HYBRID FREQUENCY SHIFT-AMPLITUDE MODULATED TONE SYSTEM

• US 3,626,417 A
• Filed: 03/07/1969
• Issued: 12/07/1971
• Est. Priority Date: 03/07/1969
• Status: Expired due to Term

• Current Assignee: Everett A. Gilbert
• Original Assignee: Everett A. Gilbert
• Inventors: Gilbert, Everett A.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Mayer, Albert J.
• Application Number:
  US04/805,294
• Time in Patent Office: 1,005 Days
• Field of Search: 178/66 325/30,163,26,307,320 179/2DP,15BY,15BM 332/17 343/200-203
• US Class Current: 370/204
• CPC Class Codes: H04J 9/00 Multiplex systems in which each channel is represented by a different type of modulation of the carrier
• CPC Class Codes: H04L 27/32 Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
• CPC Class Codes: H04L 5/04 the signals being represented by different amplitudes or polarities, e.g. quadriplex

Abstract

A two channel data transmission system using amplitude modulation of the frequency shifted carrier of one channel to transmit the data of the second channel. Both channels operate at the maximum data rate at which either a single AM or FS channel would operate over the same band width.

Claims

1. In a data transmission system, a transmitter for modulating two channels of nonsynchronous binary data into a single hybrid amplitude and frequency modulated carrier signal comprising:

a. A first channel with means for generating a frequency shift carrier with modulation products attenuated that are derived from frequency components in a first data signal that exceed the maximum dot cycle data rate, b. A limiter circuit for the frequency shift carrier, c. An amplitude modulator circuit with two sets of terminals, d. Means for connecting the limited frequency shift carrier to one set of terminals of the amplitude modulator circuit, e. For a second channel, means for clamping binary signals at a second set of terminals to one polarity, f. A means for restricting the minimum and maximum potentials of this unidirectional signal, g. A low-pass filter attenuating frequencies above the maximum dot cycle rate of the second binary signal, h. Means for connecting the unidirectional, filtered and limited second binary signal to the second terminals of the amplitude modulator, i. An output amplifier with input connected to the output of the amplitude modulator, j. A band-pass filter with input connected to the output amplifier and output connected to a common transmission circuit, the bandwidth of this filter being at least twice the maximum dot cycle rate.

2. In an amplitude-frequency modulated data transmission system, a receiver for converting a hybrid amplitude and frequency modulated signal into two independent data channels comprising:

a. A band-pass filter with a set of output terminals for connecting to a common transmission circuit, b. For demodulating the frequency shift components of the hybrid carrier signal, a limiting amplifier with input connected to the output terminals of the band-pass filter, c. A frequency shift discriminator circuit with input connected to the output of the limiting amplifier, d. A circuit for adjusting the telegraph bias of the output of the discriminator, e. A regenerative amplifier with input connected to the biased output of the discriminator, the output of this amplifier being the first data channel and a replica of the data signal carried by the frequency shift carrier modulation products, f. For demodulating the amplitude components of the hybrid signal, a variable attenuator connected to the output terminals of the band-pass filter, g. A linear amplifier with input connected to the output of the variable attenuator, h. A full wave rectifier circuit with input connected to the output of tHe linear amplifier, i. A low-pass filter connected to the output of the full wave rectifier circuit, j. For the purpose of regulating the telegraph bias of the second data channel, a two terminal voltage comparator circuit with one input connected to the output of the low-pass filter, k. Means for generating a slowly varying voltage proportional to the average signal level of the hybrid carrier at the output of the common transmission circuit, l. Means for connecting the above mentioned voltage to the second terminal of the voltage comparator, m. A regenerative amplifier with input connected to the output of the voltage comparator circuit, the output of the amplifier being the second data output channel and a replica of the data signal carried by the hybrid carrier amplitude modulation products.