Local Charleston SDR hardware
metavox at earthlink.net
Fri Jan 16 19:34:14 CST 2009
In addition to the attractive hardware there are two very attractive
things from the web site about the FPGA Logic Design.
First, there are only a small fraction of the available cells used.
This mean lots of room for growth in complexity. That growth can be
used to increase the signal processing or perhaps a way to speed it up
through more parallel processing.
Second, "all FPGA code was implemented in Verilog and bit files were
created using the free versions of the Xilinx development tools". This
means a cheap (as in free) way to learn how to program an FPGA to do
some useful things. As a learning platform, this is attractive.
Is there any interest in several of us getting these things to play, er,
make that learn with? I am game but I sure would like some help. I
have never done an FPGA before but I recall a nice talk by Hal some time
back. With more of us in the pool, we can help work out the hard spots.
I will make may lab available, with tutoring, to do the surface mount
assembly of the front end.
Terry Fox wrote:
> One of the people here in Charleston has been working on a less-expensive
> direct-downconversion (DDC) receive solution for a while. I have been
> alluding to this project for a while. At a recent meeting, he said that it
> was OK to forward information.
> His name is John Schwacke, he is a PHD, and works at Medical Univ. of S.
> Carolina (MUSC). He has worked with Mel (W4MEL) in the past, back in DC.
> The hardware is based on a Digilent Nexsys II demo FPGA board (about $100),
> and a sampling board of his design that plugs into the Nexsys II. The
> sampling board contains a simple (bypassable) 27MHz LP filter, a
> variable-gain-amp (VGA), an 80Ms/s, 12-bit A/D, and an ASIC that does some
> downsampling and VGA control. I think there is also a bypassable attenuator
> in the RF chain... The PC interface is via USB.
> John is using GNURadio software under Linux to test the hardware. He can
> presently hear 2M repeaters (bypass the LPF), and signal generators on HF
> (40M). (yes, his built prototype is working)
> John has two more PC boards (reserved for Mel and me), and I am ordering
> parts to populate these boards. John says that he is willing to have more
> boards made. The estimated parts cost to build John's board is about $60.
> So, at less than $200, you could build a DDC HF receiver.
> John has a web site showing this work:
> John uses solder paste and an electric skillet to build these boards.
> The approach that John has taken is to use a less-expensive 12-bit A/D, and
> preceed it with a VGA to reduce overload. This is NOT as good as using a
> 16-bit A/D, but is much less costly and easier to build.
> The info is still preliminary.
> Please check it out.
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