ham notes

zk/Antennas.md

@@ -0,0 +1,34 @@
+---
+tags: [radio, ham-study]
+---
+
+> Antennas convert electrical signals into radio waves and radio waves into
+> electrical signals
+
+Different sized antennae are used for different
+[frequency](./Frequency_modulation.md) bands. In general, **longer wavelengths
+(hence lower frequencies) require larger antennas**.
+
+There are five antenna that you need to know for the exam:
+
+- the half wave dipole
+- the quarter wave
+- the five-eighth wave
+- the end-fed long wire
+- the Yagi (beam) antenna
+
+## The half wave dipole
+
+![](../img/dipole-a.jpg)
+
+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.
+
+![](../img/dipole-b.jpg)
+
+For example, if 15MHz has a wavelength of 20 meters, your dipole should be 10
+meters long ($\frac{20/2} = 10$).
+
+The signal from a dipole radiates as follows:
+
+![](../img/dipole-radiation-pattern.gif)

zk/Feeders.md

@@ -0,0 +1,54 @@
+---
+tags: [radio, ham-study]
+---
+
+**Feeder** is the cable that connects the transmitter/receiver to the antenna.
+
+As the EM energy travels through the feeder, some energy is lost as heat.
+
+- The longer the feeder, the greater the loss
+- The higher the frequency being transmitted, the greater the loss
+
+> This is why for VHF and UHF thicker, low-loss feeder is needed
+
+## Types of feeder
+
+The two types of feeder you need to know for the exam:
+
+- coaxial
+- twin feeder (a.k.a "ladder line")
+
+![](../img/feeder-types.png)
+
+### Coaxial cable
+
+![](../img/coaxial-diagram.jpg)
+
+The inner conductor carries the signal. The screening keeps the signal within
+the inner cable preventing loss.
+
+It is **unbalanced** because the outer shield is at
+[ground potential](./Ground.md) whereas the central conductor has a varying
+voltage relative to ground.
+
+### Twin feeder
+
+![](../img/ladder-line-feeder.jpg)
+
+Here we have two wires with spacers maintaining seperation. The two wires carry
+equal and opposite signals.
+
+Twin feeder is balanced because neither wire is grounded. Both have the same
+impedence to ground in a symmetrical fashion. If wire A is at +5V, wire B will
+be at -5V. Because of [alternating current](./Voltage_sources.md), they swap
+over their potential difference at each cycle, making them effeectively
+interchangeable.
+
+![](../img/feeder-balance.png)
+
+## Why balanced/unbalanced feeder matters
+
+Some antennas are suited to unbalanced feeder whilst others are suited to
+balanced feeder. If you want to use an unbalanced feeder with a balanced antenna
+(or vice versa) you can do so, but this requires a Balun (balanced-to-unbalanced
+transformer).

zk/Radio_cable_connectors.md

@@ -0,0 +1,33 @@
+---
+tags: [radio, ham-study]
+---
+
+![](../img/feeder-connector-types.png)
+
+## PL259
+
+![](../img/PL259-connector.jpg)
+
+- screw-thread locking
+- common for HF
+
+## N
+
+![](../img/N-type-connector.jpg)
+
+- screw-thread locking
+- common for VHF/UHF
+
+## BNC
+
+![](../img/bayonet-connector.jpg)
+
+- 50Ohm version
+- bayonet locking
+
+## SMA
+
+![](../img/sma-cable.jpg)
+
+- screw-thread locking
+- often found on handheld radios