# Forum

## RF Math

2 posts by 2 authors in: Forums > CWNA - Enterprise Wi-Fi Admin
Last Post: December 23, 2005:
• Hi everyone.

First an introduction. My name is Tom and I live in Albuquerque and work in a sales capacity for a large ISP. I did CCNA and three Microsoft Windows 2000 certifications a few years ago but I'm still employed in sales :( I got the itch to start studying again and have been working on CWNA for about a month and will take the test sometime in January.

I've read the second edition CWNA book and most of the O'Reilly 802.11 Definitive book both of which were given to me used. Once I decided to take the CWNA I ordered the third edition CWNA book along with the voucher and started on it this morning.

I thought I understood basic RF Math but page 56 of the third edition CWNA book has me confused.

"A certain PCMCIA client transmits with a power of 30 mw. How many dBm is this?"

"1mW *10 *3 = 30mW"
"1mW +10dB +3dB = 30mW"

It seems to be saying +3dBm is the same as multiplying times 3. I thought I understood +3dBm would increase power by a factor or 2, not 3. Wouldn't 30mW be 16dBm not 13dBm? Is this errata or am I doing the math wrong?

Tom

Page 1 of 1
• 1