AKG MP 40 User Manual download pdf (Page 8)

100

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-

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.

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.

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.

HOW RADIO SIGNALS ARE TRANSMITTED

HOW WIRELESS TECHNOLOGY WORKS

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