@Dark_Horse 

Hey

It does actually mention the wifi power in the specifications

As the device has 4x antenna, its around 5db for 2.4ghz and 5.7db for 5ghz

@Philbert many thanks for the reply.

Could you explain how you arrived at the antenna gain figures please? I don't think it's as simple as dividing the transmission power by the number of antenna; the Archer VR2600 I have has the exact same transmission power but the TP-Link specs list antenna gain as 3.1 and 5 on this model. The antenna can be replaced on the VR2600 but not on the X73-DSL hence why I was asking.

  @Dark_Horse 

Yes and no is kinda the answer to your questions.   We cannot calculate the total ERP of the antenna without knowing the loss, power and gain levels...  so in short NO its not possible to say with certainty that those are 100% correct

However...  having worked at this for ... lets say too long lol     Generally these things are recorded in 'marketing' terms, so they will likely just take the total of the 4x antenna and multiply.   Yes you are correct this is not the way to do it and it makes wild assumptions but its likely what they have done, ive seen other vendors do it that way before.   Looking at other Deco products from previous, they all appear to be around the same 5ish range.

In short, while we cannot say for 100% certain that that they have just multiplied, its likely the case

Thanks for explaining @Philbert.

I understand that each country has limitations on the maximum WiFi transmission power. For the UK, this is 100mW (20 dBm) for the 2.4Ghz range so if all routers wih 4 antenna use this maximum, would not the specs all roughly be 5 dBi gain for each antenna irrespective of manufacturer? In other words, little difference between buying any 4 antenna router over another for improving range.

For custom firmware like DD-WRT, you can increase the transmission power and swap out the antenna for improving range. I think with factory standard routers though, there's little you can do and range will not be hugely different between models (I've tried 3 other 4-antenna routers including the Archer VR2600 and there was next to no difference in range).