Sunday, October 31, 2010

SDR-Audio : CQ WW DX SSB Contest.

With the CQ WW DX SSB contest in full swing, I captured some interesting callsigns audio clips on 15, 20, 40 this weekend. 
Receiving station:
Rig: Softrock SDR
Ant:  Wire vertical over salt water.

15m 1815Z

Tuesday, October 12, 2010

DSP, $5 Linux server, cognitive radio and more...

Well, it's been a while since posting here, mainly because I've been investing some time in educating myself in the world of DSP s/w.

Some new pieces of SDR gear made it past the bench and into the shack  The latest Softrock Ensemble rx is now online,
and I must say the new pcb design is much cleaner and compact from a constructor's perspective.  It's performance on par with the previous v9.0.

The next step was to dedicate a Linux system for SDR  experimentation. As the good fortune would have it, I was lucky enough to pickup a desktop PC, in immaculate condition at the local swap meet.  It became the dedicated Ubuntu platform and now serves as my main development platform.

Ubuntu desktop installation is a snap, and with the added dev-tools a scap PC is transformed into a capable development platform.  Ubuntu's S/W manager makes things really easy.

SDR and Cognitive Radio
Experiments around the automation of decision making for the purpose of detecting information via rf sensing technologies can cover a wide range of topics.  For the Amateur Radio experimenter, there are several benefits and utility to this exciting field.  Propagation studies are among the very useful outcomes of cognitive radio.  In the context of two-way communications, ionospheric path optimization could be another interesting outcome of path discovery/and auto selection between two/more terrestrial locations.

As the chip manufacturers push the A/D envelope and DSP integration becomes more affordable, we have access to a level of instrumentation sophistication which has never been available before. 

Unix/Linux is of course a very capable networked O/S - which is perfect for radio work, as well as a powerful s/w development platform for doing DSP development work.

Design considerations.
To approach the problem of concurrent decoding of multiple digital data streams, and adding a level of control logic to make decisions about decoding activities over time, an understanding of a few key concepts are necessary.  Here is an interesting write-up on the general progress and concepts of SDR.

DSP concepts.
With the advances and adoption of SDR technology, the technical components for cognitive radio are in place today.
  • First, a reasonable understanding of DSP is needed when tinkering with S/W methods for signal processing.  The several phases of processing a signal undergoes through digital acquisition, digital processing and filtering and subsequent decoding, are all significant in laying the basis for S/W DSP.
  • Secondly, DSP happens in real time, and therefore the processing speed becomes a consideration when selecting a O/S platform - when done right, interesting opportunities await - eg. dx-spotting, "steering passive antennas" by means of S/W phase shift, diversity reception, etc.  
Hopefully you will find some of this information interesting, perhaps entertaining, but most of all, somewhat useful in your own experimentation activities.

Useful references:
The Scientist and Engineer's Guide to Digital Signal Processing  is a good starting point for DSP concepts.
Do you understand the SDP concept?