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Digital Narrow Band Radio for Electric Cooperatives


Sequachee Valley Electric Goes Digital

The Country’s First Digital Narrow-Band Radio Communications System in an Electric Co-op

Sequachee Valley Electric Cooperative is a 28,000-member co-op at the foothills of the Smokey Mountains in Tennessee. Its main office is in South Pittsburg, about 25 miles west of Chattanooga, close to the Alabama border.  With an average of 11 members per mile and 2,400 miles of power lines, and only 72 employees to cover its 4-county territory, responding to power outages is a real challenge.

Meeting this challenge demands a coordinated effort between members, the office, and the service technicians.  Because the Co-op must respond quickly to restoring and maintaining safe power services, a reliable radio communications system is crucial.  In the early 1990s the Co-op found that their low-band simplex radio system just wasn’t reliable anymore, and so the Co-op turned to an outside consultant for help in upgrading their communications systems.

In early 1993, the Co-op contracted with Spectrum Resources, Inc. (SRI), a communications consulting firm located in St. Charles, Missouri.  Jay Underdown, President of SRI, met with the managers at the Co-op to evaluate their communications needs.  Managers from all four offices of the Co-op – the main office in South Pittsburg, plus the district offices in Pikeville, Dunlap, and Tracy City – were involved in the meetings to assess their current needs and plan for future ones.  In June 1993 SRI prepared  an integrated telecommunications plan that includes SCADA, telephone upgrades, and fixed and mobile data communications.  The first phase of this plan was the implementation of a very-high-frequency (VHF) digital radio system.

Why choose a digital radio system?

Implementing a digital radio system was a bold undertaking for this medium-sized electric co-op.  No other co-op had done something this cutting-edge, so it was very much uncharted territory.  They couldn’t raise members’ rates, and thus had to contain costs carefully.  They also needed to move fairly quickly because the old equipment was not reliable, nor were replacement parts easily available.  In selecting a radio communications system, they were impressed with the many advantages of a digital radio system.

System design
SRI suggested a digital system based on impending changes at the Federal Communications Commission (FCC).  The FCC’s Refarming Report and Order and Further Notice of Proposed Rule Making (PR Docket # 92-235) was published in June 1995.  One of the purposes of the Refarming Report was to make more channels available in the VHF range.  The FCC did this by making the VHF channels half as wide as those that were in use (and thus doubling the availability); this is called narrow band operations.  The way in which the digital system modulates a signal is a definite advantage in narrow band operations, and thus digital radio systems are expected to become the standard in the next few years.

The new radio system makes more frequencies available to the Co-op.  With the old low-band simplex system, all four districts operated on the same frequency.  “If a storm came through and all four districts had a power outage at once, then all four district managers would be on the same frequency, talking to at least four different mobile units, trying to manage the situation.  It was difficult to make sure the right person got the right message,” notes Danny Kirkendoll, Director of Engineering at the Co-op.  Now, the South Pittsburg and the Tracy City district offices each have a dedicated repeater.  The Dunlap and Pikeville offices share a repeater.  However, all mobile units can access any repeater when necessary.  “This has helped us tremendously in managing situations better with less stress,” says Kirkendoll.  “We can communicate more clearly with the service technicians, which helps us reduce the time our members are without electricity.  This, of course, makes it safer not only for our technicians, but also for our members.”

Furthermore, moving to a VHF radio system meant that the Co-op could improve their coverage area. The low-band frequency they had been using is very susceptible to man-made forms of noise, such as vehicle ignition systems, power lines, and noise generated from electric motors and neon signs.  The new repeaters (see below), combined with the greater transmission capability of the VHF repeater signal, means that now they can communicate where they couldn’t do so before.   “We’re very pleased with the coverage we’re getting now,”  reports Bob Pickering, General Manager of the Co-op.

Many people in this rural area have radio scanners to listen into police, ambulance, and other radio communications.  However, these scanners cannot receive the Co-op’s digital signal, and thus other people cannot listen in to Co-op radio communications.  “This is a great security feature,” says Kirkendoll, smiling.  “It gives our technicians more privacy in carrying out the repairs.  Plus, sometimes we have to communicate information about the members in order to make the repair.  With our digital system, other people can’t listen in, which also gives our members greater security.”

