ECE 329
Homework 14
Due: Wed, Dec 10, 2008, 5PM
1.
a) A student desires to construct a parallel
LC
circuit that resonates (i.e., exhibits zero equivalent
admittance and behaves as a combined “open”) at 200 MHz, but she has no inductors. Therefore,
she selects a 100 pF ±xed capacitor and a 1–10 pF variable capacitor and cuts a ¼ wavelength
section of 50ohm coaxial transmission line at 200 MHz.
Find the value of variable capacitance required that when transformed through the quarter
wave line will resonate with the 100 pF ±xed cap at 200 MHz. Hint: remember that resonance
frequency (in rad/s)
ω
o
=
1
√
LC
for the
LC
ckt.
b) What is the physical length
l
(in m) of the ¼ wavelength section T.L. used in part (a), assuming
that
v
p
=
2
3
c
for the line.
c) Does the circuit built in part (a)
resonate
at frequencies other than 200 MHz? Brie²y discuss
your answer.
2. A transmission line having a characteristic impedance of 50
Ω
is terminated by a load of unknown
impedance
Z
R
. Measurements of voltage amplitude
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 Spring '08
 FRANKE
 Transmission line, Standing wave, Vin, Characteristic impedance, unknown impedance ZL

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