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From: | Eric Blossom |
Subject: | [Discuss-gnuradio] cable modem tuner now integrated |
Date: | Sun, 25 Nov 2001 15:25:37 -0800 |
User-agent: | Mutt/1.2.5i |
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
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ch35-597.25M.png
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461.2M.png
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narrow-band-891M.png
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spread-spectrum-879M.png
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