AUTHORSHIP “I hereby declare that the work contained in this thesis is of my own and has not been previously submitted for a degree or diploma at this or any other higher education institution. To the best of my knowledge and belief, the thesis contains no materials previously published or written by another person except where due reference or acknowledgement is made.” Signature:……………………………………………… 1 SUPERVISOR’S APPROVAL “I hereby approve that the thesis in its current form is ready for committee examination as a requirement for the Bachelor of Computer Science degree at the University of Engineering and Technology.” Signature…………………………………………………………… 2 ACKNOWLEGEMENT Foremost, I would like to express my deep and sincere gratitude to my supervisor professor. Bach Gia Duong for his continuous support of dissertation, for his motivation, enthusiasm and immense knowledge. His guidance has been of great value for me in all the time of researching and writing of my thesis. My heartily thanks are due to Master. Hoang Duc Long at the Research Center of Electronics and Telecommunications for his invaluable help during the time I worked in the laboratory. I would like to give my heartfelt thanks to all professors in University of Engineering and Technology for their basic knowledge and dedicated guidance. Last but not the least, I owe my loving thanks to my family and my dear friends who always encourage and being along with me. Sincerely, Van-The Nguyen 3 ABSTRACT Currently high frequency technique is widely used in the field of communication. The wireless communications services are increasing powerful. The deployment of these types of communications in very high frequency band has become inevitable and essential. Especially boom in broadband communications to promote the exploitation of parallel frequency channels in high frequency range that allow maximum usability bandwidth. Communications in high frequency bands have advantages in complex environments, especially where high-frequency waves transmitted directly between two parallel points of contact and communication through the ionosphere, in outer space In Vietnam, information transceiver system working VHF bands have a lot of important applications. Therefore, the study of information transceiver systems in the band VHF to understand the structure, the transmission characteristics in order to master the technology to go to complete the set and apply the product on the fact that the purpose end of the study. In the framework of this thesis, I have completed the following tasks: -Study about the structure of transmitter system. -Study carefully VCO block in the transmitter system. -Study about delta modulation. -Design and fabricate successfully VCO circuit in VHF band and delta modulate circuit. 4 TABLE OF CONTENTS 5 List of Figures 6 List of Table 7 ABBREVATIONS BJT Bipolar Junction Transistor CB Common Base CC Common Collector CE Common Emitter EB Emitter-Base FM Frequency Modulation IF Intermediate Frequency KVL Kirchoff Voltage Law LNA Low Noise Amplifier UHF Ultra High Frequency VHF Very High Frquency Chapter 1 INTRODUCTION 1.1,Overview of VHF frequency band Very high frequency(VHF) is the ITU-designated range of radio frequency electromagnetic waves from 30 MHz to 300 MHz,with corresponding wavelengths of one 8 to ten meters.Common uses for VHF are FM radio broadcasting ,television broadcasting,land mobile stations,long range data communication up to several tens of kilometres with radio modems,amateur radio, and marine communications.Air traffic control communication and air navigation systems work at distances of 100 kilometres or more to aircraft at cruising altitude. 1.2 Propagation characteristics VHF propagation characteristics are ideal for short distance terrestrical communication,with a range generally somewhat farther than line of sight from the transmitter.Unlike high frequency(HF),the ionosphere does no usually reflect VHF waves so transmissions are restricted to the local radio horizon less than 100 miles.VHF is also less affected by atmospheric noise and interference from electrical equiqment than lower frequencies.While it is blocked by land features such as hills and mountains,it is less affected by buildings and can be received indoors,although multipath television reception due to reflection from buildings can be a problem in urban areas. 1.3 Thesis objectives and structure. In this thesis,I will clarify the roles and the need of a information digital transmitter in VHF band. Study the function of each block in a transmitter system and especially a VCO block will be studied.Study about delta modulation. Finally, the experience is design, fabricate a VCO and delta modulation using FX609J.This thesis is organized in five sections: -Chapter 1:Provide an overview of VHF frequency band,propagation characteristic and objectives and structure of this thesis. -Chapter 2: Study in detail about VHF transceiver system and VCO block. -Chapter 3:Modulation delta signal. -Chapter 4: Design, Fabrication a VCO circuit,delta modulation circuit and achievement results. -Chapter 5: Summarization what have been done in the thesis. 