Long distance signal communication fromshore to ship using DSBSC

Abstract— Long distance signal communication using DoubleSideband Suppressed Carrier [DSBSC] technique isone of the key areas in wireless communication. This papercontains the analysis, design, development of signalcommunication for the purpose of shore to ship two waysignal communication using the ground wave antennas. TheDSBSC travels long distance with low power as compare tocommercials AM and also range will can be more than lineof sight as in FM (more than 40km). This experiment willalso show the radiation of electromagnetic energy allowingantenna sizes to be reasonable and simultaneoustransmission of several signals over the same channel.

Introduction: The process of passing any information from one person to the other person with the aid of some mediumis termed as communication.

Electronic communication is classified as (1) one-way (simplex) or two-way (full duplex or half duplex) transmissions and (2) Analog or Digital signals. Analog signals are smoothly varying, continuous signals. Digital signals are discrete, two-state (on/off) codes. Electronicsignals are often changed from analog to digital and vice versa. This experiment we are using the digital

communication, because it flexible, compatible, reliable and accuracy than the Analog modulation. Modulation is a process that causes a shift of the range of frequencies ina signal. It is used to facilitate transmission over a given channel. Communication system in modulation contains2 types 1) base-band modulation. 2) Carrier modulation. Incarrier modulation again subdivided into 1) AM modulation.2) Angle modulation. There are 2 types in Angle modulation1) FM modulation 2) PM modulation. Here we have chosen theAM modulation technique, because communication between theshore to boat is very long. For the communication purpose here we are using electromagnetic energy waves. Advantagesof modulation are the ease of radiation of electromagneticenergy allowing antenna sizes to be reasonable and simultaneous transmission of several signals over the samechannel.Amplitude Modulation: It is the process where, the amplitude of the carrier is varied proportional to that ofthe message signal.

But in the case of AM modulation, transmission of carrier consumes lot of power. Since, only the side bands contain the information about the message, carrier is suppressed. This results in a DSB-SC wave. DOUBLE SIDE BAND - SUPPRESSED CARRIER (DSB-SC) MODULATION:General expression:c(t)=[k1m(t)+C]cos(ωct+Φc)Let k1 = 1, C = 0 and c = 0, the modulated carrier signal,

therefore: c(t)=m(t)cos ωc(t) Consider twoinformation signals like sinusoids, or cosinusoids, cosμt and cosωt. A double sideband suppressedcarrier signal, or DSBSC, is defined as their product, DSBSC = Ecos ωc (t) cosωm (t) ........ 1 ωc >> ωm ........ 2we get below eqn.cosωc (t) cosωm (t) = (E/2) cos(ωc - ωm)t + (E/2) cos(ωc + ωm)t ........ 3Equation 3 shows that the product is represented by two

new signals, one on the sumfrequency (ωc + ωm), and one on the difference frequency (ωc - ωm) - see Figure 1.Remembering the inequality of eqn. (2) the two new components are located close to the frequency ω rad/s, one just below, and the other justabove it. These are referredto as the lower and upper sidebands respectively. These two components were derived from a ‘carrier’ term on ωc rad/s, and a message on ωm rad/s. Because there is no termat carrier frequency in the product signal it is describedas a double sideband suppressed carrier (DSBSC) signal. Figure 1: spectral components The term ‘carrier’ comes from the context of ‘double sideband amplitude modulation'(commonly abbreviated to just AM).AM is introduced in a later experiment (although, historically, AM preceded DSBSC). The time domain appearance of a DSBSC (eqn. 1). Message notice the waveform of the DSBSC in Figure 2, especially near the times when the message amplitude is zero. The fine detail differs from period to period of the

