The D240x combines Time Expansion and Heterodyne detection methods allowing detection across all frequencies after which 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.
There are both manual and level-sensitive triggering modes allowing this device to be left in-situ (with an external recording device) to automatically record calls remotely using Time Expansion for later analysis. The maximum onboard memory storage time is 3.4 seconds. Via a switch, it is also possible to select a storage time of 1.7 or 0.1 sec.
Heterodyne Heterodyne bat detectors are great for beginners and offer immediate identification of bats in the field. You select the ultrasonic frequency range to listen to just like tuning in radio. Heterodyne detectors typically have a headphone socket and line-out socket for recording calls.
Time Expansion Time Expansion detection is a `broadband' method as the entire ultrasonic range audible all the time (in contrast to a Heterodyne detector, which is sensitive only to a limited range of frequencies at each time). Time Expansion detectors first stores a portion of the ultrasonic signal in its digital memory and then replays it at a slower speed, i.e. 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. Time expanded calls produce the highest quality sonograms.
Comparing Frequency Division and Time Expansion A Time Expansion detector actually stores the original signal (which is then stretched out in time), The output of such a detector provides the same information as that of the original signal. Hence, 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).
In contrast a Frequency Division 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 Frequency Division detector is only capable of tracking one frequency, consequently, it is not possible to perform any harmonic analysis from an Frequency Division signal. To do this, Time Expansion signals should be used.
Time Expansion detectors have a number of other advantages over Frequency Division detectors. For instance, the former are more sensitive and offer the user better possibilities to aurally analyse the transformed calls. Time Expansion detectors offer the highest quality and most flexible analytical options however, this is also the most expensive detection method and high-end analysis is not required for all applications.
Review Of Pettersson D240X (Shortened Version)
by Al Milano in the United States (05/02/2013). Read more at http://batdetecting.blogspot.com/
The detector was delivered to me (here in the US) much sooner than expected (in less than a week!). The unit was double-boxed, and was very well packaged. Upon un-packing, I was immediately very pleased with the included accessories!
I really liked the fact that the unit itself also has a white nylon wrist strap (permanently attached).
The large, front-facing LCD displays the center of the tuned frequency while used in heterodyne mode. This heterodyne frequency display is not related to the time-expansion section of the unit; which (when active) is always monitoring the full HF spectrum (from 10 all the way up to120 kHz!). The layout of controls was designed very thoughtfully. With the most frequently used switches on the front of the unit. The D240X is simply loaded with features! I like the Low/High Gain Switch on the front, with the useful Overload Indicator LED.
I think of this model, as being two detectors: A top-of-the-line heterodyne, and a very capable HF/time-expansion machine. The TE portion of the detector is always recording any detected ultrasonic sounds it hears. It then sends the (slowed-down) audio, to either the front firing speaker, or one of the two (3.5 mm) outputs. As one might expect, the detector is very sensitive! I found it a pleasure to use.
This detector is designed to allow a user to listen for bat sounds using the heterodyne output. Using this method, you may wait until you hear a good bat pass before triggering the TE recording. This helps you to avoid recording low-quality, or weak bat calls.
The unit was designed using an advanced electret microphone element. I’ve recently become familiar with all of the interesting advantages (and dis-advantages) of the various microphones that are used in bat detectors today. Of course, the subject of microphones alone, is fascinating to me. There is a lot to be said for the advantages of the electret microphone design.
A handheld unit, that is easy to use in the field. And, I realize that the D240X is not a new model; but it is one of the lowest-cost time-expansion bat detectors currently available; of the "stand-alone" type.
This D240X, is a worthy (and perfect example) to serve as a baseline – for it to be looked upon as an industry standard (after all, it actually is already). This unit has been used for years: By countless Bat Workers, Bat Researchers and other Professionals. As many of you are aware, Pettersson Elektronik also manufactures the D1000X model; for discriminating Professional Bat Researchers.
In the case of my regular use: I usually place bat detectors, on a small platform outside my back window (coupled to a digital voice recorder). Each of the voice recorders have some type of digital "voice activation" feature. Detector and recorder are connected by a shielded, 3.5 mm stereo cable. So, I effectively record only bat-made sounds. The Pettersson D240X fits in with my nightly routine perfectly.
What all this basically translates into – Is simply a great set-up, that produces wonderful TE recordings of nightly bat activity. This is by far, the best sounding heterodyne detector I've ever heard! I can't really describe it, other than to say the sounds are so clear & crisp. Even accidental pick-ups of harmonics from bat calls sound great!
With a relatively inexpensive stereo recorder, such as the Zoom H1: Something really cool happens – You get a recording of the Heterodyne sounds on one channel, and the time expanded sound on the other. Really neat!
Likes: Small size, fits nicely in the hand, back-lit LCD (also serves as a battery power indicator), the various sensitivity adjustments (both switch & VRs), independent output jacks, etc.
Dislikes: Battery snap should be a heavy-duty, hard plastic type, Power On (rotary) Switch should be less easy to turn on. The unit switches on with very little effort. I would prefer a "stiffer" click/indent. But, I imagine most people would prefer it the way it is.
What else can I say? The Pettersson D240X is a world class instrument. I feel as if someone gave me the keys to their Mercedes for a week... And, I'd like to thank Lars Pettersson, of Pettersson Elektronik, for the loan of the machine.
Type: Heterodyne and time expansion (x10 or x20 - selectable via switch)
Frequency range: 10 - 120 kHz (min.)
Display accuracy: +/- 0.15 kHz
Bandwidth: 8 kHz (+/- 4 kHz), -6dB
Battery: 1 x IEC 6LF22 (9V)
Quiescent current: 30 mA typ. (replay) including LCD backlight
Comment switch: Yes
Memory size: 1M x 8
Sampling frequency: 307 kHz
Resolution: 8 bits
Storage time: 3.4, 1.7 or 0.1 sec. (selectable via switch)
Trigger modes: Manual, level - broadband, level - narrowband
Pretrigger: 50% of the selected storage time
Miscellaneous: Overload indicator, adjustable input gain, replay of signal in memory through heterodyne system, control output for tape recorder
Size: 119 x 60 x 25 mm including knobs
Weight: 170 g. including battery
Outputs: 2 x 3.5 mm jacks for headphones and tape recorder
Use this cable to connect your D-240X to a hand-held recorder
This BatSound software from Pettersson is a powerful tool for the analysis of bioacoustic sound and is particularly useful for the study of bat calls
A 9V battery to power the D-240X detector
If you are interested in a detector for long-term, unattended deployment then the D500X is a great alternative
A handy guide to the bats of the U.K. produced by the FSC
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