Battery Connection; Display Initialisation; Peak-Frequency Detection; Frequency-Division - Batbox Duet User Manual

BATTERY CONNECTION

When fitting the battery, make sure that the unit is switched off and that
you fit it correctly. Connecting it the wrong way round may cause damage
to the detector.

DISPLAY INITIALISATION

When the Duet power is turned on, the display will show all used segments
(188) for one second, followed by the software version (e.g. 2) for one
second, after which the heterodyne frequency setting will be displayed.
Whilst the display is initialising, the audio output can still be heard.

PEAK-FREQUENCY DETECTION

The resonant frequency of bat sonar varies according to the species.
This resonance is often called the peak-frequency. When listening on
the heterodyne system, this is the frequency setting called the null-point;
the point at which the output of the detector is strongest and lowest in
pitch. Bats focus most of the energy in their calls at a particular frequency.
This resonance or peak-frequency will be determined by the size of the
bat and its echolocation requirements.
A good example of the importance of peak–frequency is the difference
in the calls of British pipistrelles, Pipistrellus pipistrellus (44 - 48kHz),
Pipistrellus pygmaeus (52 – 56 kHz) and the rarer Pipistrellus nathusii
(39 – 40 kHz)*. Although it is possible to find these frequencies using the
heterodyne section of the Batbox Duet, a certain amount of subjectivity
is involved. When the bat is moving at speed and might only make one
pass, there may not be time to tune-in to the peak-frequency.
By recording from the frequency division output, no bat can be missed,
regardless of the frequency set on the digital counter. The Duet listens to
the entire ultrasonic range between 17kHz and 120kHz. This means that
if you are monitoring a noctule and a pipistrelle at 55kHz flies overhead,
even though you may not hear it in the heterodyne, it will be recorded, as
well as the noctule, for later analysis.
* Individuals from each species may fluctuate by a few kHz above or below
these frequencies.
Recording ultrasound, without a bat detector, can be tricky.
Firstly, microphones need to be specially designed and very sensitive.
Also, the specialist tape recorders and other instruments able to cope
with such high frequencies are extremely expensive. Most domestic tape
recorders will only record frequencies up to 15-20kHz. Heterodyne
and frequency-division techniques make it possible for us to hear bat
echolocation calls.

FREQUENCY-DIVISION

The Batbox Duet divides the incoming sonar frequency by 10, bringing
the ultrasonic calls into human hearing range (25kHz would become