9 10 [...]... Figure 3.2) .The analog input signal of the CVSD encoder is band- limited by the input band, pass filter .The CVSD encoder compares the band- limited analog input signal with an analog feedback approximation signal generated at the reconstruction integrator output .The digital output signal of the encoder is the output of the first register in the counter .the digital output signal is transmitted at the clock(sample)... polarity as the input signal from the comparator at the time of the clock signal The digital output signal is also the digital output of the encoder and is referred to as the baseband signal Further processing for transmission such as conditioned diphase modulation may be applied to the baseband signal It is necessary that the inverse of any such processing be accomplished and the baseband signal restored... filter The decoder performs the inverse function of the encoder and regenerates speech by passing the analog output signal of the reconstruction integrator 21 through the low-pass filter Other characteristics optimize the CVSD modulation technique for voice signals These characteristics include the following + Changes in the slope of the analog input signal determine the step-size changes of the digital. .. Modulator The PAM operates with two input signals: the output signal from the syllabic filter and the digital signal from the 3-bit shift register The syllabic filter output signal determines the amplitude of the PAM output signal and the signal from the 3-bit shift register is the polarity control that determines the direction, plus or minus, of the PAM output signal The phrase “continuously variable” in. .. with time constants of 5 microseconds (ms) for both charging and discharging, the envelope characteristics of the signal at the decoder output are shown in Figure 3.3 For the case of switching the signal at 23 the decoder input from the 0 percent run -of- threes digital pattern to the 30 percent run-ofthree digital pattern, the characteristic of the decoder output signal follows the resistance/capacitance... provides band- limiting and is typically a second- or higher-order filter 3.3.2 Comparator The comparator compares the band- limited analog input signal from the filter with the output signal of the reconstruction integrator This comparison produces the digital error signal input to the 3-bit shift register The transfer characteristic of the comparator is such that the difference between the two input signals... fed to the filter by the overload algorithm,forcing a decrease in the amplitude of the slopevoltage out of the syllabic filter .the encoder and decoder have identical characteristics except for the comparator and filter functions The CVSD decoder consists of the input band pass filter, shift register, overload algorithm, syllabic filter, PAM and reconstruction integrator used in the encoder, and an... located very close to the receiver to reduce losses in the feed line Its main function is amplifying the weak signal at the receiver with suitable gain and adding very little noise The nature of downconversion is the same with upconversion, the difference is input signal and the position in system If the upconversion be used in transmitter, downconversion is inversely at the receiver The microwave signal... signal + The feedback loop is adaptive to the extent that the loop provides continuous or smoothly incremental changes in step size + Companding is performed at a syllabic rate to extend the dynamic range of the analog input signal + The reconstruction integrator is of the exponential (leaky) type to reduce the effects of digital errors 3.3.Detailed descriptions 3.3.1 Input Band Pass Filter The input... the decoder input is switched from the 0 percent run -of- three digital pattern to the 30 percent run -of- three digital pattern, the decoder output shall reach 90 percent of its final value within 9 to 14 ms When the decoder input is switched from the 30 percent run -of- three digital pattern to the 0 percent run -of- three digital pattern, the decoder output shall reach 10 percent of the 30 percent run -of- three . ionosphere, in outer space In Vietnam, information transceiver system working VHF bands have a lot of important applications. Therefore, the study of information transceiver systems in the band VHF to. structure. In this thesis,I will clarify the roles and the need of a information digital transmitter in VHF band. Study the function of each block in a transmitter system and especially a VCO block will. understand the structure, the transmission characteristics in order to master the technology to go to complete the set and apply the product on the fact that the purpose end of the study. In the framework