Just the Facts, Ma’am: Key Considerations for Selecting and Installing Antennas for Public Safety Vehicles

Adam Alevy, Vice President of Technology,
Laird’s Infrastructure Antenna Systems Group

Some people get nutty about Star Wars collectibles. Some people are bonkers for the Boston Red Sox. Others lose themselves in old stamps from countries that don’t even exist anymore. That is all well and good, but I geek out when it comes to old radio and antenna technology, especially the wireless systems that were in the police cars from back when I was growing up. All the better if they resemble the ones from the cop shows with chase scenes that were all the rage on tv then—on all three channels being broadcast at the time! Websites like this one about public safety radios from that period are essentially a virtual museum of wireless technology from the 60′s, 70′s and 80′s. It was a simpler time for sure: One police car, one radio and one antenna.

Those old Dumonts and Motorolas are from a time when police officers and other first responders had a single link to dispatch and the rest of the force, and that link was essentially cut if they took more than a step or two away from their vehicle. Today, police vehicles, fire vehicles, ambulances and other public safety vehicles are true mobile communications centers in ways that were unthinkable not long ago. All of that technology helps public safety professionals stay better connected, respond faster, serve the public better, and stay safer. But those connected devices require a variety of wireless technologies that is growing more complex each day because of factors such as wearable technology, greater bandwidth needs for onboard applications, and—most significantly—the buildout of FirstNet and First-Net-type public LTE networks.

GenericLTEAs background for readers who are not directly involved in government wireless projects, FirstNet (sometimes referred to as the National Public Safety Broadband Network) is envisioned as a series of public cell networks implemented at the county level to create dedicated wireless connectivity to public safety entities across the entire country. These networks are separate from the commercial networks in order to ensure that police, fire and other first responders have reliable communications at all times, including during emergencies when commercial networks are often overwhelmed by cell phone traffic from citizens. These networks are based on the LTE wireless protocol, with the ability to support 4G and possibly support 5G traffic in the future. Originally envisioned in the wake of the September 11th attacks, several counties across the country have implemented official FirstNet networks. Other counties have chosen to opt out of the formal FirstNet program in order to maintain independence and self-determination about how to implement and maintain these networks. Regardless of whether these LTE networks are officially part of FirstNet or separate from that federal program, these public safety-oriented wireless networks are dramatically changing the landscape for the antenna installations on public safety vehicles ranging from patrol cars to fire trucks to EMT units.

So what does all of this mean for the antennas on police cars and other public safety vehicles? These LTE public safety networks operate in the 700 MHz and higher band of frequencies, whereas the majority of current antennas on public safety vehicles are 40 MHz, 150 MHz or 450 MHz—frequencies that are not compatible with newer FirstNet systems. The most common type of antennas currently on public safety vehicles are high-profile whips, which are immediately recognizable from their multiple-foot length and the way they often bob and bounce as vehicles move. The majority of these traditional whips are low-frequency models that operate at 40 MHz, which means they are not compatible with the new FirstNet and FirstNet-style networks being built across the country. For vehicles to be FirstNet-ready—as well as to support the other wireless devices that are so vital to first responder communications—public safety organizations are increasingly making the investment to add more wireless technology that complements or replaces older antennas.

For organizations electing to make these upgrades, there are a number of best practices they should keep in mind in order to make these projects successful. And in tribute to Joe Friday from one of those police shows from long ago, I promise to focus on just the facts:

How Many Holes Do You Want to Punch? – As new devices have made their way into public safety vehicles, the number of antennas poking out of the top of their roofs and trunks have also increased. Each time a new antenna is added, it means a new hole punched into the vehicle and a complex set of additional wiring. Those are major installations that are not only expensive and that take vehicles off the street, but they can also lead to water intrusion issues that are notoriously difficult to mitigate. Even more common are the challenges related to electrical and radio interference as more and more antennas are added to the vehicle. For this reason, public safety organizations may want to strongly consider taking a consolidation approach by implementing contemporary multi-port antennas that have multiple antenna technologies embedded in them, with the tuning built-in to the design of the solution. This can eliminate the need to punch additional holes while also minimizing or eliminating the need for complex tuning by wireless engineers to ensure that all of the antennas are performing to specs. Multi-band antennas are particularly attractive for counties doing FirstNet/LTE implementations because these networks use a combination of LTE for FirstNet applications as well as Wi-Fi, GPS, UHF, VHF and other connectivity.

