@gipsasLTU 

Hi,

Your simple RF meter doesn't show the frequency of the RF noise. Therefore, there is no way of knowing whether the "RF Strenght" displayed is a result of Wi-Fi signals or Powerline signals or noise from the TL-WPA7517's internal AC/DC converter.

  @woozle 

well I've got LAN ROUTER and other stuff near by which has all atrributes you have mentioned and they dont trigger RF on this device.
I am not an expert and dont want to argue ... But I think there is a way to know... would any of your mentioned signals show RF 50cm away from the device? Well WIFI would and my other WIFI router shows about the same... 
Please can you explain a bit more... if you think it can...

  @gipsasLTU 

I am not ruling out that the RF signal shown by the meter is indeed Wi-Fi from the TL-WPA7517. I am just hinting that it could also be something other that Wi-Fi.

I found a user's manual for a device called Tenmars TM-190 that looks like the one you have and it says the frequency range of the RF Strength meter is 50MHz to 3.5GHz. So, theoretically there would be a broad range of RF sources that could trigger the RF Strength meter.

Anyway, do you happen to have a (electric) power meter available, the type that is plugged between a wall socket and an electric appliance?
In case you do, then perhaps the result of the following test would be interesting.

I have a set of 1000 Mbps Powerline adapters here, altgough made by another manufacturer. Using the power meter I see that the one Powerline adapter with the Wi-Fi draws about 8 Watts of electric power when idle. When I disable both Wi-Fi bands in the settings of the Powerline adapter the power drawn immediately drops to about 6.5 Watts.

That should be a good indication that the Wi-Fi has indeed been switched off.

If it turned out that the power consumption of your TL-WPA7517 was the same, no matter if the Wi-Fi is Enabled or Disabled in the settings, then this would be a good indication that the Wi-Fi radio doesn't switch off, as suggested by your measurements with the Tenmars meter.
 

  @woozle 
Hi thank you for your reply and some ideas...

Yes I have got a WIFI socket plug somewhere which can be controlled by APP and shows the usage/W of it...
I could try that out as well... But would be very interesting to find out what is that RF around the extender if not WIFI... as my other LAN routers (without WIFI) dont have anything similar even tested with my simple device.

OUT OF INTEREST. Pic below showing RF 30cm away from this device, next picture is placed directly on LAN ROUTER without WIFI

  @gipsasLTU 

Can you please perform a RF Strength measurement on the other Powerline adapter from the KIT for comparison? (TL-PA7017, the one without Wi-Fi)