Cameras for video surveillance are selected according to different parameters, including the type of transmitted signal. Digital models are considered more convenient and efficient today, but analog versions are still in demand. An AHD camera is one such solution.
AHD camera definition
AHD technology provides a very high resolution analog image transmission, atypical for a conventional model. This is the result of the development of the usual television standard - 25 frames per second. In contrast, AHD uses progressive scan. When recording and digitizing, an image is obtained up to 1080p. Moreover, signal transmission via coaxial cable is possible at a distance of up to 500 m.
The camera is based on high-tech CMOS sensors. They usually generate a higher noise level, but modern AHD cameras have eliminated this disadvantage. The signal from the matrix in digital format is transmitted to the processor, where the brightness and color components of the image are processed separately according to its own algorithm. In this case, a noise reduction system is used. As a result, the consumer receives a clear high-quality image without extraneous noise.
From the processor, the digital signal goes to the converter - DAC, where it is transformed into analog. Lossless data is transmitted over coaxial cable at a distance of up to 500 m.
Another plus is the ability of Ahd Camera to create equally clear and detailed images day and night. An ICR filter is installed in analog devices. It is an infrared filter that separates heat radiation during the day, which affects contrast and clarity. The filter does not work at night and, thanks to the IR illumination, provides a high-quality picture in the absence of lighting.
The main difference between the device is the lack of compression.
Subspecies and characteristics
The devices are available for indoor and outdoor installation. In the latter case, the cameras have a more durable body and protection from moisture, dust and cold. Since AHD camcorders are constantly being compared with digital ones, the main criterion for the user is the resolution and signal quality. According to this parameter, devices are divided into 3 categories.
AHD-L
This is the unofficial version of the AHD 0.8 standard. The resolution does not exceed 960 * 576, which does not meet the requirements of HD technology. The camera has a different color coding option. This improves the clarity of the image and eliminates the "ladder". However, when connected to the old D1, the picture is black and white.
AHD-M
AHD 1.0 standard with a resolution of up to 1280 * 720 pixels. The image is similar to a 1 megapixel camera. Only coaxial cable is used for data transmission.
AHD-H
AHD 2.0 standard. the resolution has reached 1920 * 1080 p. The standard supports 2 megapixel cameras, other devices with a resolution from 720 to 1080 p and provides viewing of a video stream of the same level. The speed is 30 frames per second.
All variants of the device can be connected to the DVR.
Criterias of choice
An AHD camera costs a lot less than an IP camera. If there are no ultra-high requirements for the image, this option is preferable. Which standard is better - AHD 1.0 or AHD 2.0, again, is determined by the desire to see the picture with varying degrees of clarity.
The second determining factor is the purpose of the video device:
- Miniature - they are not striking, they are used for video surveillance in an apartment or a private house.
- Dome - modular version, it is built into the ceiling. The camera is covered with a tinted hemisphere and it is impossible to follow its direction.
- Box - often equipped with long and wide angle lenses. Designed for installation in industrial premises and shopping centers.
- Outdoor AHD video surveillance is collected from PTZ cameras. Telecontrol signals are transmitted over the same coaxial wire through which the video signal passes to the recorder, so that extra wires are not needed.
The next important parameter is focal length. It is inversely related to the viewing angle, so when choosing it is worth determining which moment is more important:
- with a phased array of 2.5 mm, the viewing angle is 120 degrees, but the distance of confident identification reaches only 2 m;
- with a FR of 4 mm, the angle decreases to 65 degrees, and the distance increases to 4 m;
- with a FR of 12 mm, the angle is only 25 degrees, and the distance increases to 12 m.
If high detail is not needed, it is worth taking a camera with a low FR, since here the angle of view will be more important.
The sensitivity of the video camera is selected according to the level of illumination. If the device works around the clock, the sensitivity should be at least 0.01 lux.
The noise level is important if the cameras are located in a home or office. For a good model, the noise level does not exceed 45–48 dB.
An AED camera with a low noise level of 50 dB and a high resolution costs almost 2 times more than a model with 45 dB.
Differences from IP cameras
Which is better - AHD or IP video surveillance, depends on the purpose and device of the system. The characteristics are presented in the table.
| Parameter | IP | AHD |
| Signal | Digital | Analog |
| Signal delay | No more than 1 s. In case of unsuccessful connection scheme up to 20 | Not |
| Transmission distance | 100 m.When using optical cable 20 km | 500 m |
| Cable type | Twisted pair, optical | Coaxial |
| Power transfer | there is | Not |
| The cost | More expensive | Cheaper |
| Optional equipment | Router or switch | DVR only |
- distance - when transmitting no more than 100m, it is preferable to an IP camera. If the distance is about 400 m, AHD is better;
- if many cameras are combined into a system, it is better to take digital ones;
- if the structure is being modernized, and there are already coaxial cables, it is cheaper to buy analog ones;
- if freezing is unacceptable, video output to AHD is better.
Installation of a hybrid system is allowed, since a modern DVR can work with cameras of any kind.
Advantages and disadvantages
The advantages of an analog device are tangible:
- simplicity of connection - devices do not need adjustment;
- the signal is stable, freezes are excluded;
- ease of integration into an existing structure and the ability to work in parallel with digital devices;
- low cost compared to IP models.
Among the disadvantages is the possibility of interference caused by electromagnetic radiation. The camera is not a standalone device. Recording is possible only on a video recorder.
Connection features
A typical video surveillance scheme when connecting AHD cameras includes the following elements:
- cameras - placement points are determined in advance;
- a DVR with a hard drive of at least 1 TB, since analog recording weighs a lot;
- coaxial cables and wires;
- modular arrester - turns off the system in case of voltage surges;
- modular connectors and terminals.
The main difference between the installation of an analog system in comparison with a digital one is that apart from purely physical work on installing the mounts and connecting the cables, you do not need to do anything. Cameras start working immediately after being connected to the network.
Manufacturers overview
The most famous company in the Russian market is Dahua... It offers models for indoor and outdoor installation and with different resolutions. Installation with integrated microphone is possible.
Division - a manufacturer of analog devices of any type.Most devices support multiple standards besides AHD. Due to the successful combination of quality and cost, the models are in great demand.
Neostar - a well-known developer of video surveillance systems. Offers digital and analog recording devices, as well as recorders, video intercoms and other elements. A distinctive feature of cameras is the ability to improve the received image.
Partizan - The English manufacturer offers video recorders and video cameras, including robotic ones.
