Plant Maintenance

Introduction

As part of the Liberty Latin America group of companies, Cable & Wireless is one of the leading telecommunications and entertainment providers in the Caribbean and Latin America. Operating in the region since the 1870s, C&W offers unparalleled connectivity and a wide range of data, voice, and video services, all underpinned by over 50,000 kilometers of the most modern subsea and terrestrial fiber networks in this part of the world. FLOW is the brand that umbrellas all the services provided by C&W Communications. All technicians and employees are representatives of the Company, as such, you will be expected to contribute your talents and energies to improve the environment and quality of the Company’s products and services. This manual was created in an effort to provide customers with the highest quality products and services via highly motivated, skilled and customer-oriented staff.

Practices and procedures mentioned in this booklet are guidelines (but not limited) to assist the individual with established CATV hybrid technical engineering standards, good workmanship, and professional customer relations.

1. Safety Precautions

Technicians must observe and enforce safety practices for the protection of themselves, the public and the employees of utilities occupying the poles. Precautions include, but are not limited to, the following:

• Vehicles parked in lanes, streets or other right-of-way shall be protected with safety cones.

• Scraps of wire or cable, miscellaneous materials, empty reels, and containers shall be gathered and disposed of in an appropriate manner.

• Tools and equipment shall not be unattended while suspended from strand or poles.

• Technicians shall wear approved hard hats and assigned safety equipment, at all times.

• Ladders equipped with strand hooks and/or pole straps will be used to make attachments to poles or strand.

• All Technicians shall be supplied with a pole belt; These must be used when any work is being done on, or above 3m. The belt will be affixed to the strand, through the ladder rung or when on a tower, through and around a tower support member and attached to the installer during this time.

• Electrical hazards exist at the pole and technicians must exercise extreme caution when working in these environments.

  •  Please note when working close to overhead powerlines the minimum distance from LV is 3 feet and HV 10 feet.

• In addition, the Columbus Communications Safety Guide should be referenced.

2. HFC Network

FLOW services operate on a HFC (Hybrid fiber coaxial) network. HFC is a telecommunications industry term for a broadband network that combines optical fiber and coaxial cable. It has been commonly employed globally by cable television operators since the early 1990s. In a hybrid fiber-coaxial cable system, the television channels are sent from the cable system's distribution facility, the headend, to local communities through optical fiber subscriber lines. At the local community, a box called an optical node translates the signal from a light beam to radio frequency (RF) and sends it over coaxial cable lines for distribution to subscriber residences. The fiberoptic trunk lines provide adequate bandwidth to allow future expansion and new bandwidth-intensive services such as internet access. The HFC network can be categorized into three main segments as depicted in figure 1 below:

An HFC network may carry a variety of services, including analog TV, digital TV (SDTV or HDTV), video on demand, telephony, and internet traffic. Services on these systems are carried on RF signals in the 5 MHz to 1000 MHz frequency band. The HFC network is typically operated bi-directionally:

• The forward-path or downstream signals carry information from the headend/hub office to the home, such as video content, voice, and Internet traffic.

• The return-path or upstream signals carry information from the home to the headend/hub office, such as control signals to order a movie or internet upstream traffic.

This document would be mainly focused on the maintenance aspects of the distribution network.

3. Tools and Materials

Having worked with your tools and materials for some time, safety and efficiency should become second nature. Proper storage of equipment is of the utmost importance since these can be damaged easily and be of no use. Technicians should also keep tools and materials in a safe place to ensure they are not misplaced and minimize the chances of theft. The following is a table that includes a list of tools that is required by maintenance technicians to carry out their duties:

4. Coaxial Cable Electrical Characteristics

4.1. Attenuation

One of the greatest contributors to cable signal loss is the coax itself. On our digital system no Amplifiers are used, so signal loss is a major concern. Attention should be paid to the type of cable used and the distance of the cable used to maintain sufficient signal levels throughout the system. Attenuation can be calculated for all plant components, and it is expressed in units of decibels or dBmV. The five major contributors to attenuation are as follows:

➢ Frequency: The higher the frequency the greater the signal loss in dBmV.

