Electromagnetic Compatibility

6A1: What is EMC?

EMC (Electromagnetic Compatibility) is the ability of electronic equipment to operate without causing or suffering from electromagnetic interference.

• Your station must not cause interference to other equipment
• Your station must be able to tolerate interference from other equipment
• Both aspects are equally important

6A2: Types of Interference

6A3: Filtering

Interference can be reduced using filters:

• Ferrite beads/clamps — clip onto cables to suppress high-frequency interference
• Capacitors — filter out high-frequency noise from power supply lines
• Low-pass filters — block high-frequency interference while passing lower frequencies

6A4: Screening

Screening (shielding) uses a conductive enclosure to block radiated interference. Coaxial cable is screened — the outer braid shields the inner conductor.

• Metal cases for equipment provide screening
• Properly connected screening is essential — a floating screen is ineffective

6B1: Common Sources

Many household items can generate interference:

• Switched-mode power supplies (phone chargers, laptop supplies)
• Electric motors (washing machines, vacuum cleaners, drills)
• Digital devices (computers, LED lighting, TVs)
• Central heating systems (programmers, pumps)
• Car ignition systems

6C1: Effects on Radio and TV

Interference can affect various types of equipment:

• AM/FM radio — buzzes, whistles, crackling sounds
• TV receivers — picture distortion, snow, loss of digital signal
• Shortwave radio — noise and interference across bands
• Wireless devices — reduced range or dropouts

Remember: your amateur transmissions can also cause interference to these devices if you don't follow good EMC practices.

6D1: Good Station Design Practices

• Short leads — keep all cables as short as possible to reduce radiation and pickup
• Good earth connection — provides a path for interference currents
• Bonding — connect all metalwork together with short, heavy conductors
• Ferrite chokes — fit to cables entering/leaving the station

6D4: Antenna Placement

How you place your antennas affects both radiation and interference:

• Keep antennas away from other equipment and cables
• Avoid routing feeder cables near TV or computer equipment
• Consider the effect on neighbours — antennas should be as inconspicuous as possible
• Feeders should leave the antenna at right angles where possible

6E1: Distance from Neighbours

Consider your neighbours when placing your station and antennas. The further away from neighbours, the less likely you are to cause interference.

• Talk to your neighbours about your hobby before causing problems
• Be prepared to investigate and resolve any interference issues
• Good station design minimises the risk of interference

6E2: Antenna Placement Relative to Buildings

• Keep antennas away from mains wiring and other cables
• Avoid running antennas along building walls where possible
• Consider the visual impact — be a good ambassador for the hobby

6F1: Mobile EMC Challenges

Operating from a vehicle presents unique EMC challenges:

• The car's electrical system generates significant interference
• Ignition noise can be heard across multiple bands
• Power supply noise from the alternator
• Antenna placement on a metal vehicle affects performance

6F2: Bonding in Vehicles

Bonding is connecting all metal parts of the vehicle together with short, heavy conductors to provide a low-impedance ground plane.

• Connect the antenna mount to the vehicle body
• Ensure boot and bonnet straps are in good condition
• Use braid or heavy wire for bonding connections
• Good bonding reduces both radiated and conducted interference

6F3: Power Supply Considerations

• Use the vehicle battery directly — not the cigarette lighter socket
• Use a fused connection close to the battery
• Keep power leads short and well-bonded
• Add ferrite chokes to power leads if needed

6G1: EMC Guidance and Help

The RSGB provides extensive EMC guidance and help for amateurs experiencing or causing interference.

• RSGB EMC Committee can provide advice
• Online resources and fact sheets
• Local clubs may have EMC experts
• EMC limits are defined by CISPR (Comité International Spécial des Perturbations Radioélectriques) — the international standards body for electromagnetic compatibility

6G2: Talking to Neighbours

Being a good neighbour is essential for the reputation of amateur radio:

• Introduce yourself and explain what amateur radio involves
• Invite them to see your station — many people find it fascinating
• If they experience interference, investigate promptly and politely
• Be prepared to adjust your operation if needed