TDoA SuperDARN/Finland

Today signals from the SuperDARN radar in Finland were active around 12375 kHz and the most likely position matches quite well with the known CUTLASS radar position near Hankasalmi.

TDoA maps

TDoA cross correlations

There are pulse trains spaced by integer multiples of 2400 μsec (0,9,12,20,22,26,27), as descibed here:

SuperDARN pulse train

30 of these pulse trains are repeated, approximately each 95.3 msec, then there is a gap of two frames and some delay, and then the next 30 pulse trains follow:

SuperDARN pulse frames

The transmissions seem to repeat each minute with a small gap at the end of the minute.

Another way to verify the used pulse sequence is to compute the autocorrelation of each line of the plot above. All differences between all combinations of the individual pulses show up as peaks in the autocorrelation:

frame number vs. autocorrelation lag

KiwiSDR TDoA (LORAN)

Below is an example of using the new KiwiSDR TDoA extension on LORAN signals, see

• TDoA extension notes
• GitHub repository
• RTL-SDR.com article2 article1

The bias on the most likely position is quite small. Note that despite the fact than one sample at 12kHz is 83.3μs long, the RMS values of the cross correlations are ≤ 6μs. This is because the peaks in the cross correlations are fitted with a 2nd order polynomial.

Fig 1

Fig 2

Fig 3

Fig 4

Fig 5

Fig 6

Fig 7

Propagation delay maps based on IRI2016 electron density profiles

In order to understand better the propagation delay maps used for this blog post, the animation below was created. References for the used method are arXiv:1104.2248 and this well-known book.

Up to 2-hop propagation is considered. In case there is more than one mode of propagation, the smallest non-ground-wave propagation delay is shown in the maps. If there is no ionospheric reflection, the ground-wave delay is shown.

• hop=0: no ionospheric reflection -> ground-wave propagation
• hop=1: one reflection
• hop=2: two reflections 

Propagation delays based on IRI2016 electron density profiles

Propagation delays based on IRI2016 electron density profiles

KiwiSDR TDoA extension

KiwiSDR v1.196 includes a KiwiSDR extension (based on https://github.com/hcab14/TDoA)

Note that ionospheric delays are not taken into account, so depending on the geometry of receivers and the target the TDoA maps will be biased.

Many thanks to John Seamons, ZL/KF6VO.

In parallel I am working on a real-time version of TDoA using python/matplotlib/cartopy.