New Zealand NZART pool, section ZLI29

Subelement ZLI

Interference and How to Fix it

Section ZLI29

Interference and Filtering

ZLI2901

Electromagnetic compatibility is

A.
two antennas facing each other
Correct Answer
B.
the ability of equipment to function satisfactorily in its own environment without introducing intolerable electromagnetic disturbances
C.
more than one relay solenoid operating simultaneously
D.
the inability of equipment to function satisfactorily together and produce tolerable electromagnetic disturbances

ZLI2901

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ZLI2902

On an amateur receiver, unwanted signals are found at every 15.625 kHz. This is probably due to

A.
a low-frequency government station
B.
a remote radar station
Correct Answer
C.
radiation from a nearby TV line oscillator
D.
none of these

ZLI2902

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ZLI2903

Narrow-band interference can be caused by

Correct Answer
A.
transmitter harmonics
B.
a neon sign
C.
a shaver motor
D.
lightning flashes

ZLI2903

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ZLI2904

Which of the following is most likely to cause broad-band continuous interference

A.
an electric blanket switch
B.
a refrigerator thermostat
C.
a microwave transmitter
Correct Answer
D.
poor commutation in an electric motor

ZLI2904

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ZLI2905

If broadband noise interference varies when it rains, the most likely cause could be from

A.
underground power cables
Correct Answer
B.
outside overhead power lines
C.
car ignitions
D.
your antenna connection

ZLI2905

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ZLI2906

Before explaining to a neighbour that the reported interference is due to a lack of immunity in the neighbour's electronic equipment

A.
disconnect all your equipment from their power sources
B.
write a letter to the MBIE
Correct Answer
C.
make sure that there is no interference on your own domestic equipment
D.
ignore all complaints and take no action

ZLI2906

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ZLI2907

A neighbour's stereo system is suffering RF break-through. One possible cure is to

A.
put a ferrite bead on the transmitter output lead
B.
put a capacitor across the transmitter output
C.
use open-wire feeders to the antenna
Correct Answer
D.
use screened wire for the loudspeaker leads

ZLI2907

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ZLI2908

When living in a densely-populated area, it is wise to

A.
always use maximum transmitter output power
Correct Answer
B.
use the minimum transmitter output power necessary
C.
only transmit during popular television programme times
D.
point the beam at the maximum number of television antennas

ZLI2908

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ZLI2909

When someone in the neighbourhood complains of TVI it is wise to

A.
deny all responsibility
B.
immediately blame the other equipment
C.
inform all the other neighbours
Correct Answer
D.
check your log to see if it coincides with your transmissions

ZLI2909

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ZLI2910

Cross-modulation is usually caused by

Correct Answer
A.
rectification of strong signals in overloaded stages
B.
key-clicks generated at the transmitter
C.
improper filtering in the transmitter
D.
lack of receiver sensitivity and selectivity

ZLI2910

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ZLI2911

When the signal from a transmitter overloads the audio stages of a broadcast receiver, the transmitted signal

Correct Answer
A.
can be heard irrespective of where the receiver is tuned
B.
appears only when a broadcast station is received
C.
is distorted on voice peaks
D.
appears on only one frequency

ZLI2911

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ZLI2912

Cross-modulation of a broadcast receiver by a nearby transmitter would be noticed in the receiver as

A.
a lack of signals being received
Correct Answer
B.
the undesired signal in the background of the desired signal
C.
interference only when a broadcast signal is received
D.
distortion on transmitted voice peaks

ZLI2912

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ZLI2913

Unwanted signals from a radio transmitter which cause harmful interference to other users are known as

A.
rectified signals
B.
re-radiation signals
C.
reflected signals
Correct Answer
D.
harmonic and other spurious signals

ZLI2913

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ZLI2914

To reduce harmonic output from a transmitter, the following could be put in the transmission line as close to the transmitter as possible

A.
wave trap
Correct Answer
B.
low-pass filter
C.
high-pass filter
D.
band reject filter

ZLI2914

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ZLI2915

To reduce energy from an HF transmitter getting into a television receiver, the following could be placed in the TV antenna lead as close to the TV as possible

