 Hello, welcome to the session on frequencies for radio transmission and signals. At the end of this session, students will be able to understand frequencies and signals in wireless transmission. Frequency is the number of occurrences of waves that pass a fixed place in a given amount of time or the number of cycles or vibrations undergone during one unit of time by a body in a periodic motion. That is, at any point of the time at any particular place, the number of waves pass in a given time unit that usually we will measure it in seconds. At one second, the number of waves passes in a particular place, that is, the number of waves is a frequency. So if it takes for a wave to pass half second, the frequency is 2 per second, that frequency is measured in hertz, in SI unit that usually we will measure per second. So one wave is passed in a half second at a particular place. So then two waves can be passed at one second, so the frequency is 2 hertz. The frequency, the formula for the frequency is f equal to 1 by t. So this t is a time period that we are already familiar with this t, time period t, that is, the time required to pass one wave. In this case, the time period is half second and the frequency is also related to the wave length, that frequency f equal to c by lambda. C is the speed of light and lambda is the wave length of the light. The speed of light is 3 into 10 raised to 8 meter per second in vacuum. This the speed of light is different in different media. It depends upon the transmission media. This the standard value is in a vacuum. This is the frequency here we can see. So this is, these are the waves. So the amount of time required to complete one cycle is the time period t. So this completes one cycle. So this is the one cycle of the wave. So we usually consider this is the equilibrium position 0 degree. This is 90 degree. This is 180. This is 270 and 360. The one wave is completed in a 360 degree. So the time required to complete this one wave is the time period t. So the number of cycles completed in one second is the frequency. So here this is the time up to, this is the one second. This is time up to one second. So in this one second three cycles are completed, 1, 2, 3. So the frequency is 3 hertz. That number of three cycles in one second. This is the negative alternation and positive alternation. So these are called periods that is time period t. So this is time required to complete one cycle. Wave length. The wave length is the spatial period of a periodic waves. That is the distance between two identical peaks or crest. That wave length represents a repeating pattern of a traveling energy such as light or sound. While the traveling the energy that is the sound wave or light wave. This is, this represents the repeating pattern of the traveling energy. That is in the previous slide we can see. So here it is decreasing and here it is increasing. At this point again the same wave form will be repeats. So here, so the distance between these two peaks is a wavelength or the distance between these two crests is a wavelength. See here it repeats it from this point to this point. So this shape again repeats here between these two points. Similarly between the crest. So the distance between two peaks or the distance between two crests is a wavelength. And the frequency and wavelength are inversely professional to each other. We have seen in the previous formula that we have equal to c by lambda. So that frequency and the wavelength are inversely professional to each other. If the frequency increases the wavelength decreases and vice versa. Amplitude the maximum displacement or distance moved by a point on a vibrating a body or wave measured from its equilibrium position. That is, so in theoretical representation this is the wave form. This is the equilibrium position we can refer it as the height of the wave. So from the equilibrium position the displacement of the wave at point on a vibrating a body. So this is the distance moved by a node from the equilibrium position. So this is the height of this wave is the amplitude. Usually this amplitude is the this equals to the half of the length of the vibration path this is the vibration path is. So this is complete vibration path amplitude is half of the wave. The similar half of the wave equals to the height of the crest point. So this is the amplitude. Frequencies for communication. So this is the rough representation of the frequencies with a different range. And their frequencies divided into a different range and for which class it belongs to. So you can see here the frequencies taken from 300 hertz to 300 terahertz. So this is classified into different classes like very low frequency, low frequency, medium frequency, high frequency, very high frequency, ultra high frequency, super high frequency, extra high frequency. And the next range is considered at infrared rays, that UV rays that we have already familiar with those things. So here we can see the frequency range is classified into the different ranges. And here this is the wavelength of the light as the frequency increases. The wavelength decreases and vice versa. And these are the formula that already we have seen that speed of light, frequency and lambda, frequency for communication. So these frequencies are classified or categorized based upon the different applications and the transmissions and the transmission medias are also prepared based on the frequency capacities. So the LF, this is the low frequency is usually used in the submarines because the low frequency will be that in the submarine cases it need to penetrate the wall and earth surfaces. That is why the low frequencies are used in the submarines. The medium and high frequency these typically used for the radio transmissions and very high frequency and ultra high frequency ranges for mobile radios. Like the small antennas are fixed on the car and that also used for the mobile mobiles because the mobiles are also that we can use the radio anywhere. And deterministic propagation characteristics this very high frequency and low frequency will be having a deterministic propagation characteristics and these are very reliable connections. Anywhere with these frequencies those antennas can move anywhere and analog and digital TV and digital audio broadcasting, digital GSM phones and these technologies this VHF and UHF are applicable. SHF and higher for directed radio link satellite communications. So these super high frequencies used in high speed data communications like satellite communication and direct radio links. UHF to SHF these frequency ranges are used in typical for local area networks. These some systems use UHF and SHF and some systems also use the EHF for the LAN connections. The limitations of this range is the absorption of water and oxygen molecules that is that resonance frequencies. So this is the limitation of these ranges and it is these ranges frequencies are also having limitation of it depending on the weather condition that fading signal loss caused by the heavy rainfall. So we can see if there is a heavy rainfall then we cannot view the TV it will show the error. So there is information loss during at this range of frequencies during fading and the heavy rains. So this is the limitation of the UHF and SHF. Now think and write which frequency range is used in satellite communication. Now you pause the video and answer. Answer is A that VHF is used in satellite communication. Once again next question. This is the question I pause the video and answer for the question. The question is if the time it takes for a 4 waves to pass is 0.5 seconds then what is the frequency? The answer is 16 hertz because the 4 waves are passed in a 1 fourth of the second. So in one complete second the 16 waves are passed. That is why the 16 hertz is the frequency. So frequencies and regulations the ITR holds the action for new frequencies manages frequency bands worldwide. This is the international telecommunication union for radio communication. This is responsible for managing the frequencies for ease of use. That is the worldwide is divided into three reasons with the different frequency range you can see in this table for different technologies. These are the standard frequency range used throughout the worldwide. The signal represents the physical representation of data that at a particular point that function and location the signal parameters represent the data. That signals are divided into two types the continuous signal and the discrete signal or continuous time and discrete time. So the analog signals are the continuous time and continuous values. The digital signals are discrete and discrete values. These parameters we have already discussed t, f, amplitude and the phase phi. That's sinusoidal waveform for the sinusoidal waveform. The formula is that is s equal to a sin of 2 phi of t and phi. The a is amplitude, phi is frequency, t is time and phi is the angular difference between the two waveforms. So this is the analog signals and digital signals. This is the continuous signal and this is the discrete. There is on or off. These are the references. Thank you.