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[Discuss-gnuradio] some progress and some questions


From: Joseph DiVerdi
Subject: [Discuss-gnuradio] some progress and some questions
Date: Thu, 10 Jul 2003 10:06:03 -0600

I am pleased to report some good progress in setting up and using gnuradio 
which has, in turn, spawned a few questions. In no particular order:

aumix and aumix-X11 are pretty snappy and useful programs for controlling sound 
cards under ncurses and X windows environments, respectively. I've used them to 
"tame" my sound card so it behaves sensibly (mostly). Source is readily 
available so inclusion of initialization and control code into home-rolled 
applications is an option.

The "home-rolled" VLF complex frequency translator (CFT) is doing its job very 
nicely. FWIW, it translates a 20-60kHz (balanced) input into a complex pair of 
(balanced) signals 0-20kHz (although the sound card is single-ended). The LO 
generator is a crystal controlled, TTL walking ring counter with final 
resynchronizer providing four phases of 40kHz which deliver accurate, balanced, 
quadrature drive to the mixers. The LO generator can operate up to 40MHz 
without modification. Higher LOs are available with this scheme using different 
logic families. The mixers are commutating mixers based on CMOS 4PST switches 
(fully balanced, of course). These mixers are limited to operation to only a 
few MHz but other mixers are suitable for higher frequencies. A single pole of 
low pass filtering at 25kHz on each channel limits the signals emitted from the 
XFT and delivered to the sound card.

I've stuck with the straight forward scheme of using the examples directory as 
my working directory and modifying Makefile.am when new programs are added. It 
works well and is stable.

gnuradio is running on a 266MHz, K6 host (named "Morgie") buried in some room 
which is conveniently located relative to the antenna system and is attached to 
the LAN with wires (haven't gotten its wireless PCI card configured yet). xdm 
has been configured on Morgie accept remote X terminals. All development work 
can be performed sitting in a remote office through another (wired or wireless) 
host running an X terminal through an SSH tunnel including observing real-time 
data displays. (sweet) A "top" probe of Morgie under acquisition conditions 
shows about 40% and 10% CPU load from gnuradio and sshd, respectively. The 
network is busy but not even getting warm. I find this scheme _very_ convenient.

Learning how to string together the various modules into useful applications 
has been slowest (for me) but I'm making some headway here. It looks like some 
of the functionality that I need is not available, e.g., FT processing without 
an attached display (GrFFTSink without the display), real<->polar 
representation conversion, frequency domain "scope" display. Alternately, I 
just haven't yet found them yet. I will try my hand at writing some modules and 
offering them to the repository.

Is there a "road map" noting the characteristics of the various families, e.g., 
Gr vs. Vr, gr_, qa_, atsc_, etc.?

Best regards,
Joseph
-- 
Joseph A. DiVerdi, Ph.D., M.B.A.          
http://xtrsystems.com/           970.980.5868 (voice) 
PGP Key ID: 0xD50A9E33




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