|
|
Chapter 4
1 In an FM receiver the effect of sufficient signal arriving to
start the limiter operating, thus reducing background noise, is
known as:
a. Damping.
b. Squelch.
c. De-emphasis.
d.* Quieting.
2 The specification " one microvolt to provide better than 20 dB
signal-plus-noise to noise ratio in a passband of less than 1kHz"
would refer to:
a.* Sensitivity.
b. Selectivity.
c. Stability.
d. Image rejection.
3 The ability of a receiver to extract weak signals and amplify
them to a readable level is known as the receivers’:
a.* Sensitivity.
b. Selectability.
c. Q factor.
d. Gain factor.
4 The sensitivity of a communications receiver can best be varied
by:
a. Altering the input voltage.
b.* Altering the RF gain.
c. Changing the IF frequency.
d. Adjusting the volume control.
5 The dynamic range of a receiver can be described as:
a. Its Audio output.
b. The tuning range.
c. The operating voltage.
d.* The range of signals over which it operates satisfactorily.
6 The RF stage of a receiver is used to :
a.* Improve its sensitivity.
b. Improve its selectivity.
c. Change the frequency.
d. Change the signal tone.
7 The selectivity of a receiver is mostly controlled by:
a. Gain of IF and RF stages.
b.* Bandwidth of RF and IF stages.
c. Sensitivity of RF and IF stages.
d. Stability of RF and IF stages.
8 The ability of a receiver to receive the desired signal whilst
rejecting other frequencies is known as :
a. Sensitivity.
b.* Selectivity.
c. A Tuning scale.
d. Wavelength.
9 The circuit that lowers a radio receivers’ gain as the received
signal becomes stronger is known as a:
a.* AGC.
b. Filter.
c. Smoothing choke.
d. Selector.
10 In a super heterodyne receiver intended for AM reception, what
stage combines the received radio frequencies with energy from a
local oscillator to produce an output at the receiver's
intermediate frequency?
a.* The mixer.
b. The detector.
c. The RF amplifier.
d. The AF amplifier.
11 In super heterodyne receivers the setting of the first IF is
governed by two general principles
a.* High IF gives good image rejection but low IF gives better
selectivity.
b. High IF gives good image rejection and good selectivity.
c. Low IF gives good image rejection and high IF gives good
selectivity.
d. Low IF gives good image rejection and good selectivity.
12 The function of an IF amplifier in a super heterodyne receiver
is to:
a. Improve its sensitivity.
b.* Improve its selectivity.
c. Buffer the mixer output.
d. Amplify the loudspeaker output.
13 How can the selectivity of an IF amplifier be improved?
a. Varying the supply voltage.
b. Varying its resistance.
c.* By use of a band pass filter.
d. By use of a Low-pass filter
14 The detection of a Single Side-band signal in a receiver
requires a:
a.* Carrier Insertion Oscillator.
b. Special Aerial.
c. An SSB amplifier.
d. A special transformer.
15 A super heterodyne receiver is operating with its local
oscillator on the high side of the incoming signal. If its IF is
450 kHz and it is receiving an input signal of 14100 kHz an image
will be produced:
a.* At this tuning point if a strong signal on 15000 kHz is
present.
b. Further up the tuning band if a strong signal on 15000 kHz is
present.
c. At this point if a strong signal on 13650 kHz is present.
d. Further up the tuning band if a strong signal on 13650 kHz is
present.
16 In a single conversation super heterodyne receiver with an IF
of 450 kHz a signal is received first at 12000 kHz and then again
at 12900 kHz. These two received signals are called:
a. Cross-modulation products.
b. Band spread products.
c.* Image signals.
d. De-emphasis signals.
17 The process by which a receivers’ local oscillator and mixer
resonant circuits maintain a constant IF frequency separation is
known as:
a.* Tracking.
b. Isolation.
c. Shielding.
d. Attenuation.
18 Tracking in a super heterodyne receiver is the process of
simultaneous tuning of the
a. Local Oscillator and the Beat frequency Oscillator.
b.* Local Oscillator and the mixer.
c. Local Oscillator and the Intermediate Frequency.
d. Mixer and the RF pre-amplifier.
19 The preferred circuit for resolving an SSB signal is
a.* A product detector.
b. A full wave rectifier.
c. A Colpitts oscillator.
d. A crystal oscillator.
