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Re: [Discuss-gnuradio] Re: A Humble Request.... - "Open-Hardware"

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] Re: A Humble Request.... - "Open-Hardware"
Date: Sun, 09 Jan 2011 20:22:53 -0500
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On 01/09/2011 07:43 PM, Moeller wrote:
But a simple one like SSRP is not that complex. You're mixing two different 
worlds. Complex SDR have a real CPU and bigger FPGA like the Virtex 4 or 5
for real signal processing. This cannot be done in a small Spartan chip (only 
DDC, not much more)
SSRP does not have a single processor chip. He sells the bare board for $15. I 
assume that he did not have such costs.

The SSRP, as far as I can tell, is dead. Last status update was nearly 4 years ago.

But let's take a look at it as an example, shall we:

o The ADC board (single-channel, thus cannot handle direct-conversion with I and Q sampling) $120.00 o Uses an Off-The-Shelf ElraSoft FX2 board, which in 2007, sold for $89.00

OK, so for $209.00, you can have a 25MSps board, that can direct sample from DC to 12.5MHz, using the "developer starves" model.

But it won't do complex sampling, and it won't do DDC and decimation, so your host computer had better be prepared to receive
  25Msps and "do stuff with it".

Let's assume that a complex-mode sampler could be designed, based on the SSRP approach for only about 1.5 times what the real-mode sampler can be built for. That's now in the $300.00 range, and we're talking Rx only.

Let's assume that the Tx side can be reasonably sold for the same as the Rx side. Another $300.00 for the complex-mode Tx side of the system. Oh but wait, we can share that ElraSoft FX2, so deduct $89.00.

That's $511.00, and we still don't have DDC or decimation, since we don't have an FPGA, and that poor little FX2 isn't going to be able to do that in real time, that's for sure. It'll be working its little heart out just keeping up with the ADC and DAC. We still don't
  have any kind of daughter-card interface.

Ok, so maybe we can run the ADCs and DACs at a lower rate, so that we can do the DDC and decimation in the FX2? I'd be *astonished* if it could keep up with input rates beyond roughly about 200Ksps complex, which is cheap sound-card territory. Oh dear.


Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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