AirPort Extreme A1521, 2.4Ghz limited to 72Mbps

and it does to other routers.

This sounds like a fault in your phone. If all the other wireless routers you have tried give the same result it is not an issue with the Gen6 Airport.. for which you gave us the details.. but rather the phone for which we have no details at all.

If it is an iphone you should post this in the discussion for iPhones. If it is a different brand post in the area for that model.

But the antennas in phones are tiny.. 72Mbps being half of the magical 144Mbps you refer to can be simply one antenna not picking up signal. If you have ever dropped the phone or had some physical damage to it.. it is possible for things to happen. It can depend on the age of the phone.. check the signal levels you are getting from the phone at the router. That will be a good indication of how things are going wrong.

You can use wireless analyser software .. for iphone it is part of airport utility. There are lots of excellent analysers out there for android phones.

Since my phone is 2x2 device, even at 20Mhz channel this should be able to connect at 144 - and it does to other routers. So what's the issue here?

If I understand your statement correctly, you are saying that your phone can connect at 144 Mbps with other wireless routers, but just not with this AirPort Extreme ... correct?

If so, then I assume even after performing a "factory default" reset on this base station, that it still does not provide its designed capability on the 2.4 GHz band, then that radio may be faulty. Especially, if none of your other wireless clients, either equipped for 2x2 or 3x3 are obtaining the highest MCS Index value when connecting to it on this band.

We need some clarification from you in order to know where to start the troubleshooting process.

Are you saying that your other WiFi devices connect to the AirPort at 144 Mbps speeds with the 2.4 GHz signal, but the iPhone will only connect to the AirPort at 72 Mbps?

Or are you saying that WiFi devices connect to other routers at 144 MHz, but connect to the AirPort at 72 MHz?

Or, something else?

Szybkość połączenia na częstotliwości 2.4 GHz zależy od wielu czynników, na przykład:

1. Odległość od routera. Pamiętajmy, że to sieć WiFi i ma określony zakres odległości od stacji bazowej. Generalnie czym dalej, tym gorzej.
2. Wybrany kanał transmisji. Użyj narzędzi i dobierz odpowiedni kanał.
3. Szerokość kanału. Wybierz 20, 40, 80, w zależności od typu urządzenia.
4. Zakłóceń zewnętrznych powodujących interferencje.
5. Tłumienie sygnału przez żelbetowe ściany, wykładziny wszelkiego typu, płytki wykładzinowe i podobne.

3. Szerokość kanału. Wybierz 20, 40, 80, w zależności od typu urządzenia.

Pasmo radiowe 2,4 GHz dla Wi-Fi nie oferuje kanałów o szerokości 80 MHz. Również AirPort Extreme lub którykolwiek z pozostałych routerów AirPort nie obsługuje kanałów 40 MHz, więc w tym przypadku to stwierdzenie nie jest ważne.

Tiny WiFi antenna inside the iPhone. Not much that you can do about that. As long as the iPhone is working, I would call it a day.

On average, my iPhone gets a third to maybe half the speed of my laptop when both are in the same location.