Improving Wireless Range Performance December 08, 2015

Improving Wireless Range

Improving Wireless Range Performance 

Given the proliferation of wireless usage at large, getting proper wireless range performance has become increasingly difficult. Additionally, myths and lore have been spread into the law enforcement community about what works and what doesn’t. This article seeks to cut the clutter, is key for those starting from scratch and will give easy to implement tactics to those who already own a wireless system.


1. Get the freq’n right Freq!
All the bells and whistles in world are worthless unless your gear is on the right frequency. So from square one, you need to determine which frequency is best for you. A great first step is to figure what frequencies to avoid.

For example a constant source of frustration is WiFi, found in nearly every hotel, home and now it’s creeping into cars and personal electronics. The common WiFi types of 802.11 B/G/N crowd the 2.4GHz frequency range of 2,412MHz to 2,484MHz which also happens to be a favorite frequency range used for popular video transmitters. When the two technologies collide, both suffer. Typically the WiFi routers, AP’s, etc…are knocked out or reset. If analog video transmitters are used, symmetrical lines appear on screen polluting useable video. Digital gear in this scenario continues to have great video but experience very poor range. Other common sources of interference are cellular and ham radio. Worthwhile noting, operating non-compliant devices on cellular and ham bands could put your agency in jeopardy of FCC fines.


An excellent tactic that has proven successful is to compete with interference such as WiFi and GSM, but instead take advantage of it. There are a number of great devices that provide video, audio, telemetry transmission via WiFi and GSM.


Besides interference sources common nationwide, you may have unique sources of interference locally as a result of an industrial complex, military facility, airport, etc… Those anomalies are difficult to identify with spectrum analyzers or simply testing the gear onsite. With local issues in play, products that allow you to make slight adjustments to the frequencies are recommended. Getting frequency selectable gear also allows you to quickly adapt to other locations.

Aside from interference, there are attributes about certain frequency ranges that make them more suited for particular applications. In general, the higher the frequency the better it is for static, line-of-sight applications. Lower frequencies tend to be more ideal for mobile applications and generally, outperform higher frequencies in non-line-of-sight circumstances.

There is nothing worse than laying down thousands of precious budget dollars only to find it’s worthless because of interference. So regardless of the gear, always check to make sure your vendor has a gracious exchange program and can provide custom units to match your need.

2. Get the right power
Theoretically, any transmission could travel indefinatefly….so long as it doesn’t encounter any resistance such as buildings, cars, people, furniture…you know!...all the stuff that’s typically 6 feet and below. We’ll discuss a few methods to negotiate obstructions later but alternatively, you can punch right threw them if you have enough power.

To give us some kind of benchmark to work with, let’s take for example a 10mW (milliwatt) transmitter with a high gain receiver. The range potential for such a device can be ½ mile line of sight but perhaps only 300’ or see through residential construction. To double the range through residential construction, we’ll need to increase power 8 to 16-fold. So for instance, using a 100mW transmitter in the same scenario, we could reasonably expect 600’ of range.

Beyond factoring the raw power of the transmitter, other factors that affect performance include bandwidth and encryption. When selecting transmitters, it’s recommended to purchase one with the smallest bandwidth possible to achieve evidence quality. The more bandwidth, the more power that will be required for transmission range. Likewise, transmitters should be selected for the lowest level of encryption that meets mission requirements…the more encryption, the less range you’ll get.

In my opinion, a technology worth avoiding unless absolutely necessary is spread spectrum technology which has a cool sounding name but produces poor range results. Hence the name, SS gear spreads power over a spectrum of frequencies. To be fair, spread spectrum technology is an excellent choice to disperse information and increase interception security.

In short, when it comes to choosing a transmitter, get the most power your wallet and batteries can afford, get the smallest bandwidth allowable, and the lowest or possible no encryption to meet mission needs.

3. Go Digital
Based on my hands on experience, wireless digital gear in general produces greater range potential than that of comparable analog devices. The primary reason for this is that digital devices tend to more immune to interference.

Additionally, some digital technologies such as COFDM harnesses mutlipathing (RF reflections) that may bounce off of buildings, vehicles, terrain, etc…that work to enhance overall range performance. While on the topic of COFDM, I should mention that ODFM does not have the same capabilities and is only recommended for static, line-of-sight applications.

