From 802df7c3f33a332e02924c6c5034173f7e1f4e1d Mon Sep 17 00:00:00 2001
From: thomasabishop <thomasabishop@tuta.com>
Date: Tue, 27 Jan 2026 19:23:48 +0000
Subject: [PATCH] update antenna notes

---
 zk/Antennas.md | 79 +++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 75 insertions(+), 4 deletions(-)

diff --git a/zk/Antennas.md b/zk/Antennas.md
index 8e8cca0..57b41e2 100644
--- a/zk/Antennas.md
+++ b/zk/Antennas.md
@@ -17,9 +17,11 @@ There are five antenna that you need to know for the exam:
 - the end-fed long wire
 - the Yagi (beam) antenna
 
-## The half wave dipole
+## The half wave dipole antenna
 
-![](../img/dipole-a.jpg)
+![](../img/half-dipole-antenna.png)
+
+Typically used by amateur operators.
 
 Its total length is equal to half a wavelength. This informs the length it needs
 to be in order to pick up a certain frequency.
@@ -27,8 +29,77 @@ to be in order to pick up a certain frequency.
 ![](../img/dipole-b.jpg)
 
 For example, if 15MHz has a wavelength of 20 meters, your dipole should be 10
-meters long ($\frac{20/2} = 10$).
+meters long (because 20/2 = 10).
 
 The signal from a dipole radiates as follows:
 
-![](../img/dipole-radiation-pattern.gif)
+![](../img/dipole-radiation-pattern.png)
+
+## The quarter wave ground plane antenna
+
+![](../img/quarter-wave-antenna.png)
+
+This antenna is vertical and is omnidirectional, radiating the signal in all
+directions.
+
+It's length corresponds to 1/4 of a wavelength, hence used for VHF and UHF
+bands.
+
+The radials at the bottom form the ground plane that boosts the signal
+horizontally in addition to the vertical reach of the main part of the antenna.
+
+## The five-eighth wave ground plane antenna
+
+![](../img/five-eighth-antenna.png)
+
+This antenna is also vertical and omnidirectional and used for VHF and UHF
+bands. It has a coil at the base in addition to the radials.
+
+## End-fed long wire
+
+The length is random compared to the other antennae. The length used determines
+the wavelengths that can be picked up and it needs to be matched to a specific
+frequency.
+
+![](../img/end-fed-antenna.png)
+
+The most important thing to remember about this antenna is that it is more
+susceptible to EM interference than other types.
+
+## Yagi antenna
+
+In contrast to the others, the Yagi is directional and focused in one direction
+
+- typically the direction of the station you are trying to pick up.
+
+It basically works as a dipole with a reflector behind it. This helps to push
+the waves in the horizontal direction of travel, assisted by the director spoke
+in front.
+
+### Gain and ERP
+
+Antennas like the Yagi have **gain**. This means they can increase the power
+that they receive from the transmitter via the [feeder](./Feeders.md).
+
+Gain is measured in decibels:
+
+| Antenna gain | Power muliplied by a factor of... |
+| ------------ | --------------------------------- |
+| 3dB          | 2                                 |
+| 6dB          | 4                                 |
+| 9dB          | 8                                 |
+| 10dB         | 10                                |
+
+ERP is the **Effective Radiated Power**. This is the product of the power that
+the antenna is receiving from the feeder and the gain level.
+
+> ERP (Watts) = power feed x antenna gain
+
+Some example calculations:
+
+| Gain | Gain times | Power to antenna | ERP       |
+| ---- | ---------- | ---------------- | --------- |
+| 3dB  | x2         | 10 watts         | 20 watts  |
+| 6dB  | x4         | 10 watts         | 40 watts  |
+| 9dB  | x8         | 10 watts         | 80 watts  |
+| 10dB | x10        | 10 watts         | 100 watts |