This month, we are going to switch gears from compressors and head into the world of wireless. Next month, we'll return with the second part of the column on compressors that ran last month (FOH, Sept. 2010, page 38).
Okay, let's take a look at some ways to get the most out of your wireless rig. When wireless fails, it's almost an industry standard response for the tech to stare at you with a confused look. With this said, any "Average Joe" just needs some simple setup and operating knowledge to make their basic system reliable night after night.
The main goal in any wireless system is reliability. In a perfect world, one system would not interfere with any other system. From the beginning to the end of the show, you want to see full RF signal strength with no dropouts. The topics discussed in this article can help achieve this goal.
Let's face it – most shows don't have the luxury of a wireless coordinator or someone to scan the room before the show. It's usually the complete opposite: There is no prep, and you're in the middle of a congested wireless area like New York or Vegas. But there are a couple of things that can help you out.
A Freebie
As you may know, there is a free resource out there that anyone can see what frequencies are being used by TV stations. It's on the web from Shure at www.shure.com. You just type in your zip code and it will give you a list of frequencies to avoid. This is always a good starting point when walking into a new location.
Cabling and Antenna Placement
Things like improper cabling, antenna placement and spacing can make or break the system. An improper setup or poorly-placed antenna can make for a bad day.
Say you get to your gig and notice that there are no BNC cables included in the pack for your antennas. Just borrow some from video, right? You might want to rethink that next time the situation comes around. Video cables are usually 75 ohm. It is imperative that cables being used for antennas are 50 ohm. As a side note, it's not the cable itself that makes a cable 50 or 75 ohm. That's a topic for a different discussion.
Another thing to look out for is the correct antenna length/frequency range for your transmitter and receiver. Most antenna "whips" come in ¼ and ½ wavelengths and are usually color-coded and have the frequency range printed on the antenna, a group number/letter or a combination of these. Directional antennas have an operating range as well, but some models will work with all units within that specific manufacturer. Also remember – it is always best to follow the manufacturer's recommendations on antenna combiners.
Antenna placement can be one of the things that save your day. An improperly-placed antenna can give a less-than-desirable RF signal strength to transmitters/receivers, significantly decreasing the operating range between transmitters and receivers. When given the task to place an antenna for a wireless device such as a microphone, you need to think about where the user will be in relation to where the antenna will be. Ultimately, you want to have a line of sight free of obstructions from antenna to user. A good rule of thumb is to place the antenna above head level, so if anyone walks between the user and antenna, it will not affect the RF signal strength as much.
Most modern pro audio wireless microphone systems have diversity receivers. This type of receiver will have two antennas. A certain amount of spacing between the antennas is required to achieve proper diversity performance. Adequate spacing is at a minimum of ¼ the wavelength, which is about 16 inches for VHF and 4 inches for UHF. Better diversity performance can be achieved by spacing antennas at a distance of one full wavelength apart or more.
Another important thing to keep in mind is the angle of the antenna in relation to the user holding the transmitter/receiver. One antenna should be parallel to the other, as illustrated in Fig. 1. Since performers do alternate the orientation in which they hold microphones, it is a good general rule of thumb to compromise by tilting the antenna approximately 45 degrees from vertical.
Moisture and Frequencies
Performers who use IEMs or clip-on mics of some sort, generally have a transmitting/receiving pack of some sort clipped onto them in some way. When this is the case, keep in mind how much sweat (moisture) will be around the pack. Moisture can make RF reception drop like a stone. So if the performer is a "sweater," the easiest thing to do is to drop the transmitter/receiver pack into a dry latex condom.
It's also a good idea to do some simple things such as changing batteries and checking frequencies right before a show. For a simple check on IEM systems , just turn off the transmitting unit and check to see if the receiver pack is getting any RF hits. A technique called "burning frequencies" is popular in the tradeshow and corporate world. That technique is to simply leave transmitting units powered on from setup to tear down to ensure that if someone in another area turns on a receiving unit, they will see that your frequency is in use.
There are many tricks of the trade in making wireless function properly. Wireless systems can be unpredictable, especially to engineers in the business who are not mainly "RF Guys." It is always best to use every theoretical setup practice you can get your hands on. This will give you the best possibility of a flawless show.
