Noise Figure

95 chevy blazer screening noise,I belive its a bearing rubbing against some metal part just cant figure it?

out also my other main concern would it be expensive to repair thanks for all your feed back

need more information about the problem.

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Protecting your KVM and Video Extenders electromagnetic noise

KVM (keyboard, video and mouse) via CAT5 extenders can be used to remove computers from harsh or sensitive environments, or restrict physical access to the computer. Extended video products, such as VGA, DVI, S-Video or HDTV via CAT5 extenders are used to extend the video screens. Each extension consists of two units – local and remote unit, which are interconnected through CAT5/5e/6 cable.

The low cost and easy installation of twisted pair cables, such as, cat5, cat5e or CAT6 cable, they have become a popular choice over traditional coaxial cables to transmit KVM and AV signals. However, using a type of twisted-pair cable that is not appropriate for your installation environment can lead to erratic performance keyboard or mouse, loss of data, and the degradation of image quality, undermining the purpose of your station extension work or video.

One of the causes of the video signal and the loss of quality when using a twisted-pair cabling infrastructure Installation is an environment with extreme levels of electromagnetic interference (EMI or, also called Radio Frequency Interference or RFI).

Interference electromagnetic

Electromagnetic interference is an unwanted disturbance in an electrical circuit by electromagnetic radiation emitted by an external source.

All electronic and electrical devices produce electromagnetic radiation during operation. The current flowing in a circuit generates a magnetic field on the ground. The potential difference or voltage required for current to flow, produces an electric field. The strong electric fields magnetic and can cause an electrical device to affect another. When this is intentional, is known as electromagnetic interference, commonly abbreviated as EMI.

Electromagnetic interference can disturb the normal operation of electronic equipment. Normal levels of EMI such as those generated by computers, switches or routers not affect NTI KVM and video extenders. However, the extreme levels of EMI in the environment can interfere with the transmission signal. This can lead to distortion and loss of video image. The longer the cable and care less attention to the installation of cable, most likely the effect of EMI.

Some common sources of extreme EMI in a building with air conditioning, elevator motors, generators, radio transmitters and welders. Installation cables near large power transformers or in close proximity (less than one foot) of fluorescent lighting can also cause problems with EMI.

How EMI affect video signals

EMI affects both audio and video signals. In audio signals, concealed low level detail and environmental information. In video signals, interference and signal distortion manifests itself in different ways. Figure 1 shows an image without interference. Figure 2 represents a form of waveform of the video signal without interference.

Figure 1: Normal – No interference

Figure 2: Representation of a signal interference-free video

The noise from sources such as air conditioners, elevator motors, generators etc. noise manifests as lines or spots, as shown in Figure 3. This is caused by the electric and magnetic fields generated as the engine is running. The bigger engine, more fields larger the electric and magnetic will. Quickly turning the motor on and off can also cause interference. Figure 4 shows a waveform of the signal video with the interference of a motor.

Figure 3: Interference Caused by a motor

Figure 4: Representation of a video signal with interference from a motor

A broken and distorted image, as shown in Figure 5 is caused by running the cables near sources of strong magnetic fields such as large power transformers and fluorescent lights. The cables have to be very close (less than 1 foot) for fluorescent lighting interference occurs. Figure 6 shows a waveform of the video signal is affected by a strong magnetic field.

Figure 5: Interference Caused by fluorescent lights

Figure 6: Representation of a video signal with the interference of a magnetic field

A visible pattern of interference lines, as shown in Figure 7 is a result of interference from sources such as radio transmitters. The radio signal has to be robust and close to interfering with the video signal is transmitted in a twisted pair cable. Figure 8 shows a waveform of the video signal with interference from radio transmitters.

Figure 7: Interference Caused by a radio transmitter

Figure 8: Representation of a video signal transmitter with radio interference

Protection Video Signal EMI

A simple and cost effective to prevent EMI from interfering with the transmission of signals is to use a shielded cable to transmit the signal. Cable shielding is available in a wide range of designs. Each type of shielded cable construction offers distinct advantages that should be carefully considered when you select the best and most profitable option for a given application.

Braid Shields: Shield stranded in a twisted pair cable, shown in Figure 9, provides for effective shielding of audio and RF ranges. It also provides excellent structural integrity, while maintaining good flexibility. Braid shields are better foil to minimize low-frequency interference and have lower DC resistance.

Figure 9: Cable Braid shielded twisted pair

Foil Shields: A shield twisted pair cable, shown in Figure 10, provides excellent protection against electromagnetic interference and radio frequency audio. His weight and cost less than braid shields.

Figure 10: foil shielded cable Twisted Pair

Due to its small size, the aluminum shields are commonly used to protect individual pairs of multi-pair cables for reduce interference. Drain wires are usually used with protective foil to facilitate the completion of the connection in the connector shell.

Combination Foil / Braid Shields: A twisted-pair cable with a combination foil / braid shield, shown in Figure 11, provides maximum efficiency shield the entire frequency spectrum. The combination foil / braid combines the advantages of a coverage of 100 percent aluminum with the strength and low DC resistance of a braid.

Figure 11: Foil and Braid Shielded twisted pair cable

How shielding helps reduce EMI problems

Reflection and absorption are the main ways in which significantly reduces the force shield the EMI on the signal carrying conductors inside a shielded twisted pair cable. Figure 12 is a representation of how the cable may reflect the high frequency EMI, and from a radio station. The same shield will also absorb part of the energy EMI radio transmitter, further reducing the amount of EMI that makes internal twisted pair conductors. When properly installed with shielded connectors teams land, protection redirects a small amount of electromagnetic energy. These effects of reflection, absorption, and redirection to shield very effective at reducing the problems of high frequency interference.

Figure 12: Representation of Braid or foil reflecting EMI shielded cable

The best way to protect against EMI from low frequency magnetic fields, such as a motor or a transformer, is to provide sufficient distance between the cable and the source of the interference field. Cable shielding has only limited effectiveness in preventing interference problems of reduced frequency fields magnetic. Instead of a magnetic field to reduce the reflection or absorption, the cable produces a magnetic field opposed to the frequency low magnetic field interference. This has the effect of reducing the variable magnetic field intensity that reaches the twisted pair conductors. Figure 13 is a representation of how the shield can reduce the strength of this type of interference from reaching the inner conductors twisted pair.

Figure 13: Cable shielding reduces EMI intensity inside the cable

The Conclusion

If you have a problem of electromagnetic noise, we recommend using shielded cable. When dealing with frequency electromagnetic noise only, like a radio transmitter, foil shielded cable ensures adequate protection. To achieve effective protection against low frequency electromagnetic fields as an electric motor, a shield or braid a combination aluminum foil / braid shield is necessary. If you are unsure about the type of electromagnetic noise, we recommend a combination of aluminum / braid shielded cable, It provides the best protection against the widest range of electromagnetic noise.

About the Author

Network Technologies Inc (http://www.networktechinc.com/) manufactures keyboard-video-mouse (KVM) and audio/video switches, splitters and extenders for computers (PC, MAC, and SUN, including USB) and video sources (DVD player, satellite receiver). By consistently providing KVM and audio/video solutions that combine innovation with reliable high-performance, we empower our customers to improve efficiency, reduce equipment and energy costs, and maximize space utilization. We have been rewarded with over 20 consecutive years of dramatic growth.