# Forum

## 3 dB and 6 dB Rule

3 posts by 2 authors in: Forums > CWNA - Enterprise Wi-Fi Admin
Last Post: September 3, 2010:
• Hi,

Am having a little confusion about how these rules are used and where they are used etc...

Is 6 dB rule just for Distance etc......Inverse Square law ....

Whats the core difference between them ..

Plz can someone explain this in depth

Thanks

• First of all, you need to remember that these are both "rules of thumb". To find the true values you'd have to do calculations with logarithms. For example, 6dB is not really four times the power, but rather a factor of 3.98. Four will be close enough in most applications.

A gain or loss of 3dB corressponds to an increase of twice, or a decrease to one-half, the power respectively. But remember that's the power output, [u]not the range[/u].

So for example, an increase of 6dB would correspond to an increase of (2x2) or four times the power. Conversely, a decrease of 6 dB would be one-fourth the power.

Alternatively, for 6dB, ( 3dB + 3dB = 2 x 2 = 4 times the power) and ( -3dB -3dB = 1/2 x 1/2 = 1/4 the power).

6dB also equates to a doubling (or halving) of the range. - Think inverse square rule.

So for example, if you wanted to double the outdoor range of your point-to-point (PtP) link, you would need to increase your gain by a factor of 6 dB. (Forgetting other considerations like earth bulge etc.)

See the section starting on page 77 of the PW0-104 CWNA book for more details.

I hope this helps some.

• Thanks Wlanman,

That has surely help me and clear some doubts....

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