The cost of implementing a fiber optic network has dropped significantly over the past few years, so that revealing comparisons with other transmission lines such as twisted pair and coaxial cable systems are finally possible splicing fiber optic cable.
As long as cameras and monitors are not equipped with both coaxial connectors and optical 'ST' connectors, fiber optic lines will always suffer from additional costs associated with the cost of external components of the path. This is especially true for short-haul communication lines, where the cost of additional switching equipment is a significant proportion of the total. However, for lines longer than a few hundred meters, fiber optic systems are becoming increasingly attractive because the cost of coaxial cabling does not increase in direct proportion - either because of the need to use higher quality cables, or because of route amplifiers, or both.
Thus, there is always a line length, most likely between 500 and 1000 m, above which the use of closed-loop TV systems with fiber-optic communication lines is justified from only one point of view of costs. If the average line length is significantly less, and the minimum cost of the transmission path is your only criterion for choosing a physical transmission medium, then the use of fiber-optic lines is unlikely. On the other hand, if other factors are important, such as image quality, lack of interference and pickup, significantly less problems with drift, then why not consider using optical fiber in your system? You might be pleasantly surprised.
Optical Loss Budget
It may seem odd that the optical loss budget is calculated at such a late stage in the development process, but in fact, it can only be calculated with any accuracy after the cabling infrastructure is fully defined. The purpose of the calculation is to determine the loss for the worst-case signal path (usually the longest) and to ensure that the equipment chosen for the transmission path with a reasonable margin fits within the obtained limits.
The calculation is quite simple and consists in the usual summation of the losses in decibels of all components of the path, including the attenuation in the cable (dB / km x length in km) plus both connectors and the joint loss. The biggest challenge is simply extracting the required loss figures from the manufacturer's documentation.
Depending on the result obtained, the equipment selected for the transmission path may need to be reevaluated to ensure acceptable losses. For example, it may be necessary to order equipment with improved optical parameters, and if such equipment is not available, consideration should be given to switching to a transparency window with a longer wavelength, where the losses are less.
System testing and commissioning
Most fiber optic installers provide optical test results for a commissioning fiber optic network. As a minimum, they should include the end-to-end optical power transmission measurements for each fiber optic link - this is equivalent to a continuity check for a conventional copper network with electrical signal multiplexers. These results are reported as line loss in dB and can be directly compared with the technical data for the equipment selected for the transmission path. It is generally considered normal to have a minimum 3 dB loss margin (hardware promised minus measured value) of 3 dB for the inevitable aging processes occurring in fiber lines, especially in transmitters.
Many installers also provide OTDR (Time Domain Reflectometry) test curves - best thought of as a graphical record of the attenuation in each fiber - that can be saved for later comparison and analysis. Measurement graphs give OTDR invaluable information, however, nevertheless, they can only be an addition to measurements on end-to-end transmission of optical power, but not a replacement for the latter. This is due to the fact that the information obtained during reflexometric measurements is too complex for non-specialists to understand, has limited accuracy and is prone to distortion due to various defects in the fiber.
Under normal circumstances, only a minimal set of system acceptance procedures is required to verify that the receivers in the system are providing AGC, thereby eliminating any need for manual gain adjustments.
No comments:
Post a Comment