WEBVTT 1 00:00.000 --> 00:05.750 If our wireless signals are degrading over time, what constitutes a good signal 2 00:05.750 --> 00:07.000 or good enough signal? 3 00:07.000 --> 00:13.000 And in order to start answering that question, we have to recognize that we can 4 00:13.000 --> 00:15.000 measure our signal strength. 5 00:15.000 --> 00:20.990 We're talking about wireless signals. We need to evaluate whether a signal is 6 00:20.990 --> 00:23.000 strong enough to be read. 7 00:23.000 --> 00:26.900 And it does start with not just signal strength, but the concept of measuring 8 00:26.900 --> 00:29.000 the strength of our signals. 9 00:29.000 --> 00:35.000 A wireless waveform is sent out with a certain amount of power. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 9 00:29.000 --> 00:35.000 A wireless waveform is sent out with a certain amount of power. 10 00:35.000 --> 00:42.000 And that power is going to be measured in watts at a very high level with Wi-Fi 11 00:42.000 --> 00:46.000 , it's usually measured in milliwatts, which is a thousandth of a watt. 12 00:46.000 --> 00:53.060 So our Wi-Fi access points are wireless laptops when we're talking about Wi-Fi. 13 00:53.060 --> 00:58.000 We're typically talking about transmitting in the milliwat range. 14 00:58.000 --> 01:03.680 Furthermore, if we are transmitting at, let's say, 100 milliwatts, and it de WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 14 00:58.000 --> 01:03.680 Furthermore, if we are transmitting at, let's say, 100 milliwatts, and it de 15 01:03.680 --> 01:09.750 grades over time, but my laptop is sitting here, and it's got a really strong 16 01:09.750 --> 01:14.150 signal or whatever the situation is, we might say, "Okay, so maybe I lost a 17 01:14.150 --> 01:17.750 little bit, but I'm probably at 70 milliwatts of power, and I'm receiving that 18 01:17.750 --> 01:18.000 ." 19 01:18.000 --> 01:24.100 But what if I told you that this laptop could be saying, "Hey, I've got a great 20 01:24.100 --> 01:30.000 signal strength here, and it's receiving it at .001 milliwatts." WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 21 01:30.000 --> 01:37.000 Believe it or not, this is pretty shocking. This is considered a great signal. 22 01:37.000 --> 01:42.660 How on earth is that even possible? What is going on here? Well, wireless 23 01:42.660 --> 01:49.000 energy radiates in a, usually a three-dimensional spherical type of world here. 24 01:49.000 --> 01:53.440 I've got this transmitter in the middle, and I've got 100 milliwatts of energy 25 01:53.440 --> 01:57.000 wrapped up around the signal the moment it starts to propagate. 26 01:57.000 --> 02:03.050 But as it propagates out in 3D space, it starts to thin, again, at an WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 26 01:57.000 --> 02:03.050 But as it propagates out in 3D space, it starts to thin, again, at an 27 02:03.050 --> 02:07.000 exponential rate. It's dropping drastically. 28 02:07.000 --> 02:12.400 And yet, our wireless devices are so finely tuned that they can pick out a 29 02:12.400 --> 02:18.230 signal that is roughly, I guess that would be, let's see, that's 1/10,000, that 30 02:18.230 --> 02:24.000 's 100, roughly a millionth of the signal strength that it was propagated at. 31 02:24.000 --> 02:30.500 Actually, if I look at it, it's even a 10 millionth of it. And so either way, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 31 02:24.000 --> 02:30.500 Actually, if I look at it, it's even a 10 millionth of it. And so either way, 32 02:30.500 --> 02:34.000 we're talking about very tiny numbers here. 33 02:34.000 --> 02:38.290 Now, you and I as humans, we would have a hard time communicating this to one 34 02:38.290 --> 02:44.210 another. If I said, "Hey, I'm getting a wireless signal with .00000, 05 milli 35 02:44.210 --> 02:50.000 watts, and this other one is 00001, 2 milliwatts." 