INTRODUCTION
The ultrasound detector D240x is an easy-to-handle and very powerful instrument for conversion of
ultrasound to audible sound. It is primarily intended for studying bats and other animals emitting
ultrasound. The detector has two independent ultrasound conversion systems; a heterodyne system and
a time expansion system. The detector is equipped with a digital display to provide very accurate
readings of the tuned frequency.
Before using the detector, please read the following information carefully! Further information on the
identification of different bat species using ultrasound detectors may be found in the literature (e.g.
Barataud: The inaudible world
available from Pettersson Elektronik).
The D240x transforms ultrasound in the range 10 - 120 kHz into the audible frequency range.
Although the main application for the D240x is studying bioacoustic ultrasound (bats, rodents, bush
crickets etc.), the detector can be used in many other situations where detection of ultrasound is
involved (ultrasonic intruder systems, leaks in pressurized systems, corona discharges etc.).
The transformed sounds are monitored either through the built-in loudspeaker or through headphones
connected to the PHONES jack. A tape recorder 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).
GETTING STARTED
The detector is powered from one 9 V battery. An alkaline battery will last for appr. 15 hours.
Remove the battery compartment lid and insert a new battery. Observe the polarity! Then turn the
VOLUME control/ON-OFF switch clockwise to switch the detector on. The LCD display now shows
the tuned frequency (heterodyne system only!) and the LCD backlight is turned on. The LCD
backlight also serves as a battery condition indicator, so if the backlight is too weak to read the display
in darkness, it is time to replace the battery! To test the detector, perform the following steps.
Set the HET/TIME EXP switch to the HETerodyne position and the NORMAL/TE
→
HET switch to
the NORMAL position. Adjust the VOLUME control so that a weak noise is heard in the loudspeaker.
Then turn the FREQUENCY control to give a display reading of approximately 20 kHz and gently
snap your fingers near the microphone (at the front of the detector). A scraping sound should then be
heard in the loudspeaker. Another good ultrasound source is a jingling bunch of keys.
The frequency control works in the following way. The display shows the center of the frequency
range (approximately 10 kHz wide), to be transformed. If the control is set to 30 kHz, you can listen to
ultrasonic frequencies between approximately 25 and 35 kHz.
Next, let’s have a look at the time expansion system. First, set the HET/TIME EXP switch to the
TIME EXP position. Set the TRIG switch to the MANual position and the MEMory SIZE switch to
the 1.7 sec position (both switches are located on the time expansion control panel on the under side of
the D240x).
Hold the detector in your left hand and push the MANUAL START/STOP button on the time
expansion control panel with your pointing finger to make the red LED light up (indicating
”SAMPLING”). Produce some ultrasound (e.g. as described above) and then push the button again to
stop the sampling. The detector then replays the sounds immediately before (i.e. 1.7 seconds before)
the button was pushed the second time, at a rate ten times lower than the original rate. Replaying the
stored sequence takes about 17 seconds (34 seconds with time expansion factor 20). After replaying
