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-fs (fs 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 fd=0 is caused by an interference|
|13975 kHz 20180105T1114Z @DF0KL|
|13975 kHz 20180105T1114Z @G8JNJ|
|13975 kHz 20180105T1114Z @Izhvesk|
|13975 kHz 20180105T1114Z @Julisdalen|