36 02:50.000 --> 02:54.190 This is very tricky for us to deal with as humans. It's just a lot of zeros, 37 02:54.190 --> 02:56.000 and it's not very readable. 38 02:56.000 --> 03:01.180 And furthermore, it's pretty clear that when we're talking about wireless WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 38 02:56.000 --> 03:01.180 And furthermore, it's pretty clear that when we're talking about wireless 39 03:01.180 --> 03:05.000 signals, that the raw number doesn't matter as much. 40 03:05.000 --> 03:09.760 In other words, yeah, 100 milliwatts is what I started at, but I'm losing so 41 03:09.760 --> 03:14.000 much signal here, and yet it's still considered to be a great signal. 42 03:14.000 --> 03:19.070 I need to somehow better represent the fact that an exponential decline is not 43 03:19.070 --> 03:21.000 necessarily a bad thing. 44 03:21.000 --> 03:26.490 I want to take my exponential decline and convert it into something a little 45 03:26.490 --> 03:28.000 bit more linear. 46 03:28.000 --> 03:34.000 And so that's exactly what we're going to use the decibel to accomplish. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 46 03:28.000 --> 03:34.000 And so that's exactly what we're going to use the decibel to accomplish. 47 03:34.000 --> 03:39.960 The decibel is a fascinating conversation. It takes us back to our high school 48 03:39.960 --> 03:43.000 math days of studying logarithms. 49 03:43.000 --> 03:47.000 And while it's fun to go back and study what exactly a decibel is and what a 50 03:47.000 --> 03:52.000 logarithm is, that is going to go beyond this gop of our conversation here. 51 03:52.000 --> 03:55.620 Essentially what we're saying is we're going to take this exponential decline 52 03:55.620 --> 03:58.000 and turn it into something a little bit more linear. 53 03:58.000 --> 04:03.990 And specifically, we're going to relate the decibel, which is itself neutral, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 53 03:58.000 --> 04:03.990 And specifically, we're going to relate the decibel, which is itself neutral, 54 04:03.990 --> 04:08.000 as far as whether you're applying it to one power reading or another. 55 04:08.000 --> 04:12.320 And so we're going to specifically say that this is in relation to the millow 56 04:12.320 --> 04:18.180 att. When we call a decibel that relates to a millowatt, a unit, we're going to 57 04:18.180 --> 04:21.000 refer to this as dbm. 58 04:21.000 --> 04:25.160 And yes, the b is capital, and yes, it's because it's named after a person. And 59 04:25.160 --> 04:27.000 in this case, Alexander Graham Bell. 60 04:27.000 --> 04:31.780 And so the b does get capitalized just like what stays capitalized because it's WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 60 04:27.000 --> 04:31.780 And so the b does get capitalized just like what stays capitalized because it's 61 04:31.780 --> 04:34.000 also named after an individual. 62 04:34.000 --> 04:38.690 Either way, when we're saying that we're going to relate this back to the mill 63 04:38.690 --> 04:43.130 owatt, what we're saying is that if we have zero dbms, since we're relating it 64 04:43.130 --> 04:49.000 to the millowatt, we're going to say that this equals one millowatt. 65 04:49.000 --> 04:54.340 Furthermore, as millowatt's increase exponentially, let's say we multiply this 66 04:54.340 --> 05:00.000 by 10, to now we're at 10 millowatt's, we're going to increase this linearly. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 67 05:00.000 --> 05:04.000 And so 10 millowatt's happens to equal 10 decibels. 68 05:04.000 --> 05:09.150 Now, at this point, it doesn't look a whole lot different. 10 equals 10, but 69 05:09.150 --> 05:13.000 zero equals one. It's not super clear until we do this again. 70 05:13.000 --> 05:18.210 What happens if I multiply by 10 again? I end up with 100 millowatt's. But 71 05:18.210 --> 05:23.290 again, this is linear where I'm multiplying on one side, I'm adding on the 72 05:23.290 --> 05:24.000 other. 