Long distance signal communication from shore to ship using DSBSC

Long distance signal communication from shore to ship using DSBSC

Abstract— Long distance signal communication using Double Sideband               Suppressed Carrier [DSBSC] technique is one of the key areas in wireless communication. This paper contains the analysis, design, development of signal communication for the purpose of shore to ship two way signal communication using the ground wave antennas. The DSBSC travels long distance with low power as compare to commercials AM and also range will can be more than line of sight as in FM (more than 40km). This experiment will also show the radiation of electromagnetic energy allowing antenna sizes to be reasonable and simultaneous transmission 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 medium is 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. Electronic signals 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 in a signal. It is used to facilitate transmission over a given channel. Communication system in modulation contains 2 types 1) base-band modulation. 2) Carrier modulation. In carrier modulation again subdivided into 1) AM modulation. 2) Angle modulation. There are 2 types in Angle modulation 1) FM modulation 2) PM modulation. Here we have chosen the AM modulation technique, because communication between the shore to boat is very long. For the communication purpose here we are using electromagnetic energy waves. Advantages of modulation are the ease of radiation of electromagnetic energy allowing antenna sizes to be reasonable and simultaneous transmission of several signals over the same channel.Amplitude Modulation: It is the process where, the amplitude of the carrier is varied proportional to that of the 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.

DSBSC

DOUBLE SIDE BAND - SUPPRESSED CARRIER (DSB-SC) MODULATION:

General expression:c(t)=[k₁m(t)+C]cos(ω_ct+Φ_c)
Let k1 = 1,  C = 0 and  c = 0, the modulated carrier signal,therefore: c(t)=m(t)cos ω_c(t)
Consider twoinformation signals like sinusoids, or cosinusoids, cosμt and cosωt. A double sideband suppressed carrier signal, or DSBSC, is defined as their product,DSBSC = Ecos ω_c (t) cosω_m (t)                                                                       ........ 1
            ω_c >> ω_m                                                                                                ........ 2we get below eqn.cosω_c (t) cosω_m (t) = (E/2) cos(ω_c - ω_m)t + (E/2) cos(ω_c + ω_m)t                           ........ 3
Equation 3 shows that the product is represented by two new signals, one on the sumfrequency (ω_c + ω_m), and one on the difference frequency (ω_c - ω_m) - 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 just above it. These are referredto as the lower and upper sidebands  respectively. These two components were derived from a ‘carrier’ term on ω_c rad/s, and a message on ω_m rad/s. Because there is no term at carrier frequency in the product signal it is described as 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 ω_c and ω_m has been made
Non-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 balance state. 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 carrier feed through. In general, the optimum input range is about 0.2 Vpp to 0.8 Vpp when the carrier frequency is 500 kHz. To identify AM, DSB-SC or SSB modulated signals; we assume a typical audio spectrum shown in Fig. 5-2a. Where f mh is the 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, including electronic circuits (such as a hiss filter used in audio), anti-aliasing filters for conditioning signals prior to analog-to-digital conversion, digital filters for smoothing sets of data, acoustic barriers, blurring of images, and so on. The moving average operation used in fields such as finance is a particular kind of low-pass filter, and can be analyzed with the same signal processing techniques as are used for other low-pass filters. Low-pass filters provide a smoother form of a signal, removing the short-term fluctuations, and leaving the 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 values determines this. When choosing the values, ensure that the resistor values fall in the region between 10 k ohms and 100 k ohms. This is advisable because the output impedance of 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 one added 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 in the 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 in radio 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:-

Reciver

Tuned Radio Frequency (TRF) Receiver Circuit DiagramThe 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. Occasional further 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 mixer converts RF power at one frequency into power at another frequency to make signal processing easier and also inexpensive. A fundamental reason for frequency conversion is 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 an intermediate frequency (IF) section of the receiver.    Double-sideband, suppressed-carrier AM is a sum (upper sideband), a difference (lower sideband) and no carrier. We didn’t call its sum and difference outputs upper and lower sidebands earlier in equation 7’s neighborhood, but we’d do so in a transmitting application. In a transmitter, we call a circuit that suppresses the carrier while generating upper and lower sidebands a balanced modulator, and we quantify its carrier suppression, which is always less than infinite. In a receiver, we call such a 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 it suppresses both its input signal and LO/carrier in its output), 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 be single-ended.) Sometimes,DSB suppressed-carrier AM is called just DSB.    A sine wave at the frequency difference between Signal A and Signal B 2π(fa – fb)t,and a sine wave at the frequency sum of Signal A and Signal B 2π(fa + fb)t. (The products are cosine waves, but since equivalent sine and cosine waves differ only by a phase shift of 90°, both are called sine waves by convention.) This is the basic process by which we translate information into radio form and translate it back again. If we want to transmit a 1-kHz audio tone by radio, we can feed it into one of our mixer’s inputs and feed 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 electronic device that increases the power of a signal. It does this by taking energy from a power supply and controlling the output to match the input signal shape but with larger amplitude. In this sense, an amplifier modulates the output of the power supply.
   The term power amplifier is a relative term with respect to the amount of power delivered to the load and/or sourced by the supply circuit. In general a power amplifier is designated as the last amplifier in a transmission chain (the output stage) and is the amplifier stage that typically requires most attention to power efficiency. Efficiency considerations lead to various classes of power amplifier based on the biasing of the output transistors or tubes.
 
