[hpsdr] olpc/hf comms/etc

[stephen pearce]

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


-- 
Stephen Pearce
Whangarei
NZ