message. This is because the ratio of the two frequencies ωc and ωm has been madeNon-integral. Although the message and the carrier are periodic waveforms (sinusoids), the DSBSC itself need not necessarily be periodic.Modulator: The DSBSC modulator is based on the LM1496 balanced modulator IC. The balance circuit consisted by the VR1 is used to control the LM1496 operating in balancestate. By adjusting the VR1 properly, this will ensure that the modulator operates in balance state. In short, the major difference between DSB-SC and AM modulated signals is. the DSB-SC modulated signal containing no carrier. To achieve the requirement of suppressing carrier, we should first connect the audio input to ground, and then observe the LM1496 output to ensure no carrier presented by carefully adjusting the VR1. If this is made and then reconnects the audio signal, the DSB-SC modulated signal containing the upper- and lower-sideband signals will be presented at LM1496 output. Carrier voltage level is a very important factor, which affects the carrier suppressing. If the carrier level is too low, it will be not enough to start the carrier amplifier completely; reversely, a too high level will occur carrierfeed through. In general, the optimum input range is about0.2 Vpp to 0.8 Vpp when the carrier frequency is 500 kHz. To identify AM, DSB-SC or SSB modulated signals; we assumea typical audio spectrum shown in Fig. 5-2a. Where f mh isthe highest frequency and f ml is the lowest frequency in audio signal. If using this audio signal to modulate the amplitude of sine carrier, we will obtain an AM spectrum

Low-pass filter: A low-pass filter is an electronic filter that passes low-frequency signals and attenuates (reduces the amplitude of) signals with frequencies higher than the cut-off frequency. The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut filter when used in audio applications. A low-pass filter is the opposite of a high-pass filterLow-pass filters exist in many different forms, includingelectronic circuits (such as a hiss filter used in audio),

anti-aliasing filters for conditioning signals prior toanalog-to-digital conversion, digital filters forsmoothing sets of data, acoustic barriers, blurring ofimages, and so on. The moving average operation used infields such as finance is a particular kind of low-passfilter, and can be analyzed with the same signalprocessing techniques as are used for other low-passfilters. Low-pass filters provide a smoother form of asignal, removing the short-term fluctuations, and leavingthe longer-term trend. Although it is possible to design a wide variety of filters with different levels of gain and different roll off patterns using operational amplifiers, the filter described on this page will give a good sure-fire solution. It offers unity gain and a Butterworth response (the flattest response in band, but not the fastest to achieve ultimate roll off out of band). Operational amplifier two pole low pass filter Simple sure fire design with Butterworth response and unity gain The calculations for the circuit values are very straightforward for the Butterworth response and unity gain scenario. Critical damping is required for the circuit and the ratio of the resistor and capacitor valuesdetermines this. When choosing the values, ensure that theresistor values fall in the region between 10 k ohms and 100 k ohms. This is advisable because the output impedanceof the circuit rises with increasing frequency and values outside this region may affect he performance.R1=R2C1=2*C2F=√2/(4*pai*R*C2)

RF power amplifier

A RF amplifier is a device for electrically amplifying the power of an electrical signal, typically, but not exclusively, radio frequency signals.

An RF power amplifier is a type of electronic amplifier used to convert a low-power radio-frequency signal into a larger signal of significant power, typically for driving the antenna of a transmitter. It is usually optimized to have high efficiency, high output Power (P1dB) compression, good return loss on the input and output, good gain, and optimum heat dissipation.

Rf is a single tuned amplifier. Its functions are: - 1.improves selectivity ( i.e. rejection of unwanted signal) , so that it prevents heterodyning which results in interference frequency.2. Improves image frequency rejection 3. Improves sensitivity ( gain of amplifier )4.Improves coupling of receiver with antenna .

5. Improves signal to noise ratio.6. Reradiation of local oscillator through receiver antenna is prevented

RF Amp Devices

The primary device responsible for the signal enhancement is known as a triode, or a diode with oneadded part--a control grid. The control grid affects on the electric charge flows through the diode, and by applying small voltage variations in the current passing through, the triode can make large changes inthe strength and behaviour of the current.

Of course, this is a very basic description of the process: modern RF amplifiers employ entire circuit boards to make sure the signal is given maximum strength with as little signal distortion as possible. Today, these amplifiers are used no only inradio towers, walkie-talkies, and specialized communication devices, but also in every cell phone and cell phone tower.

