Just a quick update and some explanation from Meraki on what might be going on here.
So, according to people I have been talking to there is an explanation (I dont like it, but here we go).
Because of beamforming, when using 4 antennas for beamforming, the AP will have to turn down transmit power 6db. (of it only had two antennas for beamforming it would be 3db).
- This is how the APs are certified today.
This makes somewhat sense, since the combined power output power of the signal cannot be higher then the 20dbm EIRP max in ETSI (Still only talking 2,4 Ghz here to keep it simple).
But why then do we still see such a weak signal when just doing passive survey, where beacons are single stream, and should then be send at the highest (or higher) transmit power (if configured).
- The explanation from Meraki is that, due to the fact that you cannot be sure that beamforming is working, and your client when roaming, normally listens for beacons, could "think" that the signal to a new AP would be ok (because of the max transmit power of beacons), but in reality the signal might not be (if beamforming is not working correctly).
And because of this, the entire AP turns down transmit power for everything.
- Now this opens up a whole new bag of worms, in my opinion.
What about those legacy a/b/g/n clients that do not support beamforming, and are only 1 SS.
In this case they will lose 6db of cell size. 😕 auch.
And furthermore if you do the EIRP calculation in this case there is still a problem (at least i think so).
12 dbm radio power + 6db for 4 SS beamforming + 3 dbi antenna gain = 21 dbm EIRP - Hmmm thats higher then the 20dbm max for ETSI.
So if what they say is the way they want it to work, the AP should turn down its radio to 11dbm in order to be compliant).
- Sorry if the above explanation is a bit messy 🙂 - But this is how I experience what they are telling me.