Canadian (from VE2AAY) Basic Qualification pool, section L09a

Subelement L09a

Power Supplies.

Section L09a

B-3-8-1

In a regulated power supply, the transformer connects to an external source which is referred to as______________.

A.
filter
B.
rectifier
Correct Answer
C.
input
D.
regulator

B-3-8-1

The external source will frequently be a wall socket where 120 volts AC is available. The blocks in a Regulated Power Supply: Input, Transformer, Rectifier, Filter, Regulator, Output.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

B-3-8-2

In a regulated power supply, the _______________ is between the input and the rectifier.

A.
regulator
B.
filter
Correct Answer
C.
transformer
D.
output

B-3-8-2

Prior to rectification with diodes, a transformer lowers or raises the voltage (to bring it closer to the desired output voltage). The blocks in a Regulated Power Supply: Input, Transformer, Rectifier, Filter, Regulator, Output.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

B-3-8-3

In a regulated power supply, the _______________ is between the transformer and the filter.

A.
output
B.
regulator
Correct Answer
C.
rectifier
D.
input

B-3-8-3

The 'Rectifier' (diodes) converts AC into 'pulsating DC' which is then smoothed out into pure DC by a 'Filter' (often simply a capacitor). The blocks in a Regulated Power Supply: Input, Transformer, Rectifier, Filter, Regulator, Output.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

B-3-8-4

In a regulated power supply, the output of the rectifier is connected to the ______________.

A.
transformer
B.
regulator
Correct Answer
C.
filter
D.
output

B-3-8-4

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

B-3-8-5

In a regulated power supply, the output of the filter connects to the ____________________.

A.
transformer
B.
rectifier
C.
output
Correct Answer
D.
regulator

B-3-8-5

The pure DC available after the 'Filter' goes through the 'Regulator' which maintains a constant output voltage regardless of input variations or load changes. The blocks in a Regulated Power Supply: Input, Transformer, Rectifier, Filter, Regulator, Output.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

B-3-8-6

In a regulated power supply, the _______________ is connected to the regulator.

A.
transformer
Correct Answer
B.
output
C.
rectifier
D.
input

B-3-8-6

The 'Output' circuitry (fuses, meters, output terminals) connects to the 'Regulator'. The blocks in a Regulated Power Supply: Input, Transformer, Rectifier, Filter, Regulator, Output.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

B-3-17-1

If your mobile transceiver works in your car but not in your home, what should you check first?

A.
The speaker
B.
The microphone
C.
The SWR meter
Correct Answer
D.
The power supply

B-3-17-1

In the car, the transceiver gets power from the car battery. In the home, a power supply provides the 12 volts DC necessary for the transceiver. From the car to the home, the prime difference is the source of voltage.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

B-3-17-2

What device converts household current to 12 volts DC?

Correct Answer
A.
A power supply
B.
A low pass filter
C.
An RS-232 interface
D.
A catalytic converter

B-3-17-2

A large percentage of modern transceivers are designed to work off 12 volts DC which is readily available from a car battery. To use a rig in the home, a 'Power Supply' is required: a 'Power Supply' combines a transformer, rectifier and filter to convert 120 volts AC down to 12 volts DC.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

B-3-17-3

Which of these usually needs a high current capacity power supply?

A.
An SWR meter
Correct Answer
B.
A transceiver
C.
An antenna switch
D.
A receiver

B-3-17-3

key words: HIGH CURRENT. Receivers rarely draw more than 1 ampere at 12 VDC. A 100 watt transceiver (while on transmit) can draw 20 amperes at 12 VDC.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

B-3-17-4

What may cause a buzzing or hum in the signal of an AC-powered transmitter?

