Index


Audio/Video Wiring Page

    Audio/Video cabling introduction

    Right kind of pre-wiring is the key to successful installtion of audio/video system later on. It is always safer to pull more than you need today so that you are ready for tomorrow. Just a few years ago a single RG-6 coax to the TV was enough. But today more wires is needed.

    Today, when people are building homes and electricians are wiring them, there are many more types of cable that need to be used. The electrical contractor will still be installing pretty much the same type of wire for electricity service that was used decades ago.

    For telephone service, we are seeing homes now being built with Cat 3 or Cat. 5 cable that was originally developed for computer networks.

    Since the late 70's most homes have access to cable TV service. Analog signals (audio or video) require adequate shielding to protect themfrom interference. They also require sufficiently low capacitance (relative to the impedance of the source and load) to avoid high-frequency losses. For carrying high frequency signals (video signals, digital audio, TV/radio antenna) you need a cable with right impedance matched for signal source and receiver impdances. A ll but the cheapest right type cable usally meets these requirements easily.

    For example any good-quality 75-ohm coaxial cable will work properly foreither video or digital audio in a home system. Even in professional systems. Some people make big bucks by selling "boutique" cable for big $$$, but nobody has ever shown objectively that these cables have any advantages over ordinary good-quality cable. Generally the traditional cable for video installations has been RG-59 and RG-6. RG-59 is the default cale for many not so demanding antenna wiring applications and for baseband video.

    Audio and video cabling systems are generally build using four different types of cables:

    • 75 ohm coaxial cables for video signals (both baseband video signals and RF-modulated antenna/cable-TV signals) and digital audio, typical cable types are RG-59 and dual/quad shielded RG-6
    • shielded single wire cables (coaxial like construction) for unbalanced analogue audio signals used in consumer audio systems
    • shielded twisted pair wiring for balanced analogue and digital audio signals used in professional audio systems
    • thick insulated wire pair for speaker wiring.

    Besides that some AV-system installations use unshielded twisted pair wiring for transportingsome control signals between equipments.

    In professional TV broadcasting environment you can also see triax cables, which areare used in TV broadcast industry for TV camera interconnections. Triax Cable is designed as a 75 ohm coaxial cable with two isolated shields to provide multiple functions through one cable to your camera such as power. There are two versions of triax cable commonly used in TV industry: RG59 (3/8") and RG11 (1/2").

    Those are the basic cable types used in audio/video systems wirings. The basic wiring systems consist of those wire types.

    In some applications the unshielded twisted pair (UTP) used in a structured cabling systems can be used as part of audio/video wiring system. Use of the unshielded twisted pair cable (CAT5, CAR5e, CAT6) is increasing because more and more often used structured cabling system use this kind of cable. Generally unshielded twisted pair cable is not directly suitable for carrying the audio/vidoe signals that come from audio and video equipment. But with suitable adapters installed between equipment and wiring, it is well useable as AV media to carry audio and video signals.

    When specifying whatever cable type for AV installation, look at the specifications on attenuation, temperature ratings, voltage and currentcapacity, and the type of outer jacket used. In video equipment wiring the 75 ohm coaxial cable is the standard to carry video signals. Cable selection is important to achieving high quality design. Installers need to know when to use 75-ohm baseband or broadband coaxial cable, RG-59, RG-6 or RG-11 cable, fiber optic or unshielded twisted pair cable.

    The standard medium installed in video applications is 75-ohm baseband and broadband coaxial cable. Most manufacturers publish specification sheets listing cable property characteristics. In terms of attenuation, for example, RG-59 baseband cable can be run to 600 feet (200 meters), and RG-6 and RG-11 baseband cable are effective to 850 feet (270 meters) and 1200 feet (400 meters), respectively.

    For some applications where a small cable is needed to carry video signal RG-179/U is used quite commonly (there are also many small non-standard ccoaxial cables used mostly as part of larger cables with multiple coaxial conductors). Those smaller cables have much higher attenuation than the larger cables, so they are usable only for shorter distances. Broadband cable distances, however, vary with channel frequencies.

    For very long runs, where baseband and broadband cable would experience attenuation problems, consider using fiber optic cable. For baseband applications, the cable typically used is 62.5/125- micron multimode fiber, while broadband normally uses single-mode fiber. To be able to use fiber optics to carry the signals, you need special adapter devices on the bith ends of the fiber. There are adapters available to carry video signals, audio signals and brodband cable TV signals over fiber. Most this kind of adapters are targeted fro professional audio/video markets, and tend to be expensive.

    Baseband video signals can also be transmitted over unshielded twisted pair cable (you need suitable adapters for this). At least Category 3 UTP is recommended to provide attenuation properties similar to coaxial cable. These properties are sufficient for using UTP in such applications as video to the desktop and CCTV camera signals.

    For most baseband video applivation almost any well-made 75-ohm cable will be fine.The main requirements for video cable are adequate shield,and proper (75-ohm) impedance. A normal RG-59 cable (or better) is good to carry videosignals (compsite video, S-video, RGB, component video etc.) for long distances. For best baseband video performance avoid cheap TV aerial cable, use proper pro-grade video cable, which has much heavier shielding. NOTE: For short (less than 1m) distances video connections (composite video), you can even dispense with the 75-ohm impedance. Many consumer BNC hook-up cables that come with VCRs, etc. are not 75-ohm. Because they are so short it doesn't really matter. For any longer distances the impedance matters.

    To carry antenna signals TV aerial cable is best, because it has low attenuation at high frequencies and good shielding on those RF frequenices (some propertiessome other video cables not always have). Same applies to cableTV systems. In cable TV systems at the central point, the 5-6 MHz baseband video signals are fed into individual broadband channel modulators. These units modulate the signals to cable television frequencies of 50 to 450 MHz and distribute them to the receivers. For fixed installations to carry antenna signals installing RG-6 coax cable is recommended. Also RG-11 broadband cable is suitable for this application.

    For a good quality antenna cable wiring quad-shielded all-copper center conductor RG-6 cable is recommended. Copper-plated steel center conductors are also available, providing additional stiffness, but are unable to handle low-frequency currents used to power some devices. When wiring cable TV signals, low loss and good shielding are needed. Many cable TV companies in big cities in USA specify quadshield to comply with FCC regulations regarding signal egress and to protect their own cable infrastructure from through-the-air signal ingress. These environments do vary geographically, and in rural areas, non-quadshield RG6 might be in use. But in dense metropolitan areas, quadshield is specified. Quadshield is not as important for satellite installations. Typically dual shielded (foil+fraid) is used for satellite intermediate frequency cabling (i.e. the cabling between the LNBs and the receiver) because at those frequencies (roughly 1-2GHZ), signal egress and ingress are not much of a problem.

    For one reason or another, manufacturers started to make also specialty cables for video that are convenient to use, but exhibit poor performance. One example of such cable is S-video-cable, which is typically made of two strands of very small (and very lossy) 75-ohm coax terminated at either end with a connector that is anything but constant impedance. With cables that are very small and easy to bundle, we paypay a price in signal strength for convenience.

    Point-to-point wiring is most common for analog baseband video. Video surveillance, one such point-to-point application, is only one image per cable. Monitors in airports, and similar displays carry one image pe rcable. Classroom television is one image per cable.

