Fixing Wireless Microphone Dropout
In the world of audio, the ultimate sign of a job well done is that no one notices the sound system. When everything sounds pure and natural, microphones are turned on and off at the appropriate times, and the technology works as expected, all audience focus is on the intended subject matter and the sound system seems to disappear.
While there are many potential distractions that get the sound system noticed, like feedback, tinny sounding microphones, or latency in switching mics on and off, perhaps the most elusive and mysterious is wireless dropouts. I’ve heard a great many “theories” about how to use wireless technology and seen some pretty interesting implementations in my 30 years of pro audio experience, but had I known back then what I know now, my life could have been so much simpler and my audio so much better. Here are 6 of the most commonly overlooked practices that will drastically improve your wireless performance:
1. Use the correct antenna: Most pro-audio wireless receivers ship with a ½ wave omnidirectional antenna. It’s a thick, rubbery antenna with a wider base that tapers to a much smaller diameter about half way along its length. They get their name from the fact that the physical length of the antenna is ½ the wavelength of the frequency it’s used for. A 500MHz antenna is about .3 meters or about 12 inches long. A ¼ wave antenna, as you would expect, is half that length. They’re omnidirectional, meaning they receive signal equally from all sides, and therefore should be placed fairly closely to the transmitter.
Directional antennae, like the log periodic (paddle), yagi or helical, vastly increase sensitivity to signals in one direction and reject signals from the other, making them an excellent choice for long-distance reception. They have to be at least 50’ from the transmitter, however, to see any benefit (otherwise just use the omnis). Some come with a built-in amplifier to compensate for cable loss, but turning up the amplification doesn’t necessarily improve the signal. Too much gain can overdrive the input of a receiver and cause dropouts or make the signal bleed into other receivers. Only use signal amplification to make up for loss over long cable runs.
All antennae are made to be used for specific bands of frequencies, based on size and length. Be sure you’re using the correct antenna for the frequency band your equipment is utilizing.
2. Position the antennae correctly: Wireless signals are polarized, meaning they travel in a plane. Think of it like shaking a rope. If you shake it up and down, the rope only moves in a vertical plane or direction. If you only shake it side-to-side, it only moves in the horizontal plane. If the hand on the other end of the rope can’t move in the direction the rope is moving, the “signal” is lost.
The reason we have diversity (dual antenna) receivers is to compensate for this polarization. Except for helical antenna, each of your omni or directional antennae in a diversity setup needs to be oriented 90 degrees from the other. As the transmitter on stage rotates with normal use, a single antenna will see the signal strength drop to nearly nothing as the transmit antenna goes out of polar alignment. If the other antenna is 90 degrees off of the first, it will gain strength as the other loses it and the diversity system will seamlessly switch between them to maintain the best signal strength.
The sensitivity of the omni antenna is along its length, not out the end of the antenna. If you point the end of the antenna toward the signal source, it will reject nearly all of that signal. The antenna should be positioned so that the signal is coming at it from the side.
The most common practice with omnidirectional antennae is to position each 45 degrees off the plane of the receiver, in opposite directions, making them 90 degrees from each other. The same applies to log periodic antenna systems. Each paddle should be oriented 90 degrees from the other, pointing toward the transmitters. Because they’re typically mounted to mic stands, one is usually vertical and the other horizontal.
Position receiver antennae in such a way as to maintain line-of-sight with the transmitters. Radio frequency energy does not pass through large objects (especially metal ones) or crowds of people well.
3. Avoid metal objects: If you mount your receivers in a metal rack, you’ll need to remotely mount your antennae outside the rack. Large, grounded, metal enclosures, like racks, absorb the majority of wireless signals, preventing them from passing through from the transmitter outside to the receiver inside. Using short cables to mount the antennae outside the rack will keep the signal flowing. If you are remotely mounting your antennae, only use ½ wave (dipole) antennae. The shorter ¼ wave must be connected directly to a receiver or other grounded plane to function properly.
The metal rule also applies to jewelry. If the performer is wearing anything metal, it can act as an antenna and disrupt the transmission of the wireless device. The larger the piece of metal or the closer it is to the transmitter, the more likely the issue.
4. Avoid antennae farms: We’ve all done it. I remember years ago the piles of wireless receivers at my church, stacked on top of each other with the ½ wave antennae nearly touching each other, but with each delicately positioned just fractions of an inch from its neighbor. The issue is that when you put antennae close together like this, they interfere with each other, causing intermodular distortion. Any two antennae should not be any closer to each other than the mounting ports on the back of the receiver will allow. Most receivers are a ½ rack width, meaning no antenna should be within 9 inches of any other antenna. That’s not possible when the receivers are stacked on top of each other.
If you have more than two wireless receivers, you should be using an antenna combiner. This is a common device that allows up to 5 diversity receivers to share only two antennae. They can also be cascaded to allow more systems to share the same two antennae. All the signal amplification (and often power distribution for receivers) is built in to the unit, simplifying installation and cleaning up the cabling. This also allow systems to be installed easily in a rack.
The same holds true for wireless in-ear systems. If you have more than two, you should be using a combiner with the correct antenna to keep the systems from interfering with each other.
Shure Antenna Distribution System
If you use wireless receivers and in-ear transmitters in close proximity, use longer extension cables to get their antennae as far apart as possible. An in-ear transmitter is a high-power radio frequency transmitter and the wireless receiver is a very sensitive radio frequency receiver. The in-ear system’s transmission antenna should never be pointed at the wireless receiver’s antenna.
If you use cables longer than a couple of feet to remotely mount your antennae, be sure to use low-loss cables supplied by the manufacturer. Radio frequency signals are prone to significant loss over distances, even short ones, so special low-loss cables are required along with signal amplifiers to get adequate signal from the antennae to the receiver.
5. Keep your batteries fresh: A weak battery is the most common cause of signal loss. Batteries are cheap, especially with the newer transmitters that use AA instead of 9V. There is no reason not to change the batteries before every performance or church service. If you don’t like the effect on the environment, there are some excellent rechargeable systems available. Shure’s rechargeable battery system is a good example. It has a fairly high up-front cost, but the lifetime of the battery more than makes up for it, and the batteries last far longer than the standard alkaline. Almost all modern receivers will tell you the health of your batteries, and good receivers will connect to your network to allow you to monitor them remotely.
6. Get out of 600MHz: The recent FCC auction of the 614-698MHz band means that many wireless systems will become illegal on July 13, 2020. Before that, the new owners of those ranges (mostly T-Mobile and Dish Networks) will turn their equipment on in certain areas and start using those frequencies. When they do, any wireless audio system in that area and range of frequencies will stop working. In addition, any device caught transmitting in that range after July 13, 2020 could see fines of up to $1200 per device per day, whether it was in use or not. Any device that can transmit in that range, even if it’s currently tuned to a legal frequency, is outlawed by the new ruling. If you have 4 wireless devices in that range and you get caught on July 31, 2020, your fine could be up to $86,400.
Conclusion: When you understand the technology behind the wireless devices we use, it becomes easier to troubleshoot dropouts. Follow the guidelines in this article to clear up your wireless dropout issues and don’t be afraid to reach out to your local dealer to ask for help. VIP Production Northwest provides free consultation services to help you get the most out of your wireless (and other) gear.
