20 August, 2014

Digital Signal Processing

The Norwegian-language "The road to the international radio amateur license" came off the press this June. It is based on the RGSB International Amateur Radio Examination Manual from 2006, which RSGB graciously allowed us to use.

But the translation has been adapted on several topics. One example is the chapter on propagation due to the need in our country for more emphasis on propagation in polar regions and in mountainous terrain. Another is a completely new chapter on digital signal processing.

I got involved quite late in the project for this new chapter. The importance of digital signal processing in amateur radio has just kept on increasing as variable digital filters, adaptive noise reduction filters, adaptive notch filters, digital demodulation, and software defined receivers are everywhere.

The entire book project was handled by the Bergen group of the Assocation of Radio Amateurs in Norway. In fact it was done in order to celebrate their 90 year anniversary. The editor has been Frode Igland, LA6VQ.

My efforts resulted in a completely new chapter which was written during the first few months of this year. It was finalized with valuable input from the editor after a process of sending the manuscript back and forth lots of times. It was a fun project, where the challenge was to convey complex ideas with a minimum of equations.

The chapter has these headings:
  1. Applications of digital signal processing 
  2. Discrete values
  3. Quantization - digitization of amplitude
  4. Sampling - digitization of time
    • Aliasing
    • Nyquist frequency
    • Reconstruction filters
    • The time domain
  5. The frequency domain
    • The Fourier transform
    • The Fast Fourier Transform (FFT)
  6. Digital Filters
    • Moving average as an example of an FIR filter
    • IIR filter equivalent of a low pass RC-filter
    • IIR filter equivalent of a high pass CR-filter
  7. Example of a software defined receiver with spectral display
The final section briefly discusses the RTL-SDR and uses an example from this blog showing activity of secondary users in the 70 cm band as shown here.