Training Training Videos & Docs Part 1 Training Basic Principles of Home Networks
Part 1 Training Basic Principles of Home Networks |
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PART 1 - Basic Principles of Home Networks IntroductionHome Networks"Home Networks" is a broadly used term that means different things to different industry groups, but in this course it means the infrastructure, both wired and wireless, used to interconnect products and systems in the home to support voice, data, and broadband RF applications, and to connect those systems and applications to outside services. This covers everything from basic phone service to entertainment to home automation. New homes should be equipped with the infrastructure necessary to support the following networks: • Traditional voice telephone service • Data networks • Broadband RF networks • Control networks including automation and security • Audio and video entertainment system networks The majority of these networks rely on a structured cabling infrastructure, the communications backbone of the house, and the design and installation of this infrastructure is one of the things we’ll be focusing on. Structured CablingStructured cabling is a relatively new term used to describe a standardized arrangement, or structure, of cables and devices installed during home construction. These cables are designed to distribute existing and new telecommunications, data, and audio/video applications throughout the home. The cables originates at a central distribution device and each cable branches from here to devices or outlets throughout the home. Outlets typically have a combination of jacks to allow maximum flexibility for connecting different devices in the home. All of the outside services, the telephone company, cable company, internet broadband services, any satellite or off-air antennas, tie into this distribution device allowing you or the homeowner to select what services are available at each outlet, so a jack used for a phone line today can be easily changed to a computer network jack tomorrow. Broadband, Baseband, BandwidthIn this course, a broadband network means it supports multiple channels of data or signals at the same time typically using some form of frequency division multiplexing. It is also used to mean a high data rate, over 1 megabit per second on a data network. The term broadband RF means services like cable television where the cable carries a number of services or channels simultaneously. The bandwidth of a cable, device, or network is the difference between the lowest and highest frequency that it can support without undue attenuation and loss and is measured in kilohertz or megahertz.
For example, cable television channel 2 occupies from 54 MHz to 60 MHz or a 6 MHz bandwidth, while the entire cable service, all 120 channels, occupies over a 770 MHz bandwidth.
Typical television channel (channel 2) has a 6 MHz bandwidth A baseband signal means there is only one signal or channel on the network or cable, usually occupying a bandwidth that starts at zero hertz. The signal has the exclusive use of the cable or network, not shared with other signals A good example is a baseband video signal, the signal typically available at the video output jack of a VCR or DVD player or the signal from a security camera.
Structured Cabling StandardsThere are two important Telecommunications Industry Association or TIA standards that cover telecommunications cabling in buildings. TIA-568 is for commercial buildings, and TIA-570A is for residential buildings. They address the requirements for cable, hardware, design, and installation. You can obtain a copy TIA-570 at: http://global.ihs.com TIA-570A covers residential single and multi-family installations and concerns us directly in this course since it is specifically written to cover residential installation of home network infrastructure (TIA-570B—revision B—is due to replace 570A in the near future). The single family section of 570 covers the specifications for the network interface demarcation point, auxiliary disconnects, distribution device and cross-connects, cables and cable installation, outlets and connectors, and equipment cords. Outside services are brought to the house and terminate at a network interface device or NID, a location and/or device that defines the termination point for an outside network, like the cable TV or telephone service.
The NID contains a demarcation point where services can be disconnected from in-house wiring. There is also an auxiliary disconnect where outside services can be disconnected inside at the distribution device The telephone service NID is the box on the outside of house where service providers such as your local telephone company terminate their service. The box is provided by the service provider, but you'll provide the cable from here to the distribution device. Cable service companies also typically use a NID box that’s used to contain a grounding block and splitters or filters depending on the service to the house, or they may just supply a grounding block to act as the service demarcation point. All outside services are brought to the distribution device or distribution center. The distribution device’s primary function is to support the voice, data, broadband RF and A V networks. It is responsible for 3 functions: 1. Contains all the equipment to support network applications such as signal amplification, cross-connect, network hubs, and service termination. 2. Terminates external services such as telephone and cable and connects them to internal networks 3. Allows a flexible means to connect outlets to services. Per TIA-570A, cable runs will be home-run from the distribution device to each outlet jack. That means that each jack has a dedicated cable back to the distribution device. Older style wiring where outlets were wired together on the same cable, called daisy chaining, is no longer used. The standard also defines the minimum number and type of cables and outlets in two grades of service. Grade 1 is a minimum requirement to support traditional basic analog services. Grade 2 is intended to support "multi-media" applications. These include data network support as well as distributing in-home generated video sources.
The standard also states that each branch cable not exceed 90 meters or 295 feet to allow it to be used for data as well as analog applications. And that equipment cords not be longer than 10 meters or 32 feet.
