A VOR radio built on GNU Radio. More to come. Probably merge as an example or an app in my gr-airnav library in the near future. The VOR_flowgraph.png file in the images directory shows an overview snapshot of a working version of the flow so folks can look at it without having to download the flowgraph first. I wil try to keep this current to any major structural changes but can't promise it will stay up to date as I am continuing a lot of development work.

A couple equations I worked out for phase shifting in time using the Delay block. There is nothing ground breaking here and I am sure most DSP practitioners would consider this very basic but I had to account for a phase delay in one of the processing pipelines and didn't find these equations written down explicitly anywhere.

Depending on the resolution of the frequency shift you'll need a minimum sampling frequency. This equation tells you the minimum sample rate for a phase resolution in:

• Degrees

  samp_rate = (360 * target_frequency) / phase_resolution

• Radians

  samp_rate = ((2/math.pi) * target_frequency) / phase_resolution

Where a single sample shift with the Delay block will equal 1 resolution unit of phase shift.

Once you're satisfied you're at a sampling rate that meets your phase control resolution needs, you'll want to know how many samples to delay to meet your shift requirement.

• Degrees

  delay = (phase_shift * samp_rate) / (target_frequency * 360)

• Radians

  delay = (phase_shift * samp_rate) / (target_frequency * (2* math.pi))

Planning to gather some more sample files for testing (as well as field test) soon.

• sample_data/RBT_VOR_Sample_32768kHz.raw

  Sourced from the wave file sample on the website of sylvain (F4GKR). Down-sampled to 32,768 samples/second and saved as a complex, GNURadio compatible file. Source VOR is the Rambouillet VOR in France. The identifier is RBT (.-. -... -). I estimate the radial the data is taken from based on the website as being 291 deg (magnetic). I've used this for phase-delay calibrations but we'll see how accurate I am when I take the radio out to capture more data.

Referenced from the Wikipedia VOR Article.