Detlef Burchard, Dipl.-Ing.
Electronic Laboratory
P.O.Box 14426, Nairobi, Kenya

The paper describes the physiological and technical basics for development of a transmitter for acoustical events and gives one example of such a design.

The electro-acoustical channel has to transmit - without undue alteration - a certain audio frequency spectrum and sound pressure range. Both are depending on the vocalization ability of the species under observation. Alteration means linear and nonlinear signal as well as envelope distortion. The channel shall behave well-defined in case of out-of-range signal: Too low or too high sound pressure, frequency or transients.

The components of the transmitter contribute in different ways to the overall performance: The microphone might determine the system noise and the highest undistorted signal level, the amplifier might be designed to limit the frequency range to what is necessary, the compander might be incorporated to increase the dynamic range at the same time be the cause of significant envelope distortion, the modulation method might determine the high frequency bandwidth together with the modulation gain and the generated high frequency power and the aerial efficiency certainly have to do with the transmission range. The capacity of the battery thus, the lifetime of the transmitter, is related to the volume and weight of the pack which has to be in a certain relation to the animal's size and weight. The transmitter must not interfer with other radio frequency services thus has to be electro-magnetic compatible.

These interdependences are discussed on the example of a transmitter designed for spotted hyena (crocuta crocuta) and details given on component values and manufacturers so that the design may be reproduced in an institute's workshop. The result is a reliable transmitter with excellent signal quality and a good chance to obtain postal approval. Other details covered are pc-board, casing, receiving station, reception aerial, simultaneous visual observation, data storage and commentary recording.

Meaningful extensions of the design are possible: Higher dynamic or frequency range, more rf-power and longer battery life.