Planning The Fire Department Radio System
Editor’s Note: The author of the following article, prepared expressly for FIRE ENGINEERING, is one of the best known and qualified authorities to discuss the technical phases of radio communications in the fire service. Dr. Noble has been Chairman of Panel 13 of the Radio Technical Planning Board, which body was organized to study the entire field of radio communications and submit recommendations to the Federal Communications Commission for allocation of frequencies, including those channels for the fire service. Committee Two, of that Board, headed by Herbert A. Friede, Superintendent Fire Alarm Bureau, District of Columbia, which included Chief Roi B. Woolley, assistant editor, FIRE ENGINEERING as the representative of the International Association of Fire Chiefs, presented the case for the fire service and, as announced in previous issues of FIRE ENGINEERING was instrumental in bring about the designation by the FCC of a number of radio channels for exclusive use of the fire service.
Although there is generally nationwide recognition by the fire service of the many and weighty advantages of short-wave radio in its field, there are some factors of technical and semitechnical nature connected with the procurement and installation of the equipment on which administrative officers of the service are not fully informed. The purpose of Dr. Noble’s article is to clarify some of these details.
THE knowledge that much of fire’s tragic annual toll of over 10,000 lives and 500 million dollars property damage could be decreased by adequate communication facilities has prompted an increasing number of officials to look toward radio communication as a means of reducing this appalling loss of national life and wealth.
Though much has been written on the uses of radio in fire-fighting operations, i. e., intercepting mobile units enroute, coordinating action at the scene of the fire, etc., there is a dearth of information on the planning of 2-Way Radiotelephone Communication systems.
The prospective user is beset with a number of questions: What frequency to be used? Where to find guidance in the purchase of equipment? What about licenses? Obtaining construction permits and, after construction, how will maintenance be handled?
Three bands have been allocated for Mobile and Emergency Service by the FCC. The first of these bands, 30 to 40 megacycles, has 15 channels allocated to it for fire use. Of the three bands, the 30 to 40 mc. section has the longest “talkout” range, approximately 50 miles.
This band, however, possesses certain characteristics which reduce its usefulness. It is highly crowded, and though this may not present a local interference problem, sky-waves can play hob at distant stations sharing the same frequency. This capricious quality of the 30 to 40 mc. band to permit a signal to “skip” from its confines can cause confusing and often embarrassing directions to issue from a loudspeaker at a station located hundreds of miles away.
Another factor possessed to an unsatisfactory degree in relation to the higher frequencies is this band’s tendency to pick up noise. Where operating conditions are already noisy—and what fire isn’t!—this characteristic is certainly undesirable.
The use, then, of the 30 to 40 mc. band is chiefly in the capacity of “long” range communication when maximum coverage cannot be obtained through the use of the higher frequencies.
Shorter Range Less Noisy
Less noisy and having a somewhat shorter range is the 72 to 76 megacycle band with its 12 fire channels. Here, the property of the wave is such that skip or sky-wave interference does not appear to the extent shared by the 30 megacycle band. This band has a television channel on each side. Thus, the probability of “cross interference” is not too remote, making this band questionable for wide-scale fire use in those metropolitan a,reas where television stations are in operation until engineering investigations determine the magnitude of the interference to be expected.
High Frequency for Fire Use
Of the three available bands, there remains the very high frequency band of 152 to 162 megacycles. These very high frequency waves have properties highly advantageous for Municipal and County communications, solidly covering a 15 to 20-mile range with negligible sky-wave interference and a dramatic reduction in noise level.
Recent extensive tests conducted on 162-megacycles over flat Chicago-land and rugged Bedford, Indiana, terrain have fully attested the superiority of this particular frequency. Tall buildings, underground passes, and hills offered little challenge to communications on this frequency.
Perhaps the most dramatic characteristic of the 12-channel, 152 to 162 megacycle band is the startling clarity of speech obtained through its use. Within its reliable range reception is such that all background noise is “washed out” with resulting crisp, intelligible speech. It, therefore, is the preferred frequency for fire use.
There has been much discussion on the allocation of frequencies for the emergency services. The Federal Communication Commission’s recent allocation of exclusive fire channels evidenced wise understanding of the vital nature of fire fighting operations.
However, there remains the sharing of frequencies for municipalities of less than 150,000 population. Such sharing with the police department cannot only be awkward but extremely dangerous. It is not outside the realm of probability for two emergencies to occur at the same time.
The simultaneous occurrence of a bank robbery and a theater fire, for instance, poses the problem: who shall be first in the use of the shared frequency, the police or the fire department
Sharing Disadvantages Minimized by Technical Advances
Some of the disadvantages of sharing have been greatly minimized by recent technical advances which permit selective calling. With this system it is possible to dial only the cars desired, the police and fire systems having different dial combinations. This of course does not provide interference immunity should both central stations desire to contact their cars simultaneously. Its principal use lies in selecting the car or cars desired without transmitting information which is unimportant to the rest of the mobile units.
