Satcomm-01 Satelite communication training system ‘SR.NO. CHAPTER PAGE NO. 1. Introduction 2. Understanding the basic concepts of satellite communication. 3. To setup a direct communication link between uplink transmitter and downlink receiver using Tone signal. © setup an Active satellite communication link and demonstrate link fail operation. wvevwvwvewuevwe 5. To setup a audio video satellite link between transmitter and receiver. 6. To communicate voice signal through satellite link, “Observe the effect of Different combinations of uplink and downlink frequencies on satellite link. 8. To transmit and receive three separate signals (Audio, Video , Tone) simultaneously through satellite link -9. To transmit and receive function generator signals through satellite link. 10. To measure the signal parameters in an analog FIMW/FDM TV satelite link. to measure the CIN ratio.SSS eevee eevee vvvevseveovevevevvevuvevwvuvnvueveve Satcomm-01 Satelite communication training system. PAGE NO. SR.NO. CHAPTER 12. To measure SIN ratio 38 13. To estimate FM deviation/bandwidth 4 14. To transmit digital waveforms through a satellite 44 communication link. 15. Power Conversion Table for 75 Ohms 45 Power-RSSI conversion TablerywTeeceeuvonws. weveseveowvvvvvvvvvvvevvvvevvevvevevevvve Satcomm-01 Satellite communication training system INTRODUCTION SATELLITEDOWNLINK RECEIVER SATCOMMO2 @ @ © oe SATELLITE DOWNLINK RECEIVER SATCOMM-01 Select: This push button can be used to select the frequency of operation from 2400, 2427, 2454 and 2481 MHz respectively. RSSI: This BNC has a DC voltage in proportion to the received signal strength which can be used to monitor the C/N ratio. The chart at the back of the manual can be used to convert DC voltage to corresponding RF signal level in dBm or dBuV. Volume Speaker: Tuming this pot clock-wise increases the output of sound from speaker. Input(Audio1/Audio2): This toggle switch selects the input source of the speaker from audio1 to audio2. Audio1: This BNC gives output of the received audio1 channel. ‘Audio2: This BNC is used to output the received audio2 channel. Video: This BNC is used to output the received video channel Select (Video/data): This toggle switch is used to select the output from either video or data as the same channel is used to carry video and data. Hence both can not be received simultaneously. Data Out TTL: This BNC has TTL level data output. it is aN unfiltered output. There is no restriction of data format or data speed on this output hence can be used for receiving square waveforms. RF Input: This BNC is RF input of the receiver and is used to connect to the antenna,Vw dD DvD DODO O WDE Uewes« vbvea 3 > >’ eee ru Satcomm-01 Satellite communication training system Satellite Uplink Transmitter ‘SATELLITE UPLINK TRANSMITTER SATCOMMO2 @ @ ® o Hovwne zara stim aime Select: This push button can be used to select the frequency of operation from 2400, 2427, 2454 and 2481 MHz respectively. Input MIC: This phono input jack is used to connect the condenser microphone for transmission of voice. MIC/KHz: This-toggle switch selects either Microphone input or 1KHz sine wave for modulation. Switch should be set to mic if both channels are to be modulated externally. (Audiot/Audio2): This toggle switch selects either mic or 1 KHz sine wave for modulation on audiot or audio2 ‘Audiot: This BNC is used to input the modulating signal on audiot channel. A signal of 20 Hz to 20 KHz could be applied here. Level should preferably be limited to 1Vplp. ‘Audio2: This BNC is used to input the modulating signal on audio2 channel. A signal ‘of 20 Hz to 20 KHz could be applied here. Level should preferably be limited to 4Vplp. Video: This BNC is used to input the modulating signal on video channel. A, signal of 200 Hz to 2 MHz could be applied here. Level should preferably be limited to 1Vpip. This toggle switch is used to select the input from either video or Select (Video/data): \ce both can not be Gata as the same channel is used to carry video and data. Hen transmitted simultaneously. Data In TTL: This BNC is meant for TTL level data input. This data is modulated directly on the carrier. It has no restrictions on data format or speed etc. RF Output: This BNC is RF output of the transmitter and is used to connect to the antenna.wsevyvuevvevuseuveuuvdvuoduvowovuwouvvvuvvguvvuvuovvves Satcomm-01 Satelite communication training system Satellite Link Emulator SATELLITE LINK EMULATOR SATCOMMO2 o © © © & o® © © 0 @ fu uns 207 Wz 2esenne 2aIMNZ SELECT 2000 ue aor ue 26se M2 2atmH: SELECT © ® © © Uplink Select: This push button can be used to select the frequency of operation from 2400, 2427, 2454 and 2481 MHz respectively. Downlink Select: This push button can be used to select the frequency of operation from 2400, 2427, 2454 and 2481 MHz respectively. Press the frequency select switch of satellite emulator down link channel several times so as to set the frequency display from 2.400, 2.427, 2.454, 2.481 and then back to 2.400. This is done to ensure the emulator downlink PLL is locked and displayed frequency is generated correctly. If switching ON the 1kHz tone on transmitter will make the receiver sound to 1KHz test tone via satellite, PLL of complete link are O.K. and a successful sat link is said to be established. Link Fail: This switch is set upwards/downwards to enable/disable the link. RF level: This pot is used is increase or decrease the RF level output from the downlink transmitter. Reducing the level will reduce the C/N ratio and increase noise in the link. 6bidder Satcomm-01 Satellite communication training system Experiment #4 Aim: Understanding Basic Concepts in Satellite TV Theory : Sinusoidal electromagnetic waves (elm waves) . All radio and television signals consist of electrical and magnetic fields which, in free space, travel at the speed of light (approximately 186,000 miles per second or 3 x 10° meters per second), These waves consist of an electric field (E), measured in volts per meter and a magnetic field (H), measured in amps per meter, The E and H field components are always at right angles to each other and the direction of travel is always at right angles to both fields. The amplitudes vary sinusoidal as they travel through space. In fact, it is impossible to produce a non-sinusoidal e/m wave! (The importance of this statement will be grasped more easily when modulation is discussed). The sine wave Cycle: One complete electrical sequence. Peak value (Vp): Maximum positive or negative value -also called the amplitude. Period (t): Time to complete one cycle. Frequency (f): Number of cycles per second measured in Hertz (Hz). (One hertz = one cycle per second). It follows that period and frequency are reciprocals of each other: =f Commonly used multiples of the hertz are: Kilohertz (kHz) = 10° Hz = 1000 Hz Megahertz (MHz) = 10° Hz = 1.000000 Hz Gigahertz (GHz) = 10° Hz = 1 000 000 000 Hz RMS value: This is 0.707 of the peak value and, unless otherwise stated, any reference to voltage or current in technical literature is normally taken to mean this value. For example, the supply mains in the UK is a sinusoidal variation, stated to be "240 volts’ so the peak value is 240/ 0.707 = 339 volts. Angular velocity (w) This is an indirect way of expressing the frequency: w = 2af radians per second. Instead of considering the number of complete cycles, angular velocity is a measure of how fast the vector angle is changing. The voltage equation of a sine wave, which gives the instantaneous value (v) of a sine wave at any point in the cycle is given by: v=Vpsin0 where Vp is the peak voltage and @ is an angle measured in radians (not degrees). There are 2x radians in a circle and, since the sine wave can be visualized as a vector rotating in a circle, the above equation can be written in terms of frequency and angle: v= Vp sin 2n ftvuvwvvvv down vuvwnvvuvrewn ven eve vr ew vee a Satcomm-01 Satellite communication training system For convenience and brevity, the 8 part is often lumped together and given the title of angular velocity (w). Using this notation, the equation of the sine wave can be written as: v=Vpsin wt Wavelength Since e/m waves at a known