Active receivers and transmitters over twisted pair.
Actually, there are not so many methods of transmitting video signals and telemetry used in TSB systems today.
Depending on the task set by the customer, the installer chooses either a coaxial cable, or a twisted pair, or optical fiber.
This choice can be determined by several parameters (features of the facility, budget), but the determining factor, as a rule, is the distance over which the video signal is to be transmitted.
Using a coaxial cable or Twisted pair is most effective when the distance the signal has to travel is short.
For medium distances, experienced installers prefer twisted pair.
For long distances, fiber optics are chosen.
This article will discuss ways to solve the problem of transmitting a video signal over distances of an average of 250 to 2000 m.
I can confidently say that the optimal solution for this problem is active receivers and transmitters over twisted pair.
The source of signal transmission in the system is usually a video camera. From it, the signal is transmitted to the receiving device (monitor, digital video recorder, etc.).
The transmitter converts the unipolar asymmetric composite video signal coming to its input into two symmetrical antiphase signals.
They are transmitted via a two-wire communication line, which experts call a twisted pair.
Transmitters and receivers used in such systems can be passive or active.
There are 3 main solutions for transmitting video signals over twisted pair cables:
passive-passive (video signal transmission distance up to 200–250 m), Fig. 1;
passive-active (250–1000 m), Fig. 2;
active-active (1000–2000 m), Fig. 3.
I would like to point out that we are talking about a high-quality color video signal. Distances may vary depending on the manufacturer.
It is necessary to take into account that when choosing a passive-active solution, the receiver will always be active, and the transmitter will be passive.
In a passive-passive solution, the receiver has the same characteristics as the transmitter, so they are often called transceivers.
Active devices are strictly divided into receiving and transmitting due to the peculiarities of their internal structure.
Thus, active receivers and transmitters are used as a conscious design solution for transmission over distances that are higher than the norms for coaxial cable.
Your attention is presented with an overview of equipment from several manufacturers.
I will tell you about the basic principles of operation of active transmitters over twisted pair and the benefits that their use promises to the installer and ultimately the user.
As the signal passes through the wire, its amplitude decreases.
Often, with a cable length of over 225 m, a passive transmitter can no longer provide normal signal quality.
Moreover, this is not a consequence of the influence of the balun transformer, but the influence of the cable.
To solve the problem, you need to use active receivers.
These devices amplify the signal, provide compensation for losses and can return the signal level to a swing of up to 1 V.
Some devices have a smoothly adjustable gain, which allows for accurate compensation at a distance of up to 1.6-2 km when using active transmitters on the camera side.
Receivers and transmitters can be found on the market that have a differential input to break the ground loop, thus providing immunity to ground loops.
Ensuring galvanic ground isolation is extremely important for long lines connecting equipment installed in different buildings or on a long perimeter.
So, the main advantages of using active receivers and transmitters over twisted pair.
The first advantage is noise immunity.
When cables are laid near a potential source of interference (low-voltage power cables, data or communication cables, etc.), transceivers balance the signal and provide noise immunity.
If we measure noise immunity by the common mode rejection ratio, then transceivers generally provide noise immunity at a level of 30 dB.
You can find technologies with a common mode rejection ratio of 60 dB in a wide range of video signal frequencies (from 15 kHz to 5 MHz)
The second advantage is the ability to use a relatively cheap unshielded twisted pair of large cross-section instead of a coaxial or fiber-optic cable.
Advantage three – the ability to use high-quality analog video cameras in video surveillance systems instead of more expensive IP cameras with low performance characteristics.
Advantage four – in the future, you can easily switch from this system to structured cabling systems and IP networks.
Advantage five – by choosing an automatic active receiver, the installer provides himself with significant time savings on commissioning and video signal settings.
Advantage number six – the use of some devices allows transmitting video and telemetry via one cable, eliminating the need to lay an additional cable, which sometimes provides very significant savings.
Advantage number seven – many manufacturers build lightning protection and protection against voltage surges into active receivers and transmitters.
Advantage eight — some active receivers with a high level of interference suppression and low radiation level allow the signal to be transmitted over long distances in the same cable bundle as telemetry, and low power supply voltage.
We are talking about active receivers with a built-in power hub.
The list of advantages of using active receivers and transmitters over twisted pair can be continued.
But let's better note the main ones once again: noise immunity, good price/quality ratio, ease of installation and availability of migration of the video surveillance system into the future.
