Article Archive
Radio Daze
Has Technology Stretched Our Electronic Lifeline to the Breaking Point?
Volume 12 Issue 3

On "Star Trek," Captain Picard taps his Star Fleet badge and instantly is in verbal communication with the Enterprise. No static. No squelch. Agent Mulder on "The X Files" gets a clear signal on his cell phone even though he is sealed inside a railroad tank car buried in the desert. In "Die Hard" hero Bruce Willis broadcasts from a high-rise roof with a hand-held walkie talkie and manages to reach the police dispatcher with only minor difficulty.

So much for Hollywood. In the fire service, real life drama often results when radios fail to work. Imagine that a monster-size distribution warehouse is ablaze. Structural steel and concrete makes it difficult for the firefighters on interior attack to reach the incident commander outside. Meanwhile, the commander is unable to reach exterior firefighters behind the burning warehouse. Eye level ground-to-ground communication is obstructed by the structure itself. As for catching the nearest repeater, RF interference from mobile units on scene is blocking the signal returned from the base station.

Public safety radio communication is not always an exact science. The variables are many and unforgiving. After 9-11, a clamor has arisen for improved radio communications to better protect emergency responders. True, there is plenty of room for improvement, both immediate and long terms. The problems sketched in the warehouse scenario above can be resolved. However, it is a mistake to aspire to Hollywood fantasy rather than what is realistic and practical. The personnel on the front lines need a better understanding of how this electronic lifeline works.

HISTORY
In the beginning, the first emergency dispatchers functioned more like disc jockeys. Radio traffic with responders was one-way only with dispatchers issuing bulletins via AM radio. Then came World War II. The first fire department equipped with two-way radios was Honolulu, HI. The military provided the equipment in the wake of Pearl Harbor in case the Japanese should return. After the war, two-way radio communications spread to mainland fire departments, usually with a base station at one end and a transmitter-receiver in the fire chief's car.

By the late 1950s, most emergency vehicles were equipped with two-way radios. Also making their first appearance were personnel hand-held radios. These were commonly referred to as 'bricks.' The radios were heavy, cumbersome and had non-rechargeable battery packs good for eight hours maximum. The first two-way radio for public safety responders operated on the Simplex system. There was one radio frequency -- 154.190 -- and everybody used it both to transmit and receive.

For volunteer firefighters, a major innovation was the Plectron unit. Although not a two-way radio, volunteers could now keep a tone-activated radio at home or work through which dispatchers could immediately send them to the scene. It was a big step forward from air horns shattering the night, ordering the volunteers to gather at the fire station for further instructions. One of the earliest pager systems, Plectrons could dispatch numerous fire departments on the same frequency by assigning a specific tone to each. It would be the late 1960s and early 1970s before volunteers received individual pagers.

The next step in portable radios was the first transistorized two-way radios. As compared to today's portable radios capable of operating on many different frequencies, the first portable two-ways had one frequency, period. That frequency was determined by installing the correct crystal. If a different frequency was required, a different crystal had to be installed.

Portable units had major limitations in those early days. These were one- to five-watt radios operating at ground level. It was better than shouting at the top of your lungs. Still, the range was short compared to mobile radios in vehicles operating at 20 to 100 watts. Base stations operated at 250 watts or better, plus having the advantage of a tower mounted antenna. Increasing the height of the antenna it improves the range of coverage for your mobile unit. Doubling the height of the antenna increases a base station's power times four. Another inherent problem was the tendency of the early low band signals (30-50 MHz) to 'skip,' reflected by layers of the atmosphere. You may be trying to reach to that policeman in plain sight at the end of the street, but the person you are actually talking to could be in the next state.

The answer to skip was moving to the high band frequencies, first VHF (150-179 MHz), then UHF (450-470 MHz). But while higher frequencies reduced the skip factor, it also reduced the distance that emergency radios could transmit. Enter the first repeaters. The principal is simple. First, your radio must transmit at the receiving frequency of the repeater. The repeater, operating at as much as 250 watts, then rebroadcasts that signal on another frequency. Radios monitoring the repeater's boosted transmit signal received the original message. To use the repeaters, portable and mobile radios now had to be capable of transmitting on one frequency and receiving on a different one.