20 The product detector is used to
a. Detect square waves.
b. Balance out noise signals.
c. Deduce unwanted feedback.
d.* Resolve SSB and CW modulation.
21 In some receivers the audio content is restructured to
accentuate the lower frequencies relative to the higher
frequencies. The extent of this effect is known as:
a. Dynamic ranging.
b. Quieting.
c.* De-emphasis.
d. Image rejection.
22 What is the purpose of the detector in a receiver?
a. To amplify the incoming signal.
b. To operate the squelch circuit.
c. To operate the on/off light.
d.* To reproduce the modulating signal.
23 Electrical Interference or reception can best be limited by
means of a:
a. Squelch circuit.
b.* Noise Limiter.
c. Isolation transformer.
d. Decoupled loudspeaker.
24 The receive facility that switches the audio circuit off in the
absence of a satisfactory signal strength is:
a. A Noise limiter.
b.* A Squelch circuit.
c. A VOX circuit.
d. An AF gain control.
25 What is an S-meter?
a. A meter used to measure sideband suppression.
b. A meter used to measure spurious emissions from a transmitter.
c.* A meter used to measure relative signal strength in a
receiver.
d. A meter used to measure solar flux.
26 The majority of commercial transceivers are designed to be
connected into an unbalanced antenna load of:
a. 2 Ohm.
b. 25 Ohm.
c.* 50 Ohm.
d. 100 Ohm.
27 A circuit which enables a receiver, tuned to one band, to
receive on another is called:
a.* A transverter.
b. A frequency multiplier.
c. An oscillator.
d. A beat frequency oscillator.
28 transverter which enables a 144Mhz signal to be received on a
28 MHz receiver will have an oscillator tuned to:
a. 28 MHz.
b* 116 MHz.
c. 144 MHz.
d. 200 MHz.
29 In order to avoid image reception on VHF receivers they
normally have
a. Low IF frequencies.
b. Crystal controlled local oscillators.
c. A stable BFO.
d.* High IF frequencies.
30 A dual conversion receiver contains:
a.* Two IF amplifiers of different frequencies.
b. Two RF pre-amplifiers.
c. Stereo audio circuits.
d. Two antenna connections.
31 The output from a direct conversion receiver is the difference
in frequency between:
a. The BFO and the incoming signal.
b. The BFO and the local oscillator.
c. The mixer and IF frequencies.
d.* The incoming signal and the local oscillator.
32 Radio transmitters must:
a. Provide the output power required.
b. Not drift in frequency.
c. Generally be capable of multi band operation.
d.* All of the above.
33 An RF power amplifier in a transmitter provides:
a.* The signal to be connected to an antenna.
b. The audio output signal.
c. The signal to detect an incoming signal.
d. Voltages to stabilize the internal oscillators.
34 The RF Power amplifier in a transmitter is usually tuned to
the:
a. Local oscillator frequency.
b. The BFO frequency.
c.* The transmitter output frequency.
d. The modulation frequency.
35 A frequency doubler stage of a transmitter has:
a. Neutralization circuitry to prevent self-oscillation.
b. Two frequencies fed to the input.
c. No effect on deviation of a frequency modulated input signal.
d.* Its output tuned circuit resonant at twice the input
frequency.
36 The advantage gained by using push-pull operation rather than
parallel operation of valves or transistors in an RF power
amplifier is that:
a. Crossover distortion is avoided.
b.* Devices only conduct during a single half cycle.
c. Individual parasitic chokes would be needed.
d. No harmonic distortion is created.
37 The frequency of a SSB signal may be changed using:
a.* A heterodyne mixer.
b. A frequency multiplier.
c. An untuned buffer.
d. A harmonic amplifier.
38 A 9 MHz lower sideband signal from an SSB exciter is mixed with
a 5 MHz signal from a VFO. The output should be:
a. Upper sideband on 14 MHz.
b. Lower sideband on 45 MHz.
c.* Lower sideband on 14 MHz.
d. Upper sideband on 3.5 MHz.
39 Frequency multiplication is often used in UHF transmitters.
This is commonly achieved by applying RF power to diodes and tuned
circuits. Such a device is a:
a.* Varactor multiplier.
b. Heterodyne mixer.
c. Diode detector.
d. Power amplifier.
40 The basic RF source for a transmitter is the:
a.* Variable Frequency Oscillator.
b. Beat Frequency Oscillator.
c. IF Amplifier.
d. PA Amplifier.
