Hearing loop systems are used for broadcasting audio information
to individuals with T-Coil equipped hearing aids. They are used in public
areas such as theatres, churches, meeting and conference rooms, etc.
Target specification
Maximum audio input level: 1V peak
Maximum audio output level with the receive coil placed in the center of the transmit coil: 0.25V peak
-3dB small-signal bandwidth: 60Hz ... 15 kHz
Full-power bandwidth: 60Hz ... 5kHz
Input impedance transmitter: > 10kOhm
Load impedance receiver: > 2kOhm
Receiver output noise (no input signal, frequency range 60Hz ... 15 kHz) < 100uV RMS
Power supply voltage +/- 15V
Design tasks
Groups of four to six participants will design, build and test a hearing loop system. Two or three participants design and build the transmit coil driver, while the other two or three design and build the receive coil amplifier. All group members participate in the selection of the system architecture (amplifier types) and in the the definition and the execution of the test plan.
The design comprises the following steps:
Derive the specifications from the application description and group them in:
Performance requirements
Interface requirements
cost factors
environmental conditions
Design a lumped element network model of the transmit-receive antenna system
Set-up selection criteria for the electrical quantity driving the transmit coil and for the electrical quantity to represent the information from the receive coil
Design the system architecture, model the transfer, and derive specifications for the amplifiers:
type and gain
noise requirements
signal levels and drive capability requirements
frequency response
Design a test plan
Design the transmit coil driver amplifier
Design the receive coil amplifier
Present your project on a poster
Build the system
Execute the test plan
Discuss the results with each other and with the instructors
Data sheets
Below the link to the data sheet of the receive coil.
