Pyon Chol Ung, a researcher at the Faculty of Communications, has developed and introduced a directive communication system in pits using electric-car lines.
The system enables route directive communication with moving electric cars through electric car lines in pits.
The pit directive transceiver consists of a digital signal processing unit, an interface with electric car lines, an audio signal interface and transmission and reception units.
The digital signal processing unit is responsible for carrying various commands and status signals between all peripheral devices, compressing and coding the audio data from the audio signal interface, digitally phase-modulating the audio data in succession, digitally demodulating the high-frequency signals from the interface with electric car lines and decoding the compressed audio data.
The interface with electric car lines plays a role of blocking DC and AC noises from electric car lines and passing only necessary high-frequency signals.
The audio-signal interface converts the analog audio signals generated from the microphone into digital signals and transfers them to the digital signal processing unit. It also converts the digital audio data generated from the digital signal processing unit into analog signals and outputs them through the speaker.
The transmission unit is made up of a backup amplifier, an output terminal and a coupling transformer. It amplifies digitally modulated high frequency signals to a certain degree. As the transceiver operates on a battery, it is important to enhance the efficiency of the output terminal. Therefore, a D-grade symmetrical amplifier with a field effect output transistor was chosen for the output amplifying unit.
The reception unit is comprised of a limiter, a band-pass filter and a high frequency amplifier. It amplifies the trivial signals coming from electric car lines with noise and removes unnecessary noises.
As the system does not need additional wired or wireless communication devices such as communication cable or radio repeaters but only existing electric car lines, it saves not only a huge amount of money for communication equipment but also a lot of labour necessary for its maintenance, repair and operation.