velocity vary sinusoidally, it is possible to consider how far a wave of given frequency(f) would travel during the execution of one cycle. Denoting the speed of light as (c), the wavelength (2) is given by: er From this, it is clear that the higher the frequency, the shorter the wavelength. Satellite broadcasting employs waves in the order of 10 GHz frequency so the order of wavelength can be calculated as follows: 3.x 10°)(10 x 10°) % =3x107=3.cm In practice, the frequencies used are not necessarily a nice round figure like 10 GHz. Nevertheless, the wavelengths in present use invariably work out in terms of centimetres -they are, in fact known as ‘centimetric waves’. It is pertinent at this stage to question why such enormously high frequencies are used in satellite broadcasting? Before this can be answered, it is necessary to understand some fundamental laws relating to broadcasting of information, whether it be sound or picture information. Carrier frequency For simplicity, assume that it is required to transmit through space a 1000 Hz audio signal. In theory, an electrical oscillator and amplifier could be rigged up and tuned to 1000 cycles per second and the output fed to a piece of wire acting as a primitive aerial. tis an unfortunate fact of nature that, for reasonably efficient radiation, a wire ‘aerial should have a length somewhere in the order of the ‘wavelength’ (2) of 1000 Hz. Using the equation given above: ne cf (3 x 10°10") = 3 x 10° metres 2, = 300 000 metres which is about 188 miles! Apart from the sheer impracticalty of such an aerial, waves at these low frequencies Suffer severe attenuation due to ground absorption. Another important reason for Using high frequencies is due to the considerations of bandwidth which is treated later. The solutior intelligence’ (the 1000 H; The high frequency wav nis to use a high frequency wave to ‘carry’ the signal but allow the iz in our example) to modify one or more of its characteristic. fe is referred to as the carrier (fc) simply because it ‘carries’ the information in some way. The method of impressing this low frequency intormation on the carrier is called modulation. There are two main types, ampiitude modulation (AM) and frequency modulation (FM). Amplitude modulation iP frequency modulating signal is made to alter the amplitude of the carrier at the transmitter before the composite waveform is sent to the aerial system. If the wre ude of the modulating signal causes the carrier amplitude to vary betweeni i a 2 Satcomm-01 Satelite communication training system double its unmodulated height and zero, the modulation is said to be 100 per cent. Terrible distortion results if the modulation amplitude is ever allowed to exceed 100 per cent, Modulation factor (m) This is the ratio of modulation amplitude (Vm) to carrier amplitude ( Vc): m=VmiVc When m = 1, the modulation is 100 per cent. Although 100 per cent modulation is an advantage, it is too dangerous in practice because of the possibility of over- modulation, so 80 per cent (m = 0.8) is normally considered the safe limit. Sidebands Although the modulating signal is a simple sinusoidal waveform, in practice it will be more complex. Thus the envelope of the waveform will be non-sinusoidal. Bearing in mind that only sinusoidal waveforms can be sent through space, there is clearly something odd to explain. This is where alittle school maths comes in handy. The unmodulated carrier sine wave has the instantaneous form: v=Vp sin wet But the amplitude of this wave (Vp) is made to vary by the modulating frequency which causes Vp to have the form: Vp=Vm sin wet Substituting this expression in the first equation gives: v= Vi sin wet sin wet In school, we were told that one of the trigonometrical identities is: sin A sin B = 1/2 cos (A- B) -1/2 cos (A +B) So it follows that the modulated carrier waveform splits up in space into three pure sinusoidal components: 1. The carrier frequency. ; ; ; 2. A frequency equal to the sum of the carrier and modulating frequencies. This is called the ‘upper sideband’ : 3. A frequency equal to the difference between the carrier and modulating frequency. This is called the ‘lower sideband’. Taking a simple numerical example, if the carrier frequency is 1 000 000 Hz and the modulating frequency is 1 000 Hz, then the upper sideband is a 1 001 000 Hz sine wave and the lower sideband is a 999 000 Hz sine wave. In practice, the modulating ‘ney will seldom be anything as simple as a 1000 Hz sine wave but, more probably, may consist of speech or picture information which contains a complex aexture of frequencies. This does not invalidate the former reasoning. It just means that instead of single frequency upper and lower sidebands, there will be literally, a band of sinusoidally varying frequencies either side of the carrier. For example, the music frequency spectrum extends from about 20 Hz to about 18 kHz so, to transmit high quality sound, the upper sidebands would have to contain a spread of frequencies. extending from 20 Hz to 18 kHz above the carrier, and the lower vetbands. frequencies 20 Hz to 18 KHz below the carrier. Television transmission is frequer 9 —_—_—_——OWVVVHVVVKEID OHV KUL eEOUETOVLLVHEOHY~« lll — Salcomm-01 Satelite communication training system more difficult because pictures have a far greater information content than sound The sidebands must extend several MHz either side of the carrier. The wider the sidebands of transmission, the greater space it will occupy in the frequency spectrum, so broadcast stations geographically close together must operate on frequencies well away from each other in order to prevent interference from their respective sidebands. Since television stations occupy several MHz in the spectrum, carrier frequencies are forced into ever higher and higher frequencies as the number of stations fight for space. There are several novel solutions to the overcrowding problem. For example, it is not essential to transmit both sidebands since all the required information is contained in one of them, providing of course the carrier is sent with it. Such transmissions are called SSB (single sideband). An even more drastic curtailment is to reduce the carrier amplitude at the transmitter to almost zero and use it to synchronize a. locally generated carrier at the receiving end, a technique known as ‘single sideband vestigial carrier’ transmission. Frequency modulation (FM) Whereas amplitude modulation alters the envelope in the ‘vertical plane’, frequency modulation takes place in the ‘horizontal plane’. The amplitude of the carrier is kept constant but the frequency is caused to deviate proportional to the modulating amplitude. - Frequency deviation The maximum amount by which the carrier frequency is increased or decreased by the modulating amplitude is called the frequency deviation. It is solely dependent on the amplitude (peak value) of the modulating voltage. In the case of satellite broadcasting, the signal beamed down to earth has a typical frequency deviation of about 16 MHz/V and the bandwidth occupied by the picture information is commonly about 27 MHz. Modulation index (m) This is the ratio of the frequency deviation (fd) to the highest modulating frequency (fm): m= fd/fim In contrast with amplitude modulation, the modulal restricted to a maximum of unity. n index is not necessarily Noise ‘Any unwanted random electrical disturbance comes under the definition of noise. Such noise is all-pervading and is the worst enemy of the electronic designer. It begins in conventional circuitry, particularly with the apparently harmless resistor because, at all temperatures above zero kelvin (0 K), a minute, but not always negligible, em. (called Johnson noise) appears (and can be measured) across the gnds. This is due to random vibration of the molecules within the body of the resistor Snd nothing whatever can be done to stop it. Although the following equation for Johnson noise, is not particularly important in this text it is worth examining if only to grasp the strange connection between noise e.m.fs and temperature. RMS value of Johnson noise = (4k t8R)"? toSatcomm-01 Satelite communication taining system ee = 0 absolute