Bluetooth TX power level in advertisements

[Lukáš]

Hi,

I was randomly inspecting Bluetooth devices around in nRF Connect and I found out that many Apple devices advertise with TX Power Level 12 or 24 dBm. From my understanding, the TX power limit for Bluetooth 4.0 is 10 dBm (set by Bluetooth SIG and ETSI). Is it theoretically possible that these devices really use higher TX power than 10 dBm and they passed certifications?

Btw, I don't think that someone from my neighborhood would randomly transmit as an Apple device with overshot TX Power level in advertisements.

Thanks

[ketiljo]

The power level is just a field and may not reflect the actual power. In Europe, max power for BLE is 10 dBm. But more can be used for classic BT (BR/EDR), up to 20 dBm as there are true FHSS systems.

[Lukáš]

Well, from what I see they are advertising by using legacy advertising in BLE. And AFAIK FHSS is not possible during the advertising because of the limited channels. So any thoughts on how they might do it? Even if they could do 20 dBm then 24 dBm is over that limit. And why would Apple put false data in the TX power field? That doesn't make sense, we must overlook something.

[ketiljo]

I'm afraid you must ask Apple about that. It's a static parameter that's set by the manufacturer. nRF Connect just reads the parameter and displays it. Or it can be interpreted incorrectly by the phone or app, hard to say. Eddystone and iBeacon do this differently as well. 

[Lukáš]

Ok, was hoping to hear your thoughts about this or any practical experience. Nevermind.