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January 2001 Issue

Certification: Technical Foundations for BST Certification

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Continuing with our coverage of the Society of Cable Telecommunications Engineers’ Broadband Service Technician (BST) Certification Program, this month we examine the portion of the certification exam that tests your technical foundation level.

Technical foundation is the knowledge that a cable technician needs in order to work on systems from the subscriber terminals to bridging amplifiers. This knowledge includes both forward and reverse cable plant within an average neighborhood.

First, a BST needs a working knowledge of Ohm’s law as it applies to system powering to calculate voltage losses. Voltage is equal to current multiplied by resistance. Technicians should also know how to calculate the voltage available at any point in a system; understand coaxial cable characteristics such as direct current (DC) loop resistance, RF losses and impedance; know the effects of impedance mismatches and be able to calculate RF levels at any point in a system.

Technicians also need to have a solid understanding of carrier-to-noise (C/N) ratio, its calculations and the effects of poor C/N ratio on pictures.

They also should be aware of intermodulation problems, such as composite triple beats (CTBs) and composite second order (CSO) beats. They need to both be able to understand their effects on a picture, and also be able to calculate picture impairments.

In addition to the above requirements, a BST must possess a basic knowledge of the decibel and its use, including the dB and its various references, with a strong emphasis on dBmV. A good service technician should be familiar with signal leakage, its rules, methods of detection, calculations and fixes. The Federal Communications Commission has imposed stringent rules on the industry pertaining to signal leakage and semi-annual proof-of-performance tests. A service technician should have a strong knowledge of the rules governing these tests.

Examples include having an amplifier operate with an input of 10 dBmV, with a noise figure of 8 dB. What would the expected C/N ratio be at this amplifier? If given an output level of 32 dBmV and a gain of 22 dB at this same amplifier, what would the C/N be then, and what would it be with 10 of the same type amplifiers in cascade? If this amplifier, when operated according to the manufacturer’s specifications pertaining to number of channels, levels and so on, with a CTB of 90 dB were cascaded 10 amplifiers, what is the total CTB that exists after these 10 amplifiers?

We have discussed only a small part of technical foundation, but have endeavored to provide a look at what you might be expected to know, as well as to give you a place to start.

SCTE now offers the training manual, Foundations for Delivering Quality Broadband Services, which may be helpful, as could the series of BST manuals. Training could pay huge dividends in making your job easier and making you more efficient. You, your employer and your customers will appreciate that.

Gary L. Selwitz is the director of certification for the Society of Cable Telecommunications Engineers. He may be reached at .

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