This gives a total length of 100 meters or 327 feet from attached devices to the distribution equipment connection. Voice Network Operation and InfrastructureThe traditional voice network starts at the telephone company central office. Each telephone line to the house uses a pair of wires from the central office to the network interface device. Telephone companies typical install at least 2 voice lines to each house. A pair of wires for each line then runs to the distribution center.
Basic residential voice network The distribution center allows each incoming line to connect to branch TP cable runs to individual outlets. Each branch cable contains four pairs of wires to support up to 4 voice lines. Connecting incoming voice lines to outlet cable runs is typically done with a voice line distribution module. The voice service cable from the telco NID is terminated in a 8-pin modular plug and connected to the input jack. This becomes the Auxiliary Disconnect required by TIA-570A. The four possible incoming voice lines are applied in parallel to the 8 110-style punch down connectors along bottom. The cables to each voice jack are attached to these connectors. If more than 8 voice outlets are needed, additional modules can be added as necessary by using a jumper cable from the output jack or the punch down connector.
Voice line distribution module (punch-down) There is also a jack on the module to allow connection to a security system. When the line-1 switch is up, line-1 is routed through the 4-pair cable to the RJ-31 jack on the security system allowing the security system auto-dialer to seize line-1. The module below provides a similar function. Voice service from the telephone NID is terminated in an 8-pin modular plug and connected to the top jack. This becomes the Auxiliary Disconnect.
Voice line module (modular jack) The four voice lines are connected in parallel to the 8 modular jacks. Cables to each voice outlet are terminated in modular plugs and plugged into any output jack. This allows easy disconnection and testing of each cable run. Expansion is easily accommodated by jumpering to additional modules. This module also has a jack and associated switch to allow connection to a security system. The module can also be used to distribute the incoming lines to other modules to support up to 64 voice lines.
Voice line module expansion Other manufacturers of structured cabling equipment make similar modules for distributing voice service. While physically different, they all provide the same basic function. Over-voltage ProtectionTelephone lines, like all services that enter the house, must be protected from over-voltage conditions. Protection is provided by primary and secondary systems Primary systems are required and consist of lightning protection and the grounding electrode system of the house. Phone line primary protection is provided in the network interface device on the outside of the house.
Secondary systems consist of over-voltage and surge protection circuits built into the equipment that the cable attaches to. A good example is the surge protection module below. It provides secondary over-voltage protection on four incoming voice lines, and is connected between the NID and the voice distribution module in the distribution center.
Data Network Operation and InfrastructureThis course concentrates on data networks typically used to support computer applications and broadband internet access as well as distributing real-time digital audio and video content. Most data networks in the home use Ethernet network technology. Ethernet was developed in 1972 by Bob Metcalfe, a very bright individual working at Xerox. It’s simple and reliable (well, most of the time anyway!). EthernetEthernet is a local area network or LAN technology. It transports data within a home or office at rates typically between 10 and 100 megabits per second.
Typical Ethernet home network All data outlets are home-run to the distribution center and connect to a device called a hub or switch. This design, or star topology as it's called, allows any connected device to communicate with any other device on the network, sending text, pictures, music, and control information. The network can also be connected to the internet through a router and a gateway device such as a cable or DSL modem. Ethernet is an IEEE standard, often referred to by its standard number, IEEE 802. The most common form of Ethernet for local area computer networks is 802.3.
802.3 is commonly referred to as 10Base-T, meaning 10 megabits per second, baseband on twisted-pair cable. There is also a 10Base-F or 10 megabits over fiber and 10Base-2 and 5 which covers 10 megabits over coaxial cable. 802.3u is the specification for fast Ethernet or 100 Base T, 100 megabits/sec over category 5 or better twisted-pair. 10 and 100Base-T are the de-facto standards for the home. There is even a faster version, 802.3ab for 1000Base-T. This requires category 5e or 6 TP cable. Ethernet FramesEthernet transports data from one device to another in discrete chunks of data referred to as frames. A frame consists of a PREAMBLE, TO and FROM addresses, the message PAYLOAD, and an ERROR DETECTION CODE, comprising from 64 to 1518 bytes.
The data to be transported is fragmented into pieces that will fit into a frame by the sending application and reassembled at the receiving application. The TO and FROM address is the physical Ethernet address of the receiving and sending device. It's a hardwired 48-bit address assigned by the manufacturer.
Every Ethernet enabled device should have its 48-bit address visible on the product, written in hexadecimal notation using numbers 0 thru 9 and letters A through F. TCP/IPWhile Ethernet frames can transport any type of data, most of the time, it's TCP/IP packets, the protocol and data format used over the internet. Using TCP/IP for home networks allows an easy and seamless connection from devices in the home to the internet—a major advantage. And not just for computers. More and more A/V equipment, home automation systems, and even appliances relay on a broadband, always-on connection to the Internet for everything from remote monitoring to content download. TCP/IP stands for Transmission Control Protocol and Internet Protocol, the transport and network layer protocols used on the internet. TCP/IP packets are the Ethernet frame payload. They have a TO and FROM IP address, routing and control information, source and destination application ports (like an internal address for applications sending or receiving the data), and the real data payload. This might be part of a picture, a web page, or an MP3 file.
