Talk on KiwiSDR TDoA is available on YouTube

This is just a short note that my recent talk on KiwiSDR TDoA at the Software Defined Radio Academy 2019, which took place during the German Ham Convention in Friedrichshafen, Germany, is now available on YouTube.

For other talks from this meeting see http://youtube.sdra.io/.

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

TDoA measurements using GPS time-stamped IQ samples from KiwiSDRs (3)

DCF77 20171127T1041

Shown are the cross-correlations w.r.t. time for DCF77. The red dots indicate the time lags obtains by a pol2 fit.

77.5 kHz DCF77

TDoA measurements using GPS time-stamped IQ samples from KiwiSDRs (1)

Some relevant links are:

• http://kiwisdr.com/
• https://github.com/jks-prv/Beagle_SDR_GPS/issues/130
• http://valentfx.com/vanilla/discussion/940/direction-finding-and-linking-existing-kiwisdrs

Big thanks to John Seamons for creating this excellent receiver and for support with the GPS time stamps, as well as to all KiwiSDR owners who have enabled GPS.

All plots below were generated by a combination of 

• kiwirecorder.py (https://github.com/jks-prv/kiwiclient/tree/jks-v0.1) forked from Dmitry’s https://github.com/dev-zzo/kiwiclient
• http://octave.org/ (+signal +mapping)
• http://www.gnuplot.info/

using the code here https://github.com/hcab14/TDoA which for now is the only documentation.

Note that this is preliminary work at a very early stage.

In particular many systematic errors are for now being neglected, such as

• different delays (antenna + frond-end) per KiwiSDR
• delays due to propagation
• not using consistently WGS84 coordinates
• having only approximate locations for the KiwiSDRs

More information will be added later on.

77.5 kHz 20171127T104156Z DCF77

http://www.mwlist.org/vlf.php?kHz=77.5

DCF77 TDoA

225 kHz 20171128T104940Z Polskie Radio 1

http://www.mwlist.org/mwlist_quick_and_easy.php?area=1&kHz=225

TDoA 225 kHz PR2

10611 kHz 20171128T171256Z OTHR

https://en.wikipedia.org/wiki/RAF_Akrotiri

TDoA 10611 kHz

65.8 kHz 20171127T160437Z FUE

http://www.mwlist.org/vlf.php?kHz=65.80

TDoA 68.5 kHz