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FREQUENTLY ASKED QUESTIONS about Twisted Pair Video Transmission Systems. The following questions and answers cover many of the topics that address the design, use and installation of the V-Link systems. If your question is not covered in this area, check the Tech Support Section or Contact NITEK Tech Support. |
UTP is "Unshielded Twisted Pair" wire or cable; also called "paired" cable. This is the type of cable that works best with the NITEK Twisted Pair Video Transmission Systems. Cable that is termed "multi-conductor" is not usually "paired" and must be avoided. Always verify that the cable is Unshielded Twisted Pair (paired) cable.
The NITEK Twisted Pair Video Transmission Systems operate well over Unshielded Twisted Pair wire gages from 12AWG through 26AWG. The systems are optimized for 24AWG and distance specifications given are for 24AWG.
It is recommended that use of individually shielded pairs be avoided. The higher electrical capacitance of individually shielded pairs causes the operating range of the system to be drastically reduced. Multiple pair cable with an overall shield is acceptable.
Either solid or stranded wire may be used. The results are identical.
Category 2 through Category 5 cable is recommended. Other types of cable may work in situations where alternatives are limited. Call NITEK Tech Support for more information about specific applications.
Loop Resistance is the total electrical resistance, in Ohms, of both wires in a pair (the "loop"). The measurement is made by shorting the wires together at one end and measuring the resistance at the opposite end.
The NITEK systems utilize a "balanced output" design. Sending the video signal into a twisted pair provides an effective method of canceling extraneous noise and interference. Un-twisted pairs are not recommended, since the system becomes very much susceptible to interference, which will be exhibited in a degradation of the video display, whenever extraneous signals are present.
The wires can be spliced or connected by means of punch-down telephone connector blocks, as long as a solid (zero ohms) connection is made and if a punch down block is used, no MOV lightning protectors are connected to the circuit.
9. What are MOV lightning protectors and why are they a problem?
MOV devices are surge protectors commonly used by local telephone companies to protect from voltage surges on the lines. The problem with this type of protection is that the inherent high electrical capacitance causes attenuation of the video frequencies.
10. Is there any type of surge protection that can be used with the NITEK systems?
The NITEK Twisted Sender product line has built-in surge protection. Where additional protection is desired, there are types of non-capacitive lightning protection that can be used with the NITEK twisted pair systems. Contact Tech Support to discuss your requirements and request a list of recommended devices. Be advised that any surge suppression will provide only limited protection from lightning and that the built-in protection provided by NITEK is designed to protect only the Twisted Sender systems.
11. What are T-Taps or Bridge Taps and why are they a problem?
T-Taps, also called Bridge Taps are ancillary pairs of wires connected in parallel to the main pair being used. They are unused pairs, usually found on telecommunication circuits connected at a punch-down block or pedestal and are from previous extensions or lines that have been disconnected. In audio circuits they do not pose a problem. but in video circuits they cause reflections that appear as "ghosts" in the display. It is usually possible to tell how many T-Taps there are by the number of reflections in the display. Their existence is usually denied by telecom personnel.
12. Can twisted pair video signals share a common cable with other signals?
Twisted pair video signals can be run in a common multi-twisted pair cable, such as a telecommunication or CAT5 cable, with other video, data and control signals. The only caution in this regard is that the video signals all be run in the same direction; i.e. all transmitters on the same end.
13. How many video signals can be run in a common cable?
There is actually no limit as to the number of video signals that can be run in a common unshielded twisted pair cable.
14. Can video signals be run in opposing directions in a common cable?
Video signals should not be run in opposing directions in a common twisted pair cable; that is, with transmitters and receivers on the same end of a cable. When signals are run in opposing directions, cross-talk problems may be encountered. Before bidding a requirement for operation in opposing directions, check with NITEK Tech Support.
15. Can twisted pair video signals be run near primary power lines?
Where allowed by Local Electrical Code, twisted pair video signals can be run in close proximity to primary power lines, due to the built-in common mode rejection of interference and noise in the NITEK systems.
16. Can video signals be multiplexed over a single twisted pair?
Video signals can be multiplexed over a twisted pair the same as coax. With twisted pair transmission, however they can be extended for long distances.
17. Can transmission distance be increased if two cable pairs are paralleled?
Paralleling pairs in a cable, while decreasing the loop resistance, increases the cable electrical capacitance, so the advantage is negligible. Also, by separating the pairs the advantages of twisted pair for noise immunity are lost. This approach is not recommended.
18. Can the video signal be repeated to extend operating range?
The video signal can be repeated using a NITEK system with an active transmitter and receiver; viz. TS1000. Contact NITEK Tech Support for details regarding distance requirements and recommended design criteria for using repeaters.
19. What are the DIP switches on the NITEK active transmitters and receivers used for?
The DIP switch adjustments, unique to the NITEK Product Line are provided on all of the active transmitters and receivers. This is the only effective method of providing true video signal compensation, equalization and amplification, for the wide range of operation that is required.
20. How can pan/tilt/zoom control be done with a NITEK UTP video system?
For "up-the-coax" systems in applications under 1,000 feet, the VB37M or F Video Balun Transceiver can be used to provide video and control over a single twisted pair. For longer distances the best approach is to provide control over a second twisted pair using RS422 control.
