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Re: [Discuss-gnuradio] typical bandwidth?

From: John Gilmore
Subject: Re: [Discuss-gnuradio] typical bandwidth?
Date: Thu, 21 Mar 2002 04:16:44 -0800

Thanks, Dave, for a great and detailed summary of the kinds of signals
people might want to mess with.  I have just a tiny addendum.

While most individual signals only use 30-50kHz, software-defined
radios also let you build a "scanner" that can watch a whole band at
once.  Unlike usual scanners which retune themselves frequently, a
wideband scanner would be able to digitize a wider chunk of spectrum,
and detect and extract multiple signals from it simultaneously, saving
each to disk if desired.  E.g. one of the demo applications that comes
with GNU Radio is the ability to tune two FM stations at once (you get
mono sound from each one, out the PC's left and right audio channels).
Such applications are limited by the incoming bandwidth available, CPU
power available, and the differences in signal gain required on the
various channels.

Another example might be a translating repeater that could accept
transmissions on one set of frequencies and retransmit them (either in
realtime, or later after the second channel was clear) on another
frequency.  Such a portable repeater would be very useful in public
safety applications, e.g. when fire crews from different counties use
different frequencies or modulation parameters, but are responding to
the same forest fire or urban emergency.

Software that merely recorded minute-by-minute channel availability
across a swath of spectrum would probably be useful in the ham bands,
for example.  Humans could then examine summaries of historical usage
patterns, when allocating and reallocating frequencies for various
local uses.

        John Gilmore

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