I bought this adapter to see how well it performed with the results below.
Model: Alfa AWUS036ACH
Frequency: Dual Band 2.4GHz and 5GHz
Two 5dBi detachable antennas
Interface: USB 3.0 Micro-B
WiFi Speed Test 5GHz Band
All speed test were done to a Neatgear Nighthawk 802.11ac router 10 feet away past a wall.
Speedtest.net was used for some basic results.
WiFi Speed Test 2.4 GHz Band
The same WiFi speed test was done on with the 2.4GHz frequency
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The Alfa AWUS036ACH is a very good long range USB WiFi adapter with very good speeds.
If possible be sure to use a USB 3.0 port as to not bottleneck the transfer rate.
I am going to be doing much more testing with this adapter since it is known to be Kali Linux compatible and able to do Pen Testing.
Kali Linux announced it now comes with Driver support for RTL8812AU Chipset as of release 2017.1. Read Here for information.
This means it will be able to go into Monitor Mode and do Packet Injections.
Since it is a dual band 802.11ac device this will be the first Wireless-AC dongle able to do this.
As always be sure to read the reviews on Amazon, forums, or elsewhere to be sure a unit is a good fit for you.