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Standard trial exam
A device used to couple a co-axial transmission line to a balanced antenna is known as a
converter
feed-line
co-axial connector
balun
Parasitic oscillations are usually generated by
a frequency which is an exact multiple of the transmitted frequency
excessive drive or excitation to the power amplifier
accidental resonant frequencies in the power amplifier
a mismatch between the power amplifier and transmission line
The ability of a communication receiver to distinguish between signals that are close in frequency is known as
realiability
stability
selectivity
sensitivity
A
correctly biased
NPN transistor will conduct when
the emitter is more positive than the collector
emitter and collector are at the same potential
the collector is more positive than the emitter
emitter and base are at the same potential
The capacitive reactance of a capacitor will
fall as the applied frequency increases
remain the same at all frequencies
rises as the capacitance is increased
increases as the applied frequency increases
Resolving interference problems with neighbours requires
tell the neighbour you have a licence and can continue to transmit anyway
suggest because their equipment is unlicensed it is their problem
refer the matter instantly to a community dispute resolution centre
the exercise of diplomacy
Adjusting a tuned circuit's frequency can done by altering the DC voltage across
variable capacitor
a trimmer capacitor
a varicap
an electrolytic capacitor
Compared with an amplititude modulated signal, a single sideband signal modulated with the same audio frequency
occupies the same bandwidth
occupies approximately half the bandwidth
occupies twice the bandwidth
occupies twice the peak bandwidth
A transmitter is more likely to cause interference to TV reception when it is
100 per cent modulated
50 per cent modulated
unmodulated
over-modulated
The third harmonic of a 21.15MHz tranmission is
63.45MHz
10.57MHz
31.72MHz
42.30MHz
The radiation resistance of a half-wave dipole is about
36.6 ohms
73 ohms
146 ohms
300 ohms
Two 300 ohm resistors are connected in parallel. The total resistance is
600 ohms
300 ohms
150 ohms
200 ohms
This symbol represents a
NPN bipolar transistor
PNP bipolar transistor
N channel field effect transistor
P channel field effect transistor
A radio wave which propagates via the ionosphere is called
surface wave
sky wave
ground wave
direct wave
The unit of electrical potential difference is the
watt
volt
ohm
ampere
The highest frequency that will be reflected back to earth by the ionosphere at any given time is known as the
UHF
MUF
OWF
LUF
The velocity factor for commonly used co-axial transmission line is approximately
0.66
1.66
50
75
The purpose of AGC in superhetrodyne receivers is to
keep the local oscillator frequency constant
maintain constant power supply current drain
provide a small variation in receiver tuning
maintain a constant output level with wide input variations
A correctly biased PNP transistor will conduct when the
emitter is more negative than the collector
collector is more positive than the emitter
collector is more negative than the emitter
emitter and base are at the same potentail
In this bridge rectifier circuit, when point A is positive with respect to point B, which doides conduct?
D1 and D3
D1 and D2
D3 and D4
D2 and D4
What is the peak-inverse-voltage rating of a power-supply rectifier?
