Deck 26: Audio System Operation and Diagnosis

Question 1

Technician A says that a radio can receive AM signals, but not FM signals, if the antenna is defective. Technician B says that a good antenna should give a reading of about 500 ohms when tested with an ohmmeter between the center antenna wire and ground. Which technician is correct?

A) Technician A only
B) Technician B only
C) Both Technicians A and B
D) Neither Technician A nor B

Answer 1

A defective antenna substantial affects amplitude modulation (AM) signals and can partially affect the frequency modulation (FM) signals having short wavelength.
An ohm-meter should read infinite between the center antenna wire and ground.
Hence, neither the statement of technician A nor the statement of technician B is correct.
Thus, the correct option is,
.

Question 2

Why do AM signals travel farther than FM signals?

Answer 2

Frequency modulation ( FM ) signals with variable radio frequency can travel along a straight line, and possesses short wavelength. The FM signals can travel a short distance from a transmitter to a receiver, and cannot be reflected from the ionosphere or upper atmosphere as like as an amplitude modulation ( AM ) signal.
The travel path of a FM signal as well as reflected AM signal is represented in Figure 1:
Figure 1
In comparison to the FM signals the AM signals can be rebound from the ionosphere to obtain the maximum travel distance from the signal transmitter to the signal receiver. The amplitude of the signal is varied and transmitted in the form of AM waves, and thus the AM signals travel longer than the FM signals.

Question 3

An antenna lead-in wire should have how many ohms of resistance between the center terminal and the grounded outer covering?

A) Less than 5 ohms
B) 5 to 50 ohms
C) 300 to 500 ohms
D) Infinity (OL)

Answer 3

A connection of the grounded outer covering to the center antenna lead is represented in Figure 1:
Figure 1
An antenna case should be properly grounded to the vehicle body to form a grounded outer covering, and an infinite resistance should exist between the center antenna lead and grounded outer covering for increasing the performance efficiency of the antenna.
Thus, the option
is selected.

Question 4

What are the purpose and function of the ground plane?

Question 5

Technician A says that a braided ground wire is best to use for audio equipment to help reduce interference. Technician B says to use insulated 14 gauge or larger ground wire to reduce interference. Which technician is correct?

A) Technician A only
B) Technician B only
C) Both Technicians A and B
D) Neither Technician A nor B

Question 6

How do you match the impedance of speakers?

Question 7

What maintenance should be performed to a power antenna to help keep it working correctly?

A) Remove it from the vehicle and lubricate the gears and cable.
B) Clean the mast with a soft cloth and lubricate with a light oil.
C) Disassemble the mast and pack the mast with silicone grease (or equal).
D) Loosen and then retighten the retaining nut.

Question 8

What two items may need to be added to the wiring of a vehicle to control or reduce radio noise?

Question 9

If twO₄ohm speakers are connected in parallel, meaning positive (+) to positive (+) and negative (-) to negative (-), the total impedance will be _______.

A) 8 ohms
B) 4 ohms
C) 2 ohms
D) 1 ohm

Question 10

If twO₄ohm speakers are connected in series, meaning the positive (+) of one speaker connected to the negative (-) of the other speaker, the total impedance will be _______.

A) 8 ohms
B) 4 ohms
C) 5 ohms
D) 1 ohm

Question 11

An aftermarket satellite radio has poor reception. Technician A says that a lack of a proper ground plane on the antenna could be the cause. Technician B says that mountains or tall buildings can interfere with reception. Which technician is correct?

A) Technician A only
B) Technician B only
C) Both Technicians A and B
D) Neither Technician A nor B

Question 12

100,000 ?F means ________.

A) 0.10 farad
B) 0.01 farad
C) 0.001 farad
D) 0.0001 farad

Question 13

A radio choke is actually a _______.

A) Resistor
B) Capacitor
C) Coil (inductor)
D) Transistor

Question 14

What device passes AC interference to ground and blocks DC voltage, and is used to control radio interference?

A) Resistor
B) Capacitor
C) Coil (inductor)
D) Transistor