IP addresses are only 32 bits or 4 bytes, and are written in what’s called dot-decimal notation, a decimal number for each byte separated by a dot.
Every device in the world that communicates on the internet has an IP address. But unlike Ethernet, the IP addresses can reference either a device in the home (a private IP address) or a device anywhere in the world, a public IP address, therefore every networked device in the home will have an Ethernet address, and an IP address. The problem is, with only 32 bits, there aren't enough IP address to preassign one for every IP enabled device, so they have to be assigned manually, or by address assignment software usually in the home router. Ethernet Network InstallationThe Ethernet data network is physically installed like the voice network. Home run cables are installed from outlet locations where data network access is desired back to the distribution center. Computer and peripheral devices simply plug into the data outlets to connect to the network.
Ethernet uses two of the 4 pairs in the cable. The green pair connected to pins 1 and 2 for transmitting, and the orange pair on pins 3 and 6 for receiving.
Again, per TIA-570A, data outlets are also 8-pin modular jacks wired to the T568A configuration Data lines are typically terminated on a data cable termination module such as the one shown below. The module allows selected lines to be jumpered to Ethernet support equipment such as hubs or switches.
Data line termination module The distribution center also houses the necessary Ethernet support equipment for the network. we'll take a closer look at the most common devices including hubs, switches, bridges, and routers HubsA hub is like a network outlet strip, it connects branch cables together. It connects a small number of devices together, typically 4 to 6. Data that arrives on any port is simply retransmitted to all other connected devices. Hubs can be connected together or to switches to expand the network, but at 100Base-T, the limit is one additional link or two hubs or switches between any two devices.
The most common use for adding a hub is to connect several devices in a room to one data jack, such as in a home office. When connecting a network component such as a switch or hub to an attached device such as a PC, a straight through cable is used.
The I/O pins on the hub device are reversed from that of a PC. But when a network component is connected to another network component, such as a hub to hub, a cross-over cable should be used. It reverses pins 1 and 2 and 3 and 6. SwitchA switch is similar to a hub, but relies on the frame MAC address to route the incoming frame only to the port that has the destination MAC address attached.
This will isolate traffic between two devices at a time. The switch can support several simultaneous data transfers at a time. Switches are intended for larger networks and typically support 8 to 32 attached devices. BridgeA bridge is a device used to connect two networks together, typically networks that use a similar protocol, but different media. The most common bridges used in the home connects wired Ethernet to wireless Ethernet, IEEE-802.11. 802.11 devices are also referred to as Wireless Access Points (WAP). They allow wireless devices such as laptop computers to connect to the home LAN. 802.11 bridges come in three basic flavors: 802.11b devices operate in the 2.4 gigahertz band at a maximum of 11 Mbps, 802.11g devices operate in the same band but at a maximum rate of 54 Mbps, and 802.11a devices operate in the 5.1 GHz band also at a maximum 54 Mbps.
The range of 2.4 GHz devices is typically 100 feet in average home construction, while 5.1 GHz signals are highly absorbed by building materials, limiting their range to 25 to 50 ft. Since 802.11g devices are backwards compatible with b devices, and given their better range, b and g devices are the best choice for residential installations. They should be installed in a central, high location in the house to give the best signal coverage. The height avoids absorption from furniture and fixtures. In larger homes, multiple access points can be installed in different areas of the home or on different floors. The 2.4 GHz band is divided into 11 channels. Each channel is 24 MHz wide with a 5 MHz offset from the next channel. A wireless access point can be assigned to any one channel.
Channelization of 802.11 2.4 GHz band This allows up to three access points to operate in the same location without interference. RoutersA routers job is to selectively route packets (the payload portion of an Ethernet frame) between two different networks. In our case that means the LAN in the home to the internet. This is usually a two step hop from the router through the cable or ADSL modem that is illustrated below.
If a packets destination is someplace other than the home network, the originating device will send the frame to the router. The router substitutes the public IP address assigned to the home account by the access provider as the new FROM address, and sends it via the gateway. Likewise, if the router receives a packet from the internet via the gateway, it examines the packet to determine if it's a response to a request originated by a device in the home. If it is, it substitutes the local devices IP and MAC address and sends it on its way. If it's not, the packet is discarded. Nearly all routers intended for the home or small office have a 4 to 8 port switch built-in. Unfortunately, unless you're installing a very small home, you'll still need an additional switch since you'll typically need to support at least 16 data outlets and devices. GatewaysA gateway is the interface between two dissimilar networks. It performs protocol conversion as well as providing the physical interface between the internet access providers network and the home network.
