DECIBEL

Decibel is abbreviated "db".  It is a mathematics tool that allows wireless experts to handle the very large and very small numbers that are associated with wireless electronics theory.  For example, the difference between the power output of a transmitted signal and the value of that same signal when it is received by a cellular phone miles away might be a number such as "1" with 12 "0"'s after it, such as:  1,000,000,000,000.  As you can see, such numbers become difficult to work with.

Decibels for power in wireless is defined as 10 times the log (of the power ratio).  Some examples below - for use in comparing two power levels:

• 3 db - means one signal is twice as powerful as the second one
• 6 db - means one signal is four times as powerful as the second one
• 10 db - means one signal is ten times as powerful as the second one
• 20 db - means one signal is one hundred times as powerful as the second one
• 30 db - means one signal is one thousand times as powerful as the second one
• 60 db - means one signal is one million times as powerful as the second one
• 90 db - means one signal is one billion times as powerful as the second one

This does take some getting used to.   However, hopefully you will see that it is easier to talk about 90 db than 1,000,000,000.

Now, you may also see the term dbm.  What that means is "how far in db is the power level from one milliwatt.  One milliwatt is one thousandth of a watt of power.  For example, a 10 watt transmitter would be said to be + 40 dbm - since it would 10,000 times more powerful than a milliwatt.  A received signal by a cellular phone however might be -110 dbm - or a factor of 100 billion less than 1 milliwatt.  What is the "path loss" - which is the signal loss from transmitter to receiver?  Simply subtract the two.  +40 dbm - ( -110 dbm) = 150 db difference. 150 db difference, is well, is a whole bunch. (meaning a very large difference).