The ultrasound detector D 230 is an easy-to-handle 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 frequency division system
(divide-by-ten). The detector is equipped with a digital display to provide a very accurate value of the
tuned frequency. Before using the detector, please read the following information!
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 D230 comes with a soft carrying case. For protection of the detector we recommend you keep it in
this case when not in use. The detector should be placed with the display upwards in the case.
INTRODUCTION
With the bat detector D 230, ultrasound in the range 10 - 120 kHz may be transformed into the audible
frequency range. Although the main application for the D 230 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 socket. A tape recorder may be connected to the TAPE socket to make
recordings of the transformed sounds or the direct microhone 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).
THE FIRST TIME
The detector is powered from one 9 V battery. An alkaline battery will last for appr. 25 hours.
Insert a new
battery and turn the VOLUME control clockwise to switch on the detector. The LCD display 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/DIV switch to the HETerodyne 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), which will be transformed. If the control is set to 30 kHz, you can listen to
ultrasonic frequencies between approximately 25 and 35 kHz.
Repeat this exercise with the frequency division system (i.e. set the HET/DIV switch to the DIV position).
Here the entire frequency range is made audible regardless of the setting of the FREQUENCY control.
If the volume control is turned up too high, acoustic feedback (a howling sound) may occur, particularly
when the detector is working in the frequency division mode. This is a consequence of the broadband
behaviour of the frequency division system; the highest frequencies from the loudspeaker are picked up
by the microphone, amplified and fed to the loudspeaker again. To avoid this, simply turn down the
volume control or use headphones instead.
SOME TECHNICAL INFORMATION
The Heterodyne System.
Several different principles exist to convert ultrasound into audible sound. As mentioned above, one of
the systems in the D 230 is based on the heterodyne principle. This technique means that a limited
frequency range is selected for conversion into the audible range. If the frequency control is set to 30
kHz, the range from appr. 25 to 35 kHz will be transformed. This is illustrated in the figure below.
Assume an ultrasound source of c onstant frequency is to be monitored. When the frequency control is
turned from low frequencies to higher, a high-pitched tone w ill be heard in the loudspeaker when the
frequency setting is appr. 5 kHz lower than the frequency of the ultrasound source. The closer the
tuned frequency comes to the ultrasound's frequency, the lower the frequency fo the loudspeaker tone
gets. When both frequencies are identical the resulting output frequency becomes zero, i.e. nothing is
heard in the loudspeaker. If you continue to turn the frequency control to higher frequencies, a tone will
again be heard in the loudspeaker, however this time the frequency will increase as the tuned
frequency increases. By tuning the frequency control up and down it is possible to locate the frequency
resulting in a zero Hz output frequency (the tuned frequency then equals the frequency of the
ultrasound).
NOTE: Although the example above well illustrates the heterodyne principle, constant frequency
sounds are very rare in practice, so there you will only be able to get an approximate measure of the
signal frequency.
The Frequency Division System.
Using the detector in the frequency division mode, the entire frequency range 10-120 kHz is made
audible at the same time. This means that you will not miss any bat activity just because the frequency
control was out of tune, as may be the case with the heterodyne system. On the other hand, since the
frequency division system is a broadband system, the sensitivity is a little lower, so in order to detect
the bats at long distance the heterodyne system may be preferred.
The frequency division system counts cycles of the incoming ultrasound and generates one output
cycle for each ten cycles of the input signal, i.e. the frequency is ten times lower than the original
frequency. The frequency division system used in the D 230 is of the more advanced ”retained
amplitude” type. This means that the amplitude of the output signal will follow that of the input signal
(see the figure on next page).
OUTPUTS
The two 3.5 mm sockets are used to connect a set of headphones or a tape recorder. The TAPE output
is not affected by the setting of the volume control or the HET/DIV switch. When the COM switch is
pressed, the frequency division output signal is temporarily replaced by the amplified microphone
signal, enabling the reecording of spoken comments on the tape. The maximum length of any
connected cable is 1 meter.
The PHONES socket may be used to connect a set of stereo headphones with a 3.5 mm plug.