Typical gateways include cable and DSL modems that convert the broadband access provider’s analog signals to 10Base-T frames for the router. Gateways are equipped with as least two ports. A 10Base-T connection for the LAN, and an analog cable or DSL connection.
The network router, switch and gateway are typically installed in the structured cabling system enclosure since that’s the home-run location of the TP data network cabling, as well as cabling to the NID. Most structured cabling equipment manufacturers provide routers and switches either as modules or mounted on brackets to fit inside the enclosure. The gateway will typically have to be installed on a shelf, bracket or "cable-tied" to the inside of the enclosure. Another interesting example is this voice line to IP gateway. This device will digitize analog voice signals into IP packets. It can provide 2 standard voice grade lines with separate phone numbers using a voice over IP service provider.
Typical hook-up of a VoIP gateway to a voice line distribution module It is easily installed in the distribution center enclosure. One or two voice lines are wired directly to the voice network in place of or in addition to the lines from the traditional telephone NID. It's Ethernet port is wired directly to the router. Product CommunicationsIncreasingly, it’s not only computers in the home that are networked and connect to the Internet. Other types of devices and appliances are being connected as well, such as cameras; internet radios, music and video servers, and even traditional home appliances such as refrigerators and microwave ovens. But since there is no standard control language to communicate with non-computer equipment on an Ethernet based network, most manufacturers incorporate a web server right into their products and use the HTTP protocol to transport HTML based information.
Typical HTML configuration screen for IP camera The Panasonic networked camera is a good example. The camera “site” at the cameras IP address, accessible from any web browser, has several pages used to control the camera operation. This is also how networked devices are configured including routers and bridges.
Router configuration screen It's also important to understand that Ethernet uses what's referred to as a carrier sense, multiple access protocol (CSMA). Devices gain access to the network and to another device on a first come first serve basis. Because data is sent not as a continuous stream but in a series of individual frames, other devices can compete for network access and interrupt the data transfer. Therefore deliver time of data is indeterminent. Fine for file transfer, but not necessarily the best protocol for streaming video or audio. Other networks such as IEEE 1394, also know as Firewire, may be a better long term solution for A/V applications
TP Cable and Connectors OverviewBoth voice and data services use unshielded twisted-pair cable or UTP. It's called twisted-pair because it contains 4 pairs of wires twisted together. Older telco cable used untwisted-pairs, called quad wire. It's no longer used for new installations. The pairs of TP cable are 22 or 24 gauge copper and their insulation is color coded to identify the pairs easily. One wire usually has a solid color, and the other wire of the pair is white or is white with colored stripes. This pair with the blue and white with blue stripes is simply referred to as the blue pair.
Typical TP cable structure When used for telephone voice applications, each pair of wires is capable of carrying one standard telephone line. The blue pair is used for line 1, the orange pair is used for line 2, the green pair is line 3, and the brown pair is line 4. Category RatingsCategory ratings were established by the Telecommunications Industry Association (TIA) to standardize performance ratings for cable and equipment. The ratings give the minimum performance requirements for attenuation, resistance, interference between pairs, and so on. Category ratings start at Category 3.
Category 3 cable, or CAT3 is used for medium-speed communications up to 10 Mbps over distances of up to 100 meters. Category 5 cable, or CAT5, is used for high-speed communications up to 100 Mbps at distances of up to 100 meters. A higher performance version of CAT5 cable called CAT5e for enhanced is also readily available. It has tighter specifications on cross talk and attenuation performance although still rated for 100 Mbps service. New CAT6 cable is designed handle data transfer rates up to 1000 mbps by sending data at 250 mbps over all four pairs simultaneously. The cable incorporates new designs to physically separate the pairs to reduce crosstalk such as a plastic separator or by using a flat jacket molding.
Typical design of CAT6 cable using a plastic separator ConnectorsTP cable always uses the TP modular connector developed by AT&T. They come in 6 and 8-pin styles. The male plug is always used on the cable, the female jack is always used on equipment or wall plates. You'll hear these connectors referred to as an RJ-11 style for the 6-pin variety and RJ-45 for the 8-pin style. These are old AT&T registration numbers for the tariff used for the service the jacks were intended for, and are no longer used although the terms persist. They are just 6 and 8-pin modular plugs and jacks.
The pins on all jacks are numbered from left to right looking into the jack. The 8-pin jack is specified in TIA-570A for all residential voice and data applications. The blue and blue-white pair are connected to the center two contacts and the orange and orange-white pair are connected to the next pair out. This maintains plug compatibility with the six-pin style connector. The green pair is connected to one and two. And the brown is connected to seven and eight.
