additional ham notes

zk/EMC_and_interference.md

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+---
+tags: [radio, ham-study]
+---
+
+EMC or _Electromagnetic Compatibility_ is concerned with avoiding interference
+between different pieces of electronic equipment.
+
+> Interference is the degradation or disruption of a desired radio signal caused
+> by unwanted electromagnetic energy. It can manifest as static, noise, signal
+> loss, or distorted audio.
+
+Transmitters can _cause_ interference. Receivers can suffer _from_ inteference.
+
+**The more power a station uses, the more likely it is to cause interference.**
+
+**Immunity** is the ability of a piece of equipment to function correctly in the
+presence of strong RF signals.
+
+Different transmission modes are more or less likely to cause interference.
+
+AM and SSB are more likely to cause interference.
+
+FM and some HF data modes are least likely (remember "Friendly Modulation").
+
+## Occurences of interference
+
+Nearby radio transmissions can cause interference to:
+
+- domestic mains wiring
+- TV aerial leads
+- Speaker leads
+- Telephone wiring
+- Internal circuitry
+
+## Methods of reducing interference
+
+- Fitting **filters** (known as **chokes**) in mains or antenna leads as close
+  to the affected device as possible
+
+- Using balanced antennas at HF
+
+- Using horizontal dipoles
+
+- Avoiding the use of end-fed antenna types
+
+- Siting antennas as far from houses as possible and as high as pissible
+
+- Using a dedicated RF earth to prevent RF current from entering the mains earth
+  system
+
+## Dummy loads
+
+A dummy load is a screened resistor attached to a transmitter instead of an
+aerial. This enables the transmitter to operate without putting out a signal
+which can be useful when detecting and managing interference.

zk/Electrical_safety_for_amateur_radio.md

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+---
+tags: [ham-study]
+---
+
+## Earthing
+
+Where a safety earth has been fitted, it must not be removed. If changes are
+necessary, a competent professional must be consulted.
+
+## Plugs, fuses and circuit breakers
+
+Need to know the plug colours:
+
+| Colour  | Cable            |
+| ------- | ---------------- |
+| Live    | brown            |
+| Neutral | blue             |
+| Earth   | green and yellow |
+
+- The flex of the plug cable should be secured.
+
+- The fuse must match the plug
+
+- A fuse comprises a thin wire that melts when excessive current flows through
+  it, breaking the circuit. When a fuse blows, you should investigate the cause
+  and not just blindly replace especially if it is recurrent.
+
+- Better than a fuse is a Residual Current Circuit Breaker with Overcurrent.
+  This can detect currents to earth of over 30mA whereas a fuse just captures a
+  few amps and only detects short circuits.
+
+## General points
+
+- Only work on the inside of equipment, having first disconnected the power
+  source
+
+- Have a master switch for all radio equipment
+
+- Safety measures must be taken when using radio equipment outside
+
+- Wear protective goggles when soldering
+
+- Very high antennas require lightening protection
+
+- Antennas and feeders must not be sited close to overhead cables
+
+- A ladder should be used at a 4:1 height to base ratio and be used with an
+  assistant
+
+- The main health damage from EM radiation is heating of body tissue, especially
+  the eyes
+
+- Antennas and other conductors must not be touched when transmitting
+
+- Antennas must not be mounted in such a way that people would accidentally come
+  into contact with them
+
+- You must not look down a wave guide