        
 

Power amplifier classes:

        Power amplifier circuits (output stages) are classified as A, B, AB and C for analog designs, and class D and E for switching designs based on the proportion of each input cycle (conduction angle), during which an amplifying device is passing current. The image of the conduction angle is derived from amplifying a sinusoidal signal. If the device is always on, the conducting angle is 360°. If it is on for only half of each cycle, the angle is 180°. The angle of flow is closely related to the amplifier power efficiency. The various classes are introduced below, followed by a more detailed discussion under their individual headings further down.
In the illustrations below, a bipolar junction transistor is shown as the amplifying device, but the same attributes are found if with MOSFETs or vacuum tubes.

Class AB

Class AB is intermediate between class A and B, the two active elements conduct more than half of the time. Class AB is widely considered a good compromise for audio power amplifiers, since much of the time the music is quiet enough 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 enough that the distortion products typical of class B are relatively small. The crossover distortion can be reduced further by using negative feedback.
Reference oscillator :
Antenna: Ground Antenna:
In radio communication, a ground dipole also referred to as an earth dipole antenna, transmission line antenna, and in technical literature as a horizontal electric dipole. A ground dipole consists of two ground electrodes buried in the earth, separated by tens to hundreds of kilometres, linked by overhead transmission lines to a power plant transmitter located between them. Alternating current electricity flows in a giant loop between the electrodes through the ground, radiating ELF waves, so the ground is part of the antenna. To be most effective, ground dipoles must be located over certain types of underground rock formations.
A ground dipole functions as an enormous vertically-oriented loop antenna (see drawing, right). It consists of two widely separated electrodes (G) buried in the ground, connected by overhead transmission cables to a transmitter (P) located between them. The alternating current from the transmitter (I) travels in a loop through one transmission line, kilometres deep into bedrock from one ground electrode to the other, and back through the other transmission line. This creates an alternating magnetic field (H) through the loop, which radiates ELF waves. The axis of the magnetic field produced is horizontal, so it generates vertically polarized waves. The radiation pattern of the antenna is directional, with two lobes (maxima) in the plane of the loop, off the ends of the transmission lines. In the U.S. installations two ground dipoles are used, oriented perpendicular to each other, to allow transmission in all directions.
The amount of power radiated by a loop antenna is proportional to (IA)2, where I is the AC current in the loop and A is the area enclosed, To radiate practical power at ELF frequencies, the loop has to carry a current of hundreds of amperes and enclose an area of at least several square miles. Christofilos found that the lower the electrical conductivity of the underlying rock, the deeper the current will go, and the larger the effective loop area. Radio frequency current will penetrate into the ground to a depth equal to the skin depth of the ground at that frequency, which is inversely proportional to the square root of ground conductivity σ. The ground dipole forms a loop with effective area of A = Lδ / √2, where L is the total length of the transmission lines and δ is the skin depth. So ground dipoles are sited over low conductivity underground rock formations (this contrasts with ordinary radio antennas, which require good earth conductivity for a low resistance ground connection for their transmitters). The two U.S. Navy antennas were located in the Upper Peninsula of Michigan, on the Canadian Shield (Laurentian Shield) formation, which has unusually low conductivity of 2×10−4 siemens/meter  resulting in an increase in antenna efficiency of 20 dB.The earth conductivity at the site of the Russian transmitter is even lower.
Theoretical calculation :

Advantages:

Lower power consumption

Disadvantage:

 -  Complex detection

Applications:

 - Analogue TV systems: to transmit colour information
 - For transmitting stereo information in FM sound broadcast
   at VHF

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