HF over the horizon radar (OTHR)

Here are some notes about an OTHR radar signal (likely the one described  on page 28 here http://www.iarums-r1.org/iarums/radar-2013.pdf) 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

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