Local Charleston SDR hardware

Terry Fox tfox at knology.net
Fri Jan 16 15:30:58 CST 2009

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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