Power gain or loss?

Unanswered Question
Mar 4th, 2010

I am reading a section that says that when you change a power level from 1 to 2 for a specific AP, the power decreases by 50% ans so on. My question is: If FCC says that transmit power should not exceed 30 dBm (I guess that is power level 1 in the AP), then setting the power level to 2 would mean the power is reduced to 15 dBm

I have this problem too.
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Kayle Miller Thu, 03/04/2010 - 10:10

That is incorrect Below is a table showing the power levels in dbm along with a link to the document and a conversion chart for the dbm to mw.

Table 3-5 Example of Output Power Levels

Controller
Tx Power Settings1
Radio Output Power
802.11b/g (dBm)
802.11a (dBm)

1 (maximum)

202

173

2

17

14

3

14

11

4

11

8

5

8

5

6

5

2

7

2

-1

8

-1

-


http://www.cisco.com/en/US/docs/wireless/access_point/channels/lwapp/reference/guide/1130_chp.html

20dBm = 100mw

17dBm = 50mw

14dBm = 25mw

11dBm = 12.5mw

each 3dbm of change results in either a Halving or Doubling of of the power.

Does this help? If so please feel free to rate it.

Thanks,

Kayle

fjcardenas-1 Thu, 03/04/2010 - 11:03

So, the power that is cut in half by going from power level 1 to 2 is in mw and not in dBm. The statement that each 3dbm of change results in either a Halving or Doubling of of the power, and the example made it very clear . Thank you.

Johannes Luther Mon, 06/14/2010 - 03:01

The WLC power levels always confuses me a little bit.

From my  understanding it depends on the regulatory domain.

For the -E regulatory domain, the setting "1" would represent 17dBm (50mW) not 20dBm.

Check out "http://www.cisco.com/en/US/docs/wireless/access_point/channels/lwapp/reference/guide/lw_chp2.html"

Example for a 1240AG:

At the bottom of the page is the table "Table 6-7     Example of Output Power Levels"

The note "2" sais: "The maximum output power levels obtained from Table 6-2 and Table 6-3"

If you check out the mentioned tables, you'll see, that the maximum power levels differs between each regulatory domain.

So again, from my understanding the power level 1 means:

- 20dBm in the US (-A)

- 17dBm in the ETSI (EUROPE) (-E)

Can someone confirm my theory?

EDIT:

I just checked some live systems. The above statements are correct

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