Lab-Report(Make-up Lab) EE381 Electrical Engineering Lab II Name:- Nand Kishor MeenaRoll No.: Y6278 Lab:-Electronics Circuit labDate of Experiment :4th April 2009 {Wednesday}Date of Submission : 31st March 2009 {Tuesday}Experiment : 4. Study of Terminated Transmission Lines Goal :To study the behavior of terminated coaxial transmission line in both frequency and time domain. Introduction : A loss less transmission line can be represented by distributed network of series inductors (L H/m) and shunt capacitors (C F/m). Two important characteristics of the transmission line are the phase velocity (v =LC1) and the characteristic impedance (Zo =CL). For coax transmission lines, these parameters are given by |.|

\|=abln2tcCF/m|.|

\|=abL ln2t where a and b are the radii of the inner and the outer conductors respectively and the coax cable is filled by a material of dielectric constant c = cocr . In this experiment we use a 15 m long RG58 coaxial cable, which has a phase velocity of about 0.7c and characteristic impedance 50 Ohm. Time Domain Response : The time domain response of a terminated transmission line is measured exciting the line by a step signal. The response at the input, measured using an oscilloscope can be used to measure the properties of the line with a known termination. This technique is known as Time Domain Reflectometry (TDR). TDR can also be used to identify the faults in the transmission line and measure the termination impedance connected at the end of a known transmission line. Frequency Domain Response : A quarter wavelength long transmission line is excited by a sinusoidal signal and the voltage at the input is measured as a function of frequency for open and short circuit termination. This measurement demonstrates the principle that a quarter wave long transmission line, also known as a quarter wave transformer, can be used as a matching element. A load impedance (ZL) can be matched to the source impedance (ZS) by using a quarter wave transmission line whose characteristic impedance is given by ZT = L SZ Z . Observation : 1.Measurement of Output Impedance of the signal source : For a step input, the following outputs were obtained

2.Measurement of Phase Velocity : For the open circuit, we have Open Circuit Response V1 (without R) = 812.5 mVV1 (with R = 50 O) = 1.578 V 50578 . 1+ o ZV*50 = 812.5 mV Zo = 47.1 O L = 14.5 m At = 150 ns Phase velocity, v = tLA2 = 1.93 108 m/s Short Circuit Response 3.Transmission Line Terminated in a Resistive Load : Time domain response a)ZL = Zo (= 50 O)

b)ZL ~ 0.5Zo (= 22 O)

c)ZL ~ 2Zo (= 100 O) For the short circuit, L = 14.5 m At = 157 ns Phase velocity, v = tLA2 = 1.85 108 m/s 4. Transmission Line with source mismatch : Time domain response of an open circuitedline a)ZS > Zo : For this a 150 O resistor is connected in series between the signal source andthe transmission line. b)ZS < Zo : For this a 22 O resistor is connected in shunt between the signal source andthe transmission line. 5.Transmission line with capacitive termination : Time domain response for C = 1nF.

6 . Capacitive obstacle in a transmission line : Another piece of transmission line (L = 10m) is added at the far end of the first transmission line. The time domain response is

Now a Capacitor (C = 1nF) is added in shunt at the junction of the two lines. The time domain response is 6.Frequency domain response of a terminated quarter wave transmission line : The frequency at which the length of the transmission line is quarter wavelength long is For open circuit, fo = 3.086 MHz, Vo = 112.5 mV (peak-to-peak) For closed circuit,fo = 3.003MHz Vo = 1.875 V (peak-to-peak) Open Circuit Short Circuit 8. Impedence Matching with a quarter wave transmission line : A 150 O impedance is connected in series with the signal source (sinusoidal). A 220 O resistor is connected to calculate the collective output impedance.

A 12 O resistor is now connected in place of 220 O resistor and the voltage is measured. The response is given as At the matching frequency(fo =3.035 MHz), the response is V1 (without R) = 921.9 mVV1 (with R = 50 O) = 1.750 V 220750 . 1+ o Z*220 = 921.9 mV Zo = 197.6 O Hence the output impedance is approximately close to 200 O. >>>>>>>>>>>>>>>>>>>>>>END>>>>>>>>>>>>>>>>>>>>>>>>>>>>>