temperature kelvin (room temperature may be taken as around k = Boltzman’ s constant = 1.38 x 10 R = the resistance in ohms B = the bandwidth of the instrument used to measure the em. Those with sufficient zeal to work out the noise from a one megohm resistor at room temperature would come up with a value of about 0.4 millivolts! This may seem small but itis relative, rather than absolute values that are important. If the wanted signal is of the same order as this (in practical cases it could be much smaller) then the noise will swamp it out. Note from the equation, which incidentally is not restricted to man- made materials, the noise depends on the temperature, and the bandwidth of the ‘instrument used to measure it’. Such an ‘instrument’ includes a broadcast receiving station! A high quality transmission has wide sidebands so the receiving installation must also have a wide bandwidth in order to handle the information in the sidebands. The occurrence of this form of noise entering the chain can seriously limit the quality of reception. Although Johnson noise has been used as an example, there are many other forms of noise (including ground and the man-made variety). Comparison of FM and AM . - There are two features of AM which, in the past, have been responsible for its popularity: 1, The demodulation circuitry in the receiver, called ‘rectification’, is simple, requiring only a diode to chop off one half of the composite waveform and a low pass filter to remove the carrier remnants. 2. The sidebands are relatively narrow so the transmission does not occupy too much space in the available frequency spectrum. The most serious criticism of AM is that noise, at least most of it, consists of an amplitude variation. That is to say, any noise e.m-f.s present ride on the top of the envelope. So, apart from meticulous design techniques based on increasing the S/N ratio, nothing much can be done about reducing noise without degrading signal quality by crude methods such as bandwidth reduction. FM, on the other hand, is often stated to be ‘noise free’. This is not true! A FM transmission is as vulnerable to noise pollution as AM but, due to the manner in which the information is impressed on the carrier, much of the noise can be removed by the receiver circuitry. Since noise rides on the outside of an FM waveform, it is possible to slice off the top and bottom of the received waveform without destroying the information (remember that the information is inside the waveform rather than riding on the top and bottom). The slicing-off process is known as ‘amplitude limiting’. A disadvantage of FM is the wide bandwidth required. FM is only possible if the carrier frequencies are relatively high. Fortunately, satellite broadcasting is well above 1 GHz so this is a trivial disadvantage. It cannot be denied that the circuitry required to extract the information from an FM carrier is, to say the least, awkward! The circuitry which performs this function is called an 'FM demodulator’ which often takes bizarre forms. Among the various circuits that have been developed for FM demodulation are discriminators, ratio detectors and phased locked loops. This latter type is the most often used method LO 2 2 ia 2 ‘Satcomm-01 Satellite communication training system Decibels (dB) ; Decibels provide an alternative, and often more convenient, way of expressing a ratio between two powers. Instead of the actual ratio, the logarithm to base 10 of the ratio is used as shown below: dB = 10 log Py/P2 The sign of the result is positive if P, is greater than P2 and negative if Py is less than P2. To avoid the trouble of evaluating negative logarithms, it is a good plan always to put the larger of the two powers on top and adjust the sign afterwards in accordance with the above rule. Examples: IF P; = 1000 and P2 = 10 then, dB = 10 log 1000/10 = 10 log 100 = +20 dB. (IP; was 10 and P2 was 1000, the absolute value in decibels would be the same but it would be written as -20 dB). There are several advantages of using dBs instead of actual ratios: 1.Because the human ear behaves logarithmically to changes in sound intensity, decibels are more natural than simple ratios. For example, if the power output of an audio amplifier is increased from 10 watts to 100 watts, the effect on the ear is not 10 times as great. : 2. Decibels are very useful for cutting large numbers down to size. For example, a gain of 10000000 is only 70 dB. 3. The passage of a signal from the aerial through the various stages of a receiving installation is subject to various gains and losses. By expressing each gain in terms of positive dBs and each loss in negative dBs, the total gain can be easily calculated by taking the algebraic sum. Example: (+5) + (-2) + (+3) + (-0.5) = 5.5dB, A few of the more commonly used dB values are as follows: Decibels (dB) Relative power increase 0 1.00 1.5 1.12 1.0 1.26 2.0 1.58 3.0 1.99 6.0 3.98 12.0 15.85 15.0 31.62 18.0 63.09 21.0 125.89 50.0 100000 100.0 10000000000 Voltage dB | ‘Although dBs are normally used in conjunction with power ratios, it is sometimes convenient to express voltage ratio in dB terms. The equation in these cases is: B= 20 log ViV2Satcomm-01 Satellite communication training system The use of 20 instead of 10 is because power is proportional to the square of the voltage so the constant is 20 instead of 10. Ku-band satellite TV The European nations have almost exclusively adopted Ku-band (10.95: to 14.5 GHz) for the transmission of satellite TV signals. The Clarke belt Back in 1945, Arthur C. Clarke, the famous scientist and science fiction novelist, predicted that an artificial satellite placed at a height of 35803 km directly above the equator would orbit the globe at the same speed with which the earth was rotating. As a result, the satellite would remain stationary with respect to any point on the earth's surface. This equatorial belt, rather like one of Saturn's rings, is affectionately known as the Clarke belt. Any satelite within this belt is termed geostationary, and is placed in a subdivision known as an orbital slot. Signals are sent up to a satellite via an uplink, electronically processed and then re-transmitted via a downlink to earth receiving stations. we~vvd~dovovwvvovvuvrsw ’ The antenna The antenna or ‘dish’ is concerned with the collection of extremely weak microwave 5 signals and bringing them to a focus. The surface must be highly refléctive to > microwaves and is based on a three-dimensional geometric shape called a paraboloid which has the unique property of bringing all incident radiation, parallel to , its axis, to a focus. There are two main types of antenna, one is called prime focus and the other offset focus. Briefly, a prime focus antenna has the head unit mounted 5 in the central axis of the paraboloid whereas the offset focus configuration, has the a head unit mounted at the focal point of a much larger paraboloid of which the observable dish is a portion. Antennas are normally made from steel, aluminium or 9 fibreglass with embedded reflective foil : Feedhorn ee > The feedhom, positioned at the focal point of an antenna, is a device which collects reflected signals from the antenna surface whilst rejecting any unwanted signals or > noise coming from directions other than that parallel to the antenna axis. These are Carefully designed and precision engineered to capture and guide the incoming microwaves to a resonant probe located at the front of the LNB.A feedhom is really a fe. They normally consist of rectangular or circular cross-section tubes and tant properties, dictated by waveguide theory. First, signals having than half the internal dimensions are severely attenuated as the down its length, Secondly, wavelengths shorter than the ed dominant mode become rapidly attenuated; thus the feedhorn like a band pass filter. The reason for the fluted horn is to match dance of the air with that of the waveguide. waveg exhibit two impor wavelengths.longer signal progresses waveguides design 7 behaves, in effect, the free space impe* ise block (LNB) . 7 Teal of a LNB is to detect the weak incoming microwave signals via an ion . 