0
1
00:00:01,110 --> 00:00:03,690
In the same way we use decibels for power ratio.
1

2
00:00:04,020 --> 00:00:06,660
We're going to use decibels for the power value itself.
2

3
00:00:07,290 --> 00:00:08,940
The unit is dBm.
3

4
00:00:09,810 --> 00:00:15,660
When we speak about power in decimal, we use the value compared to one milliwatts, and that's where
4

5
00:00:15,660 --> 00:00:17,160
the name dBm comes from.
5

6
00:00:17,520 --> 00:00:19,110
The m stands for 
6

7
00:00:19,110 --> 00:00:19,410
milliwatt.
7

8
00:00:20,010 --> 00:00:22,920
That means that if we have a power of 1 mW.
8

9
00:00:23,370 --> 00:00:24,180
What's 1 mW
9

10
00:00:24,180 --> 00:00:25,410
in relation to 
10

11
00:00:25,410 --> 00:00:25,890
1 mW?
11

12
00:00:26,070 --> 00:00:26,730
It's equal.
12

13
00:00:27,330 --> 00:00:28,920
So we have 0 dBm.
13

14
00:00:29,640 --> 00:00:34,500
If we have two milliwatts. What's 2 mW in comparison to 1 mW?
14

15
00:00:34,950 --> 00:00:36,180
It's multiplied by two.
15

16
00:00:36,810 --> 00:00:44,190
So we have 3 dBm, and if we have a multiplication by ten, so ten milliwatts then the power
16

17
00:00:44,190 --> 00:00:47,850
is 10 dBm and we have exactly the same operation
17

18
00:00:47,850 --> 00:00:51,450
for values below 1 mW. If we divide by two?
18

19
00:00:51,450 --> 00:01:00,750
So 0.5 mW we have minus 3 dBm. And if we divide by ten, so 0.1 mW, we have minus
19

20
00:01:00,750 --> 00:01:01,560
-10 dBm.
20

21
00:01:02,280 --> 00:01:03,780
So let's take an example.
21

22
00:01:04,290 --> 00:01:09,930
We'll use the example of the Walkie-Talkie, which has a transmission power of 2 W, and we tried
22

23
00:01:09,930 --> 00:01:13,470
to find a transmission power in dBm.
23

24
00:01:13,770 --> 00:01:16,110
For that, we just have to compare this value to 1 mW.
24

25
00:01:16,110 --> 00:01:18,750
To what is 1 mW
25

26
00:01:18,750 --> 00:01:27,210
multiplied by ten, ten, ten, which makes 1000 and I multiply it again by two, which gives
26

27
00:01:27,210 --> 00:01:29,400
2W.
27

28
00:01:29,640 --> 00:01:39,810
Now what's the value in dBm ? 1 mW is 0 dBm and multiplication by ten gives each time 10 dBm and
28

29
00:01:39,840 --> 00:01:42,300
the multiplication by two gives 3 dBm.
29

30
00:01:43,050 --> 00:01:50,370
So the transmission power of the Walkie-Talkie is therefore 33 dBm. Now that we've understood how decibels
30

31
00:01:50,370 --> 00:01:50,730
work.
31

32
00:01:50,940 --> 00:01:56,190
We can study a LoRa transmission and verify if the values representing this transmission are interesting
32

33
00:01:56,190 --> 00:01:57,120
for long range.
33

34
00:01:57,750 --> 00:01:59,670
That's what we're going to do in the next video.