# Watt's this RF Math all about?

No, I didn't misspell the title of this post. I’m actually talking about the unit of measure called a Watt (W). The Watt and the Decibel (dB) are values that CCNA Wireless candidates should be familiar with. So what is a Watt? Simply put, a Watt is one amphere (A) of current at one volt (V). Don’t worry yourself too much with it. Just think of a fireman that’s putting out a fire. He has a firehose that is full of water ready to smother the fire. The pressure of the water can be likened to the voltage and the flow of the water as he releases it on the fire can be compared to the amphere. Now moving on, we need to discuss another term frequently used, the MilliWatt (mW). The milliwatt value is used because wireless networks operate at lower power levels so representing everything with the Watt value would be way too much. Next up, the lets talk about a Decibel (dB). Decibels compare powers. In fact, you could say that a dB is based on a logarithmic relationship to the literal value of a Watt. Remember this is a comparison, so therefore 0dB means that there is zero difference in power or mW. 3 dB means that there is twice the power in Miliwatts, and 10 dB meands that you have 10 times the power in Milliwatts. Decibels can also be negative numbers such as -3 dB meaning half the power in Miliwatts, and -10 dB meaning one-tenth the power in Milliwatts. Some people use the rule of 3s and 10s to remember this. So what is the point in knowing what these terms mean and the rule of 3s and 10s? Simple, you can use these values to figure out how much input or output power a wireless device has. So I thought it would be fun before we wrap up here to pose a little challenge. Ready? Here it goes: Suppose I have an Access-Point that is capable of 50 mW of output power. This AP is connected to a cable that has 3 dB of loss, then to an antenna with of 6 dB of gain. How would you figure out the actual power? Use the comment section of this blog post to record your answer. In the next post I'll provide the answer and we can see how you all do. Also don’t forget to sign up for the free CCNA Wireless Technical Introduction webinar being held this Wednesday, Feb. 11th, at 11:30 am PST. To register simply click on the link below. Register for the free CCNA Wireless Technical Introduction

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