There are many reasons that a signal might be degraded. The connection between the antenna and the receiver and/or the transmitter might not be tight or it has become corroded. The transmitter and receiver electronics can degrade over time. Metal objects and building construction can degrade and reflect the signal. The reflected signals can interact with the actual desired signal, causing a signal loss at the receiver.
Interference can also come from power lines, pumps, transformers and motors that produce radiated electromagnetic interference (EMI). It is important to verify that the equipment will provide the needed distance in your particular application.
The antenna used can also impact the operation of a wireless system. There are two basic types of antennas: directional and omni-directional. A directional antenna receives or transmits in a single direction, thus requiring a line-of-sight, while the omni-directional antenna will transmit or receive from any direction.
To help clarify the difference, consider this example: A security control center operator cannot dispatch response instructions to the security officer in a remote building several miles away. The remote building is in a low spot in the terrain, but the officers can hear the control center radio from the remote building's parking lot. To solve the problem, a directional antenna is placed on the roof of the remote building pointed toward the security control center-transmitting antenna. To relay the radio signal inside the remote building, an omni-directional antenna is placed inside.
The two antennas can be connected together via coax or a bi-directional amplifier can be added between the two antennas. If only coax is used, the approach is a passive antenna system. If an amplifier is used, it is best to incorporate a notch filter to pass only the radio frequencies used by the company and an FCC license may be required, depending upon power levels transmitted.
Configuring the System
Wireless security equipment is available in two basic configurations. One form uses a separate transmitter and receiver. When a wireless application is required to operate on an existing security product, such as a badge reader for access control, the security product is connected to a separate transmitter. In this example, to allow the access control capability to operate in a wireless application, a transmitter and a receiver are necessary. The transmitter is connected to the reader, enabling badge data to be sent wirelessly to the receiver located at the access control panel.
The other approach has a transmitter that is an integral part of the actual security product, with the receiver separated or incorporated into another security product. For example, there are many wireless CCTV cameras that have a built-in transmitter. The receiver could be physically separate and send the CCTV video signal to a switcher or directly to a video monitor. A combined wireless camera/transmitter and a monitor/receiver are often sold for covert security applications.
Wireless options in security systems are endless. Any link in the security system can be changed from hardwire to wireless. The primary reason for incorporating wireless technology is convenience, flexibility and cost. In this article we are considering wireless communication to be provided by RF technology. If a CCTV camera needs to be mounted in an existing parking lot, wireless can be a very cost effective and an easy-to-install solution. Otherwise, the parking lot must be dug up or tunneled under to allow wires to be installed to obtain the video signal from the camera.
If temporary CCTV cameras, badge readers, motion detectors, etc., need to be installed, wireless technology adds placement flexibility, ease of installation and rapid deployment. In situations where esthetics and access for limited physical wiring exists, wireless is an excellent choice.
Wireless applications allow links to exist in any security system to provide conductivity where a hard-wired link is cumbersome, cost-prohibitive or impractical. Many hard-wired systems will become hybrid security systems (hardwire and wireless), as it expands. The expansion will often require wireless technology for the system enhancements where hardwiring a security application is not the best solution.