Detectors 058
Detectors 058 : Particle Detectors: (4.2) Bat Detector: (2) Bat Detector Types: (2. 1. 2) Pros and Cons: Advantages, As with a heterodyne detector, an FD detector works in real time with or without a heterodyne function. Bat calls can be heard in their entirety over their whole range rather than over a limited frequency range. Retuning with an FD detector is not required although this is done with a dual type with heterodyne. By analysing the recording later, the entire call frequency range and the call pattern can be measured. A serious disadvantage with real time listening is that the speed of a bat call remains fast, often too fast for the species to be recognised. The frequency changes of CF calls are not exaggerated as with a heterodyne detector and so are less noticeable. Also with some species such as the Lesser Horseshoe bat with a call around 110 kHz, the resulting frequency is still quite high although it can be recorded. The synthesising of the call means that only one bat call can be reproduced at a time and a muddle is caused by simultaneous calls. Surprisingly, this is not a great disadvantage when analysing a recording later. Time expansion: Time expansion (TE) detectors work by digitising the bat calls at a high sampling rate using an analog-to-digital converter and storing the digitised signal in an on-board memory. TE detectors are "real time" devices in that they can be monitored at the time of recording, but there is an inevitable delay while the high speed sampled extract is slowed down and replayed
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