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Advanced trial exam
The approximate forward bias value for a germanium transistor is
0.2 volt
0.6 volt
0.9 volt
1 volt
To convert microfarads to nanofarads requires
multiplication by 1,000
division by 1,000
multiplication by 10,000
division by 10,000
RF radiation from transmitting equipment
increases in danger with increase in frequency
can cause tissue damage in the short term
can cause cumulative eye damage
all of the above
The frequency of an electromagnetic wave which has a single cycle duration of 2.25 nanoseconds is approximately
28MHz
54MHz
144MHz
444MHz
In satellite communications, Doppler effect causes an apparent
frequency increase as the satellite moves towards the ground station
frequency decrease as the satellite moves towards the ground station
frequency doubling at the point of closest approach
frequency increase as the satellite moves away from the ground station
The standard colour code used to identify the earth conductor of a flexible 3-core AC power cord is
green/yellow
red/yellow
brown
blue
A half wave dipole antenna resonant at 28 MHz, would have an approximate length of
5 metres
10 metres
38 metres
56 metres
A single side band transmitter could cause interference to stations on adjacent frequencies if it
had shorted turns in the tank coil
had ripple on the power supply
had leakage of RF into the mains cable
was overdriven
The depth of modulation of a transmitter may easily be monitored by means of an oscilloscope. The following displays, from left to right, show approximate modulation percentages of
0% 100% over 100%
30% 100% over 100%
80% 0% -10%
60% 0% 10%
When tuning a mobile antenna the test instrument being used to measure the amount of RF radiated is a
noise bridge
antenna impedance meter
field strength meter
digital frequency meter
The term "horizontally polarised electromagnetic wave" refers to a wave in which the
magnetic component oscillates vertically
electric component oscillates vertically
magnetic component has been eliminated
electric component has been eliminated
If the voltage across a resistor is tripled the power dissipated is multiplied by
2
3
4
9
A 120 watts 21.1 MHz frequency shift keyed radioteletype transmitter has a duty cycle of
1
2
3
4
The sensitivity of a meter with a full scale deflection (FSD) of 300V and an internal resistance of 300,000 ohms is
100 ohms/volt
300 ohms/volt
1,000 ohms/volt
3,000 ohms/volt
An unterminated long wire "V" beam antenna has a radiation pattern which is
omnidirectional
bidirectional
dependent on the ionosphere
unidirectional
A semiconductor has
very high resistance
high conductivity
less conductivity than an insulator
greater conductivity than an insulator
Filter capacitors in power supplies are sometimes connected in series to
resonate the filter circuit
increase the total capacity
reduce the ripple voltage further
withstand a greater voltage than a single capacitor
This block diagram represents a
balanced modulator
discriminator
PLL synthesizer
triple conversion superheterodyne receiver
Which of the following statements is incorrect in relation to a full wave bridge rectifier circuit
its transformer does not require a centre tap
the circuit requires two diodes
all diodes conduct at the same time
the output ripple frequency is 100Hz
To increase the efficiency of a simple electromechanical relay the relay coil (motor) is wound on
aluminium
soft iron
ceramic
lead
The bias used in this amplifier circuit is
fixed bias
grid leak bias
cathode bias
combination bias
The voltage across terminals A, B is
0 volts
3 volts
6 volts
10 volts
The time constant of a 500 microhenry inductor and a 50 ohm resistance is
0.2 microsecond
5 microseconds
10 microseconds
125 microseconds
The maximum frequency deviation in an FM transmitter is 3000Hz. The modulation index, when the highest modulating audio frequency is 1000Hz is
0.3
1
3
30
A pi-coupling network used at the output of the final power amplifier stage in a transmitter
doubles the output frequency and improves neutralisation
suppresses parasitic oscillations and enhances spurious sidebands
matches the P.A. output impedance to the antenna load and suppresses harmonics
enables a half-wave dipole antenna to be voltage fed at
When comparing series and switching voltage regulators, the major disadvantage of the series regulator is its
higher power dissipation
difficulty in adjustment
