Telecommunications – Transmitter – Amplitude modulation
Patent
1978-03-14
1980-09-30
Bookbinder, Marc E.
Telecommunications
Transmitter
Amplitude modulation
179 1F, 179 1VL, 332 38, 455 91, H04B 104, H03C 106
Patent
active
042258227
ABSTRACT:
An amplitude modulation circuit for a transmitter has an automatic level controlled circuit (ALC circuit), including in its negative feedback loop a series circuit of a high-pass filter, a rectifier circuit and an eliminator circuit, for modulation degree suppression, thereby avoiding overmodulation. The high-pass filter is so designed that the negative feedback signal level for modulation degree suppression of the ALC circuit is raised as the audio-signal frequency supplied to the transmitter increases. In the modulation circuit having such ALC circuit, a sufficiently high mean modulation degree may be obtained without encountering overmodulation if the main spectrum components of the input audio-frequency signal are distributed in the intermediate range of the audio-signal frequency band. On the other hand, if the main spectrum components of the audio-frequency signal are distributed in the higher (high-pass) range, the upper limit of the modulation degree is restricted to a moderately lower value so as to reduce production of spurious signals. Here the ALC circuit operates so as not to change the frequency characteristic of the audio-frequency input signal but to suppress the modulation degree uniformly throughout the frequency band of the audio-frequency input signal. Therefore, the modulation circuit does not cause variation in a tone quality of the input signal.
REFERENCES:
patent: 1734219 (1929-11-01), Lorance
patent: 2255683 (1941-09-01), Singer
patent: 2312260 (1943-02-01), Miller
patent: 3292116 (1966-12-01), Walker et al.
patent: 3398381 (1968-08-01), Torick et al.
patent: 3571529 (1971-03-01), Gharib et al.
"Installation & Operating Instructions of AM citizen's Band Transceiver"--Browning Laboratories, Inc. P. 10.
Bookbinder Marc E.
Tokyo Shibaura Electric Co. Ltd.
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