dBi Calculation Question

Guys I am working on ym CWNA paper and have hit a little point that I cannot get passed (although you will probably think this is pretty simple).

It is the calculation for a circuit as below.

AP--connector (A) -----Cable----Connector (B)----cable----Connector (C)---Antenna (D)

AP is 100mW and the paper is explaining the calculation as below.

AP Point A Ponit B Point C Point D

100mW -3dB -3dB -3dB +12dBi =100mW /2 /2 /2 (x2x2x2) =100mW /2 /2 /2 x16 =50mW /2 /2 x16 =25mW /2 x16 =200mW

It was my understanding that all dB units (including dBi) are relative units and can be added and subtracted from other dB units - therefore the overall dB should be +3db = doubling the power - hey presto the right answer!

What I cant fathom is the calc shown above - why have they suggested a multiple of x2x2x2 ?

Can someone please explain why......only a little point but bloody annoying when your are learning this stuff for the first time!


Reply to
Rob D
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Yep, it is simple. Of course you have to be confident enough to know when you are looking at a typo! They left off one "x2", because 12 dB is one 2x for each 3 dB, so that is a total of *4* x2's that should be in that string.

Looks like your understanding of it is perfect, and what you lack is understanding that you do understand it! :-)

Reply to
Floyd L. Davidson

Thanks guys - still a little worried about this but I will face it down come final week before exam.

- I will probably put another post up here later...lol!

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