Bat detector
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A bat detector is a device used to detect the presence of bats by converting their echolocation ultrasound signals (with frequencies between 12 and 160 kHz) to audible frequencies. They can both be bought from professional manufacturers and self-built. They can be used to detect what types of species of bats may be present in a given area. Each species has signals with distinct frequencies and durations. There are several types of bat detectors:
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[edit] Bat detector types
[edit] Frequency division detectors
Frequency division detectors work by dividing the frequency of ultrasound signals to translate them to audible sound; they typically do not conserve the ultrasound's amplitude.
[edit] Heterodyne detectors
Heterodyne detectors work by subtracting a tunable frequency from the ultrasound; unlike frequency division detectors, they do not compress the frequency range, so only a relatively narrow band of the ultrasound spectrum used by bats can be scanned at any one time. They do, however, preserve amplitude, and also make it easier to detect small frequency changes in bats' ultrasound signals.
[edit] Time expansion detectors
Time expansion detectors work by recording the bats' ultrasound signals at a high speed and replaying them at a lower speed later; they are typically used for professional work, as they allow a complete analysis of the bats' signals at a later time. Unlike frequency division and heterodyne detectors, however, they are not suitable for real-time bat detection.
[edit] DSP detectors
DSP detectors are detectors that utilise a digital signal processor to map bats' ultrasounds signals to audible sounds; different algorithms are being used to accomplish this, and there is active development and tuning of algorithms going on.
