Telephone Breaks the Sound Barrier in Connecticut
New system overcomes obstacles of community noise level and home insulation to alert volunteers
—Photos by Arnold Walter
THE FIRE ALARM sound barrier is being broken in Connecticut these days with the use of telephone company facilities. The trend toward more thoroughly insulated homes, the increasing use of storm windows and the ever-blaring television or radio sets have been building up a sonic wall between the volunteer fireman and his firehouse whistle or siren.
The Glenbrook Fire Department, which covers a section of Stamford, Conn., has found that more and more the public alarm signals are not getting into the homes of the volunteer firemen. The men are there and eager to respond, but the coded whistle cannot breach the walls of their sound-tight homes.
But the installation of a command telephone circuit has changed things. When the Glenbrook dispatcher receives a fire call, she transmits both the usual whistle signal and a command circuit phone signal.
The dispatcher depresses a lever which rings the ordinary telephone bell in the homes of 21 firemen. In Glenbrook, there are three command circuits, each controlled by a separate lever, so a total of 63 firemen can be alerted. By keeping the lever depressed for several seconds, the telephone bells in the homes ring for that length of time. Thus, the fireman at home recognizes the extended ring as a fire call. Firemen are beginning to -Answer the phones by the time the dispatcher finishes ringing each of the three circuits.
The dispatcher can then talk over all three circuits at the same time. She announces the location of the fire—or any other emergency—and she may give any other pertinent information at that time. This message is repeated several times so that the last men answering their telephones get the complete alarm details.
After a fireman receives the full message, he merely hangs up his telephone and automatically disconnects it from the fire alarm command circuit. It is again ready for family use.
Automatic cutoff
If the dispatcher thinks that some heavy sleepers need an extra ring, she keeps her receiver off the hook and depresses the ringing levers again. The neat part about this is that the bells of the telephones that have already been answered will not ring this second time. The family doesn’t have to endure the jangling of the command circuit while pop is on his way to a fire.
What about the telephones that are being used when the dispatcher starts to sound the alarm? That’s been taken care of by the engineers of the Southern New England Telephone Company. Operation of the ringing lever by the dispatcher creates a distinctive tone in any telephone in use. This is a signal for the person in the fireman’s house to say: “A fire alarm is coming through. Please hang up your phone.”
Both parties to the conversation hang up their telephones. Then the fireman lifts his receiver and is automatically connected to the command circuit to get the fire location as it is repeated by the dispatcher. The only hitch occurs sometimes when the fireman’s telephone is being used for a long distance call routed through a manual switchboard instead of entirely dial equipment. Then it is necessary for the fireman to ask the operator to pull the plugs out so that his phone can get on the command circuit.
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TELEPHONE ALARM SYSTEM
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When all-dial equipment is used in completing a personal telephone call, then the calling party must hang up his telephone before the line is cleared for the fireman to get on the command circuit. If the fireman originated the personal call, he can get on the fire alarm command circuit just as quickly as he can hang up his phone and pick it up again. If someone called the fireman, then that person must hang up before the fireman’s phone is free to join the command circuit.
Private line required
There is one restriction that the Southern New England Telephone Company puts on the installation of command circuit service to firemen’s homes. The fireman must have a private line. This rule was made to avoid unnecessary ringing or a disrupting warning tone in the homes of other persons on a party line. However, if all the customers on a party line are firemen, there is some indication that the telephone company will waive its rule and give them command circuit service.
There is, of course, a distance limitation to the command circuit. But from a practical standpoint, it is negligible. The service can be made to any telephones in the same exchange, or even to any telephones in exchanges located in the same central office.
The limitation of 21 telephones on a command circuit keeps the circuit within the capabilities of the phone exchange’s ringing equipment. For that reason, although three command circuits may be used by a fire department, only one circuit ringing lever may be depressed at a time. However, by using each ringing lever successively, all 63 phones are brought into simultaneous communication with the fire department dispatcher.
The command circuit alarm service inaugurated in Connecticut represents an important refinement of a system first used by the Mountain States Telephone Company in Colorado. The use of amplifiers by Southern New England Telephone engineers gave them their biggest advance—the satisfactory transmission level of the voice. The result was a better transmission level on the command circuit than between any two telephones connected to the same phone exchange.
In the central office, or telephone exchange building, a hybrid connection was used to tie in voice frequency amplifiers and a four-wire telephone circuit to the Glenbrook firehouse—the remote control point for this particular circuit. Incidentally, it is possible to have three remote control points.
The use of the two-way voice amplifiers and the four-wire line to the control point removed the singing from the line caused by changing load conditions. Also, the amplifiers maintain a lower level of transmission from the home phones than from the dispatcher’s phone. This tends to keep the command circuit line quieter as numerous home phones with their background noises operate on the command circuit. But by keeping the dispatching phone transmission level a bit higher, the receiving fireman hears messages over home noises. It adds up to an efficient conversational circuit that can handle emergency conferences among fire officers as well as fire alarms.
The application of amplifiers eliminated one of the major barriers to efficient service—distance. During World War II, command circuit phone service was developed to allow officers in different locations on the same base to confer. The very fact that the phones were on the same base sidestepped the eventual problem of varying lengths of telephone wire from central office to firemen’s homes. At first, it was necessary to keep the lines to somewhat equal length to minimize the variance in current drop. The introduction of amplifiers in Connecticut designs got around the line drop bottleneck.
Circuits may be selective
Because the distance from the telephone exchange building to a fireman’s house is no longer a transmission problem, the men can be assigned to each command circuit according to the desire of the fire chief. He may have all his officers on one circuit so that staff conferences can be held by telephone without disturbing other firemen. A rescue squad, special service company or fire patrol can have one circuit to itself.
Inside the telephone company central office, the operation of the fire department dispatcher’s lever activates a tripper relay that knocks off the regular ringing current. Then a transfer relay switches the individual firemen’s telephones from private line service to the command circuit. If a fireman is using his telephone, then a busy test relay puts the special fire alarm tone, which was mentioned earlier, on his line to notify him that a fire call is being transmitted.
Once a fireman answers a fire call, a line supervisory relay acknowledges his action by permitting the telephone to disconnect from the command circuit with the hanging up of the phone. The private telephone is then back in general service.
All the relays, switches, wires and other components to handle the 63 telephones divided among three command circuits can be installed in one standard telephone central office relay rack bay about 11 feet high and 23 inches wide. Or to put it another way, it’s approximately the same central office space required for servicing a 50 to 75-line PBX or private switchboard.
The reliability of the telephone fire alarm circuit is protected by several type: of checks. First, there is a daily test at 8 p.m. each night when the Glenbrook fire dispatcher rings all three circuits. As she announces that it is a test, the men answering their phones merely hang up. Once a week, a roll call test is made. Then the name of each fireman is called by the dispatcher over the combined three circuits and as a man answers “present” to his name, he hangs up his phone. In this test, not only does the fireman get a chance to see that his telephone is working, but the dispatcher gets a record of the men who responded. By this means, the fire department has a positive record that a member’s telephone was operating on the last date he responded to a roll call. Conversely, an unexplained failure to respond can be checked out. Actually, a constant check of each fireman’s telephone line is being run by his family in their daily calls. Any disruption in service would be noticed the next time a member of the household tried to place a call.
Each telephone on a fire alarm command circuit is specially identified by the telephone company to insure expedited repair service to get a faulty line back in operation. As far as the fire department is concerned, the maintenance problem is no more than a call to the telephone company’s repair service.
