International Telemetering Conference Proceedings / October 27-30, 1997 / Riviera Hotel and Convention Center, Las Vegas, Nevada / This paper describes a kind of Microwave Digital Frequency Synthesizer used for S-band telemetry receivers. As well known many modern electronic systems employ a Frequency Synthesizer whose spectral purity is critical. The characteristics of a PLL (Phase-Locked Loop) Frequency Synthesizer, such as frequency resolution, phase noise, spurious suppression and switch time, should be compromised in our design. A heterodyne Frequency Synthesis is often considered as a good approach to solve the problem. But it is complicated in structure and circuit. A variable-reference-driven PLL Frequency Synthesizer was introduced which can give an improved trade-off among frequency resolution, phase noise, spurious suppression. In this paper the phase noise and spurious suppression characteristic of variable-reference-driven PLL Frequency Synthesizer is analyzed theoretically and compared with that of the heterodyne Frequency Synthesizer. For engineering application, a practical Microwave Digital Frequency Synthesizer used for telemetry receiver has been designed, which is characterized by simply structure, low phase noise and low spurious output. The output spectrum of experimental measurements is given.

Made available in DSpace on 2014-12-17T14:56:17Z (GMT). No. of bitstreams: 1 AndreTS_DISSERT.pdf: 5024853 bytes, checksum: c24b983c0dd71456069c554e6c343968 (MD5) Previous issue date: 2014-01-24 / Quadrotors aircraft are composed by four propellers mounted on four engines on a cross or x disposition, and, in this structure, the engines on the same arm spin in the same direction and the other arm in the opposite direction. By rotating each helix generates vertical upward thrust. The control is done by varying the rotational speed of each motor. Among the advantages of this type of vehicle can cite the mechanical simplicity of construction, the high degree of maneuverability and the ability to have vertical takeoffs and landings. The modeling and control of quadrirrotores have been a challenge due to problems such as nonlinearity and coupling between variables. Several strategies have been developed to control this type of vehicle, from the classical control to modern. There are air surveillance applications where a camera is fixed on the vehicle to point forward, where it is desired that the quadrotor moves at a fixed altitude toward the target also pointing forward, which imposes an artificial constraint motion, because it is not desired that it moves laterally, but only forwards or backwards and around its axes . This restriction is similar to the naturally existing on robots powered by wheels with differential drive, which also can not move laterally, due to the friction of the wheels. Therefore, a position control strategy similar to that used in this type of robot could be adapted for aerial robots like quadrotor. This dissertation presents and discusses some strategies for the control of position and orientation of quadrotors found in the literature and proposes a strategy based on dynamic control of mobile robots with differential drive, called the variable reference control. The validity of the proposed strategy is demonstrated through computer simulations / Quadrirrotores s?o ve?culos a?reos compostos por quatro h?lices montadas sobre quatro motores em uma disposi??o em cruz ou x, sendo que, nessa estrutura, os motores sobre o mesmo bra?o giram no mesmo sentido e os do outro bra?o em sentido oposto. Ao girar, cada h?lice gera empuxo vertical para cima. O controle ? feito variando-se a velocidade de rota??o de cada motor. Dentre as vantagens desse tipo de ve?culo pode-se citar a simplicidade mec?nica de constru??o, o alto grau de manobrabilidade que possui e a capacidade de pousos e decolagens verticais. A modelagem e o controle de quadrirrotores tem sido um desafio devido a problemas como n?o-linearidades e acoplamento entre vari?veis. V?rias estrat?gias j? foram desenvolvidas para o controle desse tipo de ve?culo, desde as de controle cl?ssico at? as mais modernas. H? aplica??es de supervis?o a?rea em que uma c?mera ? fixada no ve?culo de forma a apontar para a frente, onde ? desejado que o quadrirrotor procure se movimentar a uma altitude fixa em dire??o ao alvo tamb?m apontando para a frente, o que imp?e uma restri??o artificial de movimento, pois n?o ? desejado que se movimente lateralmente, mas para frente ou para tr?s e que gire ao redor dos seus eixos. Tal restri??o ? semelhante ?quela existente de maneira natural em rob?s movidos a rodas com acionamento diferencial, que tamb?m n?o podem se movimentar lateralmente, mas devido ao atrito das rodas. Portanto, uma estrat?gia de controle de posi??o semelhante ? usada nesse tipo de rob?s poderia ser adaptada para rob?s a?reos do tipo quadrirrotor. Este trabalho apresenta e discute algumas estrat?gias de controle de posi??o e orienta??o de quadrirrotores encontradas na literatura e prop?e uma estrat?gia baseada no controle din?mico de rob?s m?veis com acionamento diferencial, o chamado controle por refer?ncia vari?vel. A validade da estrat?gia proposta ? comprovada atrav?s de simula??es computacionais