All chiefs would agree that fire service communication equipment must provide superior performance, durability and reliability under adverse conditions. But while the basic function requirement at the heart of all communications equipment — the ability to send and receive signals — is a constant, the form that equipment takes has evolved to fulfill many specialized needs and operational environments.

Headsets can be worn over the ear, in the ear or, in the case of bone-conduction units, not touch the ear at all. Microphones can be handheld or hands-free, with push-to-talk keys or voice activation. Components can be hardwired or wireless. And the list goes on. The point is, the concept of “standard” communications gear no longer applies. Perhaps more accurately, standard communications gear today can have the capability to be adapted to a wide range of usage requirements and applications.

In the context of emergency services communication, interoperability is usually assumed to mean the need for communications among and between disparate systems — analog and digital, conventional and trunked, operation on VHF, UHF and 800MHz bands. But the “interoperability” of a microphone and a radio or a headset and a microphone to facilitate application-specific use can be important as well.

Otto Communications, for example, has developed adapters that allow a common set of accessories to work with a variety of radio variations. Another example from the same company is a speaker microphone with a multi-pin connector that supports a full array of headsets, throat microphones and PTT options in addition to providing key load and cloning input without removing the radio from the tactical vest or removing the accessory connector from the radio. Each user can quickly load the desired operating frequencies from a laptop computer or clone a radio without removing any equipment.

Convertible headsets

The concept of adaptable equipment includes the ability to convert a headset or earpiece for use in the range of relatively quiet or very loud ambient noise environments first responders encounter. Headsets can be fitted with traditional rubber ear tips, left and right flexible ear inserts for long-term comfort, or noise-attenuating plugs for noisy areas. Noise-attenuating plugs can provide a significant level of noise protection and receive excellent audio quality from the radio in noisy environments. Changeable earpieces allow headsets to be converted easily for use in a high-noise crowd-control situation and back again to allow normal conversation. Similar earpiece options are also available in single-ear designs with form-fitting ear loops, suitable for low- to moderate-noise environments.

High- to extreme-noise environments may require a traditional heavy-duty noise-attenuating headset with passive noise protection or an active noise-reduction headset with a combination of active electronic noise canceling and passive noise insulation. Active noise-reduction headsets use microphones and circuitry in the ear cups to detect incoming noise and create the inverse frequency to cancel the noise. ANR is particularly effective with the constant low-frequency noise found in heavy equipment operations. Similar technology also can be employed to provide normal levels of conversation and background noise to the headset user, with the noise-reduction circuit configured to maintain safe levels in the event of a sudden increase in noise, such as an air horn blast or even an explosion.

Multipurpose microphones

Hearing your radio is important, but being heard is equally important. The most efficient means of transmitting remains the traditional boom microphone placed in front of the user's mouth. Omnidirectional electret condenser microphone cartridges perform well in low- to moderate-noise environments and are very user-friendly. They tolerate a wide range of positioning relative to the user's mouth and still get the message out.

First responders in higher-noise environments will benefit from some form of noise cancellation when transmitting. Many products claim to be noise-canceling, but some homework is required to determine the degree of noise cancellation actually provided. The most basic approach to background noise reduction is decreasing the microphone “gain” or amplification so less background noise is transmitted. This has limited effectiveness because the reduced gain also affects the desired voice portion of the signal, often forcing the user to speak louder to be heard.

More effective noise cancellation can be achieved by changing to a unidirectional microphone cartridge. Omnidirectional microphones accept sound from all directions, making microphone position less important. However, they also pick up more background noise. Unidirectional microphones only accept sound from a single direction and inherently reject noise coming from other directions. However, just using a noise-canceling unidirectional microphone element doesn't ensure adequate noise-canceling performance. The microphone housing geometry, air volume and porting all must be designed correctly to allow the microphone element to function properly.

Another key issue with noise-canceling microphones is microphone position. Unidirectional microphones perform best when positioned directly in front of and as close to the mouth as possible. This provides the most background noise rejection and most voice input to the microphone. The concept of signal-to-noise ratio applies to many areas of communications technology, including microphones — the more you can do to reduce the background noise and increase the signal, the better chance you have of being heard and understood. User training is an important part of this process.

Bone conduction and ear microphone technology is another more specialized alternative. Vibrations can be picked up by transducers at various points on the body, converted to electrical signals and transmitted just like a traditional voice through a microphone. Vibrations can be picked up from the throat, skull, cheek bones or ear canal using bone conduction. One application found that a traditional skull microphone performed well when positioned against the sternum and held in place by a tactical vest. Other devices seal to the ear canal and pick up the pressure waves created when a person speaks. The principle advantage of both technologies is that they don't require a microphone element positioned in front of the mouth, which can be an asset if your department's SCBA equipment doesn't have provisions for traditional microphones.

However, ear, throat and bone microphones do not provide the same level of clarity available from traditional boom microphones. From the standpoint of signal-to-noise ratio, they all have a weaker signal that must be amplified to a greater level than a typical microphone. Since the signal starts out weaker, there's some compromise in audio quality. These devices also can be affected by the physical attributes of the user. People with very thick hair may have problems with skull units. Throat microphones require some experimentation to find the optimum voice quality position on each person. Ear microphones may require a custom ear mold to correctly seal the ear canal. No communications device is perfect, but bone conduction, throat and ear microphones can provide a functional alternative for first responders who aren't able to use a traditional microphone.

Wireless connectivity

Until recently, it has been necessary for headsets and microphones to be connected by cables to radios. The problem inherent in the design is that cables tend to get caught on things, and their points of connection are often a point of failure.

The wireless technologies employed in the manufacture of cordless and hands-free telephones would seem the logical solution — and it is in many applications, although there are acknowledged limitations of the technology. Wireless units still require power, and that power is provided by batteries. The additional expense associated with batteries and the need for monitoring their charge are both factors to be considered. Loss of power in many situations could be critical or even life-threatening.

The number of wireless devices that can be in operation in the same area without encountering interference or cross-talk is a potential problem. Security of transmissions is also an issue not to be discounted. The bottom line is that while wireless technologies do offer a certain level of user convenience, hardwired communications equipment still provides superior reliability and security. The industry, however, is addressing those issues with considerable effort, and solutions will be found.

“Standard” communications gear? The array of equipment options and accessories available today should leave no department, or even an individual responder, making do with gear that does not fulfill virtually every need in virtually every circumstance.

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John Towns is vice president of sales for Otto Communications, Carpentersville, Ill.