Antenna Gain Configuration - non SIA antenna

[luiggi-moreira]

Hello all.

We are using some 9120AXE APs at some Warehouses with external Hubbel antennas which are not Self Identifying Antennas.

FYI, the antennas we are using are 8dBi, 6dBi and 13dBi patch antennas in some cases.

However, after the deployment of those APs to the WLC, I was just cross checking the configuration and noticed the following.

Looks like no matter the antenna type we are using (all non SIA types), WLC (17.9.4a) configures all external antenna gains with 4dBi (screenshot below)

Therefore, I would like to know if we should have these values corrected reflecting correct/real antenna gain and what is the practical effect of this configuration?

Thank a lot!

[marce1000]

   - Ref: 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
   >...For APs that do not support SIA, the APs send the antenna gain in the configuration payload, where the default antenna gain depends on the AP model.

          If you think that those values are not applicable then use the  commands provided in the document
          to set the antenna gain as needed ;    I advise to use the CLI for that 

  M.

[luiggi-moreira]

Hi @marce1000 , first of all, thank you so much for your quick answer! I really appreciate.

Continuing to the topic, I guess I will have to change then, right?

Because as per based on design we did, 8dBi antenas are to be used, and the antenna gain configured is 4dBi.

Practical effect means that I'm limiting the antenna gain by 4, and not using its full 8dBi gain?

[marce1000 · Accepted solution]

 - That is true  , you can change the values as needed for your antenna  

 M.

[luiggi-moreira]

Thank you so much, @marce1000 ! You rock!

[eglinsky2012]

@luiggi-moreiraThe language in the config guide does not spell this out with a specific example, so it was confusing to me, but I believe if the antenna gain is 6 dBi, you enter 12 due to the 0.5 multiplier. 13 dBi would be entered as 26, and so on. If someone else could confirm or correct, I'd appreciate it.

[luiggi-moreira]

I agree with you @eglinsky2012 . That's what we did actually. All 13dbi antennas, we changed to 26, 8dBi, we changed to 16, and so on.

[JPavonM]

Take care when configuring external antenna gains improperly, as from that configuration it depends the maximum TX power that the AP's radio interface is allowed to use. If you setup a lower antenna gain value (lets say we wrongly configure an antenna gain of 8 for 5-Ghz slot, when the antenna is 8 dBi), that will tell the AP to reduce the maximum TX power level by 4 dBm only (and not 8 dBm, due to that 0.5 factor in the gain value). Under this scenario, the AP will be able to use a maximum TX power of 19 dBm (in ETSI the maximum EIRP is 23 dBm, minus 4 dBi antenna gain we have configured), and now let's add the real antenna gain we have of 8 dBi. That gives us an EIRP of 27 dBm so you are exceding what is mandate in the regulatory domain and you can be fined!!

In the correct setup, we will configure an antenna gain of 16 for an external antenna with 8 dBi gain, and the AP will adapt the maximum TX power to be 15 dBm (23 - to be ETSI compliant. You can see this information by issuing the command "show ap name <APNAME> config slot 1 | sec Tx Power|Antenna Gain"

[luiggi-moreira]

Hi @JPavonM ! Thank you very much for your great inputs.

Yes, we are not exceeding the EIRP limits and mostly because I'm talking about Warehouses and we are usually very carefull on having very specific coverage cells to have a better roaming performance.

My concern was more about the non SIA antennas being added to 9120AXE model.

We use 6, 8 and 10dBi patch antennas, but since they are Hubbel (not SIA antennas), they are not being self identified by the WLC and due to that factor, 4dBi is automatically being added to all APs from WLC. And I was worried about that, because mostly deployments with 8 or 10dBi antennas, are being now limited to 4dBi.

We are planning to adjust this accordingly from now on, because we are picking these patch 8 or 10dBi antennas for a reason right.