Tech Talk: Being Receptive to Wireless Video

Wireless technology can be highly beneficial both in spanning hard-to-reach areas and realizing substantial cost savings as an alternative to trenching and long cable runs. Find out some of the basics you need to successfully deploy wireless video surveillance solutions.

Wireless video presents many advantages compared to projects that call for trenching and cable runs to perimeter locations. This month, we are going to look at some of the latest wireless video technologies, plus review important terms and commentary from experts in the field.

Applying wireless video systems can involve a significant educational curve. Given the demand on today’s radio spectrum we must have a better understanding of utilizing this critical medium. We’ll cover some key bases to help get you started or nudge you further along on your path to delivering and profiting from these technologies and associated services.

Picking Up on Antenna Selection

Let’s get started with important info about wireless antenna properties (courtesy WLAN Antennas; wlanantennas.com):

Front-to-back ratio (F/B)  — This is the ratio (in dB) between the forward gain to the gain off the rear of the wireless antenna. The forward gain is the peak gain on the main lobe of the wireless antenna.

Antenna polarization — Most point-to-multipoint (PtMP) WLAN systems use V-Pol (vertical polarization). This allows the use of inexpensive vertical, omnidirectional wireless antennas. Higher density areas are beginning to use more H-Pol (horizontal polarization) antennas for PtMP.

Circular polarization  — Normally, a wireless LAN or wireless ISP has a set of channels, or frequency sets, that are either vertically or horizontally polarized, or some of each. Since the circular polarized (CP) wireless antenna responds (theoretically) equally to either polarization at a level of 3dB down from maximum signal, there is not much reason to add CP to a system that already has vertical, horizontal or both polarizations.

Voltage standing wave ratio (VSWR)  —  This is the ratio of the maximum/minimum values of a standing wave pattern along a transmission line to which a load is connected. VSWR values range from one (matched load) to infinity for a short or an open load. For most WLAN antennas the maximum acceptable VSWR value is 2.0, and a VSWR of 1.5 or less is excellent.

Another important term used in antenna specifications is dB isotropic (dBi). This is the gain an antenna has over a theoretical isotropic (point source) antenna. Unfortunately, an isotropic antenna cannot be made in the real world, but it is useful for calculating theoretical fade and system operating margins. The gain of microwave antennas (above 1GHz) is generally given in dBi. A dipole antenna (rated as dBd) has 2.15dB gain over a 0dBi antenna. So if an antenna gain is given in dBd, not dBi, add 2.15 to it to get the dBi rating, For example, if an omni antenna has 5dBd gain, it would have 5 + 2.15 = 7.15dBi gain. If an antenna gain is only specified in dB from a manufacturer, ask if it is dBi or dBd. If they cannot tell you the difference consider another vendor!

Tech Talk Tip: Every time you double (or halve) the distance from the transmitter to the receiver, the signal level is lowered (or increased) by 6dB.

Experts Impart Wireless Wisdom

Understanding that the nuances of wireless video can be challenging, I decided to query some experienced experts for their comments. I posed this question to them: To some integrators the transition to wireless video can have unforeseen pitfalls. From your experience what would you say are the three most common problem areas with reference to specifying or installing? Their responses follow:

Todd Flowers, president, Surveillance Systems Integration (SSI): — First is using the right frequency. Choosing the right frequency for the environment is critical but can be hindered by limited channel availability and bandwidth. Finding a good balance requires knowing what other wireless frequencies are being used in the area and which open channels can be used in a LOS [line-of-sight] or NLOS [non-line-of-sight] situation. A spectrum analysis is always highly recommended.  

Second is having the right amount of bandwidth for the application. Since gigabit wireless links are expensive, many wireless video networks have to settle for lower bandwidth solutions. A few megapixel cameras can easily choke a 200Mbps MIMO link if you aren’t careful with your system design. Be mindful of additional bandwidth utilization from replicated video streams and archiving services if the NVR and client workstations are also connecting to the network wirelessly. Mitigating bandwidth consumption is necessary to keep the system functional/usable and can include event/motion recording, reduced frame rates and decreased resolution.

Third is having a predictable impact of the wireless network when connecting to a client network. Despite the fact that many wireless and mesh network manufacturers automate network management and keep it invisible from the camera network, an integrator should do their homework and verify that the wireless network they implement will not conflict with any other network equipment it may interface with. Bench testing prior to the installation can identify issues if the wireless routers have problems propagating protocols or passing certain types of traffic to and from the wired network.

Tom Sharples, president, Qorvus Systems: — First would be system design and/or layout by unqualified personnel. You have to know what you are doing both with respect to wireless and IP camera technology and how that feeds into the choice of VMS and the customer requirements. My company, Qorvus, makes that much easier for newbie integrators by designing and preconfiguring the entire system up to and including VMS if needed, prior to shipment. It arrives as close to plug-and-play as possible.

Second is incorrect antenna selection and/or installation. This is caused by lack of understanding of antenna patterns and coverage optimization techniques.

Lastly would be incorrect installation techniques. Poor or no waterproofing of antenna cable ends/NEMA box feed-throughs, missing lightning protection, no or poor grounding, improper Ethernet termination, inappropriate use of unshielded Ethernet cables outdoors, etc.

Kevin Busto, consulting electronics engineer & sales agent, Vega Technology Group LLC, offers this advice: “Of the systems we have designed and built, the most reliable have been the 900MHz direct connection systems. Using dipole and yagi antennas, we have been able to transmit/receive video and sound at up to five miles line of sight on the ground, 10 miles over water, 15 miles in flight.”

Bob Dolph has served in various technical management and advisory positions in the security industry for 30+ years. To share tips and installation questions, E-mail Bob at [email protected]. Check out his Tech Shack blog at securitysales.com/blog.

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About the Author

Bob Dolph
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Bob is currently a Security Sales & Integration "Tech Talk" columnist and a contributing technical writer. Bob installed his first DIY home intercom system at the age of 13, and formally started his technology career as a Navy communication electronics technician during the Vietnam War. He then attended the Milwaukee School of Engineering and went on to complete a Security Management program at Milwaukee Area Technical College. Since 1976, Bob has served in a variety of technical, training and project management positions with organizations such ADT, Rollins, National Guardian, Lockheed Martin, American Alarm Supply, Sonitrol and Ingersoll Rand. Early in his career, Bob started and operated his own alarm dealership. He has also served as treasurer of the Wisconsin Burglar and Fire Alarm Association and on Security Industry Association (SIA) standards committees. Bob also provides media and training consulting to the security industry.

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