Amateur radio practice exam question about voltage drop
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up vote
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down vote
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So the question is as follows:
"Your mobile HF transceiver draws 22 amperes on transmit. The
manufacturer suggester 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?"
and the options are as follows:
A) Number 8, 0.05 V per metre (0.01 V per foot)
B) Number 12, 0.11 V per metre (0.03 V per foot)
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)
I believe that the answer is option B as it is the highest voltage drop that is below .5 volts for 10 feet of cable. But the answer key states that answer C is correct.
voltage test ham-radio
edited Sep 13 at 8:14
Colin
2,3042919
asked Sep 13 at 3:25
Mohammad Ali
1837
add a comment |Â
up vote
15
down vote
favorite
1
So the question is as follows:
"Your mobile HF transceiver draws 22 amperes on transmit. The
manufacturer suggester 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?"
and the options are as follows:
A) Number 8, 0.05 V per metre (0.01 V per foot)
B) Number 12, 0.11 V per metre (0.03 V per foot)
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)
I believe that the answer is option B as it is the highest voltage drop that is below .5 volts for 10 feet of cable. But the answer key states that answer C is correct.
voltage test ham-radio
edited Sep 13 at 8:14
Colin
2,3042919
asked Sep 13 at 3:25
Mohammad Ali
1837
1
I take it, if anyone can answer, that the stated drops in the possible answers are per metre for the given load and not just per amp per meter as they would usually be stated in reference guides? - I haven't gone and looked for my guide in the library to check.
– Willtech
Sep 13 at 11:10
What exam is that? You should tell the professor that voltage drop depends on amperage. The way this is stated gives the impression of voltage drop being independant from current. Especially when you throw a trick like "distance back and forth" while dropping the important part "voltage drop is linear on current"
– Jeffrey
Sep 13 at 17:20
@Jeffrey the question states that voltage drop is related to current "Given the losses below at that current", also the exam is for an amature radio license in my country
– Mohammad Ali
Sep 13 at 23:17
add a comment |Â
up vote
15
down vote
favorite
1
up vote
15
down vote
favorite
1
1
So the question is as follows:
"Your mobile HF transceiver draws 22 amperes on transmit. The
manufacturer suggester 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?"
and the options are as follows:
A) Number 8, 0.05 V per metre (0.01 V per foot)
B) Number 12, 0.11 V per metre (0.03 V per foot)
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)
I believe that the answer is option B as it is the highest voltage drop that is below .5 volts for 10 feet of cable. But the answer key states that answer C is correct.
voltage test ham-radio
edited Sep 13 at 8:14
Colin
2,3042919
asked Sep 13 at 3:25
Mohammad Ali
1837
So the question is as follows:
"Your mobile HF transceiver draws 22 amperes on transmit. The
manufacturer suggester 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?"
and the options are as follows:
A) Number 8, 0.05 V per metre (0.01 V per foot)
B) Number 12, 0.11 V per metre (0.03 V per foot)
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)
I believe that the answer is option B as it is the highest voltage drop that is below .5 volts for 10 feet of cable. But the answer key states that answer C is correct.
voltage test ham-radio
voltage test ham-radio
edited Sep 13 at 8:14
Colin
2,3042919
asked Sep 13 at 3:25
Mohammad Ali
1837
edited Sep 13 at 8:14
Colin
2,3042919
asked Sep 13 at 3:25
Mohammad Ali
1837
edited Sep 13 at 8:14
Colin
2,3042919
edited Sep 13 at 8:14
Colin
2,3042919
edited Sep 13 at 8:14
Colin
2,3042919
2,3042919
asked Sep 13 at 3:25
Mohammad Ali
1837
asked Sep 13 at 3:25
Mohammad Ali
1837
asked Sep 13 at 3:25
Mohammad Ali
1837
1837
1
I take it, if anyone can answer, that the stated drops in the possible answers are per metre for the given load and not just per amp per meter as they would usually be stated in reference guides? - I haven't gone and looked for my guide in the library to check.
– Willtech
Sep 13 at 11:10
What exam is that? You should tell the professor that voltage drop depends on amperage. The way this is stated gives the impression of voltage drop being independant from current. Especially when you throw a trick like "distance back and forth" while dropping the important part "voltage drop is linear on current"
– Jeffrey
Sep 13 at 17:20
@Jeffrey the question states that voltage drop is related to current "Given the losses below at that current", also the exam is for an amature radio license in my country
– Mohammad Ali
Sep 13 at 23:17
add a comment |Â
1
I take it, if anyone can answer, that the stated drops in the possible answers are per metre for the given load and not just per amp per meter as they would usually be stated in reference guides? - I haven't gone and looked for my guide in the library to check.
