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FSK Transmission System with Data Synchronized to Shift Frequency

IP.com Disclosure Number: IPCOM000094497D
Original Publication Date: 1965-Feb-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Connors, WE: AUTHOR

Abstract

Usually in frequency shift keying systems it is necessary to insert a bandpass filter at the output to eliminate undesirable frequency components. These are incidentally generated by the frequency shift keyer. In this frequency shift keyer, the need for a bandpass filter is eliminated. Such is achieved by synchronizing the frequency shift transitions with the zero voltage points in a low-frequency f1 signal.

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FSK Transmission System with Data Synchronized to Shift Frequency

Usually in frequency shift keying systems it is necessary to insert a bandpass filter at the output to eliminate undesirable frequency components. These are incidentally generated by the frequency shift keyer. In this frequency shift keyer, the need for a bandpass filter is eliminated. Such is achieved by synchronizing the frequency shift transitions with the zero voltage points in a low- frequency f1 signal.

Balanced Modulators (BM' s) I and II cooperate to perform single sideband modulation. BM I receives a signal from both oscillators f(1) and f(2). BM III receives these same two signals after they are phase-shifted 900. The outputs from BM' s I and III are summed to form either the upper or lower sideband. BM II acts as a phase reversal switch for the f(2) frequency being fed to BM I. If BM II passes the frequency f(2) without a phase change, the output of the system is the lower sideband. If BM II operates to shift the phase of signal f(2) 1800, the output of the system is the upper sideband.

When two constant frequency sources f(1) and f(2) are used, the system becomes a frequency shift keyer. The frequency shift keying is used to transmit data. The data source provides a binary +/- signal to BM II and thus controls the phase reversal of the frequency f(2) to BM I. When f(2) is passed through BM II without a phase reversal, the output is f(2) - f(1). When f(2) is shifted 1800 before going to...