---
title: '"Borrowing" a Better WiFi Signal'
date: '2018-02-15'
draft: true
words: 804
collection: ramblings
---

Let me start by saying that "stealing" WiFi (or anything for that matter) is
wrong, and bad. Please don't do it. But if you happen to find yourself
"borrowing" someone elses WiFi with permission, i.e. they gave you the password,
then the next step is clearly improving the link quality.

### Attenuate like Hell

I'm currently living in the mountains of Colorado, in a place that doesn't have
it's own ISP hookup. One of our neighbors is nice enough to let us borrow thier
WiFi though, so all is not lost. If I had to guess I'd say that I'm about 100ft
from the access point (AP), and about 6 or so walls stand in the way. It's not
an ideal RF setup by any means, but it works.

The AP is broadcasting at 2412MHz (channel 1 of the 2.4GHz band), the bandwidth
is 20MHz.
TODO: Other link stats.
TODO: wavemon screenshot.

However, it's nowhere near good enough. Enter the world of fancy antennas. In
the RF antenna world there exists a device named "Yagi", after one of it's
creators. A Yagi is a directional antenna which operates with a single driven
element, a reflecting element, and many directing elements. These are the same
design as many household TV antennas from the old days.

I'm not going to get into the design of these things, because frankly that's
above my pay-grade at the moment, but there are a few key things to know about
these antennas:

- They are directional, TODO: angles?
- The antenna should be arranged to match the polarization of the AP.
- The frequency range (bandwidth) is very narrow, so there's no way a 2.4GHz
  antenna will work on the 5GHz band.

So I bought [one](amazon), and a [USB WiFi adapter](amazon) to go along with it. I
chose the adapter to meet the following requirments:

- 802.11n, 802.11ac isn't needed because we're only dealing with the 2.4GHz
  band.
- Drivers must be included with Linux by default.
- External antenna connection (typically SMA).

I After ordering the wrong kind of SMA adapter I finnaly got the [right](amazon)
one, and we're in business. Simply moving from my laptop's built-in WiFi to this
new setup improved signal level by TODO, and link quality by TODO.

TODO: another wavemon screenshot.

### Share the World

It's one thing to have access to a nice, fast network on a single computer, but
I want my roomates to be able to benifit from this high quality link as well.
Enter the [NAT](wiki).

Building a NAT device isn't too hard. I've got an extra Rasperry Pi (v1) lying
around running [ArchARM], so we'll work with that, but these techiques should
work for any modern Linux machine.

TODO: more words, and links to GitHub sources.

#### Manually Configure

First let's connect to the WiFi network, and make sure it's working.

```sh
netctl start <profile>
…
ping 8.8.8.8
```

We need to tell the kernal to route packets accross network interfaces. For
more information about kernal ip forwarding start with
[this Stack Overflow post](https://unix.stackexchange.com/questions/14056/what-is-kernel-ip-forwarding).

```sh
sysctl net.ipv4.ip_forward=1
```

Once we've enabled packet forwarding, we need to setup the NAT between
the wireless interface, and the Pi's ethernet interface.

```sh
iptables -t nat -A POSTROUTING -o $from -j MASQUERADE
iptables -A FORWARD -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i $to -o $from -j ACCEPT
```

Finally, we enable [DHCP](wiki) to allow clients to negociate for an IP address
on the new local network.

```conf
# /etc/dhcpd.conf
option domain-name-servers 8.8.8.8, 8.8.4.4;
option subnet-mask 255.255.255.0;
option routers 192.168.0.1;
subnet 192.168.0.0 netmask 255.255.255.0 {
  range 192.168.0.150 192.168.0.250;
}
```

```sh
systemctl start dhcpd4@$to.service
```

With that all said and done we should be able to connect a computer via ethernet
and access the internet. Woot!

#### Systemd Unit

Ideally we should be able to simply power up the pi (or whatever machine) and
have all the needed networking configuration happen automatically. This is the
domain of systemd services and targets.

TODO: Actually figure this all out...

#### Setup our own Wireless Network

All that's left is to connect the ethernet cable from the pi to a functional
wireless router, and we've got our own WiFi network with good connectivity.

The observent reader will notice that we now have two NATs, the NAT between
our WiFi borrower, and the NAT for our personal WiFi hotspot. It's NATs all the
way down!



### Going Futher (literally…)

One thing that I'm now dying to test is how far a 2.4GHz signal can go, with
modern, FCC complient hardware like I have. If I were to buy another one of
these antennas and point them at each other, how many meters, or kilometers
could it go.

Another factor in all this is the TX (sending) power.
TODO: a bit of info on this.

With an optimal setup, I've heard of people beaming WiFi over a kilometer, so
this could be fun indeed! Tune in next time...