This wiring configuration is also a standard for the commercial TIA568 specifications, and is referred to as the T568A configuration or the A configuration. This configuration is used for ALL residential TP jacks. There is an alternative 8-pin wiring configuration called T568B. This configuration swaps the green and orange colors on pins 1,2 and 3 and 6. It is used in some commercial installations and you'll see it on some jack labeling usually with just the letter B. This configuration is NOT used for residential installations. Also, you must use jacks with the same category rating as the cable you are using.
Broadband RF Network Operation and InfrastructureA broadband RF network must support the distribution of external sources such as cable service, off-air service, and satellite service. Cable ServiceThe cable television industry uses a standard channelized frequency allocation on their distribution system. Downstream channels start at channel 2 and go up beyond channel 125. As a carryover from the early years of the cable industry, the channel spectrum is divided into the low-band, mid-band, high-band, super band, and hyper band.
By using digital compression techniques, cables companies can squeeze 6, 8, or more digitized NTSC channels in to a single 6 MHz channel space, greatly expanding their potential channel capacity. But it requires a digital set-top box to convert the digital channels back into NTSC analog format. Deci-BellsThe amplitude of cable channel signals, as well as all RF signals we’ll be using, are expressed in dB or deci-Bells. They’re used to express the ratio of any two values, such as power or voltage and greatly simplify calculating gains and losses of RF systems and components. For example if we know the signal voltage into an RF amplifier is 1 volt and the output voltage is 2 volts we know by the formula shown that the amplifier has a +6 dB voltage gain.
Likewise if we know the signal voltage into a length of coax cable is 1 volt and the output at the other end is .3 volts we know that the coax has a loss at the frequency of the signal of –9.5 dB. By convention the minus sign means a loss.
The following Table lists common signal level dB gains and losses. Notice that increments of 20 dB voltage gain or loss is equivalent to powers of 10 increase or decrease. +20 dB is equal to a 10 time increase, +40 to 100 times, and so on.
Fortunately, when designing RF distribution systems, the dB gain or loss of a component such as an amplifier or coaxial cable is given by the manufacturer so all you have to do is add them together for each path through the system. For example, if we know that the loss of a brand of coax cable is –8 dB per 100 ft. then the system shown below, with 100 feet from the cable service NID to an amplifier with +10 dB of gain, then another 50 ft. length of coax to a TV will have an overall gain or loss of –8 +10 and –4 or a total of –2 dB of loss.
If we know the input signal level we can easily figure the output signal level. dBmVWhile DB’s express a ratio, absolute cable signal levels are typically given in a unit of measure called a dBmV or deci-bell milli-volt. The mV after the dB means an actual signal level referenced to 0 dBmV
Zero dBmV is a standard reference level of 1 mV of the visual signal level across a 75 ohm resistance. 75 ohms because the cable system is built around 75 ohm impedance cables and equipment. A 3 dBmV signal would have a signal level of 1.41 millivolts across a 75 ohm load, and a 10 dBmV signal would have a voltage of 3.2 volts. Likewise, a –6 dBmV signal would have a voltage level of .5 millivolts.
The nice thing about expressing signal levels as dBmV is that they can be added to the dB gain or loss of a system. A minus 3 dBmV signal applied to an amplifier with a 10 dB gain would result in an output signal level of +7 dBmV. Signal Level RequirementsThe cable company visual signal level at the NID or connection point at the house should not be less than +3 dBmV on any channel. The signal level in the house at the point of connection of the customers equipment is supposed to be not less than 0 dBmV on any channel. The only upper limit given by FCC Part 76 is “A maximum level such that signal degradation due to overload in the subscriber's receiver does not occur.” This is usually not more than +15 dBmV and is ideally in a range of 0 to +10 dBmV This is also the range that the cable tuners in televisions are designed to handle.
Coax Cable and Connector OverviewSince everything RF is interconnected with coax cable, you’ll need a good working knowledge of it’s characteristics, especially loss performance, to design and install RF systems. Like TP cable, coax cable also comes in various performance ratings, established by standards organizations such as the SCTE, Society for Cable Television Engineers. CoaxCoax consists of a center conductor surrounded by one or more shields. The cable is divided into numbered series such as 6 or 59, with common characteristics in each series. You can think of coax as a two wire cable where one of the wires has been flattened and wrapped around the other.
Typical coax cable construction (tri-shield RG6) The center conductor is usually a solid 18 gauge copper clad steel for strength. The shield is separated from the center conductor by a dielectric insulation typically foam polyethylene. The cable may have a single foil or braid shield or a combinations such as this tri-shield with foil, braid and foil. A quad-shield cable will have an extra braid. The inner foil is used for shielding as well as being one of the signal conductors. A braid does provide shielding but is primarily used for strength. Extra foils and braids provide extra interference protection and cable strength. Finally, an outer PVC jacket covers the shields By far the most common coax cable for residential use recommended by TIA-570 is Series 6. The most common designation for Series 6 cable is RG6. RG6 offers a good combination of size, cost and low loss performance for the distances typically found in homes and it will be your cable of choice for residential installations. TIA-570 recommends using either three or four shield or quad-shield coax.
