In the same way we use decibels for power ratio. 1
We're going to use decibels for the power value itself. 2
The unit is dBm. 3
When we speak about power in decimal, we use the value compared to one milliwatts, and that's where 4
the name dBm comes from. 5
The m stands for 6
milliwatt. 7
That means that if we have a power of 1 mW. 8
What's 1 mW 9
in relation to 10
1 mW? 11
It's equal. 12
So we have 0 dBm. 13
If we have two milliwatts. What's 2 mW in comparison to 1 mW? 14
It's multiplied by two. 15
So we have 3 dBm, and if we have a multiplication by ten, so ten milliwatts then the power 16
is 10 dBm and we have exactly the same operation 17
for values below 1 mW. If we divide by two? 18
So 0.5 mW we have minus 3 dBm. And if we divide by ten, so 0.1 mW, we have minus 19
-10 dBm. 20
So let's take an example. 21
We'll use the example of the Walkie-Talkie, which has a transmission power of 2 W, and we tried 22
to find a transmission power in dBm. 23
For that, we just have to compare this value to 1 mW. 24
To what is 1 mW 25
multiplied by ten, ten, ten, which makes 1000 and I multiply it again by two, which gives 26
2W. 27
Now what's the value in dBm ? 1 mW is 0 dBm and multiplication by ten gives each time 10 dBm and 28
the multiplication by two gives 3 dBm. 29
So the transmission power of the Walkie-Talkie is therefore 33 dBm. Now that we've understood how decibels 30
work. 31
We can study a LoRa transmission and verify if the values representing this transmission are interesting 32
for long range. 33
That's what we're going to do in the next video.