Benthowave Instrument Inc.

BENTHOWAVE INSTRUMENT INC. Acoustic Transducer & System 

Sonar Signal Demodulator: Complex Demodulation

Sonar Signal Demodulator

BII-2040 series demodulates a narrowband Sonar signal such as pulsed SINE and CHIRP around its carrier frequency fc in time domain and keeps only the meaningful frequency content of the signal, and thus limits the amount of sampled digital data to process at later signal processing. The demodulated signal contains in-phase and quadrature components which describes the received signal truthfully. The envelope and phase shift can be extracted with signal processing in software. Real-time signal processing of high frequency SONAR is practical in field with BII-2040 series.

Besides, BII-2040 series can also be used to convert ultrasound to audible sounds for real-time listening of marine animals, Sonars, etc....

BII-2040    Sonar Signal Demodulator: Complex Demodulation

Suggested Application  
Target Angle Estimation/Target Tracking
Doppler Sonar System
Underwater Positioning: LBL, SBL, USBL
Sonar Signal Recording, Data Logging
Underwater Communication, Sound Ranging
Active Sonar Signal: pulse/burst SINE and Chirp
Imaging, Multibeam, Split Beam and Interferometry Sonar
Education on Sonar Signal Processing
Listening Ultrasound Signal
Quadrature Sampling


SONAR Demodulator BII-2041 BII-2042 BII-2043 BII-2044 BII-2045 BII-2046 BII-2047 BII-2048 BII-2049
OUTPUT FILTER                  
Type: Bessel
Low Pass
Low Pass
Low Pass
Low Pass
Low Pass
Low Pass
Low Pass
Low Pass
Low Pass
Attenuation(dB/Decade): 40 40 40 40 40 40 40 40 40
-3dB Cutoff: 1kHz 10kHz 20kHz 30kHz 40kHz 50kHz 60kHz 80kHz 100kHz
Note: Choose appropriate -3dB low pass cut-off frequency to match the information bandwidth of the SONAR signal.
Type: Complex Signal Demodulation
Reference Signal: Built-in, SINE and COSINE
Reference Frequency: Fixed, specified by buyer when ordering. Factory-set. See "How To Order".
Available Range: 20 kHz to 2 MHz
Input Coupling: AC Coupling
Input Impedance: 1. Default: 1 kΩ
2. Customized: 50 Ω, specify when ordering.
Input Level Range: 2 mVpp to 10 Vpp
Input High Pass Filter: 1. Default: 1.6kHz
2. Customized
Cable: Coax
Cable Length: 1. Default: 0.15m
2. Custom
Connector: 1. Default: Wire Leads
2. Male BNC
Outputs: Two Channel, Complex Demodulated Signals: In-phase and Quadrature Components.
Output Coupling: DC Coupling
Output Impedance: 50 Ω
Cable Drive Capability: 100 m
Cable: Coax
Cable Length: 1. Default: 0.15m
2. Custom
Connector: 1. Default: Wire Leads
2. Male BNC
Supply Voltage: ±8 to ±15 VDC
Current (Quiescent): 12 mA @ ±12 VDC
Power Supply Cable: 0.15m Wires, Red Wire: +VDC, Blue Wire: -VDC, Black Wire: Common.
Suggested DC Supply: +9VDC Battery, Marine Battery, Automobile Battery, Fixed DC Linear Power Supply, Not Included.
DO NOT use variable power supply whose maximum supply voltage is higher than the above rated voltage.
DO NOT use switching mode DC power supply.
Size: Rectangular PCB, LxWxH=68.6x36.1x36mm
Mounting: 4xΦD3.2mm through-holes
Operating Temperature: -40°C to 85°C
Storage Temperature: -50°C to 105°C
How to Order:
BII-204x /XXXX
Part Number Frequency of Reference Signal.
Generally the buyer shall specify this parameter to be Carrier Frequency of Narrowband Signal, or Start Frequency of CHIRP Signal.
in kHz
Description: For example:
BII-2041/24: BII-2041, Frequency of Reference Signal: 24kHz.
BII-2042/120: BII-2042, Frequency of Reference Signal: 120kHz.
BII-2043/200: BII-2043, Frequency of Reference Signal: 200kHz.
BII-2044/420: BII-2044, Frequency of Reference Signal: 420kHz.
BII-2049/2000: BII-2049, Frequency of Reference Signal: 2MHz.

Technical Note

According to Nyquist–Shannon sampling theorem:
If the highest frequency in the original signal is f, the lower bound on the sampling frequency for perfect signal reconstruction is 2f, called Nyquist sampling rate.
To get better resolution in particular applications such as underwater acoustic image, Sonar signal frequency is quite high up to 2MHz. This imposes cost on electronic processing circuit such as A/D converter and data storage.
With BII-2040 series, which shifts high frequency signal to low frequency signal containing the signal bandwidth only, your electronic system only processes the low bandwidth signal, which decease the cost incredibly.

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