[Discuss-gnuradio] cable modem tuner now integrated

[Eric Blossom]

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:

  fm92.png
        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

  ch35-597.25M.png
        Local TV channel 35.  Should be able to extract the audio.

  461.2M.png
        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-891M.png
        Narrow band FM.  Note close channel spacing.  Some are FM, some
        are digital.

  spread-spectrum-879M.png
        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.

Eric

fm92.png
Description: PNG image

ch35-597.25M.png
Description: PNG image

461.2M.png
Description: PNG image

narrow-band-891M.png
Description: PNG image

spread-spectrum-879M.png
Description: PNG image