7 : The funcliped resonant probe, provide low noise amplification, and finally down- a block of frequencies to one suitable for cable transmission. It is whole / ‘ conven nowadays for the combination of feedhorn, polarizer and LNB to be ; es —_——~~ www eve vwevvvovov~vwrvsvwers. Satcomm-01 Sateltite communication training system manufactured as a single sealed unit. The entire assembly is often referred to as an LNB, for convenience, but it should be remembered that this is not strictly the case Satellite receivers The purpose of a satellite receiver is the selection of a channel for listening, viewing, or both, and transforming the signals into a form suitable for input to domestic TV and stereo equipment. Down-converted signals of about 1 GHz are fed by coaxial cable from the LNB to the input of the receiver. The various subsections of a receiver are listed below: 1 Power supply. 2 Second down-conversion and tuner unit. 3 Final IF stage. 4 FM video demodulator. 5 Video processing stages. 6 Audio processing stages. 7 Modulator. It will be increasingly common to find TV sets with built-in satellite receivers designed to cover both the FSS and DBS band. Effective isotropic radiated power (EIRP) and footprint maps An isotropic radiator is defined as one which radiates uniformly in all directions. For purposes of illustration it is perhaps better to use a lightbulb analogy. Imagine a 40 W lightbulb suspended from a ceiling so as to be in line with a keyhole. An observer looking through the keyhole would see just a 40 W isotropic radiator. If a parabolic reflector from an old car headlamp is placed directly behind it, then the energy from the bulb will be reflected and magnified in one general direction, toward the keyhole, similar to a car's headlamp on main beam. To an observer, with a restricted field of view, the light source will appear as an isotropic radiator of much higher power. In other words, the effective power appears much higher than the actual power. This effect is somewhat similar to that which occurs with a parabolic transmitting antenna of a satellite. To a distant observer, which in this case is the receiving site antenna, the radiated power appears much higher than that of an isotropic radiator because the transponder antenna has a parabolic reflector and the receiving site antenna (‘eye at the keyhole’) has a restricted view of the transmitted beam. We know that the EIRP of the Astra 1A satellite is 52 dBW in the central service area, and that the transponder power is 45 W, therefore we can calculate the effective isotropic radiated power in watts as seen by the antenna. EIRP = 10 log (effective power) effective power = 10°"°" = 108") = 158489 W or 158.5 KW a From this we can calculate the magnification factor of the transponder’s transmitting antenna: : magnification = 158489/45 = 3522 times Repeating the calculation for a typical DBS satellite with a transponder power output of 110 Wand an EIRP value of 61 dBW in the central service area we get: effective power = 10eee . #1258925 W or 1.25 MW magnification = 1258925/110 = 11445 times MWSatcomm-01 Satellite communication training system As with the lamp analogy the intensity of the beam will fall off as the distance from the main axis increases, since the beam will naturally diverge, in a conic fashion, with distance. A satellite EIRP footprint map is constructed by linking contours or lines through points of equal EIRP in the service area. The values will decrease away from the center which shows footprint maps for the four beams generated by the Astra 1A satellite. The above calculations show that large and unwieldly numbers start to emerge when we talk in effective power terms; this is why EIRP is measured in logarithmic decibel units relative to 1 watt. Remember that a 3 dB increase corresponds to a doubling of power. Therefore the apparent small increases in the values seen on footprint maps correspond to large changes in power levels. In this way relatively small numbers can be used to describe large power changes. Most footprint maps have this characteristic circular shape with EIRP levels falling off linearly away from the main service area. An isotropic radiator is defined as one which radiates uniformly in all directions. This is not obtainable in reality but is easy to visualize. By using a reflector an isotropic radiator can concentrate all its energy into a narrow beam which appears to some distant observer, at the other end of the beam, as an isotropic source of several magnitudes greater power output. Thus the term equivalent isotropic radiated power is used as a measure of signal strength that a satellite transmits to earth. EIRP is measured in dB relative to one watt (dBW) and is highest at the beam centre. This value decreases logarithmically at distances away from the beam centre. The EIRP of any satellite can be obtained from the appropriate footprint map, as contours of equal magnitude. Modem satellites can shape their EIRP contours to a certain extent to fit the desired service area although the methods used need not concem us here. A typical value of EIRP for medium power semi-DBS satellites such as Astra is 52 dBW. High power DBS satellites have EIRP values in excess of 60 dBW Downlink frequency allocations The ITU has split the world up into three regions, The approximate frequency allocations above 10 GHz are as follows. Region 1: Europe, CIS, Africa and Middle East Fixed satellite service (FSS) band: 10.70-11.70 GHz 12.50-12.75 GHz 17.70-21.20 GHz Direct broadcast service (DBS): 11.70-12.50GHz Broadcast satelite service (BSS): 21.40-22.00 GHz (from 2007) Region 2: The Americas and Greenland Fixed satellite service (FSS) band: 11.70-12.20 GHz 17.70-21.20 GHz Direct broadcast service (DBS): 12.20-12.70 GHz Broadcast satelite service (BSS): 17.30-17.80 GHz (from 2007) Region 3: India, Asia, Australasia and the Pacific Fired ‘satellite service (FSS) band: 11,70-12.75 GHz 17.70-21.20 GHz Direct broadcast service (DBS): | 11.70-12.75GHz Broadcast satelite service (BSS): 21.40-22.00 GHz(from 2007) Is~ y~wwwvvuvvvese Satcomm-01 Satelite communication training system Pre-emphasis (de-emphasis) improvement . ith Since the noise power density of a receiver demodulator output increases wit frequency. high frequencies are boosted or pre-emphasized prior to transmission. When the signal is subsequently demodulated in the receiver the signal aaa ie acquired noise is de- emphasized or reduced by an equal amount. The overall o a is to reduce the noise component and leads to a typical improvement in SIN of 2 for PAL | signals or 2.5 dB for NTSC M signalsvvvVv TVTVY VvvVvvVvvvuvevKnveuvuvUUHD Ee vVuUvevee Satcomm-01 Satellite communication training system Experiment # 2 Aim : To set up a direct communication li i : link link transmitter and d receiver using Tone signal. atin nk beeen uel anemia a downs Equipment required: Satellite uplink transmitter and Satellite downlink receiver, connecting cables, Pair of Dish antennas with mounts. . Procedure: 1. Connect the Satellite uplink transmitter to AC mains outlet with the lead provided 2. Switch ON the transmitter and the frequency LED will come on 3. The LED will read — 2.400 GHz, 4, The transmitting frequency can be selected by means of a select switch provided on the front panel. 5. Pressing the select switch will increase the frequency from 2.400GHz, 2.427GHz, 2.454 GHz, 2.481 GHz and back to 2.400GHz in cyclic manner. This indicates that each channel is allocated a bandwidth of 27 MHz. 6. The best part is that it holds good for receiver also and PLL means that when both receiver and transmitter show same frequency, they are accurate to'less than 10 KHz of each other and no tuning and repeated adjustments are required. 7. Now bring the transmitter to 2.400 GHz and connect the Dish antenna with BNC lead to RF. out of Tx. 8. Set the output level of Tx to maximum by turning the RF level fully clockwise. 9. The Dish of Tx should be rotated with the antenna pointing in the same direction to that of Dish of Receiver. 40. The satellite Downlink receiver could be switched on now after plugging into AC mains outlet 11. The LED will read ~ 2.400 GHz 12. The receiving frequency can be select the front panel. 