Transmitting the Video
When choosing a transmission medium, test, try and test again.
Transmitting the video signal from point A to point B was the very thing that gave the CCTV industry its name. We had, for the first time, a closed circuit between the camera and the monitor—a direct, private connection. Coaxial cable was the carrier. When you consider that this method of transmission has given us more than 50 years of dedicated service, you have to be impressed. However, as with everything technical, innovation has driven us past cable and into the new world.
Today, we transmit via coaxial cable, fiber optics, twisted pair (two wire, Category 3, POT lines, Category 5), wireless (RF, microwave, WiFi, FM) and satellite signals. It is not uncommon to find our more sophisticated systems using a combination of two or more transmission methods. The idea of a closed circuit has now taken a back seat, so we’re eventually going to have to stop calling it CCTV.
Mistake 1: Trying to save money by using cheap cable or non-copper cable. The dictates are really simple. Use a cable that has a braided copper shield, a 75∑ impedance dielectric, and a solid or stranded copper center core with a jacket that meets the requirements of the environment.
Mistake 2: Overrunning the cable length. Different types of coaxial cable have different run lengths. RG-59/U is the most common type of coax, and it can be used on runs of 750 feet or less. RG-6/U is good for up to 1,200 feet, and RG-11/U can be stretched out to almost 3,000 feet. These limits shouldn’t be pushed.
Mistake 3: Wrong connections. Even though we standardized on the BNC connector some 30 years ago, I still see folks insisting on using F connectors, UHF connectors and RCA connectors, with every negative result in the book. Stand back and scratch your head. Why can’t you get a clean picture? Because you tried to cheat.
The three biggest downfalls of coaxial cable have always been its bandwidth, distance restrictions and susceptibility to outside interference from RF and electrical magnetic induction (EMI). The newest problem with coaxial cable is that it cannot carry digital transmissions at the levels and bandwidth we need. So coax is on the way out.
Need More Fiber?
The beauty of fiber is that it can be used for analog and digital signals alike. A single fiber can be used to transmit up to 64 high-definition, 30 fps, bi-directional analog video signals at a time. Not only that, fiber can be used for analog and digital signals simultaneously. A single fiber can easily be converted into a 1GB network. However, all good things have a limit, and you must stay realistic. A 1GB fiber network has a 60% load factor. This means you have the potential for about 600MB of bandwidth to work with. That’s still one heck of a lot of video transmission work in today’s market.
The best part about fiber is that distance, although still a factor, is no problem in most CCTV applications. You can transmit signals up to 40 miles with an off-the-shelf system.
Do you need training and special tools to work with fiber optics? Absolutely. However, the cost and the training required to competently design, install and/or troubleshoot a fiber system have become extremely realistic over the past 10 years. I remember my first fiber optic meter. It worked on 16 AA batteries—you can imagine the weight. I had approximately 30 minutes of field time to test my cables. The best part was the cost: $1,200. Today, a good fiber meter works with a 9-volt battery, gives you about 24 hours of field time, weighs in at a few ounces and costs less than $300.
Training is fully available through various vendors including the manufacturers, NAAA and NBFA. David Engebretson of the Security Networking Institute in Chicago (securitynetworkinginstitute.com) has developed about the best fiber optic training I have seen in this country and is fully supported by SIA.
Wireless transmission systems are fast becoming very popular. I personally love this format of transmission, because it truly moves us into the plug-and-play mode. Set up a proper wireless transmission system and you have an image at your head-end just by plugging a camera into a power source. For general purposes, you can use public bands with no licensing or related issues. Wireless transmission systems can be used to cover areas of up to 40 miles. Please understand that this is a point-to-point transmission and it works in the licensed bandwidth. Some cities across the United States have installed massive wireless nets that are used to carry all sorts of signals including video, voice and data. There are some issues, however.
Your wireless system may interfere with cell phone transmissions. This doesn’t bother me too much, since I have yet to have a cell phone that wasn’t interfered with by something. However, you may not be too happy with this. If your neighbor installs something wireless, it might interfere with you, or vice versa.
Filtering and encryption are the key factors with all wireless systems. Penetration is also a key factor. Wireless signals are easily blocked or reflected by brick, steel, aluminum, your neighbor’s pet pit bull, etc. Your system may work great on the ground floor but won’t penetrate to the second floor. You might cover a hallway with incredible penetration, but can’t pick up a single thing two feet around a corner. This problem is handled by installing additional antennas.
If your wireless system doesn’t have a good filtering system, it is possible for echoes to cause you all sorts of problems. Wireless, for the most part, is restricted to a 54MB bandwidth with a 40% load factor. This leaves you with about 20MB to work with. For a general, very loose understanding, you can use a guide factor of 1MB to 1.75MB of bandwidth per channel of video.
The last major concern of wireless is interception of signal. Anyone with a receiver tuned to your frequency can pick up and use your signal. Therefore, you want to make sure that you use a proper encryption or coding process with good password protection.
As with everything else, training, research and hands-on testing are the best ways to create good wireless systems. Some companies will sell you a demo kit. I highly recommend trying a demo before you choose a final solution. Unfortunately, the cost of such units can quickly exceed $10,000. This is a bit of a stretch if you are only installing a single unit, one time. However, if you plan to do a bunch of wireless, get a demo kit and test your site in advance. You will be a lot happier in the end.
The true costs involved with this technology are the transmitters and receivers. The video signal must be converted to be properly carried over the wires. However, as is the case with fiber optics, the cost of the twisted pair transmitters and receivers is usually offset by the reduction of cost in materials and labor.
The most common formats of twisted pair technology are Category 3 and 5 cabling. Category 3 is unused pairs of wire installed with the building for the first phone systems. This is the part I love the most. Think about walking into a large office building or warehouse. Imagine that the majority of your video system cable is already installed. It was done by good ol’ AT&T when the building was built. The phone system in most commercial buildings consists of massive trunks of Cat 3 cabling. Only two thirds of it is usually in use. The rest was pulled at the time of installation to save costs on future expansion. Find your telephone closets and you may have found a gold mine of pre-installed cabling.
Cat 3 cabling is a lower-grade cable than Cat 5, but they work on the same principals. Cat 3 has fewer twists per inch and less overall quality. The maximum transmission rate is 15MB with a 60% load factor at 3,000 feet. This works out to about 8MB of transmission capability for video. Using our previous guideline of 1MB to 1.75MB of bandwidth per camera, your standard Cat 3 system can be used for up to four cameras per channel. Cat 3 can be converted into a simple network, which means you can work with the newer digital technologies.
Category 5 cabling works just like Cat 3 but with more twists per inch, higher-quality wire and a 100MB transmission rate with a 60% load. This leaves you about 60MB of usable carrier over 300 feet. This also means you can transmit about six times as much information on a Cat 5 as you can on a Cat 3 cabling system. Unfortunately, you will not walk into the lost and forgotten telephone closets of most buildings and find Cat 5 installed. You will need to install it yourself or jump onto the existing LAN.
Keep in mind that your maximum run length is 300 feet. If you push this limit you won’t be happy. If you need to do longer runs, work with encoders and routers as you go. Will you need training and special tools? Yes. But both are fairly simple and available through the majority of manufacturers.
In the end, all formats of cabling/transmission require special tools and educations. Test, try and test again. Read, research and ask questions. It’s all out there, and the answers most often come in the form of experience and investigation.
By Charlie R. Pierce
LeapFrog Training & Consulting