Tuned Radio Frequency (TRF) Receiver The most important part of the circuit is the input stage, where positive feedback is used to achieve good sensitivity and selectivity. The first stage is adjusted so that it is not quite at the point of oscillation. This increases the gain and the selectivity, giving a narrow bandwidth. To achieve this, the potentiometer connected to the drain of the FET must be adjusted very carefully: optimal performance of the receiver depends on its setting. In ideal conditions several strong stations should be obtainable during the day using a 50 cm antenna.At night, several times this number should be obtainable. The frequency range of the receiver runs from 6 MHz to 8

MHz. This range covers the 49 m and the 41 m shortwave bands in which many European stations broadcast. Not bad for such a simple circuit! The circuit employs six transistors. The first stage is a selective amplifier, followed by a transistor detector. Two low-frequency amplifier stages complete the circuit.

Circuit diagram:-

Tuned Radio Frequency (TRF) Receiver Circuit Diagram

The final stage is a push-pull arrangement for optimal drive of the low-impedance loudspeaker. This circuit arrangement is sometimes called a ‘1V2 receiver’ (one preamplifier, one detector and two audio-frequency stages). Setting-up is straightforward. Adjust P1 until the point is reached where the circuit starts to oscillate: a whistle will be heard from the loudspeaker. Now back off the potentiometer until the whistle stops. The receiver can now be tuned to a broadcaster. Occasionalfurther adjustment of the potentiometer may be required after the station is tuned in. The receiver operates from a supply voltage of between 5 V and 12 V and uses very little current. A 9 V PP3 (6F22) battery should give a very long life.

Mixer

Mixers are used for frequency conversion and are critical components in modern radio frequency (RF) systems. A mixerconverts RF power at one frequency into power at another frequency to make signal processing easier and also inexpensive. A fundamental reason for frequency conversionis to allow amplification of the received signal at a frequency other than the RF, or the audio, frequency. A receiver may require as much as 140 decibels (dB) of gain.It might not be possible to put more than 40 dB of gain into the RF section without risking instability and potential oscillations. Likewise the gain of the audio section might be limited to 60 dB because of parasitic feedback paths, and microphonics. The additional gain needed for a sensitive receiver is normally achieved in anintermediate frequency (IF) section of the receiver. Double-sideband, suppressed-carrier AM is a sum (uppersideband), a difference (lower sideband) and no carrier.We didn’t call its sum and difference outputs upper andlower sidebands earlier in equation 7’s neighborhood, but

we’d do so in a transmitting application. In atransmitter, we call a circuit that suppresses the carrierwhile generating upper and lower sidebands a balancedmodulator, and we quantify its carrier suppression, whichis always less than infinite. In a receiver, we call sucha circuit a balanced mixer, which may be single-balanced(if it lets either its RF signal or its LO [carrier]signal through to its output) or double-balanced (if itsuppresses both its input signal and LO/carrier in itsoutput), and we quantify its LO suppression and port-to-port isolation, which are always less than infinite.(Mixers [and amplifiers] thatafford no balance whatsoever are sometimes said to besingle-ended.) Sometimes,DSB suppressed-carrier AM is called just DSB. A sine wave at the frequency difference between SignalA and Signal B 2π(fa – fb)t,and a sine wave at the frequency sum of Signal A andSignal B 2π(fa + fb)t. (The products are cosine waves, butsince equivalent sine and cosine waves differ only by aphase shift of 90°, both are called sine waves byconvention.) This is the basic process by which wetranslate information into radio form and translate itback again. If we want to transmit a 1-kHz audio tone byradio, we can feed it into one of our mixer’s inputs andfeed an RF signal.

Modulated carrier is the output of the mixer.

Circuit diagram:- IC NJM2552

Demodulation :

Demodulation is the act of extracting the original information-bearing signal from a modulated carrier wave. A demodulator is an electronic circuit (or computer program in a software defined radio) that is used to recover the information content from the modulated carrier wave.[1]

These terms are traditionally used in connection with radio receivers, but many other systems use many kinds of demodulators. Another common one is in a modem, which is a contraction of the terms modulator/demodulator.

