Tuning Into Wireless Technology (part 2 of 2)

The use of radio-based security systems, commonly known as short-range wireless, has grown considerably during the past two decades. There are those within the industry who believe wireless has a real chance of becoming the de facto standard in signaling technology in the electronic security marketplace.

Because today’s wireless security technology is supervised and the equipment design more advanced than in years past, reliability is no longer an issue in most cases.

“Reliance on wireless in whole or part has increased dramatically over the past few decades,” says Susan Ellerin, president of STAT Resources Inc. of Chestnut Hill, Mass. “When we did the very first industry study on the burglar alarm market in 1983 for SIA [then SEIA], wireless panels were used in 7 percent of all residential installations, 2 percent in light commercial, and almost none in other applications.”

As of last year, STAT estimates one out of three residential systems installed were wireless and more than half of all installed burglar alarm control panels were hybrid.

“With wireless, you can put a motion in any location you want at any time, and that’s a big advantage to us as a security company,” says Brian Reese, president of Sentry Security Inc. of Canton, Ohio. “It also solves a big problem when we need to protect a certain area of a home and we’re not able to hardwire.”

Because these components do not utilize wires, they can be installed just about anywhere without a major effort on the part of the installation company.

Now that you have the set-up, welcome to Part 2 of Security Sales & Integration’s two-part series on wireless technology. In Part 1 (see page 42 of the January issue), we covered the theoretical side of radio signaling. In this installment, we’ll cover the practical side of the technology by applying it directly to intrusion, access control, video surveillance applications and more.

Selection of Wireless Sensors and Manual Devices Is Growing
A typical wireless system is comprised of an alarm control panel equipped with a radio receiver. In some cases, the panel is specifically designed with a receiver on board for wireless-only operation. In other cases, a wireless receiver can be added to the panel, giving the system the ability to accommodate both hardwire sensors and wireless components.

In the latter case, the panel is commonly referred to as a hybrid alarm control panel. In some hybrid systems, the receiver is built into the alarm panel along with a number of hardwire initiating zone inputs, while in others a receiver must be added, as mentioned earlier. Most radio-based systems, whether wireless-only or hybrid, are designed with a full complement of wireless sensors and detectors. Just about any sensor or detector that you can connect to by using a wire you‘ll find in today’s wireless systems.

Common wireless components include motion detectors, passive and active wireless keypads, glass breakage detectors, photoelectric smoke detectors, hand-held and necklace panic buttons, single- and multiple-button panic devices, wristwatch panic buttons, single- and dual-button keyfobs, money clips, man-down transmitters, and more.

2 Types of Supervised Systems Are Active and Passive
There are two basic types of wireless systems on the market: nonsupervised and supervised. Most of the wireless systems sold today are supervised, which means the alarm control panel, through a connected receiver, knows which transmitters are physically and operationally in place and doing their job.

Be aware there is more than one flavor of supervision in use. For example, in a passively supervised system, the transmitters will send a trouble signal when something goes wrong. In a system that uses active supervision, each transmitter automatically transmits a supervisory signal on a periodic basis. The intent is to constantly update the control panel so when something happens to a transmitter, the alarm firm and end user are notified.

Where automatic supervision is used, transmitters are designed to send supervisory signals every one to eight hours. If the alarm panel fails to receive a transmitter’s supervisory signal in a specific period of time, usually within eight to 24 hours, it will display the lost transmitter’s identity at the keypad and will automatically notify the central station.

Many of the supervised systems made today will also send a supervisory update to the receiver every time a change occurs in the sensor’s status. Usually included in this transmission is the condition of the transmitter battery, the status of the sensor, the transmitter identification number, and any other information that the manufacturer decides is important.

There Are Pros and Cons to Both Narrow Band and Wide Band
There are two basic radio transmission technologies employed in today’s wireless security systems. They are narrow band and wide band. Knowing the particulars behind each of these technologies will help you make a better-informed decision when choosing a wireless system for your firm.

Narrow-band wireless systems differ in that they use a super-heterodyne receiver that typically listens to a relatively small portion of the radio spectrum. This wireless technology requires tighter tolerances in its manufacture and operations, so many of the narrow-band components made use crystal-controlled oscillators. By contrast, wide band often uses surface acoustical wave (SAW) and inductor/capacitive (a.k.a. LC)-tuned circuits.

Proponents of narrow-band technology say these receivers enjoy greater sensitivity because they do not have to “listen” to so many other radio transmissions. This is helpful when transmitters are positioned in a fringe area, which can make it difficult for the receiver to “hear” transmissions. Detractors say for the added benefit, narrow-band systems are not worth the additional dollars.

Wide-band wireless systems, on the other hand, typically use a super-regenerative receiver that hears a relatively wide portion of the radio spectrum. Transmitters within this receiver’s area of concern are identified by certain characteristics contained in each radio transmission.

This is made possible through encoded identification data buried in the data that a transmitter sends. Because there is an almost limitless number of possible ID numbers employed by the average manufacturer’s wireless product line, duplication in transmitter identification code is nearly impossible.

Proponents of wide-band technology say this type of system is better than narrow band. They claim this technology is more forgiving of problems in the field, such as transmitters that are slightly off frequency.

Detractors of wide band say the receiver is forced to sort through a multitude of radio transmissions and that this can possibly cause it to miss a critical signal sent from a valid transmitter.

How Propagation, Frequency and Environment Interact
The successful application of short-range wireless in the field requires a rudimentary knowledge of wave propagation and the effects of environmental conditions on the radio signal. Examples of obstructions that often adversely affect wireless communications include steel construction and large metallic objects (see next section on attenuation).