The above chart gives the typical loss in 100 ft. of RG6 (many manufacturers RG6 cable exceeds these values). Coax cable loss is additive, 200 feet has twice the loss of 100 feet, 50 feet has half the loss, and so on. Remember, the loss is frequency dependent, increasing with increasing frequency and it is also additive, 200 feet has twice the loss of 100 feet, 50 feet has half the loss, and so on. Coax ConnectorsRG-6 cable uses F style connectors developed by the cable TV industry. The mating jack is usually a barrel style connector, requiring a plug on both sides. The cable in the wall also has an F plug on the end so there is only one connector to apply. F connectors are available for 2 and 3 shield RG-6 and for quad RG-6. The most common F connector uses a threaded hex end and a barrel or crimp ring designed to be mechanically compressed to the cable. They come in a one piece and two piece style
The most common one piece connectors are the hex crimp and compression crimp. These incorporate an integral crimp ring for strength and ease of installation. The most common two piece is the snap-and seal connector, applied with a special tool.
Newer versions of this connector the plastic sealing ring already in position on the barrel. NEC Cable ListingsThe NEC requires that all cables used in a building have a rating identifier marked at regular intervals on the jacket to identify if the cable meets safety requirements for various spaces and cable run applications. Any low voltage cable you use, such as security, control, or speaker cable, must have at least an NEC class 2 or class 3 marking. This will be the letters CL typically followed by another letter to identify the allowed application. • “P” for plenum, ducts and air handling spaces. • “R” for use in risers, or vertical shafts that penetrate more than on floor. • “G” or no letter, stands for general purpose: meaning locations other than plenums or risers. • And “X” for residential, designed for single and multi-family dwellings and in raceways. Any of these designations are acceptable for residential applications.
Copper communications cable such as TP or coax may have a CL marking but will typically have a marking such as “CM” followed by another letter. The “C” stands for communications and the “M” for multipurpose. The third letter is the same as for CL markings.
Fiber optic cable has a similar designation. The “OF” stands for, you guessed it, optical fiber. The next letter, either “N” or “C”, indicates whether the cable has a conductive metal element, typically used for cable strength. And the last letter is the same as for copper cable.
Off-air ReceptionsThere are a number of good reasons to incorporate off-air antenna signals into the RF distribution system. • It’s free! • When local television stations are not carried by satellite providers, • When cable television is not available, • To receive new digital television signals. Nearly all broadcast television stations must begin broadcasting digital television signals or DTV by 2006 and most already have. With a good antenna installation, there is no reason why the picture quality from off-air can’t be just as good as the picture from cable or even satellite. This frequency chart, similar to the one we saw for cable channels, shows the VHF and UHF frequencies for each 6 MHz TV channel.
Notice that the VHF channels are divided into two groups, channel 2 to 6, and 7 to 12, sometimes referred to as the low and high VHF bands at 54-86 MHz and 174 to 216 MHz respectively. Between these bands lie a number of other radio services such as FM stations between 88 and 108 MHz, and the aviation band between 108 and 136 MHz. UHF channels 14 through 69 occupy channel frequencies from 470 to 806 MHz Off-air and cable channels above channel 13 use different frequencies. Therefore televisions or other receivers all have tuning modes that select between cable or off-air antenna tuning channel plans. Which service is primarily used in the home will determine the distribution channel plan for the home. Off-air AntennasRF broadcast signals need to be captured by an antenna designed for the range of frequencies in the VHF or UHF bands that the customer is interested in receiving If you plan to incorporate digital off-air television only, then you only need to select a good quality UHF antenna or antennas. Most antennas are designed to receive either the VHF band, VHF with the inclusion of the FM band, the UHF band, or a combination of VHF and UHF band.
To receive a good quality analog, noise free picture, the antenna needs to deliver a signal level of 0 dBmV to the receiver, similar to a cable signal, although most receivers will give an acceptable picture down to about -10 dBmV. Note: DTV receivers can tolerate a digital encoded signal level down to about -15 dBmV To deliver this signal level the antenna requires a certain gain. The amount of gain required is dependent on the line of site distance to the desired stations transmitting antenna and the power transmitted by the station.
In general, the gain of an antenna is dependent on it's size and the number of elements Due to the smaller size of the elements, UHF antennas can utilize more creative shapes to achieve high gain.
