TDOA (Time Difference Of Arrival), also known as multilateration, is a well-established technique for the geolocation of RF emitters. Using three or more receivers, TDOA algorithms locate a signal source from the different arrival times at the receivers.
In this case, TDoA measurements are related to a CIS-12 signal (modem AT-3004D) spotted this morning on 11414.0 KHz/usb and use GPS time-stamped IQ samples from four KiwiSDRs: F1JEK (JN05hs, southwestern France), SV3EXP (KM07qx, west Greece), UR5VIB (KN68DL, central Ukriane) and KHIMKI (KO85qw, near Moscow city Russia).
In this case, TDoA measurements are related to a CIS-12 signal (modem AT-3004D) spotted this morning on 11414.0 KHz/usb and use GPS time-stamped IQ samples from four KiwiSDRs: F1JEK (JN05hs, southwestern France), SV3EXP (KM07qx, west Greece), UR5VIB (KN68DL, central Ukriane) and KHIMKI (KO85qw, near Moscow city Russia).
Cross correlations suggest the Crimean peninsula as the area of Tx antenna. Since CIS-12 is widely used by Rus-Ny, it's quite reasonable to assume that the Tx be in Sevastopol, Black Sea fleet HQ. Note the scattering in the correlations involving the French SDR (F1JEK) which are due to multipath propagation.
Plots are obtained using my (old) Ubuntu 12.06 LTS updated to gcc 6.6 and gnuplot 4.4; TDoA algorithms implemented by Christoph mayer:
and GNU Octave, scientific programming language, version 4.4:
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