Welcome to the next installment of going digital. I know, your probably wondering just how many installations to this series there could possibly be ... right? Hang tight, I just don't see an end close by, and you should never stop learning.
This time, we are going take a quick look at the various types or choices that we have for video transmission. I know, you are thinking that this is another article about coaxial cable or something along those old tired analog paths ... right? Sorry, I wouldn't be much of a friend if I put you back that many years. However, since most of the world is still using coaxial cable, it is only right that we at least review it. Then we will get to the juice.
Coaxial cable has been the primary source of our CCTV woes for over 50 years. But there is a misconception that what works for cable TV should work for CCTV. Wrong! Cable TV is frequency based, not video-based. Cable TV likes and requires cheap and inexpensive cable. CCTV, on the other hand, is a very sophisticated electronic signal and so requires special treatment. The coax that we use must have specific qualities or your images will suffer greatly. There are three things that you must pay attention to with the coax itself.
The first is the shield. The shield works because of the harmonics (frequency) of the video signal. If you use anything other than pure copper, the harmonic frequency base of the video signal will not be able to support the shield and you will or could have all sorts of problems. Therefore the shield should be braided copper or reverse foil over braided copper. Lastly, with the shield, you should have a 95% efficiency rating (ER).
The next portion of the coaxial cable is the dielectric. This too must be very specific. It should have an impedance of 75 ohms. This sets the speed of the cable or how far the video signal can travel before it starts to deteriorate. I don't care what material the dielectric is made of, as long as it is rated for seventy five ohms, but I will tell you that foam dielectric will give you the best performance.
Under the dielectric we have the center core. The center core, like the shield, must be 100 percent copper. It can be either solid or stranded. Stranded will give you better results. Stranded center cores are also flexible so they can be used in applications where the cable is being flexed, such as situations feeding into a camera housing that is mounted to a pan/tilt.
Once you have the proper cable, you must then fit the size to that application. If your runs are less than 750 feet, you should use an RG59/U. If you need to go up to 1,200 feet, you can use an RG6/U. Want to run up to 2,500 feet? You must use an RG11/U. The RG stands for "Real Good." The number represents the size of the cable and the slash U is the designator for Copper, CCTV coax.
From here you get into connectors. I'm not going there this week. I will tell you that the only thing you should be using is a three piece, crimp on connector. Anything else will give you problems. If not today, then it will cause problems next week sometime at two in the morning. Oh, yes, there's one last thing. If your center core is too big for the center tit of the connector, don't cut strands or whittle the center core down to size. Go get the connector that has the right inner diameter on the center tit to match the outer diameter of the center core of the coaxial cable that you are using.
The next two forms of transmission that come to mind are fiber optics and microwave. I could write volumes on these two transmission methods (and I have). However, for the sake of moving into new stuff, I will pass them by this week.
Right after that comes twisted pair. This stuff is great. Imagine using a good ol' twisted pair of copper wires to transmit the video signal. This type of wiring saves money, increases distance and performance. It can also be used with any analog or IP camera. The cost comes in with the transmitter (mounted at the camera via a direct connection or coaxial pigtail) and the receiver (mounted at the head end via a direct connection or a coaxial pigtail). However, the cost of the transmitter and receiver are usually off set by the reduction of cost in materials and labor.