Selection of the right antenna for a particular location has been made simpler by the CEA. There antenna web will help you select the best antenna type for a particular location. Satellite ServiceIn this section of the course we're going to cover the direct broadcast satellite system, the systems behind such services as DirecTV and the DISH network. These systems are also referred to technically as Ku band DBS systems due to the designation of the 12 gigahertz downlink frequency spectrum it uses as the K sub U or Ku microwave band. Source television signals are converted to a digitally compressed MPEG 2 data stream. The data stream is transmitted on a 17 GHz uplink carrier up to a geostationary satellite. In the satellite, the received signal is converted in a device called a transponder to a 12 GHz downlink carrier and broadcast over a wide geographic area visible by the satellite.
Basic operation of the Ku band DBS satellite system The signal is received by a small high gain dish antenna pointed at the satellite connected to a specialized receiver. The receiver converts the signal from the MPEG 2 data stream back to the original analog form for viewing on a local television Satellite services in the US seems to be constantly changing, but at the time we made this course, there were two major suppliers of DBS service, DirecTV owned by Hughes, and the DISH network, owned by Echostar. The Receiving DishThe dish receiving antennas for both providers look similar but differ in how they convert arriving signals for the receiver.
DirecTV antennas are equipped with 1 to 3 LNBs to receive the networks signals from satellites at the 101, 110 and 119 degree orbital positions. New DISH PRO antennas are equipped with 2 LNBs to receive the networks signals from satellites at the 110 and 119 degree positions. The LNB or low noise block converter, converts the received 12 GHz band of downlink signals to an intermediate frequency band from 950 to 1450 MHz. Power for the LNB is supplied by the receiver over the same coaxial cable used to feed the signal to the receiver.
For DirecTV LNBs, the voltage level is used to select the odd or even transponder channels carried on the left or right hand circular polarized signals respectively from the satellite.
DISH network LNBs incorporate a European standard called digital satellite equipment control technology, or DISEQC for short. It allows two way signaling between the LNB and the receiver.
Both even and odd transponder channels are output at the same time using two blocks of intermediate frequencies 950 to 1450 and 1650 to 2150 MHz. Multi-switchesIn order to view two different programs at the same time on two different TV sets, two receivers are required—one for each TV. There are two approaches to installing multiple receivers in the same house. The obvious approach is to simply install a separate receiving dish for each receiver. The other approach is to allow one antenna to be shared by multiple receivers. This requires a device called a multi-switch. it's designed to allow any receiver access to any transponder channel from any satellite that the dish can see. A typical DirecTV multi-switch receives the polarity voltage and a tone from each receiver and switches the appropriate left or right channel from the correct LNB to that receiver This requires a dual output LNB. The LNB has two connectors that output the left and right hand polarized transponder channels at the same time. These are very common on most new satellite dishes.
DirecTV multi-switches typically have 4 inputs, the left and right outputs from two LNB’s, and 4 to 8 outputs for receivers.
DirecTV multi-switch Multi-switches for DISH Network have two inputs for the dual LNB dish that supports both primary satellites, and an extra input for a secondary dish. This model supports 4 receivers but is cascadable to support up to 12 receivers.
DISH network multi-switch Be sure and check to make sure the multi-switch you use is compatible with the version of the LNB technology in the dish. Because multiple receiver installations are so popular, several manufacturers build multi-LNB dishes with built-in multi-switches. Unfortunately, LNB and multi-switch designs seem to be constantly evolving, even the satellites and transponders change so be sure and check to which dish and LNB design is recommended by the service you’re using.
RF Signal DistributionNow that we've covered sources, lets cover how they’re combined in the distribution center and the components involved All of the external sources, cable, off-air, even satellite are cabled to the distribution center. Here, cable or off-air service is split to support branch coax cable runs to outlets throughout the home. Distribution ComponentsLets first cover some component characteristics you'll need to know starting with splitters, SplittersA splitter divides an input signal equally between 2 or more output ports. They typically come in 2, 4, 6, and 8 way versions. They are also referred to as a combiner since they bidirectional and can be used to combine 2 or more signals.
They may or may not be DC passing, that is they may pass a DC signal either for power or IR signals over the coax. Because they divide the signal, they divide the power or amplitude between the outputs. The outputs of a two way splitter are typically 3.5 to 4 dB less than the input. The following Table give the typical loss for 2 through 16 way splitter/combiners.
Splitters also have a frequency range specification over which they operate. This can range from as little as 5 – 54 MHz up to over 1000 MHz. AmplifiersWhen a source signal such as cable or off air is split to four or more destinations, an amplifier should be used between the source and the splitter The gain of the amplifier is chosen to overcome the signal loss in the splitter and coax cable runs to outlets. Amplifier gain is a measure of how much the amplifier amplifies and is always given in dB. A 10 dB amplifier will increase the input signal amplitude by 10 dB. Gains of from 5 to 20 dB are typical for broadband RF amplifiers.
