Pros: Very solid, well made detector that feels like a quality item in the hand. Large array of controls and options offer lots of customisation and tweaks for the discerning enthusiast or bat research professional. Very sensitive microphone picks up bats with ease. High quality speaker, dials and excellent backlit LCD display. Tuneable heterodyne detector great for listening in to bats. Time expansion detector perfect for recording bat sounds for further analysis. Excellent protective nylon case with belt loop and shoulder strap. Handy integrated wrist strap on the unit itself.
Cons: Price… time expansion detectors are expensive, putting this detector beyond the budget for many casual wildlife observers. The speaker on the detector seems susceptible to mobile phone interference which could prove irritating in the field.
Rating: Highly Recommended (for professionals and serious bat enthusiasts)
View the Pettersson D240X on the company website.
You can download a user manual for the D240X here (PDF 326kb).
Pettersson D240X Bat Detector: Full Review
A bat detector, put very simply, takes the high frequency ultrasound echolocation calls emitted by bats and, through some internal jiggery-pokery that we don’t need to get into, makes them audible to our human hearing. Pettersson is a long established Swedish company that has built a solid foundation as a leading bat detector manufacturer, and the D240X Time Expansion Bat Detector is the staple workhorse detector used by many bat researchers and professional bat workers around the world.
While not quite “top of the range” (the all-singing-all-dancing Pettersson D1000X fills that role, and costs silly money), the D240X is a very serious bit of wildlife monitoring kit.
When you unpack the D240X the first thing that strikes you is that this is a high-quality instrument — the second is the completely utilitarian design. This is a unit that’s made to do a job — without superfluous flourish or embellishment. It looks and feels like a very capable piece of equipment.
The case itself is a hard black plastic. On the front of the unit there’s a high quality backlit LCD display that shows the tuned frequency of the D240X’s heterodyne bat detection system, a red LED that indicates the time expansion loop is running and various switches and controls that allow you to switch between detector modes and adjust the gain level to avoid distorted audio if bats are very close.
It was good to see that the highly sensitive advanced electret microphone was well recessed on the top / front edge of the unit to avoid knocks and potential damage.
On the right hand side of the case there’s an on/off/volume dial, and on the left a tuning dial that allows you to manually select the heterodyne sampling frequency. On the right hand side you’ll also find two 3.5mm jack ports — one for headphones (labelled “Phones”) and one line out port to connect the detector to a recording device (labelled “Tape”, which perhaps dates the detector a little).
If you turn the detector over you’ll see a host of other controls and ports that allow you to manually trigger time expansion recording, set Time Expansion options, and set and adjust auto-trigerring levels for the time expansion system. The D240X really is a very configurable detector.
The D240X is in reality two bat detectors rolled into one. There’s a high-end heterodyne detector that allows you to listen to / monitor bats in real time out in the field, and a time expansion detector that allows you to record full-spectrum bat calls for detailed analysis later using special audio rendering computer software.
Heterodyne bat detectors are the most common kind of bat detectors on the market, and are a great choice for beginners or for listening to bats in real time in the field. The heterodyne system transforms bat calls into sound we can hear — but it only monitors a narrow frequency range around the detector’s tuned frequency, and doesn’t capture the full scope of the bats’ calls. That means it’s not suitable for detailed subsequent analysis.
Time Expansion detection is different. It offers a “broadband” sampling method, recording a short snippet of the actual bat call, and playing it back at a slower speed to bring it within the range of human hearing (hence time-expansion). Time expansion detectors record the entire ultrasonic spectrum, and don’t change the sound in any way, other than slowing it down. That means they capture every nuance of the bats’ echolocation calls, making time expansion sound files perfect for detailed study and analysis.
Time expansion detectors like the D240X typically produce the highest quality sonograms and are often used for professional bat studies and research work.
