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Re: [Discuss-gnuradio] OLPC - next generation with SDR?

From: Frank Brickle
Subject: Re: [Discuss-gnuradio] OLPC - next generation with SDR?
Date: Mon, 24 Dec 2007 23:53:55 -0500

On Dec 24, 2007 5:11 PM, John Gilmore <address@hidden> wrote:

The Odyssey board operates at 10MHz IF; so wouldn't it need an external

Yes, but many different tuners (band sets) can be serviced by the same IF processor.
What kind of antenna would this require?  Something external to the
laptop?  Or something that could be built into the plastic case?

Depending on the band it could be either or both. A multiloop MW/HF could be embedded in the plastic case. A gender-bent SMA could accommodate a wide variety of V/U/SHF antennas.

We won't need a processor; the laptop will come with a processor much
faster than 40 MIPS.  (The current XO CPU is a Geode LX 433 MHz x86,
with MMX, 3DNow, and some SSE instructions.)

We can argue that a "radio coprocessor" would greatly enhance the range of possibilities -- DRM (Digital Radio Mondiale) for example, and see below.
> We need a DDS and a QSD (we do not need the QSE for the receive only
> version) if we are going to tune the HF shortwave broadcast bands and
> get reasonable performance at low cost.

I think that single chips are available that do broadcast-band AM and
FM decoding for cheap; has nobody done this for the television and
shortwave bands?  Or is the problem that nobody's done this digitally?

Two problems. One is that the off-the-shelf chips use proprietary IP. The other is that the off-the-shelf chips are locked up and it's next to impossible to do anything interesting with them that you can't already do with a cheap external radio. I'm not aware of commercial devices that could be used to capture and detect *all* of the signals within a 50 kHz bandwidth, which could probably be done with ease with the assistance of a radio coprocessor. This is an essential step towards "cognitive" functions -- make the radio functions mutable and dynamic.
If we can provide something that gives real benefit for the target
kids, we shouldn't be dogmatic about analog versus digital.
Alternatively, if OLPC provided a million-unit order for a digital
tuner chip that would target all these bands, others could then buy the
cheap chip for a variety of projects.

> This would provide a clear example of how it could be done.  It does not
> meet the price point, but it shows the capabilities and then we can
> negotiate.

I'm glad you-all are pointing out low volume prototypes...

I'd think in part we'd be providing not just sealed up applications but also programmable devices and an API, capable of being used in innovative ways in software *without* requiring the chronic intervention of large-scale chip producers. Part of the SDR mission, isn't it?


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