– Willtech
Sep 13 at 11:10
What exam is that? You should tell the professor that voltage drop depends on amperage. The way this is stated gives the impression of voltage drop being independant from current. Especially when you throw a trick like "distance back and forth" while dropping the important part "voltage drop is linear on current"
– Jeffrey
Sep 13 at 17:20
@Jeffrey the question states that voltage drop is related to current "Given the losses below at that current", also the exam is for an amature radio license in my country
– Mohammad Ali
Sep 13 at 23:17
1
1
I take it, if anyone can answer, that the stated drops in the possible answers are per metre for the given load and not just per amp per meter as they would usually be stated in reference guides? - I haven't gone and looked for my guide in the library to check.
– Willtech
Sep 13 at 11:10
I take it, if anyone can answer, that the stated drops in the possible answers are per metre for the given load and not just per amp per meter as they would usually be stated in reference guides? - I haven't gone and looked for my guide in the library to check.
– Willtech
Sep 13 at 11:10
What exam is that? You should tell the professor that voltage drop depends on amperage. The way this is stated gives the impression of voltage drop being independant from current. Especially when you throw a trick like "distance back and forth" while dropping the important part "voltage drop is linear on current"
– Jeffrey
Sep 13 at 17:20
What exam is that? You should tell the professor that voltage drop depends on amperage. The way this is stated gives the impression of voltage drop being independant from current. Especially when you throw a trick like "distance back and forth" while dropping the important part "voltage drop is linear on current"
– Jeffrey
Sep 13 at 17:20
@Jeffrey the question states that voltage drop is related to current "Given the losses below at that current", also the exam is for an amature radio license in my country
– Mohammad Ali
Sep 13 at 23:17
@Jeffrey the question states that voltage drop is related to current "Given the losses below at that current", also the exam is for an amature radio license in my country
– Mohammad Ali
Sep 13 at 23:17
add a comment |Â
1 Answer
1
active
oldest
votes
up vote
24
down vote
accepted
There's 6 metres of wire. 3 metres to the radio and 3 metres back to the battery.
0.11V/m * 6m is 0.66V which is more than 0.5V.
This is one of those questions that's easy to get wrong if you haven't seen it before.
answered Sep 13 at 3:28
immibis
1,477913
2
And in real life situations, be careful of the difference between voltage drop per meter in a wire and a cable (several wires, for example two wires in a power cable).
– alephzero
Sep 13 at 10:56
3
+1. Dave Jones would call this a "trap for young players". :)
– Wossname
Sep 13 at 12:55
1
The actual test question aside, 12 gauge is pretty skinny for 22 amps, and you'd get a fair amount of heating. For household wiring, you would only ever put 20 amps or less on 12 gauge.
– Tristan
Sep 13 at 16:08
If it was continuous current then I'd agree with you but radio transmitters for Hams don't run at 100% duty. You only talk in short bursts therefore the same heating concerns don't apply as much.
– Chef Flambe
Sep 22 at 5:51
add a comment |Â
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
24
down vote
accepted
There's 6 metres of wire. 3 metres to the radio and 3 metres back to the battery.
0.11V/m * 6m is 0.66V which is more than 0.5V.
This is one of those questions that's easy to get wrong if you haven't seen it before.
answered Sep 13 at 3:28
immibis
1,477913
2
And in real life situations, be careful of the difference between voltage drop per meter in a wire and a cable (several wires, for example two wires in a power cable).
– alephzero
Sep 13 at 10:56
3
+1. Dave Jones would call this a "trap for young players". :)
– Wossname
Sep 13 at 12:55
1
The actual test question aside, 12 gauge is pretty skinny for 22 amps, and you'd get a fair amount of heating. For household wiring, you would only ever put 20 amps or less on 12 gauge.
– Tristan
Sep 13 at 16:08
If it was continuous current then I'd agree with you but radio transmitters for Hams don't run at 100% duty. You only talk in short bursts therefore the same heating concerns don't apply as much.
– Chef Flambe
Sep 22 at 5:51
add a comment |Â
up vote
24
down vote
accepted
There's 6 metres of wire. 3 metres to the radio and 3 metres back to the battery.
0.11V/m * 6m is 0.66V which is more than 0.5V.
This is one of those questions that's easy to get wrong if you haven't seen it before.
answered Sep 13 at 3:28
immibis
1,477913
2
And in real life situations, be careful of the difference between voltage drop per meter in a wire and a cable (several wires, for example two wires in a power cable).
– alephzero
Sep 13 at 10:56
3
+1. Dave Jones would call this a "trap for young players". :)
– Wossname
Sep 13 at 12:55
1
The actual test question aside, 12 gauge is pretty skinny for 22 amps, and you'd get a fair amount of heating. For household wiring, you would only ever put 20 amps or less on 12 gauge.
