Audio Transmission over Power Lines
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I designed power line communication hardware because I intended to transmit audio waves from one end to another using power lines as a medium of transmission. The sound wave was modulated by frequency using a 200 kHz square wave which would further be demodulated using a demodulation circuit operating at the same frequency. Theoretically, everything appeared achievable and easy. Trying to realize the circuits proved that the reverse was true for reasons to be explained later. Switching to sinusoidal carrier achieved my goal, if I get over security problems.
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After many trials, I designed an isolation circuit that can be implemented between each of the transmitter and receiver circuits on one hand and the power lines on the other hand. The main purpose of the isolation circuit is to filter the low frequency waves and pass the high frequency waves.
Testing was conducted to each item individually then the whole system was tested all together.
The circuits that I designed are relatively small and use already installed power lines so that the setup is effective and at low cost. Normal copper power lines give us the ability to use a wide range of frequencies that makes no sense if we do not exploit it.
Whenever someone hears about my project, s/he directly argues why not use a wireless transmission that uses air as a medium? This may be true if security is not important. Wired system is not a practical option for longer distances and the reliability of a completely wireless system is not the best. The goal of my project is to reduce hacking possibilities using cheap means achieving the highest reliability. In areas where security utters the most, analog wireless broadcasting may be easily intercepted especially if the used frequency is known. My project does not differ a lot except that the transmission medium is more secure, especially that high frequencies becomes highly attenuated after passing through power transformers of the grid. High frequencies will not even survive after they pass the inductance of the circuit breaker.
In addition, using simple components like resistors and capacitors keeps my project at low cost, while getting a very good sound quality due to minimized data loss. Cost and quality of sound had priority in mind from the time I started my project.
My project goals may be extended to different households. A stereo does not need to be directly connected to its speakers. Plugging the speakers in any outlet inside the house will make it receive the audio signals sent from its base that is found in a fixed place. Telephone lines are not needed anymore, especially in historical places where re-installing telephone cables causes a headache.
The circuits were designed to carry audible audio signals that happen to be between 20 Hz and 20 kHz. Considering my intended goals, I did not care much for transmitting signals above 4 kHz. Ideally, the transmitter and the receiver must be able to be used anywhere in a house as long as they are on the same circuit breaker with no remarkable loss in quality. Unfortunately this was not achievable using the square carrier signal. Both the transmitter and the receiver were able to be connected to power lines without damaging the components or causing any danger for the user. The system I used allows the transmission of one channel. Carrying the implementation of multiple channels would require repeating the same project but using a different carrier frequency. This product can be considered as a “neat” system without wires running throughout the place……….
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