Television Interference ( TVI ) is a case of certain electromagnetic interference that affects television reception. Many natural and man-made phenomena can interfere with the reception of television signals. This includes the removal of natural and artificial sparks, and effects due to the operation of radio transmitters.
Analog television broadcasts display different effects due to different types of interference. Digital television reception generally provides good quality images until the interference is so great that it can no longer be eliminated by the recipient's error checking system, at which point the video display becomes pixelated, distorts, or becomes empty.
Video Television interference
Co-channel dan multipath (hantu)
During unusual atmospheric conditions, remote stations that can not normally be detected in a particular location can provide a much stronger signal than usual. Analog television images can display the sum of two signals, producing images of strong local signals with traces or "ghosts" from a distant, weak signal. Television broadcasting stations are placed and assigned to the channel so that such events are rare. Re-adjusting the receiving antenna allows more distant signals to be rejected, improving image quality.
Local signals can travel more than one path from the transmitter to the receiving antenna. The "Multipath" acceptance is seen as multiple impressions of the same image, slightly shifting along the width of the screen due to the varying transmission path. Multiple times the reception is momentary because of road vehicles or passing aircraft; Other multipath problems can survive due to reflections from high buildings or other landscape features. A strong multipath can cause an analog image to "tear" or lose sync for a moment, causing it to roll or fall.
Maps Television interference
Static electricity and sparks
Sparks generated by static electricity can produce interference.
Many systems where radio frequency interfaces caused by sparks can be modeled as the following sequences. The energy source charges C1 through resistance, and when the spark gap is damaged, the power passes through L and excites the resonant LC circuit. The energy in the LC circuit is then radiated through the air.
For example, when someone walks on nylon rugs, rubbing shoes on the carpet performs the role of batteries and resistors, while the person acts as a capacitor (C1 and C2), and the air between the hands and the door of the button is a split gap. The stray inductance acts as L.
Sparks and cognate phenomena
Horizontal lines randomly arranged on a television screen may be caused by a spark on a non-functioning electrical device. Electric trains can also be a powerful source of this type of disorder.
Other possible sources of disturbance include:
- Thermostat, refrigerator, freezer, fish tank heater, central heating system
- This can create sparks as they live or die; as they get older they can get worse. In some rare cases, they can create endless interruptions through sparks.
- Electric motors
- A motor that has a commutator can experience a splash on the brush.
- Ignition system on cars and motorcycles.
Devices that switch on powerline frequency
- Power line hardware, this can generate sparks at 100 or 120 Hz levels
- Dimmer light and other solid state power control devices.
Thyristor and Triac Regulators without proper choking are the common sources of EMI as well. It is possible that the thyristor power controller (SCR) using variable phase angle method will produce harmonics from the main supply, while the spark on contact will be a very wide band source whose frequency is unrelated to the frequency of the power supply. In the Thyristor control system, potential EMI problems can be minimized by using zero crossing switching in which the thyristor is switched on at a time when the AC voltage changes from one direction to another.
Devices that switch faster than 200 Hz
- Computers and other digital electronic equipment. This device creates and uses signals that are turned on/off at high speed. This is the case that any repeating signal can be reduced to a Fourier sine wave series. It just so happens that the perfect square wave is
E = E or sin o sin (2? T)/2 {E o sin? t)}/3......
As the term continues to run for higher and higher frequencies, square waves contain harmonics of fundamentals that continue to rise in frequency for good, this harmonic is responsible for many of the interference made by computers. Modern PCs are devices that operate within the VHF/UHF frequency range using square wave. Because the case on many computers is not a perfect shield, some of these radio frequency energies can leak and cause interference to radio reception (and sometimes TV).
- The power supply or alternate packaging mode can be a source of interference. It is used in consumer electronics/electrical products and in some lighting systems.
Strong TV signal
It is also possible to get a bad picture if the signal strength of the TV transmitter is too high. An attenuator inserted into the antenna cable can be used if the television receiver displays signs of overload on the RF front end. Strong out-of-band signals can also affect television reception and may require a band-pass filter to reduce unwanted signal levels in the receiver.
See also
- Television Interference (ghosting)
- Television Interference (Co-channel reception)
- EMC (overground strength) issue
References
Source of the article : Wikipedia
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