As described briefly earlier, a "head end" is the central, single location in a coaxial cable system, where a data signal is received via a satellite dish, and is "captured" and rebroadcast in an RF signal form through coaxial cable to users. This "head end" then, is the most important part of the cable plant. Without it, no signals can be sent.

It may also be possible for a community to purchase signal from another nearby head end if one is available. This can be a benefit, as a purchased signal will already have gone through the head end process and can be immediately redistributed. These signals can be expensive, and a data network still requires a head end. Purchasing a signal also means that you become dependent on the discretion of another organization or company that may dictate particular signals. Creating a community-owned independent signal will always be the most flexible option, but "fostered relationships" can help greatly. Try to keep doors open as different communities will have different situations and partnership potential could mean that anything is possible! The head end of a cable plant, once together, has the potential of providing any kind of communication and/or entertainment available today (and tomorrow).

Cable "head end" technology is constantly changing. New developments all the time mean that no one technology can be recommended in a manual of this sort, as the information will quickly be outdated. When choosing headend technology, a community needs to research all that is available at the time the installation is going to be completed, and purchase that technology which best meets their needs for performance and cost.

The diagram above briefly illustrates how a cable system works. In this system, the original signal is being received through a satellite dish from a satellite orbiting the earth.The original signal is most commonly brought into a cable head end from satellite dishes, however the signal can come from other sources, such as a fibre optic line brought into a community. Generally speaking, there is a greater cost associated with purchasing rights to redistribute a signal from a fibre optic source.

1) One or more satellite dishes receive signals from satellites orbiting the earth.

2) The satellite signal is carried from the dishes via regular coax cable. This cable attaches to a LNB or "Low Noise Block-down" converter. The LNB is responsible for collecting the high freq. from the sky and converting it down to the lower frequencies before it is send into the headend to be used by cable equip.

3) One signal is split into as many signals as required.

4) Each signal is then ‘received’ in its own receiver.

5) The receiver sends the signal to a modulator. (One modulator per signal.) This is where the signal is adjusted by the administrator.

6) Once correctly modulated, the signal is sent to the outgoing combining system which sends all of the signals out on one coaxial cable to be delivered to the users.

Receiving a signal: satellite dishes - Many different satellite signal service providers have many different kinds of dish technology available, and many different satellite signals. This may mean that there will be a few or many dishes set-up to receive the signal. Depending upon which services are required, current technology will have to be chosen that will provide the best services. As with the head-end technology, communities need to research available technology at the time of the installation, and choose one system based on cost. Once a service provider and system is chosen, it is best to stay with that system as not all systems are cross compatible, so intermixing technologies within a system may mean that the system won't function properly. While it would be nice to say that it would be simple to mix technologies and be able to distribute this way to subscribers, in order to eliminate big problems from happening, it's necessary to do some homework first to make sure that the system will do what is required.

Don't fix what ain't broke: Satellite information receiver technology, for the most part, is now a "black box" technology, meaning that it is a sealed system that is not easily repairable by the end user. There seems to be a level of "black magic" involved in the production of the technology. This means that if the technology doesn't work, it is simply sent back to the manufacturer for repair or replacement. Because of this, it is important to ensure that warranties for any equipment purchased are adequate to meet the needs of the community.

Mounting and connecting dishes: Most satellite dishes come with specific mounting hardware, and a good vendor will ensure that everything is provided that is required to make the technology work properly. Satellite dishes generally come with their own "waveguide" - this 'wire' is called an LMD lead, and it is very similar to the lead that attaches to the back of a common VCR. The familiar connectors make this equipment easy to connect to the "head end" equipment.

TIP: It is important to mount satellite dishes on a solid, SECURE structure. The dishes need to make continuous contact with satellites (which are on average 450 km away from earth). Wind can make life very difficult if dishes arent' mounted on a solid base, as the dishes will move too much to keep the signal. Keeping them somewhere secure and hard to reach by idle hands is important because this equipment is expensive to replace, and can be vandalized.

Split the signals that come in: Once the line has come into the building where the headend is located, the signal is then split. These signals are then translated later in the headend into television or data channels. Splitters, as the name implies, split an incoming signal into multiple signals of two or more. There is a vast range of splitter types available, from simple splitters similar to those used for splitting a home cable signal <picture> to rack mounted signal splitters with multiple ports. Splitters are supplied in multiples of two (as each is capable of making one signal into two.) They come in two, four, six, eight, ten spiggot, etc. Each can then be either a simple unpowered splitter, or an amplified splitter. Determining which splitter type is best is based on research of looking at available types and determining which best meets needs for signal number, signal strength, and cost.

