EE198B Senior Project May 12th, 2004 Transceiver for Wireless Speaker System By Ahmed, Naseem Noor, Masood Pang, Gary Yu, Aaron Advisor: Dr. Ray Kwok PDF created with FinePrint pdfFactory trial version http://www.pdffactory.com1 Table of Content Title Page No. Abstract 2 Introduction 3 Theory of Modulation 4 Advantages and Disadvantages of Frequency Modulation 6 The Parts of the Project 7 Transmitter 8 Receiver 12 Testing Equipment 16 Test One 17 Result Analysis of Test One 18 Budget 19 Specification 21 Conclusion 22 Reference 23 PDF created with FinePrint pdfFactory trial version http://www.pdffactory.com2 Abstract The demands of the transceiver are increasing in home entertainment uses. There are many different signals are transmitting at the same time. For the receiver to pick up the right signal, the original message signal must be modulated with a carrier signal before sending out. There are several different kinds of modulation technique available. Because of power efficient, frequency modulation is used in this project. In this project, the transceiver’s abilities of transmitting and receiving are tested. If the transceiver is able to pass this test, it is considered to be a success product. PDF created with FinePrint pdfFactory trial version http://www.pdffactory.com3 Introduction Using wireless communication technology for home entertainment becomes popular. Wireless speaker system is not a new invention for this century; however, the goal of this project is to improve the size, quality and range of the communication system. In order to build a good communication system, a good transceiver is necessary. Generally speaking, each transceiver is designed for its own purpose and for some specific applications. A transceiver works perfectly for one application may not suit for another situation. The transceiver of this project is designed a wireless speaker system. Theory of Modulation There could be many signals transmitting at the same time, for example, there are many different signals transmitted by radio stations and TV stations at the same time. Figure 1 shows that there are several signals exist at the same time, and those signals are displayed by a spectrum analyzer. Figure 1: Several signals with different frequencies are displayed by the spectrum analyzer. For the receiver able to receive the desired signal, the desired signal is need to be modulated before it is transmitted. Explain it in simple way, modulation is like multiplying the message signal, m(t), and the carrier signal, c(t), and become a modulated signal, u(t). Depending on the carrier frequency, the modulated signal will be picked up by the receiver tuned at a specified channel or frequency. There are several different modulation technologies, for instances, amplitude modulation (AM), frequency modulation (FM), pulse amplitude modulation (PAM), and frequency shift keying (FSK). The AM and FM are used for analog communication. On the other hands, PAM and FSK are used for digital communication. The concepts of the amplitude modulation and pulse amplitude modulation are similar. The amplitude of the modulated PDF created with FinePrint pdfFactory trial version http://www.pdffactory.com4 signal varies, and different amplitudes represent different data. Vice versa, the frequency modulation and the frequency shift keying are similar. Instead of the amplitude, the frequency of the carrier signal is varies, and different frequencies correspond to different data. Certainly, there are many other different modulations like phase modulation for analog and phase shift keying for digital. Sending and receiving an audio signal is one of the analog communications. So, in this project, either amplitude modulation (AM) or frequency modulation (FM) can be used. One of the primary advantages of FM is that the modulation is contained in carrier frequency variations and not in amplitude changes like AM, which would be susceptible to noise and interference. This means that it can remove any noise and not affecting the desired information. Using FM to send and receive the audio signal in this project is more appropriate. In angle modulation, the spectral components of the modulated waveform are not related in any simple fashion to the message spectrum. Furthermore, superstition does not apply, and the bandwidth of the angle-modulated signal is usually much greater than twice the message bandwidth. The increase in bandwidth and system complexity is compensated for by the improved performance in the face of noise and interference. Figure 2: The typical waveform of the AM and FM signals. The idea of frequency modulation, where the carrier frequency would be varied in proportion to message m(t). The carrier frequency ω(t) = ωc + km(t), where k is an arbitrary constant. If the peak amplitude of m(t) is mp, then the maximum and minimum PDF created with FinePrint pdfFactory trial version http://www.pdffactory.com5 values of the carrier frequency would be ωc + kmp and ωc - kmp. Hence, the spectral components would remain within this band with a bandwidth 2kmp centered at ωc. The bandwidth is controlled by the arbitrary constant k. In the project, 89.90MHz had been chosen as the carrier frequency in FM radio band because using any normal FM radio can receive the signal inside the range. Both of the transmitter circuit and the receiver circuit can be tuned from 87.75MHz to 108MHz. PDF created with FinePrint pdfFactory trial version http://www.pdffactory.com6 Advantages and Disadvantages of Frequency Modulation Advantages: ♦ Frequency varies and amplitude stays same ♦ Another method of modulating the carrier is to vary its frequency ♦ during the positive portion of the audio signal the frequency of the carrier gradually increases; during the negative period the carrier frequency is decreased ♦ The maximum modulating frequency permitted by FM broadcast stations is 15 kHz ♦ slight changes in amplitude don't matter since the audio signal is conveyed through changes in frequency Disadvantages: ♦ Does not have linear-modulation method ♦ Amplitude does not vary and frequency stays same ♦ Can not superimpose the sound on the carrier by varying the amplitude of the carrier ♦ Cannot transmit the video, or picture, signals by FMPDF created with FinePrint pdfFactory trial version http://www.pdffactory.com7 The Major Parts of the