TDoA maps 6950 KHz 20180112T2138Z |

Cross-correlations 6950 kHz 20180112T2138Z |

abs(z) vs. time 6950 kHz 20180112T2138Z |

TDoA maps 6950 KHz 20180112T2138Z |

Cross-correlations 6950 kHz 20180112T2138Z |

abs(z) vs. time 6950 kHz 20180112T2138Z |

Yesterday I found the OTHR from Cyprus operating with 25 Hz pulse repetition rate and μ=500kHz/s sweep rate. The most likely geo-location is just north of the known location:

I was thinking about an alternative way of geo-location using an extended Kalman filter, and found this reference: www.dtic.mil/dtic/tr/fulltext/u2/a285972.pdf. It is written very well and I was able to implement it quickly in octave using dfpdp from the optim toolbox for the Jacobian. More on this later.

TDoA plots 17030 kHz 20180113T1126Z |

Cross-correlations 173030 kHz 20180113T1126Z |

This is a follow up to this blog post. Again the signals of the OTHR in Cyprus were analyzed using GPS time-stamped IQ samples from several KiwiSDRs.

In this case the OTHR signal was found between 13965 and 13985 kHz. The slope of the FMCW signal is μ=1MHz/s, and there are 50 sweeps per second. This results in a bandwidth of about 20kHz.

As is well known, the frequencies Δf of the spectrum of the de-chirped signal correspond to time delays τ=-Δf/μ in the case of a stationary target.

_{d} vs. Δf where f_{d} = v•λ/2 (for velocity v and wavelength λ). Here one has to be careful to adjust the phases in each bin to correct for the fact that the sampling times are not exactly aligned to multiples of 0.02 seconds.

Plots for 5 KiwiSDR are shown below. The splitting of the ionospheric reflection is most likely due to O- and X-mode propagation in the F layer.

Thanks to all KiwiSDR owners who make their receivers available and do connect a GPS antenna.

In this case the OTHR signal was found between 13965 and 13985 kHz. The slope of the FMCW signal is μ=1MHz/s, and there are 50 sweeps per second. This results in a bandwidth of about 20kHz.

As is well known, the frequencies Δf of the spectrum of the de-chirped signal correspond to time delays τ=-Δf/μ in the case of a stationary target.

- for this one has to multiply the received signal with the original waveform
- tuning offsets w.r.t. center frequency of the OTHR signal correspond to a time delay of the original waveform
- when Δf is positive the delay corresponds to the frequency Δf-f
_{s}(f_{s}is the sampling frequency), i.e. the ranges wrap around the x-axis.

Plots for 5 KiwiSDR are shown below. The splitting of the ionospheric reflection is most likely due to O- and X-mode propagation in the F layer.

13975 kHz 20180105T1114Z @CS5SEL; the band at f_{d}=0 is caused by an interference |

13975 kHz 20180105T1114Z @DF0KL |

13975 kHz 20180105T1114Z @G8JNJ |

13975 kHz 20180105T1114Z @Izhvesk |

13975 kHz 20180105T1114Z @Julisdalen |

Subscribe to:
Posts (Atom)