    The requirements for audio are adequate shield (to fend off interference along the way)and proper cable to suit the termination (balanced, unbalanced, etc.). Because audio is sent by voltage, if you use cable with high capacitance over very long distance, the capacitance of the cable forms an R-C network with the output impedance of the source (also the input impedance of the destionation has some effect on this, but typically very small). This results in alow-pass (high rolloff) "filter". The higher the equipment impedance and larger cable capacitance, more rolloff. High output impedance (typically up to several kilo-ohms) is feature in many consumer audio equipment, and this limits the distance you can carry the signal without noticable high frequencyattenuation. Consumer audio equipments with lower output impedanceand professional audio equipment (always low impendance output, usully 50-600 ohms) will happily run 10-30 maters of cable without noticable loss (professional devices with balances connections runs up to 100-300 meters are not uncommon).

    Audio lines are generally not impedance-matched. Practically speaking, electrical engineering transmission line theory does not apply to real world audio lines that carry analogue audio signals. To carry audio signals without interference use something with proper shield, at least 85% coverage braided, but prefereably 100% coverage foil shield with braid.

    For balanced audio a proper shielded twisted pair cable (like "professional microphone cable") is best. Typical this type of microphone cable has around 70-150 ohm/km resistance on conductors, typically around 50-70 pF capacitance between the conductors and around 90-130 pF capacitance from conductor to shield.

    For unbalanced audio shielded single conductor cable (coaxial construction)is the most commonly used, but shielded twisted pair cable works also well. Cable shielding is offered in a wide range of designs and configurations. Each type of shielding has its own distinct advantages and disadvantages that need to be considered when selecting the best and most cost-effective option for a given application. Shields available on the market today include:

    • Braid Shields: Braid shields provide superior structural integrity while maintaining good flexibility and flex life. These shields are ideal for minimizing low frequency interference and have lower DC resistance than foil. Braid shields are effective at audio, as well as RF ranges. Generally, the higher the percentage of braid coverage, the more effective the shield.
    • Foil Shields: Foil shields consist of aluminum foil typically laminated to a polyester or polypropylene film. Foil shields provide 100 percent cable or component coverage, improving protection against radiated emission and ingress at audio and radio frequencies. Because of their small size, foil shields are commonly used to shield individual pairs of multi-pair cables to reduce crosstalk. Foil shields are more flexible than braid but have a shorter flex life. Drain wires are generally used with foil shields to ease termination and ground electrostatic discharges.
    • Combination Foil/Braid Shields: Combination shields consist of more than one layer of shielding and provide maximum shield efficiency across the frequency spectrum. The combination foil/braid combines the advantages of 100 percent foil coverage with the strength, flexibility, and low DC resistance of a braid. Typical braid coverages range from 60 to 95 percent.
    • French Braid Shields: A relatively new development in cable shielding technology, especially suited to audio and RF cable applications, is an ultra-flexible double spiral shield. This design consists of dual spirals of bare or tinned copper conductors, with the two spirals tied together by one weave. The French braid shield construction provides longer flex life than standard spiral shields, and greater flexibility than conventional braid shields.

    Cable capacitance is sometimes quite much talked about. The cable capacitance is simply a function of the diameter ratios of the inner and shield, and the permittivity of the dielectric. Typical microphone cable has around typically around 50-70 pF capacitance between the conductors and around 90-130 pF capacitance from conductor to shield.

    Also, impedance and capacitance are separate issues. For analogue audio, impedance is irrelevant (unless your run is kilometers long). For analogue audio capacitance is relevant and cable impedance for audio freuquencies is typically not specified. For digital audio, or for video, impedance is relevant and capacitance is practically irrelevant.

    For digital audio the typical wanted impedances are 110 ohms for twisted pair shielded cable and 75 ohms for coaxial cable. Usually a normal "analogue audio cable" does not fullfill those needs, because their impedance can be easily anything between 40 and 150 ohms depending on the cable construction and materials. Impedance can vary considerable between different cable manufacturers and cable batches.

    In general wiring case to be future proof you need multiple RG-6 coax runs, Cat 3 or 5 wire phone lines, Cat 5 network lines, and possibly fiber optic lines.

    In live sound and video systems lots of temporary cabling needs to be installed on the floor, hanging from roof and to the walls. For safety reasons this kidn of cables on the floor should always be secured to the floor with gaffer's tape or otherwise protected. Gaffer's tape is a special kind of colored tape (usually matte black) similar to duct tape, but more expensive due to the non reflective surface and special adhesive that doesn't leave gummy reside behind. Used for everything from securing mic cables to the floor, to holding speakers in place on the stack.

    Cable types

      Cable data

      Propably most common type of cable used to carry video signals is RG-59 B/U type 75 ohm coaxial cable. The general data for this cable is RG-59 B/U

      • Specification : MIL - C - 17
      • Impedance : 75 ? 3 Ohm
      • Attenuation : at 1 MHz 1,5 dB / 100m , at 100 MHz 12,0 dB / 100m
      • Capacitance : 67 pF / m
      • Frequency : 3 GHz
      Here is some more detailed data on the cable (data from Belden 8263 RG-59 B/U type cable, data can vary slightly from manufacturer to manufacturer:
      • Impedance: 75 ohms
      • Inductance: 0.115 michohenries/feet
      • Capacitance: 20.5 pF/feet
      • Progapagation velocty: 66%
      • Delay: 1.54 ns/feet
      • Conductor DC resistance: 49 ohms / 1000 feet
      • Shield DC resistance: 2.6 ohms / 1000 feet
      • Max. operating voltage: 150 VRMS (UL) / 1700 VRMS (non-UL)
      • Temperature: -40 to +60 degrees Celsius
      • Min. bendign radius: 2.5"
      • Max. pulling tension: 78 LBS
      • Nominal weight: 35 LBS / 1000 feet
      • Conductor material: 23 AWG solid bare copper codered steel 0.023"
      • Insulation material: Polyethylene
      • Conductor insulation diameter: 0.146"
      • Shield type: Bare copper braid with 95% coverage
      • Jacket: Non-contaminating PVC (black color)
      • Cable diameter: 0.242"
      • Use: Suitable for indoor and outdoor
      • Transfer impedance at 3 MHz: 36 mohms / m.
      Attenuation data for RG-59 B/U:
      MHzdB/100 feet
      1 .6
      10 1.1
      50 2.4
      100 3.4
      200 4.9
      400 7.0
      700 9.7
      900 11.1
      1000 12.0
      The original RG-59 B/U MIL-C-17 uses Copper Plated Steel center condictor, In addition to this type many cable manifacturers manufacture also RG-59 versions with Bare Copper center conductor (less resistance, more flexible cable construction). Another commonly used cable type is RG-6. It is a high quality 75 ohm coaxial cable used generally for antenna and CATV wiring. RG-6 is a higher-grade cable than RG-59 and therefore a better choice where performance is important. It uses a larger, higher-capacity center conductor (18 AWG) and a larger insulating dielectric. It may also have additional foil shields or braids (as in tri-shield and quad-shield types) to fight electromagnetic interference. Both broadband RF video, and baseband (lower-frequencyRF) are commonly carried using 75-ohm coaxial cables. There are often differences between the construction of these cables, depending on thefrequency ranges being carried.Broadband (antenna, cable-TV, and satellite) video signals range upinto the high hundreds of MHz, or even higher in the case of some satellite-dish downfeeds. Because the frequencies are so high, the"skin effect" in the cable conductors limits the current flow to avery thin layer on the surface of the conductor. To keep losses inthe cable low, you need a fairly large-diameter conductor (with arelatively large surface area). Most RG-6 cable is of this type...some variants use a stranded-copper center conductor, some a solidcopper, and (I believe) some use a "copperweld" (steel core, thincopper cladding) for tensile strength on long cable-TV runs. As aresult of the conductor thickness and construction, RG-6 is often afairly stiff cable.Composite and component video are usually referred to as "baseband"signals, and their frequency content doesn't go up above a few MHz (few tens of MHz or up to something like 150-200 MHz on some very high frequency computer signals). You can get lower losses with a thinner (often stranded) conductor,and thus have a more flexible and easier-to-route cable. Hence composite-video cables are probably bettersuited for carrying basedban videon than RG-6 broadband coax would be. Same that applies to composite video applies to component video as well. Individual component video signalsare not significantly different from composite.