Another source of aggravation to security installers when using short-range wireless is electromagnetic interference (EMI). A short list of examples include heavy radio frequency (RF) environments, such as large airports; industrial facilities that use arc welders, steel smelting furnaces and noisy electric motors; and high-powered transmission equipment common to ham radio operators and those who abuse the citizens band (CB) frequencies by transmitting 21MHz signals and a host of harmonics at a higher pow
er than what is allowed by the FCC.


Another source of interference is the emission of harmonic frequencies. In most cases of EMI, the situation can often be remedied via adjustments to the offending equipment or contacting the FCC with respect to the CB abuse issue.

Obviously, many of the above EMI sources are not under the control of the security dealer or client. However, knowing what the potential sources of EMI are before embarking on a wireless job can help security personnel control expenses and assure a profitable outcome.

Attenuation Can Diminish Signal Strength at the Receiver

Probably the most important issue that dealers face when installing short-range wireless systems is wave attenuation. Attenuation is essentially the encounter of anything in the environment that diminishes the radio signal’s power before it reaches the receiver.

Attenuation can cause intermittent supervisory problems as well as missed alarms and other trouble conditions. Intermittent problems of this kind can drive labor costs through the roof, as it’s the installer’s job to correct them, especially before turning a new system over to a client.

Factors to consider include metallic obstructions in and about the structure; possible sources of electromagnetic interference (EMI), internal and external; the equipment’s operating frequency; the specific radio technology in use; composition of structural walls and floors; and operating temperatures. All of these things can play a part in the attenuation of a transmitter’s radio signal.

In residential settings, some of the most common materials encountered are furniture, wood, glass, sheetrock and plastic. These types of materials have very little effect, if any, on short-range wireless signals. Sometimes it’s what under the sheetrock or wood façade, or above ceiling that can adversely affect these signals, such as a large complement of metallic cable or a corrugated steel pan.

Of special concern are relatively large commercial, institutional and office complexes. These facilities commonly contain more metal than their residential counterparts. All of these metallic obstacles can, and will, affect how a transmitter’s radio waves propagate through the facility.

To offset the effects of metallic obstructions inside a building, when installing wireless systems in large facilities or when securing a number of outside buildings that are remote from each other, repeaters and multiple receivers are sometimes used, as well as external antennas.

To learn more about external antennas and the addition of a receiver or two, ask the manufacturer of the equipment your firm uses. Where some wireless equipment manufacturers have them, others may not.

Transmission Frequency Helps Determine Distance and Reliability

The radio frequency of the intended short-range wireless system is also important. The frequencies used by short-range wireless equipment manufacturers fall under Part 15 of the FCC Rules and Regulations. This means the FCC does not allocate these frequencies to specific manufacturers or users, thus reducing the cost of a wireless system.

Each band of radio frequencies has its pros and cons. For example, the high-frequency (HF) band, 3MHz to 30MHz, has a relatively long wavelength and, thus, is more suited to longrange transmissions.

The drawback to this particular frequency band, however, is that it requires relatively large antennas for the receiver and its associated transmitters. Also, it precludes the use of frequency modulation (FM) technology, which is somewhat immune to many sources of EMI. Amplitude modulation (AM) is the most common technology used in this frequency band, but it’s more prone to EMI, such as electrical storms, motor noise and general line noise from the public electric bus.

Historically, the frequencies most used in today’s short-range wireless security include the very-high frequency (VHF) and ultra-high frequency (UHF) bands.

The VHF band, 30MHz to 300MHz, is essentially a compromise between the low and high frequency bands, and is characterized by a relatively long transmission range and a reasonably sized antenna. Another plus associated with the VHF band is the use of FM. However, the number of frequencies available within this band with regard to the security industry is relatively small. For this reason, UHF is used predominantly in the wireless market.

The UHF band, 300MHz to 3GHz, is where the majority of wireless security systems reside at this time. This is because UHF offers a compromise in signal range and the antennas are relatively small in a physical sense. Penetration of building materials also is fairly good in most cases.

Explaining 900MHz Band and Spread- Spectrum Technology

Spread spectrum falls into the UHF band, between 890MHz to 902MHz and 928MHz to 952 MHz. Although it’s long been said that spread spectrum will take over the market, it has failed to do so. However, because spread spectrum offers greater signal redundancy, this technology is finding its uses in other areas of security (see sidebar on wireless access).

This type of wireless system uses wide-band transmissions when sending information. The advantage of spread spectrum is it creates a noise-like signal that is difficult to discern and equally difficult to decrypt. By its very nature, the signal bandwidth is a lot larger than the bandwidth of the information that it carries. There are two basic types of spread spectrum in use today: frequency hopping and direct sequencing.

“We use direct sequence spread spectrum in the 902MHz to 928MHz range. The advantage to our technology is the dealer or end user can choose the subchannel on which it operates,” says Lester La Pierre, marketing manager with Ingersoll Rand Security Technologies (IR) of Chicago. “We use dynamic channel switching where the system will jump from one channel to another.” This is done to avoid interference with other radio sources that happen to be using the same frequency.

Although spread-spectrum technology has its advantages, the 928MHz to 953MHz band it utilizes is not as effective in the outdoors as it is indoors. This frequency band also works well in heavy urban settings where conventional building materials are commonly used and outdoor foliage minimal. This is because attenuation of radio signals due to foliage at this frequency range is greater than when using lower frequencies. This can be a problem where a client wants to link a number of outdoor buildings.

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