Airspace Measurement Of CATV System CLI (1986)

By Leslie W. Read, Field Service Engineer, Sammons Communications, Inc.

This paper discusses the signal leakage measurements made in the airspace above Dallas and Fort Worth, Texas to determine cable system Cumulative leakage Index (Cll).

Discussed is the monitoring equipment used, the pre-flight and in-flight calibration tests, and the outfitting of the aircraft used in the flyover.

Cable systems with shielded and unshielded cable fittings, as well as new (quad shield) and old (60\ braid), were included in the measurements. The systems with the best procedure to prevent leakage also had the most aggressive monitoring program and, as expected, had little problem complying. The systems with fewer precautions to prevent leakage had a more casual monitoring program and, judging by ground measurements, had more severe leaks.

The measurements were made at an altitude of 450 meters (1,476 feet) above average terrain and at Channel C carrier frequency. The purpose was to determine the compliance with anticipated FCC requirements for 10 uv/meter maximum leakage.

The first test (April, 1985) indicated that the best system had 2 uv/meter in the airspace, an intermediate system, i.e., shielded cable fittings, a monitoring program, but with some old house drops --- had approximately 4 to 8 uv/meter and a worst case system had higher than 20 uv/meter. The test in December showed house wiring to be less of a factor than originally thought, with 3 uv/meter being a typical value for a good system, even those with some older drops.

It is concluded that a system with shielded fittings and an aggressive ground leakage monitoring program would easily comply with the future FCC requirements of 10 uv/meter at 450 meters above the cable system being tested.

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