If our wireless signals are degrading over time, what constitutes a good signal
or good enough signal?
And in order to start answering that question, we have to recognize that we can
measure our signal strength.
We're talking about wireless signals. We need to evaluate whether a signal is
strong enough to be read.
And it does start with not just signal strength, but the concept of measuring
the strength of our signals.
A wireless waveform is sent out with a certain amount of power. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
A wireless waveform is sent out with a certain amount of power.
And that power is going to be measured in watts at a very high level with Wi-Fi
, it's usually measured in milliwatts, which is a thousandth of a watt.
So our Wi-Fi access points are wireless laptops when we're talking about Wi-Fi.
We're typically talking about transmitting in the milliwat range.
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
Furthermore, if we are transmitting at, let's say, 100 milliwatts, and it de
grades over time, but my laptop is sitting here, and it's got a really strong
signal or whatever the situation is, we might say, "Okay, so maybe I lost a
little bit, but I'm probably at 70 milliwatts of power, and I'm receiving that
."
But what if I told you that this laptop could be saying, "Hey, I've got a great
signal strength here, and it's receiving it at .001 milliwatts." WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Believe it or not, this is pretty shocking. This is considered a great signal.
How on earth is that even possible? What is going on here? Well, wireless
energy radiates in a, usually a three-dimensional spherical type of world here.
I've got this transmitter in the middle, and I've got 100 milliwatts of energy
wrapped up around the signal the moment it starts to propagate.
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
But as it propagates out in 3D space, it starts to thin, again, at an
exponential rate. It's dropping drastically.
And yet, our wireless devices are so finely tuned that they can pick out a
signal that is roughly, I guess that would be, let's see, that's 1/10,000, that
's 100, roughly a millionth of the signal strength that it was propagated at.
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
Actually, if I look at it, it's even a 10 millionth of it. And so either way,
we're talking about very tiny numbers here.
Now, you and I as humans, we would have a hard time communicating this to one
another. If I said, "Hey, I'm getting a wireless signal with .00000, 05 milli
watts, and this other one is 00001, 2 milliwatts."
This is very tricky for us to deal with as humans. It's just a lot of zeros,
and it's not very readable.
And furthermore, it's pretty clear that when we're talking about wireless WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And furthermore, it's pretty clear that when we're talking about wireless
signals, that the raw number doesn't matter as much.
In other words, yeah, 100 milliwatts is what I started at, but I'm losing so
much signal here, and yet it's still considered to be a great signal.
I need to somehow better represent the fact that an exponential decline is not
necessarily a bad thing.
I want to take my exponential decline and convert it into something a little
bit more linear.
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
And so that's exactly what we're going to use the decibel to accomplish.
The decibel is a fascinating conversation. It takes us back to our high school
math days of studying logarithms.
And while it's fun to go back and study what exactly a decibel is and what a
logarithm is, that is going to go beyond this gop of our conversation here.
Essentially what we're saying is we're going to take this exponential decline
and turn it into something a little bit more linear.
And specifically, we're going to relate the decibel, which is itself neutral, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And specifically, we're going to relate the decibel, which is itself neutral,
as far as whether you're applying it to one power reading or another.
And so we're going to specifically say that this is in relation to the millow
att. When we call a decibel that relates to a millowatt, a unit, we're going to
refer to this as dbm.
And yes, the b is capital, and yes, it's because it's named after a person. And
in this case, Alexander Graham Bell.
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
And so the b does get capitalized just like what stays capitalized because it's
also named after an individual.
Either way, when we're saying that we're going to relate this back to the mill
owatt, what we're saying is that if we have zero dbms, since we're relating it
to the millowatt, we're going to say that this equals one millowatt.
Furthermore, as millowatt's increase exponentially, let's say we multiply this
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
And so 10 millowatt's happens to equal 10 decibels.
Now, at this point, it doesn't look a whole lot different. 10 equals 10, but
zero equals one. It's not super clear until we do this again.
What happens if I multiply by 10 again? I end up with 100 millowatt's. But
again, this is linear where I'm multiplying on one side, I'm adding on the
other.
So when I'm multiplying here, I'm going to add again, and this ends up being 20
decibels. So all of these values are equal to one another. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
decibels. So all of these values are equal to one another.
Now, I can't just say, hey, if I'm going to multiply it by anything, let's
multiply it by 5 here, and then I add 5, it doesn't work that way.
So there's actually two sets of numbers that we like to use.
One of those is 10, because 10 and 10 match up very nicely.
The other one is when we multiply by 2, we can increase this by 3 decibels.
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
So if I were to multiply this by 2 and get 200 millowatt's, I can add 3 and say
that this equals 23 decibels.
So this is the rule of 3's and the rule of 10's. If I'm going to increase by 10
, I have to multiply the millowatt's by 10.
If I'm going to increase decibel by 3, I have to multiply the millowatt's by 2.
So yes, it is 3 and 2, so we have to keep that in mind.
Furthermore, if I end up going negative, let's say I want to subtract 3 deci
bels, then indeed I would divide. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
bels, then indeed I would divide.
So back down to 20 decibels, from 23, I subtract 3, that means I have to take
200 and divide it by 2, and I'm back down to 100 millowatt's.
I can do the same thing by subtracting 10 and dividing by 10, and we'll look at
some examples here.
