[amsat-bb] Re: [Discuss-gnuradio] OLPC - next generation with SDR?
rwmcgwier at gmail.com
Sat Dec 22 12:43:59 PST 2007
John Gilmore wrote:
>> The thing does appear to have sufficient horsepower to do some DSP.
>> I would like to think we can make several things available to this
>> project. For example, I think a tunable HF receiver for shortwave AM
>> broadcast is easiy achievable for very modest cost. Further out, I
>> would to see the use of this machine and OFDM skywave to provide WAN
>> capability to large areas of the world without such capability.
> If we were given a square inch of circuit board space, twenty cents
> for components and wires and connectors, four pins, 0.2 watts of power
> when operating, and half a million gates colocated with the CPU and
> memory bus, what radio capabilities could we offer to the next
> generation OLPC project?
> That's the fun challenge. Here's some background.
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:
# 15 meters – 18.90–19.02 MHz – Seldom used.
# 16 meters – 17.48–17.90 MHz – Day reception good, night reception
varies seasonally, with summer being the best.
# 19 meters –15.00–15.825 MHz – Day reception good, night reception
variable, best during summer. Time stations such as WWV are clustered
around 15 MHz.
# 22 meters – 13.57–13.87 MHz – Similar to 19 meters; best in summer.
# 25 meters – 11.50–12.16 MHz – Generally best during summer; said to be
ideal during the period before and after sunset.
# 31 meters – 9250–9995 kHz – Good year-round night band; seasonal
during the day, with best reception in winter. Time stations are
clustered around 10 MHz.
# 41 meters – 7100–7600 kHz – Reception varies by region – reasonably
good night reception, but few transmitters in this band are targeted to
# 49 meters – 5800–6300 kHz – Good year-round night band; daytime
reception is lacking.
# 60 meters – 4400–5100 kHz – Mostly used locally in tropical regions,
though usable at night. Time stations are clustered around 5000 kHz.
# 75 meters – 3900–4050 kHz – Mostly used in Eastern Hemisphere, not
widely received in the Americas.
# 90 meters – 3200–3400 kHz – Mostly used locally in tropical regions,
with limited long-distance reception at night.
# 120 meters – 2300–2495 kHz – Mostly used locally in tropical regions,
with time stations clustered around 2500 kHz. Not technically a
shortwave band; resides in the upper reaches of the medium wave band
The dsPIC33 has more than enough horsepower to provide good
(synchronous) detected AM and even some modest AGC.
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.
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
AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,
TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair
“An optimist may see a light where there is none, but why
must the pessimist always run to blow it out?” Descartes
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