13, Pressing the select switch will increase the frequency from 2.400GHz, 2.427GH2, 2.454 GHz, 2.481 GHz and back to 2,400GHz in cyclic manner. 14, Set the frequency to 2.400 GHz using frequency control 18. Now connect Dish with BNC lead to the receiver. The receiver noise will be squelched to silence. ; 16, Point the Rx Dish to Dish of Transmitter. 17. Keep the switch audio 1 audio 2 to audiot and also mic 1 KHz switch to 4 KHz. Similarly, the switch audio 1 audio 2 to audiot at Rx end also. This will make the receiver sound to 1KHz test tone. \e at the receiver indicates that the microwave communication -essfully. ted by means of a select switch provided on Result: A cléar test ton link has been set up suce eS 7 aLee Satcomm-01 Satelite communication training system Experiment #3 Aim: To set i i ov ee eaeenone ‘etup an Active satellite communication link and demonstrate link fail Equipment required: Satelite uplink transmitter and Satellite downlink receiver, ite link emulator, connecting cables, Pair of Dish antennas witti mounts. Theory: The uplink In uplink station, the signals have to be sent at a differing frequency, usually in the higher 14 GHz band, to avoid interference with dow! Signals Another function performed by the uplink station is to control tightly the intemal functions of the satellite itself (such as station keeping accuracy). Uplinks are controlled so that the transmitted microwave power beam is extremely narrow, in order not to interfere with adjacent satellites in the geo-arc. The powers involved are several hundred watts. The downlink Each satellite has a number of transponders with access to a pair of receiveltransmit antennas and associated electronics for each channel. For example, in Europe, the uplink sends signals at a frequency of about 14 GHz, these are received, down- converted in frequency to about 11/12 GHz and boosted by high power amplifiers for re-transmission to earth. Separate transponders are used for each channel and are powered by solar panels with back up batteries for eclipse protection. The higher the power of each transponder then the fewer channels will be possible with a given number of solar panels, which in turn, is restricted by the maximum payload of launch vehicles as well as cost. Typical power consumption for a satellite such as ASTRA 1A is 2.31 kW with an expected lifetime of 12.4 years. Satellites are conveniently categorized into the following three power ranges: These have transponder powers around the 20 W mark and are tion satelites. Due to the tow transmission power of Bach transponder they can support many channels with the available collected solar energy. Many of these transponders link emulator programme material for cable TV operators across Europe. Small numbers of enthusiasts eavesdrop on these proadeasts but, unfortunately, receiving dishes of monstrous proportions. are revessary for noise free reception, often in excess of 1 meter. This state of affairs is Tlearly not too popular with the general public who consider them, quite ce aey tandably, as dinosaurs of a past age. Even so, domestic TV reception is not the primary reason for the existence of such high channel capacity satelite. Transponder bandwidths can vary. 1, Low power - primarily general telecommunica vwuueocuvwowveveweewvwvevveeeweveewvwrere ee i _ These satellites have typical transponder powers of around 45 W, ae these on board Astra 1A. Such satellites are now commonly termed semi- DBS (direct broadcast service) and represent the first serious attempt to gain public approval by offering the prospect of dustbin-Lid-sized dishes of 60 cm diameter. Fee oan transponders are average for this class at the present time. Medium boul sixterean satelites usually operate in the frequency band 10.95 GHz to 11.70 Bie and form the fixed satelite service (FSS). The transponder bandwidths are “(iSatcomm-01 Satelite communication training system ‘common oo Beer or 36 MHz. Some medium power satellites, such as the Eutelsat Il . ‘@ number of transponders that can be active in the 12.5 GHz to 12.75 GHz band, origi - originally te 2 International Telecommunerfin wee lee band service (BBS) by the Sigh power These pure DBS satelites have transponder powers exceeding 100 channels. The s reepondingly reduced channel capacity of around four perhaps five Sean ge nected dish size is minimal, about 30 to 45 om in the central service 7 are perhaps the ideal size as far as the public are concemed and interest in satellite TV is expected to blossom as these come on stream. European transponder frequencies are in the band 11.70 to 12.50 GHz which is known as the DBS band. It has been agreed that the transponder bandwidths are 27 MHz. Microwaves and the receiving site The medium used to transmit signals from satellite to earth is microwave electromagnetic radiation which is much higher in frequency than normal broadcast TV signals in the VHF/UHF bands. Microwaves still exhibit a wave-like nature but inherit a tendency to severe attenuation by water vapour or any obstruction in the line of sight of the antenna. The transmitted microwave power is extremely weak by the time it reaches earth and unless well designed equipment is used, and certain installation precautions are taken, the background noise can ruin the signal; A television receive only (TVRO) site consists of an antenna designed to collect and concentrate the signal to its focus where a feedhorn is precisely located. This channels microwaves to an electronic component called a low noise block (LNB) which amplifies and down-converts the signal to a more manageable frequency for onward transmission, by cable, to the receiver located inside the dwelling, Procedure: 4. Bring the transmitter to 2.400 GHz and connect the Dish antenna with BNC lead to RE. out of Tx 2. Set the output level of Tx to maximum by turning the RF level fully clockwise. 3. The Dish of Tx should be rotated with the antenna pointing in the same direction to that of Dish of Receiver. 4, The LED will read - 2.400 GHz. 5, The receiving frequency can be selected by means of a select switch provided on the front panel. ; 6. Pressing the select switch will increase the frequency from 2.400GHz, 2.427GHz, 2.454 GHz, 2.481 GHz and back to 2.400GHz in cyclic manner. 7 Set the frequency to 2.400 GHz using frequency control 8 Now connect Dish with BNC lead to the receiver. The receiver noise will be squelched tosilence. . 9. Point the Rx Dish to Dish of Transmitter. / 40. Keap the switch audio 1 audio 2 to audio? and also mic 1 KHz switch to 1 KHz - Sinisahe the switch audio 1 audio 2 to aucio% at Rx end also, This wil make the i \d to 1KHz test tone. tering eee anemitter to 2.481 GHz and connect the Dish antenna with BNC lead a eH level of Tx to maximum by turning the RF level fully clockwise. 19~vwwwuvvsevvuvvuveouuvovouvuvoves Salcomm-01 Satelite communication training system 13. The Dish of Tx should be rotated wit i i to that of Dish of uplink Satellite inkemulaton poiing in te same reat 14. Bring the uplink Satellite link emulator to 2.481 GHz. R Sea bad Peet is normally carried out at a higher frequency. There are arene icy channels 2.481 GHz & 2.454 GHz having a bandwidth of 27 16. Bring the Downlink Satellite link emulator to 2.400 GHz. 17. Set the frequency of Down link Rx to 2.400 GHz using frequency control. 18. Now connect Dish with BNC lead to the receiver. 19. Point the Dish to Dish of Downlink sat-link emulator. 20. Downlinking from a satellite is carried out at lower frequencies. There are two downlinking frequency channels 2.400 GHz & 2.427 GHz having a bandwidth of 27 MHz each. 21. Setup the link in a TRIANGLUR fashion with Tx, Rx and Sat-link emulator at 3 vertices of a triangle. Make sure that Dish of Tx should point towards Dish of satlink emulator and Dish of Rx should point towards Dish of sat-link emulator. Set the distance between antennas to approx. 5 meters center to center by measuring tape 22. Check the link with the help of 1KHz test tone. 23. Repeat the experiment by selecting a different uplinking & downlinking’ channel frequencies. 