June 14, 2009
June 14, 2009
June 17, 2009
Computers in Education
14.1162.1 - 14.1162.9
Teaching with Software Deﬁned Radios
This paper discusses the utilization of a relatively inexpensive wideband radio receiver in combination with a digital down converter (DDC) based data recorder to capture and record real world radio signals. The resulting in-phase (I) and quadrature (Q) data ﬁles are then imported into M ATLAB for processing. This batch processing of real world radio signals allows for a tremendous amount of classroom ﬂexibility in the discussion of software deﬁned radio topics.
There is a great deal of interest in the DSP algorithms necessary to demodulate communications signals. While a number of existing courses cover these topics, the use of real world communi- cations signals to develop and test these algorithms can be problematic. For many universities, the largest challenge in working with real world signals is the cost of the equipment necessary to detect, track, and capture the signals of interest. Two instrument grade, but costly, solutions to this signal capture problem can be found in references1 and.2
An alternative to the instrument grade test and measurement equipment solution is the use of a commercial-off-the-shelf system that was originally designed to support the amateur radio com- munity. A photograph of the high speed streaming digitizer, SDR-14,3 is shown in Figure 1. In this capacity the system provides ﬁltering, ampliﬁcation, and samples for signals from 0.1 MHz to 30 MHz. The resulting information is then streamed as decimated in-phase (I) and quadrature (Q) data to a host computer using a USB connection. Figure 2 shows a typical display for a system setup to capture a weak commercial AM radio station’s signal.
Unlike a number of available signal capture devices, this system is reasonably priced (approxi- mately 1,000 USD) and is only limited in its recording capability by the available storage of the host computer’s hard drive. For example, a one minute recording of an AM radio station created a 10 MB ﬁle.
2 Commercial AM
Using only a simple loop antenna connected directly to the SDR-14, the signal is captured and the resulting ﬁle is imported into M ATLAB for processing and algorithm development. For AM
Welch, T., & Wright, C., & Morrow, M., & Kent, T. (2009, June), Teaching With Software Defined Radios Paper presented at 2009 Annual Conference & Exposition, Austin, Texas. https://peer.asee.org/4938
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