    Connectors

    The most commonly used connector in video wiring is BNC connector. Because the cable used it 75 ohms cable, the right connector type for this cable is 75 ohm BNC connector. The traditional usage of 50 Ohm BNC connectors on 75 Ohm cable with analog equipment (video & telco) has little distortion effect on the signal at frequencies below 300 MHz. However, digital signals in video and telephony applications have necessitated the usage of 75 Ohm connectors.

    "BNC" connectors have a bayonet-lock interface which is suitable for uses where where numerous quick connect/disconnect insertions are required. BNC connector are for exampel used in various laboratory instruments and radio equipment. BNC connector has much lower cutoff frequency and higher loss than the N connector. BNC connectors are commonly available at 50 ohms and 75 ohms versions. Power handling of this connector is 80 Watts at 1 GHz. The frequency range is 0-4 GHz for 50 ohm connector and 0-1 GHz for normal 75 ohm connector (higher frequency 75 ohm connectors could be available). A often asked question is what is the difference of 50 and 75 ohm connector. The connector metal parts are identical in both versions in the contact area. The 50 ohm connectors have additional 'insulation' members, which are actually dielectric to increase the shunt capacitance and thus lower Zo from 75 to 50 ohms. The difference can be different insulation shape and/or different insulation material. The main visible physical difference is that the 75 Ohm plug does not have extended dielectric around its outer spring fingers. The current BNC connector standard is IEC 60169-8. In the distant past, there were also other variations (the centre pins of the 50 and 75 ohms connectors were once of different diameters, either the connectors won't mate or the '75 ohm' pin will not make good contact with the '50 ohm' sleeve).

    If the BNC plugs and sockets in question, and indeed other types of connectors, are to be used only at a few hundred MHz and below, then the user should be aware that a 75/50 ohm mismatch over a distance considerably less than the length of a connector will cause absolutely negligible measuring errors in such matters as SWR. For example in video applications you can see sometimes 50 ohm BNC connectors used sometimes in otherwise 75 ohm system. Start worrying only when there is a large energy content in the signal above 1 GHz. It is necessary only to ensure a good, solid, electrical contact in connectors at DC and the HF properties will look after themselves. Mechanically wobbling, intermittent, connectors are not good at any frequency. If the dimensions of pins of mixed 50/75 ohm BNC connectors allow good, solid, DC connections then there's nothing whatever to worry about. The HF properties and performance of single mixed plugs and sockets up to and including VHF will look after themselves quite satisfactorily. There's far too much importance attached to actual impedances below 1 Ghz. The 50/75 issue is important in standard definition serial digital video running at 270 mbits (ccir 601). The impedance variations can cause the serial receivers to lose lock (takes more than 1 connector to mess things up).

    When talking about RF modulated video, cable TV and TV receiving antenna systems you can also see other connector types optimized for those applications. The most commonly seen connectors on those RF applications are "F" connector and "IEC antenna connector".

    "F" connectors were primarily designed for very low cost high volume 75 Ohm applications much as TV and CATV. In this connector the center wire of the coax becomes the center conductor. High quality F connectors can handle 0-3 GHz frequency range. Technical specifications typically specified at 1 GHz frequency. "F" connectors are seen in all kind of antenna cabling systems inside system. "F" connector is used as the connector in antenna outlets at house and also as equipment connector in USA. Standard practice on "F" connectors is that equipment and outlets have femate connectors, while cables have male connectors.

    "IEC antenna connector" is a very low-cost high volume 75 ohm connector used for TV and radio antenna connections around Europe. This connector is primarily designed for antenna signal input primarily into consumer audio and video equipment. The typical frequency range this is used is 0-1 GHz. This connector can be found on both equipment and on fixed wiring wall outlets in Europe. The connector is defined in IEC 169-2 standard. Typically the female connector is found on TV antenna input, and TV antenna outlets have male connection in them. The normal cables have male connector on one end and female on another end. The antenna connectors on FM radio receivers typically have male connectors in them and FM/radio outlet has female connector on them.

    Cable TV and antenna cabling

    The earliest cable TV system and house antenna wiring, in effect, are just strategically placed antennas (or other signal sources) with very long cables connecting them to subscribers' television sets. So it just basically a very large RF signal distribution network. Cable TV systems and other large TV antenna systems are traditionally built using RG-6 or RG-11 coaxial that is terminated with F-connector(or IEC antenna connector on European countries). RG-6 cable is the preferred cable for in-house antenna wiring. RG-6 is a rating of quality; some manufacturers use RG-59 or lower grades, but you should avoid these as your picture quality will not be as good (more loss is cable and not so good shielding at high frequencies).

    Despite being shielded, some interference can occur on coaxial cable lines. This interference can be a considerable problem when low level high frequency signals are transported. For cable television it is important to use the correct type of coaxial cable. RG-59/U should be avoided, and only RG-6/U, or in cases of severe interference, RG-6/UQ (quad-shield) used. Many consumers have purchased the cheaper RG-59/U to use as an extension for cable television, only to find it causes severe interference. The reason for the interference is that cable channels 2-13 share the same frequency as those from television broadcast towers. If the cable consumer is too close to a television tower and the cable company provides the same station on the like channel, interference and 'ghosting' may result. If the same frequencies transport different programs, severe cross interferences of two program signals exist. Leakage of cabe TV signals can also cause interference to aircraft communications which operate on the same frequency as several cable channels. This may even be a violation of the law.

    In a coaxial cable like the one that brings CATV signals to your house, radio signals travel at about two-thirds the speed of light. The system bandwidth has effect on what and how many TV channels can be transported through the wiring.Early cable TV systems in USA operated at 200 MHz, allowing 33 channels. As technology progressed, the bandwidth increased to 300, 400, 500 and now 550 MHz or even up to nearly 1 GHz. Today it is estimated that there are over 60 million cable TV subscribers in the USA. Antenna networks generally consists of signal source (antenna or modulator rack), signal amplifiers, cable, splitters and antenna outlets. The whole TV antenns system is matched for 75 ohm impedance, which means that all components are matched for this impedanse.

