Uploaded October 2025 | Updated September 2026, 1 week ago
Decibels Playlist.
youtube.com/watch?v=roSyhY0Azqk&list=PLFxhgwM1F4yxLwyj39jhuWnMwRLzQDPL4
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Decibel #1. Power in dB or Watts. Why dB/dBm is Used for Power Gain & Loss Instead of Absolute Value
Decibel #1. Reason We Use Decibels (dB, dBm) Instead of Absolute Power/Watts in Communication System
Think of turning the volume knob on a stereo. The sound gets louder as you turn it, but not in a simple, linear way. Moving the knob from "1" to "2" is a small change but turning it from "9" to "10" feels like a massive, potentially ear-shattering jump.
The decibel (dB) scale operates on a similar principle. It's not a unit of sound itself (like meters for distance), but a unit for measuring ratios and comparing intensities—most commonly, the intensity of sound.
This is the most important thing to understand. The decibel scale is logarithmic, not linear.
Linear Scale: Each step is the same size. 2, 4, 6, 8, 10...
Logarithmic Scale (like dB): Each step is a multiplication. 2, 4, 8, 16, 32...
What does this mean in practice?A small increase in decibels represents a huge increase in actual physical power.
+10 dB means the sound is 10 times more intense.
+20 dB means the sound is 100 times more intense.
+30 dB means the sound is 1,000 times more intense.
Why we need to express number in Decibel?
Signals in communication have extremely wide ranges (Very very small or very very big numbers) in magnitudes which make graphical representation and relative comparison between signals very difficult.
Example
An input signal having a power level of Si = 1 x 10-12 (0.000000000001) watts and an output signal power level of So = 0.001 watts
Ratio of So / Si is equal to 109 which is 1000000000
It is very cumbersome to operate with such big numbers and is also very prone to arithmetical errors!
The Bel: The Precursor
The original unit was the Bel (B), named after Alexander Graham Bell. It is defined as the base-10 logarithm of the ratio of two powers:
Bel = log₁₀ (P₁ / P₀)
Where:
P₁ is the power you're measuring.
P₀ is your reference power.
The Bel was too large for practical use, as a 2:1 power ratio corresponds to only about 0.3 B. Consequently, the decibel (one-tenth of a Bel) was adopted as the standard.
In the context of signal detection, the decibel (dB) is not a unit of absolute power or intensity like volts or watts. Instead, it is a logarithmic ratio that compares two values. This makes it incredibly powerful for dealing with the vast range of power levels encountered in communications, audio, and electronics.
Advantages of using decibel scale
Less prone to arithmetical errors with very big / small numbers and easier relative comparison between signals
Easier calculation when comes to multistage system
1. Sound Pressure Level (dB SPL)
Reference (P₀): 20 micropascals (µPa).
What it is: This is approximately the quietest sound the average human ear can hear at 1kHz.
Usage: Measuring the intensity of sound in the air.
Examples:
0 dB SPL = Threshold of hearing.
60 dB SPL = Normal conversation.
120 dB SPL = Threshold of pain.
2. Telecommunications & Signal Strength (dBm, dBW)
dBm:
Reference Point: 1 Milliwatt (mW) = 1/1000 of a Watt.
Definition: dBm is the power level in decibels relative to 1 milliwatt.
Use Case: The most common unit for measuring signal strength in practical telecommunications equipment, like cell phones, Wi-Fi routers, and spectrum analyzers.
dBW
Reference Point: 1 Watt (W).
Definition: dBW is the power level in decibels relative to 1 Watt.
Use Case: Used for higher-power systems where using Watts is more convenient than milliwatts, such as broadcast radio/TV transmitters, satellite uplinks, and radar systems.
3. Antennas (dBi, dBd)
dBi:
Reference: The gain of an isotropic antenna (a theoretical antenna that radiates power equally in all directions).
Usage: Describing antenna gain. A 3 dBi antenna focuses power to be twice as strong as an isotropic radiator in its best direction.
dBd:
Reference: The gain of a dipole antenna.
Usage: Also for antenna gain. Since a dipole has a gain of about 2.15 dBi, dBd = dBi - 2.15.
4. Relative Measurements (Pure Ratio - dB)
Sometimes, you just want to compare two values, like the gain of an amplifier or the attenuation of a cable.
Example: An amplifier has an input of 1 watt and an output of 100 watts.
Its gain is 10 * log₁₀(100 / 1) = 20 dB.
Here, we're just using dB to express a ratio, with no external reference.
It's a Ratio, Not an Absolute Unit: Decibels always express a comparison between two values.
It's Logarithmic: This allows us to represent huge ranges with small, manageable numbers.
