Bat detector briefing
A bat detector is an indispensable tool for anyone studying bats in the field. The detector enables you to hear the otherwise inaudible ultrasonic calls of the bats. This is most useful to identify different species as well as just determining bat activity.

The transformation of ultrasound into audible sound can be made with at least three different technologies. The most common are:

Heterodyning: This method works by frequency subtraction and only a very narrow part of the spectrum is scanned at any given time, so a tremendous amount information is lost. Hetrodynes produce low quality analog output and cannot be used for analysis.

Frequency division: This technique will map 16 cycles of the original bat signal to 1 cycle of a new, frequency divided, signal. It will map a wide range of ultrasounds (16 to 122 khz) and the new signal will have a frequency in the audible range. Division detectors lose all power info and plays the call at a constant level.

Time expansion: The ultrasound pulses are recorded at high speed and replayed at lower speed later. This method allows a complete analysis of all features of the bat signal, including amplitude, or power. The drawback is that the analysis is delayed, so this approach may not be suitable for very simple bat detection in real time.

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, however in time expansion detectors digital techniques are used to store the signal instead of a large and expensive high speed tape recorder. Obviously this is not a real-time conversion method, but in return it offers a number of important advantages. Since the signal is stretched out in time, it is possible to hear details of the sound not audible with other methods (e.g. you can actually hear frequency differences within one short pulse or between different pulses). Time expansion is also the only technique that preserves all characteristics of the original signal, making time expanded signals ideal for sound analysis in the laboratory.

Pettersson 240x
The bat detectors from Pettersson Elektronik are high quality instruments, designed in close cooperation with leading bat workers for optimum performance.

Features
Frequency range 10 - 120 kHz

Select between hetrodyne or time expansion technology by flipping a switch

Time expansion memory selectable between 0.1, 1.7, and 3.4 seconds.

Very accurate, backlit digital display showing tuned hetrodyne frequency

Built-in loudspeaker

Single-handed operation

Very small size: 119 x 60 x 25 mm

Manual and level-sensitive automatic triggering

Optional frequency-selective trigger in the level-sensitive mode

Capable of automatically capturing the bat calls and, using a separate control box, dump the time expanded calls to a connected tape recorder.

The signal stored in the time expansion memory can be replayed at its original rate through the heterodyne system, i.e. the "original" signal can be carefully examined with the heterodyne system.

Power: (1) 9-volt alkaline battery

Output: (1) audio line out, (1) headphone port

Price
Pettersson 240x: $1599.00 USD
$15 shipping in the USA. In stock for immediate shipping. Email for international shipping quote.

More info?
Download a PDF brochure on the Pettersson 240x...

Time Expansion or Frequency Division?
A frequency division (FD) detector transforms the ultrasonic calls in real time; the calls are heard through the detector at the same time they were emitted by the bat. A time expansion (TE) detector first stores a portion of the ultrasonic signal in its digital memory and then replays it at a slower speed; it is does not transform the calls in real time. The delay depends on the actual storage time, and if this is very short (up to around 100 msec), the replay is also made fairly quickly and the detector gives an "almost real time" response.

Since the TE detector actually stores the entire original signal, the output of such a detector provides the same information as that of the original signal. It is possible to make any type of analysis and obtain useful and accurate results. This includes spectral analysis of all types (e.g. spectrogram/sonagram).

A FD detector counts the number of cycles of the ultrasonic signal and generates an output cycle (pulse) for each N input cycles, where N is often 10. This effectively divides the frequency by N. A FD detector is only capable of tracking one frequency (harmonic) at each time. Usually (but not always!), This is the fundamental frequency. Consequently, it is not possible to perform any harmonic analysis from an FD signal. To do this, TE signals should be used.

TE detectors have a number of other advantages over FD detectors. For instance, TE detectors are more sensitive and offer the user better possibilities to aurally analyze the transformed calls. If you require a broadband bat detector, a TE detector is usually the best choice.

This quality hetrodyne bat detector features a large LCD displaying the center of the tuned frequency in kHz. The detector in real time plays any ultrasound that is approximately 4 kHz above and below the tuned frequency.This method works by frequency subtraction and only a very narrow part of the spectrum is scanned at any given time, so a tremendous amount information is not detected.

Hetrodynes produce low quality analog output and is not used for detailed computer analysis. However, many people are able to discern different species with practice in areas where there is little overlap in call frequencies. For example, a bat heard best at 19 kHz in the eastern US is most likely a hoary bat, as no other species typically calls that low.

Similarly, an experianced user may be able to group calls by genus to a fair extent, suitable for interperters doing bat walks, or bat enthuesists looking for a low cost acoustic detector. Tone qualities of the output change if the bat is calling above or below the present frequency of the detector. This enables users listening in real time to rapidly "tune into" the bat as it flies by and get a good estimate of the bat's dominant frequency, the basis for species identification.

Please note: hetrodyne detectors -are not- intended for computer analysis and precise species identification. They can be used for passage rates at mine entrances, etc.

Pettersson D200

• Type: Heterodyne
• Frequency range: 10 - 120 kHz (min.)
• Display accuracy: +/- 0.15 kHz
• Bandwidth: 8 kHz (+/- 4 kHz), -6 dB
• Battery: 1 x IEC 6LF22 (9V)
• Quiescent current: 17 mA typ. including LCD backlight
• Size: 119 x 60 x 25 mm including knobs
• Weight: 150 g. including battery
• Outputs: 2 x 3.5 mm jacks for headphones and tape recorder.
• Single handed operation
• Backlit display

Price
Pettersson 240x: $359.00 USD
Free shipping in the USA. In stock for immediate shipping.