~bfiedler/website

c7db52b910816a81f1acb6b8669404cf3adc27e0 — Ben Fiedler 5 months ago 221776b
rev Balz v2
1 files changed, 25 insertions(+), 20 deletions(-)

M content/blog/build-your-own-wi-fi-antenna.md
M content/blog/build-your-own-wi-fi-antenna.md => content/blog/build-your-own-wi-fi-antenna.md +25 -20
@@ 1,6 1,6 @@
---
title: "Build Your Own Wi-Fi Antenna"
date: 2020-11-28T02:01:10+01:00
date: 2020-11-28T16:00:00+01:00
draft: true
tags: hardware, diy, math
---


@@ 27,8 27,9 @@ Antennas which are sensitive to the angles of incoming radio waves are called
but also satellite TV antennas or military and civilian radars. They allow for
efficient communication over much greater lengths than omnidirectional or
isotropic antennas. Directional antennas come in different forms, a well-known
one being the *parabolic* antenna, which uses a parabolic dish to focus the
electromagnetic waves on a single point.
one being the [*parabolic*
antenna](https://en.wikipedia.org/wiki/Parabolic_antenna), which uses a
parabolic dish to focus the electromagnetic waves on a single point.

# The build



@@ 49,16 50,18 @@ surface, poor antenna placement and other errors.

Balz, a friend of mine, helped us model and print the antenna using
[Fusion360](https://www.autodesk.com/products/fusion-360/personal)[^1] and his
[Prusa MK3S](https://www.prusa3d.com/original-prusa-i3-mk3/). The 3D model can
[Prusa i3 MK3S+](https://www.prusa3d.com/original-prusa-i3-mk3/). The 3D model can
be downloaded [here](/blog/static/antenna-model.stl). Of course, any decent 3D
modeling software and printer will do.

{{< figure class="resizable" src="/blog/img/antenna-render.png" caption="Rendered antenna model" >}}

Unfortunately, the surface of 3D prints commonly has a rough texture, which
lowers the effectiveness of the antenna. We attempted to fix this by taping a
high-density rubber foam sheet in the dish and covering the now smoother surface
in aluminium tape. Both materials can be bought cheaply in a hardware store.
Due to the layer-by-layer operation of 3D printing, shallow slopes often end up
with an uneven surface[^2], which lowers the effectiveness of the antenna. We
attempted to fix this by taping a high-density rubber foam sheet in the dish,
and covering it with aluminium tape. This better reflects the electromagnetic
waves that hit the inside of the dish. Both materials can be bought cheaply in a
hardware store.

{{< figure class="resizable" src="/blog/img/antenna-build.png" caption="The completed build" >}}



@@ 75,10 78,11 @@ created a Wi-Fi network on the TP-Link adapter and connected to it from the Alfa
adapter. We measured the signal strength using `iwconfig`.

There are many effects which influence the signal strength at the receiver, such
as the sending and receiving antenna gains, the distance between sender and
receiver, the carrier medium, and so on. Except for the receiving antenna all
other properties stay the same. Thus it suffices to measure the received signal
strength only - we can infer the relative gain between the antennas that way.
as the transmission power, sending and receiving antenna gains, distance between
sender and receiver, the carrier medium, and so on. Except for the receiving
antenna all other properties stay the same. Thus it suffices to measure the
received signal strength only - we can infer the relative gain between the
antennas that way.

We are interested in determining the recipient's antenna gain, i.e. how much the
antenna amplifies a signal when receiving. This is generally measured in


@@ 139,14 143,14 @@ we estimate it to be closer to 2-3 dBi.

There are many possible improvements to this design. The easiest way to increase
antenna gain (and directionality) is to increase its diameter. While 200mm is
close to the maximum of the Prusa MK3S, it would for example be possible to
split the design into quarters. Using a smoother material to cover the inside of
the dish may also help. Finally, replacing the copper wire with a receiver only
at the focal length of 100mm should increase directionality, at cost of a
significantly more complex model.

A variety of other DIY antenna models also exists, such as the
[cantenna](https://en.wikipedia.org/wiki/Cantenna),
close to the maximum of the Prusa i3, it is possible to split the design into
quarter dishes, assembling a dish twice as large. Using a smoother material to
cover the inside of the dish may also help. Finally, replacing the copper wire
with a receiver only at the focal length of 100mm should increase
directionality, at cost of a significantly more complex model.

A variety of other DIY antenna models also exist, such as the
[cantenna](https://en.wikipedia.org/wiki/Cantenna) model we compared against,
[Wok-Fi](https://en.wikipedia.org/wiki/WokFi) (using woks or similar kitchenware
as antenna dish), and many more. Hopefully this post showed you that building a
Wi-Fi antenna is doable using only cans or a 3D printer, as well as some


@@ 158,3 162,4 @@ out to me via my [public inbox](https://lists.sr.ht/~bfiedler/public-inbox).
[^1]: See his [reddit
  thread](https://www.reddit.com/r/Fusion360/comments/ejg226/accurate_parabolas_in_fusion_360/)
  about parabolic antennas in Fusion360.
[^2]: also called the "staircase effect"