    The cable used in TV antenna networks is 75 ohm coaxial cable. Cable runs with copper braid RG59 should not exceed 750 ft (250 meters) (RG59 is not recommended cable nowadays beacause of poor shielding), while RF6 copper braid is good for 1,500 ft (500 meters).

    The RF signal is generaly split to multiple TV antenna outlets using splitters. The loss of a 2-way splitter is approximately 4-6dB and 6-9dB for a 4-way type. Signal loss should be compensated by an amplifying signal with suitble amplifier. Splitters are used to split one incoming wire to two or more outputs. Splitters split the incoming signal power to the outputs evenly and maintain the impedance matching on the systems. Splitters provide isolation between receivers (Withoutisolation one receiver could degrade the quality of the signals goingto other receivers). When using splitters be sure that all unused outputs are terminated with 75 ohm load or terminator to avoid signal reflections and degration of thesplitter performance.

    Add amplifiers to compensate the losses when signal needs to travel long distances of cable (add amplifiers to the signal source end of the cable). Long cable runs will weaken the signal, which means increased noise in analogue TV transmissions and increased number of transmission errors in digital TV broadcasting. Amplifiers are also needed to compensate for the loss from splitting the signal. Add attenuators when the signal is too high. Many amplifiers have a gain control that canbe adjusted to prevent strong local stations from causing signaloverload. Add tilt compensators on long runs (long cables attenuate higher frequencies more than low frequencies, tilt compensator compensates for this). Only industrial-quality cable TV amplifiers (generally not available at retail) should be used to amplify weak signals. Cheaper ones, sold at consumer electronics stores, often cause more problems than they solve.

    The simplest antenna outlets are just F-connectors on the end of the antenna cable coming from the wall (this is commonly used in USA). The antenna outlet can also be a wall jack with F-connector.In Europe IEC/DIN45325 antenna connectors (9.5 mm coaxial connectors) are generally used. In large antenna networks special antenna outlets are used. Those outletshave the following functionality: attenuate the signal from the incomingwire to outputs and filter the different frequencies to different outlets(TV and radio). The signal attenuation is generally used to provide someisolation between the incoming antenna signal cable and the output connector so that what is connected to outlet does not disturb what is in the line (so it does not matter if there is emply outlet, jsut piece of antenna cableor TV connected). The isolation between the output and signal cable is specifically needed in antenna networks which use daisy-chained antennaoutlets. Typically the systems are aiming 20 dB or better isolation between the different antenna outlets in the system.

    A standard procedure for new homes is to have a junction box in the basement. The cable from antennas or cable TV source will come into the junction box, and there will be cables going to every placethere might be a need for a TV. With this,you can do most any splitting you might need. Well almost everything.

    The ideal video distribution system has balanced signal strengths at all termination points. This means that all signal outlets have prety much the same signal level within the specifications. In many European countries the signal level on antenna connector should be between -60..80 dBmW. Lower signal strenght causes noise to the picture and higher levels can also cause problems. Usually it is a good idea to keep the signals close to the maximum allowed strength (especially if splitters are use for multiple TV sets), as this will increase the signal-to-noise level (the "noise" being the pickup of the broadcast tower, other way to reduce that is to use better shielded cables). In USA maximum signal strength to TV outlet allowed by the FCC is 15.5dBmV (systems aim to supply at least 10 dBmV, devices generally work well in 0-20 dBmV range).

    Nowadays the preferred method to wire the antenna network inside s house isto use "star" form antenna wiring. This means that from each antenna outletthere is one cable from the outlet to the antenna distribution center, wherea large splitter splits the signal to all those outlets. This arrangementgives best performance and is the most flexible (if you have two or more splitters in distribution center with different services comign to them, it is possible to wire different services to different antenna outlets).

    Note on 300 ohm cable: Once in the history of antenna networks a flat 300 ohm "twinlead" antenna cable was popular. The use of it is not much used nowadays, because of poor performance compared to today's standards.You would almost certainly get better results with coaxial (round) antennacable rather than 300-ohm "twinlead" (flat) cable. The flat cable is notshielded and recieves (and radiates) along its entire length. If you have some device still in use which has 300 ohm connections, thenuse an antenna balun for conversion between 300 ohm interface and standard75 ohm coaxial wiring. In some special applications "twinlead" can still be useful with careful planning. The advantage of coax over flat 300-ohm cable is that longer runs can beused without signal degradation (flat ladder line is the lowest loss cable) .Flat cable when twisted in the prescribed manner (6 turns per metre) is actually quite impervious to spurious signals of placed away from objects. Coax is certainly better when placed close to objects, as flatcable should be floating free of objects, especially metal. I do not recommend using 300-ohm "twinlead" in any new installation.

    Triaxial cable

    Triaxial cables are primarily used for electrical connections for video cameras and transmission systems.Their high-quality materials and high-precision balanced design maximise their transmission properties (lowattenuation, even characteristic impedance). The smooth outer braided screen enables cameras to be supplied with power. Triaxial cables are used in TV broadcast industry for TV camera interconnections (connecting camera to CCU and supplying power to camera). Triax is a clever (though complex and expensive) system to enable a broadcast television camera to 'communicate' with its base station by means of a single fairly light weight co-axial cable. Triax is a cable used primarily in analog video camera applications, but there are also digital camera systems that use triax cable. Typical triax system can have 300-500 meters of cable between CCU (camera control unit) and the actual camera device.

    Triax cable contains a coax, inner jacket, braid, and overall jacket. The coax is used to transmit the video signal. The two braids are used to send power and multiplex various other signals from the CCU to the camera. Triaxial cables are constructed with a solid or stranded center conductor and two isolated shields. Triaxial cables which are essentially coaxial cables with an added outer shield that lowers ground loop interference and eliminates radiated noise or cross-talk. Various triax cables are available in RG-59/U RG-6/U and RG-11/U 75 ohm constructions. The standard sizes include RG59/U and RG11/U types. The RG59/U is the smaller of the two and is generally more flexible. RG11/U has lower attenuation values that will allow longer cable runs. The metric size triaxial is similar, being the smaller size is generally more flexible and the larger size having lower attenuation values. Global metric cable outer diameters are 8mm, 11mm and 14mm.

    The center conductor and the inner isolated shield make up a coaxial cable configuration that functions to carry the video signal. The outer isolated shield can be used for several separate signals by means of multiplexing that may include power feed, teleprompter feeds and control for automation. Triax Cable is designed with two isolated shields to provide multiple functions through one cable to your camera such as power. There are two versions of triax cable commonly used in TV industry: RG59 (3/8") and RG11 (1/2"). In Triax applications the cable types used are generally referred with their thickness: 14 mm, 11 mm and 8 mm Triax cable. Triax cables use special triax connectors. The TV industry generally uses the connectors made by Lemo and Fischer. There are at least three different commonly used triax connectors in TV production industry. Typical triax camera system can send the picture from over a triax cable for up to 500 meters with no degradation. Camera set-ups that can be remotely adjusted though the cable, as well as usually intercom functions.

