WLC98000 external antenna gain configuration

[denisjaworski]

Hi community,

we have a customer running a 9800-80 and several 9120AXE-E are planned together with AIR-ANT2544V4M-R which are going to be extended by (sometimes) longer cables. I found the data sheets for those cables which state a cable loss of 0,49 db/m (for 2,4GHz) and 0,808 db/m (for 5GHz). If it comes to the configuration of the external antenna gain according to https://www.cisco.com/c/en/us/td/docs/wireless/controller/9800/17-3/config-guide/b_wl_17_3_cg/m_configuring_80211_parameters_for_cisco_aps.html we would have to configure a negative value in the command. For example:

Using a 5m long cable my config would be:

ap name AP001 dot11 24ghz antenna selection external
ap name AP001 5ghz antenna selection external
ap name AP001 24ghz antenna ext-ant-gain 3
ap name AP001 5ghz antenna ext-ant-gain 0

Would I have a disadvantage in leaving it at 0 since I am not able to configure a negative value here?

Thanks a lot in advance

[JPavonM]

You only need to add the gain for the antenna without considering cable loss. Remember that for the gain value configuration you need to double the antenna value (4dBi == gain 8):

ap name AP001 dot11 5ghz antenna ext-ant-gain 8
ap name AP001 dot11 24ghz antenna ext-ant-gain 8

HTH

- Jesus

[denisjaworski]

Thanks Jesus,

This means that this part of configuration isn't meant to balance the EIRP in terms of antenna gain and cable loss?

[JPavonM · Accepted solution]

That's correct,

This configuration is to tell the WLC to operate the AP within the regulation, and not to configure it with as high Tx powers than after adding the antenna gain the EIRP would be greater than the regulated.

Take into consideration that you don't need to account for the cable loss of the included cords which are about 90cm length.

BUT, if you are not using smart antennas, you can trick the WLC to allow higher Tx power levels in order to mitigate the cable loss in case you are using very long ones, but always under the regulation please (https://wlan1nde.wordpress.com/2014/11/26/wlan-maximum-transmission-power-etsi/)

HTH
-Jesus
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[denisjaworski]

Super helpful, thanks a lot again!

We are indeed thinking about mitigating the cable loss. But to do that we would have to use negative values in the configuration since we are effectively loosing gain with our cable loss. But as far as I see it this won't be possible and we would have to stick with the 0, right?

[JPavonM]

Yes you are right, the only way to do mitigate for high cable loss figures is to lower that "gain" value in Cisco antenna close to 0. Doing it thiss way you can have a maximum Tx power of -23dBm from the AP, then substract the cabel loss, and then add antenna gain. Remember the constraints for maximum Tx power on every domain (Attached picture from WLAN Pros).

HTH
-Jesus
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