So in fact, let's just dive right into those.
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
So let's start with some calculations and we will look at 30 dBm.
So 30 dBm equals how many millowatt's?
Well, we have to have a starting point, and our starting point is always going
to be right here. 0 dBm equals 1 millowatt.
So if we're going to say that 0 dBm equals 1 millowatt, now I just have to get
0 up to 30.
So how do I get 0 up to 30?
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
And again, especially considering I want to work in tens, and I want to work in
threes.
Well, if I can work in tens, I could get here to 30, simply by adding 10 three
times.
So I would say I'm going to add 10 and add 10 and that gets me to 30 dBm.
Now, on the millowatt side, I have to multiply.
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
And again, 10 plus 10 for dBm is a times 10 plus 3 is a times 2 on a dBm versus
millowatt scale.
So if I'm adding 10 three times, I am multiplying by 10 three times 10 times 10
is a thousand.
So this is equal to a thousand millowatt's, which is no longer millowatt's.
It's just regular watts. That's one watt.
But we'll just go ahead and keep it in millowatt's.
So 30 dBm equals a thousand millowatt's.
Pretty straightforward example.
And we could do something similar and say what?
About 12 dBm. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
About 12 dBm.
Well, 12 dBm. I've got to start with my zero and say, well, if I start with
zero and I've got to get to 12,
I could do plus 3 plus 3 plus 3 plus 3.
And so this is going to get me to my 12 decibels.
If I start with one millowatt over here and every plus 3 is a times 2.
That's times 2 times 2 times 2 times 2.
2 to the fourth power. That would be 16.
So 12 dBm equals 16 millowatt's. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So 12 dBm equals 16 millowatt's.
Again, at that point, we just use the rule of 3 instead of the rule of 10.
And that allowed us to multiply out by 2's this time instead of by 10's.
Now, that's great in all, but we can actually combine these two rules together
as well.
So for example, if I said, what is 26 dBm?
Well, think about it in terms of 10's and 3's.
How can I use 10's and 3's to get to 26?
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
Well, I could add 2 tens and add 2/3 and that would give me there.
So plus 10 plus 10 plus 3 plus 3.
Of course, from a millowatt perspective, this is times 10 times 10 times 2
times 2.
So this is 26.
I guess we're going to written right there.
26 decibels equals.
Again, I start with one.
So at times 10, this is 10.
Then times 10 again is 100, then 200, then 400 millowatt's. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Then times 10 again is 100, then 200, then 400 millowatt's.
So we can combine the rules of 10's and 3's to get us to a particular value.
Now, we can do the same thing except we could go in the negative direction.
So what if I wanted to do negative 40 dBm?
Well, now I can do minus 10, minus 10, minus 10, minus 10.
But keep in mind that I've got to take 1 millowatt now and divide it by 10.
And divide it by 10 and divide it by 10.
So we think back to old school math here. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So we think back to old school math here.
I've got a 1 millowatt and I've got to divide it by 10.
I have to move this decimal places or place 4 times over 1, 2, 3, 4.
Put my zeros in place.
And so the answer if I want to write it out a little more cleanly would be 0.00
1 millowatt's.
Is equal to negative 40 dBm.
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
And I want to do one last example here because we need to consider how we could
combine addition and subtraction as well.
For example, what about 17 dBm?
How can I get to 17 dBm using 10's and 3's?
I cannot. There's nothing I can do to add 10 and then add 3.
And then add 3. I get to 16 fine but I can't get to 17.
But what happens when I consider the fact that I can do minus 10's and minus 3
's as well?
Well, now I can get a little more creative. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Well, now I can get a little more creative.
I could say, you know what? Instead of just plus 10 and plus 3's,
I can say plus 10 plus 10 to get to 20 and then minus 3.
So what does this look like? Well, 10 and minus 3, that does equal 17.
So that's great. Over here I would say times 10 times 10.
But then I have to divide it by 2.
So I start with my 1 millowatt. I get to 10. I get to 100.
100 divided by 2. This results in 50 millowatt's. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
100 divided by 2. This results in 50 millowatt's.
So that is how we can do our decibel math.
Again, we just have to keep in mind the rules of 10's and the rules of 3's.
And what we'll find in the wireless world is that for the most part,
we do want to stick with dBm as our primary means of measurements.
We will see millowatt's specified.
We might see that our wireless access point is broadcasting at 100 millowatt's
or 200 or 250 millowatt's or something like that. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
or 200 or 250 millowatt's or something like that.
When it's a positive value, or maybe I should say when it's over 1 millowatt,
we often see it specified as 1 millowatt.
As soon as it goes less than 1 millowatt, that's where we get into negative dBm
's.
And when we're talking especially about site surveys and looking at our
wireless devices receiving signal,
we're usually going to see that specified as a negative value.
Anything from, you know, negative 50s, negative 60s, those are considered to be
pretty good signals. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
pretty good signals.
The wireless devices, believe it or not, can detect signals that are negative
80,
and maybe even getting close to negative 90 dBm.
For the most part, we want to stay in that negative 50, negative 60, maybe
negative 70 range.
But either way, just recognize that we will see both.
But when it comes to measuring wireless signals, we're almost always going to
see that we're measuring them in terms of dBm's.