Antenna-Exp.-1.1.docx

Experiment No. 1 WAVE PROPAGATION IN A TRANSMISSION LINE DEMONSTRATING THE EFFECTS OF LOSSES, ATTENUATION, AND STANDING WAVES Course: ECE503 Group No.: 6 Group Members: ANTHONY SAGCAL PAULA ISABEL SIGNO, BRYAN TADURAN GRACE AMIEL TUPAS

Experiment No.: 1 Section: EC51FC1 Date Performed: 06/19/2017 Date Submitted: 06/23/2017 Instructor: ENGR. FRANCIS B. MALIT

1.Objectives(s): This activity aims to introduce the basic concepts of transmission line and its abnormalities and effects. This experiment will provide the students to analyze how the electrical signal propagates inside the transmission line and how it reacts to the irregularities on the line. This will also help the students to understand the concepts of characteristics impedance impedance and reflections in transmission lines. 2.Intended Learning Outcomes(ILOs): The students shall be able to: 2.1 Understand and explain the propagation of a signal in a match or non-resonating line. 2.2 Determine the effects of losses, attenuation, and dispersion, on the amplitude, frequency, and phase of a signal 2.3 Define the characteristic impedance and reflections 3.Discussion: Propagation in a Transmission Line

There are many situations in which it is desired to connect a generator (source of electrical power) to distant load (power – (power – absorbing  absorbing device). The generator usually is of high power source, as in a power station, and the load is of low power, as with in a microphone; microphone; which maybe in of low frequency. Usually the power station, is a radio transmitter. In each case a pair of conductors is required to convey the power from the generator to the load. Such a pair of conductors conductors is called a “transmission line” or to simply a ‘line’ when convenient. When a signal is applied at one end of transmission tran smission line at one end, the other end is not immediately affected. Instead the signal travels along the line with finite velocity, and reaches the load somewhat later. The potential difference between the conductors is associated with the magnetic field. Those fields interact with each other and with the line to form a guided electromagnetic wave travelling along the line. The maximum speed that a wave can have is similar to the speed of light which is 3108  m/s. In lines li nes having solid materials around the conductors the speed or propagation could be much lesser. If a sinusoidal signal is applied to the t he line, different phases of the sine-wave will be distributed in distance along the line owing to its propagation characteristics. characteristics. A complete cycle of the wave occupies a distance λ along the line which is called the wavelength. The wavelength wavelength is inversely proportional to the frequency f of the wave. They are related to the propagation velocity v using the formula v= λf .

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Attenuation and Dispersion

The flow of current in the t he conductors’ resistance gives rise to energy losses. Further losses arise due to imperfections in the isolation between conductors, such as surface leaking across insulators, known as dielectric losses. In consequence if the power of a signal is W(watts) at the sending end of the line, it may be reduced to 1/2W at some distance along the line; the same further on again it will be 1/4W. The signal is said to be attenuated. The diminution in power is exponential: the decrease is by a given factor per unit distance. In mathematical treatment of a transmission line, all the properties (velocity of propagation, attenuation, distortion of signals) are explain in terms of four f our ‘line constants’. These are: L = the inductance of line per unit distance (H/m) C = the capacitance of the line per unit distance (F/m) R = the resistance of the line per unit distance (Ω/m) G = the conductance of the line per unit distance (S/m) The line constants in fact are only constant for a particular frequency, and may vary from one frequency to another. However, the variation is not usually so rapid as to spoil the usefulness of this theory. 4.Equipment: 1 - Transmission Transmission Line Demonstrator (TLD511) 1 – Function  – Function Generator, Sine (eg Feedback VPG608) 1 – 600R  – 600R Terminator  – Links 2 – Links  – Extension Cord 1 – Extension 5.Procedure: PART A: PROPAGATION IN A TRANSMISSION LINE 1. Set the TLD511 controls as follows: i. Hold/run set to ‘run’ set to ‘8L’ ii. Line length iii. Distributed attenuation set to ‘min’ 2. Set the function generator’s output voltage to zero. The generator frequency should on a range allowing continuous variation between 2 and 0.5Hz. Set the frequency f requency to 0.75Hz. 3. Connect up the system as shown in Figure 1.1

