A new technique to combat upstream noise, developed by
ComSonics Inc., was the buzz of the Society of Cable Telecommunications Engineers'
recent Cable-Tec Expo, with several cable engineers putting it into the "why
didn't we think of this before?" category.
Called the "Ingressor," the test system is a new
part of ComSonics' "CyberTek" system, said Dick Shimp, technical-support
manager for the manufacturer.
The system combines a transmitter, a headend receiver, a
vehicle-mounted global-positioning-satellite receiver, computer mapping software and a
leakage detector. When combined, the system "sniffs" plant for upstream-path
leaks, then zips the information back to the headend, inserts it on the cable plant and
lets operators quickly locate and correct "ingress."
Ingress, loosely defined, is a bothersome problem that
strikes when signals leak into the cable plant. It is particularly problematic for
upstream communications, because the noise gets amplified, then funneled upstream with
other valid information.
"In the past, nobody cared all that much about
ingress. But now, with two-way communications, it's fast becoming one of those things
that is critical to resolve," said Jeff Krauss, a telecommunications consultant who
helped to design the ComSonics Ingressor.
Signal egress -- when cable signals leak out of cracked
cable -- became a large industry concern in the late 1980s, when the Federal
Communications Commission mandated regular "cumulative leakage index" reports
from operators. The idea was to protect passing aircraft from inadvertently receiving
leaked cable signals, which could deleteriously affect air communications.
"How this works is that operators measure signal
leakage, mix any leaks with the GPS location information and put it into a data stream at
around 27 megahertz," Shimp explained. "They emit that into the [plant], and
then, if they're driving past and pick up a shielding flaw, some of that signal
emitted will be absorbed into the cable, so it'll follow the active upstream path to
its terminal point."
That's usually at the headend, where a receiver breaks
the information into parts -- the positioning, leakage and transmitted power -- and the
parts are placed on a map so that technicians can readily find problems and fix them.
And that's exactly what ComSonics did at the Cable-Tec
Expo in Denver -- it outfitted a Tele-Communications Inc. metro headend with the
equipment, and it mapped leakage information for display in its booth.
Notably, TCI's system "appeared pretty
clean," Shimp said.
The Ingressor is not yet commercially available, and Shimp
said it was premature to discuss pricing. The manufacturer is looking at making it widely
available by the first quarter of next year.