    Triaxial cables are terminated with various connectors that are designed for hard field use in mind (that makes them expensive). European triax system use Fischer, Lemo 4M connectors, Lemo 3T connectors and Lemo 4E connectors. US systems have their own connectors. This means headaches for camera technicians on internationally televised events, because typically the locally installed fixed wiring is terminted with the locally standardizes plug type, which could be different that what your camera cabling uses. Here is a quick overview of some of those types:

    • LEMO 3T: Lemo 3T series is particarly intended for outdoor use. This connector guarantees IP 66 protection per IEC 529 when connectors are mated. The 3T Series triaxial connectors are fully intermatable with the ULC Series size III TCX75 (triaxial 75 ohm) connectors. Lemo 3T Series connectors are used widely in France.
    • LEMO 4A: Lemo 4A series is widely used by the most manufacturers of professional video camera. This connector can be used outdoors or indoors. Lemo 4A connectors are mainly for USA and associated markets. Similar to the 4M Series, these 4A connectors are compatible with the Kings Tri-Loc KP80 Series.
    • LEMO 4E: Lemo 4E is designed for harsh enviroments. The non-keyed shell is designed for blind mating. This connector guarantees IP 66 protection per IEC 529 when connectors are mated. The rugged metal outshell provides very good protection. The 4E Series of triaxial connectors are commonly used for microwave links in broadcast operations throughout Europe as well as camera cables.
    • LEMO 4M: Lemo 4M is a series of 50 ohm and 75 ohm triaxial connectors especially designed for video cameras and for harsh environments (IP66 protection). The construction is the same as in Lemo 4E connector, added with mechanical key/guide that to avoid both connector/contact rotation and signal interruption. This reliable and versatile Lemo 4M model has been adopted by the British Broadcasting Corporation (BBC) as its standard camera connector.
    • Redel F series: Redel F Series self-latching triax connectors are compact connectors designed for TV cameras. They are deisgned to be easy to assemble and have good electrical characteristics. REDEL F Series is quite similar to the 4M Series, these connectors are fully intermateable with the 1051 A004 Series. Redel F series connectors are for UK and European markets.
    • Fischer 1052: The 1052 series for USA market is intermatable with existing standards and ideal for 3/8" and 1/2" in 75 ohm cables.
    • Fischer 1051: The industry standard self-locking Fischer 1051 triax connector series is ideal for 8mm & 11mm Triax cable is already in service by all major users worldwide. The development of the 1051 Series Triaxial connectors was achieved in close co-operation with leading TV Camera manufacturers. The waterproof and rugged design assures a reliable transmission between camera and control unit in studios or outside broadcast vehicles.
    • Kings Electronics Tri-Loc: Tri-Loc ctriax connector series from Kings Electronics is wiely used in USA for triax camera connections. Often used connector series are 700, 730 and 80. King's Tri-Loc? Camera Connectors King's Tri-Loc Series of triaxial camera connectors was developed to solve video interconnect challenges faced by major networks. The user-friendly connectors have push-on and pull-apart mating that has proven durable in the field. They quickly and accurately terminate 75 Ohms 3/8" and 1/2" triaxial cables, ensuring low loss between digital cameras and control units. Specially designed seals make these connectors, when engaged, completely weatherproof and well suited for outdoor use.
    • ADC ProAx? Triax Camera Connectors: ProAx connectors feature field-repairable center conductors. If you need to make a repair or reverse the gender, simply remove the outer shell and insulator, unscrew the center conductor housing, and replace the center conductor assembly. With ADC?s ProAx connectors, gender parts can be swapped back and forth between males and females in only a few seconds. ADC?s patented ProAx connectors can be format reversed between U.S. and global formats (Fischer?, Lemo 4M, Lemo 3T, Lemo 4E) in only seconds. Plus, ADC?s ProAx connectors are designed to fit standard U.S. triax cables as well as global metric 8mm, 11mm and 14mm cables. ProAx connector can be either cable-mounted or panel-mounted.

    Triax connectors can really take a beating ? especially in field applications where dirt, sand and moisture are everywhere. When the female center conductor breaks, or the male latches are worn, the entire assembly must be cut off and reterminated. Many connectors used are difficult to terminate, and even more difficult to field repair. Connectors from Lemo use Lemo push-pull latching system, that means that the connectors are easy to connect and disconnect in the fiels, and stay well in place when connected. This system enables the connectors to be mated by simply pushing together, after which it provides a safe connection that cannot be disrupted by pulling on the cable. Disconnection is achieved by pushing back the outer latch sleeve. Fischer has it's own self-locking mechanism.

    There are (at least have been) two types of triax systems in use in broadcast industry: analogue triax and digital triax.In conventional Analog Triax the signals (component video, audio, intercom, control etc.) are modulated onto different frequency carriers which are carried through the same cable. The audio, video and control signals are then modulated to those carriers using suitable modulation (for example FM modulation). Typically the various video and audio signals from thecamera are modulated into various FM radio carriers, and sent down the centre conductor. At the same time RFmodulated communication, video feeds and control instructions were travelling in opposite direction back to thecamera. The triax adapter sorted all of this out. The camera had power, syncronising and control signals, thecameraman had video feeds and two way communication, and the director had 'perfect' video and audio signals. For example Triax-HD used by Philips uses Y/Cr/Cb transmitted as 30/15/15 MHz frequencies. In Digital Triax system Component Digital video (plus other signals) running down the cable in digital from (data rates up to around around 300 Mbit/s). Triax cable is not used in home video systems. Triax cable is extensively used in professional video broadcasting industry. Triax cabling is typically installed to many places where large events (concents, sports events etc.) take place for the video system to easily allow for professional broadcast applications. In a typical triax system there are the following parts:

    • Video camera
    • Camera Adapter Unit (CAU): Adapter box on the camera end that connects triax cable to camera. This adapter receives signals from triax and connect those to camera.
    • Camera Control Unit (CCU): This is the unit on the video control room where the triax cable. It sends camera power to triax cable and adapts all the signals on triax cable to suitable signals that can be connected to rest of video production system. All camera control functions are available from the control panel located at the CCU.
    • Triax cable: The cable between CCU and CAU
    When using triax cable, the overall system is powered by AC power at the CCU. Because the cable length can be very long (up to hundreds of meters) and considerable power needs to be transported (large camera and local monitor), the voltages transported through the triax cable can be quite high (up to 160V DC or 250V AC on some systems) to allow long distance power transfer (resistance can be 5-30 ohms per kilometer).The high supply voltage is converted in the camera adapter to 12V DC by a switched mode power supply. Because of high voltages on the cable, there are various special precautions that are taken in account to monitor earth leakageetc. to prevent electric shock under fault (damaged cable) conditions. Do not connect or disconnect the triax cable with the system powered up. Avoid the possibility that anyone can get into contact with the signals on the cable. For professional video use, it is recommended that the used triax cable that is made of pure copper. The DC resistance of copper-coated steel triax cable is much higher andmaximum cable length may be limited to one-third or less of ratedlength due to power losses in the cable. A typical triax system has the bi-directional signal multiplexing capability that provides power, genlock, return video, program audio, intercom, tally and complete camera control from the CCU to the CAU. Adaptation to use coax cable: The same multiplexing idea as used in triax can be used also with coax cable. In coax adaptations, the same signals are carried through 75 ohm coaxial cable but the cameras are locally powered from some other source than through the cable.

