Specifications include, but are not limited to: Specific features should include: • Teacher Transmitters will operate on the 2.4 GHz ISM band and be globally license-free. • Teacher Transmitter must include automatic frequency hopping which guarantees no interference with other 2.4GHz ISM networks or Wi-Fi systems • The Teacher Transmitter microphone must allow for creating new networks (The network shall allow the use of up to 35 microphones) o All networks must be license-free o Frequency planning must not be required, independent of the number of networks o The privacy in the network must be guaranteed • The Teacher Transmitter microphone must start in the last used network after powering off and powering back on. • The Teacher Transmitter microphone shall automatically adjust the gain of the teacher’s speech signal depending on the environmental noise • The Teacher Transmitter microphone must feature automatic working voice activity detection (VAD) which will suppress the ambient noise if the teacher is not talking and automatically activate the receivers if the teacher starts talking • The audio bandwidth shall be 100Hz – 7.3 kHz • The Teacher Transmitter microphone shall allow to connect an additional receiver to the network with one button press • The Teacher Transmitter microphone must allow another educational transmitter to join the network just by pressing the connect button on the teacher microphone • The Teacher Transmitter microphone used as secondary transmitter microphone in the network must be allowed to create a sub-net to talk to an individual child spontaneously • The Teacher Transmitter microphone must not require programming through a separate software application • The Teacher Transmitter microphone must feature a manual on/off switch and an LCD • The Teacher Transmitter microphone must feature a mini USB for charging • The Teacher Transmitter microphone must have audio input capabilities • The Teacher Transmitter microphone must feature a Mute button with a clearly visible indicator when activated • The Teacher Transmitter microphone must feature a touchscreen display. • The Teacher Transmitter microphone shall include a with directional microphone characteristics