• Attenuation at 55 MHZ is 0.44 dBmV per 100ft on Series 540 cable.

• Attenuation at 865 MHz is 1.98 dBmV per 100ft on Series 540 cable.

➢ Size of cable: The longer the length of the cable based on its size will determine its loss in dBmV.

➢ Temperature: The hotter the temperature, higher the resistance, the greater the lost in dBmV level.

➢ Insertion loss: Loss incurred due to any addition of passive devices added to cable.

➢ Dielectric material: The type of material used for the dielectric could cause a percentage of attenuation or form some resistance to RF transmission.

• Plastic poses the highest resistance in dielectric materials.

• Foam poses a lesser resistant to RF transmission.

• Air poses little or no resistance to RF transmission.

Note: Foam dielectric is the material used in our cable and is most found in cable companies throughout the world.

4.2. Signal loss Calculation

All coaxial cable is subject to cable loss over distance. Below are typical examples of signal loss that occurs over 100 feet of coaxial cable.

5. Operating Frequencies

The forward-path and the return-path are carried over the same coaxial cable in both directions between the optical node and the home. To prevent interference of signals, the frequency band is divided into two sections: 108–1000 MHz for forward-path signals, and 5–85 MHz for return-path signals. The different downstream services offered by FLOW are segmented across the frequency spectrum, as seen below:

5.1. BER

One of the most important ways to determine the quality of a digital transmission system is to measure its Bit Error Ratio (BER). The BER is calculated by comparing the transmitted sequence of bits to the received bits and counting the number of errors. The ratio of how many bits received in error over the number of total bits received is the BER. A bit error ratio of 10-9 is often considered the minimum acceptable BER for telecommunication applications. A BER of 10-9 means that 1 bit out of every 1,000,000,000 bit is, on average, read incorrectly ({1.0e-9 or 1E-9} -> represented in this format on most signal meters).

5.2. MER

MER stands for Modulation Error Ratio. It is a measure used to quantify the performance of a digital TV transmitter or receiver in a communications system using digital modulation. Acceptable operational MER levels should be above 35dB on the FLOW network. Once MER drops down to 28 dB and below, data transmission can be lost, thus delivering poor quality service.

5.3. Signal Parameters

The following table represents the operating frequencies and signal parameters for each service:

5.4. Node Set-up Parameters

Table 4 identifies the signal levels that should be present at the node for optimal service distribution throughout the network:

6. Node setup

6.1. Forward Setup Procedure

➢ Using a digital multi-meter check that the node is receiving the necessary AC voltage (44 to 95 VRMS @ 47–70 Hz)

➢ Using a light power meter measure the optical power to the Node Receiver (0 dBm +/-4dBm).

➢ Using a RF signal meter measure and set the output RF power of the Node Receiver to (28dBmV) using the appropriate plug-in module (pad).

➢ At the node output ports set the RF power levels at 37dBmV@CH 15 and 50dBmV@CH 123 respectively using the appropriate plug-in module.

6.2. Return Set-up Procedure

➢ On the optical node’s node tray (node board) insert a 6dB plug-in module at the return input.

➢ Using a Signal generator, inject 10dBmV into the node Return input via the test port @32Mhz. Please note that the node test port is -20dB and the injected signal level should be 30dBmV to achieve 10dBmV at the input port.

➢ A Headend Technician must verify receipt of the injected levels from the node and adjust the return signal accordingly. Optimal return signal measured at the node’s test ports should be 30dBmV.

➢ The signal must be injected at all four test ports on the node and verified by the Headend Technician.

7. Distribution Network Components

The following table lists some of the components that can be found on the RF distribution network in Trinidad.

RF Network Components

8. Node Components

As mentioned before, the node receives the optical light signal from the headend and translates it to radio frequency (RF) and sends it over coaxial cable lines for distribution to subscriber residences. It consists of several components that work in coherence to achieve this task. The following table is a synopsis of these components.