# Forum

## arg!

1 posts by 1 authors in: Forums > CWNA - Enterprise Wi-Fi Admin
Last Post: October 16, 2006:
• Nate,
Don't be discouraged by RF math. Give me 20 minutes and you would be good to go. Hey, that gives me a business idea. How much would someone pay to talk to a trainer for problems like this? Hmm...

\$1 per minute... PayPal.. hey... :)

Rules of 10's and 3's, although you can get these anywhere. Here it is.

-3dB (1/2 Power) - You could lose 3 dB in a cable for example.
+3dB (2 times Power) Say, a 3dBi antenna (Don't worry about the "i" part yet)
-10dB (1/10th power) - You could lose 10dB is Free Space (the air)
+10dB (10 times Power) - High gain antenna

That is it for the rules.

Lets take this problem:

100mw power from AP. Your cable has been rated for a 3dB loss. How much power do you have at the end of your cable now? a 3dB loss (-3dB) gives you 1/2 power, so you have 50mw. That is RF math.

Next Problem.

100mw AP. 9dBi antenna. How much power now? 9dB is a 3dB gain 3 times. So...

100mw input power
+3dB = 200mw
+3dB = 400mw
+3dB = 800mw

So, your AP with 100mw of output power with a 9dBi antenna will net your 800mw of power. How is that?

Page 1 of 1
• 1