Putting a Face on Theatre
Wireless everything. Or so it seems. It almost seems quaint to connect something with wire these days. Our WiFi computers, tablets, & cell phones; DMX and AV control connections; microphones, IEM's, and speakers, too. Along with great convenience comes great interference. There is only so much useable space in the radio frequency spectrum, and it seems to be getting claimed or allocated at an alarming rate.
Back in the day (the analog television day), low power TV broadcasters left holes allover the TV broadcast spectrum, and even the high-powered stations had a few sweet spots in a 6MHz slot that you could sneak in several wireless mic channels between the audio and the video carriers. Then came digital TV, and a 6MHz television channel suddenly had it's channel crammed with digital hash and static.
Oh, but that wasn't good enough. Then the FCC (Federal Communications Commission) decided to lop-off all those pesky UHF stations above Channel 51 (698MHz and above). Poof! MORE bandwidth gone.
But let's not forget about the insatiable need for more digital bandwidth for God knows what. The unused spaces in the TV spectrum are also to be used for various content delivery systems. POOF!, the rest of the spectrum is now unpredictable. Where are we to find a slice of heaven that we might use for our own production needs?
Well, in a manner of speaking, the FCC did listen to the rants of raves of their spectrum-loving constituents. They came-up with a plan that requires us 'average Joe' non-professional wireless mic users to carve-out a slice of the pie. But the burden of doing so is on each and every one of us. It doesn't happen automatically. It requires some doing on our part.
The Federal Communications Commission is taking its unlicensed microphone registration system nationwide and authorizing the activation of white-space databases. The mic registration system enables qualifying major venues to register in TV white-space databases for interference protection from other unlicensed devices. The mic system was beta launched in September by the FCC’s Office of Engineering and Technology on the Eastern Seaboard.
The databases serve as a repository of unoccupied frequencies in the 54-698 MHz TV band. Consumer unlicensed devices, once they are deployed, will have to communicate with these databases in order to operate. Licensed operations register in the databases to indicate what frequencies they occupy. These include TV stations, fixed broadcast auxiliary service links, TV translator, and cable headend receive sites, land-mobile operations, offshore radio telephone service, certain radio astronomy operations, and certain wireless mic venue sites.
Unlicensed wireless mic venues must request FCC approval to register in one of the databases 30 days in advance of an event. The system had been previously beta-tested along the East coast and the OET (FCC's Office of Engineering and Technology) said East Coast venues now had sufficient time to “become aware of the availability of the registration system to accommodate the 30-day processing cycle. We therefore conclude that it is now appropriate to allow the TV white-space database systems to provide service to devices located in that region.”
What this means to you: If you don't register your venue's devices at least 30 days prior to a show, then you will have no grounds to complain if some other wireless signal source interferes with your event. To register your gear go here: https://wireless2.fcc.gov/UlsEntry/licManager/login.jsp
Harsh. No wonder so many wireless microphone manufacturers have started developing and selling products that work in the 900MHz and 2.4GHz bands. Good luck with that. These are unregulated bands that may, or may not be useful to you.
What you can do: Well, the obvious thing is to use wire in lieu of wireless wherever possible. After that, the next solution lies in better Radio Frequency engineering practices. That means boning-up on the knowledge you need to use your gear effectively. Knowledge is power.
The Not-So-Obvious: Turn-down the RF (radio frequency) power. Yes, that seem counter-intuitive. RF is not like loudspeakers. Louder is not better. More power means that your receivers and antennas may have to work harder, and frequently unsuccessfully, to discriminate between signals. Use what you need to get a signal, and no more.
Focusing on your target: Just like a cardioid microphone rejects sound from off-axis, a directional antenna is more sensitive in one direction and less sensitive in others. Replacing omni-directional 'whip' antennas with professional class directional antennas can help to keep interfering signals out of your system. Pay attention to both spatial diversity and phase diversity when deploying antennas, and place them high enough that you aren't trying to pick-up radio signals that are blocked by bodies (we 'carbon-based life forms' are 98% water, and water is RF's enemy). Also keep antennas away from other metal objects (conduits, metal wall studs, plumbing pipes, rebar, steel cabinets, metal door and widow frames, other antennas, and lay-in ceiling tile T-grid). When they are too close to other metal objects, the radio frequency reflection from that other item may create a null (low energy or signal cancellation) point right at the frequency you are trying to utilize.
It's a brave new world, welcome to it.