    Video and audio over twisted pair wiring

    Normally video transmission is done using 75 ohm coaxial cables, but unshielded twisted pair or UTP cable is a very inexpensive interconnection when compared to a coaxial cable connection. Modern unshielded twisted pair wiring (CAT5 or better) can be used to transport video signals when this is done in the right way.

    The secret to sending signals over UTP is to balance them well in order to limit both radiation and noise pick up. This kind of unshielded twisted pair wiring method is used in many CCTV applications nowadays to use existing in-house twisted pair wiring instead of installing new coaxial cable for the CCTV camera. For at least 20 years products have been available capable of transmitting video using UTP wire.

    When wiring A/V signals to unshielded twisted pair wiring (RJ-45 comnnectors),two of the eight conductors found in Cat 3 or Cat 5 cables are used for each signal. Line noise, cross talk and attenuation are low in this way. This means that one eight conductor (4 pairs) cable can be usedto carry up to four different signals. Extra, unused conductors can even be used for carrying power to the device or other signals. Unshielded twisted pair or UTP cable is a very inexpensive interconnection when compared to a coaxial cable connection. The attenuation characteristics of the UTP are an order above those of coaxial cable. Here is some data on loss in dB per 100ft (~30m) of common cable types:

    Freq.(MHz)  RG59  RG6  CAT-5
    1 0.4 0.2 1.8
    10 1.4 0.6 5.8
    50 3.3 1.4 11.0
    100 4.9 2.0 19.3
    200 7.3 2.8 29.3
    400 11.2 4.3 42.0
    The data presented on table above was taken from http://www.intersil.com/design/elantec/DataTransmissionOverUTPCable.asp.

    Video signal can be adapted to UTP wiring using a special balun transformer between BNC video connector and the wisted pair wiring. This converter converts the unbalanced audio signal to balanced signal which nicely travels through the cable. A similar transformer can be used on the other end of the cable to convert the video signal back to unbalanced format which fits to BNC connector. There are both passive solutions (balun transformers) and active converters available on the market for this application. Generally this kind of adapters do not care on the video standard being trasported, meanign the same adapters generally work for both NTSC and PAL video signals.

    Simple UTP baluns just convert an unbalanced coax signal to a balanced signal for use on the twisted pair. Some companies add gain with active converters to extend the distance. There are difference how well different products perfom. Some products provide inadequate noise immunity, some perform very well. Some products provide also ground loop isolation and surge protection. You can also find special adapters for S-video and VGA signals.S-video adapter included two baluns in one case to transport both S-videosignals (Y and C) through separate wire pairs. VGA baluns generally use four pairs to transmit RGB signals and sync signal.

    It is interesting to note that one of the major problems with baluns and analog video is not the high-frequency limit but the low frequency limit. Very low frequencies are difficult to pass through a transformer and other similar devices. Higher frequencies are much easierto pass. If you wish to use UTP for analog video, be sure you get performance data on the baluns that show the entire operating range. Broadcast-quality video requires performance all the way down to DC. Since a traditional transformer cannot pass DC, other methods are used to design these baluns (current mode baluns).

    Balance is also a critical parameter. The nature of a balanced line means that the two conductors in the twisted pair are identical (identical length,identical size). The more identical they are, and the closer together they are, the easier it is for the balun to reject noise and interference generatedoutside the pair. The less identical the two conductors, (and standard POTS lines are often very unequal), the more noise will get through. For best perfomance choose a cable that is verywell balanced. For example Category 5 is better balanced than Category 3. Balancing is specified by the amount of capacitance difference ('unbalance') built up over a given distance. The standard for Category 5 is 1000 pF/1000 ft. capacitance unbalance. Some of the best cables have less than 150 pF/1000 ft. To help reduce this problem, a number of companies have special passive and active devices to attempt to balance lines more perfectly. Active adapters contain circuitry to "adjust" the balancing, cost more but can send a video signal much farther than with a simple passive device.

    One a characteristic of Category-5 cable is that the pairs of wires are twisted at different rates inside the cable (this is done intentionally to reduce pair to pair crosstalk). Therefore, for a given length of Cat-5 cable the total length of aparticular pair could be longer than others. Since the signals travel in the cable at a fixed rate (approximately 90% of light speed), the arrival times of signals can be skewed in a long cable (those that have to travel farther arrive later and the corresponding image shifts to the right). This can be a problem in high resolution video systems where for example RGB signals are transported. This is seen on the monitor as separation, or lack of convergence in colors. For example a vertical white line on the screen may look to havea red tinge on the left edge and blue tinge on the right edge.This effect gets worse at high resolutions, high refresh rates, long cables (in excess of 200-300 feet), and depends on the cable construction itself. To compensate for this skew, many commercial VGA to UTP adapters have "skew compensation" potentiometers. The poterntiometers are typically adjusted by a screwdriver and need to be only set once per installation (adjustment is independent ofresolution and refresh rate). The skew effect is very subtle, it can only move the colors for a few pixels.

    Bottom line is that CAT5 cable is not great stuff for video signals. Certainly no better than any cable designed for video transmission UNLESS the CAT5 is combined with some sort of box that handles the conversion between what is good for video cable and what is good for CAT5. With such combination of devices you can get good results with video signal transmission over CAT5 cable.

    The converter will convert the unbalanced video signal to the balanced signal that can nicely go though the twisted pair cable without picking up too much noise or radiating too much interference. The converter will also made the necessary impedance conversion (75 ohms to 100 ohms and back). The converters have generally good common mode rejection characteritics (some prodicts boast over 60 dB common mode rejection). Some converters will pass DC and some other don't.

    How about using UTP cable to carry audio ? Unshielded twisted pair is suitable cable to carry balanced signals (balanced audio, 10/100Base-T Ethernet,telephone, etc.), but is far from optimal for unbalanced signals (like home hifi audio interfaces with RCA connductors). To properly transfer unbalanced signal over UTP thesignals need to be balanced (there are baluns for this). If you are carrying unbalanced audio signals through some short distances, I recommend you to use a cable with coaxial construction (typical shielded audio cable) or use shielded twisted pair cabling (best cable for balancedaudio, works well also with unbalanced signals). When audio signals are transferred with video, a separate wire pair (or two pairs for stereo) is used for audio signal. The audio signal is also converted between unbalanced (RCA connectors) and balanced formats (in wire pair) using audio signal transformers on both ends of the UTP cable.

