Amplifiers – With control of power supply or bias voltage – With control of input electrode or gain control electrode bias
Patent
1980-10-03
1983-01-11
Mullins, James B.
Amplifiers
With control of power supply or bias voltage
With control of input electrode or gain control electrode bias
179 1VL, 330 2, 330126, 330281, 330306, H03G 706
Patent
active
043684351
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to audio processing and modulation systems and, more particularly, to an improved audio processing system intended for maximizing the efficiency of transferring audio frequency signals for providing high modulation power and for enhancing signal intelligibility and clarity while avoiding loss of audio dynamics.
In the radio frequency transmission and reception of modulated signals a major problem has always been to obtain a high level of dynamic amptitude while not only containing the full spectrum of speech harmonics but also keeping the audio band width of the transmitted radio signals as narrow as possible.
Many modes of radio operation and types of audio or other signal modulation have been used where these matters are of great concern. Principle forms of modulation presently in use are AM, SSB and FM. AM and FM utilize a constant carrier principle while SSB has a direct audio-into-power-out relationship, and is not a constant carrier mode of transmission when the carrier is suppressed, as is quite common.
Frequency Modulation (FM)
In constant carrier FM modes, the dynamic content of the signal and the audio band width of the signal are directly proportional to the amount of deviation allowed to be imposed on the carrier. E.g., in narrow band FM transmissions, an audio band width of 5 kHz may be imposed. As a result, dynamic harmonics of voice characteristics are restricted and lost.
Amptitude Modulation (AM)
In the constant carrier mode of amptitude modulation, dynamics are expressed in a direct relationship with the amptitude of the constant carrier and audio frequency band width being theorectically limited only by the radio frequency band width available. In commercial communication systems utilizing the amptitude modulation mode of transmission, the audio band width usually is restricted to eliminate spurious amptitude modulated pulses resulting from ignition and other electrical noise and atmospheric conditions, etc., inter alia. An AM mode now commonly used takes the form of pulse amptitude modulation (PAM), as in teletype and data transfer systems.
Single Side Band (SSB)
The more recent mode of SSB modulation is by far the most efficient form of transmitting an audio modulated radio frequency (RF) signal. The major drawback of this mode of modulation is the extremely restricted audio band width imposed, resulting in extreme losses of dynamic intelligibility. These losses are often traded off against the high efficiency of SSB systems.
Characteristics of Human Speech With Reference to Radio Transmission
Relative to radio transmission, attributes of human speech of concern are dynamic amptitude and harmonic relationship. The latter is extremely important in identification intelligibility.
Dynamic amptitude can be defined as the varying level of audio received by a modulation stage in any mode of modulation. The human voice is made up by a complex structure of harmonics, the main bands of harmonics falling within a 3 kHz band width. A speech band pass frequency commonly selected is 300 Hz to 3,000 Hz, and all other harmonics are generally suppressed. However, these out-of-bands harmonics define voice character and, thus, intelligibility. But the suppressed harmonics fall in such a wide spectrum that if the entire speech harmonic make-up were to be transmitted, a transmission band width of some 15 kHz would be required. With modern narrow band voice transmission systems, this would become impossible.
Consequently, speech processing has been utilized heretofore.
For example, the use of band pass frequency filters in speech transmission systems is very common. Although speech band pass frequencies often vary, the pass band rarely exceeds 3 kHz. This type of processing is used chiefly with narrow band audio transmission systems. It has the advantages of being not only simple and economical to provide but also offering the expedient of limiting the power band of speech to a 3 kHz window that can be readily utilized in audio transmis
REFERENCES:
patent: 3818149 (1974-06-01), Stearns et al.
patent: 4045748 (1977-08-01), Filliman
Coghill Marvin
Eberhardt Alfred F.
Mullins James B.
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