This article is about the basics of CCTV and is intended for beginners who have no experience in the field if that is your case keep reading.
In this article, I will explain in detail the basic concepts of analog CCTV, and how a small recording system with 4 cameras and a digital recorder works.
Just in case you are interested in learning even more about security camera, please check the Ultimate Security Camera Guide.
Let's begin the explanation for the most basic element, an analog camera.
What is an analog camera?
At first, a CCTV camera has characteristics similar to any traditional camera you know (like the camera on your cell phone) because it has a lens that directs light to an internal image sensor, but the similarities end there because in an analog camera there is no internal SD card for recording.
An analog camera captures images using a lens, image sensor and the internal circuitry system generates the analog electrical signals that are sent through coaxial cables to an external recorder (known as DVR) that converts analog signals to digital format for local recording and remote access.
What is an analog CCTV system?
It's a system with analog security cameras that send the signals to a DVR (Digital Video Recorder) usually located in a rack or a surveillance room.
This type of system is not purely analog because there is a conversion of analog signals to digital, it is, in fact, a hybrid system, but it is very common to hear technicians referring to this type of system as analog.
Connecting Multiple Cameras to a DVR
It is possible to connect several analog cameras to a digital recorder (DVR), just get the equipment with an adequate number of channels.
The following image shows 4 analog cameras connected to a DVR that in turn is connected to an analog monitor that displays the images. The system uses coaxial cables designed for CCTV.
Take a look at the diagram, the first block shows the analog cameras that are responsible for generating the video, the second block has the DVR that converts the signals from analog to digital to record and send the video stream to be displayed in the third block where the analog monitor is located.
Note that the analog cameras have different physical formats, in this example, there is a box camera, a dome camera, a PTZ, and a bullet camera successively.
Here is an image that shows a 4-channel DVR and 4 analog cameras.
One of the cameras has the coaxial cable connected to the DVR so that it can send the electric signals to the DVR for digitization and recording.
The purpose of this image is only to illustrate the simplicity of the concept of connecting analog cameras to a digital recorder, it is also necessary to power all devices with a power supply.
The next image shows the back of a DVR, note that there are 4 inputs for the cameras and that the connection of the coaxial cable to the DVR is made by a BNC connector.
There are different types of coaxial cables on the market, in the picture above it is possible to notice that the black cable is thicker than the white one, but the last one has a parallel cable to carry the power to the camera (this type of cable is known as siamese cable).
Cables and connectors for CCTV cameras
Note in the following image that a siamese cable has a BNC connector at both ends and a pair of wires that to power the camera, at one end there's a power connector (also known as P4 connector in some countries) and on the other side the red and black wires are connected to a power source.
If a cable without parallel power cord is used (such as the black cable shown in the picture), it will be necessary to use a separate power cable, which may make the project a bit more expensive, but in some cases this solution is more professional, especially when the cameras are installed far from the DVR and the parallel cable is not good enough to carry the power.
Professional Analog Cameras connectors
This type of separate power connection is quite typical of professional cameras, especially box models that are usually used in special projects.
Note in the image below, this professional camera can be powered with either 24-volt AC (Alternate current) or 12-volt DC (Direct Current) power.
In day-to-day situations for small projects, it is rare to find professional analog cameras of this type due to cost-effectiveness, especially when it is better to use modern IP cameras rather than expensive professional analog cameras.
If the design is small and your concern is cost, it is currently more common to use traditional analog cameras with siamese cables and power connectors.
CCTV camera resolution
There are different analog camera technologies on the market and therefore different types of resolutions, let's discuss this topic.
The resolution of an old traditional analog camera (CVBS) is measured in TV lines, which is nothing more than the number of vertical lines that appears on a monitor. The higher the number of lines, the higher the resolution.
Note in the picture below that there are lines on the monitor screen that make up the image, depending on the number of lines the camera can generate it is considered a higher resolution camera, although it is an old technology, we still find cameras with resolutions of 480, 540, 600 and 1000 TV lines, however I do not recommend the use of such cameras.
As you saw before, after going through a DVR the image is converted to the digital format.
When converted to this format another measurement unit is used to refer to the resolution of the camera. The term TV lines is not used for digital resolution because the number of pixels that is available in the image is used.
Nomes such as CIF, 2CIF, 4CIF, VGA, SVGA, XVGA, HD, Full HD, Mega Pixel and 4K are used to refer to CCTV digital resolution.
See in the picture below that there are several dots that form an image, they are the pixels and the higher the number of pixels, the higher the digital resolution.
It is possible to have thousands of pixels in an image, in this example, we could have cameras that generate 0.3 to 8 million pixels, that's the reason the resolution is referred in Mega Pixels (MP).
Here a video that explain in the details how the CCTV digital resolution works.
DVR network output
As you saw earlier, a DVR converts the analog camera signals into a digital format so it can be recorded on an internal hard drive, but not only that, the DVR also has a digital output that allows sending the camera images over a computer network and the Internet.
See the following image that illustrates the concept.
Note in this picture that the analog cameras are connected to the DVR that receives the signals in traditional analog format with 600 TV lines (TVL) that are converted to the digital format 4CIF that represents 704 x 480 pixels horizontally and vertically respectively.
This video in digital format is displayed on a computer screen with specific software, note in the diagram that there is a blue cable (network cable) connecting the digital output of the DVR to a computer.
It is also possible to connect a coaxial cable from the DVR to an analog monitor and also obtain a traditional analog video output with the 600 TV lines.
Connecting monitors to the recorder (DVR)
After receiving signals from the analog cameras, the DVR can display them on a monitor or TV, just use the available BNC, VGA or HDMI outputs on the back.
Note in the following image that there is a BNC connector output to use a coaxial cable and connect to a traditional analog monitor and an HDMI type output to connect to a digital monitor.
Analog cameras with modern technologies
So far I have talked about traditional analog cameras that have the analog resolution measured in TV lines, the type of technology used in these cameras is called CVBS and is not the most appropriate to be used these days.
Modern technologies such as HD-TVI, HD-CVI, and AHD are suitable for CCTV projects where it is still necessary to use analog cameras.
When connecting a camera using this type of technology in a modern DVR, the digital output will be much higher than the 4CIF resolution (704 x 480 pixels) previously seen. It is common to find these modern cameras in the market with Full HD resolution (1920 x 1080 pixels) and even higher resolutions such as 3 Mega Pixel, 5 Mega Pixel, and 8 Mega Pixel.
When buying your CCTV cameras use this new type of technology.
Final words and conclusion
Analog CCTV systems are no longer used in large projects, as there is a preference for IP systems, but there is still a market for analog cameras and DVRs in small projects where cost is a key factor.
If you need to use an analog system, avoid the old traditional technology (CVBS) and use modern technologies with high-resolution analog CCTV cameras such as HD-TVI, HD-CVI, and AHD.
==> To learn more about these technologies I recommend that you read the articles below (be sure to read as they are important information):
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Claudemir Martins is a former Samsung Engineer with 15+ experience in the surveillance industry. He has been traveling around 17 different countries to teach people how to design, and install CCTV systems.