How does antenna size correlate to gain?
Antenna gain does have a correlation to size to some degree, but gain is not a unit of measurement. Therefore, antennas that have the same gain do not have to be the same height, and a higher gain antenna can be larger than a lower gain antenna.
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The best driver for Atheros AR9271 chip devices, such as ALFA Tube-UNA or AWUS036NHA for Windows 10 is this driver. Note that after installing, the device will appear in Device Manager as "TP-LINK Wireless USB Adapter" instead of Atheros or Alfa. This is because TP-Link is associated with Microsoft as the Device Developer ID of the Atheros chipset.
Soon ALFA will roll the driver into their own branded release but until then, it will be normal to see the Atheros device identified this way in Device Manager after doing the driver installation.
We have tested the driver extensively and it works with well.