The repeaters had advantages and disadvantages. An entire city could be monitored through a single base station with a tall enough tower. Of course, any radio in the system could monitor all the traffic. The phrase "public service this office" meant pick up a telephone unless you want the world to know. But even with the repeaters, portable and mobile radios still had trouble reaching the base station. Sometimes the problem was terrain such as tall buildings and hills. Even with a nice flat surface, hitting a repeater 15 miles away with a signal from a three-watt portable was still a neat trick to pull.

Next came the voting receiver. In a big city, these went up on little towers all over town. These were essentially repeaters feeding the repeater. For example, a firefighter with a portable calls for extra help. The signal from the portable might reach two or three of the voting receivers. An electronic device would then pick out which voting receiver was receiving the strongest signal. That signal would then be sent to the repeater, either by telephone line or microwave link. Voting receivers were a big advancement in emergency radio technology. However, the bigger the city, the more voting receivers you needed. Installing and maintaining all those voting receivers could get expensive quick.

Enter 800 trunking, the system in use today in most major metropolitan areas. This system amounts to a very sophisticated juggling act involving multiple frequencies. Simplifying it to the ridiculous, take a city where the fire department has five frequencies, the police 10 and the sheriff's department 10. All three dispatch through the same base station where a computer monitors the use of the available frequencies.

In the field, a firefighter uses a portable unit to call the dispatcher. The scanner in the radio selects a frequency that is clear of traffic and transmits. When the repeater boosts the signal, it is broadcast to the base station on a different available frequency. The dispatcher's reply to the firefighter uses yet another. And when the firefighter acknowledges the reply, still another frequency is used. Every time the person transmitting keys their radio, the computer chooses a different frequency that is available at that moment. During a single conversation, many different frequencies may be used.

The magic of trunking is that while the fire department once only had five frequencies, it now has access to 25. The public safety agencies involved -- fire, police and sheriff -- share the available frequencies. Now an old timer used to the old system might say "Great, now we have to listen to the police and sheriff's traffic as well as our own." How this is avoided takes us back to the days of the old Plectron units. A special tone activates those radios for which the message is intended. Fire radios get fire dispatches; police radios get police dispatches. (WARNING! Whereas the 800 trunking system separates traffic for the varying agencies accordingly, labeling this a 'private line' is a misnomer. Any private citizen with a scanner can hear both the incoming and outgoing traffic throughout the system. Having a private line is not the same thing as having a personal scrambler. "Public service this office" still applies.)

In 800 trunking, the various frequencies are organized into 'fleets.' Whereas in the old days a firefighter on the scene might be instructed to switch to a different frequency, today a firefighter on an 800 trunking system might be instructed to go to fire 1, fire 2, etc. The private lines are grouped together by the computer to facilitate the department involved. Or, if the incident commander decides it is best, modern portables and mobile radios can drop the repeater and go simplex, meaning radio to radio communication at the fire scene. This is the preference of many fire departments.

TRUNKING TRAUMA
Older readers will remember how the radio in the family sedan would temporarily fade to static whenever it passed close to a broadcasting tower. Something like that happens with 800 trunking too.

Say the firefighters battling that big warehouse blaze opts to stick with using the repeater. Two companies have staked out positions on either side of the warehouse. The chief keys his mike to issue instructions to the second company. First, that signal has to go all the way to the repeater, then the base station, then back to the fire scene. But the second company might never hear a word. Even though the transmit and receive frequencies are different, the chief's powerful 110-watt mobile radio is blanketing the immediate area with RF interference. That strong interference close by on another frequency is enough to block the returning signal from the repeater.

Nor is 800 trunking a solution for the key problem that has plagued portable emergency radios since their inception. The power remains at the base station, not with the emergency units in the field. A small low-powered radio is often unable to pierce surrounding steel and concrete to reach the distant repeater or base station. That means that firefighters on interior attack deep inside a modern structure may well be able to hear the strong signal from the base station, but their reply is never heard.

Since 800 trunking carries even shorter distances than UHF, even more repeaters and voting receivers are necessary. This is particularly true if your city is hilly or boasts a congested skyline. Some cities are beginning to require a repeater to obtain a high rise construction permit. Still, anyone with a personal cell phone knows that 100 percent coverage is impossible. Woe to the responder working in one of those areas where coverage is not so great.

