---
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.