Amplifiers come in both variable gain and fixed gain models. Fixed gain amplifiers are typically available for 10, 15, and 20 dB gain. In residential applications the distribution amplifier is often combined with splitters in one package since the two are so commonly used together. One input is amplified to several outputs.
To support cable set-top boxes, many distribution amplifiers have a 5-50 MHz return path built-in to allow upstream signals from the set-top box back to the cable company central office. An amplifier with a return path should not be used when the input is an off-air antenna since it could radiate any signal in the return path frequency range. AttenuatorsThe opposite of an amplifier is an attenuator, used to lower the amplitude of a signal. The typically come packaged in a barrel shape marked with the dB attenuation level. You’ll find these commonly in 3, 6, and 10 dB versions. You can screw them together to achieve any amount of attenuation you need.
TerminatorsScrew on terminators are used on the output of any unused cable or device for two reasons. To prevent possible radiation of RF from the system and to prevent an output signal from being reflected back to the source and causing possible signal distortion. They contain a 75 ohm resistor from the center conductor to ground. Make sure there is no DC voltage on the cable.
Internal Signal DistributionStructured cabling systems should also incorporate the distribution of in-home generated video sources such as the output of a DVD player, satellite receiver, or camera so they can be viewed on any television in the home. Distributing in-home sources requires installing an additional coax cable and jack at outlets where DVDs or other sources are located The downstream cable from the distribution center to outlets that carry cable company or off-air signals is referred to as the EXTERNAL cable. The added upstream cable is referred to as the INTERNAL cable since it caries in-home RF sources to the distribution center for redistribution on the external cable. At the distribution center, the internal cable runs are combined, mixed with the external signals from off-air or cable service, and split as before to all external outlets.
Internal signal distribution Lets take a look at how this works to view a movie from a DVD in the family room on a TV in the master bedroom, The DVD player audio and video outputs connect through an RF modulator to the internal coax connector. The television is connected to the external coax connector. To view the DVD player, it tunes to the channel set on the modulator. ModulatorsModulators are really small television stations that broadcast a baseband audio and video source onto a cable or off-air television channel. They have baseband audio and video inputs, and an F connector RF output They come in a wide range of sizes, from single source single channel to four source four channel models.
Typical modulator showing baseband inputs and modulated RF output All the modulators you’ll be using are frequency agile. That is, you can select the output channel in either the cable or off-air channel range. You need to do this to set the modulator channel to one that is not used by local off-air or cable channels. To make modulators relatively inexpensive, they transmit both sidebands of a television picture leaving out the expensive circuitry required to remove the lower sideband. This means they require a 12 MHz bandwidth, twice the normal 6 MHz television channel.
Therefore, if you’re using multiple modulators in a system or combining modulator outputs with cable or off-air signals, you need to leave one unused channel between selected modulator channels. The output level of modulators is usually high, typically from 25 to 35 dBmV. This comes in handy since they’re placed in the internal path of a coax distribution system where losses are high. FiltersFilters are used to pass one range of frequencies while blocking others. The most commonly used are the low-pass and band-stop. The low pass filter passes signals below a specified frequency and blocks signals above that frequency. Filters are specified by their pass frequency or by the pass channels – usually given as cable channels. Real life filters are not perfect. The attenuation increases gradually in the blocked part of the spectrum and reaches a maximum of –30 or 40 dB. Low-pass filters are typically used with cable or off-air service to block channels above a certain channel so that in-home modulators can be inserted into the channel space above the blocked channel.
A band-stop filter blocks a range of frequencies. These are also called notch filters and can be used to remove one or a group of frequencies or channels.
This notch filter shown above blocks cable channels 61 through 68, providing 4 channels, 63 through 66, for use by modulators DiplexerA diplexer is a combination of a high pass and low pass filter in one package. They’re used to either combine or split two signal frequency ranges. The most common example is this diplexer that will combine the output from an off-air antenna, up to 850 MHz, with the output of an LNB, between 900 and 2150 MHz.
Typical use of diplexer for combining off-air antenna and satellite output
Distribution System OverviewDistribution centers come in a variety of sizes and configurations to accommodate different size houses and a variety of applications. They have to contain all of the network support equipment for each network as well as power supplies, power strips, and accessory equipment. Manufacturers typically provide some mechanical means to mount the network support modules and equipment where you need it depending on the design of the enclosure. Many manufacturers use snap-in modules that can be easily moved around in the enclosure. The size of the enclosure you need depends on the modules you need to support your applications. So once you determine the number and type of outlets you need and applications you need to support, you work backwards and select modules and other support devices you'll need. Then do a trail layout of the modules leaving enough space route cables, place tie-downs and so on. We're going to cover how to design and plan the enclosure and the network support components you'll need in Part 2 of the course.
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