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The decibel
Mike, K6FMI wrote this great article about the decibel. Enjoy!
The Decibel
By Mike Cappi / K6FMI, February 2025
The Decibel is widely used in ham radio and indeed all of electronics. You find it in equipment specifications, especially for cables of various types. It makes for good exam questions. It is thrown about in conversations about our equipment. Yet, it is poorly understood by some and is even a source of confusion.
There is math involved; there is no way around that. I know of some who were working through the license study guides to prepare for the tests and gave it all up when they hit the section on the decibel. The math put them off. Maybe it was the way it was explained. The texts can assume prior knowledge of the underlying concepts. For many, math class was a long time ago.
To understand the decibel, we need to use some algebra, then exponents and exponential notation, logarithms and end with the decibel.
CALCULATORS AND COMPUTERS
I was in school before the hand-held calculator and the personal computer. We lugged around a heavy reference book of tables for logarithms and roots and other functions. We also had our slide rules, which we were allowed to use on tests. We had to because there was no time to work out squares, cubes, roots and logs otherwise. From the time I bought my first HP calculator many years ago after I was out of school, I no longer needed to consult those tables.
It is true that a good calculator or a spreadsheet can do this math. So why do you need to know this stuff? Just put the numbers into the computer and let the answer spring forth.
Without a good foundation and understanding of the basics, how do you know you correctly set up the problem? If you get an answer, how do you know you asked the right question? Calculators and computers are wonderful aids, but you still need to know how things work.
I assume you have a calculator that does functions like logs and roots and powers to work through what follows here. You can use a spreadsheet program, too. We will let the calculator do the messy arithmetic for figuring out logarithms, powers and roots for inconvenient numbers. Our task is to enter the initial data correctly and then let the calculator (or computer) do the rest.