– Tristan
Sep 13 at 16:08
If it was continuous current then I'd agree with you but radio transmitters for Hams don't run at 100% duty. You only talk in short bursts therefore the same heating concerns don't apply as much.
– Chef Flambe
Sep 22 at 5:51
add a comment |Â
up vote
24
down vote
accepted
up vote
24
down vote
accepted
There's 6 metres of wire. 3 metres to the radio and 3 metres back to the battery.
0.11V/m * 6m is 0.66V which is more than 0.5V.
This is one of those questions that's easy to get wrong if you haven't seen it before.
answered Sep 13 at 3:28
immibis
1,477913
There's 6 metres of wire. 3 metres to the radio and 3 metres back to the battery.
0.11V/m * 6m is 0.66V which is more than 0.5V.
This is one of those questions that's easy to get wrong if you haven't seen it before.
answered Sep 13 at 3:28
immibis
1,477913
answered Sep 13 at 3:28
immibis
1,477913
answered Sep 13 at 3:28
immibis
1,477913
answered Sep 13 at 3:28
immibis
1,477913
1,477913
2
And in real life situations, be careful of the difference between voltage drop per meter in a wire and a cable (several wires, for example two wires in a power cable).
– alephzero
Sep 13 at 10:56
3
+1. Dave Jones would call this a "trap for young players". :)
– Wossname
Sep 13 at 12:55
1
The actual test question aside, 12 gauge is pretty skinny for 22 amps, and you'd get a fair amount of heating. For household wiring, you would only ever put 20 amps or less on 12 gauge.
– Tristan
Sep 13 at 16:08
If it was continuous current then I'd agree with you but radio transmitters for Hams don't run at 100% duty. You only talk in short bursts therefore the same heating concerns don't apply as much.
– Chef Flambe
Sep 22 at 5:51
add a comment |Â
2
And in real life situations, be careful of the difference between voltage drop per meter in a wire and a cable (several wires, for example two wires in a power cable).
– alephzero
Sep 13 at 10:56
3
+1. Dave Jones would call this a "trap for young players". :)
– Wossname
Sep 13 at 12:55
1
The actual test question aside, 12 gauge is pretty skinny for 22 amps, and you'd get a fair amount of heating. For household wiring, you would only ever put 20 amps or less on 12 gauge.
– Tristan
Sep 13 at 16:08
If it was continuous current then I'd agree with you but radio transmitters for Hams don't run at 100% duty. You only talk in short bursts therefore the same heating concerns don't apply as much.
– Chef Flambe
Sep 22 at 5:51
2
2
And in real life situations, be careful of the difference between voltage drop per meter in a wire and a cable (several wires, for example two wires in a power cable).
– alephzero
Sep 13 at 10:56
And in real life situations, be careful of the difference between voltage drop per meter in a wire and a cable (several wires, for example two wires in a power cable).
– alephzero
Sep 13 at 10:56
3
3
+1. Dave Jones would call this a "trap for young players". :)
– Wossname
Sep 13 at 12:55
+1. Dave Jones would call this a "trap for young players". :)
– Wossname
Sep 13 at 12:55
1
1
The actual test question aside, 12 gauge is pretty skinny for 22 amps, and you'd get a fair amount of heating. For household wiring, you would only ever put 20 amps or less on 12 gauge.
– Tristan
Sep 13 at 16:08
The actual test question aside, 12 gauge is pretty skinny for 22 amps, and you'd get a fair amount of heating. For household wiring, you would only ever put 20 amps or less on 12 gauge.
– Tristan
Sep 13 at 16:08
If it was continuous current then I'd agree with you but radio transmitters for Hams don't run at 100% duty. You only talk in short bursts therefore the same heating concerns don't apply as much.
– Chef Flambe
Sep 22 at 5:51
If it was continuous current then I'd agree with you but radio transmitters for Hams don't run at 100% duty. You only talk in short bursts therefore the same heating concerns don't apply as much.
– Chef Flambe
Sep 22 at 5:51
add a comment |Â
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1
I take it, if anyone can answer, that the stated drops in the possible answers are per metre for the given load and not just per amp per meter as they would usually be stated in reference guides? - I haven't gone and looked for my guide in the library to check.
– Willtech
Sep 13 at 11:10
What exam is that? You should tell the professor that voltage drop depends on amperage. The way this is stated gives the impression of voltage drop being independant from current. Especially when you throw a trick like "distance back and forth" while dropping the important part "voltage drop is linear on current"
– Jeffrey
Sep 13 at 17:20
@Jeffrey the question states that voltage drop is related to current "Given the losses below at that current", also the exam is for an amature radio license in my country
– Mohammad Ali
Sep 13 at 23:17