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I hope you'll forgive me for including a few questions at once. I'd appreciate insight into any of them.

I've got a camper stored legally in town to use as an office. I'm situated between two free WiFi Xfinity transmitters, each about 300ft away. I have access to electricity while I'm there.

I'd like to set up a pogoplug running Arch Linux to pick up the Xfinity signal with a long range antenna, and then retransmit the signal so that I can use my phone, tablet, Roku, etc. inside the camper.

My research so far indicates that I might want either a stick or dish shaped antenna, and that I need a USB wifi adapter to connect the antenna to the pogoplug. So, products might be (with Amazon product ASINs, to link like this https://www.amazon.com/dp/B008Z4I7WQ):

TP-Link-Directional-Parabolic-Connector-TL-ANT2424B
(Amazon ASIN B003CFATOW)

or

Yagi WiFi Antenna 2.4GHz 17dBi Angle H:25° V:24 Outdoor Directional Wireless
(Amazon ASIN B008Z4I7WQ)

for the antenna, and

Alfa Long-Range Dual-Band AC1200 Wireless USB 3.0 Wi-Fi Adapter w/2x 5dBi External Antennas - 2.4GHz 300Mbps / 5Ghz 867Mbps - 802.11ac & A, B, G, N
(Amazon ASIN B00MX57AO4)

for the WiFi adapter. Just typical examples of what I'm considering.

My questions:

  1. Is there an innate limitation within Arch Linux about which wireless protocols can be supported (a,b,g,n,ac)? Ditto frequencies (2.4Ghz,5Ghz)? If so, that would guide my choices on hardware.

  2. Is dBi the metric I should be looking for when shopping for the antenna? Any best guesses what dBi I might need for 300 ft across a parking lot? Any reason not to go higher?

  3. Any recommendations for particular WiFi adapters to work the easiest with Arch, which also support a high gain antenna upgrade?

I've already researched the Linux configuration for a wireless repeater and it seems that this is easily accomplished. I'm new at all of this, so please do let me know if you think I'm off track in any way.

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A) There is no innate limitation within Arch Linux about protocols or frequencies, but of course it depends on the hardware, and sometimes also on the drivers. So make sure the device you buy is supported under Linux. Also, ac support doesn't work for that many chipsets at this time, so if you want ac, make sure you pick a chipset that has a working driver.

Finding out the chipset from the product description can be a pain, because vendors don't tell you. So you'll need to google (a lot). If you have actual hardware, use lsusb to get vendor and product it, and google in the form 0123:4567 to find out about it.

You can use iw phy as root to find out what capabilities (protocols, frequencies etc.) your hardware/driver supports.

Important: You need to run the WIFI interface both as access point ("AP") for your local devices, and client ("managed") to relay the Xfinity connection. The valid interface combinations line in iw phy will tell you if that is possible. You also want this on two different frequencies, if possible, to avoid interference. This means you want something like #channels <= 2 in the above descruption, which few chipsets support, or different radios for 5GHz (your local devices, if all of them support it) and 2.4GHz.

If possible, you also want this on different antennas (because of the way the 802.11 protocol works: Collisions will slow down both communication channels otherwise). So if you get bad results, consider using two WIFI adapters.

Bottom line: A custom build of a wifi-repeater isn't as easy as it looks. There are ready-made products (for example the CPE models by TPE-Link, or Ubiquity Nanostations) that have in-built directional antennas and are made for exactly such a situation as yours. Consider using one of these.

B) Depending on the actual situation, e.g. free line of sight etc., you might not need a special antenna at all. 300 ft outdoors is not that much. Definitely test first with a normal antenna. iw dev wlan0 station dump will tell you the signal measurements of the hardware. The numbers are not particularly exact and vary from device to device, but something around -70 dBm (measured) is servicable, -80 dBm is problematic.

C) There's so many USB adapters and they change so quickly I can't give a recommendation, sorry.

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