Basismekanismen i detektorene er at de omformer flaggermusenes
artskarakteristiske ultralyder som de bruker til ekko-lokalisering, til hørbar
lyd (for oss). Dette gir en lyd der vi kan kjenne igjen de ulike artene.
De enkleste modellene (inkludert denne) har bare denne
lydomformingsfunksjonen kalt heterodyning, som oversetter lyden i
nåtid på en valgt frekvens. Slike detektorer gjør det mulig å gjenkjenne de
fleste artene, og for eksempel finne kolonier. Zoologisk Forening anbefaler
dette for nybegynnere.
En mer avansert form for direkte hørbar oversettelse er frekvensdeling
der alle frekvensene av flaggermusens ultralyd blir oversatt.
De mer kostbare modellene for viderkommende entusiaster og
fagfolk har i tillegg tidsekspansjon. Lyden lagres da først i et
minne. Deretter kan den spilles i et redusert tempo der alle detaljene kommer
fram. Dette gir også bedre muligheter for opptak, arkivering og dokumentasjon.
Mer om
ekkolokalisering og flaggermus på Norsk Zoologisk Forenings sider
Produsentens info:
* Clear backlit 4 digit LCD frequency display – Quartz accurate – Highly visibility day and night
* Large digits – ideal for users who needs glasses
* Enhanced oscillator frequency range 10kHz to 130kHz
* Extended low frequency coverage – suitable for insects and some birds
* Magenta custom molded platic case – Compact efficient design
* Front faced low distortion loudspeaker
* Specially contoured microphone housing for enhanced frequency sensitivity
* 4 AAA Alkaline, NiCd, or NiMH ‘environmentally friendly’ rechargeable cells (not provided)
* Low power design gives very long battery life
* Large diameter frequency dial
* Conveniently placed output sockets on the bottom edge of the case
* Constant level recorder output socket
* Headphone socket which automatically mutes loudspeaker
* Build in LED torch
* Edgewise volume and frequency controls for easy one-handed operation
* Wrist strap for added security and convenience when taking notes.
Using the Magenta Bat4 Bat detector
1 Introduction
2 How it Works!
3 Controls
4 Display
5 Batteries
6 Checking
7 In the ‘field’
8 Technical Specification
Introduction
Bats use inaudible ultrasonic ‘sounds’ like a sophisticated radar
system to avoid obstacles and locate prey.
The bat5 detector takes the inaudible high frequency ultrasound and
converts it to frequencies between 100Hz and 12kHz which are in the
range of human hearing.
The detector can be tuned to receive a range of frequencies from 10
to 130 kHz. The sounds are heard via a built in waterproof loudspeaker,
and there is a socket to connect standard stereo ‘walkman type’
headphones. A separate constant ‘low level’ output is provided for
connection to a tape recorder or PC sound card.
How it Works
The detector uses the Heterodyne principle. Ultrasound is picked up,
amplified, and mixed in a special way with another signal generated
in the bat detector. The mixer produces the audible difference
frequency between the two. In a typical situation the bat will be
sending ultrasound at 45kHz, the bat detector signal will be set to
43kHz and the audible output will be the difference between the two
– which is 2kHz.
Controls
There are two rotary controls. A combined volume on/off switch, and
a large calibrated frequency control which adjusts the signal to be
mixed with the ultrasound from the bat.
A small push button switch turns on a bright white LED torch light.
Display
A large ‘LCD’ Display shows the frequency with Quartz accuracy to
within 100Hz. A low current backlight illuminates the display with a
soft even light for night use.
Batteries
Four AAA alkaline or rechargeable batteries are used. The Bat5
works equally well with both types. Alkaline give very long life, whilst
modern rechargeable cells – especially NiMH are an environmentally
friendly alternative.
Note: Make sure the detector is switched OFF when changing
the batteries.
Checking
There are many common sources of ultrasound – jangling keys,
rustling newspapers, rubbing two fingers together, and dropping
paper clips onto a hard surface all produce interesting and different
responses. Computer fans also produce steady ultrasonic whistles.
Any of these sources can be used to check that the detector is
working. Start with the volume half way, and set the frequency control
to 40kHz.
The ‘heterodyne’ principle is demonstrated very well if continuous
source such as a computer fan is available. As the frequency control
is rotated, the pitch of the detector output will change and fall to zero
when the frequency of the fan noise and the local signal are equal.
Rotating the Frequency control in either direction will result in the
pitch rising, as the difference between the two signals increases.
In the Field
When looking for bats, set the frequency to 45kHz. Many different
bats echolocate at around this frequency. When looking for a particular
species set the control to the appropriate frequency and ‘scan’
the area by pointing the detector in different directions. Ultrasound is
very ‘directional’ and the microphone is much more sensitive to ‘head
on’ signals than to signals from either side. It is often possible to
locate a bat by pointing the detector to the strongest ultrasound long
before it can be seen.
Once bats are detected, the frequency control can be ‘fine tuned to
get the best signal. If there are two relatively close frequency settings
that give similar signals, always chose the lower one*.
The detector only receives ultrasound, it does not transmit anything
that will disturb the bats. The only output is the audible signal from
the loudspeaker – which (presumably) is of no interest to the bats
even if they could hear it.
*Heterodyne detectors produce the difference between the bat frequency
and the local signal. If the bat frequency is below the local
signal frequency, a fall in the bat frequency will result in a rise in the
pitch of the audible signal – because the difference will be greater.
This is an inversion of the ‘frequency spectrum’.
If the Bat frequency is above the local signal, a fall in the bat frequency
will reduce the difference and so produce a fall in the audible
signal – so the ‘frequency spectrum’ is the right way round.
Technical Specification
Type: Heterodyne
Frequency Range: 10kHz – 130kHz
Bandwidth: +/- 9kHz
Output power: 0.5 watts
Headphone socket: 3.5mm Stereo
Tape Socket: 3.5mm stereo jack
Tape Output: 100mV typical
LED torch White 5mm led.
Batteries: 4 x AAA
Speaker: Waterproof low profile mylar
Microphone: Wide band electret.
