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FW: [Discuss-gnuradio] Slashdot Q & A / Beginning of our FAQ
From: |
Matthew Burnham |
Subject: |
FW: [Discuss-gnuradio] Slashdot Q & A / Beginning of our FAQ |
Date: |
Thu, 26 Sep 2002 00:25:01 +0100 |
Naively, I've just had a look to see what RS Components do in the way of
ADCs... and found that there's quite a few available with sample rates
in the region of 10MSPS for around UKP20 to UKP30 and some with 20MSPS+
for a little more (around UKP40) for single units. Would it not be
possible to come up with a cheap alternative to the Measurement
Computing board? I assume the minimum spec necessary with an I/F of
5.75MHz is 11.5MSPS?
Just a thought, which I'll look into further, but wondered if anyone had
considered this? I know it could get 'interesting' designing such
high-speed digital circuits... but I've got a Wavefinder Digital Radio
in front of me which squirts a considerable amount of data down the USB
port so it can't be THAT difficult. Has anyone else considered this
previously?
Perhaps as a starting point some lower-speed stuff could be done, if we
got a lower I/F than the cable TV tuner, with lower bandwidth, we'd need
a correspondingly lower ADC (maybe even something reasonably cheap
off-the-shelf?) which would allow those not able/willing to get the
Measurement Computing board to get into wide-band-ish stuff (for
examaple, be able to play two FM stations, provided they were much
closer to each other).
> The other path I'll call "wide band". This is personally the
> area that I find most interesting because it is with wide
> band that you are
> able to do things that you can't do with a conventional radio. Chief
> among these is the ability to concurrently receive (or
> transmit) multiple channels/stations/frequencies. In the
> examples directory of the GNU Radio code, you'll find an
> example that receives and demodulates 2 FM broadcast stations
> and puts one out the left channel and one out the right.
> Matt Ettus, another GNU Radio developer, has built a demo
> that receives 4 narrow band FM channels concurrently. These
> demos run fine on a 1800+ Athlon, or 1.7 GHz P4.
>
> For the wide band stuff our "standard configuration" is a TV
> tuner module designed for cable modems that tunes from 50MHz
> to 890MHz with an IF of 5.75 MHz. The module is a Microtune
> 4937 DI5. We connect the output of the tuner directly to a
> 20M sample/second 12-bit A/D converter. The converter we're
> using is the Measurement Computing PCI DAS4020/12. It'll do
> 4 channels at 10M sample/sec or 2 channels at 20M
> sample/second. From the hobbyist's point of view, it's not
> cheap, about $1300, but it is the cheapest, fastest off the
> shelf solution that we found.
>
> With our "standard configuration" we ought to be able to
> handle IS-136. GSM would be possible if our RF front end
> would cover the
> 1.9 GHz range. Vanu, Inc has a GSM receiver running on a
> 1GHz pentium laptop, so we know it's possible.