Impact of incorrectly set antenna gain

Unanswered Question
Jul 8th, 2009
User Badges:

Hi,


I was hoping someone could tell what the impact of incorrectly setting the antenna gain on a the b/g radio of an AP would have on a WLAN?


I've come across a site where around a 3rd of the AP's had their antenna gain set to 0. I can only assume someone missed setting this during setup.


The site uses 1242ABG AP's and each has 2 4941 antennas and i believe the gain should be set to 4 x 0.5dBi


Thanks for any info.


Neil

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Loading.
carenas123 Tue, 07/14/2009 - 12:53
User Badges:
  • Silver, 250 points or more

External antenna gain is factored into the maximum transmit power of the access point. Antenna gain is an indicator of how well an antenna focuses RF energy in a preferred direction. Antenna gain is expressed in dBi (the ratio of the power radiated by the antenna in a specific direction to the power radiated in that direction by an isotropic antenna fed by the same transmitter). Antenna manufacturers normally specify the antenna gain for each antenna they manufacture.

Impact of incorrectly settings Antenna gain.


You might see a decrease in transmit power output.


Scott Fella Tue, 07/14/2009 - 18:57
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    The Hall of Fame designation is a lifetime achievement award based on significant overall achievements in the community. 

  • Cisco Designated VIP,

    2017 Wireless

What I was told about this is that if the gain is set too high, the algorithm will adjust the TX power so that you will not go beyond the regulation of the country the wlc is set to. So if the current EIRP is below the maximum for the country code, it will not have any effect.

Edgar Khachatrian Sat, 03/09/2013 - 06:14
User Badges:

Hello everyone,



I was also looking for an answer to this...



However I found this in the Cisco AP Manual.



"

Specifies the resultant gain of the antenna attached to the device. Enter a value from -128 to 128 dB. If necessary, you can use a decimal in the value, such as 1.5.

#

Note This setting does not affect the behavior of the wireless device; it only informs the WLSE on your network of the device's antenna gain.

"

Seems light this setting doesnt really affect the way the AP performs.



Also where does it say to enter 8 in the field if you have a 4 dBi antenna? Been looking but cant find this information, please show me. (Do you mean Qty-2 Antennas multiples by Gain-4 = 8 ?

Or just 8 just because?





Ed





Link to Manual

(http://www.cisco.com/en/US/docs/wireless/access_point/12.4_10b_JA/comman...)

Sent from Cisco Technical Support Android App

Edgar Khachatrian Sat, 03/09/2013 - 06:15
User Badges:

Just trying to see if anyone can confirm this.

Thank you


Sent from Cisco Technical Support Android App

Scott Fella Sat, 03/09/2013 - 06:47
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    The Hall of Fame designation is a lifetime achievement award based on significant overall achievements in the community. 

  • Cisco Designated VIP,

    2017 Wireless

If your using external antennas, then yes you should set it. Now if I have a mix of 3602e and 3602i, but the gain on the external antennas are the same gain or real close, then I don't bother changing the gain, but that's me. I have not had any issues. Now if I'm using a higher gain antenna like a 6db or more, then yes.

Sent from Cisco Technical Support iPhone App

Actions

This Discussion