AKG Acoustics WMS 4000 manual HOW Radio Signals are Transmitted, Case for wireless mics

AKG WMS BASICS

HOW WIRELESS TECHNOLOGY WORKS

HOW RADIO SIGNALS ARE TRANSMITTED

The case for wireless mics

The popularity of wireless systems is gro- wing continuously, and they are no longer found only at open-air events, in theaters, and conference centers. The increasing sel- ection of small portable wireless systems is the key to virtually unrestricted wireless free- dom even for amateur musicians and low- budget users, opening up a huge diversity of applications.

The decisive factors behind the dramatic success of wireless systems are the easy handling and reliable, interference-free ope- ration now offered by most of the medium- price wireless systems available on the mar- ket today. In practice, however, wireless technology is often unreasonably put down when minimal technical conditions are not met, usually by people who do not know any better.

The following section examines the princi- ples of trouble-free wireless transmission and

gives an insight into what is technically pos- sible, and how to achieve the best results.

Just like a radio set

At first it may sound simplistic to maintain that the operation of a wireless system is almost as simple as that of a radio set. However, in practice closer inspection shows that this comparison is entirely appropriate. Everybody knows that the reception quality of radio signals depends not only on the locati- on of the receiver, but also on the quality of the transmitter, i.e. whether or not you are inside a building, and which transmission frequency is selected (FM 100.4, for instance). If the reception is poor, the first thing we do is to try and change the position of the receiver (the radio set). Then we try to change the position of the antenna, and if none of these remedies helps, we try to recei- ve the desired radio station on another fre- quency (FM 94.7, for instance). This is a per- fectly normal procedure, and no one would think of calling a radio set defective or unre-

liable, simply because each of us can opera- te a radio with our eyes shut.

Since reasonably priced, high-quality wire- less microphone systems have only been available to the general public for a few years, it will probably take a while for people to become as familiar with this new techno- logy. However, the comparison with a radio set is particularly appropriate and helpful for the technically uninitiated, since most peo- ple are able to operate radio sets correctly thanks to their intuition and experience.

Radio waves instead of cables!

With wireless technology, radio waves are used instead of a microphone cable to trans- mit a signal. For this purpose, we need a transmitter that transforms the audio input signal (voice, instrument, etc.) into a UHF or VHF signal and broadcasts it just like a miniature FM radio station. The receiver then transforms this high-frequency UHF or VHF signal back into an audio signal and ampli-

Reflection and scattering

Every wave has certain physical properties, and this also applies in the case of wireless transmission. When a wave travels from one medium to another, part of it is reflected and another part of it absorbed. Propagation of the absorbed part of the wave in the denser medium is considerably reduced, whilst the reflected part is returned at the same angle as the angle of incidence (diagram on left).

When a wave meets an irregular surface, it is not reflected uniformly and linearly, but is scattered in several partial waves, each deflected by a differing amount (diagram on right). The energy level of the wave naturally declines every time it is reflected, absorbed or scattered.

Transmitter/receiver

The situation with a transmitter and a receiver can be com- pared to the transmission of a signal between a radio stati- on and a radio set. When we encounter problems with recep- tion, we will either reposition the antenna, or look for the sta- tion on another frequency. The principles are exactly the same when it comes to a wireless microphone system. One of the most important rules is that you can only receive one sta- tion at a time with a radio, never several simultaneously.

Shadowing

When a wave passes close to an obstacle, it is deflected slight- ly from its linear path. Thus a number of small obstacles in a room, such as wire screens, etc., can result in shadowing los- ses although visually they appear transparent.

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