What are common RF noise sources?
In response to the Federal Communications Commission’s inquiry on whether it should study changes in the radio frequency noise floor, a number of commenters identified common sources of RF noise and interference that they encounter. The most common RF noise sources include:
Harmful LED lamp interference. “The solution in most cases is to replace the lamp with a different brand that does not cause harmful interference. … The bottom line is that the interference is strong enough to affect a 700/800 MHz cellular base station,” said Pericle Engineering in its FCC comment.
Large [electronic] display signs. “Two examples are the Fashion Show Mall on the Las Vegas Strip and several gambling casinos in Black Hawk, CO,” said Pericle. “The culprits here are the switching DC power supplies powering the LED lamps. Because these signs have large metal backings, they act as a reflector and focus the interfering power in one direction. At 800 MHz, harmful interference has been measured to cell sites within 100 feet of display signs while at VHF, harmful interference was measured as far as 900 feet from display signs.”
Wi-Fi access points, which can cause interference in the 2.3 GHz band where AT&T operates, according to Pericle. The company cites an instance in which Wi-Fi radios “were manufactured for use in the UK, but somehow ended up in the U.S.” and cause interference. Pericle also mentioned “many cases of 2.4 GHz [bi-directional amplifiers] installed improperly or not adequately shielded, causing interference as far away as 849 MHz.
Passive intermodulation (PIM) effects from “corroded joints, dissimilar metals, gaps in metal fabrication, metal fasteners and sharp edges or corners. Passive intermodulation is a problem caused primarily by poor installation practice or poor choice of materials. In many cases, materials on the rooftop in front of the base station panel antenna cause PIM,” said Pericle.
In the indoor environment, Pericle said that noise-like interference can come from “fluorescent light ballasts, LED lamps, cable TV set top boxes, and a variety of consumer electronics devices.”Â
CTIA said in its comment on the noise floor inquiry that “several different kinds of devices, including incidental radiators and unintentional radiators, may contribute to the noise floor by generating unwanted RF emissions. Incidental radiators, like electric motors, light dimmers, and power supplies, for example, are not designed to generate or emit RF energy, but do so as a result of their operation. Unintentional radiators, on the other hand, are designed to generate RF energy for internal use or send RF signals by conduction, but are not intended to emit RF energy. Examples of unintentional radiators include high efficiency lights, computers, and garage door receivers.”
Join RCR Wireless News for our upcoming webinar on monitoring, testing and analyzing spectrum on August 16th at 2 p.m. ET. A special report on the topic will be available for download that day.Â
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