Transmitting a Digital Signal without an Analog Carrier Signal?

  • Thread starter Mirza Vaseem Raza
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Thread Starter

Mirza Vaseem Raza

Can a Digital Signal be transmitted without using a Carrier Signal (Analog)? If it is possible then can you tell me the technique..
 
Yes, a digital signal can be transmitted on a balanced two-wire network without an analog carrier signal. The technique used by Foundation Fieldbus H1 and PROFIBUS-PA uses Manchester encoding. A trapezoidal wave signal is generated similar to an AC sine wave at a synchronous clock frequency. This signal is modulated by the data stream to shift the clock pulses differently for "one" bits and "zero" bits. For each bit, the signal crosses zero voltage once, but the voltage between the two wires will be + followed by zero followed by - for a value of binary one, and then -, zero, an + for a value of binary zero.

See the method described in terms of square waves (used by most networks including Ethernet) here:
http://upload.wikimedia.org/wikipedia/commons/9/90/Manchester_encoding_both_conventions.svg

Dick Caro
 
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Mirza Vaseem Raza

Mr. Caro thank you very much for your valuable information. It almost cleared my most of my doubts. Thank you once again.

Regards
Mirza Vaseem Raza
 
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