Tagged: gnuradio

Using the RTL-SDR to help Program a TI Chronos RF Watch

Over on our Facebook page, member Александр has posted about a project he found by Georg Campana which involves using an RTL-SDR to capture signals from his TI Chronos watch which has a programmable 433 MHz RF transmitter built into it.

Georg used his TI Chronos watch to transmit a signal copied from remote controls which are used to open his house gate, garage door, light switches and set his house alarm. When he discovered that the watch signal was not transmitting properly, he used his RTL-SDR to compare the signal coming from the watch to the original signals from the remote controls to help him with debugging. In order to detect the bit stream from the RF signal, he used a GNURadio program for decoding wireless temperature sensors, which he modified slightly to work with his watch.

Tools used to program the TI Chronos watch
Tools used to program the TI Chronos watch

Locating an Interfering Signal with Radio Direction Finding and the RTL-SDR

The people at the MIT Haystack Observatory discovered recently that someone was transmitting an interfering signal on their licensed radar band. The interferer was effectively jamming the radar, preventing them from carrying out any experiments.

After checking for local causes of interference and finding nothing, they decided that the interferer must be coming from further away. To find the location of the jamming signal they did some radio direction finding. This involved driving around with Yagi and magnetic loop antennas and RTL-SDR and USRP N200 SDRs and then measuring the signal strength at various points.

For the software they used a custom GNURadio block which calculated the power spectra using the FFTW C library, and averaged the results to disk. They then post processed the data to calculated the RFI power, and correlated the data with GPS coordinates recorded on his phone.

After all the data was processed, they discovered that the interference originated from an FM radio tower which had a faulty FSK telemetry link. They notified the engineer responsible who then replaced the link and the interference disappeared.

RFI strength at various geographic locations
RFI strength at various geographic locations