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:
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg4svv1_uXcJ95Y5up9H12y9ibaIXPtxt3B6VB8bmyqdDqrfUU-r4HISeNHsLHf08P6OSaaxhcWoceHghQ5oEC0qMDUwu2f80rJKk8vFFTfToZBkX_ZIVSIQ5D9fgncrteB-re1a8z2Ko4/s400/OTHR_5590_20171207T1448_SM2BYC_3.png) |
Autocorrelation |
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgUo4u1jkopqXwDti8PDCypRkKzH_rvEsGZ-9IR2BnWwd13wj-fS4IKMuOlNm8RbbLXz4ThIjIM87CBIBBI5J7dYqAXkZtUw88MO3Zq3vL5EAaZUA84unoim_TQaS47qYFICt28Ef6fFDk/s400/OTHR_5590_20171207T1448_SM2BYC_4.png) |
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:
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh_L9OGqdYoJYF7Hqzs2_VllBvEjudIcq-aTrgRzaEQ-V7Um4ZoNCi1p5d-gvqmCTnDRqHIrzJ_unr_ClXFJjzWfoIP87FuOlGHUQ_CoHpYeD3UE8z1mFTQeCplud9qvV1x4myrpD9RmiQ/s400/OTHR_5590_20171207T1448_SM2BYC_1.png) |
OTHR pulses |
There is a discrete structure in the pulses:
pulses with pulse number mod 4 = 0,1,2,3 look more similar:
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiul8lklr1-QdPNdogi5mX0L8zd375a1eI7ZSjkHavxxiqjdvzQ5Cx54KkOKpUslg7x2Or_HXcqj_MRxMg649lKJE0UalDsvET90xumzyQlaG2gtCuQNx5gkoB7p1T1tKk5TEsoVuVkJEo/s400/OTHR_5590_20171207T1448_SM2BYC_2.png) |
OTHR pulses - pulse number mod 4 |
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