24. Selecting different frequencies at Uplinking end say, Transmitter(2.481) and uplink channel of satellite(2.540) and also different frequency at Receiver(2.400) and Downlink channel of satellite(2.427) will result in link fail Result: Uplinking in commercial C band is at 5.925 ~ 6.425 GHz and uplinking jn commercial Ku band is at 14.000 — 14.500 GHz. Downlinking in commercial C band is at 3.700 ~ 4.200 GHz and Downlinking in commercial Ku band is at 11.700 - 12.200 GHz In our case, uplinking is carried out at 2.481 & 2.454 GHz whereas Downlinking is carried out at 2.400 & 2.427 GHz, In our case the uplink and downlink frequencies are closer as compared to a commercial setup to conserve bandwidth and limit channel usage. The bandpass fitore inside the receiver and transmitter are real good with steep curves and aecurate frequencies for optimum performance which can be tested by watching the feoviver noise floor with transmitter at different frequency. tellite communication simulation as it is a license free band We use ISM-band for sa for institutional use. This band is from 2400 MHz to 2500 MHzEE EE EE BOBO OOH 06 6 6.6 OOH OO 6 OH OKE Satcomm-01 Satelite communication training system Experiment #4 Aim : To setu io Vi P.an Audio Video tink between transmitter and Receiver. Equipment requi ee pied: Satelite uplink transmitter and Satellite downlink receiver, 'g cables, Pair of Dish antennas with mounts. Procedure: 1. Brin 4, Bring ie Iransmitter to 2.400 GHz and connect the Dish antenna with BNC lead to 2. Set the output level of Tx to maxi imum by turning the RF level fully clockwise. 3. The Dish of Tx should be rotated wi i ji atari Disworneceoee with the antenna pointing in the same direction to 4. The satellite Downlink receiver could be switched on now after plugging into AC mains outlet. 5. The LED will read — 2.400 GHz. 6. The receiving frequency can be selected by means of a select switch provided on the front panel 7. Pressing thé select switch will increase the frequency from 2.400GHz, 2.427GHz, 2.454 GHz, 2.481 GHz and back to 2.400GHz in cyclic manner. 8. Set the frequency to 2.400 GHz using frequency control 9. Now connect Dish with BNC lead to the receiver. The receiver noise will be squelched to silence. 10. Point the Rx Dish to Dish of Transmitter. . 11. Keep the switch audio 1 audio 2 to audio1 and also mic 1 KHz switch to 1 KHz . Similarly, the switch audio 1 audio 2 to audio1 at Rx end also. This will make the receiver sound to 1KHz test tone. 42. Connect the video camera output to Video in of Tx and connect the power supply of camera. Set the input select switch to video. 43. Connect the video Monitor to video out of Rx and connect the power supply of Monitor. 14, See if you are able to receive both the audio & video sent at different channels learly. $5. Now, connect a T connector at video in of Tx so that the video signal from CCD camera can be simultaneously viewed on CRO. Similarly, connect another CRO at Foe end using T connector for visualizing the received video signal via satcom link. Aco view the audio channel on the other channel of CRO at both Tx and Rx end tors. Rene eleva level of video signal fed using CRO. If you put a black sheet of T your hand in front of CCD camera so that no light can enter into lens of Paper oF yor negligible signal is present to modulate the video carrier. Therefore, wat you eon LED of CRO is the intemal sync. level of camera. Measure how much mV is it. much my is I intensity of light in front of camera, meaning that you remove black y ) Ten varying light from object etc. will modulate the video signal sheet in Ge oe continuously varying complex video signal on CRO. See if same and you will see 2, ived at Rc end. Bringing your hand infront of camera and varying signal cay the Fit deviation of sgnal, See fithappens at Rx end also aking i_ , SIVVVGOUHHUHOHOUHUHUVbUOUKOKHbKvbHOKEEOKVKTOVEVoS Satcomm-01 Satelite communication taining system oS rticationtraining system RESULT: This is an analog FM/FOM system where audio and video both are FM modulated on carrier at transmitter and transmitted to the receiving station. The system uses a channel allocation of 27 MHz as specified for satelite video link. Within this band there are audio sub carriers of 6 & 6.5 MHz, which can carry different audio channels simultaneously for different languages or stereo. The video amplifier has a bandwidth of 5 MHz. The fm deviation is 4MHz for a video signal of 1V pip. - The process of modulation and demodulation is analog FM with wide bandwidth for video signal and narrow bandwidth for audio signal. The FM demodulation is carried out using PLL demodulators for wide band response and good linearity.Experiment #5 Aim: To communi ice si ‘unicate voice signal through satellite link. Equipment required: ae Satellite link emulate: elite uplink transmitter and Satelite downlink receiver, microphone. + connecting cables, Pair of Dish antennas with mounts, Procedure: Sea eeulaes 0 2.481 or 2.454 GHz and connect the Dish antenna with in les a ope to mic in of Tx. Also connect a BNC-T connector to AUDIO Fee once nat the same audio signal can be observed on one channel of CRO. ish of Tx should be rotated with the antenna pointing in the same direction to that of Dish of uplink Satellite link emulator. 4. Bring the uplink Satelite link emulator to 2.481 or 2.454 GHz. 5. Bring the Downlink Satellite link emulator to 2.400 or 2.427 GHz. 6. Set the frequency of Rx to 2.400 or 2.427 GHz using frequency control. 7. Connect the Audio out of Rx to other channel of CRO for comparing the signal received. 8. Now connect Dish with BNC lead to the receiver. 9. Point the Rx Dish to Dish of Downlink sat-link emulator. 40. Setup the link in a TRIANGLUR fashion with Tx, Rx and Sat-link emulator at 3 vertices of a triangle. Make sure that Dish of Tx should point towards Dish of sat-link emulator and Dish of Rx should point towards Dish of sat-link emulator. Set the distance between antennas to approx. 5 meters center to center by measuring tape. 11. Listen to the voice spoken into the mic at the speaker of the receiver. Also observe that the audio signal that was sent and received are exactly’ same. Result : The speech spoken into mic is converted into electrical signal and FM modulated 1 GHz. The same holds true for any other audio signal onto a carrier of 2.4854 or 2.48 : Siso, The modulated carrier is then radiated from the antenna and received by the Satellite transponder. The satelite then transverts this carrier to another frequency SF retransmit to receiving base station at different frequency. This frequency is hon received by the earth station and demodulated to give the audio output. Base- buen analog (Voice) Signal could be received only because the Tx. Uplink sat-tink oaitator Downlink satlink emulator and Rx all are PLL locked to accuracy of less than 10KHz.> ® . . . . . > . > > > » I SEN OT Sat oman tang yen raining system. TT Experiment # 6 Aim: Observe the eff on satellite link, °° & different combinations of uplink and downlink frequencies Equipment require Satellite link mutator Satetine uplink transmitter and Satellite downlink receiver, microphone, video camera, idea saath, Pair of Dish antennas with mounts, Procedure: 4. Bring the tran: 3 BNC lead to RE ouatte 2.481 or 2.454 GHz and connect the Dish antenna with 2.6 i . ‘onnect the video camera output to Video in of Tx and connect the power supply to camera. 3. Also connect a microphone to Mi ‘ lic in of Tx. 4. The Dish of Tx should be rotated with the antenna pointing in the ‘same direction to that of A Dish of uplink Satellite link emulator. 5. Bring the uplink Satellite link emulator to 2.481 or 2.454 GHz. 6. Bring the Downlink Satellite link emulator to 2.400 or 2.427 GHz. 7. Set the frequency of Rx to 2.400 or 2.427 GHz using frequency control. 8. Connect the video Monitor to video out of Rx and connect the power supply to Monitor. 9. Now connect Dish with BNC lead to the receiver. 10. Point the Dish to Dish of Downlink sat-link emulator. 11. Setup the link in a TRIANGLUR fashion with Tx, Rx and Sat-link emulator at 3 vertices of a triangle. Make sure that Dish of Tx should point towards Dish of sat-link emulator and Dish of Rx should point towards Dish of sat-link emulator. Set the distance between antennas to approx. 