| This thesis studies wireless video transmitting system to complete the PAL video signals radiation by phase-locked loop frequency synthesizer. It is purpose of bringing the wireless video radiation system on a small grenade to achieve the high-altitude military reconnaissance. Therefore, the requirements of the system are small size, light weight, portable, low power consumption and long transmission distance. At present, the main shortage of a number of wireless video products is that they can not have the small size and the long transmission distance at the same time. The main purpose of the thesis is to solve this problem.Through access to relevant information, as well as the comparison of several wireless transmitting systems, this study identified the wireless video transmitting system as the final program. The entire system is consists of two parts: phase-locked loop (PLL) frequency synthesizer and the signal radiation; signal radiation in part by the power amplifier and antenna radiation pose.PLL frequency synthesizer has three major components: Phase-Discriminator (PD), Loop-Filter (LF), Voltage Controlled Oscillator (VCO). Through the structure of such a frequency synthesizer for radiation to provides a stable source as a carrier. Phase-locked loop uses a negative feedback loop for the entire network to provide a stable platform for the output. It was tested VCO (Voltage-Controlled Oscillator) and phase reference frequency at the same frequency, and thus to determine whether the phase-locked loop in order to lock the VCO output frequency. Reference frequency and voltage-controlled oscillator (VCO) output frequency to be sent at the same time to phase-discriminator (PD) in comparison. The results enter into the loop filter to control the VCO. The most important parameter is the loop filter. In this thesis, relying on the software simulation and theoretical calculation, the loop filter parameters and the detailed design are ultimately determined. PLL frequency synthesizer to achieve the following specific chips; VCO: MAXIM, MAX2754; PD: MOTOROLA, MC145152-2; LP: PHILIPS, LM358; Divider: MOTOROLA, MC12022.The PLL frequency synthesizer is the role to provide a stable carrier on which PAL video signal load. In this thesis, the selection of VCO, MAX2754 can directly modulate PAL video signal. In this process the video signal due to the particular frequency domain characteristics needs to adopt a high-pass filter. So it can be to high quality signal to noise ratio for the signal transmission. This part of the design is pre-emphasis in the thesis.Another important part of the whole system is the radiation part, which includes power amplifier and antenna radiation. In this thesis, Agilent's power amplifier, MGA83563 is selected. Its maximum output power is +22 dBm, with a receiver of +75 dBm sensitivity, the transmission theoretical distance is 1.32km. However, due to the limitations of VCO output power, the amplifiers can not be in its maximum power output, the quiescent operating point of power amplifier is in the middle zone of its linear amplification, the output power of +16 dBm. The radiation antenna is also important in the whole system. A small portable omnidirectional dipole antenna can have been selected. The radiation part is different from the PLL frequency synthesizer design, which focuses on how to design the rational the schematic diagram and parameters settings, but the former, the main parameters of the power radiation in the circuit and chips are fixed by the company's engineer datasheet. In this part, the main task is to achieve impedance matching.To improve the first sample of non-ideal experimental data, this thesis carried out to remove electromagnetic interference and strengthen electromagnetic compatibility solution. Since the operating frequency of the transmitting system is 1.2GHz, the UHF-band high-frequency signals. Therefore its electromagnetic compatibility is particularly important. The high-frequency signal transmission line needs impedance matching as a result of high-frequency reflection problem, as well as the power amplifier and the antenna part. It provides a better electromagnetic environment for this whole system and enhances the system anti-interference. In addition, the thesis also improves the printed circuit board layout, the ground connection and the decoupling bypass capacitor settings designed for electromagnetic compatibility. The part of the analog video, the digital circuit, the power, the crystal oscillator and the part of radiation have been on isolate. In the application of hybrid ground connection, it further improves the overall electromagnetic compatibility. At the same time, the electromagnetic shielding has been done for the samples to improve electromagnetic compatibility. In order to better prevent the edge of the printed circuit board high frequency signal leakage, the thesis design the through-hole fence for printed circuit board in order to solve the two-tier printed circuit board reference ground point of the unstable defects, this thesis designed a full-closed electromagnetic shielding box effectively reducing electromagnetic interference.This thesis successfully developed the small size, low power consumption, long-distance transmission wireless video transmitting system, transmitting distance of 1180 m, applying of the 3.7V lithium battery (750mAh) to the normal work of five hours. The innovation of this thesis is to address the contradictions of small size and long-distance transmission, in order to further improve the small size, long-distance transmission of wireless video delivery system. Moreover, in the electromagnetic compatibility problems, the overall analysis and consider of the system is necessary. Ultimately the thesis improves the electromagnetic compatibility problem and achieves a good sample of the better parameters. |
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