DDS Final Project - Digitally Synthesized AM/FM/PM...

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1 Digitally Synthesized AM/FM/PM Multi-Purpose (DigiSAM) Radio Transmitter by Albert Ho Technical Report April 28, 2006 ECE 488: Radio Frequency Electronics Cornell University Ithaca, NY 14850 Project Team Anthony Tay, Sid Ghosh, Erik Wright Instructor Professor Wes Swartz
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2 Abstract The Digitally Synthesized AM/FM/PM Multi-Purpose Radio Transmitter (DigiSAM) is a radio transmitter designed to take both analog and digital signals as input and transmit them at carrier frequencies in the AM range. The DigiSAM product is fully customizable, with the ability to choose among 20 different carrier frequencies in the AM range, 3 different radio transmission modes (amplitude, frequency or phase modulation), and 6 different sources of audio. Transmitted waves from the DigiSAM can be picked up by a nearby radio receiver. The DigiSAM takes advantage Direct Digital Synthesis (DDS), a powerful technique for generating a modulated signal used in a wide variety of radio applications. Digital circuitry is used to effectively mix two signals (carrier and modulating) for AM transmission, add to or subtract from carrier frequency in proportion to the modulating wave for FM transmission, and add to or subtract from phase in proportion to the modulating wave for PM transmission. Additional circuitry is added to allow a user to choose the mode of transmission using 2 switches, to choose the carrier frequency using 5 switches, and to choose the audio source using 3 switches. Finally, a digital-to-analog converter and low-pass filter allow an RF signal to be formed at the output with digital step noise filtered out, to be transmitted over the air to a nearby receiver. A key assumption that influenced the design of the DigiSAM radio transmitter included the idea that an Altera FPGA board could be utilized to build the digital circuitry needed to accomplish all major functions. In our initial designs, we noted that the majority of the DigiSAM circuitry was digitally programmable. We took advantage of this fact to reduce the time needed to wire an entire digital system together at the IC level, as well as to reduce the amount of noise associated with possible inductive loops and long wiring. The result was a high quality, fully customizable DigiSAM unit.
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3 Table of Contents Title Page …………………………………………………… i Abstract …………………………………………………… ii Table of Contents …………………………………………………… iii Introduction …………………………………………………… 1 Detailed Specifications …………………………………………… 4 Operator Instructions …………………………………………………… 5 Theory of Operation …………………………………………………… 8 Test Results …………………………………………………… 19 Potential Uses …………………………………………………… 22 Division of Labor
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