Advances in Wireless Technology

We Talk to Tim Vear

Tim Vear, Senior Applications Engineer

 

 

Those of you familiar with Shure probably have a copy of "Selection and Operation of Wireless Microphone Systems" written by Senior Application Engineer Tim Vear. A longtime veteran of Shure and a Shure Notes editorial advisor, it only made sense to talk to Tim about the changes and the innovations in wireless microphone systems.




Here’s what he had to say:

What’s new in wireless technology?
There have been recent developments in each part of the wireless system: transmitters, receivers, antennas and accessories.

What is the driving force behind these developments?
The primary driver behind new wireless technology is the demand for greater numbers of wireless systems to work together successfully. "Greater" numbers means twenty, thirty, or more wireless systems in simultaneous use. Working "successfully" means delivering the highest quality of sound with the least difficulty of operation.

Have things changed in touring wireless applications?
A typical touring application of some years ago may have consisted of a wireless handheld system for the lead singer and one or two wireless bodypacks for the lead guitar players. A large application today may require handheld wireless for all the frontline singers, more handheld systems for the backup vocalists, wireless instrument systems for all the guitars, as well as wireless systems for horn players, keyboard players, and even percussionists. In addition, a multi-channel wireless in-ear monitor setup is fairly standard these days. With complex and variable stage designs it may also be the case that multiple areas have to be covered by the same set of wireless systems. Thirty or more wireless units is not an uncommon number.

What is the main difference between a "touring" application and an "installed" application?
Other than perhaps a requirement for greater durability, the main difference is the changing radio environment from venue to venue. In each city there is a different set of broadcast television stations on the air. With power levels of more than one million watts, local television stations are the primary source of interference for wireless audio systems. For this reason, it is necessary to use a wireless frequency set that avoids the local television frequencies in each city. Obviously, this would not be possible without "frequency-agile" (tunable) wireless equipment and the ability to calculate appropriate frequency sets for each city.

What about touring in different countries?
Due to local government regulations that are specific to each country, there is not a single wireless system that can operate legally in multiple countries. Generally, it is recommended that international productions obtain wireless equipment locally for each country on the tour.

How have transmitters improved?
For transmitters, the main improvements have been in miniaturization and battery life. A new feature that speeds transmitter setup is an infrared link that allows a transmitter to be automatically synchronized to the frequency of its receiver channel. Finally, most tunable (frequency-agile) transmitters can be set so that the frequency cannot be accidentally changed (frequency lock) and the transmitter cannot be accidentally turned off (power lock).

What about receiver developments?
The newest high-performance systems combine wide tuning range with high selectivity to achieve the greatest number of simultaneous systems. In addition, more frequency bands within the UHF spectrum are available.

Maximum tuning range is now as much as 60 MHz, the equivalent of ten TV channels. The wider the tuning range, the more wireless frequencies that can operate in that range, particularly when some of the range is already in use by local TV stations. By using multiple frequency bands, it is now possible to operate throughout the available UHF spectrum.

What is "Track Tuning"?
"Track tuning" is a receiver technology that is used to maintain high selectivity across a wide tuning range. A narrow front-end filter automatically tracks the tuned frequency reducing interference from transmitters on nearby frequencies. This allows more wireless systems to be used in the available range.

Can computers now be used with wireless receivers?
Some high-performance multi-channel wireless systems can be interconnected to form a self-aware network. In this mode, they can find and setup their own compatible frequency groups, within certain limits.

By adding a computer connection to the network, it is possible to monitor and control all of the networked receivers in real time. With available software, the receivers can also serve as scanners that provide a detailed picture of the radio environment during setup. The computer then calculates compatible frequency sets not only for the connected receivers but also for any other wireless systems that may need to be coordinated with them. Finally, the computer can automatically update all connected receivers with the calculated frequencies.

Clearly, this capability is highly desirable for multi-city touring in order to achieve a reliable, coordinated set of frequencies at each venue.

Have there been developments in antennas?
Antenna designs have improved for both transmitters and receivers. Handheld transmitters are much less sensitive to hand position due to new antenna designs. Receivers have benefited from several new antenna choices, such as wideband omnidirectional types.

What about the "helical" antenna?
The helical antenna is a special case of a unidirectional antenna that combines high gain with a wide frequency range. It is somewhat higher gain than the traditional log periodic or "paddle" antenna (12dBi vs. 7dBi) but it has a narrower coverage angle, typically about 60 degrees compared with 120 degrees for the log periodic.

A unique characteristic of the helical antenna is that it does not have a "preferred" polarization angle. That is, it works equally well with other antennas that are oriented vertically or horizontally. For this reason, it has become popular as a wireless in-ear transmitter antenna. In this application, the belt-pack receiver is a non-diversity (single antenna) device and will pickup the signal from the helical antenna equally well at any orientation.


Are there any useful new accessories?
For integrating large numbers of wireless systems, several accessories have become very important. The use of active and passive antenna combiners and splitters greatly simplifies the antenna requirements for multiple systems. With wideband devices it is possible to use one diversity pair of antennas to provide signal to many wireless microphone receivers. Likewise, it is possible to connect multiple in-ear transmitters to a single transmit antenna.

In both cases, it is much easier to put one set of antennas in the most strategic spot than it is to put up a large number of antennas in a limited space. This also minimizes the amount of coaxial antenna cable required which in turn minimizes the resulting cable loss.

In addition, coaxial cable for wireless antennas is now available in several low-loss versions allowing longer antenna cable runs without amplification.

Is it possible to cover more than one area with the same set of wireless microphones?
By using multiple pairs of antennas, it is possible to have wireless coverage in multiple areas. For example, to provide coverage for an auxiliary stage as well as the main stage, locate one pair of antennas (diversity "A" and "B") in a suitable spot near the auxiliary stage and locate a second pair of antennas (diversity "A" and "B") in a suitable spot for the main stage. The two "A" antennas are connected with a passive combiner whose output becomes the "A" antenna signal to the diversity receiver(s). The two "B" antennas are connected in a similar manner.

This method can be expanded to cover multiple areas as long as the total loss due to antenna cables and passive splitters is less than about 5dB. If the loss is greater, then a lower loss cable and/or in-line antenna amplifiers must be used.

What about batteries?
For many years, alkaline batteries have been the only viable battery choice, particularly for 9-volt applications. Recently, single use lithium batteries have become available. These typically have about twice the operating time of an equivalent alkaline, though they often cost almost twice as much.

Rechargeable batteries have long represented an attractive alternative to single-use alkaline types, particularly in large, multi-channel installations. NiCd (nickel cadmium) and NimH (nickel metal hydride) types have been fairly suitable for AA size battery use. However, in a 9-volt size these provide only about 1/4 the operating time of a 9-volt alkaline.

Lithium-ion types have now become available that finally meet or exceed the capabilities of alkalines. In some cases, they are standard-size cells while in others they are a special size built in to a transmitter. The lithium-ion types should have the longest operating time of any comparable rechargeable battery.

Has sound quality improved?
Traditional companding schemes have been significantly improved by using variable compression/expansion rates and low noise components. The result is better dynamic response and higher signal-to-noise ratio. The audible difference between wired and wireless microphones is smaller than ever.

What can we expect in the future?
The wireless environment is changing as new uses are proposed for existing equipment and as new users are entering the existing spectrum. Changes to the radio spectrum are dictated by the FCC and other parties. We can expect that manufacturers will respond to these changes by developing new wireless technologies and techniques that continue to insure high performance even as the wireless landscape becomes more challenging.