% FILENAME = N26.TXT
% Transmission Lines 
% Release version 2, January 2000

%Question: 1
#26.1 Any length of transmission line may be made to appear as an infinitely 
long line by: 

shorting the line at the end 

leaving the line open at the end 

terminating the line in its characteristic impedance 

increasing the standing wave ratio above unity 

% ans 3

%Question: 2
#26.2 The characteristic impedance of a transmission line is determined by the: 

length of the line 

load placed on the line 

physical dimensions and relative positions of the conductors 

frequency at which the line is operated 

% ans 3

%Question: 3
#26.3 The characteristic impedance of a 20 metre length of transmission line is 
52 ohm. If 10 metres is cut off, the impedance will be: 

13 ohm 

26 ohm 

39 ohm 

52 ohm 

% ans 4

%Question: 4
#26.4 The following feeder is the best match to the base of a quarter wave 
ground plane antenna: 

300 ohm balanced feedline 

50 ohm coaxial cable 

75 ohm balanced feedline 

300 ohm coaxial cable 

% ans 2

%Question: 5
#26.5 The designed output impedance of the antenna socket of most modern 
transmitters is nominally: 

25 ohm 

50 ohm 

75 ohm 

100 ohm 

% ans 2

%Question: 6
#26.6 To obtain efficient transfer of power from a transmitter to an antenna, 
it is important that there is a: 

high load impedance 

low load impedance 

correct impedance match between transmitter and antenna 

high standing wave ratio 

% ans 3

%Question: 7
#26.7 A coaxial feedline is constructed from: 

a single conductor 

two parallel conductors separated by spacers 

braid and insulation around a central conductor 

braid and insulation twisted together 

% ans 3

%Question: 8
#26.8 An RF transmission line should be matched at the transmitter end to: 

prevent frequency drift 

overcome fading of the transmitted signal 

ensure that the radiated signal has the intended polarisation 

transfer maximum power to the antenna 

% ans 4

%Question: 9
#26.9 A damaged antenna or feedline attached to the output of a transmitter 
will present an incorrect load resulting in: 

the driver stage not delivering power to the final 

the output tuned circuit breaking down 

excessive heat being produced in the transmitter output stage 

loss of modulation in the transmitted signal 

% ans 3

%Question: 10 
#26.10 A result of mismatch between the power amplifier of a transmitter and 
the antenna is: 

reduced antenna radiation 

radiation of key clicks 

lower modulation percentage 

smaller DC current drain 

% ans 1

%Question: 11
#26.11 Losses occurring on a transmission line between a transmitter and 
antenna result in: 

less RF power being radiated 

a SWR of 1:1 

reflections occurring in the line 

improved transfer of RF energy to the antenna 

% ans 1

%Question: 12
#26.12 If the characteristic impedance of a feedline does not match the antenna 
input impedance then: 

standing waves are produced in the feedline 

heat is produced at the junction 

the SWR drops to 1:1 

the antenna will not radiate any signal 

% ans 1

%Question: 13
#26.13 A result of standing waves on a non-resonant transmission line is: 

maximum transfer of energy to the antenna from the transmitter 

perfect impedance match between transmitter and feedline 

reduced transfer of RF energy to the antenna 

lack of radiation from the transmission line 

% ans 3

%Question: 14 
#26.14 A quarter-wave length of 50-ohm coaxial line is shorted at one end. The 
impedance seen at the other end of the line is: 

zero 

5 ohm 

150 ohm 

infinite 

% ans 4

%Question: 15
#26.15 A switching system to use a single antenna for a separate transmitter 
and receiver should also: 

disable the unit not being used 

disconnect the antenna tuner 

ground the antenna on receive 

switch between power supplies 

% ans 1

%Question: 16
#26.16 An instrument to check whether RF power in the transmission line is 
transferred to the antenna is: 

a standing wave ratio meter 

an antenna tuner 

a dummy load 

a keying monitor 

% ans 1

%Question: 17
#26.17 This type of transmission line will exhibit the lowest loss: 

twisted flex 

coaxial cable 

open-wire feeder 

mains cable 

% ans 3

%Question: 18
#26.18 The velocity factor of a coaxial cable with solid polythene dielectric 
is about: 

0.66 

0.1 

0.8 

1.0 

% ans 1

%Question: 19
#26.19 This commonly available antenna feedline can be buried directly in the 
ground for some distance without adverse effects: 

75 ohm twinlead 

300 ohm twinlead 

600 ohm open-wire 

coaxial cable 

% ans 4

%Question: 20
#26.20 If an antenna feedline must pass near grounded metal objects, the 
following type should be used: 

75 ohm twinlead 

300 ohm twinlead 

600 ohm open-wire 

coaxial cable 

% ans 4