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| Mepakos:
How do i calculate dBm with these Values. R= 50Ω and 40dB |
| richard.cs:
dBm is a measure of power, dB referenced to 1 mW. Your starting information doesn't include a way to calculate power so you can't get to dBm. |
| radiolistener:
dBm means "decibel milliwatt", this is more convenient to represent power. If you have power in Watts - Pwatt, you can convert it to power in dBm: dBm = 10 * log10( Pwatt * 1000 ) = 30 + 10 * log10( Pwatt ) If you want to get power in Watts from power in dBm: Pwatt = 10^( (dBm-30)/10 ) dB is just a ratio in logarithmic scale. dBm means power ratio to 1 mW, represented in logarithmic scale. |
| radiolistener:
If you have 40 Vrms (Volts RMS) on a load with R= 50Ω, then there is a power: Pwatt = Vrms^2 / R = 40^2 / 50 = 1600 / 50 = 32 Watt dBm = 30 + 10 * log10( 32 Watt ) = 45 dBm Don't confuse RMS voltage with peak voltage, because for peak voltage power will be different. If you have 40 Vpk on a load with R= 50Ω, then there is a power: Pwatt = Vpk^2 / (2*R) = 40^2 / (2*50) = 1600 / 100 = 16 Watt dBm = 30 + 10 * log10( 16 Watt ) = 42 dBm This calculation for peak voltage is valid for a sine waveform only. This is why RMS voltage is more proper way for AC measurements. |
| Bud:
--- Quote from: Mepakos on August 02, 2019, 08:49:52 am ---How do i calculate dBm with these Values. R= 50Ω and 40dB --- End quote --- You cant calculate that from your data. dB is a measure of ratio, not an absolute value. I have two sticks in my hands, one stick is twice as long as the other. Can you tell how long my sticks are in inches ? |
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