Partizan Technical Service tested the transmission of video signals of different standards depending on the length and type of transmission media, as well as the use of terminal transceivers.

Transmission through the coaxial cable

The dependence of image quality on the length of transmission channel and the type of transmitted video was tested. As a reference the image transmitted along the 5 meters segment of coaxial cable was used. The further increase was carried by the coils of cable of 100 meters (RG-6/U 75OHm). To obtain the required lengths they were consistently joined via BNC-connectors, clamped with a standard tool. It is worth noting that the connectors were only clamped but not sealed.

As the source of video Partizan COD-631H ver. 3.0 camera with fixed focus for outdoor installation was used in testing, ant the image was received and digitizes by hybrid 8-channel Partizan ADH-18V HD. It provides simultaneous processing of various types of analogue video streams (AHD-L, AHD-M, CVBS) through the coaxial cable and ddigitized ones through IP- network.

The received image was recorded for each channel length in three camera modes: standard analogue CVBS (resolution 960h, i.e. 960x576 pixels), AHD-L (960h standard picture transmitted with the help of AHD-technology, the same 960x 576 pixels) and AHD-M (720p standard picture of AHD format. Resolution 1280x720 pixels)

Test Results

Test results as screenshots after the image transmission are shown below:

Coaxial cable
CVBS 5 meters	AHD-L 5 meters	AHD-M 5 meters
CVBS 100 meters	AHD-L 100 meters	AHD-M 100 meters
CVBS 200 meters	AHD-L 200 meters	AHD-M 200 meters
CVBS 300 meters	AHD-L 300 meters	AHD-M 300 meters
CVBS 400 meters	AHD-L 400 meters	AHD-M 400 meters
CVBS 500 meters	AHD-L 500 meters	AHD-M 500 meters

Analyzing the obtained images leads to the following conclusions:

• The transmission quality obtained in CVBS and AHD-L modes up to 400 m. is very similar. In fact, the advantage of AHD standard at the transmission of images of such resolution is the ability to transmit audio information, PTZ commands and "alarm" signals through the same channel. But at 500-m CVBS gives a much more blurred image, the advantage of AHD-L at this distance is obvious.
• The picture in AHD-M mode is noticeably clearer and more detailed than others at the same distance of transmission. With increasing the length of coaxial cable the image gradually loses its sharpness, but even at the limit distance it is more informative than at any variant of 960h standard. AHD technology enables preserving the advantages of transmission of increased resolution via coaxial cable at any distance up to 500 meters . That confirms the possibility of simple upgrading of surveillance system by installing new AHD-M cameras and relevant DVRs preserving old cable network.

Conclusions

In the course of testing good image was received from the cameras after the transmission to the limit distance of 500 m through a composite coaxial cable. The benefits of increased resolution standard 720p were visible even after the transmission through the channel of maximum length. This means that the installation of equipment of AHD-M standard gives real and not imaginary effect of increasing quality while the use of coaxial cable network, even if this network is from the devices of previous generation.

Video transmission through twisted pair

Next point of testing was the research of the possibility of video transmission through twisted pair.

The coils of cable 305 meters long (Cat 5E UTP cable 4PR 25AWG ISO) were used, at the first stage camera and DVR were connected to twisted pair with the help of passive transceivers DL-402. The results as screen shots:

Twisted pair
CVBS 305 meters	AHD-L 305 meters	AHD-M 305 meters
CVBS 610 meters	AHD-L 610 meters Mode is not supported	AHD-M 610 meters
CVBS 915 meters Mode is not supported	AHD-L 915 meters	AHD-M 915 meters Mode is not supported

Conclusions

Video signal transmission through twisted pair with passive adapters is available for short distances up to 305 meters. And the quality of the resulting image will be lower than if using the coaxial cable even with joints. In our experiments, AHD image transmitted through 305 m of twisted pair was approximately in line with that obtained after passing 500 m of coaxial cable. It is interesting that transmission of CVBS signal through 305 m of twisted pair, on the contrary, went much better than through the coaxial up to 300 m.

As the length of UTP cable increased up to 610 m, the used pair of camera-DVR could only work in CVBS and AHD-M modes. Only the first of them retained colour, but image sharpness significantly decreased. Increasing the leverage of transmission up to 915 meters enabled only AHD-M node to switch, and only in monochrome mode. But the clarity of the image became unacceptable, it was not possible to work with such a picture, and so, the transmission of video up to 915 meters over twisted pair with passive transceivers is not feasible.

During testing the transmission of video over twisted pair an experiment was carried out on the direct connection of camera and DVR contacts without passive transceiver adapters. The results of the experiment are given as images of transmitted pictures:

Twisted pair without adapters
CVBS 305 meters	AHD-L 305 meters	AHD-M 305 meters

As a result of the experiment, it was found that connection of camera and DVR to twisted pair without adapters, even at a relatively short distance of transmission causes harmful interference. In modes with low resolution (CVBS, AHD-L) the flaws of transmission are seen as geometry distortion in the form of horizontal stripes, in AHD-M they also receive colouring. At big length of transmission channel the flaws will be even more noticeable.

Testing of transmission through long lines of twisted pair using active signal amplifiers.

As a next step, Partizan Technical Service performed testing the possibility of video transmission over long lines of twisted pair using active amplifiers. It was divided into two phases: with the installation of active amplifiers from one or both sides of the cable.

