AMATEUR RADIO TRAINING Electromagnetic Compatibility Release: v1.21 hamtrain.co.uk

Electromagnetic Compatibility What causes interference? Ways to reduce interference Transmission modes Antennas & earths Good station design

What is EMC? Electromagnetic Compatibility (EMC) is the avoidance of interference between two pieces of electronic equipment Transmitters can cause interference to other equipment, such as a neighbour’s TV and radio You need to understand the impact, and how to minimise the likelihood of causing unwanted interference

Interference There is a chance that your signals can cause interference to: TV sets / computer monitors FM, AM & DAB Radio Hi-fi units Cordless and fixed-line phones Touch lamps Baby monitors Security alarms / CCTV

Causes of Interference Aerial and/or aerial cabling pick-up Speaker cable pick-up Equipment with poor immunity / unshielded equipment Via mains earth

Digital TV Interference RF interference to digital TV will pixelate the picture and cause breakup to sound Worse if weak Freeview signal, or using a TV signal booster

Video: Digital TV Interference

Digital TV Pixelation

Minimising Interference Depending on the problem: Reduce field strength by moving the transmitting antenna further away Reduce the power Fit filters to the ‘pickup’ cabling Using filters on mains power supply leads Addressing earth problems

Filters Clip-on ferrite High-pass or band-pass TV filter Wound ferrite ring Ferrite filter on a power lead Safety note: Home-made filters are potentially dangerous

Modes and EMC FM – Causes less interference “friendly modulation” AM / SSB – Causes more interference, as the amplitude varies with the signal Morse / CW – “Key clicks” can be a problem if on-to-off is not smooth Data – Normally constant modulation, so less of a problem than speech Frequency Modulation Amplitude Modulation Data

RF Earth Use an RF earth to minimise RF leaking into mains Do not use mains earth for RF! Do not use radiators / water pipes Use a copper stake in the ground close to shack Use heavy-gauge wire to connect from transmitter or ATU

Antennas and EMC Dipole is commonly used for HF This is a ‘balanced’ antenna Connected to transmitter / ATU using unbalanced coax cable Uses a ‘balun’ (balanced-to- unbalanced) The shield of the coax is connected to the RF earth

Station Design Use good quality cables and connectors Have a good RF earth Use mains and RF filters Balanced antenna Balun Coax PSU Transmitter Filter ATU VSWR Filtered Mains RF Earth

Balanced Antenna Setup HF antenna sited away from house & TV antenna Good quality co-ax RF earth close to shack Balanced Antenna Balun

End-fed Antenna Setup Unbalanced system Feed from the end of the garden RF earth close to shack

Example of Poor EMC Setup Fed from upstairs shack No RF earth Proximity to TV antenna

EMC and Neighbours It pays to be helpful and co-operative Most problems can be resolved easily and cheaply Get free advice from the RSGB EMC Committee Your neighbour may consult Ofcom (for a fee). Ofcom may ask you and the neighbour to keep a log to confirm interference is related to your transmissions

EMC Summary EMC – Electromagnetic Compatibility Understand the symptoms & causes Have a good RF earth Use the right type of antenna and good quality cable Understand how to position an antenna to minimise interference Correct station and shack set-up FM is more “friendly” than other modes such as AM / SSB Understand the type (and correct use) of filters Resolving problems – Keep a log, and consult RSGB EMC Committee

Electromagnetic Compatibility Any questions? HamTrain.co.uk © EssexHam.co.uk