41 The circuit forming the basis of a frequency synthesizer is a :
a.* Phase locked loop.
b. Automatic Gain Control.
c. Beat Frequency Oscillator.
d. Power Amplifier.
42 A VFO in a transmitter should ideally be followed by:
a. A volume control.
b. A band switch.
c.* A buffer amplifier.
d. A RF amplifier.
43 To maintain a stable VCO output frequency from a synthesizer,
the control voltage fed to the oscillator must be derived from :
a. A varicap diode.
b.* A phase comparator.
c. A fixed voltage regulator.
d. A voltage divider.
44 What is the process called which alters the amplitude, phase or
frequency of a radio frequency wave for the purpose of conveying
information ?
a. Alternating.
b. Micro phonics.
c. Rectifying.
d.* Modulation.
45 The process of extracting information contained in a RF or IF
carrier frequency signal is called:
a. Delineation.
b. Degeneration.
c. Decoupling.
d.* Demodulation.
46 What does suppressing the carrier in an AM signal change the
emission type to?
a. Single-sideband suppressed carrier.
b.* Double-sideband suppressed carrier.
c. Frequency modulation.
d. Phase modulation.
47 What is one advantage of double-sideband suppressed-carrier
transmission over standard full-carrier AM?
a. Only half the bandwidth is required for the same information
content.
b. Greater modulation percentage is obtainable with lower
distortion.
c.* The transmitter is more energy-efficient.
d. Simpler equipment can be used to receive a double-sideband
suppressed-carrier signal.
48 A Class C frequency multiplier stage is unsuitable for raising
the frequency of an SSB signal because of:
a. Impedance mismatch.
b.* Severe distortion.
c. Lack of a carrier.
d. Untuned output circuits.
49 What type of emission is produced by a radiotelephone
transmitter that uses a balanced modulator followed by a 2.5 kHz
band pass filter?
a. PM.
b. AM.
c.* SSB.
d. FM.
50 What signal component appears in the center of an amplitude
modulated transmitter's emitted bandwidth?
a. The lower sidebands.
b. The sub carrier.
c.* The carrier.
d. The pilot tone.
51 In a frequency modulated signal, deviations from the carrier
frequency depend on:
a.* Amplitude of the audio signal.
b. Ratio of amplitude to frequency of the audio signal.
c. Frequency of the audio signal.
d. Frequency of the original carrier signal.
52 Generation of a frequency modulated signal can be achieved
using a :
a. Low level amplitude modulator.
b. A frequency discriminator.
c.* Reactance modulator.
d. Balanced modulator.
53 In producing a narrow-band frequency modulated signal the audio
peak amplitude and frequency bandwidth should be restricted to
prevent transmitted signals with excessive bandwidth. This is
usually achieved using:
a. A crystal filter in the multiplier chain.
b.* An audio clipper and low pass filter.
c. A low voltage on the reactance modulator.
d. A step down microphone transformer.
54 What sideband frequencies will be generated by an am
transmitter having a carrier frequency of 7250 kHz when it is
modulated less than 100 percent by an 800 Hz pure sine wave?
a. 7250.8 kHz and 7251.6 kHz.
b. 7250.0 kHz and 7250.8 kHz.
c.* 7249.2 kHz and 7250.8 kHz.
d. 7248.4 kHz and 7249.2 kHz.
55 Limiters are important in FM receivers since:
a. Discriminators will cross-modulate with AM.
b.* Noise received is essentially AM.
c. FM circuits do not derive AGC from the limiter.
d. They provide an automatic squelch circuit.
56 The suppression of the carrier wave and one sideband in a
transmission is known as:
a. Amplitude Modulation.
b. Frequency Modulation.
c.* Single side-band modulation.
d. Double side-band modulation.
57 What determines the bandwidth occupied by each group of
sideband frequencies generated by a correctly operating amplitude
modulated transmitter?
a.* The audio frequencies used to modulate the transmitter.
b. The phase angle between the audio and radio frequencies being
mixed.
c. The radio frequencies used in the transmitter's VFO.
d. The CW keying speed.
58 The term Narrow Band FM modulation usually refers to a signal
of:
a.* +/- 2,5 kHz deviation.
b. 75 kHz deviation.
c. Low power levels.
d. Very stable frequency.