The difference between analog and digital 800 trunking is another area of concern. With analog equipment, a less than perfect signal can be received and interpreted. Part of a distress message getting through the static is better than nothing at all. In digital 800 trunking, the computer rejects all but a perfect signal. Is part of a message better than no message at all? Digital technology may be great when what matters is getting a perfect television picture. However, in emergency response a garbled message can sometimes tell as much as crystal clarity.

Speaking of cell phones, something close to war is raging between commercial cell phone providers and public safety radio systems. Cell phone networks operating in the 800 MHz bands are known to cause electrical interference that disrupts both analog and digital 800 MHz systems used for public safety. Proposals and counter proposals are being weighed by the Federal Communications Commissions. The solution is likely to be costly and complicated.

A host of other new problems have become apparent with the advent of 800 trunking. These problems are all the more troublesome given the post 9-11 push for interoperability between the individual communication systems operated by public safety agencies. Before 800 trunking, radios that shared the same frequencies could talk to each other. That is not true with different types of 800 trunking systems. Taller antennas, more power and mutual aid frequencies mean nothing if the radios brought by the various responders are basically incompatible due to the different manufacture trunking styles.

Interoperability becomes impossible for a variety of reasons. Suppose your community operates an older analog 800 trunking system that is made by brand A. Your neighbor who requests mutual aid help has a new digital 800 trunking system that is made by brand B. Without An expensive cross-connect patch or gateway interconnecting the two systems, the visiting firefighters may as well shut off their radios and save the batteries.

Another issue is 'restrictive architecture.' A videotape made in one VCR plays just as well in another. That's standardization. But the ink cartridge from your printer at work might not fit in the brand you have at home. In most cases, 800 trunking radios made by one manufacturer are simply not compatible with an 800 trunking system by a different manufacturer. Rather than a marketing tool, restrictive architecture results from manufacturers taking different innovative approaches to solving the same problems. Unfortunately, the result in a mutual aid crisis can be an interoperability Tower of Babel.

As for industrial fire brigades and emergency response teams, the dye has been cast. In most cases, industrial plants have been relegated to the 900MHz bands. With industrial emergency responders tied into 900 trunking systems, a major resource of personnel and equipment in mutual aid emergencies has been effectively isolated. Again, without a cross connect patch of some type, radios used by most industrial responders will be useless in mutual aid situations involving municipal firefighters.

SOLUTIONS
With the right engineering, the system that lies beyond 800 trunking will resolve all these problems. But that next step may be many years away. In the short term, emergency responders must find solutions that work today. With portable radios, short range and inability to penetrate steel and concrete are the chief problems. One solution is moving the repeater closer to the firefighters.

Mobile repeaters take advantage of the higher power mobile radios in emergency vehicles. Installed in a fire truck, the repeater is actually on scene to boost the weak signal received from portable units and sends them on their way to the base station. Portable radio would no longer have to reach out miles to hit the nearest available voting receiver or repeater. A mobile repeater sitting in the parking lot at a burning warehouse is in a much better position to pick up portable radio traffic from firefighters on interior attack.

Another solution is a return to mutual aid radio frequencies. Officially, there are no mutual aid frequencies in the 800MHz range. Some agencies have taken it upon themselves to include such frequencies in pre-planning with other departments. In the VHF range, there are designated mutual aid frequencies for fire and police. None were ever officially established in the UHF range. Also, dedicated frequencies with 800 trunking would make the use of pagers and data terminals more practical.

With regard to interoperability, the first best fix is the cross-connect box. As opposed to a cross-connect patch or gateway, which is an expensive unit installed at the base station, a cross-connect box operates at the scene. For example, a fire department that is UHF based must accommodate mutual aid responders that operate using VHF radios. At incident command headquarters, a UHF radio and a VHF radio are connected using a cross-connect box. Firefighters from both departments are now able to communicate using predetermined mutual aid frequencies.

Radio was never perfect. Stop to think about why we watch television using cable and satellite dishes instead of antennas today. Radio reception is susceptible to interference from sunspots, weather and a multitude of other influences. Unfortunately, we can not string a cable from every emergency responder. What radio gives us in mobility sometimes costs us in clarity. Improvements can be made now. Reinventing the wheel on short notice is impossible, however.

 
 

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