[hpsdr] olpc/hf comms/etc

[Robert McGwier]

That is clearer.  We are comparing apples and oranges.  They just both
want to be an SDR.

Your NVIS system for providing a WAN is a perfect idea and was on my
plate but I believe this will need a fairly serious facility to pull off
and will not be done on the OLPC itself. In order for this to provide
usable communications it will have to have serious FEC,  time,
frequency, and probably spatial diversity to use low power.  All of this
requires compute horse power.  But it is exactly where I would like to
go with HF comms work.   And you are right, this will require good IMD
dynamic range as well as a clean linear (not necessarily efficient)
transmitter.  The Phil's are bringing us some serious HF toys with the
Mercury and Penelope and it might be very useful and inexpensive way to
provide the WAN NVIS comms for (say) villages, schools, etc.

I on the other hand was talking about a few dollars for a broadcast
receiver.  With the 3DNOW enabled 400 MHz CPU in the OLPC,  I think we
can do a simple receiver for very little money.

Both clearly have their place.  One is for lazy people like me and the
other is for brave souls like you!

All kidding aside, I suspect there is real support for providing both.

Happy Holidays to one and all,
Bob
N4HY



stephen pearce wrote:
> Our plan was to build a tx/rx pair that could pass low volume email
> traffic using
> a nvis path .. outside the range of the mesh network ...
> 
> To get the dynamic range to select out adjacent channel interence and
> still demodulate the signal would require good dynamic range in the
> adc would it not .. in the absence of a narrow band receiver and front
> end filtering .. which I admit is an alternative ... but you then
> loose frequency adility .. a superhet design
> using a first mixer/local oscillator to provide frequency agility
> and some narrow filtering initially would reduce the requirements on
> the adc speed and dynamic range .. hence my comments on ceramic filters ..
> which is a sort of compromise of both options ..
> 
> I would be interested in your further comments
> Thanks
> 
> stephen
> zl1any
> 
> 
> On 12/23/07, Robert McGwier <rwmcgwier at gmail.com> wrote:
>> It is my opinion that there is little to be gained by use of 24 bit
>> A/D's since there is insufficient dynamic range in the QSD on softrock
>> 40's to use it.  I cannot see the need for 192 kHz. I cannot see the
>> need for this to be more than 12000 Hz which greatly reduces the
>> computational complexity.  I think we are trying to help kids who are
>> getting a $200 laptop for nothing receive news from around the world and
>> their neighborhood on HF broadcast bands.  What is needed is proper
>> design and gain management to "match the noise floor to the dynamic range".
>>
>> Bob
>> N4HY
>>
>

-- 
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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