By Patrick Stox
Where does radio frequency interference come from?
Radio frequency interference (RFI) can originate from a wide number of sources-from natural phenomena such as lightning and sun spots to a host of man-made generators. Typically, those trying to guard from interfering signals are concerned more with man-made sources. These sources of RF interference include high power broadcast systems like AM/FM radio and TV transmitters and a multitude of other communications systems, including 2-way radio, paging, mobile telephone, and emergency and public safety communications systems. There are also unintentional emitters that are sometimes a source of RFI. Power lines, transformers, medical equipment, electro-mechanical switches and many others-produce RF energy as they perform their functions. Still other sources of radio frequency interference are microwave ovens, cordless phones, Bluetooth devices, wireless video cameras, outdoor microwave links, wireless game controllers, Zigbee devices, fluorescent lights, WiMAX, and so on.
What problems are caused by RF interference?
The impact of RFI depends on what you are doing. Radio frequency emissions are very carefully guarded around explosives, for instance, because it can cause detonation! In common communications systems, radio frequency interference degrades or completely disrupts signal quality, overall system performance, connectivity between two or more stations, and system carrying capacity. Simply put, RFI can make a RF based system totally non-functional, it can cause an intrusion of music, conversation or noise, or it can create problems in system performance that are extremely difficult to trace back to the radio frequency interference source.
What are the benefits of RF shielding?
When properly designed and installed in accordance with the specific requirement at hand, facility RF shielding can effectively eliminate the impact of RFI on systems that are contained within the shield. The proper shield serves as an impermeable barrier to the incoming radiated radio frequency that would otherwise create interference. It allows for the safe and proper operation of otherwise sensitive equipment in high RF environments. In some cases, the RF is high enough to be considered a health hazard, in which case a RF shield would not only protect the equipment but also the people required to be at that location, as well.
How is RF shielding installed?
The RF shielding materials and components (a shielding system) must be installed in accordance with the procedures that are particular to the facility being shielded, the degree of shielding effectiveness to be achieved, the special materials being employed, and the environmental conditions in which the system will be operating. In short, the installation should be performed by a competent and experienced shielding professional with the necessary tools and RF measuring equipment available to assure a thorough and long-lasting shield.
What RF levels will impact equipment operations?
This is truly a case-by-case issue. There are no set regulations defining a single RF level that will cause radio frequency interference. Among other things, it depends on the sensitivity of the equipment under consideration, or how low an RFI signal can be in the presence of the equipment and cause problems. Also, equipment can be particularly sensitive to very low signal levels of one frequency and yet quite immune to high signal levels of another frequency-so frequency is an important factor. Some electronic system components are internally shielded and have a very high immunity to interference. But generally, most equipment has not been so engineered.
Electronic equipment is often tested to RFI sensitivity by the manufacturer, but the results are not always easily obtainable. Communications facilities are often studied for the potential for radio frequency interference conditions, and unless there are specific threshold limits that are known beforehand, we use 1 Volt/meter as a point of concern. We do realize, however, that some systems are rendered incapacitated by radio frequency interference levels of more than one hundred times smaller values.
What are some typical manifestations of shielding problems in communications systems?
In a wireless system Electromagnetic Interference (EMI) often does not cause problems in providing quality reception but it does cause problems in providing quality service. Typically a wireless operator will raise or lower tower height, add ratios or change system configurations in an attempt to eliminate service problems. These approaches do not work when electromagnetic interference occurs. Well-designed shielding systems provide cost-effective and lasting solutions.
LBA Group is a leading source in RFI shielding and EMI shielding.