59 The bandwidth of an AM transmission should not exceed:
a. 10 KHz.
b. 20 KHz.
c. Ultrasonic frequencies.
d.* 5 to 6 KHz.
60 When the modulation signal reduces the amplitude of modulated
wave to zero, this represents:
a. 50 % modulation.
b. 200% modulation.
c.* 100% modulation.
d. Over modulation.
61 The switching on and off by a Morse key of a transmitter to
produce different lengths of carrier pulses is called:
a. Current Injection.
b.* Keying.
c. Demodulation.
d. Rectification.
62 Keying of a transmitter could cause sparking on the contacts of
the key switch, therefore:
a. Only a high power circuit should be keyed.
b. Only an oscillator should be keyed.
c.* It should only take place at a point where the power or
current is at a minimum.
d. Only the antenna should be keyed.
63 CW, SSB FM and AM are all types of:
a. Time measurement.
b.* Carrier modulation.
c. Radio Waves.
d. Amateur Licenses.
64 What is the approximate dc input power to a Class B power
amplifier stage in a transmitter when the emission is F3 and the
PEP is 1500 watts?
a.* Approximately 900 watts.
b. Approximately 1765 watts.
c. Approximately 2500 watts.
d. Approximately 3000 watts.
65 What result might be expected when using a single-sideband
transmitter even with a properly-adjusted speech processor?
a. A lower plate-current reading.
b.* A less natural-sounding voice.
c. A cooler operating power supply.
d. Greater PEP output.
66 The effective power of a 100% modulated carrier is:
a. Half the unmodulated carrier wave power.
b. Always equal to the unmodulated carrier wave power.
c.* 1.5 times the unmodulated carrier wave power.
d. Twice the unmodulated carrier wave power.
67 To 100% AM modulate a 150W DC input power RF amplifier the
audio power required would be:
a.* 75 Watt.
b. 100 Watt.
c. 150 Watt.
d. 15 Watt.
68 Morse code transmissions without a modulating audio frequency
are classified by the mode:
a. A1.
b.* A1A.
c. CW1.
d. A3E.
69 Single side-band suppressed carrier transmissions are
classified by the mode:
a. A3E.
b.* J3E.
c. A1A.
d. F1A.
70 Adjustment of a transmitter should always be carried out:
a. Wearing rubber gloves.
b.* Using a dummy load.
c. Without an antenna.
d. With the power switched off.
71 The ripple frequency appearing at the output of an AC-fed power
supply using a full wave rectifier will be:
a.* Twice the input frequency.
b. Half the input frequency.
c. The same as the input frequency.
d. Dependent on the number of rectifier diodes.
72 To obtain a full-wave rectified output from a transformer using
two diodes the transformer must be:
a. An isolation transformer.
b. A step-down transformer.
c.* Centre tapped on the secondary winding.
d. Earthed.
73 A circuit which only allows half of an AC waveform to pass
through is called:
a. A regulator.
b. A bridge circuit.
c. An attenuator.
d.* A half wave rectifier.
74 Diodes are devices which can be used directly:
a. To smooth the output ripple on a power supply.
b. To remove the noise on a power supply line.
c.* To rectify an AC waveform to a DC voltage.
d. To amplify weak signals in an amplifier.
75 A four diode circuit to produce full-wave rectified DC from a
transformer is called:
a. A balanced circuit.
b.* A bridge rectifier.
c. A dummy load.
d. A regulator.
76 By introducing a smoothing capacitor and an inductor in a power
supply output:
a. The output voltage will increase.
b. The load can be increased.
c. The output voltage will be regulated.
d.* The ripple will be reduced.
77 A smoothing circuit using an inductor and capacitor is a
standard:
a.* Low pass filter.
b. Voltage regulator.
c. Rectifier.
d. Discriminator.
78 A voltage regulator in a power supply:
a. Introduces a continuous ripple signal.
b. Allows large currents to be supplied.
c. Protects connected loads from short circuits.
d.* Stabilizes the output voltage of the power supply.
79 A zener diode is used in a power supply to:
a.* Stabilize a reference voltage.
b. Load an output circuit.
c. Introduce a noise signal.
d. Prevent excessive current flow.
80 An advantage of a switch mode power supply is:
a. It is free of noise.
b. It has no active components.
c.* The loss of power in the regulator is low.
d. It has a larger transformer.
|
|
|
