Kickin' It Old Skool: SDR for Ye Olde Signals

DEF CON 24

Presented by:
Date: Friday August 05, 2016
Time: 16:00 - 17:50
Location: Wireless Village

Software Defined Radio is a wonderful tool for experimenting and decoding modern-day digital signals, but what about the pre-digital days? Transmitting audio using analog modulation techniques is still common (e.g. broadcast FM, AM, HAM bands, trunked radio networks), but what about more complex signals? Terrestrial digital television (ATSC & DVB-T) has replaced the old NTSC/PAL/SECAM channels we were used to, but NTSC has made an interesting comeback in First Person Video links for drones (digital solutions are becoming more popular, but latency has to be kept very low). GNU Radio can be used to develop a prototype NTSC demodulator for viewing these FPV links. It’s back to the old world of interlacing and the ‘back porch’! I’ll describe how a NTSC signal is constructed, and interactively demonstrate how to build a simple flowgraph to display video frames. If you have an FPV system, please bring it along so we can capture another source! Another analog signal still very much in use, which does not transmit your traditional idea of information, is RADAR. One type is Frequency Modulated Continuous Wave (FMCW). It is an intuitively simple waveform, and has some great properties for seeing ‘what’s out there’ (for example, it is all over the HF band). GNU Radio can be used to synthesise and process FMCW signals. I’ll show why FMCW works, demonstrate signal processing with offline tools, and construct some simple flowgraphs to do it real-time with GNU Radio. If there’s time, I’ll preview some other SDR experiments, such a decoder for the downlink path of the INMARSAT Aero aviation satellite service, and a spot jammer.


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