June 22, 2008
June 22, 2008
June 25, 2008
Electrical and Computer
13.367.1 - 13.367.17
Design of a Hardware Platform for Analog Communications Laboratory
In the typical electrical engineering curriculum, analog communications is usually a junior or senior year elective. Such a course typically focuses on analog radio, covering the topics of amplitude modulation (AM) and frequency modulation (FM). Also included is the study of noise effects in communication systems and other related concepts in signals and systems. Increasingly, the laboratory portion of an analog communications course has migrated to simulation-based experiments using MATLAB1 or to quasi- simulation methods based on the capabilities of LabVIEW2. The motivation for this move has been to sidestep the difficulties associated with having the students construct analog communications circuitry where often the communications experimentation is undesirably dominated by analog hardware build and debug. While simulation is a useful supplement, the move away from hardware does not fully satisfy the desire of students to experiment with “real” signals and systems.
Fortunately, with the increase of integration of communications circuitry towards stand alone ICs the difficulty associated with constructing analog communications circuits has been greatly reduced. It is thus possible to quickly assemble and begin experimenting with analog communications. Our approach has been to combine several of these circuits onto an all-in-one communications board that can be simply configured for a variety of experiments. The communication circuits, along with filtering and amplification stages, are connected in various configurations to allow for the emulation of a full communications system, including modulation, transmission, reception under the conditions of noise, tuning and demodulation. Furthermore, these circuits allow for experimentation at relatively low frequencies, thus avoiding higher frequency measurement issues while requiring only standard medium-range laboratory test equipment.
Our communications board allows for the emulation of modulation and demodulation for both AM and FM. AM is generated using the MC1496 balanced modulator3, with demodulation achieved via envelope detection. FM modulation is achieved through the use of the VCO ICL838 IC4. Alternatively, FM generation is also achieved through the use of a modified Colpitts Oscillator5 circuit. FM Demodulation is performed through a bandpass discriminator combined with an envelope detector. Filtering and buffering stages are included, along with an audio output circuit and signal multiplexor. Other circuitry includes a tunable broadcast quadrature detector FM receiver based on the TDA7000 IC6. Furthermore, other similar complexity circuits, which could optionally be used for this type of platform, are described including AM DSB-SC modulation using the SA6027 and PLL-based FM demodulation using the LM565C8. The communications
Dunne, B., & Cooke, M. (2008, June), Design Of A Hardware Platform For Analog Communications Laboratory Paper presented at 2008 Annual Conference & Exposition, Pittsburgh, Pennsylvania. 10.18260/1-2--4333
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