Some of the key features of the D240X are:
- High sensitivity advanced electret microphone to detect bat calls
- Simultaneous high quality Heterodyne / Time Expansion detector
- Unattended recording mode with variable trigger (with suitable external recording device)
- Dual channel recording (Heterodyne signal on the left channel, Time Expansion signal on the right channel)
- Monitor Heterodyne and Time Expansion signals through headphones
- Fully adjustable microphone gain to accommodate varying field conditions
- Manual or auto-trigger options for time-expansion system
- 0.1, 1.7 or 3.4 second time expansion recording with pre-trigger
- Selectable 10x or 20x time expansion value
- Variable auto-trigger level
- Auto trigger across the full spectrum or set an auto-trigger frequency through the heterodyne tuner
- Powered by a single 9v battery
The D240X in use
For general use the tuneable heterodyne detector in the D240X is as good or better than anything on the market. It sits comfortably in the hand and is a joy to use. The LCD display is accurate and clear, and the subtle green glow of the backlight makes reading it a breeze even in complete darkness.
The controls are intelligently arranged so that holding the detector in your left hand puts your thumb on the tuning dial, and your second finger on the on/off/volume dial. It also places your index finger conveniently close to the manual time-expansion trigger button on the underside of the unit. The sound quality from the speaker is also very good, with minimal hiss and background noise and clear sound. For best quality monitoring I prefer to use headphones, but for sharing bat sounds with others the D240X speaker is great. One thing to note is that it does seem a little sensitive to interference from mobile phones… so keep your mobile well clear to avoid the annoying repetitive stutter through the speaker.
For manual time expansion recording you simply listen for bat calls on the heterodyne system, and push the manual time expansion trigger. That stops the recording loop to the on-board digital memory, and starts playing back the time expanded call 10x slower (or 20x slower, depending on your settings). If you connect the detector to an external digital recording device you can then record this signal for later analysis on a computer.
Auto trigger / unattended recording
If you have a recording device that supports automatic / voice activated recording you can set up a completely automated bat recording system. You simply set the D240X time expansion system to auto-trigger mode, set your recorder to voice activated mode and it will automatically record time expanded calls for every bat call that exceeds the set trigger threshold on the D240X.
In practice getting the settings spot on for the recorder and the D240X can be a bit fiddly, but once you’ve found the right settings you have a very effective setup. Just bear in mind that neither the D240X or your digital recorder are weather proof, so you’ll only want to leave it out for short periods on dry nights.
You’ll find instructions on using the D240X and a Zoom H2 recorder for unattended monitoring on the Pettersson site.
The D240X records the heterodyne output to the left channel and the time expansion recording to the right channel — so depending on your needs you may need to split these into individual files using free audio software like Audacity before importing the single time expansion file into your bat analysis software.
Analysing Time Expansion Recordings
Pettersson have their own specialist bat call analysis software called Batsound. You’ll find the details — and can download a demo from their website. Other options include the free BatExplorer software from Elekon, which will import single channel D240X time expansion recordings individually as WAV files, and does a good job of providing extensive call details and even suggesting possible species matches.
The D240X is designed to be a serious research tool and is probably overkill for the average wildlife enthusiast looking for a way to monitor bats on their local patch or when travelling. That said if you have a particular interest in bats, and want to start studying them in a bit more detail the D240x is certainly worth considering as an all-round bat detector. It gives you the flexibility in a single, portable unit of monitoring bats in real time through the heterodyne system, and of obtaining high-quality full-spectrum time-expansion recordings either manually or automatically for more detailed study and analysis later.
I’d like to thank Pettersson for submitting the D240X for review on Ireland’s Wildlife.
NB. Ireland’s Wildlife has no specific affiliation to any optics or gear manufacturer and all reviews on the site are completely independent and objective. If you’re an optics or gear manufacturer and would like to submit your wildlife related product for review on the site please drop us a line using the contact form and we can take things from there.
Taken from the Pettersson website
|Type:||Heterodyne and time expansion (x10 or x20 – selectable via switch)|
|Frequency range:||10 – 120 kHz (min.)|
|Display accuracy:||±0.15 kHz (min.)|
|Bandwidth:||8 kHz (± 4 kHz), -6 dB|
|Battery:||1 x IEC 6LF22 (9 V)|
|Quiescent current:||30 mA typ. (replay) including LCD backlight|
|Memory size:||1M x 8|
|Sampling frequency:||307 kHz|
|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|
|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|
|Miscellaneous:||Overload indicator, adjustable input gain, replay of signal in memory through heterodyne system|