Bat Detectors

A bat detector (or ultrasound detector) is an invaluable tool for anyone studying bats in the field. The detector enables you to hear the otherwise inaudible ultrasonic calls of bats. This is not only useful for identifying different species but also for monitoring bat activity.

The large range of detectors from Pettersson Elektronik are high quality instruments, designed in close co-operation with leading scientists and ecologists for optimum performance and durability.

The most common techniques for transformation of ultrasound into audible sound are Heterodyning, Frequency Division and Time Expansion.

Heterodyne and Frequency Division are real time methods (i.e. you hear the sound from the detector at the same time as it is emitted by the bat.) Heterodyning is the most sensitive of the two but transforms only a small portion of the ultrasonic frequency range. The user selects the range to transform using a tuning control. The most advanced detectors have a scanning heterodyne system which eliminates the need for manual tuning.

The frequency division method transforms the entire ultrasonic range without the need for tuning. All of the Pettersson detectors are of the more advanced retained amplitude type ie. the amplitude of the transformed signal is relative to that of the original signal.

The Time Expansion method is similar to making a high speed tape recording of the sound and then playing it back at a lower speed. In time expansion detectors digital technology is used to make the recording and slow it down for play back. Clearly this is not a real time conversion method but it does offer a number of benefits over and above these methods. Since the signal is stretched out in time, it is possible to hear details of the sound not audible with other types of detector; for example you can actually hear frequency differences in a single short pulse. Time expansion is also the only technique which preserves all characteristics of the original signal, which makes time expanded signals ideal for sound analysis in the laboratory.

As an alternative to time expansion techniques modern lap top computers allow for direct high speed sampling of the ultrasonic signals using a separate data acquisition card. Although a laptop based method is slightly less portable than other detectors it does have a number of advantages; the signal is available for immediate sound analysis, the sound quality is usually better and the opportunities to control sound recording / playback are much better as the computer functions as an infinitely more versatile time expansion recorder. The sound analysis software Batsound 3.1 provides an excellent user interface for making these recordings.

One of the best places to buy a detector is Alana Ecology