I’ve been saying this for a number of years now: Technical Directors—paid and volunteer—are going to need to learn RF coordination. The RF landscape is as hostile as it has ever been, and it’s only going to get worse. Even if you are only using a half-dozen channels of wireless mic’s or IEM’s in your facility, you need to know how to coordinate them. Let’s talk about the why first.
Wireless gear doesn’t automatically play nice with other wireless gear. It takes work, time and careful consideration of frequencies to have more than a few channels in one room at a time. There are a lot of very technical reasons for this but to keep it simple, we’ll distill it down to two main problems. First is interference. When two transmitters are operating on identical or near identical frequencies, they will interfere with each other. The corresponding receivers are going to have trouble figuring out which signal to listen to, and the result will be either no signal out of the receiver (because it was muted) or noise, static, pops and even other signals leaking through.
The second issue is intermodulation. A classic two-to-three intermodulation is when two signals from two transmitters (that might work fine by themselves and with each other) combine to form a third signal that also happens to be the same frequency as another wireless device. This third, created signal will interfere with the legitimate signal just as if it was created from a device directly.
There are other wireless issues that we have to deal with, but most problems come down to those two. Thankfully, while dealing with these issues is important, it’s not impossible. And today, we have better tools than ever to sort it out.
Wireless manufacturers are there to help. The best, first place to start is with the manufacturer of your wireless equipment. They typically offer lists of frequencies that are safe in your area (typically based on the zip code), and are calculated to play nice together. If you have a small number of wireless channels (under 6-8, say), you can usually make things work well by going from this list.
Most modern wireless gear will let you perform a scan and will choose clean channels based on interference in your building. This is also good to do, though I recommend sticking with the channel list as you choose clean channels. If you simply scan on each device, you may well end up with a 2-3 inter mod. Compare the channels chosen with those on the list provided by the manufacturer.
Use software for larger installations. Once you cross the 6-8 channel barrier, you really need to use software to coordinate your frequencies. Again, most manufacturers offer free software to do this. We use a lot of Shure equipment (along with Sennheiser in our ancillary rooms), so I use Wireless Workbench 6.
WWB will let me connect to my UHF-R wireless mic’s, use them as a scanner to scan the room, then build a list of compatible frequencies based on the scan. It can also build lists of compatible frequencies for other company’s equipment (and even consider other rooms as different zones). WWB can also import scans, which is what we did. I asked my Shure rep to stop by one day with an Axient Spectrum Manager to do a full-spectrum scan. Once we had that, I loaded that into WWB and can coordinate frequencies based on what is happening around me (or at least, what was happening that day).
If that fails, pull out the big guns. Companies like Professional Wireless Systems and Kaltman Creations make hardware/software packages that will not only scan the entire spectrum, but also develop lists of compatible frequencies for you. These systems are not inexpensive, but in a large installation (30-40 channels and up) they can be life savers.
I’ve been hearing from a few people who have large installations of 40+ channels who have never done a frequency coordination. They simply scan for a new open channel every time they add another device. As you might expect, this doesn’t work very well. As the system grows, so does the need for proper coordination. If you are really unclear on how to do this, contact the manufacturer. Quite often, they can send a rep your way with the tools needed to get things sorted.
Wireless is hard. If you can wire something, do it. It’s going to get harder as we go. For those cases when you do have to go wireless, make sure everything is coordinated properly and your musicians and pastors—not to mention the congregation—will be a lot happier.