Analysis, optimization and miniaturization of a basic 18-MHz AM transmitter

Amplitude Modulation is one of the oldest and most known modulation techniques. It is still widely used because of its simplicity. Practical RF Electronics: First Principles Applied course at Tampere University of Technology used a basic AM transmitter to make the students put into practice many concepts of RF electronics. This thesis project focuses on the optimization of the original design of the AM transmitter. The thesis provides the future students of the course with a functioning demonstration device similar to the original one. Because of the didactic purpose of the transmitter, the schematic should remain as simple as the original one. Simplicity has been the most important restriction of this optimization project, so that every block and component in the circuit has a clear purpose, helping students understanding. To highlight the weakest points of the transmitter design, an analytical work was made for a deeper characterization of the transmitter performance. Analytic methods, circuit simulations, and laboratory measurements were carried out for the optimization process. Improvements, modifications and replacements were implemented on the original schematic design. These changes involved the use of low-current transistor types, adjustment of several passive component values, and the design of a custom crystal oscillator to generate an 18.432-MHz carrier. As a result, the optimized transmitter provides 26% lower power consumption, 5 times higher power efficiency, and double transmission distance using the same dipole antenna. On the other hand, the first harmonic distortion degraded by some 9 dB from the original design. Once the schematic was optimized, the device was miniaturized by designing and fabricating the transmitter on a printed circuit board (PCB). The project included an additional task of 3D modelling and printing for the package of the final device. As a result, the final fabricated transmitter has a small, reliable, and user-friendly form factor to be used as a demonstration