5 meters center to center by measuring tape. 12. See if you are able to receive audio & video sent at different-different channels clearl $3. Transponder in a satelite is a receive transmit pair. Change the updlinking frequency of sat-link emulator keeping down-linking satlink emulator freq. constant. Then change the down-linking frequency of sat-link emulator keeping up-linking sat- link emulator freq constant. This forms different transponder pairs. tal Prose the frequency select switch of satelite emulator down link channel several times so as to set the frequency display from 2.400, 2.427, 2.454, 2.481 and then back to 2,400. This is done to ensure the emulator downlink PLL is locked and i noy is generated correctly. Seri aking to *atslite is normally carried out at a higher frequency because of ao oe ainens width, for pinpointing distant satellites, at higher frequency, There are two up-linking frequency channels 2.481 GHz & 2.454 GHz — 16 The satellite link emulator consists of transponder (transmit-eceive pair). It receives frequency in 2.4-2.5 GHz band and has the capability to retrasmit after "5 GHz band. It can be set to receive at one particular frequency amplification in 2.4-2. and transmit at some different frequency. / 17. Down-linking from @ ‘satellite is carried out at lower frequencies because wider ent ‘5 more footprint coverage , There are two down-inking frequency beam-width gives channels 2.400 GHz & 2.427 GHz., . » » > . . . > » ° > > ) > > 2 > > > > > , Satcomm-01 Satelite commu cation trainin Raion training system 18. Repeat the experime, frequencies. 19. Also, two C, 20. Normally, sep can be connected at Tx and Rx end for signal analysis downlinking that why oo ¢8_ OF path loss occurs during actual uplinking and '¥ Power amplification is mandatory at satellite. nt by selecting a different uplinking & downlinking channel Result : pele a analog FMM system where audio and video both are FM modulated on “ds it back to the pas, 2laved to satellite which then transverts the signal and Sends It back to the receiving station. The system uses a channel allocation of 27 Miz as specified for satelite video link. Within this band there are audio sub carriers which can carry different audio channels simultaneously for different languages or stereo. The process of modulation and demodulation is analog FM with wide bandwidth for video signal and narrow bandwidth for audio signal. The FM demodulation is carried out using PLL demodulators for wide band response and good linearity, | 27 MHz — Satellite Receiver Response | 2.454 2.481 Frequency GHz Satellite Receiver Channels | 27 MHz — Satelite Transmitter Response 2.400 2427 Frequency GHz Satellite Transmitter ChannelsSatcomm-01 Satellite com, IMunicatio nt Experiment #7 Aim: To transmit and rece; simultaneously through saa tree separate signals (Audio, Video, Tone) Equipment required: Sat Satellite link emulat mI microphone, video lite uplink transmitter and Satelite downlink receiver, for, : : arene esting cables, Pair of Dish antennas with mounts, mera, Video Monitor Procedure: 1, Set up the fi P the link as before. Press the frequency select switch of satelite emulator down link channel several times so as to set the frequency LED from 2.400, 2.427, 2.454, 2.481 and then back to 2.400. This is done t hi lator downlink PLL is locked and LED frequency «, ne to ensure the emulator down tone on transmitter wi arenes generated correctly. If switching ON the tkHz complete Tink are OF snake the receiver sound to 1KHz test tone via satelite, PLL of mace - and a successful sat link is said to be established. 2, Connect the video camera output to Video in of Tx and connect the power supply of camera. Set the input select switch to video. 3, Select the 1KHz tone at audio1 channel and feed a 2 KHz sine wave externally at audio2 channel. a aes the video Monitor to video out of Rx and connect the power supply of lonitor 5. See if you are able to receive both the audio & video sent at different channels clearly. This would perform the functionality of a satellite MODEM: Modulating the baseband on a carrier at Tx end and Demodulating the received Carrier at Rx end after being passed through satellite, 6. Now, connect a T connector at video in of Tx so that the video signal from CCD camera can be simultaneously viewed on CRO. Similarly, connect another.CRO at Rx end using T connector for visualizing the received video signal via satcom link. Also view both the the audio channels one by one on the other channel of CRO at both Tx and Rx end using T connectors. Use a function generator to feed sine waves at Tx end 7. See if you can receive video as well as both audio frequencies simultaneously. This is a complete Analog FM/FDM TV satcom link, In commercial broadcast the two audio channel are the left & right stereo channels and the video is the motion picture, i , comprise the signal content. Sunn eens The path loss al both ends by increasing the distance between antennas and see if you can receive both audio as well as video simultaneously. Why does video signal remain hardly Ce whereas audio reception is highly i .ss and multipath effec : Siena Patt vel of video signal fed using CRO. If you put a black sheet of rer or your hand in front of CCD camera so that no light can enter into tens of caer eon negligible signal is present to modulate the video carrier. Therefore, Mitrat you see on LED of CRO is the internal sync. level of camera. Measure how 08 fr my se intensity of light in font of camera, meaning that you remove black Post yor ont of fens. Then varying light from object etc. will modulate the video signal Seer et see a continously varing complex veo signal on CRO, See it same 20 ee Satcomn01 Satelite communication tain ing system i varying signal can be taking it away will vary the eat Rx end. Bringing your hand in front of camera and 11. Now, connect a sine wave ¢ation of signal. See if it happens at Rx end also. sine wave source from 20 tt input at video in of Tx end and vary the frequency of Gistorion on CRO. Now 2a,tz lo 7 MHz and measure its level, frequency, and wave at Rx end on each ones the level, frequency, distortion, noise added to sine 12, Measure the noi 7 being fed to the transmitter ik cutput of audio2 channel of receiver when no signal is Fad'ta the video input of ta Measure the noise level when a ‘KHz sine wave is being roe channel Or eager Tx: Now measure the noise on increasing the FM deviation of increase in audio2? Dae ea A higher amplitude into video input. Does the noise at what level at video input. iz signal of video breaks into audio. If it does then fea es as wave signal of § MHz into video input. Gradually increase the sae iz and monitor the audio2 channel. Does a frequency of 6.5 MHz of video input result in noise at the audio2 channel. Similarly does a frequency of 6 MHz result in noise at audio1 channel. See that the video input frequency crosses the audio sub carriers resulting in noise in audio channels. 14, Observe the demodulated frequencies of 100Hz, 1KHz, 100 KHz, 1MHz and 10 MHz at video output of the receiver on the CRO. Does the video output gets distorted at 1MHz and 10MHz. Does reducing the deviation at Tx end help reduce the distortion at Rx end. RESULT: This is an analog FWFDM system where audio and video both are FM modulated on carrier at transmitter and link relayed to satellite which then transponds the signal and sends it back to the receiving station. The system uses a channel allocation of 27 MHz as specified for satellite video link. Within this band there are audio sub carriers of 6 & 6.5 MHz, which can carry different audio channels simultaneously for different fanguages or stereo. FDM is implemented because three different frequencies are used for transmission of three separate signals. The video amplifier has a bandwidth of 5 Miz. The fm deviation is 4MHz for a video signal of 1V p/p. “The process of modulation and demodulation is arialog EM with wide bandvvidth for Video signal and narrow bandwidth for audio signal. The FM demodulation is carried Sut using PLL demodulators for wide band response and good linearity.3 s v a 3 3 % a a 9 . ° ° 3 ° ° 3 ° 3 ° 3 3 3 > > > > > > > > > > > > > > Salcomm-01 Satelite communica n training sy stem Experiment #8 Aim : To transmit & rece) Sc communication link *¥ve the Function Generator waveforms through a satellite Equipment required: Satelite ink emulator con® Uplink transmitter and Satelite downlink teceiver, ‘onnecting cables, Pair of Dish antennas with mounts. Procedure: * ring th ic ; E ing the | transmitter 102.481 GHz and connect the Dish antenna with BNC lead to 2. The Dish of Tx shouk rn at 3. Bring the uplink Satellite link emulator to 2.481 GHz. 4. Bring the Downlink Satelite link emulator to 2.400 GHz. 5. Set the frequency of Rx to 2.400 GHz using frequency control. 