73 05:24.000 --> 05:29.120 So when I'm multiplying here, I'm going to add again, and this ends up being 20 74 05:29.120 --> 05:33.000 decibels. So all of these values are equal to one another. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 74 05:29.120 --> 05:33.000 decibels. So all of these values are equal to one another. 75 05:33.000 --> 05:36.650 Now, I can't just say, hey, if I'm going to multiply it by anything, let's 76 05:36.650 --> 05:41.000 multiply it by 5 here, and then I add 5, it doesn't work that way. 77 05:41.000 --> 05:46.000 So there's actually two sets of numbers that we like to use. 78 05:46.000 --> 05:51.000 One of those is 10, because 10 and 10 match up very nicely. 79 05:51.000 --> 05:57.000 The other one is when we multiply by 2, we can increase this by 3 decibels. 80 05:57.000 --> 06:02.650 So if I were to multiply this by 2 and get 200 millowatt's, I can add 3 and say WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 80 05:57.000 --> 06:02.650 So if I were to multiply this by 2 and get 200 millowatt's, I can add 3 and say 81 06:02.650 --> 06:06.000 that this equals 23 decibels. 82 06:06.000 --> 06:11.150 So this is the rule of 3's and the rule of 10's. If I'm going to increase by 10 83 06:11.150 --> 06:14.000 , I have to multiply the millowatt's by 10. 84 06:14.000 --> 06:19.000 If I'm going to increase decibel by 3, I have to multiply the millowatt's by 2. 85 06:19.000 --> 06:23.000 So yes, it is 3 and 2, so we have to keep that in mind. 86 06:23.000 --> 06:28.410 Furthermore, if I end up going negative, let's say I want to subtract 3 deci 87 06:28.410 --> 06:31.000 bels, then indeed I would divide. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 87 06:28.410 --> 06:31.000 bels, then indeed I would divide. 88 06:31.000 --> 06:37.110 So back down to 20 decibels, from 23, I subtract 3, that means I have to take 89 06:37.110 --> 06:43.000 200 and divide it by 2, and I'm back down to 100 millowatt's. 90 06:43.000 --> 06:47.640 I can do the same thing by subtracting 10 and dividing by 10, and we'll look at 91 06:47.640 --> 06:49.000 some examples here. 92 06:49.000 --> 06:51.000 So in fact, let's just dive right into those. 93 06:51.000 --> 07:01.000 So let's start with some calculations and we will look at 30 dBm. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 93 06:51.000 --> 07:01.000 So let's start with some calculations and we will look at 30 dBm. 94 07:01.000 --> 07:06.000 So 30 dBm equals how many millowatt's? 95 07:06.000 --> 07:10.960 Well, we have to have a starting point, and our starting point is always going 96 07:10.960 --> 07:14.000 to be right here. 0 dBm equals 1 millowatt. 97 07:14.000 --> 07:21.100 So if we're going to say that 0 dBm equals 1 millowatt, now I just have to get 98 07:21.100 --> 07:23.000 0 up to 30. 99 07:23.000 --> 07:25.000 So how do I get 0 up to 30? 100 07:25.000 --> 07:31.080 And again, especially considering I want to work in tens, and I want to work in WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 100 07:25.000 --> 07:31.080 And again, especially considering I want to work in tens, and I want to work in 101 07:31.080 --> 07:32.000 threes. 102 07:32.000 --> 07:37.300 Well, if I can work in tens, I could get here to 30, simply by adding 10 three 103 07:37.300 --> 07:38.000 times. 104 07:38.000 --> 07:46.000 So I would say I'm going to add 10 and add 10 and that gets me to 30 dBm. 105 07:46.000 --> 07:50.000 Now, on the millowatt side, I have to multiply. 106 07:50.000 --> 08:01.010 And again, 10 plus 10 for dBm is a times 10 plus 3 is a times 2 on a dBm versus WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 106 07:50.000 --> 08:01.010 And again, 10 plus 10 for dBm is a times 10 plus 3 is a times 2 on a dBm versus 107 08:01.010 --> 08:03.000 millowatt scale. 108 08:03.000 --> 08:10.570 So if I'm adding 10 three times, I am multiplying by 10 three times 10 times 10 109 08:10.570 --> 08:12.000 is a thousand. 