How to Choose a Radio Mic System

This article was commissioned by Audio Pro magazine in 2012 – here’s the article we wrote them in full!

With so many wireless systems on the market today, how can you choose which one would be the most suitable for your own needs?

Regardless of what you are planning to use your wireless system for, there are a number of common elements that make up a professional wireless system. TheMicStore’s Managing Director, Matt Lawless, helps to steer you through the various options.

Who’s In Your Gang?

One of the primary factors that will affect system choice, is how many simultaneous wireless users you have. This is because each receiver/transmitter (Rx/Tx) system has a maximum number of available channels that can be used at the same time.

The actual number will depend on the sophistication of its Compander (compressor/expander) and how much of the frequency spectrum it uses. Tighter, narrower companders will allow more systems to be used side-by-side within the transmission band. As a rule of thumb, the more simultaneous systems, the higher the equipment cost.

What’s Your Type?

Wireless systems, or more specifically the transmitters, are provided principally in one of two core types: Handheld and Beltpack. Once again, depending upon the usage, there are choices to be made.

Handheld Transmitters have a standard body but then will typically offer different microphone capsules (or heads). Capsules vary by the pickup pattern (such as cardioid, super-cardioid or omnidirectional), as well as its operating principle (dynamic or condenser). The different available types will determine how much sound is picked up, and also from which direction(s).

Beltpack Transmitters are common to both lapel (also known as lavalier or tie-clip) and headworn microphone types. These devices provide the necessary power to the microphone choice. Care will need to be taken over the pickup pattern of the mic itself especially where the ability to control feedback is limited.

Give Me Power!

For a multi-channel system, it is likely you will want to consider how the receiver units are going to be powered. As each receiver (other than those on location wireless systems) will require mains power, it will quickly become problematic to try to power each unit individually. For this reason, you are likely to require some method of power distribution. This facility is often built into an antenna distribution unit (see below) whereby mains supply is transferred over the antenna link cables, thus alleviating the need for multiple PSUs.

Can You Hear Me?

Similar to the requirement for power handling, careful consideration will be needed over the deployment of antennae, and how they should be positioned. Also, unless you are planning to run only a handful of systems, it will become more practical to utilise a common set of aerials to support the overall system rather than rely on an antennae pair per receiver.

Antenna Distribution Units (ADUs) refer to hardware appliances that allow multiple receivers to share the same set of antennae. These devices will also enable power to be supplied to multiple receivers (see above). Most ADUs will support a finite number of receivers, but can be daisy-chained together to support larger installations.

Antenna Splitters are also needed where receivers on multiple frequency ranges are being used. These devices allow a common set of antennae to be split out to feed each set of wireless systems – useful when the installation exceeds the potential number of supported systems within a single frequency range.

Antenna Combiners can also be deployed where a single pair of antennae is insufficient to support the wireless installation (due to adverse environmental factors).

Antennae Types. Typically, in the case of a permanent installation such as a theatre, directional antennae would be used to focus the RF pickup within a specific area (such as the stage). This does not however suit all purposes. Alternative antennae include yagi antennae for long-range pickup and omnidirectional antennae.

(A word about cabling…)

Wireless antennae are designed to be used with 50-Ohm cables. These cables are very reliable but do suffer from signal loss so should be kept as short as possible. Boosters can be used to compensate for signal loss although there are limits as to what is feasible before ultimately compromising the system as a whole.

Out And About…

For on-location wireless systems, an additional complication arises whereby mains power may not be available. For this reason, a number of wireless systems are available which include a battery-powered receiver for complete portability.

Channel Types

No introduction to professional wireless installations would be complete without a section on the various RF channels in use. In broad terms, these can be broken down as follows:

Deregulated Channels include TV Band Channel 70 (863-865MHz) and 2.4GHz ranges. These channel ranges have been reserved for public use and as such are the most crowded and susceptible to interference. Professional users should avoid shared public ranges, however there have been successful deployments of multi-channel wireless systems utilising the 2.4GHz range within locations that are reasonably isolated (such as university campuses).

Shared-Use Channel Ranges include TV Band Channel 38 (608-614MHz), which has been reserved for professional users needing systems that will be moved around the country. Depending upon the sophistication of the wireless system, around 12 systems can be used simultaneously in Channel 38. These systems require an annual licence to be obtained prior to use, although a single licence covers any number of systems within the Channel 38 range.

Co-Ordinated Frequencies refer to individual frequencies that can be obtained for exclusive use within a fixed location. Once again, these frequencies require a licence, but this time on an individual basis. This is the most common choice for permanent installations as interference from other wireless users is effectively prevented.

Who’s The Boss?

A final word goes to how the whole system is managed and maintained. Users of single and low-number wireless deployments are likely to be comfortable managing the system from within the front-panel menus of the devices themselves. For more in-depth installations however, the ability to address the system as a whole is likely to be useful. Management capabilities are available both on-device and via software control interfaces if needed.

The Last Word…

The rule of thumb with any new or replacement wireless installation is to plan, plan, plan. The above introduction should help you to define your requirement, resulting in an effective and trouble-free wireless deployment.

Most people would be advised to talk through their options before deploying a wireless mic system. For free, unbiased advice, call TheMicStore to discuss your individual requirements.

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