Review Of The D240X From Pettersson Elektronik

I’ve always wanted to buy a good quality, hand-held time-expansion detector. So, I was really excited about the opportunity, to test and review this unit! If after testing it for a few nights, I determine that it is the perfect bat detector - Then, I may have to start saving up to actually buy one!

The detector was delivered to me (here in the US) much sooner than expected (in less than a week!) from the manufacturer in Sweden. The unit was double-boxed, and was very well packaged. OK: Upon un-packing, I was immediately very pleased with the included accessories!

I really liked the very nice nylon case it comes with (see photo), it features a belt loop and comes with an over-the-shoulder strap; the cutest little yellow screwdriver for adjusting the VRs - The variable resistor sensitivity adjustment points. I like 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 to120kHz!). 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 (3.5mm) 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.

It seems that a lot of manufacturers are starting to make more and more detectors that function by simply using a high sample rate. Such as 200kHz and above. Reminiscent of a top-of-the-range recording device - Interesting.

Perhaps one day soon, almost all time expansion detectors will work this way? The way Dodotronics's Ultramic200K does, as an example. 

Well, I was interested in reviewing a "typical" (real) time expansion detector. 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.  

Perhaps more importantly, the D240X may serve as a model, for all of these new types of "time expansion" bat detectors to be compared to.

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, 3.5mm stereo cable. So, I effectively record only bat-made sounds. The Pettersson D240X fits in with my nightly routine perfectly.

Technical specifications:
 
Type: Heterodyne and time expansion (x10 or x20)
Frequency range: 10 - 120 kHz (min.)
Display accuracy: +/- 0.15 kHz
Bandwidth (het.): 8 kHz (+/- 4 kHz), -6 dB
Sampling frequency: 307 kHz
Memory size: 1M x 8 bits
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
Battery: 1 x IEC 6LF22 (9V)
Quiescent current: 30 mA typ. including LCD backlight
Size: 119 x 60 x 25 mm
Weight: 170 g. including battery
Outputs: 2 x 3.5 mm jacks for headphones and recording device (appr 350 mVrms/3.3 kohm).
Comment switch: Yes
Miscellaneous: Overload indicator, adjustable input gain, replay of signal in memory through heterodyne system,
control output for relay
Using the detector in intense electromagnetic fields may cause interference and/or temporary signal loss.

From the User Manual: "The transformed sounds are monitored either through the built-in loudspeaker or through headphones connected to the PHONES jack. A tape recorder or other recording device may be connected to the
TAPE jack to make recordings of the transformed sounds or the direct microphone signal (if the COMment button is pressed, the microphone signal is directly connected to the TAPE output to enable the recording of spoken comments on the tape)." Now that is very clever! 
When you see a bat detector, that was designed with both a Headphone and a Tape-Out (or Line out) jack....you know that serious thought went into it's design. Features like these, remind you that you're using a serious piece of equipment.

What all this basically translates into, for me - Is simply a great set-up, that produces wonderful TE recordings of nightly bat activity. I'll also mention, that I've tested the D240X using both inexpensive models of digital voice recorders, as well as a Zoom H1 stereo recorder. Recording is possible with mono recorders, but only the heterodyne portion will be recorded. 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, very nice custom case, 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.

Click here for heterodyne sonograms from The Pettersson D240X

Happy bat detecting!