Wednesday, December 4, 2019

Fsk Modulation and Demodulation free essay sample

FSK MODULATION AND DEMODULATION PROGRAM USING MATLAB LIST OF TABLES: CHAPTER 1: INTRODUCTION. 1. 1-INTRODUCTION TO WIRELESS MODEM. 1. 2-INTRODUCTION TO FREQUENCY SHIFT KEYING 1. 2. 1-FSK MODULATOR 1. 2. 2-FSK DEMODULATION CHAPTER 2: COMPONENT DESCRIPTION. 2. 1-LIST OF COMPONENTS 2. 2-DESCRIPTION OF FUNCTIONAL DIAGRAM 2. 2. 1 IC 555. 2. 2. 2 565 PLL. CHAPTER 3: CIRCUIT DIAGRAM AND WORKING. 3. 1-CIRCUIT DIAGRAM OF FSK MODULATOR USING IC555. 3. 2-CIRCUIT DIAGRAM OF FSK DEMODULATOR USING PLL 555 CHAPTER 4: OPERATION OF FSK. 4. 1-OPERATION OF FSK MODULATOR USING IC555. 4. 2-OPERATION OF FSK DEMODUALTOR USING PLL 565. CHAPTER 5: PROGRAMING USING MATLAB. 5. 1-FSK MODULATION USING MATLAB. 5. 2-FSK DEMODULATOR USING MATLAB. CHAPTER 6: OUTPUT WAVEFORMS. 6. 1-OUTPUT OF FSK MODULATOR. 6. 2-OUTPUT OF FSK DEMODULATOR . CHAPTER 7: CONCLUSION. 7. 1-CONCLUSION. 7. 2-REFERENCES. List of Figures Fig a: Pin diagram of IC 555 Fig b: Pin diagram of NE 565 Fig c: FSK Modulator using IC 555 Fig d: Fsk Demodulator using NE 565 Fig e: Fsk Output model Fig f: Output waveform of FSK Modulator. Fig g: Output waveform of FSK Demodulator. CHAPTER -1 INTRODUCTION 1. 1: INTRODUCTION TO WIRELESS MODEM: A wireless modem is a type of modem which connects to a wireless network instead of a telephone system. When a mobile Internet user connects using a wireless modem, theyre attached directly to the wireless ISP (Internet Service Provider) and can then access the Internet. Mobile phones, smartphones, and PDAs can be employed as data modems to form a wireless access point connecting a personal computer to the Internet (or some proprietary network). In this use the mobile phone is providing a gateway between the cellular service providers data network technology and Point-to-Point Protocol (PPP) spoken by PCs. Almost all current mobile phone models support the Hayes command set, a standard method of controlling modems. To the PC, the phone appears like an external modem when connected via serial cable, USB, IrDA infrared or Bluetooth wireless. Some cellular providers forbid this kind of usage, or charge an extra fee Wireless FireWire, USB and Serial modems are also used in the Wi-Fi and WiMAX standards, operating at microwave frequencies, to give a laptop, PDA or desktop computer an access point to a network. The modems may be as large as a regular cable modem to as small as a WiFi dongle/USB-stick. If combined with VoIP technology, these computing devices can achieve telephone-like capability to make and receive telephone calls. PCMCIA, ExpressCard and Compact Flash modems are also used. These card-modems can also have GPS included. Most early telephone-line modems used audio frequency-shift keying to send and receive data, up to rates of about 1200 bits per second. The common Bell 103 and Bell 202 modems used this technique. [2] Even today, North American caller ID uses 1200 baud AFSK in the form of the Bell 202 standard. Some early microcomputers used a specific form of AFSK modulation, the Kansas City standard, to store data on audio cassettes. AFSK is still widely used in amateur radio, as it allows data transmission through unmodified voiceband equipment. Radio control gear uses FSK, but calls it FM nd PPM instead. The CHU shortwave radio station in Ottawa, Canada broadcasts an exclusive digital time signal encoded using AFSK modulation. 1. 2: INTRODUCTION TO FREQUENCY SHIFT KEYING: Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave. [1] The simplest FSK is binary FSK (BFSK). BFSK uses a pair of discr ete frequencies to transmit binary (0s and 1s) information. With this scheme, the 1 is called the mark frequency and the 0 is called the space frequency. The time domain of an FSK modulated carrier is illustrated in the figures to the right. | 1. 2. 1: FSK MODULATOR The FSK (Frequency Shift Keying) modulator circuit works by shifting the carrier, a sine wave of a given frequency, to another frequency back and forth as the input signal changes. On the receiving end, the demodulator works by detecting one or both of the frequencies, often with a band-pass filter, regenerating the input signal. You can also use a signal processor to convert the carrier from time domain to frequency domain with a fourier transform, and then pick off the signal that way. The FSK method of modulating/demodulation is typically limited to low frequency signal rates, such as 300 bits per second 1. 2. 