Power amplifier: A power amplifier or (informally) amp is an electronicdevice that increases the power of a signal. It does thisby taking energy from a power supply and controlling theoutput to match the input signal shape but with largeramplitude. In this sense, an amplifier modulates theoutput of the power supply. The term power amplifier is a relative term withrespect to the amount of power delivered to the loadand/or sourced by the supply circuit. In general a poweramplifier is designated as the last amplifier in atransmission chain (the output stage) and is the amplifierstage that typically requires most attention to powerefficiency. Efficiency considerations lead to variousclasses of power amplifier based on the biasing of theoutput transistors or tubes.

Power amplifier classes: Power amplifier circuits (output stages) areclassified as A, B, AB and C for analog designs, and classD and E for switching designs based on the proportion ofeach input cycle (conduction angle), during which anamplifying device is passing current. The image of theconduction angle is derived from amplifying a sinusoidalsignal. If the device is always on, the conducting angleis 360°. If it is on for only half of each cycle, theangle is 180°. The angle of flow is closely related to theamplifier power efficiency. The various classes areintroduced below, followed by a more detailed discussionunder their individual headings further down.In the illustrations below, a bipolar junction transistoris shown as the amplifying device, but the same attributesare found if with MOSFETs or vacuum tubes.Class ABClass AB is intermediate between class A and B, the twoactive elements conduct more than half of the time. ClassAB is widely considered a good compromise for audio poweramplifiers, since much of the time the music is quietenough that the signal stays in the "class A" region,where it is amplified with good fidelity, and by

definition if passing out of this region, is large enoughthat the distortion products typical of class B arerelatively small. The crossover distortion can be reducedfurther by using negative feedback.

Reference oscillator :Antenna: Ground Antenna:In radio communication, a ground dipole also referred toas an earth dipole antenna, transmission line antenna, andin technical literature as a horizontal electric dipole. Aground dipole consists of two ground electrodes buried inthe earth, separated by tens to hundreds of kilometres,linked by overhead transmission lines to a power planttransmitter located between them. Alternating currentelectricity flows in a giant loop between the electrodesthrough the ground, radiating ELF waves, so the ground ispart of the antenna. To be most effective, ground dipolesmust be located over certain types of underground rockformations.A ground dipole functions as an enormous vertically-oriented loop antenna (see drawing, right). It consists oftwo widely separated electrodes (G) buried in the ground,connected by overhead transmission cables to a transmitter(P) located between them. The alternating current from thetransmitter (I) travels in a loop through one transmissionline, kilometres deep into bedrock from one groundelectrode to the other, and back through the othertransmission line. This creates an alternating magneticfield (H) through the loop, which radiates ELF waves. The

axis of the magnetic field produced is horizontal, so itgenerates vertically polarized waves. The radiationpattern of the antenna is directional, with two lobes(maxima) in the plane of the loop, off the ends of thetransmission lines. In the U.S. installations two grounddipoles are used, oriented perpendicular to each other, toallow transmission in all directions.The amount of power radiated by a loop antenna isproportional to (IA)2, where I is the AC current in theloop and A is the area enclosed, To radiate practicalpower at ELF frequencies, the loop has to carry a currentof hundreds of amperes and enclose an area of at leastseveral square miles. Christofilos found that the lowerthe electrical conductivity of the underlying rock, thedeeper the current will go, and the larger the effectiveloop area. Radio frequency current will penetrate into theground to a depth equal to the skin depth of the ground atthat frequency, which is inversely proportional to thesquare root of ground conductivity σ. The ground dipoleforms a loop with effective area of A = Lδ / √2, where Lis the total length of the transmission lines and δ is theskin depth. So ground dipoles are sited over lowconductivity underground rock formations (this contrastswith ordinary radio antennas, which require good earthconductivity for a low resistance ground connection fortheir transmitters). The two U.S. Navy antennas werelocated in the Upper Peninsula of Michigan, on theCanadian Shield (Laurentian Shield) formation, which hasunusually low conductivity of 2×10−4 siemens/meterresulting in an increase in antenna efficiency of 20dB.The earth conductivity at the site of the Russiantransmitter is even lower.Theoretical calculation : Advantages:Lower power consumption

Disadvantage: - Complex detectionApplications: - Analogue TV systems: to transmit colour information - For transmitting stereo information in FM soundbroadcast at VHF