110 08:12.000 --> 08:16.000 So this is equal to a thousand millowatt's, which is no longer millowatt's. 111 08:16.000 --> 08:18.000 It's just regular watts. That's one watt. 112 08:18.000 --> 08:20.000 But we'll just go ahead and keep it in millowatt's. 113 08:20.000 --> 08:23.000 So 30 dBm equals a thousand millowatt's. 114 08:23.000 --> 08:25.000 Pretty straightforward example. 115 08:25.000 --> 08:28.000 And we could do something similar and say what? 116 08:28.000 --> 08:32.000 About 12 dBm. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 116 08:28.000 --> 08:32.000 About 12 dBm. 117 08:32.000 --> 08:36.870 Well, 12 dBm. I've got to start with my zero and say, well, if I start with 118 08:36.870 --> 08:39.000 zero and I've got to get to 12, 119 08:39.000 --> 08:43.000 I could do plus 3 plus 3 plus 3 plus 3. 120 08:43.000 --> 08:46.000 And so this is going to get me to my 12 decibels. 121 08:46.000 --> 08:53.000 If I start with one millowatt over here and every plus 3 is a times 2. 122 08:53.000 --> 08:56.000 That's times 2 times 2 times 2 times 2. 123 08:56.000 --> 08:59.000 2 to the fourth power. That would be 16. 124 08:59.000 --> 09:03.000 So 12 dBm equals 16 millowatt's. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 124 08:59.000 --> 09:03.000 So 12 dBm equals 16 millowatt's. 125 09:03.000 --> 09:07.000 Again, at that point, we just use the rule of 3 instead of the rule of 10. 126 09:07.000 --> 09:13.000 And that allowed us to multiply out by 2's this time instead of by 10's. 127 09:13.000 --> 09:17.470 Now, that's great in all, but we can actually combine these two rules together 128 09:17.470 --> 09:18.000 as well. 129 09:18.000 --> 09:21.000 So for example, if I said, what is 26 dBm? 130 09:21.000 --> 09:24.000 Well, think about it in terms of 10's and 3's. 131 09:24.000 --> 09:27.000 How can I use 10's and 3's to get to 26? 132 09:27.000 --> 09:32.000 Well, I could add 2 tens and add 2/3 and that would give me there. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 132 09:27.000 --> 09:32.000 Well, I could add 2 tens and add 2/3 and that would give me there. 133 09:32.000 --> 09:37.000 So plus 10 plus 10 plus 3 plus 3. 134 09:37.000 --> 09:43.550 Of course, from a millowatt perspective, this is times 10 times 10 times 2 135 09:43.550 --> 09:45.000 times 2. 136 09:45.000 --> 09:47.000 So this is 26. 137 09:47.000 --> 09:49.000 I guess we're going to written right there. 138 09:49.000 --> 09:50.000 26 decibels equals. 139 09:50.000 --> 09:52.000 Again, I start with one. 140 09:52.000 --> 09:54.000 So at times 10, this is 10. 141 09:54.000 --> 10:01.000 Then times 10 again is 100, then 200, then 400 millowatt's. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 141 09:54.000 --> 10:01.000 Then times 10 again is 100, then 200, then 400 millowatt's. 142 10:01.000 --> 10:07.000 So we can combine the rules of 10's and 3's to get us to a particular value. 143 10:07.000 --> 10:11.000 Now, we can do the same thing except we could go in the negative direction. 144 10:11.000 --> 10:15.000 So what if I wanted to do negative 40 dBm? 145 10:15.000 --> 10:19.000 Well, now I can do minus 10, minus 10, minus 10, minus 10. 146 10:19.000 --> 10:25.000 But keep in mind that I've got to take 1 millowatt now and divide it by 10. 147 10:25.000 --> 10:28.000 And divide it by 10 and divide it by 10. 148 10:28.000 --> 10:31.000 So we think back to old school math here. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 148 10:28.000 --> 10:31.000 So we think back to old school math here. 149 10:31.000 --> 10:34.000 I've got a 1 millowatt and I've got to divide it by 10. 150 10:34.000 --> 10:42.000 I have to move this decimal places or place 4 times over 1, 2, 3, 4. 151 10:42.000 --> 10:45.000 Put my zeros in place. 