NV-653T (NVT)
The NV-653T video signal transmitter is an active (with amplification) device that allows transmission of a video signal of black-and-white or color images over a distance of up to 1.6 km (1 mile) using a Category 5 cable in the form of unshielded twisted pairs.
The NV-653T's superior noise rejection and low radiated emissions allow video signals to be transmitted over the same wiring harness as telephone, data, or low voltage power. This allows for cable sharing or the use of existing cable equipment. Ground lift eliminates annoying «hum bars» when there is a potential difference in the ground circuit. Built-in protection circuitry eliminates the problem of dangerous voltage surges.
The transmitter has a three-position range switch, a blue power indicator LED, and a green active LED. Up to 10 NV-653T can be mounted in a hardware rack using a rack-mount panel kit.
GEC-1PVTC-F Single-Channel Passive Transceiver (IFS)
Single-channel passive twisted pair transceivers are multifunctional devices. These transceivers are capable of transmitting video signals at a distance of up to 228 m, and also exchanging signals with active receivers at a distance of up to 1.067 m. They support all major formats
video files, including NTSC, PAL and SECAM, as well as coaxial signals for video file transmission and bidirectional PTZ signals. Due to their compact size and lack of need for power, these transceivers are easy to install, and crosstalk of at least 60 dB and noise immunity allow the device to be used in conjunction with data, audio files and other low-voltage signals.
NV-1672 (NVT)
The NV-1672 is a 16-channel, amplified hub that delivers real-time monochrome or color video up to 1 mile (1.6 km) over Category 2 unshielded twisted pair cable. The hub and DigitalEQ™ receiver continuously and automatically compensate for cable attenuation, ground loops, and wire polarity independent of the video signal. The 1U hub has dual outputs per channel for high-density distribution amplifiers and features multi-stage transient protection. Video inputs are available with screw-type terminals or RJ45 connectors for unshielded twisted pair cable (NV-RJ45A). Compatible with certified video cameras for operation via unshielded twisted pair.
TW3000 (Pelco)
Video transmission systems over twisted pair, both active and passive, are widely represented in the Pelco product range. There are single-channel active transmitters and 1-, 4-, 16- and 32-channel receivers. Among them, the TW3000 series is the most popular.
The TW3001AT series transmitter is a compact device with dimensions of 5.7 x 7.6 x 2.8 cm, which allows it to be placed in outdoor casings. Temperature range from 0 to +75 degrees.
Active receivers are available in a 19-inch rack design. For ease of installation, there are special rack-mount baskets, special power supplies, fasteners, and other elements.
The «active transmitter — active receiver» combination allows you to achieve a transmission distance of up to 1524 m, «passive transmitter — active receiver» — 915 m, «passive transmitter — passive receiver» — only 230 m.
TTA111VH (SC&T)
The noise-protected active signal receiver is used in video signal transmission systems over long distances, provides high image quality by minimizing the introduced distortions. The video signal is transmitted via inexpensive and widely used Category 5 twisted pair cable.
The video signal transmission distance depends on the transmitter type: when working with a passive transmitter, the transmission range of a black and white signal will be 2400 m, and of a color signal — 1500 m; when working with an active transmitter, the transmission range will be 3000 m and 2400 m, respectively. If you use 3 series-connected pairs of passive transmitters (TTP111VT) and active receivers, the transmission range of a color video signal will be up to 3000 m.
The TTA111VH receiver has a built-in matching device, an interference filter, and a system for compensating for the graininess of the color signal at different frequencies.
Built-in lightning protection will protect the equipment from static electricity and lightning strikes.
VT-1500N/VRD («BIK-Inform»)
The equipment for transmitting a video signal is designed to transmit a full (color) video signal over a distance of up to 1800 m via symmetrical communication lines of the «twisted pair» type, which include cables of the TPPep, UTP brands, etc.
The set of transmission equipment consists of a transmitting (transmitter) and receiving devices (receiver), which are connected to a symmetrical communication line.
DIN rail mount. The bandwidth frequency range is from 50 Hz to 6.5 MHz. Nominal swing of the input full video signal on the load is 75 Ohm 1 V.
Maximum swing of the output symmetrical signal is ± 5 V. The receiver has line protection against overloads and induced voltages. Number of frequency corrector stages: at the transmitter — 3, at the receiver — 16. Stabilized DC supply voltage — 12 ± 1.2 V. Operating temperature — from minus 35 ° C to plus 50 ° C.