| Television Interference Electrical Interference |
Article Index for Television |
Website Links For Television |
Information AboutTelevision Interference Electrical Interference |
| CATEGORIES ABOUT TELEVISION INTERFERENCE ELECTRICAL INTERFERENCE | |
| television technology | |
| radio electronics | |
|
STATIC ELECTRICITY AND SPARKS The sparks generated by static electricity can generate interference. Many systems where radio frequency interface is caused by sparking can be modeled as the following circuit. 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. The energy in the LC circuit is then radiated through the aerial. As an example, when a person walks over a Nylon carpet, the rubbing of shoes on carpet performs the role of a battery and resistor, while the person acts as a Capacitor (C1 and C2), and the air between a hand and a Door Knob is a Spark Gap . Stray inductance acts as L. SPARKS AND ALLIED PHENOMENA Horizontal lines randomly arranged on a television screen may be caused by sparking in a malfunctioning electrical device. Electric railways can also be a strong source of this type of interference. Other possible sources of such interference include:
DEVICES WHICH SWITCH AT POWERLINE FREQUENCY
Thyristor and Triac regulators without proper Chokes are a common source of EMI as well. It is likely that a Thyristor (SCR) power controller using the variable phase angle method will generate harmonics of the mains supply, while the spark at a contact will be a very wide band source whose frequency is not related to the power supply frequency. In Thyristor control systems the potential for EMI problems can be minimised by using Zero Crossing switching where the Thyristor is switched on at the moment of time when the AC voltage changes from one direction to the other. DEVICES WHICH SWITCH FASTER THAN 200 HZ
E = Eo sin (ωt) - {Eo sin (2ωt)}/2 + {Eo sin (3ωt)}/3 ...... As the term goes on for ever to higher and higher frequencies the square wave contains harmonics of the fundamental which go on upwards in frequency for ever, these harmonics are responsible for much of the interference created by Computer s. Always remember that a modern PC is a device which is operating in the VHF / UHF using Square Wave s. 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.
|
|
|