Monday, December 11, 2017

TDoA measurements using GPS time-stamped IQ samples from KiwiSDRs (7)

14370 kHz OTHR 20171211T1040


The autocorrelation function has peaks at multiples of 0.02 seconds: (as is well known)
14370 kHz OTHR autocorrelation
The pulse shapes and the FM demodulated phases are shown below w.r.t. GPS seconds mod 0.02 seconds. Of the full bandwidth of this signal is 20kHz the KiwiSDRs sample 12 kHz. Therefore only part of the chirp signal is seen:
14370 kHz OTHR pulse shape and FM demodulated phase
Correcting for the sample rate the chirpyness becomes 12001*83.326 = 1e6, i.e., one sweep covers 20 kHz.

In the time differences different paths of propagation can be seen; it looks like the ionosphere at this time was quite patchy:
TDoA 14370 kHz

The TDoA location is consistent with the known position of the transmitter:
TDoA maps 14370 kHz

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