Radio Interference

OverviewWhat is it?Radio InterferencePreventing

What is it?Unwanted signals

◦Effect electronic circuits

Radio InterferenceInternational Electrotechnical

Commission◦1933 set up International Special

Committee on Radio InterferenceEU

◦EMC Directive (89/336/EC) Immunity Emissions

Radio Interference TypesNarrow band

◦TX equipmentBroad band

◦Power lines◦Motors◦Computers and TV

Antenna◦Outside of antenna cable◦Unbalanced

Power supplies

Radio Interference SourcesTransmitting equipment

◦Harmonics◦Wrong frequency

Faulty electronic equipmentSunAurorasSplatter

RX interference sourcesClipping

◦Square wave Harmonics

Clipping from◦Power◦Microphone

PreventingFilterDon’t over drive the systemUse balunsRF chokeFaraday CageCablesElectric Earth

PreventingBaluns

◦Matching between balanced and unbalanced lines

◦Conver between 300/450 W lines and 75 W coax

PreventingBaluns

◦Wound around a iron core

PreventingRF choke

◦inductor

PreventingFaraday Cage

◦Metal cage or mesh◦Can block radio waves

Small gapes depending on wavelength

PreventingCables

◦Twisted pair Cancelling out

◦Coax Inner conductor Outer “shielding” conductor

PreventingElectrical earth