# Forum

## CWNA Guide v3 - RF Math Section has mistake

5 posts by 3 authors in: Forums > CWNA - Enterprise Wi-Fi Admin
Last Post: April 22, 2007:
• Please correct me if I'm wrong:

In Page 56:

Question: PCMCIA card has 30 mW output. What is it in dBm?

30 mW = 1 mW * 10 * 3
= 0 dBm+ 10 dBm + 3 dBM
= 13 dBM

I think it is completely wrong. It should be:
30 mW= 1 mW * 10 * 3
= 0 dBm + 10 dBm + 1,5 dBm (appr.)
= 11,5 dBm

or opposite,
13 dBm = 0 dBm + 10 dBm + 3 dBm
= 1 mW * 10 * 2
= 20 mW

Also same goes on in P:57

Question: Power source 30mW, cable loss 2 dB, amplifier 9 dB, result?

30 mW = 13 dB
-2+9 dB= 7 dB
13 dB+7dB = 20 dBm
20 dBm = 100mW

However, I think answer should be:
30 mw = 11,5 dBm
-2+9 dB= 7 dB
11,5 dB+7dB = 18,5 dBm
18,5 dBm = 70mW (appr.)

if the given output was 20 mW it should be:
20 mw = 13 dBm
-2+9 dB= 7 dB
13 dB+7dB = 20 dBm
20 dBm = 100mW (appr.)

What do you think?

• Hi I think this is correct :

13 dBm = 0 dBm + 10 dBm + 3 dBm
= 1 mW * 10 * 2
= 20 mW

If 20dbm = 100mw and 10 * 10 = 10 + 10 then the above should be correct.

I vote for the mw amount to be wrong, should've been 20mw instead of 30mw.

• Hi I think this is correct :

13 dBm = 0 dBm + 10 dBm + 3 dBm
= 1 mW * 10 * 2
= 20 mW

If 20dbm = 100mw and 10 * 10 = 10 + 10 then the above should be correct.

I vote for the mw amount to be wrong, should've been 20mw instead of 30mw.

• Hi,

There is no need for the all the fuss, this has already being corrected in errata

http://www.cwnp.com/cwna/CWNAStudyGuideErrataV3.pdf

This is most likely why no CWNP guru replied your post.

regars

Okechukwu

• Hi, thanks for the replies.

I didn't know there was an errata for the book. It is strange to see such a mistake in a 3rd edt of a book.

Page 1 of 1
• 1