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Police Vehicle Antennas 101

Written by Brad Brewer

In the ever-changing world of mobile computing, fleet managers are faced with getting the right pieces to maximize their wireless computing solutions. One of the critical pieces of that system is the vehicular antenna. Surprisingly, it is one of those parts in the system that often gets overlooked. In reality, the antenna is one of the most vital pieces to the puzzle. An agency may spend huge money on the best laptop, best mounting setup, and best software only to have the entire system weak because they bought the wrong or cheap antenna.

Vehicle antennas started out as big, tall “whips” used mostly for Land Mobile Radio. That was long before both “voice” and “data” were both something we wanted from a vehicle with a computer system. These whip antennas were susceptible to damage in car washes, vandalism, undergrounds, bushes, or any type of external obstruction. They were also designed strictly for a single frequency.

Along came GPS availability and the demand for compact GPS antennas. The military’s GPS research and development also carried over to the data side. As technology advanced, more demand was created with mobile data terminals in vehicles and so did the demand for smaller packaging, better construction, and multiple frequencies in a single housing. The first multi antennas were cellular and GPS in a single housing. That became the now-popular, low-profile “Hockey Puck” antenna.

 

Voice Plus Data

The technology advanced, multiple cellular frequencies and multiple data frequencies were combined in one unit. First generations of these low-profile antennas combined 2G, 3G frequencies usually in the 800 MHz to 2.4 GHz cellular range and included embedded GPS transceivers all in one housing.

As law enforcement moved to computers in vehicles, data connectivity became more important. Simple text transmissions from older Mobile Data Terminals have given way to high-speed data transfer of  text, photographs, mobile video, and other large files. To push WiFi, 4G cellular and GPS through the same docking pass-through, you need more options in your external antennas. The other option is to use a USB connector coming from the same multi-purpose antenna.

 

Antenna Differences

For the most part, the major antenna makers make a decent product. However, there are differences that fleet managers need to know about. From an appearance standpoint, most police antennas look about the same, but they are definitely not. Fleet managers need to determine which mobile technologies they need the antenna to transmit. Then the manufacturer can combine these technologies in one housing for simple installation, be they wireless PC cards (AirCard), rugged trunk modems, embedded wireless in rugged laptops, or wireless mobile access routers (MARs).

Don’t get caught with legacy technology! Fleet managers must make sure to future-proof their agency against the constant technology changes by the cellular carriers. Just because your area of responsibility might still be 3G doesn’t mean you buy a single-purpose 3G antenna. Always purchase the combo antennas that have both 3G and 4G technologies built in. The life span of fleet vehicles can be years and within those years, cellular data technology will advance at a much faster rate.

It is common place to have antennas with multiple voice, data and GPS frequencies all in a single housing. There are three basic types of antennas: omni-directional, semi-directional and highly directional. For mobile data transfer in a moving vehicle, omni-directional, low-profile antennas are clearly the most preferred.

 

Best Ground Plane

The best ground plane location on a moving vehicle is the roof, period. The trunk “can” be used, but it is definitely not the best location. Being mounted higher on the vehicle will allow for less possibility of obstruction or reflection. In policing, lightbars do play a role in how the rooftop is laid out on your vehicles. The standard rule is to place the antennas 15-20 inches to the rear of the lightbar and to separate the voice and data antennas equally to each side of the roof.

In the early days, some agencies would have wireless cellular data transfer through AirCards inserted into their vehicle laptops. The AirCards came with a small 3-inch antenna that stuck out the side of the laptop. Most of the time it worked fine. However, the environment inside of a police vehicle is “RF tight.” The coated, sound-deadened auto glass, metal siding, and insulation all act to shield both radio and cellular data transfer rates.

If that vehicle is in an urban environment with lots of cell towers around and high signal strength, it’s probably all right. But if that same vehicle is moving from urban to rural, then connectivity will be significantly reduced. Moving the antenna to the outside of a vehicle will improve signal strength 5-10 dB, and that is significant.

When buying police vehicle antennas, the quality of the design and manufacturing must always take precedence over price. This is more important than in what country the antenna is built. There many subtle differences in quality that greatly affect communications. Consider antenna body materials. Manufacturers like Antenna Plus use glass-filled polypropolene for all antenna housings. This prevents UV fade or cracking even in extremely sunny areas. With a cheaper antenna made from polycarbonate, you may end up with a yellow antenna on the roof of your white police unit.

