Detectors 056
Detectors 056 : Particle Detectors: (4.2) Bat Detector: (2) Bat Detector Types: (2. 2) Frequency Division: Frequency division (FD) bat detectors synthesise a sound which is a fraction of the bat call frequencies, typically 1/10. This is done by converting the call into a square wave, otherwise called a zero crossing signal. This square wave is then divided using an electronic counter by 10 to provide another square wave. Square waves sound harsh and contain harmonics which can cause problems in analysis so these are filtered out where possible. Some recent all-digital detectors can synthesise a sine wave instead of a square wave. One example of a detector which synthesises a sine-wave FD output is the Griffin Some FD detectors output this constant level signal which renders background noise and bat calls at the same high level. This causes problems with both listening and analysis. More sophisticated FD detectors such as the Batbox Duet measure the incoming volume level, limiting the noise threshold, and use this to restore the output level variations. This and other sophisticated FD detectors also include a heterodyne detector and provide a jack output so that independent outputs can be recorded for later analysis
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