lower power dissipation
instability
The total effective capacitance of this circuit is
400 picofarads
800 picofarads
200 picofarads
3200 picofarads
A 10.7MHz first stage IF is commonly used in VHF receivers to
provide a high degree of adjacent channel selectivity
reduce noise generated in the receiver
achieve the high gain required
provide an adequate degree of image rejection
Interference seen as "cross-hatching" on a TV screen occurs when
the front end is overloaded
harmonics of an amateur transmission beat with the sound carrier
an SSB signal is demodulated by the TV set
an interfering carrier signal beats with the picture carrier
The three electrodes of the Silicon Controlled Rectifier (SCR) are
source, emitter and base
anode, cathode and grid
anode, cathode and gate
source, drain and gate
Critical frequency is defined as
the highest frequency on which it is possible to communicate with another station
the highest frequency at which waves sent vertically are returned to earth
the frequency of the greatest skip distance
the highest frequency with which a station may be contacted by ground wave
The AGC system in an AM receiver works by sampling the level of the
carrier
modulation
frequency
deviation
A five-eighth wave length antenna is made with a loading coil at its base to make the antenna electrically three-quarters of a wavelength long. The reason for the antenna being electrically three-quarters of a wavelength long is to
allow for easy matching to a 50 ohm transmission line
increase the radiation angle
decrease the radiation angle
increase the bandwidth of the antenna
Tropospheric ducting may
cause high frequency signals to fade suddenly
allow long distance VHF communications
occur as a result of meteor showers or auroral activity
occur more frequently at HF than at VHF
In an SSB transmitter the balanced modulator suppresses
both sidebands
the carrier an one sideband
one side band
the carrier
On entry to a power supply the active lead of the mains should be connected to a
indicator lamp
filter capacitor
transformer
fuse
An oscillator that slowly moves in frequency of "its own accord" is said to
over modulate
drift
have distortion
chirp
Two tone tests are done to test the
linearity of an FM transmitter
power output of a CW transmitter
linearity of an SSB transmitter
symmetry of an FSK transmitter
A capacity hat or capacitive top loading is used on a vertical antenna to
to increase the bandwidth of the antenna
make the antenna more stable in high winds
to decrease the electrical length of the antenna
to increase the electrical length of the antenna
A linear repeater station accepts
FM signals only
SSB signals onlys
SSB, FM and CW signals
RTTY signals only
The approximate wavelength of the second harmonic of a 144 MHz transmission is
1 metre
2 metres
3 metres
4 metres
In this circuit R1 dissipates 10 watts. What power is dissipated in R2?
10 watts
5 watts
2.5 watts
20 watts
A power gain of 30 dB is an equivalent power ratio of
1,000
10,000
100,000
10
The hfe or beta of a transistor is
noise figure
current gain
operating speed
breakdown voltage
Spurious emissions from a amateur transmitter may be caused by
ripple on the power supply
under modulation
oscillation of the RF power amplifier stage
the antenna being too near the ground
Image interference in a superheterodyne communications receiver is caused by an unwanted signal operating on
half the frequency to which the receiver is tuned
the same frequency as the local oscillator in a dual conversion receiver
twice the frequency to which the receiver is tuned
twice the intermediate-frequency away from the desired signal frequency
A television receiver suffers ghosting interference, a possible cure for this is to
fit a high pass filter to the receiver antenna input
change the direction of the antenna
install an RF choke to the antenna lead
use a small by-pass capacitor across the antenna
Distortion occurring in a non-linear device driven by a signal containing more than one frequency is called
frequency distortion
phase distortion
harmonic distortion
intermodulation distortion
Which of the following solid state devices has the highest input impedance?
PNP bipolar transistor
JFET
NPN bipolar transistor
MOSFET
The transistor circuit used to match a high impedance source to a low impedance is the
common emitter
common gate
emitter follower
common base
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