A.
active filter
B.
low-pass filter
Correct Answer
C.
high-pass filter
D.
band reject filter

ZLI2915

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ZLI2916

A low-pass filter used to eliminate the radiation of unwanted signals is connected to the

A.
output of the balanced modulator
Correct Answer
B.
output of the amateur transmitter
C.
input of the stereo system
D.
input of the mixer stage of your SSB transmitter

ZLI2916

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ZLI2917

A band-pass filter will

A.
pass frequencies each side of a band
B.
attenuate low frequencies but not high frequencies
Correct Answer
C.
attenuate frequencies each side of a band
D.
attenuate high frequencies but not low frequencies

ZLI2917

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ZLI2918

A band-stop filter will

Correct Answer
A.
pass frequencies each side of a band
B.
stop frequencies each side of a band
C.
only allow one spot frequency through
D.
pass frequencies below 100 MHz

ZLI2918

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ZLI2919

A low-pass filter for a high frequency transmitter output would

Correct Answer
A.
attenuate frequencies above 30 MHz
B.
pass audio frequencies below 3 kHz
C.
attenuate frequencies below 30 MHz
D.
pass audio frequencies above 3 kHz

ZLI2919

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ZLI2920

Installing a low-pass filter between the transmitter and transmission line will

A.
permit higher frequency signals to pass to the antenna
B.
ensure an SWR not exceeding 2:1
C.
reduce the power output back to the legal maximum
Correct Answer
D.
permit lower frequency signals to pass to the antenna

ZLI2920

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ZLI2921

A low-pass filter may be used in an amateur radio installation

A.
to attenuate signals lower in frequency than the transmission
Correct Answer
B.
to attenuate signals higher in frequency than the transmission
C.
to boost the output power of the lower frequency transmissions
D.
to boost the power of higher frequency transmissions

ZLI2921

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ZLI2922

Television interference caused by harmonics radiated from an amateur transmitter could be eliminated by fitting

A.
a low-pass filter in the TV receiver antenna input
B.
a high-pass filter in the transmitter output
Correct Answer
C.
a low-pass filter in the transmitter output
D.
a band-pass filter to the speech amplifier

ZLI2922

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ZLI2923

A high-pass filter can be used to

A.
prevent interference to a telephone
B.
prevent overmodulation in a transmitter
Correct Answer
C.
prevent interference to a TV receiver
D.
pass a band of speech frequencies in a modulator

ZLI2923

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ZLI2924

A high-pass RF filter would normally be fitted

A.
between transmitter output and feedline
Correct Answer
B.
at the antenna terminals of a TV receiver
C.
at the Morse key or keying relay in a transmitter
D.
between microphone and speech amplifier

ZLI2924

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ZLI2925

A high-pass filter attenuates

A.
a band of frequencies in the VHF region
B.
all except a band of VHF frequencies
C.
high frequencies but not low frequencies
Correct Answer
D.
low frequencies but not high frequencies

ZLI2925

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ZLI2926

An operational amplifier connected as a filter always utilises

A.
positive feedback to reduce oscillation
Correct Answer
B.
negative feedback
C.
random feedback
D.
inductors and resistor circuits only

ZLI2926

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ZLI2927

The voltage gain of an operational amplifier at low frequencies is

Correct Answer
A.
very high but purposely reduced using circuit components
B.
very low but purposely increased using circuit components
C.
less than one
D.
undefined

ZLI2927

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ZLI2928

The input impedance of an operational amplifier is generally

Correct Answer
A.
very high
B.
very low
C.
capacitive
D.
inductive

ZLI2928

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ZLI2929

An active audio low-pass filter could be constructed using

A.
zener diodes and resistors
B.
electrolytic capacitors and resistors
Correct Answer
C.
an operational amplifier, resistors and capacitors
D.
a transformer and capacitors

ZLI2929

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ZLI2930

A filter used to attenuate a very narrow band of frequencies centred on 3.6 MHz would be called

A.
a band-pass filter
B.
a high-pass filter
C.
a low-pass filter
Correct Answer
D.
a notch filter

ZLI2930

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