Rutherford County Emergency Communications District

Mobile Communications Unit

In 1993, RCECD activated the first Mobile 9-1-1 center in the United States.  This unit provides a complete back-up system for any of our five PSAP sites across the county.   This unit has been used to assist departments while doing routine maintenance and is ready at anytime to take the place of a PSAP in the event of a major on site equipment failure or other emergency.

In the Spring of 1998 upgrading and remodeling  work was completed to the dispatch console inside the unit.  The existing computers were upgraded with MMX chips and 64 MB RAM.  A third computer was added to support an additional dispatch station, now enabling three telecommunicators to dispatch from the trailer.   All three computers are networked with the capability of sharing drives and files.   This allows for additional backup and accessibility to resources for each of the dispatch positions.  Positron TDD keyboards were added, freeing up additional console space. 

(The following article was originally published in the April 1994 APCO Bulletin.   Reprinted with permission.)

"9-1-1 Is Too Important to Fail"

9-1-1 is too important to fail.  This is a sentiment shared by all of us in the 9-1-1 service, but we also know that no system is fail-safe.  Bearing this in mind it is still advantageous to look through your 9-1-1 system and try to plan for as many contingencies as possible.

Our 9-1-1 District is comprised of four primary and one secondary PSAP's.  We have taken the normal precautions such as prearranged default re-routing of trunks, uninterruptible power supplies on critical components, surge and spike protection, closely scrutinized grounding of all the system components, as well as each facility equipped with its own generator.  This type of preparation seems to be common among PSAPs nationwide.

There are other methods and applications that you could employ to make your system more reliable.  We chose to build a fully self contained Mobile 9-1-1 PSAP, which we believe is the first of its kind in the nation. 

Rutherford County is a Tennessee county of about 130,000 residents and 614 square miles.  Most counties of this size have some sort of emergency communications unit.   However, while the emergency service in our county is exemplary, a mobile communications unit had never evolved.

This proved to be to our advantage because there was no structure to try to fit the components into.  We were able to start with a clean sheet of paper.

We chose to go with a trailer instead of a motorized unit.  This gave us more flat floor space and eliminated the need to maintain another drive train.

TPD Trailers of Sacramento, California built the shell and kitchen area.  The unit has a floor space of just under eight feet by 32 feet, and is of steel-frame construction covered in laminated composite with a plywood core.  This makes for a strong and unified outer skin.

After the arrival of our trailer came the task of building and assembling the working hardware.  Of course the most unique item on board is Positron's Life Line 100 9-1-1 equipment.  South Central Bell, our predominate telephone company, greeted the concept with great interest.  I cannot say enough about its technicians, engineers and installation personnel.

Other components include a Telular cellular transfer system.  This unit switches the wireline phone system automatically to cellular in the event wireline service is lost.

We also have installed a digital central recorder, something not normally included in mobile units.

Our generator is propane-powered and is designed to be deployed outside the trailer via a ramp and electric winch.  This eliminated the vibration transferred to the trailer by the generator, along with the risk of carbon monoxide poisoning or fire.  It also makes for a quieter working environment.

The antennas are from Comet Industries and are a four-band design.  When used with one triplex and two duplexers, cellular, UHF, VHF, and low-band can operate on one antenna.  We have two of these systems on board.  This eliminates the antenna farm appearance and cuts the antenna assembly time considerably.  Adding to the speed of deployment, the antenna masts are pneumatic and extend 30 feet.  Hydraulic leveling devices round out the external system.  Now the system:  as stated earlier, the system is completely self contained, but it still has to connect to the 9-1-1 trunks and data circuits.  We have accomplished this by using a junction box with a transfer switch.  When connected by means of a 25 pair cable, the mobile unit and PSAP are joined.

Upon activation of the transfer switch, the trunks and circuits are routed exclusively to the mobile unit.  These junction boxes are mounted on the outside of each PSAP.   We currently are seeking to have them installed at each of our central offices in case of line damage at the site.  We also have cellular units via the Telular interface that we could route the 9-1-1 calls through, but with the current technology, we would not be able to translate ANI and ALI information by cellular.

Radio equipment includes Midland's new Tri-band low-band, VHF, and UHF single control head radio system.  One Tri-band and one Dual-band makes for a much cleaner looking console front.  Two control heads instead of five, these are flushed mounted to the panels.  Also included are aircraft, citizen's band, and high frequency amateur, and paging encoders complete the radio system. 

Our on-board computer system uses two 486DX units on an Ethernet network.  They conation multi-agency CAD system, digitized map and statewide phone listing on CD-ROM.  We also have loaded all of the equipment-programming software.

On the rear wall is the electrical panel.  It is designed to handle and distribute both 12 volt and 110 volt.  We power the trailer by one 240-volt circuit then divide that into two 120 volt branches.

The primary equipment, 9-1-1, Battery Charger, and dispatch heat and air are on the first branch.  This can also be powered by a single 20-amp, 120-volt source in case 240 is not available.  All other electrical needs are met on the second branch.

All radios and interior lights are powered by 12 volt through a large battery bank.  So, even if the AC power and generator fail, radio communication can continue for several hours.

What you won't find in our unit are bunks, showers or areas to lounge in.  This unit is designed for the dispatchers to work their normal shift and be relieved by the next shift.  If this unit has been deployed, their PSAP is no longer operational and normal shift work can take place.

We have included the normal amenities found in their regular work place, such as kitchen facilities, restroom, air conditioning, etc.  The intent here was to be mission-specific and not try to build something that could do it all, but not do it well.

When designing and building this system, I read every article on the subject I could find.  There have been several articles in the APCO Bulletin on this subject.  Trade shows and conferences also have provided much information.

I highly recommend to anyone contemplating such a project to go see what other agencies have done. Nothing provides a clearer picture of any project than to confer with someone who has been through it.

To those who allowed me to tour their facilities, I wish to thank you for your time.  You might see some of your unit in ours. While on the subject of acknowledgments, I must credit our 9-1-1 Board of Directors.  Without their support and interest, this unit never would have been built.

While the unit was under construction, one board member, Chief James Farmer, passed away, and the unit was dedicated in a ceremony in his memory.   If you see something in our unit that you would like to incorporate, please give me a call.  Here are the vendors of the major components:

                        (Click on camera to see pictures of the Mobile Unit)

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