home wiki

- Power and Power Gain to dBm and dB Conversion Chart.
- EIRP calculation
- Wireless Calculators
- Calculating Decibels
- Interesting Mathematics

Gain | Gain(dB) |

0.0001 | -40 |

0.001 | -30 |

0.01 | -20 |

0.1 | -10 |

0.125 | -9 |

0.2 | -7 |

0.25 | -6 |

0.33 | -5 |

0.4 | -4 |

0.5 | -3 |

1 | 0 |

1.26 | 1 |

1.58 | 2 |

2 | 3 |

2.5 | 4 |

3.3 | 5 |

4 | 6 |

5 | 7 |

8 | 9 |

10 | 10 |

20 | 13 |

40 | 16 |

50 | 17 |

100 | 20 |

1000 | 30 |

10000 | 40 |

Power | Power(dBm) | |

1uW | -30 | |

10uW | -20 | |

100uW | -10 | |

1mW | 0 | |

10mW | 10 | |

100mW | 20 | (RA legal EIRP limit for WLAN in Europe) |

200mW | 23 | |

1W | 30 | |

4W | 36 | (ACA legal EIRP limit for WLAN, also legal RF power limit for 27 MHz AM CB) |

5W | 37 | (UHF CB legal RF power limit) |

10W | 40 | |

12W | 41 | (27 MHz SSB CB legal RF power limit) |

25W | 44 | (typical mobile 2 way radio) |

100W | 50 | (typical power level for off the shelf amateur HF transmitter) |

OR

e.g. 30 mW WLAN card into a 24 dBi dish with 3dB coax and connector loss

This system is right on the legal limit of +36dBm (4W) EIRP.

The decibel (dB) is a logarthmic representation of a ratio between two quantities. Unless qualified with a suffix (e.g. dBm), a decibel is simply a power ratio. This means saying "I have a radio that puts out 36dB" is meaningless - that's equal to saying "I have a radio that puts out 40 times"... 40 times what?

There are some important variations of the dB. These are typically dB referenced to a particular quantity (i.e. the dB ratio between a power level specified and the reference).

dB(A) - Referenced to the sound intensity of the weakest sound an average healthy person can hear, after a specific 'weighting function' (which compensates for the ear's characteristics) is applied. - 0dB(A) @ 1 kHz is the weakest sound most people with good ears can hear.

There's heaps more

So how does one calculate dB? (or how did I manage to create the tables above?). The formula for calculating dB ratios is simple:

where

I have a 2.4 GHz amplifier that has an output power of 1W when fed with an input of 30mW from a WLAN card l-arginine. What is the gain in dB?

therefore

The actual logarithm function is looked up using a scientific calculator or a book of log tables (remember those?). women clothing Looking up the logarithm, we get:

So our amplifier has a gain of 15.23 dB (compare that answer with using the tables above).

I have an amplifier which has been found to have 12dB of gain. If I feed it with 100mW, how much power will I get out of it?

First, lets get the gain in terms of a ratio (there is another way of doing this, but this way serves my purpose best). Back to the formula...

Transposing, we get

Therefore, substituting gives

Back to the calculator (I'm not silly )

So our amp has a gain of 15.85. How much power will we get out of it?

Also of interest, WirelessMathematics

Enjoy!

Version 8 (current) modified Thu, 24 Feb 2011 09:20:37 +1100 by Fendy

[EditText] [Spelling] [Current] [Raw] [Code] [Diff] [Subscribe] [VersionHistory] [Revert] [Delete] [RecentChanges]
currently *0* users online

Node Statistics | |
---|---|

building | 124 |

gathering | 194 |

interested | 469 |

operational | 248 |

testing | 200 |