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Figure 1.1

4. Operate the switch for ‘step input to A’ briefly until the light has appeared in the second column. Observation: All the lines lighted up from left to right until the second column but we need to hold the step input switch to A or else only a few columns of lines will light at a time. 5. Send a pulse from terminal ‘B’ to ‘A’ by operating ‘ step input to B’. Observe that the pulse disappear at the end. Why? The same can be observed when we switched the step input to B but it is reversed. 6. Change line length to 2L and raise the output voltage of the generator to give full height indication in each column. Describe the shape of the wave. It moves in a sinusoidal-like pattern and we need to set the output voltage of the function generator to 5V peak to peak. 7. Operate hold. What part of the wave is shown? All the lines will hold up except for the first one. 8. Release ‘hold’ and operate again at a different part of the input cycle: different parts of the sine wave are displayed, but always the same fraction of a wavelength. 9. Release ‘hold’ again and raise the frequency gradually to 2Hz. Point out the reduce wavelength and operate ‘hold’ again. Observation:  The wave moves faster. 10. Determine v (for TLD511) using the formula 4L m/s where L is the length in meters. Find the propagation time of the line length L. If we increase the frequency to 2Hz, the total wavelength shall be reduced.

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1. Set the TLD511 controls as follows: i. Hold/run set to ‘run’ set to ‘2L’ ii. Line length iii. Distributed attenuation set to ‘min’ 2. The generator frequency should on a range following continuous variation between 2 and 0.5 Hz. Choose a frequency about 1.75Hz. 3. Connect up the system as shown in Figure 1.2

Figure 1.2 4. Raise the generator’s output voltage to give a t ravelling sine wave display of full column amplitude. Point out that amplitude is the same at all points in the line 5. Gradually raise the distributed attenuation to the ‘max’ Observation: We need a 9V peak to peak voltage to raise the amplitude of each lines to max. The traveling pulse only reach the 9th column and the amplitude of each line decreases. 6. Reduce the frequency of the generator. Observation: The output wave becomes slower. 7. Disconnect the line connecting to the generator. Set the length to ‘8L’ Set the distributed attenuation control about mid-way. 8. Operate the ‘step input to A’ switch until the second display column lights, to produce a travelling pulse.

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10. Transfer the 600R terminator to the end ‘A’ end of the line. Operate the ‘step input to B’ switch. Observation: Observation: The amplitude moves at 2 line lights at a time in the reversed direction and the amplitude varies.

PART C: TERMINATIONS, SIMPLE CASES

1. Set the TLD511 controls as follows: i. Hold/run set to ‘run’ ii. Line length set to ‘8L’ iii. Distributed attenuation set to ‘min’ 2. Set the function generator’s output voltage to zero and its frequency to 1.5Hz. 3. Connect the equipment as shown on Figure 2.1

Figure 2.1 4. Operate the switch for ‘step input to A’ briefly until the light has appeared in the second column. A pulse, two columns as wide as in Figure 2.2, will then travel t ravel to terminal ‘B’ e nd of the line and disappear. Why? The pulse disappeared because of the 600R terminator.

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5. This time remove the terminator from ‘B’ end of the line and send a pulse from ‘A’. Observe and record the results. The light line still travel 2 columns at a time but at the end of the light line, the amplitude increased and the light lines traveled back.

Figure 2.3 6. Place a short-link short-link across the line at ‘B’ (where the 600R terminator was) and again send a pulse from ‘A’. Observe and record the results. The light lines with 2 columns of amplitude travelled from left to right except for the last line, and then the traveled back from right to left but in the negative peak amplitude.

Figure 2.4 7. Reconnect the set-up set-up of Figure 2.1. Operate the ‘step input to ‘A’ switch to send a pulse from ‘A’, then immediately operate it in the reverse direction to send a pulse from ‘B’. Record the results below. The light lines from both directions each with 2 columns of amplitude traveled towards the middle and collided with each other.

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Figure 2.5 8. Operate the ‘step input to A’ switch. Release only the switch after the signal has reached ‘B’. When the line is at rest remove the 600R terminator. Observation: All the light lines travelling with 2 columns of amplitude each lighted up and removing the 600R terminator cause the amplitude to increase and the eventually reverted back to its original amplitude. 9. Operate the ‘step input to A’ switch. Release only the switch after the reflected signal has returned to ‘A’. Observation: blank!!!!!!!!!!!!! 10. Repeat procedure 8 and 9 of part C, using short-circuit short- circuit link at termination ‘B’. Explain: blank!!!!!!!!!!!!!!!! 11. Set the line length to ‘2L’. Replace the 600R terminator at ‘B’ ( a value lower or higher than 600R) 12. Raise the function generator output to give a traveling wave of about half-scale amplitude.

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6. Observation: 7. Interpretaion: 8. Conclusion: 9. Questions and Problems: 1. Give examples of causes of attenuation.

2. Compare the reflected wave in an open, short and properly matched line? 3. Why do we need to terminate a line at its characteristic impedance? What are the effects of not doing so? 4. Why is an ordinary extension extension cord usually is not considered a transmission line, while a television antenna of the same length would be? 5. What is the relationship between the frequency and attenuation? attenuation?

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