By: Carol R. Emmens
Last December Times Square was packed with people waiting to hear the World AIDS Day concert. But the organizers were worried; they were not sure the microphones were going to work – the airwaves were as jammed as the Square – they needed open frequencies. True, frequency congestion is at its worst in New York City but it is a nationwide problem and we have all heard the results: buzzing, signal drop out or static.
Radio frequency interference (RFI) is generally caused by a device “listening” for one signal at a specific frequency and “hearing”, and therefore transmitting, a different one. The growing use of wireless microphones and the proliferation of wireless devices has caused already congested airwave channels to become overloaded. As a result, RFI and intermodulation distortion (IMD) occur because the signals cross when there are too many devises in a limited spectrum. And the problems are only going to get worse.
In 2010 the Federal Communications Commission prohibited the operation of wireless microphones and similar devises on the 700 MHz Band and now it is planning to auction or “repurpose” a portion of the TV band spectrum – the 600 MHz Band, possibly the upper 500 MHz band and two ENG channels (channels used exclusively for electronic news gathering). As the space decreases for wireless microphone users, congestion on the remaining UHF TV band will increase as early as 2016. The transition to fewer frequencies will continue until mid-2019. It is possible that using your current frequency will be illegal in the future.
Microphone operation is classified as licensed and unlicensed; typically professional sports and entertainment producers are licensed and corporations, theaters, houses of worship, and educational institutions are unlicensed. The one bright note (no pun intended) is that the FCC is going to allow more licenses for professionals who regularly use 50 or more devices at major events or productions. If you qualify, begin the application process now. To do so, visit the FCC website at this link:
Most wireless users will have to deal with the interference on their own and that can waste a lot of time and effort. To ensure that your wireless audio and video systems will be as reliable as possible, it is necessary to analyze your environment using a diagnostic tool designed to find usable frequencies in your location such as RF Venue’s Clear Waves software.
Clear Waves helps you detect the presence of the RF transmissions that are the source of interference. It offers RF spectrum analysis, intermodulation analysis and automatic charting of open RF frequencies known as white space. It can be used to adjust wireless microphones, in-ear monitors, security, access control and more. It is sometimes possible to eliminate the source of the “noise”. More often it will be best to simply change the wireless frequency.
The software Clear Waves runs on a Signal Hound or RF Explorer which connects to a PC via a USB cable and displays graphs showing the optimal channel assignments in your area. Clear Waves performs the RF spectrum scan and intermodulation analysis in real time; you can specify up to 160 different frequencies to monitor to allow users to coordinate channel assignments for wireless transmitters and troubleshoot RF interference. It is necessary for frequency coordination to be accurate and fast, so in short, it can save your performance or speech.
No computer at the live event? Combine Clear Waves with the RF Explorer RackPRO, which has a front panel LCD and rotary marker. For live applications, it goes wherever a portable rack goes. It can also be integrated in installed audiovisual equipment racks or sound booths.
Now is the time to review your wireless systems and their use. It is necessary to budget and to prepare, to identify current or potential problems. If you decide to purchase new wireless microphones, purchase those that use frequencies below 600 MHz.
Wireless audio and video systems are often subject to additional problems such as signal drop out, poor choice of equipment and/or its location; for example, the antenna is top quality but it is not installed in the best location. For a full analysis of your systems and recommendations or a professional installation of your audiovisual or audio systems, rely on Zeo Systems. Zeo has just launched a partnership with RF Venue for access to the full line of their products. So, whether you have a temporary or permanent wireless need, Zeo Systems or their sister division Zeo Rental/Retail can assist you in solving it.
Wondering how that concert came out? It was a success. Bruce Springsteen and Chris Martin filled in for Bono, who was seriously injured in a bike accident in Central Park and the audio crew worked feverishly throughout the concert to find available frequencies to use in real-time.