the maximum transient voltage the rectifier will handle in the conducting direction
1.4 times the AC frequency
the maximum voltage the rectifier will handle in the non-conducting direction
2.8 times the AC frequency
A Yagi beam antenna usually consists of a driven element, a reflector and additional elements called
refractors
directors
radiators
rejectors
A frequency multiplier will not oscillate because
its input and output frequencies are different
there are no tuned circuits in a frequency multiplier
its output and input frequencies are the same
transistors cannot be used as frequency multipliers
The standard color code used to identify the active conductor of a flexible 3-core AC power cable is
yellow
green
brown
blue
The main advantage of ground wave propagation is that it
reduces power requirements
requires a small antenna array
is not affected by ionospheric disturbances
has highly directional properties
In an SSB transmitter the sideband filter is normally placed
between the balanced modulator and mixer stages
in the speech amplifier stage
as close as possible to the final stage
in the variable frequency (VFO) stage
The purpose of the capacitor in this filter circuit is to
pass the low frequency
attenuate the low frequencies
bypass the high frequencies
amplify the high frequencies
To measure resistance using a moving coil meter the minimum extra componants needed are
diode and battery
resistor and battery
resistor, capacitor and diode
resistor, diode and battery
In an SSB transmitter the output from the Balanced Modulator is
one sideband and no carrier
both sidebands with a suppressed carrier
one sideband with carrier
both sidebands and no carrier
Improvement to the RF immunity of an electronic device can include
replacement of its mains power lead to industrial rather than domestic standard
the use of non-metallic adhesive tap
a high pass filter on the out of the nearby radio transmitter
use of a filter in combination with the electronic device
The best way to eliminate TV set front-end overload caused by a nearby 80, 15 and 10 metre amateur transmitter is to
use a low-pass filter on the transmitter
install a wave-trap in the TV set's feedline
install a power-line filter
use a high-pass filter on the TV receiver
The ripple frequency of a full-wave bridge rectifier is
one-half of the frequency which is rectified
equal to the frequency that is rectified
twice the frequency that is rectified
unrelated to the frequency which is rectified
To extend the range of an ammeter you should use a
resistor in parrallel with the meter
resistor in series with the meter
rectifier in series with the meter
capacitor in parallel with the meter
The approximate forward bias values for germanium and silicon diodes are
germanium 0.2 volt, silicon 0.6 volt
germanium 0.6 volt, silicon 0.2 volt
germanium 0.6 volt, silicon 1.6 volt
germanium 1.6 volt, silicon 1.6 volt
The stages in a superhetrodyne receiver which are normally tuned simultaneously are the
IF stage and detector
local oscillator and detector
RF stage and local oscillator
RF and IF stages
The most reliable amateur band for communication over a path of 160 kilometres during daytime hours is
10 metres
15 metres
20 metres
80 metres
Single sideband SSB transmissionss
occupy about twice the bandwidth of AM transmissions
contain more information than AM transmissions
occupy about half the bandwidth of AM transmissions
can also be detected by an FM receiver
If the frequency of the AC supply is increased, the current through the inductor L will
increase
decrease
remain the same
be zero
To lower the resonant frequency of an antenna requires
lengthening the antenna
centre feeding the antenna with TV ribbon
shortening the antenna
insertion of a variable capacitor
In this transmitter block diagram, the Power Amplifier
Increases the mains voltage to drive the antenna
Amplifies the audio frequency component of the signal
Amplifies the selected signal band to a suitable level
Amplifies the RF signal to a suitable level
An instrument to check whether RF power is being fed into an antenna transmission line is
a Standing Wave Radio Meter
an Antenna Tuner
dummy Load or Artificial Antenna
an ohmmeter or continuity checker
This diagram represents a
high pass filter
low pass filter
band pass filter
band stop filter
Capacitors may be connected in series to
increase the total capacitance
decrease the total reactance
decrease the voltage rating
increase the total voltage rating
Interference to home entertainment equipment can enter via
the mains power and power lead
unshielded speaker leads
RF and IF stages
all of the above
The process of mixing audio and radio frequency voltages is called
amplification
impedance matching
neutralisation
modulation
The IF stage in a superheterodyne receiver
mixes the received signal for the Detector
rejects the unwanted sideband
amplifies a fixed narrow band of frequencies
purely provides a buffer for the RF stage
When a current of 20 millamps flows through a 50 ohm resistor the voltage drop across the resistor will be
100 millivolts
10 millivolts
1 volt
10 volts
The best conductor on the following list is
iron
silver
carbon
glass
The ratio of the collector current Ic to the base current Ib of a transistor is called
resistance gain
voltage gain
power gain
current gain
Two capacitors of 400 microfarad are connected in series, their total effective capacitance is
200 microfarad
800 microfarad
400 microfarad
4,000 microfarad
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