 

Technology Changes

The best advice is to educate yourself on the technologies in your area of responsibility. Talk to your IT people and cellular company technicians. Determine what is coming down the road. The latest antenna technology is called MIMO, which stands for Multiple-Input, Multiple-Output.  With a MIMO antenna configuration, you can realize the fastest speeds LTE offers, as the antennas are working simultaneously on both the uplink and downlink. Engineers determined that if you add another antenna, you can significantly increase the transfer rate.

While the newer protocols are the bigger reason speeds have increased, these new antennas enable the peak speeds, and are an important part of the whole setup. In the mobile environment, it is now possible to encroach on data transfer speeds that were once reserved for hardline cable networks. This allows anytime, anywhere data transfer for things like video, mugshots, software updates once reserved for updating only when the vehicles were within range of private or public WiFi.

 

Multiple Antennas & Bandwidth

Since the beginning of radio technology, we have become accustomed to a mobile phone, wireless laptop, or Land Mobile Radio transmitting with a single antenna. This transmission travels through the air and is received by a much larger antenna on a cellular provider’s tower, which in turn rebroadcasts the signal to your intended destination. For transmitting a phone call, this technology is simple and effective. As wireless technology itself continues its increasing demand for faster and more reliable 3G/4G wireless data transfer, more complex methods of transmitting were needed.

Most agencies have been using 3G wireless data for a few years now but the top speeds have been rapidly increasing, starting around 3.6 Mbps for the first series of mobile broadband modems, to 7.2 Mbps around 2007, to 21 Mbps in 2008, to 42 Mbps shortly after, and now 100 Mbps with the 4G LTE introduction in late 2011.

In the theoretical world, the biggest factor in limiting speed is bandwidth. Each phone tower has a given total width of frequencies on which it can transmit, with each person who connects being allocated a small channel of a certain width. This means that each tower has a limited number of vehicles it can service before becoming congested, especially in densely populated urban areas.

As engineers max out the performance, they can from single antenna to single antenna transmission, but they had to approach the problem differently. This is where MIMO comes in to play. Since they cannot improve single antenna air transmission any further, why not increase the number of antennas?

MIMO technology has gained attention in wireless communications because it offers significant increases in data throughput and link range without additional bandwidth or increased transmit power. It achieves this goal by spreading the same total transmit power over the antennas to achieve a gain that improves the spectral efficiency as well improves the link reliability (reduced signal loss or fading). Because of these properties, MIMO is an important part of modern wireless communication standards such as 802.11 (Wi-Fi), 4GLTE, WiMax and HSPA+.

Many of the latest rugged trunk-based modems and mobile access routers now come standard with two cellular/LTE antenna ports, a WiFi port (sometimes two), as well as GPS. Antenna manufacturers have also started to come out with antennas that build all of this into one low-profile housing. 

Antenna Plus has recently come out with the cutting-edge AP-Mobile-Access-Router-MIMO Antenna, which provides the two MIMO Cellular/LTE antennas, two MIMO WiFi, and a GPS antenna all in one low-profile housing. When you consider that in making just the cellular/LTE antenna part, they have to build in frequency ranges for 800/1900 MHz for 3G and then 700/1700/2100 MHz for LTE, it is really amazing that they can do all this in such a small housing. When you are making your antenna choice, it makes sense to go with those who have been in the business for a long time and have demonstrated a commitment to public safety, building in the highest technical standards.

Antenna support is also important; however, 90 percent of all issues or failures in antenna troubleshooting usually end up being the connectors at the end of the coax. Typically, the center conductor gets disconnected from the connector due to poor installation or no strain relief.

Upfit tip: buy the connectors attached by the antenna manufacturer or make sure they are installed with care and connected properly. Equipment downtime is a killer in any profession and even more critical if the front line officer can’t get instant access to mission-critical information to make decisions that often escalate to life-and-death decisions. At that point, it won’t matter what you paid for the antenna, only that you bought the right one for your application.

 

Sergeant Brad Brewer is a 23-year member of the Vancouver Police Department. He sits on the Ford Police Advisory Board and regularly gives presentations at law enforcement conferences on mobile computing, wireless technology and police vehicle ergonomics. He can be reached at sgt1411@gmail.com.


Published in Police Fleet Manager, Jan/Feb 2014

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