Generally speaking, passive splitters which are not powered, and therefore not amplified, will be cheaper. "Active" splitters are powered and amplified, contain their own power supply and are generally more expensive. Also, the larger a splitter is, (i.e. the higher the number of signals it will split) the more expensive it will be.

Signals are sent to receivers: Each receiver gets an input signal from dish. Initially, all of the receivers are getting the same signal from the dish, so every receiver takes the same signal, but finds its own individual 'channel' information. Receivers are thus programmed by a technician at the head end with a specific transponder number, channel, virtual channel, the frequency, and whether the receiver should be looking in the horizontal or vertical portion if the incoming signal stream. <need to explain horizontal/vertical stuff more> Once the appropriate channel is found, the receiver is also responsible for separating the video info from the audio info and sending these two portions of the signal separately to a modulator.

Modulation: Modulators are one of the most important part of the system, where the signal control takes place. Both the levels of the signal carrier and the signal itself may be controlled. The purpose of the modulation is to ensure that the outgoing signal is at the correct frequency and strength, such that when it reaches the end user, there is a minimum loss of data. Levels are set for different signals as different signals will experience different rates of data loss (attenuation or distortion) depending upon their frequency. Modulators may be either set to a specific frequency (these are generally less expensive), or they may be "agile" modulators, meaning that they may be adjusted to a number of different frequencies. In building a cable system, a common practice is to have set frequency modulators for the main part of the system, but to have one or more "agile" spare modulators, so that they may be used to replace (permanently or temporarily) any modulator that malfunctions.

Outgoing Combining System: Once the signals are properly modulated, they are then sent for distribution to the users. This is done by combining all of the signals from all of the modulators, through a system called an "outgoing combining system." This system takes all of the leads from the modulators, and combines them down, so that the combined signals may all be passed through one coaxial cable.

Signal "launch": Once the signal has been combined and proper levels are achieved, the signal is then amplified and distributed to the trunk portion of the plant, which is the portion dedicated to transmission and preservation of the signal. The size of the trunk mainline cable and the amount of frequency spectrum being broadcast will dictate the next amplification point. The distance that an amplifier can launch a signal varies depending upon its size. Launch amplifiers capable of amplifying a signal over a greater distance are generally more expensive than those capable of launching a shorter distance. Also, because this system is copper based, temperature will effect the system, particularily the amplifiers. It is important to designand install the backbone system very well, and in such a way that takes into account any changes in data amplification as a result of temperature changes.

Signal Maintenance: Presently, most trunk (mainline) transmission amplifiers and most bridger, line extender, or distribution amplifiers (all the same) are quite automated and are able to self adjust signal levels to some degree in accordance to changes in temperature ( which is the largest single
uncontrollable force that will affect system levels. This automatic feature goes a long way towards keeping maintenance to a minimum, though maintenance will never go away completely.

Within the cable plant itself, good building and installation techniques will also help maintain a longer-lasting and more reliable system. This includes making sure that cable joints are installed correctly and work well, and that they are sealed at the time of building to be protected from weather always. This will help maintain the clean signal coming from the dedicated backbone "trunk" line throughout the system. Additionally, signal maintenance devices such as in-line amplifiers will ensure signal quality right to the end of the line.

End-of-line signal distribution flexibility: Once at the end of the line, there are multiple signal distribution options for both end-users and the cable plant installers. These include:

• direct cable connection: this is the most common solution, having coax extending from the distribution plant directly to house
  
  
• wireless: both directional and omni-directional, antennas can be installed. These could be broadcasting partial or complete portions of the signal to meet specific needs. These can also be point-to-point, or point to multi-point. Wireless distribution is discussed in Module Two.
  
  
  
• Combination distribution solution: The signal may be divided to distribute a portion of over coaxial cable, and a portion via a wireless signal. For example, it may prove easier to deliver Internet connectivity throughout particular areas using an omni-directional antenna, using only a
  small portion of the full spectrum. With all types of amplifier, less spectrum means lower equipment costs, especially with wireless.