2: FSK DEMODULATION: FSK demodulation is the process of recovering the original signal by detecting the frequencies involved in the original modulation. Typically, this is done with a bandpass amplifier tuned to one of the two frequencies, followed by a amplitude demodulator. The output is the original signal. It is possible, though often unecessary, to use two bandpass ampliers, one for each frequency, but this is redundant. It is also possible to use a digital signal processing technique to perform a fourier transform on the input signal, but that can be complex and costly. This is the method used in very early modems, up to around 1200 baud. It is also possible, using FSK, to send multiple signals across one line. Simply pick suitable frequencies for each modulation state, and mix the outputs into one consolidated analog signal. On the other end, you have multiple bandpass filters running at the same time and, as long as the chosen frequencies are appropriately spaced apart, they will not interfere. CHAPTER-2 COMPONENT DESCRIPTION 2. 1: LIST OF COMPONENTS: S. NO NAME OF THE COMPONENT SPECIFICATION QUANTITY 1. IC 555 1 2. SK100 1 3. Resistor 47k ,2,2K,10K,30K,1. 2K, 2,1,4,1,2. 4. Capacitor . 01  µF,1  µF,. 047  µF, 0. 022  µF, . 22 µF. 2,2,1,3,1. 5. PLL 565 1 6. OP-AMP BC 741 1 7. Power supply 2 2. 2: DESCRIPTION OF FUNCTIONAL DIAGRAM 2. 2. 1 IC 555. The 555 timer is a highly stable device for generating accurate time delay or oscillation. Signetics corporation first introduced this device as the SE555/NE555. A single 555 timer can provide time delay ranging from micro seconds to hours where as counter timer can have a maximum timing range of days. The 555 timer can be used with supply voltage in the range of +5v to +18v and can drive load up to 200mA. It is compatible with both TTL and CMOS logic circuits. Because of the wide range of supply voltage, the 555 timer is versatile and easy to use in various application In the functional diagram for IC 555 timer three 5 kilo ohms internal resistors act as a voltage divider providing bias voltage of (2/3) Vcc to the upper comparator (UC) and these two voltages fix the necessary comparator threshold voltage, they also aid in determining the timing nterval. It is possible to vary time electronically too, by applying a modulation voltage to the control voltage input terminal ( pin 5). In application where no such modulation is intended, it is recommended by manufactures that a capacitor (0. 001 uf) be connected between control voltage terminal ( pin 5) and ground to bypass noise or ripple from the supply. In the stand by (stable) state, the output Q of the control flip-flop (FF) is hig h. This makes the output low because of power amplifier which is basically an inverter. A negative going trigger pulse is applied to pin 2 and should have its DC level greater than the threshold level of the lower comparator (ie. Vcc/3). At the negative going edge of the trigger, as the trigger passes through (Vcc/3), the output of the lower comparator goes high and sets the FF ( Q=1,Q=0). During the positive excursion, when the threshold voltage at pin 6 passes through (2/3)Vcc the output of the upper comparator goes high and resets the FF(Q=0,Q=1). The reset input(pin 4) provides a mechanism to reset the FF in a manner which overrides the effect of any instruction going to FF from lower comparator. This overriding reset is effective when the reset input is less than about 0. 4 V. when this reset is not used , it is returned to Vcc. The transistor Q2 serves as a buffer to isolate the reset input from the FF and transistor Q1. The transistor Q2 is driven by an internal reference voltage Vref obtained from supply voltage Vcc. . 2. 2. 2: 565 PLL: The phase locked loop(PLL) is an important building block of linear systems. The high cost of realizing PLL in discrete form limitied its use earlier. Now with the advanced IC technology, PLLs are available as inexpensive monolithic ICs. This technique for electronic frequency control is used today in satellite communication systems, air borne navigations systems, FM communication systems, computers etc. Characteristics of SE/NE 565 PLL * Operating frequency range: 0. 001Hz to 500 kHz. * Operating voltage range:  ± 6 to  ±12 V. * Input impendance: 10kQ typically. * Output sink current:1mA typically. * Output source current: 10mA typically. * Drift in VCO centre frequency with temperature: 300ppm/ °C typically. * Bandwidth adjustment range:  ±1 to  ± 60% CHAPTER-3 CIRCUIT DIAGRAM 3. 1: CIRCUIT DIAGRAM OF FSK MODULATOR USING IC555. . 2: CIRCUIT DIAGRAM OF FSK DEMODULATOR USING PLL 555 CHAPTER-4 OPERATION 4. 1: OPERATION OF FSK MODULATOR USING IC555. Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave. [1] The simplest FSK is binary FSK (BFSK). BFSK uses a pair of discrete frequencies to transmit binary ( 0s and 1s) information. With this scheme, the 1 is called the mark frequency and the 0 is called the space frequency. The time domain of an FSK modulated carrier is illustrated in the figures above. . 2: OPERATION OF FSK DEMODUALTOR USING PLL 565. A very useful application of the 565 PLL is as a FSK demodulator. In the 565 PLL the frequency shift is usually accomplished by driving a VCO with the binary data signal so that the two resulting frequencies correspond to the logic 0 and logic 1 states of the binary data signal. The frequencies corresponding to logic 1 and logic 0 states are commonly called the mark and space frequencies. Several standards are used to set the mark and space frequencies. An FSK signal demodulator can be built as illustrated in figure. The demodulator receives a signal at one of the two distinct carrier frequencies, 1,270 Hz or 1,070 Hz representing the RS-232 C logic levels of mark (- 5 V) or space (+ 14 V), respectively. Capacitance coupling is used at the input to remove a dc level. As the signal appears at the input of 565 PLL, the PLL locks to the input frequency and tracks it between the two possible frequencies with a corresponding dc shift at the output. Resistor R1 and capacitor C1 determine the free-running frequency of the VCO. Capacitor C2 is a loop filter capacitor that establishes the dynamic characteristics of the demodulator. Capacitor C2 is chosen smaller than usual one to eliminate overshoot on the output pulse. A three-stage RC ladder filter is employed for removing the sum frequency component from the output. The VCO frequency is adjusted with R1 so that the dc voltage level at the output (pin 7) is the same as that at pin 6. An input at frequency 1,070 Hz drives the demodulator output voltage to a more positive voltage level, driving the digital output to the high level (space or + 14 V). An input at 1,270 Hz correspondingly drives the 565 dc output less positive with the digital output, which then drops to the low level (mark or – 5 V). CHAPTER-5 MATLAB CODING 5. 1: FSK MODULATION USING MATLAB: g=[1 0 1 0 1]; f0=1; f1=2; t=0:2*pi/99:2*pi; cp=[];sp=[]; mod=[];mod1=[];bit=[]; for n=1:length(g) if g(n)==0 die=ones(1,100); c=sin(f0*t); se=zeros(1,100); else g(n)==1 die=ones(1,100); c=sin(f1*t); se=ones(1,100); end cp=[cp die]; mod=[mod c]; bit=[bit se]; end fsk=cp. *mod; subplot(2,1,1); plot(bit,LineWidth,1. 5); grid on; title(Binary Signal); axis([0 100*length(g) -2. 5 2. 5]); subplot(2,1,2); plot(fsk,LineWidth,1. 5); grid on; title(FSK modulation); axis([0 100*length(g) -2. 5 2. 5]); 5. 2: FSK DEMODULATOR USING MATLAB: ormat long; clear all; close all; N = 8; bit_stream = round(rand(1,N)); f1 = 3; f2 = 5; fs = 100; t = 0: 1/fs : 1; time = []; FSK_signal = []; Digital_signal = []; for ii = 1: 1: length(bit_stream) FSK_signal = [FSK_signal (bit_stream(ii)==0)*sin(2*pi*f1*t)+ (bit_stream(ii)==1)*sin(2*pi*f2*t)]; Digital_signal = [Digital_signal (bit_stream(ii)==0)* zeros(1,length(t)) + (bit_stream(ii)==1)*ones(1,length(t ))]; time = [time t]; t = t + 1; end subplot(2,1,1); plot(time,FSK_signal); xlabel(Time (bit period)); ylabel(Amplitude); title(FSK Signal with two Frequencies); axis([0 time(end) -1. 1. 5]); grid on; subplot(2,1,2); plot(time,Digital_signal,r,LineWidth,2); xlabel(Time (bit period)); ylabel(Amplitude); title(Original Digital Signal); axis([0 time(end) -0. 5 1. 5]); grid on; CHAPTER-6 OUTPUT VERIFICATION 6. 1: OUTPUT OF FSK MODULATOR: 6. 2: OUTPUT OF FSK DEMODULATOR CHAPTER-7 CONCLUSION AND REFERENCE 7. 1 CONCLUSION: A modem and antenna that transmits and receives over the air. Wireless modems support several technologies, including 802. 11, Bluetooth, CDPD, DataTAC, Mobitex and Ricochet. There are wireless modems for laptops, handhelds and cellphones. Except for a few analog cellphone models, you cannot plug your cellphone into your laptops land-based modem even if the cable fits. You generally need a wireless modem on a PC card and a cable designed for your type of phone. Industrial wireless transmission has arrived providing clear and significant advantages. Nevertheless, security is always an important issue and a question often asked is, Will information be secure when broadcast via Data-Linc Group wireless modems? The answer can be found in understanding the technologies employed in these products and, to that end, this paper will provide the understanding needed.

No comments:

Post a Comment

Note: Only a member of this blog may post a comment.