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Re: [Discuss-gnuradio] cable modem tuner now integrated

From: Darrin John Eden
Subject: Re: [Discuss-gnuradio] cable modem tuner now integrated
Date: Mon, 26 Nov 2001 01:15:20 +0100

Awesome! I can't wait to be in a position to acquire said hardware.

The "find interesting signals" is such a classy problem. I suppose it runs the Information Theory gamut in a big way.

I wonder if serving a normative subset of the data a node collects might enable those of us without handy access to The Hardware to do our part and explore interesting signals? The address@hidden folks have a lot of us working on it now, but who wants to be tied to just one antenna?


On Monday, November 26, 2001, at 12:25 AM, Eric Blossom wrote:

Hi Folks,

I've now got a very nice cable modem tuner module (eval board) hooked
into GNU Radio. From a hardware point of view it was a zero glue
operation. Just a couple of cables and rigging up a power supply.

FYI, it's a Microtune 4937DI5 3x7702 module. Tunes from 50M to 860M
and has about a 6MHz wide IF centered at 5.75M. Very convenient for
our 20M sample A/D board. Cables right up. You control it by bit
banging it over the parallel port. It has a I2C interface plus a few
additional bits.

I've attached some FFT graphs from various parts of the spectrum.
Lots of good stuff to work with. The center of the IF is indicated at
5.75MHz. The displayed frequency axis values don't currently take
into account where the module is tuned.

Here's what they are:

Lots of broadcast FM stations. Should be able to cook up a
cool demo that demods more than one station at a time without
retuning the RF front end. This will show something that you
can't do with a regular radio. Existing code demods the
channel that is tuned to 5.75M

Local TV channel 35. Should be able to extract the audio.

Not too exciting in the snap shot, but in real time there are
all kinds of signals coming and going. Some are conventional
push-to-talk FM, but some appear to be burst transmissions.

Narrow band FM. Note close channel spacing. Some are FM, some
are digital.

Right hand side of graph is spread spectrum lump.
Conventional narrow band on left hand side.

One thing I've noticed out of watching the FFT for a while is we need
software that "finds interesting signals".

I plan on reworking the spectrum display so that there are a few
markers available that can be positioned to show signals of interest,
select this one to demod, etc. Annotations into a data base might be
nice too.


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