Status Report: Leakage Detection

Cable system RF signal leakage sounds like an old hat, ho-hum subject, but back in the 1980s there was the possibility that the regulators could break instead of make cable. (See sidebar.)

In the following decades, operators learned to deal with what some have labeled the burden of compliance with federal leakage detection rules. But as time has progressed and advanced services have come into play, the story has changed from one of grudging adherence to self-motivation.

"Systems (today) are doing fairly well in terms of leakage control, not just because they want to control leakage, but (also) because they want to protect digital services," said Jonathan Kramer, principal attorney of Kramer Telecom Law Firm. He called leakage, a.k.a. egress, the "ugly cousin" to ingress.

"A correlation has been noted between where signals leak out of a system and where offending signals can leak into a system," said Jim Harris, vice president of marketing for Trilithic’s instruments division. "A system that doesn’t leak has far less ingress. Return signals are fragile. They are all associated with revenue-generating services. They are more susceptible to interference, so you want to keep ingress low."

The FCC mandates a leakage limit of 20 microvolts per meter (µV/m) (see sidebar); David Haigh, lead engineer for Midcontinent Communications, said his company’s limit is 5 µV/m.

"In the past, with cable modems if you lost a few packets, it didn’t matter, but with EMTAs (embedded multimedia terminal adapters), it’s crucial that you keep telephony up and running," said Haigh. "Any ingress will cause dropped packets and broken voice quality."

Gone, therefore, is the "outrageous" leakage of the past, said Ron Hranac, technical leader, broadband network engineering, for Cisco Systems and CT senior technology editor. "If you or I were to drive around with a leakage detector in a rental car today, the odds are we would find very little signal leakage," said Hranac.
Equipment evolutions Much like the motivation for leakage detection has evolved, so too has the technology. The first leakage detection solutions were time consuming and manpower intensive.

"We had to have one technician or many technicians use a portable receiver," said Daniel Babeux, vice president business development broadband networks, VGI Solutions. "They had to make sure they drove out all the streets, and when they did encounter a leak, they made sure they peaked the leak by driving slowly and estimat(ing) the distance at which the leak (was) located."

The biggest technological change in the ensuing years has been the addition of global positioning system (GPS) technology to the equation. It can correlate signal leakage data to a street map.

"With the satellite views that we have nowadays, you can look at not just a graphic depiction of a map with lines or streets, but you can (also) see the houses and the backyard easements," said Ken Eckenroth, vice president of technology for Cable Leakage Technologies.

Moving map technology is another advancement.

"As (the driver) rides the neighborhood, the streets are highlighted as they are ridden," Eckenroth said. "Also, he has at his disposal what areas of town have already been ridden out that quarter. This previously was done with a highlighter manually drawn on a paper map."

The data collected by the GPS unit can be uploaded via Wi-Fi hotspots when the trucks return to the yard and deciphered to determine the location and strength of leaks.

"This is a good development," said Michael McDonald, vice president of technical operations for the North Texas Division of Time Warner Cable. "Even though you direct all employees to gauge leakage, you can’t guarantee they are always doing it."

Some vendors have begun offering cellular systems, said Andy Parrott, corporate vice president of technical operations for Suddenlink Communications. "(There are) truck-mounted GPS units that use cellular service to immediately dial up and call back to the main terminal and dispatch out or print work orders on a real time basis." Covering all bases There are two leakage detection methodologies: the shotgun approach and the rifle approach. In the shotgun approach, equipment is placed in all trucks, and detection occurs during the normal course of business. In the rifle approach, dedicated leakage detection personnel drive out the system quarterly. While shotgun is perhaps more timely, rifle is more methodical.

"The two methods complement each other. The best solution would be to have a hybrid of both," Eckenroth said.

To meet the annual cumulative leakage index (CLI) requirement (see sidebar), the choice is between a flyover or ground-based approach. Operators have personal preferences. Some feel sticking to the ground is more accurate.

"You are riding out the actual plant and comparing leaks found only on the plant," said Jerry Knights, vice president of engineering, network and infrastructure, for Insight Communications.

For Suddenlink, it’s also a matter of cost. "As (technicians) do their daily routes, they can drive most of the system out vs. the cost of hiring an aerial crew to go out and do a flyover," Parrott said.

Midcontinent uses flyovers for the CLI, but perhaps more interestingly eschews GPS in its overall leakage detection program. The company uses the shotgun approach, but the leakage detection meters are not GPS-based. The company wants technicians to be alerted to the leak immediately and to stop and fix it if possible, Haigh said.

"(You have to) trust the technicians to do their job right," he said. "(You’ve) got to put some sort of trust in these guys."

Monta Monaco Hernon is a contributor to Communications Technology. Reach her at [email protected]. Sidebar: Once Contentious Rules Haven’t Changed Much While not the hottest of topics today, in the 1980s, leakage occupied the minds of the cable industry, the FCC and the Federal Aviation Administration given that cable occupied some of the same frequencies (108-137 MHz and 225-400 MHz) as over-the-air users, including air traffic controllers.

The regulators were concerned about a connection between cable system leakage and interference with aircraft navigation and communications. There was even talk of forcing the cable industry to abandon the shared spectrum.

"That would have frozen cable forever in place with something around 18 channels," said industry veteran Ted Hartson, principal, Scottsdale Television Labs. "That would have been a death sentence for cable …. We fought long and hard and finally got a series of concessions, which resulted in the now current standards."

In the March 2007 issue of CT, Ken Eckenroth, vice president of technology for Cable Leakage Technologies, deftly summarized the resultant FCC leakage detection rules.

"Since 1985, cable operators must completely drive out their plant four times a year, logging all leaks 20 µV/m and above," he wrote. "Since 1990, we must conduct a drive-out of at least 75 percent of the plant and file a CLI report to the FCC showing all leaks 50 µV/m and above, indicating which leaks are repaired and their locations. As an alternative to the annual rideout, a flyover of the plant is permitted."

The meat of these rules hasn’t changed, but operators can now file Form 320 electronically.