3702E AP: TX power question

[Clem58]

Hello,

On 802.11a/n/ac 5Ghz WLC 5520 configuration, for on of our Cisco 3702E APs, the power is currently configured to 1 (17 dbm ~50 mW) when we are below this AP with a scanner Datalogic FalconX3+, in the status of the scanner it shows 80 mW for tx power. Is this normal for you ? I though normally the scanner should not have a power above 50mW ? Is this a bug ? I've reverted this AP from custom power to auto, maybe I have to reboot it for this setting to be taken in account ?

Here is the configuration given by WLC for the concerned AP:

Tx Power
Num Of Supported Power Levels ............. 6
Tx Power Level 1 .......................... 17 dBm
Tx Power Level 2 .......................... 14 dBm
Tx Power Level 3 .......................... 11 dBm
Tx Power Level 4 .......................... 8 dBm
Tx Power Level 5 .......................... 5 dBm
Tx Power Level 6 .......................... 2 dBm
Tx Power Configuration .................... AUTOMATIC
Current Tx Power Level .................... 1
Tx Power Assigned By ...................... User

[Mikey Boy]

It depends what country you are in, what part number is your AP? Basically 17dBM is not factoring in the antenna gain either and you have a 3702E AP, what antenna are you using? Your gain will most likely be higher than 50mw.

The 80mW seen on the datalogic will refer to the scanner TX power, are you seeing this with the Summit client?

[Clem58]

Thanks for your answer, here are more details;

• The APs are located in Belgium, I'm not on site, I'm administrating remotely
• The 3702E APs are behind a centralized WLC 5520, via flexconnect
• They are connected and powered on CE500 switches with 15.4W poe ports
• There are 4 antennas AIR-ANT2535SDW-R= on the 3702E
• Here are their configuration regarding antennas, I don't understand why there is 0x0.5dBi here, but we definitely have some gain within them.
• 
• I confirm for Datalogic Falcons, it's the status from summit
• 
• You mean AP tx power and Wifi client device tx power are not related ?

[Mikey Boy]

Hi, ok, from what you are saying I do not think you have a problem but I think you need to check what gain is on the antenna fitted internally to the Datalogic to be sure.

• There are 4 antennas AIR-ANT2535SDW-R= on the 3702E
  • These are 5dB of gain on 5Ghz

So if your AP is operating at 17dbm with a 5dB antenna you are running at 158.5mW

If your datalogic is running at 80mW and has a 3db antenna (assumed here) that is able to transmit at 159.6mW (You need to check the antenna gain on the data specs)

So in the above scenario you have a balanced TX power between client and AP, you just don't want to end up in a scenario where one can transmit a lot higher than the other.

If you look at Cisco's official TX power specs for the AP's, 5db antenna with your 5Ghz channel is within spec for the E domain:

Regarding the gain config on the WLC, you could fill this in to match the gain on the ones you are using, but it shouldn't change anything as the Cisco antennas are designed to work with the AP reg domain. That config option is more relevant if you are using high gain or third party antenna which potentially allow you to go above the levels permitted for your region. 

Within the summit client on the datalogic you can also change the TX power options to tailor to suit your requirements. 

Regards

Regards

[Clem58]

Ok, thanks very much for these elements, that is really helping me ! The table is very interesting.

According to your post, what I've understood is within the 5Ghz channels, it depends on how many antennas are running, and on which channels as per UNII band are used.

For example if I have a 3702E AP in 5Ghz band with channel 140 (UNII2-E) the max gain should be 23 dbm.

What I think is not all the 4 antennas are used when you are in 15.4W (medium power) then that's why most of our APs have max power at 17dbm (~50mW).

Do you know if we can check how many antenna are in use as per AP ?

[Mikey Boy]

Unfortunately to check how many antenna are fitted I think you will need someone to take a photo of an AP.

If you are running in low power mode due to legacy PoE then the number of transmit antennas in use will be reduced dependant on code level as below. If you think that not all 4 antenna are fitted I would say you really need to find out....

#

Regards

[Clem58]

Many thanks for you answer, all the APs are mounted with 4 Antennas, but as they are powered on 15.4W POE, I think indeed some antennas are not used. According to your table it should be on 3x3:3, our WLC, APS are on 8.2.130 code.

[Clem58]

Do you know why on some 3702E APs we have this configuration :

      Tx Power Assigned By ...................... DTPC

And for others

      Tx Power Assigned By ...................... CHDM

It seems we have some troubles with the ones in CHDM mode.

[Mikey Boy · Accepted solution]

CHDM is the coverage hole detection system. It runs separately to DTPC which is dynamic transmit and channel control. APs that are being assigned values based on CHDM are reacting to clients reporting low signal strength. So that may be why they are the ones having issues - they have adjusted to allow for coverage holes but in reality it still isn't enough if they are on maximum

Regards

[Clem58]

Thanks very much for this answer !