A.
Using an antenna which is the wrong length
B.
Energy from another transmitter
C.
Bad design of the transmitter's RF power output circuit
Correct Answer
D.
A bad filter capacitor in the transmitter's power supply

B-3-17-4

key word: HUM. Remember the 'Power Supply' block diagram: a 'Rectifier' (diode) converts AC into 'pulsating DC'. A 'Filter' then turns the 'pulsating DC' into pure DC. If the 'Filter' is deficient, hum or buzzing will appear on the transmitted signal.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

B-3-17-5

A power supply is to supply DC at 12 volts at 5 amperes. The power transformer should be rated higher than:

A.
6 watts
Correct Answer
B.
60 watts
C.
17 watts
D.
2.4 watts

B-3-17-5

Power, expressed in watts = voltage, in volts, TIMES current, in amperes. P = E * I. Watts = volts * amperes.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

B-3-17-6

The diode is an important part of a simple power supply. It converts AC to DC, since it:

A.
allows electrons to flow in only one direction from anode to cathode
Correct Answer
B.
allows electrons to flow in only one direction from cathode to anode
C.
has a high resistance to AC but not to DC
D.
has a high resistance to DC but not to AC

B-3-17-6

A DIODE, vacuum tube or semiconductor, has two electrodes: Anode and Cathode. Electrons flow from Cathode to Anode in a forward-biased (i.e., a diode subjected to a voltage polarity which permits conduction) diode.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

B-3-17-7

To convert AC to pulsating DC, you could use a:

A.
resistor
Correct Answer
B.
diode
C.
transformer
D.
capacitor

B-3-17-7

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

B-3-17-8

Power-line voltages have been made standard over the years and the voltages generally supplied to homes are approximately:

A.
130 and 260 volts
Correct Answer
B.
120 and 240 volts
C.
110 and 220 volts
D.
100 and 200 volts

B-3-17-8

Nominal household voltages have slowly come up since the early 20th century from 110 V, to 115 V, to 117 V, to 120 V. The current standard is 120 V and 240 V. 240 V is used for energy-hungry devices like water heaters, clothes dryers, electric ovens AND high-power linear amplifiers.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

B-3-17-9

Your mobile HF transceiver draws 22 amperes on transmit. The manufacturer suggests limiting voltage drop to 0.5 volt and the vehicle battery is 3 metres (10 feet) away. Given the losses below at that current, which minimum wire gauge must you use?

A.
Number 12, 0.11 V per metre (0.03 V per foot)
B.
Number 8, 0.05 V per metre (0.01 V per foot)
Correct Answer
C.
Number 10, 0.07 V per metre (0.02 V per foot)
D.
Number 14, 0.19 V per metre (0.06 V per foot)

B-3-17-9

Understand that DC power is brought to the radio over a pair of wires. Each wire must not drop more than 0.25 volt (half the given value) over 3 metres. Thus, the loss per metre must be below 0.08 volt. The run must be at least number 10 gauge. Voltage drops (E = R x I) at that current were computed for you from resistance value per unit length available from wire tables. [ # 14 = 1.63 mm (0.06 in.), # 12 = 2.05 mm (0.08 in.), # 10 = 2.59 mm (0.10 in.), # 8 = 3.26 mm (0.13 in.) ]

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

B-3-17-10

Why are fuses needed as close as possible to the vehicle battery when wiring a transceiver directly to the battery?

Correct Answer
A.
To prevent an overcurrent situation from starting a fire
B.
To prevent interference to the vehicle's electronic systems
C.
To reduce the voltage drop in the radio's DC supply
D.
To protect the radio from transient voltages

B-3-17-10

A car battery can deliver a hundred amperes or more into a short circuit; the voltage drop in any current-carrying wire and such large currents produce heat (P = E x I), enough heat to melt wire insulation and other plastics which abound in cars. Fuses close to the battery ensure excessive current is interrupted regardless of where the fault occurs over the DC power line to the radio.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

B-3-17-11

You have a very loud low-frequency hum appearing on your transmission. In what part of the transmitter would you first look for the trouble?

Correct Answer
A.
The power supply
B.
The variable-frequency oscillator
C.
The driver circuit
D.
The power amplifier circuit

B-3-17-11

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

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