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Re: [Discuss-gnuradio] Hi

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] Hi
Date: Thu, 31 Jan 2002 14:59:16 -0800
User-agent: Mutt/1.2.5i

On Mon, Jan 28, 2002 at 08:36:52PM -0000, Philip Mackenzie wrote:
> Hi,
> I just came across the gnuradio project - I think its great. I'm a graduate
> student in Ireland and we've been working on our own software radio system
> for the past year. (http://ntrg.cs.tcd.ie/swradio.php)

Thanks for the pointer.

> Some quick details: For our hardware we are using an AR8600 and a 10.7 MHz
> IF amplifier we built. Without knowing about gnuradio we also chose the
> PCI-DAS4020/12 for acquisition - (good board but it can crash the system
> sometimes). 

Nice board.  Best bang for the buck.

> On the software side of things we are developing on Windows
> 2000. Our system is written in C/C++ and we have our own component structure
> for coding up radios. There are some early papers on our site which may be
> of interest and more substantial ones will be available soon.


> I'm going to try out your code with our receiver, etc. I got the impression
> that some people are using some type of cable modem. Does anyone have any
> tech specs on this? Has anyone has used any portion of the code on windows?

Let me know how it works for you.

We're currently using the Microtune 4937 DI5 cable modem tuner module
as our front end.  The module has the output IF centered at 5.75 MHz
and it's about 6 MHz wide.  We connect it directly to a 50 ohm
terminated input on the PCI DAS4020/12.  Works pretty well.  Tunes
from 50 MHz to about 890 MHz.  It's got an I2C bus interface which we
bit bang using the PC parallel port.  We control the RF and IF AGC
using the DACs on the 4020.

Being "free software" kind of guys, we haven't tried to build it under
windows.  I wrote a driver for the 4020 that DMA's directly into user
space under linux, and we're using that as the primary high speed
input path.

The GNU Radio code takes serious advantage of the linux/unix mmap
system call to create circular buffers by mapping a given piece of
memory in at two consecutive virtual memory locations.  This may be
hard to duplicate under windows.

Assume you want a 64K circular buffer.  We allocate a 64K chunk of
shared memory, and then map it in to the user address space twice, at
immediately adjacent virtual addresses.  This hack works on pretty
much every unix/linux box running on a machine that does not have a
virtual mapped cache.

Please keep me posted as to your progress.  

We are currently building an off the air (H)DTV receiver.  In the San
Francisco bay area there are now about 8 stations broadcasting digital


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