High-Profile Antennas Can Work…If You Do Them Right – The most easily identifiable high-profile antennas on public safety vehicles are the long whip antennas that are often more than a meter long. These whips are typically low-band VHF that operate at the 40 MHz These high-profile whips can play an important role, but it is critical that these antennas receive a careful custom tuning that is optimized for the exact location where they are mounted as well as for the physical shape and electromagnetic profile of the vehicle. When tuned and mounted properly, these can be excellent solutions for public safety vehicles, with great range and reliability. But when the mounting and tuning is not done properly, the range and reliability can decrease dramatically, undermining connectivity for the user in the process. To illustrate the importance of this, take the example of a sundial, which can be very accurate at telling time when used properly, but its positioning and location have an enormous impact on its accuracy. If you are in Boston locating your sundial in San Francisco, for example, it will function, its accuracy will be thrown off by its positioning on the earth in relation to the sun. Essentially, it is not tuned correctly to tell time in Boston, and the same can be true for antennas.

Low-Profile May Work Best for High-Frequency – Although it is possible to make high-profile antennas work with FirstNet networks, the most natural fit for most public safety vehicles may be low-profile antennas that integrate multiple wireless technologies into their design. These multi-port antennas typically have high-frequency LTE technology as one of their core connectivity technologies, and they use MIMO architecture to allow LTE to perform well alongside multiple other signals such as Wi-Fi, UHF and VHF. The most common designs used for public safety are 4-port or 5-port low profile antennas that are designed and tested as a complete unit, eliminating the complexity of that process when multiple antennas are on the roof or trunk of a vehicle. These next-generation multi-port integrated antennas simply need good grounding from the surface they are attached to (see below for more on this topic), and their MIMO performance is maintained to ensure the ability of each of the technologies to operate according to specs. In this way, low-profile antennas can simplify the process of adding LTE, minimize installation costs, and achieve better performance than multiple separate antennas.

Get Grounded – Low-frequency technologies installed on a vehicle utilize the vehicle as the ground, but the location of the antenna can affect whether or not that ground exists through the surface material or needs to be added by the installer. For example, if the antenna is mounted on a steel surface, that grounding is likely to be provided naturally through the metal in the roof/trunk. Most public safety vehicles have steel surfaces where these antennas would be mounted, but sometimes these surfaces are made of fiberglass instead, which eliminates a natural route for grounding. Ambulances are a good example of this because they often have fiberglass or composite panels that do not provide effective grounding. Public safety organizations should therefore be certain to factor materials/grounding analysis into their implementation plan because incorrect grounding and installation will lead to poor VSWR (aka Return Loss) that negatively impact performance and that can lead to degradation of the radio and other equipment. If the material surrounding the antenna is not suitable to provide grounding, the organization will need to account for the additional work and expense of installing a grounding element to the installation in order to protect their investment.

Test, Test, Test – Even if you take two police cars that look similar, with similar equipment inside and similar antenna installations on the exterior, they are likely to have dramatically different electro-magnetic profiles because even minor differences can lead to very different wireless environments. For example, if one vehicle has a steel roof and another has a fiberglass panel on top, those two differing surfaces will create very different radiation patterns. And even minor differences in the distance between antennas can have similarly significant impacts. How cables are routed inside the vehicle can also have a major effect. And there are many other variables that can play a role as well. For these reasons, organizations should treat each vehicle as its own antenna installation project rather than use a cookie-cutter approach to installations. That is why testing with a network analyzer is so valuable. When done by an experienced wireless engineer, this testing can ensure that antennas are physically located and installed in ways that reduce return loss, address isolation/coupling issues, and achieve the radiation pattern and range that match the project’s target specifications. An experienced RF engineer will also do an analysis with a methodology that factors in the impact of cabling, radio location, and other issues that ensure the testing is thorough and accurate.

Wireless systems for public safety vehicles have clearly come a long way since the days of “Dragnet,” “Starsky and Hutch” and “Hill Street Blues.” We’re a long way from the days of one car, one radio, one antenna. It’s a bit more complicated today, but my hope is that some of the guidance above proves valuable for tackling these projects successfully. I started this article by quoting Detective Joe Friday, but it seems appropriate to wrap up a piece all about public safety with the famous parting words of another famous TV cop, Sergeant Phil Esterhaus: “That’s it. Let’s roll. And hey…let’s be careful out there.”

About the Author:
Adam Alevy is the Vice President of Technology for Laird’s Infrastructure Antenna Systems Group, which provides a full range of antenna solutions that make the world a more wireless place. Alevy has over 30 years of experience designing and managing the development of antennas for telecom, Wi-Fi, and military applications, including radars and satellite communications terminals. He joined Laird in 1998, and has managed Laird’s antenna technology team since 2007. Adam graduated from Northeastern University in Boston with a B.S. in Electrical Engineering.

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