Television interference

These include naturally occurring and artificial spark discharges, and effects due to the operation of radio transmitters.

Digital television reception generally gives a good quality picture until the interference is so large that it can no longer be eliminated by the error checking systems in the receiver, at which point the video display becomes pixelated, distorts, or goes blank.

"Multipath" reception is visible as multiple impressions of the same image, slightly shifted along the width of the screen due to the varying transmission path.

The source of energy charges C1 via a resistance, and when the spark gap breaks down, the electricity passes through L and excites the resonant LC circuit.

Stray inductance acts as L. Horizontal lines randomly arranged on a television screen may be caused by sparking in a malfunctioning electrical device.

Other possible sources of such interference include thermostats, fridges, freezers, fish tank heaters, central heating systems.

As the cases on many computers are not perfect shields, some of this radio-frequency energy can leak out and cause interference to radio (and sometimes TV) reception.

An attenuator inserted in the antenna lead-in wire may be used if the television receiver displays signs of overload in the RF front end.

Diagram of a spark transmitter
A typical SCR based light dimmer which dims the light through phase angle control. This unit is wired in series with the load. Diodes (D 2 , D 3 , D 4 and D 5 ) for a bridge which generates DC with much ripple. R and C form a circuit with a time constant, as the voltage increases from zero (at the start of every halfwave) C will charge up, when C is able to make ZD conduct and inject current into the SCR the SCR will fire. When the SCR conducts then D 1 will discharge C via the SCR. The SCR will shut off when the current falls to zero when the supply voltage drops at the end of the half cycle, ready for the circuit to start work on the next half cycle.