152 10:45.000 --> 10:50.380 And so the answer if I want to write it out a little more cleanly would be 0.00 153 10:50.380 --> 10:53.000 1 millowatt's. 154 10:53.000 --> 10:58.000 Is equal to negative 40 dBm. 155 10:58.000 --> 11:03.000 And I want to do one last example here because we need to consider how we could WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 155 10:58.000 --> 11:03.000 And I want to do one last example here because we need to consider how we could 156 11:03.000 --> 11:06.000 combine addition and subtraction as well. 157 11:06.000 --> 11:09.000 For example, what about 17 dBm? 158 11:09.000 --> 11:14.000 How can I get to 17 dBm using 10's and 3's? 159 11:14.000 --> 11:19.000 I cannot. There's nothing I can do to add 10 and then add 3. 160 11:19.000 --> 11:23.000 And then add 3. I get to 16 fine but I can't get to 17. 161 11:23.000 --> 11:28.050 But what happens when I consider the fact that I can do minus 10's and minus 3 162 11:28.050 --> 11:29.000 's as well? 163 11:29.000 --> 11:32.000 Well, now I can get a little more creative. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 163 11:29.000 --> 11:32.000 Well, now I can get a little more creative. 164 11:32.000 --> 11:36.000 I could say, you know what? Instead of just plus 10 and plus 3's, 165 11:36.000 --> 11:41.000 I can say plus 10 plus 10 to get to 20 and then minus 3. 166 11:41.000 --> 11:47.000 So what does this look like? Well, 10 and minus 3, that does equal 17. 167 11:47.000 --> 11:51.000 So that's great. Over here I would say times 10 times 10. 168 11:51.000 --> 11:54.000 But then I have to divide it by 2. 169 11:54.000 --> 11:58.000 So I start with my 1 millowatt. I get to 10. I get to 100. 170 11:58.000 --> 12:04.000 100 divided by 2. This results in 50 millowatt's. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 170 11:58.000 --> 12:04.000 100 divided by 2. This results in 50 millowatt's. 171 12:04.000 --> 12:08.000 So that is how we can do our decibel math. 172 12:08.000 --> 12:13.000 Again, we just have to keep in mind the rules of 10's and the rules of 3's. 173 12:13.000 --> 12:17.000 And what we'll find in the wireless world is that for the most part, 174 12:17.000 --> 12:21.000 we do want to stick with dBm as our primary means of measurements. 175 12:21.000 --> 12:23.000 We will see millowatt's specified. 176 12:23.000 --> 12:28.000 We might see that our wireless access point is broadcasting at 100 millowatt's 177 12:28.000 --> 12:32.000 or 200 or 250 millowatt's or something like that. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 177 12:28.000 --> 12:32.000 or 200 or 250 millowatt's or something like that. 178 12:32.000 --> 12:37.000 When it's a positive value, or maybe I should say when it's over 1 millowatt, 179 12:37.000 --> 12:39.000 we often see it specified as 1 millowatt. 180 12:39.000 --> 12:43.790 As soon as it goes less than 1 millowatt, that's where we get into negative dBm 181 12:43.790 --> 12:44.000 's. 182 12:44.000 --> 12:48.150 And when we're talking especially about site surveys and looking at our 183 12:48.150 --> 12:50.000 wireless devices receiving signal, 184 12:50.000 --> 12:54.000 we're usually going to see that specified as a negative value. 185 12:54.000 --> 12:59.390 Anything from, you know, negative 50s, negative 60s, those are considered to be 186 12:59.390 --> 13:01.000 pretty good signals. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 186 12:59.390 --> 13:01.000 pretty good signals. 187 13:01.000 --> 13:05.710 The wireless devices, believe it or not, can detect signals that are negative 188 13:05.710 --> 13:06.000 80, 189 13:06.000 --> 13:09.000 and maybe even getting close to negative 90 dBm. 190 13:09.000 --> 13:13.200 For the most part, we want to stay in that negative 50, negative 60, maybe 191 13:13.200 --> 13:14.000 negative 70 range. 192 13:14.000 --> 13:18.000 But either way, just recognize that we will see both. 193 13:18.000 --> 13:21.720 But when it comes to measuring wireless signals, we're almost always going to 194 13:21.720 --> 13:25.000 see that we're measuring them in terms of dBm's.