Friday, December 8, 2017

HF over the horizon radar (OTHR)

Here are some notes about an OTHR radar signal (likely the one described  on page 28 here which is audible every evening/night in most of Europe.

Note that there is a bias due to the fact that the KiwiSDR bandwidth (12 kHz) is less than the bandwidth of this radar signal (40-50 kHz)

This is how the autocorrelation looks like:

Autocorrelation zoom

  • fundamental period: dt = (11573.3 ± 0.2) μs
  • the autocorrelation function shows peaks at multiples of dt, 4×dt, and 150×dt

Using GPS time-stamped IQ samples each pulse can be plotted on top of the other pulses:
OTHR pulses
There is a discrete structure in the pulses: pulses with pulse number mod 4 = 0,1,2,3 look more similar:
OTHR pulses - pulse number mod 4

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