Part One – Watt? I Can’t Hear You Over The Bels

If you’re going to call yourself an engineer, you need to do math.  Sorry, but that’s a rule.  When I was an electrical engineering student, we always held ourselves above civil and mechanical engineers, because we had to do more complex mathematics in order to graduate (Now you ME’s and CE’s don’t go getting your noise out of joint.  Chem E’s did the same thing to us).  Go ahead and ask a mechanical engineer what a LaPlace or Fourier transform is, and you’ll see the expression on their faces.

I also learned that part of being an engineer was learning to learn engineer speak.  So let’s look at some of the basic math involved with, and the language used with RF networks.

IT engineers have had it pretty easy when it comes to math.  Not that they don’t have the ability to learn it, but that’s what we have computers for anyway, isn’t it?  Outside of learning a little binary arithmetic to do subnetting, we don’t do much math, and with IPv6, even that is going away.  But, if you happen to be a wireless network engineer, you don’t get off that easy.  Especially if you want to do your job properly, and provide a network that will perform close to laboratory specs.  These days, connectivity isn’t good enough, our WiFi networks need to be high performance, high client density networks.

I have found through years of study, that the more you know about something, the easier it is to understand, and explain to someone without your level of knowledge (also known as your customer or end user).  So let’s get down some basic math and language to help you better do your job.

Let’s start with watts and decibels.  Both are measure of power, but they mean different things.  In basic electronics, power in watts is the product of the voltage and current in a DC circuit.  In AC circuits it’s a little more complicated because the voltage varies with time, but the principle is the same.

P(watts) = Voltage (V) * Current (I)

Now if you know a little about exponential math, you know that a kilowatt it 1000 watts, and a milliwatt is one thousandth of a watt.  Remember those values, they’re the most commonly used measurements in power discussions.

Decibels are different.  As Webster defines a decibel “a unit for expressing the ratio of two amounts of electric or acoustic signal power equal to 10 times the common logarithm of this ratio.”

In mathematical terms:

Power (Db) = 10 log (Measured Power/Reference Power),

Assuming both powers (measured and reference) are in watts.  In the example, the power is measured in watts and our reference power would be 1 watt.  If we were to change that reference power to one milliwatt, then our power would be in dBm.  We use dBm in WiFi because transmit and receive powers are so low, they are always a fraction of a watt.

To keep it simple, watts and decibels are both power measurements.  Watts are direct measurements, decibels are ratios.

That’s enough for part one.  In part two, we’ll look at some more in depth mathematics involving these terms and some tricks to avoid having to do that math.

Part Two – Three Is a Magic Number (and 10 Really Rocks)

Coming Soon!