12-bit, 40 MSPS ADC SE/Diff inputs.

It only has 16 pins, so the wireing could be simple and the tech specs on TI's website give a complete buffered, ac-coupled setup. You can pick it up from digikey in single unit packages for $41.82

One need only to connect this chip to an existing data bus with enough capacity (12bits * 40Msps = 480 Mbps, at least). This would mean (in my experience) pretty much either pci, gigabit ethernet, or Firewire-2.

There is where I have gotten stuck. I haven't been able to find a single chip firewire-2 solution, which would be ideal. It would require less configuration that ethernet, and I believe that Firewire-2 can provide enough power to power the ADC without an external powersuppy.

On the other hand, I don't have a tremendous amount of hardware design experience and putting together 40-50 pin firewire chips is a bit intimidating.

But the idea of a single input, single output, firewire powered, external, high sample rate ADC is very sexy, and, it would seem, fairly close to reality. Not to mention a WHOLE lot cheaper that some of the other commericial ADC's out there.

I am curious what others who may have experience in things like this think.


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