    When transmitting audio and video signals through twisted pair wiring, use the adapters from the same manufacturer on the both ends of the cable. There are no generic standards how this kind of adapters work, so adapters from different manufacturers are most propably not compatible with each other. For example CCTV industry is shifting to UTP video transfer. Until recently, closed-circuit television (CCTV) security and surveillance equipment has been predominantly installed using coax cable. Although the technology to support twisted pair in the CCTV environment has been around for many years, today more and more CCTV dealers and installers are specifying twisted pair for the entire cabling system simply because it makes good business sense. Promoted as a simple, inexpensive way to drive SVGA, XGA and SXGA signals long distances, Cat5 converters (or sometimes referred to as Twisted Pair converters) are catching on. Routing or driving RGBHV signals through high-resolution coax cable is certainly still the defacto-standard for the majority of the ProAV systems market, but more and more integrators are starting to use RGBHV to Cat5 converters for cost and simplicity. Why? Simple. It's a lot less expensive. Cat5 cable is very inexpensive (15 cents per foot price range) and pulling Cat5 cable through a wall and ceiling is a lot easier and faster than pulling Coax cable. Finally, crimpling Cat5 means two crimps per run versus 10 per run with RGBHV cable. With good converters Cat5 cabling will work out just fine. This kind of converter converts a asymmetrical RGB video signal (as used for coaxial video transmission) in a symmetrical one. This symmetrical one will transport nicely through CAT5 UTP cable. On the receiving end the signals are converted back to asymmetical one.

    One word to the wise: not all Cat5 converters are alike. Not all of them are good and there is a quality difference. They don't all use the same technology to do the signal conversion and you need to compare which one is good enough for your application. Then user over UTP is used, the system will generally over wire gauges from 26AWG through 12AWG. Category 2, 3, 4 or 5 cable may be generally used. The better the cable, less possibility to interefence and longer range is supported. Individually shielded pairs should be avoided, as they usually drastically reduce the operating range of the systems.

    Video can generally be operated in the same communication cable coexistent with telephone, computer, control signals, powervoltages and other video signals. While video may be routed through telephone punch down block terminals, any bridgetaps,also called T-taps and any resistive, capacitive or inductivedevices MUST BE removed from the pair.

    There are also some products for running broadband RF video through CAT5 or better twisted pair wiring. One of the most demanding applications on the market today is broadband video, commonly known as CATV or cable television. It carries a broad range of signals extending from 54 MHz to beyond 600 MHz (usually up to around 900 MHz). Coaxial cable (RG-59 or RG-6) is commonly used for these applications, primarily for home networks and those systems are designed for 75 ohms impedance. The ever-increasing bandwidth available on modern twisted pair wiring systems has created ideas to carry RF video like cable TV signal through twisted pair wiring. The solution is to use a small transformer to convert from an unbalanced to a balanced signal on the sending end and and vice-versa on the receiving end. Baluns also make the necessary impedance transformation between coaxial cable (75 ohms) and twisted pair wiring (100 ohms). The use of CAT 5 for wireband RF video has been pretty limited because of quitehigh attenuation, especially at higher frequencies. The standard specifies attenuation of 24 dB per 100 meters of CAT5 cable, and when frequencies go higher, the attenuation increases quicly. The recent publication of the Category 6 standard by TIA marks an importantmilestone in this cabling system evolution. Category 6 at least doubles the bandwidth (usable frequency range) compared with Category 5/5e cabling. How far can you transmit video signals over Category 5e and Category 6 cabling? Most video receivers (e.g. TV sets) are designed to accommodate a wide dynamic range of signals. The minimum signal level at the remote television receiver is around 1 mV (-10 dBmV). For weaker signals, the picture is snowy and also much more susceptible to external noise. The maximumoutput level from the local amplifier is 50 dBmV, giving a dynamic range of up to 60 dB for the cabling. It should be noted that the signal level may need to be reduced below 50 dBmV because of radiated emission requirements that can further limit the dynamic range for the application. If the maximum allowed attenuation is 60 dB and cable length is 100 meters, we get the following maximum frequencies that stay within the limits expecting that the cables are well-behaving at high frequencies (data based on http://www.nordx.com/public/htmen/pdf/Video_over_Twisted_Pair_Cabling.pdf):

    Cable     Frequency
    CAT5 not specificed (propably 250-300 MHz)
    CAT5e 400 MHz
    CAT6 500 MHz
    CAT6+ 650 MHz
    In real-life you can't usually accept the 60 dB attenuation, thus the maximum distance and/or frquency range is reduced. Distance achievable is a function of signal level, balance and the degree to which the cable used unbalances the signal. Cat5e maintains signal balance at least 5 dB better than Cat5. Level 7 or equivalent cable is another 5 dB better, providing for a signal drive level of not more than 46 dBmV. Broadband video is definitely one application that can take full advantage of the improvedtransmission performance offered by Category 6 cabling and beyond. A low Insertion Loss and a high Signal-to-Noise Ratio are the most important cabling parameters for the broadband video application. Although the composite video signal is an analog signal today, future digital television signals will use the same broadband frequency spectrum and channel allocation but a different digital modulation scheme. Category 6 or better cabling is well positioned to meet thebandwidth requirements for these applications.

    • A Question of Balance: Voltage, Current, Video, and Cables - information on running video signals on UTP cables    Rate this link
    • Broadband Video over Twisted Pair Cabling - Over the last 10 years we have seen some tremendous advances in the manufacturing technology of balanced twisted pair cabling. This is reflected in the impressive improvement in transmission performance for both cables and connecting hardware from the early days of Category 5. What applications can take advantage of this additional performance? This article tries to answer these questions by defining the benefits of improved cabling performance.    Rate this link
    • Clarification for question about balance    Rate this link
    • FREQUENTLY ASKED QUESTIONS about Twisted Pair Video Transmission Systems - questions and answers cover many of the topics that address the design, use and installation of the    Rate this link
    • Question of Balance - Video and coaxial cable. The two seem to go together like soup and sandwich. In fact, we have been using coaxial cable with video signals for so long that it almost seems as though both made their appearance simultaneously. Well, coaxial cable may be the most expedient way to move video (and audio) signals around, but it is not necessarily the best, nor is it the only way.    Rate this link
    • RGBHV over shielded Cat 5 success! - This plan uses 25ft if shielded CAT5 cable to carry good quality VGA video signals (RGBHV). Originally 100 ohm shielded twisted pair cable works for 75 ohm vidoe signals, because the shield tied to ground on the shielded version CAT5 would help lower the impedance to closer to video's 75 ohm requirement.    Rate this link
    • Video and UTP - Paper originally presented to the Society of Motion Picture and Television Engineers Advanced Imaging Conference, Seattle, Washington, February 2, 1996. Enlarged and Updated 5/16/00.    Rate this link
    • Video and UTP - Paper originally presented to the Society of Motion Picture and Television Engineers Advanced Imaging Conference, Seattle, Washington, February 2, 1996. Enlarged and Updated 5/16/00.    Rate this link
    • Video Baluns - Some Designs Give the Product a Bad Name - With the development of structured wiring systems and high performance unshielded twisted pairs (UTP), many people are looking for devices that prepare various signals to travel on these "wire highways". There are many companies that offer passive boxes that prepare the baseband video signal for transmission over UTP. These boxes come in various flavors depending on the application. The secret to sending signals over UTP is to balance them well - in order to limit both radiation and noise pick up. However, mere balancing is not enough, we have to be concerned about interaction between the various elements.    Rate this link
    • Whole House Audio/Video Signal Distribution and Control over Structured Wiring - This article describes a novel approach to whole house audio/video signal distribution and control over structured wiring. A brief review of the traditional approach is presented and its problems and limitations are identified. A novel approach that provides higher performance and greater flexibility is described in detail. The benefits and advantages of this novel approach are also explained.    Rate this link

