DIY Wireless, Part 4: Antennas
Wireless is one of the most mysterious and misunderstood parts of audio. But selecting and installing new wireless microphones for a small school, church, or theater is something that you can probably do yourself.
In this article we’ll talk about what is by far the most overlooked part of a wireless microphone system: the receiving antennas. The signal from the transmitter weakens considerably as it travels, so it’s important that the receiving antennas are located so that they can harvest as much of the remaining signal as possible. Mistakes involving antennas can easily result in 80% of the signal being lost, which can cause intermittent audio dropouts that make the system virtually unusable.
Most systems include antennas that are designed to mount directly to the back of the receiver. This is fine if the receiver is sitting on a shelf or table so the antennas have a clear line of sight to the transmitter. In many institutional applications, however, the receivers are either permanently mounted in a closet or packaged in a portable equipment rack for use in different rooms. Either way, special attention to antenna selection and placement is essential.
The Worst Place To Put Wireless Microphone Receiver Antennas
By far, the worst place to mount receiver antennas is horizontally on the back of a receiver that is inside of an equipment rack. Don’t do it! Here’s why this is a bad idea:
- The sides of the antennas are sensitive but the ends are not, so if they’re pointing at the stage or presentation area they’ll pick up almost no signal at all.
- If the rack is made of metal, not much signal will get to the antennas because metal blocks radio signals. Even if the rack is plastic, the metal devices above and below the receiver can greatly reduce the signal getting to the antennas.
- The closely-spaced antennas on adjacent receivers cause unpredictable reflections inside the rack that can result in poor reception and reduced range.
The right thing to do is to mount the antennas on the front of the rack, using holes that are usually provided in the rack mounting brackets. Some wireless systems are shipped with short antenna cables and mounting hardware for this purpose, while for other systems it’s an optional accessory. Pro tip: this only works well if the receiver is in the top rack space, so that the antennas can stick up above the rack to get a clear line of sight to the transmitters.
How to Connect One Pair of Antennas to Multiple Receivers
If you have multiple rack-mounted receivers, the way to make sure they all get the strongest possible signal is to use an optional antenna distribution system like the Shure UA844+SWB/LC that feeds one pair of antennas (and DC power) to multiple receivers. The “antenna distro” goes in the top space of the rack and the antennas mount to connectors on the front of it. Short antenna cables connect from the back of the antenna distro to the antenna inputs on each receiver.
How Many Receivers Can Be Connected To An Antenna Distribution System?
The number of receivers that can be connected to an antenna distribution system depends on the receiver and the antenna distro. If the antenna distro has 4 pairs of RF outputs, it can connect to 4 single-channel receivers or to 4 dual-channel receivers – which lets 8 channels of wireless use one pair of antennas. Dual-channel receivers are a big advantage in multi-channel installations because they cut the number of antenna distribution units required in half.
What If The Wireless Rack Is In A Closet?
If the receivers are mounted in a closet, it’s possible that not much signal will get through the door when it’s closed, so the antennas will need to be remotely mounted somewhere where they can be seen by the presenters, actors, or whoever is holding or wearing the transmitter.
Here are the important things to know about remotely mounting your wireless receiver antennas.
The short “1/4-wave” antennas that come with most wireless receivers have to be mounted on the receiver or antenna distribution unit; they can’t be remotely mounted on a stand or wall bracket. For remote mounting, you need longer “1/2-wave” antennas. When it’s more than 100 feet from the transmitters to the antennas, consider directional antennas, like “paddle-style” units that mount on a stand or bracket, or wall-mount models that look like an access point.
The most important thing is to mount antennas with a clear line of sight to the transmitters – above the heads of people in the audience if at all possible. Why? Because water absorbs RF energy, and the human body is about 60% water; an audience literally soaks up the signal. To get the antennas up in the air, they can be mounted on a stand or on brackets on the wall (as long as the wall isn’t metal).
Antennas need to be spaced apart for good diversity performance, but it only takes a foot or so at UHF frequencies. More separation is fine if you’re trying to cover a large area, but it’s not critical in most cases. Elevation is more important than separation.
Antennas should be roughly upright, ideally oriented in a V-shape. A 60-degree to 90-degree angle between them is ideal, but the exact angle isn’t critical.
Modern wireless systems in typical locations have no trouble transmitting 100 feet or more under normal conditions. If your receiving antennas will be more than 100 feet from the transmitters, you should talk to Shure Applications Engineering about whether directional antennas or a different mounting location might be appropriate.
The longer the cable is between the antenna and the receiver or antenna distro, the more signal loss occurs. Make sure that the antenna cables you buy are suitable for the length that you need. Shure Applications Engineering can help you figure out which type of antenna cable is required for your situation.
Wireless microphone systems have evolved from a technical novelty reserved for broadcast and Broadway to a mainstay in classrooms, churches, and city councils, thanks to their exceptional convenience and reliability. Still, wireless audio technology can be one of the more confusing areas of AV to many people.
Shure continues to push the limits of performance, reliability, and ease of use in an effort to bring superior wireless audio to government agencies, educational institutions, houses of worship, and meeting venues. Our goal is simply “wireless excellence wherever required.”
For more information about Shure wireless microphone systems, visit https://www.shure.com/en-US/products/wireless-systems. For help selecting or configuring wireless systems, contact Shure Applications Engineering or your local Shure representative.