As preface, I'm not a radio engineer. I'm a software guy with pretentions to understanding digital hardware. I have a few signal processing books on a dusty shelf. You lose me as soon as you start talking "Q signals".
The Odyssey board operates at 10MHz IF; so wouldn't it need an external tuner?
I am in agreement with Frank that we can currently do it for a few tens of dollars ~$50 in small quantities and that include parts and boards. We can even put together a prototype which will allow HF shortwave reception from low bands through about 21 Mhz covering these bands: [15m thru 120m]
What kind of antenna would this require? Something external to the laptop? Or something that could be built into the plastic case?
The dsPIC33 has more than enough horsepower to provide good (synchronous) detected AM and even some modest AGC.
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 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?
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 hope we'll get someone interested who has designed high volume digital radio electronics. High volume ~= million-unit. (Do any people like this exist? Perhaps Matt's bluetooth design has shipped in that quantity; WiFi does too.) There's already an entire high speed digital radio transceiver in the existing XO: it's the Marvell "Libertas" WiFi 88W8388 controller chip and 88W8015 radio chip. It's reprogrammable, though the ARM code that runs in it isn't open source yet (the high level code can be open sourced, but it runs on a proprietary RTOS).
I think the best strategy for a $50 laptop's radio would be to have either an internal antenna or a single connector; a small number of cheap analog components; perhaps *one* analog/digital chip (multi channel DAC/ADC "radio chip"); and stuff *everything* else into a corner of the digital system-on-chip that implements the rest of the laptop. It's hard to prototype such a thing, though perhaps using an FPGA that come with a fast embedded MIPS or ARM CPU would be the closest.
The current XO uses two custom chips (the DCON display controller, and the CAFE camera/flash/SD controller), some very custom "mesh" firmware for the ARM core inside the WiFi chip, and some very custom firmware for the EC embedded controller battery charger chip. A $50 laptop version would probably mash all these chips together with the CPU, GPU, and its "southbridge" support chip, leaving only one system-on-chip, plus flash, DRAM, a few external analog chips, and a pile of analog electronics for power supply and such.
John