Greatest hope, however, for free fire channels lies in the proposal of the FCC for the elimination of the rule regarding population.
It may be stated here that Mutual Aid will function with greater effectiveness now that the 152 to 162 megacycle band has shown such great promise. This particular band is more or less tailor-made for Mutual Aid, for its fairly well confined service area permits smooth transition from one station area to another without objectionable distant interference.
One of the biggest problems confronting the prospective user of 2-Way Radiotelephone is: what make of equipment shall I purchase? Though cost is a decided factor in choosing equipment, the old story of the cheapest being the most expensive can be a true story when maintenance costs are taken into account.
What yardsticks, then, shall the prospective user employ? Company reputation, of course, is important. The shrewd buyer will investigate other emergency communication systems, ask questions, and learn much from this “on the spot” appraisal of what the other man is using.
Equipment should meet the Radio Manufacturers Association’s proposed minimum equipment standards.
As to receivers, it will be wise to observe such factors as power requirements (automobile battery current drain), sensitivity, image ratio and signal-to-noise ratio, and the selectivity characteristics.
The purchase contract should include provisions for the supervision of installation by the manufacturer, as well as for all tests and adjustments necessary to get the system into proper operation. The ethical manufacturer, of course, will not leave an installation until it is in perfect working condition.
Even though good engineering practice includes the designing of equipment so as to be fool-proof and long-lived, there are times when servicing is required.
Questions the user, “Shall I hire the local radio serviceman, or, must I engage an expert on communication equipment for handling my maintenance work?”
The answer is yes and no! For it is possible that the local serviceman may possess the technical ability to service the communications equipment. More than likely, however, he does not possess this knowledge. The alternative, then, is to employ the services of the department’s own engineer, or contract with an outside expert on a retainer basis. Qualified individuals capable of performing this service advertise in certain technical publications.
Preventive maintenance in the form of periodic check-ups of equipment will usually prevent a potential source of trouble from becoming serious enough to cause a breakdown.
The same foresight should be employed in the choice of storage battery and generator capacities. Recommended are storage batteries of ample amperehour capacity, as well as generators capable of maintaining a generous current output. Of course, the service department should be outfitted with good battery charging equipment in order to re-charge storage batteries which are subjected to excessive drains.
Illustration courtesy Herbert A. Friede
Communication installations for fire-fighting service present problems not found with most of the other emergency services. Equipment must be intelligently selected. Loudspeakers should be located as close to the ear as possible. Earphones and lip microphones should be employed, both of which take into account the roar of fire-fighting operations. However, a handset similar to those used in desk telephones can be used for truck operation.
Water, so essential to fire control, can raise hob with sensitive radio equipment, unless suitable housing and moisture-proof components are used in the system. Incidentally, the acceleration of progress due to war’s needs has done much in whipping the moisture problem. Indeed the Motorola “Handy Talky” radiotelephone could be dunked into salt water without impairing performance.
Much has been said about the use of the “Handy Talky” 2-Way Radiotelephone for fire operations. It has already proved invaluable in coordinating aerial fire fighting with ground action. Firemen, high aloft in burning buildings can communicate with the Battalion Chief, receive and give directions that would otherwise necessitate a foot messenger. In the recent Empire State Building tragedy, firemen who were hundreds of feet above the surface were able to coordinate their activities with those below. Time, effort and lives are saved by this “mighty mite” of communications.
However, the “Handy Talky” 2-Way Radiotelephone as used by the Military does not lend itself to the overall flexibility required by firemen. A radio cannot be held in one hand and an extinguisher in another. To circumvent this awkward condition, Motorola engineers are developing new FM equipment which will be worn on the belt of the user. A lip microphone and earphone, as one unit, will permit full freedom of the hands.
Of course, every radio transmitter must be licensed by the Federal Communications Commission. The main station, which is usually capable of 250 watts output may be adjusted by any operator holding a 2nd class license, or higher. A recent ruling by the FCC permits operators of network stations to be unlicensed if they are under the supervision and control of an operator, at the main station, who holds a 2nd class, or higher, license.
Operation itself is the essence of simplicity, amounting to little more than pressing a microphone button and speaking. Aiding simplicity are a series of “10” signals which have been prepared by the Associated Police Communication Officers, Inc., and can be called the “shorthand of speech”. Here are a few of those coded figures 10-4, “O. K.”; 10-8, “in service”; 10-20, “What is your location?” Of course, there is no law prohibiting an organization from making up its own code. All that the FCC requires is that speech be kept to a minimum, and that dignity be maintained at all times.