[hpsdr] olpc/hf comms/etc

[Robert McGwier]

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

stephen pearce wrote:
> ***** High Performance Software Defined Radio Discussion List *****
> 
> Hi
> 
> we were interested in this as well ... so far we have been considering the
> softrock 40 design ... and the recent si570 oscillator design would give it
> frequency agility ... the i/q demod would need to be handled by a dsp
> such as maybe the dspic30 .. though to get optiml dynamic range 24 +
> bit resolution would be preferable and the dspic30 is predominately 16
> bit ... we have yet to identify the optimal codec .. when I last
> looked 24 bit 192 KHz devices with a serial bnit stream out were not
> readily available ... and the bit rate places a high requirement on
> the input to the dsp which I don't think the dspic could easily cope
> with ... maybe an fpga type of solution would be better though I have
> no experience with these .. our idea had been to do all the i/q and hf
> digital demod on the dsp/fpga and feed an ascii or binary data stream
> from this into the olpc via a
> usb port .. this minimises the processor demands on the olpc ...
> 
> there is a recent artilce in qex on the use of ceramic resonators as
> if filters .. this would lower the cost and the softrock is by default
> quite broad and compensates by dynamic range in the
> adc .. if a superhet design was used the tuning steps of the vfo could
> be quite coarse ..
> which might improve loop stability/phase noise ...
> 
> we would be keen to help in such a project .. however parts can
> sometimes be a bit of pain obtaining here in small lots for
> prototyping purposes ...
> 
> cheers
> zl1any
> 
> 


-- 
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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