Quality of communications
“With digital radio, either the signal is picked up completely, or it’s not picked up at all,” explains Underdown.  “The only distortion happens when the signal isn’t strong enough; in this case you hear a ‘warble’ just as the signal fades, then the receiver squelches.”  Given the size and the rocky terrain of the territory they cover, the Co-op’s service technicians were used to hearing static when they were out of range of the old stations.  “With the digital system, there’s no static whatsoever,” says Kirkendoll.  In fact, this has been one of the biggest changes that the service technicians have noticed.

“We don’t have to strain to make out words in a message,” notes Kirkendoll.  “Now if a technician is not picking up the signal, he or she will move to a location where the signal is obviously clear.”  And their new equipment and repeater locations have significantly expanded the coverage area, so that there are now fewer areas where signals cannot be received.  Again, the ability to communicate clearly increases safety not only for the service technicians, but also for the members.

Voice and data transmissions
A digital system enables its users to mix voice and data.  This capability has many advantages for future upgrades.  For example, putting mobile data computers in the service trucks would give the technicians remote access to the main database.  This would enable technicians to double-check addresses, quickly retrieve information about past problems at a customer’s site, check pertinent customer data, and other advantages.  One of the Co-op’s goals is to build upon the recommendations of SRI and ultimately create a SCADA system.  “We wanted a good foundation for our future plans,” explains Tim Sallee, District Manager of the South Pittsburg office.  “The digital backbone will give us more flexibility in implementing other improvements.”

Another welcome aspect of the digital system is that, anytime a mobile or a base unit keys up, that unit number is displayed on everyone else’s units for quick identification.  And if a technician isn’t nearby the service vehicle when an emergency call comes in, then the office can signal the mobile units to turn on a hazard light or even honk the vehicle’s horn to get attention.  Furthermore, each district has portable radio units that can also be signaled to beep by the base units.  These portables are used by contractors, by employees walking the right-of-way, and by on-call supervisors, who can take the hand-held unit home and monitor situations in the evening.   “This type of signaling is not a unique feature of digital radio,” notes Underdown, “but it is a feature that is built into the digital system, and therefore it doesn’t cost anything extra.”

Equipment and training needs for the digital system

SRI’s plan called for three new digital VHF repeaters.  A new 240-foot tower at Suck Creek primarily serves the Marion County District.  This tower can ultimately be expanded to 380 feet for mounting microwave dishes.   A second, new 220-foot tower is located at Hobbs Hill, and primarily covers the area around Tracy City.  The Co-op also leases space on a commercial 280-foot tower northwest of Pikeville; this third repeater covers primarily the Pikeville and Dunlap areas.

All four district offices have a base control station, remote control consoles in the offices, mobile units in service vehicles, and a few portable radios.  Additionally, there is a second control base at the South Pittsburg office that gives general supervisory access to all three repeater stations.  The remotes look like telephones, and the voice analog signal is converted to a digital signal through a control panel bridge to the radio control base.

The radio equipment was selected from Motorola’s Astro product line, and the towers were manufactured by Pi-Rod.  The buildings at the antenna sites were manufactured by Fiber-Bond per SRI’s specifications to suit the Co-op’s needs (places to store materials and so forth).

The new state-of-the-art equipment is music to an engineer’s ears.  “So far with the new equipment I haven’t had any problems,” says Kirkendoll.  “With the old equipment, I was having problems every week.”  In particular, one of the old low-band stations was a magnet for lightning, being struck 2 or 3 times a year.  “SRI built in a tremendous amount of lightning protection at the towers,” notes Kirkendoll.  “I don’t think we’ll have any more problems with lightning now.”

Training has not been a problem either.  “The system is very easy to use,” says Sallee.  “We only spent an afternoon on training, and we all quickly learned what we need to know to operate the system.  The most difficult thing we’ve had to do is get used to the digital quality of the signal.  The voice quality takes some getting used to.”

The upgrade in the communications system, and ultimately in service to the members, has not cost the members anything.  “We haven’t had to raise the rates,” says Kirkendoll, “because Bob Pickering has very carefully managed our monies.”  The Co-op’s digital system went on the air in November 1996, and its implementation and functioning have been very satisfactory. Based on the Co-op’s experiences, their boldness in implementing the country’s first narrow-band radio systems in an electric co-op is indeed a sound investment for the future.

Motorola and Astro are trademarks of Motorola, Inc.

Pi-Rod is a trademark of Pi-Rod Corp.

Fiber-Bond is a trademark of Fiber-Bond Corp.