 Hello everyone. I am Mr. Praveen Yalapa Kumbar. Today we want to see transmission theory. The learning outcome of this topic is, at the end of the session, students will be able to explain the concept of transmission theory in satellite communication. The contents of these topics are first introduction, second basic transmission theory, first introduction. A satellite communication network consists of a number of earth stations which are interconnected via satellite. With the help of this satellite, we can communicate to each of the earth stations. Now the concept for this communication, the factor is the radio links. The radio links is defined as designed to deliver message at the destination with acceptable fidelity. But to deliver a large amount of information of very high quality we require and for the high quality, unacceptably high cost. So for that one, for the link design, following factors are considered. First operational frequency, if we use the frequency as low as possible then the cost will decreases. Second one is propagation effects. For this propagation effects as low as possible for this design. Third, acceptable spacecraft complexity is low as possible with design for that one. Fourth, effects of noise. As noise is very less, that will be more effective. And last one is regulatory requirements. Now this figure one, it shows the source destination radio link for the purpose of end to end link design. Here if you observe in this diagram, there are two earth stations. We can use this one earth station first one and this one is the second earth station. And with the help of this satellite path, we can communicate these two earth stations. For if I transmit the data from one earth station to another earth station, the following procedure we have to do with the help of this uplink, we can data uplink the data to this satellite. And with the help of this satellite we download that data and pass through this earth station. In this way, we can communicate from one earth station to another earth station. Now the source to destination path can be partitioned for the purpose of radio link design as the earth station satellite link or uplink. Second one is the satellite path. And third one is the satellite earth station link or downlink. Each component of the link has its individual characteristics. For example, we take an example of a mobile terminal. If we suppose I want to transmit the data towards the mobile to mobile communication, then destination earth station is a mobile terminal. And the receiver antenna size is also small. And due to that one resulting in low receiver carrier level and frequency also for this one, if you use size of antenna small, then frequency also requirement is very small. For such an application, the design of mobile terminal satellite link is critical. To optimize the overall link taking into consideration, the characteristics of each component of the link is the earth station size, cost and complexity. Basic transmission theory. Fundamental of satellite communication is defined as the power received by an earth station from a satellite transmitter. There are two approaches for this basic transmission theory. The first one is flux density. And second one is link equation. Now we see here the diagram shows flux density produced by an isotropic source. Now here in this diagram, this one is isotropic source. Isotropic source means it will transmit the data in all the directions. That is PT watts. That PT watts, which is a bombarded on this area, a meter square, which is a flux density of F that is in watts per meter square. Now from that diagram, the flux density crossing the surface of the sphere with the radius r is given by F is equal to PT by 4 pi r square. That is the flux density, the unit is watt per meter square, where PT is the hypothetical isotropic source transmitting radiofrequency power in watts. r is a distance in meters. Now the real antenna gain is defined as is a ratio of power per unit solid angle radiated in a direction theta to the average power radiated per unit solid angle. Now this real antenna gain we can define in the term of mathematical equation that is g theta is equal to P theta divided by P0 by 4 pi. Now P theta is the power radiated per unit solid angle by the antenna. P0 is the total power radiated by the antenna and g theta is the gain of the antenna at an angle theta. Now theta is the direction in which maximum power is radiated often called the boreside direction of the antenna. The boreside direction of the antenna is very much important for this design of flux density. The flux density in the direction of the antenna boreside at a distance r meter is defined as f is equal to PT gt divided by 4 pi r square that is watt per meter square. Now this product of PT gt is called as effective isotropic radiated power that is PT is the transmitted power and gt is the gain of the antenna. This figure 3 shows flux density produced by an isotropic source that is power instead of y an ideal antenna with the area a meter square. In this diagram we show the isotropic source which is radiated in all the direction that's the airp is equal to PT watts that is bombarded on this incident flux density as f watt per meter square it pass through and it will bombarded on the receiver with the help of power pr that receiving antenna with the area a meter square and gain is gr. For ideal receiving antenna with an isotropic area of a meter square that for that one collecting power is represented by pr watts is given by pr is equal to f into a that's unit is watts. Energy incident on the aperture is reflected away from the antenna and some energy is absorbed by the lossy compress. Therefore, the this radiation inefficiency is described by using the effective aperture a e is equal to n is the aperture efficiency of the antenna that is value from 50 to 75 percentage and air is a physical receiving area. Thus the power received by an real antenna is pr is equal to PT gta divided by 4 pi r square that's unit is receiving power is watts. Now here if we know the PT gt means airp a and 4 pi r square this above equation if you observe this equation is independent of the frequency. Therefore, the power received at an earth station depends only on the airp of the satellite means the product of PT gt the effective area of the earth station antenna and the distance r. The gain and area of an antenna are related by gt is equal to 4 pi a divided by lambda square where lambda is the wavelength in meters at the frequency of operation. Now substitute for this a from equation 7 into equation 6 we get pr is equal to PT gt gr divided by 4 pi r by lambda square. Now this equation 8 is known as the link equation. Now collecting the various factors we can write that equation it as power received is equal to product of airp and receiving antenna gain divided by the path loss divided by the path loss that is in watts. Now above equation the number equation number 9 in decibel the become as pr is equal to airp plus gr minus lp that is unit is dbw where airp is equal to 10 log base to 10 PT gt and the unit is dbw and gr is equal to 10 log 10 4 pi a divided by lambda square that unit is in db path loss lp is equal to 10 log base to 10 4 pi r lambda square and is equal to 20 log 10 4 pi r by lambda that is in db. This equation number 10 represents an idealized case in which there are no additional losses in the link. In practically equation 10 become as pr is equal to airp plus gr minus lp minus la minus lta minus lra and the unit of this pr is dbw where la is attenuation in atmosphere lta is losses associated with the transmitting antenna lra is losses associated with receiving antenna. Now you solve the problem based on this above equations the question is a satellite at a distance of 40 000 kilometer from a point on the earth surface radiates the power of 10 watt from an antenna with a gain of 17 db in the direction of the observer find the flux density at the receiving point and the power restored by antenna at this point with an effective area of 10 meter square. Now everyone pause the video and recall the equation of flux density okay. Now flux density f is equal to pt into gt divided by 4 pi r square now put the values into that equation we get the flux density. Now when we put the values then pt is 10 watt and gt we convert that db into normalized function that is we get 50 divided by 4 pi the r square we convert into kilometer into the meter square that is 40 000 kilometer we have to convert it the meter that we get 4 into 10 raise to 7 into square after the calculation we get 2.49 into 10 raise to minus 14 watt per square meter. Now another in this question we another we have to calculate the power restored by antenna at this point with an effective area of 10 meter square that we calculate with the help of the equation that is the power restored with an effective collecting area of 10 meter square is therefore p r is equal to 2.49 into 10 raise to minus 13 this one we got it by multiplying 10 to this f equation f that p r is equal to 2.49 into 10 raise to minus 13 that is unit is where to the references for this topic is thank you.