Decibels Playlist.
youtube.com/watch?v=roSyhY0Azqk&list=PLFxhgwM1F4yxLwyj39jhuWnMwRLzQDPL4
For access to this presentation materials, membership is required: I need the Material PPT
Sent me an email to Technologies.Discussion@gmail.com
If you need the whole playlist material, send me email and we discuss.
Give me some time to response. Thanks.
Decibel #1. Power in dB or Watts. Why dB/dBm is Used for Power Gain & Loss Instead of Absolute Value
Decibel #1. Reason We Use Decibels (dB, dBm) Instead of Absolute Power/Watts in Communication System
Think of turning the volume knob on a stereo. The sound gets louder as you turn it, but not in a simple, linear way. Moving the knob from "1" to "2" is a small change but turning it from "9" to "10" feels like a massive, potentially ear-shattering jump.
The decibel (dB) scale operates on a similar principle. It's not a unit of sound itself (like meters for distance), but a unit for measuring ratios and comparing intensities—most commonly, the intensity of sound.
This is the most important thing to understand. The decibel scale is logarithmic, not linear.
Linear Scale: Each step is the same size. 2, 4, 6, 8, 10...
Logarithmic Scale (like dB): Each step is a multiplication. 2, 4, 8, 16, 32...
What does this mean in practice?A small increase in decibels represents a huge increase in actual physical power.
+10 dB means the sound is 10 times more intense.
+20 dB means the sound is 100 times more intense.
+30 dB means the sound is 1,000 times more intense.
Why we need to express number in Decibel?
Signals in communication have extremely wide ranges (Very very small or very very big numbers) in magnitudes which make graphical representation and relative comparison between signals very difficult.
Example
An input signal having a power level of Si = 1 x 10-12 (0.000000000001) watts and an output signal power level of So = 0.001 watts
Ratio of So / Si is equal to 109 which is 1000000000
It is very cumbersome to operate with such big numbers and is also very prone to arithmetical errors!
The Bel: The Precursor
The original unit was the Bel (B), named after Alexander Graham Bell. It is defined as the base-10 logarithm of the ratio of two powers:
Bel = log₁₀ (P₁ / P₀)
Where:
P₁ is the power you're measuring.
P₀ is your reference power.
The Bel was too large for practical use, as a 2:1 power ratio corresponds to only about 0.3 B. Consequently, the decibel (one-tenth of a Bel) was adopted as the standard.
In the context of signal detection, the decibel (dB) is not a unit of absolute power or intensity like volts or watts. Instead, it is a logarithmic ratio that compares two values. This makes it incredibly powerful for dealing with the vast range of power levels encountered in communications, audio, and electronics.
Advantages of using decibel scale
Less prone to arithmetical errors with very big / small numbers and easier relative comparison between signals
Easier calculation when comes to multistage system
1. Sound Pressure Level (dB SPL)
Reference (P₀): 20 micropascals (µPa).
What it is: This is approximately the quietest sound the average human ear can hear at 1kHz.
Usage: Measuring the intensity of sound in the air.
Examples:
0 dB SPL = Threshold of hearing.
60 dB SPL = Normal conversation.
120 dB SPL = Threshold of pain.
2. Telecommunications & Signal Strength (dBm, dBW)
dBm:
Reference Point: 1 Milliwatt (mW) = 1/1000 of a Watt.
Definition: dBm is the power level in decibels relative to 1 milliwatt.
Use Case: The most common unit for measuring signal strength in practical telecommunications equipment, like cell phones, Wi-Fi routers, and spectrum analyzers.
dBW
Reference Point: 1 Watt (W).
Definition: dBW is the power level in decibels relative to 1 Watt.
Use Case: Used for higher-power systems where using Watts is more convenient than milliwatts, such as broadcast radio/TV transmitters, satellite uplinks, and radar systems.
3. Antennas (dBi, dBd)
dBi:
Reference: The gain of an isotropic antenna (a theoretical antenna that radiates power equally in all directions).
Usage: Describing antenna gain. A 3 dBi antenna focuses power to be twice as strong as an isotropic radiator in its best direction.
dBd:
Reference: The gain of a dipole antenna.
Usage: Also for antenna gain. Since a dipole has a gain of about 2.15 dBi, dBd = dBi - 2.15.
4. Relative Measurements (Pure Ratio - dB)
Sometimes, you just want to compare two values, like the gain of an amplifier or the attenuation of a cable.
Example: An amplifier has an input of 1 watt and an output of 100 watts.
Its gain is 10 * log₁₀(100 / 1) = 20 dB.
Here, we're just using dB to express a ratio, with no external reference.
It's a Ratio, Not an Absolute Unit: Decibels always express a comparison between two values.
It's Logarithmic: This allows us to represent huge ranges with small, manageable numbers.
