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Basic question regarding 802.11a power levels

I am trying to verify something regarding the 802.11a power settings using a WLC:

If the power setting for the 802.11a radio is a divisor (i.e.: Power setting of "1" is full power, power setting of "2" is half power, etc.), how am I to interpret the settings that the max power setting for "lower" channels (5150 to 5250 MHz chan 36-48 FCC) is limited to a lower transmit power (i.e.: 15 dBm) than the transmit power for other "higher" channels (uni 3 from 5725 to 5850 MHz chan 149-161 FCC) which is able to transmit at 17 dBm.

Please refer to table Table 3-3 to in the following document:

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

In other words, what is being divided? The 15dBm or the 17dBm? Does changing the channel from a lower-numbered channel in the 5150 to 5250 MHz range to a higher-numbered channel in the 5725 to 5850 MHz range result in an increase in power (since the max transmit power is now higher)?

Or to phrase it a different way, when my power setting on the WLC is "1" for an 1131AG access point, what is my transmit power level? 15 or 17dBm? Does the power level vary - depending upon which channel I choose?

- John

4 REPLIES

Re: Basic question regarding 802.11a power levels

I would suspect that it is limited by the channel you select but will ask for clarification from our friends at Cisco.

New Member

Re: Basic question regarding 802.11a power levels

This is an old post, but you can verify what power level (in dBm) your AP is running by using the cli command 'show ap config 802.11a ' and yes, it does vary by channel.

Re: Basic question regarding 802.11a power levels

I posted this on my site last week. I found that if you use UNII1 channels 1 = 11dBm, UNII 2 / 3 1 = 17dBM..

http://www.my80211.com/cisco-labs/2009/10/30/what-you-need-to-know-about-tx-power-and-80211a-5ghz-on-a-ci.html

__________________________________________________________________________________________ "Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin ___________________________________________________________

Re: Basic question regarding 802.11a power levels

Good post. Here is part of your data.

UNII 1                                                 UNII 2 / 3

1 = 11 dBm / 12.5 mW                          1 = 17 dBm / 50mW
2 = 8 dBm / 6.25 mW                            2 = 14 dBm / 25 mW
3 = 5 dBm / 3 mW                                3 = 11 dBm / 12.5 mW
4 = 2 dBm / 1.5 mW                              4 = 8 dBm / 6.25 dBm

This is VERY important when planning a network in WCS planning tool or Airmagnet Planner.

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