141. An 'ion spot' on the CRT screen is caused by
A. excessive screen brightness
B. high line voltage
C. high electron velocity
D. ion bombardment of the flourescent screen

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142. Ghost images are produced on the screen of a TV receiver when
A. brightness control is misadjusted
B. contrast control is under-adjusted
C. centring magngent is misadjusted
D. both direct and reflected signals are received

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143. In the receiving aerial system, rhombic aerials are preferred because
A. they are cheaper
B. their gain is high
C. they can be installed at smaller heights
D. the large gound plane below them makes them immune to static noise

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144. In strong-signal areas, a suitable receiver antenna would be a
A. simple dipole antenna
B. Yagi or rabbit-ear antenna
C. short lead-in with a signal splitter
D. long lead-in with a booster

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145.  In fringe areas, a suitable receiving antenna would be a
A. simple dipole
B. turnstile
C. high-gain V-antenna
D. high-gain Yagi antenna with rotor

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146. For satisfactory reception in farfringe areas, it is often necessary to use
A. a CATV system
B. a MATV system
C. interference filters
D. an all-channel antenna

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147. To be most effective, a booster amplifier should be installed
A. at the antenna end of the lead-in
B. at the receiver end of the lead-in
C. half-way between the antenna and the receiver
D. between the receiver and contrast control

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