As mentioned earlier, some digital devices are designed to coexist with others. WiFi based transmitters and GSM transmitters scan the environment and establish operation on a friendly channel thus minimizing worries of interference. This attribute of GSM and WiFi devices can also be used to confusing counter-surveillance measures as it’s masked with other benign transmissions.

4. Get the antenna right
With most transmitters, there are little to know options for antennas. Do to the nature of use, the antennas are small and often affixed. On the other hand, the receiver is quite a different story.


A. Proper tuning
Getting an antenna that is tuned to the proper frequency is critically important to the degree that it outweighs gain in affecting range performance. For example, in a recent field test we were operating a transmitter on 389MHz. Someone on the team accidently had a 3dB 140 to 175MHz antenna connected to the receiver. As a result, the range was a poor ½ mile. Once the mistake was recognized, we connected a 0dB gain antenna tuned to 389MHz and achieved a range of over 2 miles….that made a huge difference!

Related to antenna tuning is the subject of wideband vs. narrowband antennas. Wideband antennas are an attempt to make antennas capable of receiving transmissions over a wide spectrum of frequencies i.e. a scanner antenna that works from 30MHz to 3000MHz. Wide band antennas are excellent choice if you are conducting counter-surveillance or if simply need the agility of working with multiple different frequencies. The problem with wideband antennas that they tend to be low gain. Narrowband antennas are designed to work on small portion of the spectrum i.e. 2400MHz to 2450MHz and are typically much high in gain and work to a small degree as a band pass filter (filtering out unwanted RF junk!)


B. High Gain
As implied, the gain of antenna makes a significant difference in range performance and higher the gain the more range you’ll get. It’s difficult to give concrete answers as to how much more range will be achieved, but here is a great rule of thumb: If you obtain a weak and barely useable signal with a 0dB rubber whip antenna, when a high gain antenna (say 8dB) is applied, you should have a useable to perhaps even a perfect signal.


C. Mounting location
The pinnacle location for both transmitter and receiver antennas is as high as possible in effort to avoid obstructions and to avoid the fresnal zone effect that occurs with being too close to the ground. Given covert scenarios your choices on how you mount the transmitter antenna may be slim to none. However, in many missions there is a lot more leeway on the receive side.

For discussion, let’s take a look at the common deployment of a wireless body-worn device used in a buy/bust op. The transmitter antenna of course should be placed on the body to where it will have the best line-of-sight to the receiver. Where the mission allows, the receive side should employ a high gain antenna that is externally mounted to the monitoring vehicle. By having the antenna externally mounted, you will avoid the major obstruction of the vehicle itself and increase the elevation, minimizing Fresnel zone issues.

D. Antenna cabling
Cabling between the antenna and device (RX or TX), is often overlooked item. The old adage you get what you pay for rings true…don’t skimp by getting the cheap stuff or repurposed cable.

At a bare minimum, the cable should have a 50 OHM rating to properly work with RF equipment. Coaxial cable used for video equipment is made with 75OHM rating. Common cable used for RF connection is RG58 and RG174.

Antenna cabling should have the best shielding possible to prevent interference from entering into the signal and precious, power from escaping. When installed, care should be given to ensure the cable doesn’t get bent (curved bends are OK) and become pinched from doors, windows, trunk lids, etc…

Another important performance factor is the length of the antenna cable, it should be as short as possible. Even with the best cable available, there will be some level as loss and the longer the cable, the more loss will occur. Most vendors should be able to cut and terminate your cable to length. If not, it’s worth investing in some good tools so that you can do it yourself.

5. Receiver
The industry gives a lot of attention to transmitter features and performance but most neglect to consider RX performance. After all, a great receiver can make a substandard transmitter perform like a champ.

When comparing receivers, the primary factor in range performance is dB gain. Like antennas, the higher the gain the more range you’ll experience. Another expression of RX gain is dBm and when its applied, the lower the number the better. For example, a receiver with a -102dBm will produce greater range potential than a receiver having a -95dBm gain.

Thanks for reading! If you have any comments or suggestions about future topics that should be explored, please drop me a line. Also, if you need assistance in finding the right system for you agency, please contact me directly at jlahmann@maxsur.com


Thanks again,

 

Jake


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