Difference between revisions of "SDRDF"
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| − | Finding the direction to the transmitter requires one to measure phase difference of pseudo-doppler signal against a known reference (e.g. 'North'). The pseudo-doppler signal is introduced (superimposed on the demodulated signal) by electronically rotating the antenna array against a reference signal of the same frequency as the switching rate. | + | Finding the direction to the transmitter requires one to measure phase difference of pseudo-doppler signal against a known reference (e.g. 'North'). The pseudo-doppler signal is introduced (superimposed on the demodulated signal) by electronically rotating the antenna array against a reference signal of the same frequency as ''half'' the switching rate. |
To calculate the phase difference in GNU Radio, please refer to part 5 of my [http://www.youtube.com/playlist?list=PL618122BD66C8B3C4&feature=view_all GNU Radio Tutorial series]: | To calculate the phase difference in GNU Radio, please refer to part 5 of my [http://www.youtube.com/playlist?list=PL618122BD66C8B3C4&feature=view_all GNU Radio Tutorial series]: | ||
Revision as of 16:12, 11 June 2012
Contents
[hide]Introduction
Radio Direction Finding (RDF) is the act of locating the position of a transmitter. This can be done in a number of ways, using different hardware configurations depending on the properties of the signal-of-interest and the chosen RDF technique.
This page is based around a presentation I gave on the subject. You are encouraged to watch the video to learn about RDF, and how it can be done (mostly) in the software domain (using Software Defined Radio, such as a USRP). I refer to this as Software Defined Radio Direction Finding (SDRDF).
Traditional Hardware-based RDF
Pseudo-doppler DF setups usually perform the antenna switching, filtering and 'direction finding' all in hardware. Only the AF (Audio Frequency) output of a separate radio is required as input.
Here is a great homebrew example:
- http://www.pi4wag.nl/index.php/pseudo-doppler-radio-direction-finder
- http://members.chello.nl/~w.hofman/pa8w/dopplerRDF.htm
There are many others. One common design is known as the Roanoke Doppler.
References
To learn more about the fundamentals of RDF, please consult the following sources. If you can think of any other helpful ones, please feel free to contact me.
- "Transmitter hunting: radio direction finding simplified" By Joseph D. Moell, Thomas N. Curlee
http://books.google.com.au/books?id=RfzF2-fHJ6MC&lpg=PA126&pg=PA120#v=onepage&q&f=false
Historical perspective:
Presentation
This is a presentation I gave on SDRDF for Ruxmon in early 2012 at Google's Sydney HQ:
Theory
Finding the direction to the transmitter requires one to measure phase difference of pseudo-doppler signal against a known reference (e.g. 'North'). The pseudo-doppler signal is introduced (superimposed on the demodulated signal) by electronically rotating the antenna array against a reference signal of the same frequency as half the switching rate.
To calculate the phase difference in GNU Radio, please refer to part 5 of my GNU Radio Tutorial series:
Implementation
Antenna clock must be in lock-step with reference signal on computer.
SDR allows for same clock to be used to drive array, as that which is being used as external time reference for software DSP.
USRP
Modify firmware to output switching signal directly from FPGA. Same clock is used to time samples to computer, so a software signal source can be used as reference (orientation requires phase calibration).
References
Google Books
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