    Wireless audio and video

    Wireless video links have been used by professional vidoe broadcasters for a long time to transfer video from moving cameras and form remote locations to the video production systems. Nowadays wireless video is withing reach of consumers with the introduction of cheap ($100 price range) wireless video transmitters/receivers that operate at 2.4 GHz ISM band (license free band). Those devices enables television viewers and music listeners to enjoy stereo audio and video reception anywhere in or around their homes or offices without having to run wires. The 2.4 GHz signal penetrates quite well through walls, doors, ceilings, and floors.Typical devices use few tens of milliwatts of transmitting power and provide typically 30-100 meters of distance on clear line of sight connection (somewhat less if walls are on the way). There are also longer distance special models available. The video signal is usually frequecy modulated to the 2.4 GHz carrier in this kind of wireless video systems. There are different wireless video systems in use. Most of 900 MHz systems are very good for transmitting the video signal trough walls. On the market you can get 900 MHz AM (amplitude modulation) or FM system. It is better to go with AM system. The reason is that 900 MHz AM system has 6 MHz bandwidth - compare to FM (frequency modulation) that has 18 MHz - 27 MHz bandwidth. This is why FM system is more sensitive for interferences. Sensitivity of receivers is important factor. For AM receivers the best results you can get with receiver that has app. -90 dBm /10 dB S/N or better. With 1 mW video transmitter (maximum allowed by FCC) and AM receiver you can obtain 100-300 ft range line-of-sight. Most of small video transmitters on the market have 5 mW -25 mW power and they can go maximum 500-750 ft or with a high gain antenna 6 dB gain on the receiver side up to 1000 ft line-of-sight. If you transmitting trough walls it is much different. The range will be decreased drastically. 2.4 GHz systems are little bit different. Transmitters for 2.4 GHz will send a much higher video band then AM 900 MHz for example. They can transmit a broadcast quality picture. 2.4 GHz wireless video transmitters use generally FM modulation method for audio/video transmission. Typical low power transmitters have power rating in range of 10-100 mW, although also more powerful devices are available. Typical cheap consumer equipment ($100-200 price range) typically promise 50-100 meters range in open space and less if used inside building. The high 2.4 Ghz frequency is not the best for transmitting trough walls even if you have a high power transmitter 1 W or more! Concrete wall will block the signal. Other thing to note with 2.4 GHz system is that those wireless video systems are not the only equipment that use this frequency band. For example WLAN systems and microwave ovens operate at the same frequency band and can cause interference to the operation of 2.4 GHz video link. There are also several other frequencies that are used for wireless video systems. Wireless video surveillance systems typically operate at 2.4 GHz or 1.2 GHz frequency bands. When using wireless video systems you need to take into consideration the local radio regulations and allocations of different frequency bands. What is free to use and legal on one country could be illegal or need a license in other country. The 2.4 Ghz systems are the most universal of all, because those frequencies are free to use uin very many countries (there can be variation of what is allowed maximum power on different countries). When considering system operating at other frequencies you need to carefully check that this frequency can be used for this application and if you need a license to operate. Using a wireless system at frequency you are not allowed can cause lots of inteferences to original users of those frequencies and can get you into trouble (possibly expesive fines to pay, losing the equipment etc.). For example 900 MHz band is used in many countries for cellular phone systems. The frequencies at 1.2 GHz and around it are used in some countries for example for satellite communications and air traffic navigation.

    Sending signal from one source to many receivers

    Somethimes there is need to split the video signal from one source tomultiple receiving devices. It is doable, but in addition to the cabling you usually need some extra devices to do this. If you want to use RF (antenna), you can get an "antenna amplifier" and thensplit it with antenna splitters into all the receivers. If you use a baseband video like composite video, you need a distributionamplifier to take your signal and give the many enough outputs foryour receiving devices (one for each device). Video Distribution Amplifiers are used to buffer a video signal so that it can be sent to more than one piece of equipment without undesirable loading effectsVideo distribution amplifiers are available from many sources which sell video system components, This kind of amplifiers can be found easily for composite video(RCA or BNC connector) and for S-video. For special applications there are also multichannel video distributionamplifiers suitable to be used with RGB and component video signals. There are also special distribution amplifier designed for RGBsignals used by PC graphics cards (those come with 15-pin VGA connector and are available from computer outlets). If your video monitors happens to be professional video monitorswith "feed-through" or "looping" capability, it is possible do video signal distribution to many monitors without use of distribution amplifiers. Just wire the the signal source to the first monitor video in and get signal out from the same monitor video out connector. Wire this signal to next monitor video input. Go on like this untill all monitors have picture. Remeber to terminate the video line at the last monitor with a video terminator or make the lastmonitor to terminate the line. Many professional monitors have hi-z setting for feedthrough operation and 75 ohm mode which terminated the cable.

    Grounding and groundloops

    Grounding in the electrical world generally centres around personal protection by providing a low impedance path for fault currents to travel to a safe earth for dissipationThree types of grounding are commonly used, not necessarily in isolation to each other:

    • Single Point ground for low frequency operation
    • Multi-Point ground for higher frequency operation
    • Floating or capacitive coupled ground for ground isolation
    Most audio/video and low data rate systems will recommend a single point ground. In the area of audio/video signal transmission the fault currents are not generally lethal to humans, rather to the integrity of the data being transmitted. Depending on the nature of the interference various grounding philosophies are available, however there may be conflicts between grounding methods within a single system. The most important thing to remember is that a clean ground is the key to a 'noise free? system. A clean ground is expressed as having an earth potential relative to the device of less than what would cause problem (very much below s 1 Volt peak to peak), and with frequency characteristics within system design limits. Ground loops are annoying thing which exist in many audio and video systems and cause humming noise to sound and disturb the picture usually with dark moving bars. Ground loops are often things that only after the system is installed it can be determined if a problem will exist. Ground loops are an after-the-fact type of problem in which the end-user blames the installer, the installer blames the manufacturer, and actually nobody is at fault. Fortunately ground loop problems can be corrected if can locate the source of the problem and you know what to do to solve that problem. There are four ways to cope with Ground Loop Interference. You can use equipment that doesn't create them in the first place, eliminates them, ignore them, or compensate for them.

    Testing audio/video wiring

    Usually the best way to test cables is to do the test in the intendedsystem - provide a known input from the intended source and analyzethe output at the input or output of the intended load. One example of this is would be to use a test CD as the signalsource, and monitor the voltage at the speaker terminals with asuitable measuring equipment. This can work for eitherinterconnects or speaker cables. The most common cable fault is an open circuit, usually due toproblems close to or at the ends of the cables. A simple ohm metertest generally suffices. 75 ohm coaxial cable testing includes the following tests:

    • Continuity test for centre conductor and shield
    • Attenuation measuring
    • Length measuring
    Checking the coaxial cable length and impedance continuityis usually done using a time domain reflectometer (TDR), which transmits a pulse down the cable, and measures the elapsed time until it receives a reflection from the far end of the cable. Each type of cable transmits signals at something less than the speed of light.


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