dBm signal minus dB
I've got a 27dBm signal that I'm going to put through a 6dB attenuator. How do I work out the resultant signal in dBm?
I've tried Googling that without any luck.
rf-power measurement math
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I've got a 27dBm signal that I'm going to put through a 6dB attenuator. How do I work out the resultant signal in dBm?
I've tried Googling that without any luck.
rf-power measurement math
New contributor
add a comment |
I've got a 27dBm signal that I'm going to put through a 6dB attenuator. How do I work out the resultant signal in dBm?
I've tried Googling that without any luck.
rf-power measurement math
New contributor
I've got a 27dBm signal that I'm going to put through a 6dB attenuator. How do I work out the resultant signal in dBm?
I've tried Googling that without any luck.
rf-power measurement math
rf-power measurement math
New contributor
New contributor
edited Dec 21 at 20:48
Mike Waters♦
2,9822634
2,9822634
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asked Dec 21 at 20:26
Chris Pavey
232
232
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2 Answers
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Decibels are all "ratios" at their core. A unitless dB is a simply a ratio of one number to another, perhaps input power relative to output power. We can also use decibels for absolute values, by fixing the denominator to a standard reference — e.g. one milliwatt in dBm. But the most convenient thing about decibels is that, although they are ratios, because they have been "logarithm"-ed, we can add and subtract them instead of having to multiply and divide.
So if you have a 27 dBm signal attenuated by 6 dB, the result will be a 21 dBm signal, since 27 minus 6 is 21.
We could have looked at this by saying "I've got a 500 mW signal which I'm going to put through an attenuator which divides signals by 3.98" and gotten a result of 125.6 mW. That's not so bad with a calculator, but a bit harder to do precisely in our head especially after we add in more links (amplifiers, antenna gain, coax/path losses, etc.) to a communications system.
I found a page dB: What is a decibel? that goes more in depth if you're interested in the underlying math. That page is in the context of audio, but the concepts are generalizeable. In fact, going beyond decibels entirely, a slide rule uses the same underlying principle to make general multiplication/division easier without an electronic calculator.
add a comment |
Think about it this way.
27 dBm means 27dB above a milliwatt.
Take 6dB away.
Now you have something that's 21 dB above a milliwatt.
Or, 21 dBm.
add a comment |
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2 Answers
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2 Answers
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Decibels are all "ratios" at their core. A unitless dB is a simply a ratio of one number to another, perhaps input power relative to output power. We can also use decibels for absolute values, by fixing the denominator to a standard reference — e.g. one milliwatt in dBm. But the most convenient thing about decibels is that, although they are ratios, because they have been "logarithm"-ed, we can add and subtract them instead of having to multiply and divide.
So if you have a 27 dBm signal attenuated by 6 dB, the result will be a 21 dBm signal, since 27 minus 6 is 21.
We could have looked at this by saying "I've got a 500 mW signal which I'm going to put through an attenuator which divides signals by 3.98" and gotten a result of 125.6 mW. That's not so bad with a calculator, but a bit harder to do precisely in our head especially after we add in more links (amplifiers, antenna gain, coax/path losses, etc.) to a communications system.
I found a page dB: What is a decibel? that goes more in depth if you're interested in the underlying math. That page is in the context of audio, but the concepts are generalizeable. In fact, going beyond decibels entirely, a slide rule uses the same underlying principle to make general multiplication/division easier without an electronic calculator.
add a comment |
Decibels are all "ratios" at their core. A unitless dB is a simply a ratio of one number to another, perhaps input power relative to output power. We can also use decibels for absolute values, by fixing the denominator to a standard reference — e.g. one milliwatt in dBm. But the most convenient thing about decibels is that, although they are ratios, because they have been "logarithm"-ed, we can add and subtract them instead of having to multiply and divide.
So if you have a 27 dBm signal attenuated by 6 dB, the result will be a 21 dBm signal, since 27 minus 6 is 21.
We could have looked at this by saying "I've got a 500 mW signal which I'm going to put through an attenuator which divides signals by 3.98" and gotten a result of 125.6 mW. That's not so bad with a calculator, but a bit harder to do precisely in our head especially after we add in more links (amplifiers, antenna gain, coax/path losses, etc.) to a communications system.
I found a page dB: What is a decibel? that goes more in depth if you're interested in the underlying math. That page is in the context of audio, but the concepts are generalizeable. In fact, going beyond decibels entirely, a slide rule uses the same underlying principle to make general multiplication/division easier without an electronic calculator.
add a comment |
Decibels are all "ratios" at their core. A unitless dB is a simply a ratio of one number to another, perhaps input power relative to output power. We can also use decibels for absolute values, by fixing the denominator to a standard reference — e.g. one milliwatt in dBm. But the most convenient thing about decibels is that, although they are ratios, because they have been "logarithm"-ed, we can add and subtract them instead of having to multiply and divide.
So if you have a 27 dBm signal attenuated by 6 dB, the result will be a 21 dBm signal, since 27 minus 6 is 21.
We could have looked at this by saying "I've got a 500 mW signal which I'm going to put through an attenuator which divides signals by 3.98" and gotten a result of 125.6 mW. That's not so bad with a calculator, but a bit harder to do precisely in our head especially after we add in more links (amplifiers, antenna gain, coax/path losses, etc.) to a communications system.
I found a page dB: What is a decibel? that goes more in depth if you're interested in the underlying math. That page is in the context of audio, but the concepts are generalizeable. In fact, going beyond decibels entirely, a slide rule uses the same underlying principle to make general multiplication/division easier without an electronic calculator.
Decibels are all "ratios" at their core. A unitless dB is a simply a ratio of one number to another, perhaps input power relative to output power. We can also use decibels for absolute values, by fixing the denominator to a standard reference — e.g. one milliwatt in dBm. But the most convenient thing about decibels is that, although they are ratios, because they have been "logarithm"-ed, we can add and subtract them instead of having to multiply and divide.
So if you have a 27 dBm signal attenuated by 6 dB, the result will be a 21 dBm signal, since 27 minus 6 is 21.
We could have looked at this by saying "I've got a 500 mW signal which I'm going to put through an attenuator which divides signals by 3.98" and gotten a result of 125.6 mW. That's not so bad with a calculator, but a bit harder to do precisely in our head especially after we add in more links (amplifiers, antenna gain, coax/path losses, etc.) to a communications system.
I found a page dB: What is a decibel? that goes more in depth if you're interested in the underlying math. That page is in the context of audio, but the concepts are generalizeable. In fact, going beyond decibels entirely, a slide rule uses the same underlying principle to make general multiplication/division easier without an electronic calculator.
edited Dec 21 at 21:36
answered Dec 21 at 21:15
natevw - AF7TB
2,4711831
2,4711831
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Think about it this way.
27 dBm means 27dB above a milliwatt.
Take 6dB away.
Now you have something that's 21 dB above a milliwatt.
Or, 21 dBm.
add a comment |
Think about it this way.
27 dBm means 27dB above a milliwatt.
Take 6dB away.
Now you have something that's 21 dB above a milliwatt.
Or, 21 dBm.
add a comment |
Think about it this way.
27 dBm means 27dB above a milliwatt.
Take 6dB away.
Now you have something that's 21 dB above a milliwatt.
Or, 21 dBm.
Think about it this way.
27 dBm means 27dB above a milliwatt.
Take 6dB away.
Now you have something that's 21 dB above a milliwatt.
Or, 21 dBm.
answered Dec 21 at 23:48
mike65535
5601316
5601316
add a comment |
add a comment |
Chris Pavey is a new contributor. Be nice, and check out our Code of Conduct.
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