At the first stage camera was connected to twisted pair with the help of a passive transceiver DL-402. On the opposite side transmission channel was connected to an active receiver DL-410R.

During testing, the length of the transmission channel was increased sequentially with coils of cable of 305 m. The segments were connected by twist. For each distance DIP switches of the amplifier selected such a gain at which the picture was the best.

The screens for each of tested modes and distances are shown below.

High-quality twisted pair
CVBS 305 meters	AHD-L 305 meters	AHD-M 305 meters
CVBS 610 meters	AHD-L 610 meters	AHD-M 610 meters

Further increase in cable length up to 915 meters led to the fact that camera-DVR pair was able to transmit the image only in AHD-M mode, the screenshot is shown below.

AHD-M 915 meters

At even greater increase of the transmission channel (1220 m) and the use of active-passive pair of adapters the image was not transmitted in any of the modes.

During the test it was able to verify the dependence of video transmission quality on the cable used. The use of coils of heterogeneous wires with the same transceivers although made possible the transmission of video to the distance up to 1075 meters, but the quality was not acceptable because of strong noise and reduction of sharpness that did not appear when working with homogenous coils of the same UTP cable. Transfer images at dissimilar channel are listed below.

Heterogeneous twisted pair
CVBS 840 meters	AHD-L 840 meters	AHD-M 840 meters
CVBS 1075 meters	AHD-L 1075 meters	AHD-M 1075 meters

Conclusions

• At short distances (305 m) the use of active video receiver on the channel with twisted pair gives an opportunity to get better picture quality than without it. This is evident if we consider images from the first part of the test.
• If transmission distance is doubled (610 m), an active amplifier makes the picture sharper, but still quite acceptable. In AHD-L and CVBS light noise introduced by the amplifier is visible. It is worth noting that between these two modes with the same resolution the image in AHD-L is noticeably clearer than in CVBS.
• At a distance of 610 m the picture in AHD-M has noticeably better resolution than in AHD-L and CVBS, its blur is slight.
• With further increase of the transmission distance (915 m), only a single AHD-M mode is available, which offers good image quality. The addition of the next section of the cable (up to 1220 m) shut it down.
• At middle transmission distances (over 600 m) and with the use of passive-active pair of transceivers, the quality of transmission is greatly influenced by the characteristics of the cable used.

At comparable distances, with the inclusion of the same transceivers, the use of heterogeneous UTP cable gives very noisy image. Its quality is unlikely to be acceptable for most applications of video surveillance systems.

The use of active amplifiers at both ends of the transmission channel will theoretically raise the distance of confident performance. We will check this assumption during the second phase of the test.

For this purpose an active transmitter DL-410T was installed on the part of the camera, on the other side UTP cable is connected to an active receiver DL-410R. The gains at the receiver and transmitter were selected so that the transmitted image had the best quality. The resulting screenshots are shown below:

Twisted pair with active transceivers
CVBS 915 meters	AHD-L 915 meters	AHD-M 915 meters
CVBS 1220 meters	AHD-L 1220 meters Mode is not supported	AHD-M 1220 meters

Conclusions

The use of amplifying transmitters and receivers on both sides of UTP cable enables confidently transmitting the video of good quality at a distance of 915 meters. Slightly higher contrast and colour saturation can be even useful for the purposes of surveillance.

But at the maximum transmission distance (1220 m) “smart” AHD-M transmits only a monochrome image. Obviously, it “believes” that quality b/w picture has more useful video than noisy colour one. At the same time, analogue CVBS works flawlessly in colour, although it has much lower resolution than AHD-M. As a result, the customer may have to make a choice between these two alternatives: definition of b/w or colour informativeness.

Study of mutual influence of adjacent twisted pairs

During the test an experiment was conducted to study mutual influence of AHD channels transmitted through adjacent twisted pairs in one UTP cable.

First, Partizan COD-631H ver 3.0 and Partizan COD-454HM ver 3.0were connected to the coil of wire of 305 m length. The cameras were connected to twisted pairs with passive transceivers DL-402. In AHD-L mode they produced adequate pictures; no mutual influence on each other was noted. P.S. The scene was shot with nearby devices equipped with common lens. The images clearly show the difference in the view angles of two cameras.

The screenshots at the transmission through two adjacent twisted pairs of UTP cable are given below

Partizan COD-631H ver 3.0

Partizan COD-454HM ver 3.0

It was decided to complicate the task, and in the next step, all four twisted pairs were used in the cable. The following HD cameras were used for testing:

• Partizan COD-631H ver 3.0
• Partizan COD-454HM ver 3.0
• Partizan CDM-VF33H-IR ver 3.0
• Partizan CDM-VF333H-IR ver 3.0

Cameras were connected to twisted pairs with passive transceivers DL-402. Images transmitted in AHD-M mode individually, and the screenshot of Partizan CMS program with all four images at the same time are shown below.

Camera 1	Camera 2
Camera 3	Camera 4

DVR screen

Conclusions

Comparing these images with the images transmitted over a single twisted pair of the same length and with passive transceivers, it can be noticed that transmission quality did not practically changed. In our experiment, mutual influence of channels on each other was not detected; at such distance you can really use one quality UTP cable to obtain information from two to four AHD-M cameras simultaneously.