6. Now connect Dish with BNC lead to the receiver. 7. Point the Rx Dish to_Dish of Downlink sat-link emulator. 8. Setup the link in a TRIANGLUR fashion with Tx, Rx and Satink emulator at 3 vertices of a triangle. Make sure that A Dish of Tx should point towards A Dish of sat- link emulator and Dish of Rx should point towards Dish of sat-link emulator, Set the distance between antennas to approx. 5 meters center to center by measuring tape 9. Set the Function Generator O/P to 0.5V pip and don't exczed this level else clipping will occur. 10. Connect the Function Generator O/P to video In of Tx and video Out of Rx to CRO. 11. Now vary the frequency of Function Generator and see the same O/P on CRO. Result ; The Function Generator O/P waveforms can be transmitted over a distance via a satcom link. —7 a ” a 2 » , ” a a » 2 > a a 3 3 a a 3 9 > 2 > a > > > > 5 ‘Satcomm-01 Satelite coy FMMUNcation Experiment #9 Aim: To measure s) ‘97a! Parameters in an analog FM /FDM TV satelite tink Equipment required: s, Satellite link emulator, conn Pink transmitter and Satelite downlink receiver, microphone, video camer tn cables, Pair of Dish antennas with mounts, . itor Procedure: received spoke eoanScanaTe CRO ge iia Satcom link can also be displayed at Rx end by panera Output at Rx end. Analyse the similarity in signals at : iMod comee au! KHz sine wave with a BNC-T connector to AUDIO 2 of Tx so that signal can also be observed on one channel of CRO. Ensure that the level of sine wave fed is less than 1V plp i Connect | the ato 2 out of Rx to the other channel of CRO for comparing the sp 'y of signal received via satcom link. The transmitted & received waveforms are being monitored simultaneously on the same CRO on dual channel chopped mode. 5. Measure the level of signal being transmitted and the level of signal being received. 6. Find the levels of signals received on transmitting signal level of 10 mV to 2V in steps of 50mV. Draw a graph between transmitted and received signal levels. If the graph shows straight line then there is no companding being used in the system. Companding is used to increase the level of low level signals from microphones and reduce the level of high level signals in telephony. 7. From the graph measure the level of signal for which the graph deviates from a straight line by 14B. 148 would mean that the signal level is lower than the expected level by 11%. This level will be the 148 compression level of the system for audio2 channel. 8. Find the minimum level of audio signal that can be received over the noise floor of the equipment. : 9. Find the ratio of the maximum level unclipped sine waveform to minimum signal This would give the dynamic range of audio signal the link can handle. 40. Now set the frequency of input sine wave signal to 10Hz and measure the level of signal being received. Vary the frequency of input signal to 100 KHz in steps and measure the level of received signals at different frequencies : 11. Draw a graph between frequency of the signal and level of input sine wave Haat the Suid show the frequency response of the signal source. Alsé draw a sare pete requency of the signal and evel ofthe received signal. This would aon pe reaueney response of the communication link for audio2 channel. Show the frequency i bandwidth of the audio2 channel, -24B would be the level for 12. Measure Me cod signal i 30% lower than its level a a reference frequency of say 13, Repeat the same experiment fr audiot channel, Find the difference rom audio2 channel= commu tion taining system 14, Now feed a signal i ignal " channel for different Tevenudiet ch: channel to the signal in a Of FM dk channel separation, Udio2 ch; 45. Now repeat the s, ann , mia Measure the received signal in audio2 abst ind the ratio of received signal in audio1 |. This would be a measure of cross-talk or ame hannel, meas chan clan " urements of frequency response etc for video . © hi , out of Rx. ighest unclipped sine wave that can be received at video 17. Find the difference i channel show a better treet difference in frequencies of aud: 18. Now remove the sine wave ¢ at Tx end on CRO, Revll beng SOure® at TK end. Measure the noise at audio2 input 49. Measure the noise at'audio2 vicinity of few millivolts. few tens of millivolts output at Rx end on CRO. It will be in the vicinity of 20. Measure how much noise is various circuitry of Tx, Re ant ames jedded to signal after it has passed through 21. Also measure the noise when the satelit same frequency with antennas pointing to each removed and Tx and Rx are kept at ieee teria ive peseculenen ing to each other, See if the incase in noe is addition in satellite transponder. ee hen lea 22. Also see how much noise increases or decreases if path loss (path loss can be increased by keeping the Tx and Rx antennas apart) at Tx, Rx and satellite end is varied. 23, Now, connect a sine wave input at video in of Tx end and vary the frequency of Sine wave source from 20.Hz to 7 MHz and measure its level, frequency, and distortion on CRO. Now, measure the level, frequency, distortion, noise added to sine wave at Rx end on each channel. 24. Measure the noise level at output of audio2 channel of receiver when no signal is being fed to the transmitter. Measure the noise level when a 1KHz sine wave fs being fed'ta the video input of Tx. Does the noise increase in audio2? Does the 1KHz signal of video breaks into audio. If it does then at what level at video input. 35 Feed a sine wave signal of § MHz into video input. Gradualy inereate the frequency to 7MHz and monitor the audio2 channel. Does & frequency of 6.5 MHz of video input result in noise at the audio2 channel Similarly does a frequency of 6 MHz result in noise at audio1 channel. See pat ae input frequency crosses the ting in noise in audio channels. 36, Observe mers modulated frequencies of 100Hz, 1KHz, 100 KHz, 1MHz and 10 MHz at video output of the receiver on the CRO. Does the video output gets distorted eee tatie and 10MHz, Does reducing the deviation at Tx end help reduce the distortion at Rx end. cy Fesponse from audio channels. Does the video Ponse at higher frequencies? Does it correlate to and video signals? - ere audio and video both are FM modulated on ite which then transponds the signal and RESULT: irDM system wh stem uses a channel allocation of 27 This is an analog FM! ri ink relayed to satell cartier at transmitter and link relay Soy Sends it back to the receiving AT Winin this band there are audio sub carriers MHz as specified for satellite YT audio channels simultaneously for different of 6 & 6.5 MHZ, which Mt oaimplemented because three different frequencies are languages or stere0- ee 30weve vw vvvvvewvsevvevewvvrvewovvunrsesooseursesrrnnusce _—_ used for transmission of thre of § MHz. The ation eo i rene fm deviation ig sparate Signals. The video amplifier has a bandwidth m Bi nd demodulation is anaiy for a video signal of 1V pip. The process of narrow bandwidth for audio sig, an2!09 FM with wide bandwidth for video signal and demodulators for wide band recat, The FM demodulation i -d out using PLL The speech ‘spoken into mic Pons and good linearity. nes OM USING onto a sub-cartier of 6 ey Mt Converted into electrical ‘signal and FM modulated 2. The sub-carrieris then mixed with main carrier at at 2.454 GHz. The sub-cartiars arg ots Naud aa vaio channels are more prone to fading. The modulated antenna and received by the satellite transponder. ler to another frequency and retransmits the