US4332978A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Low frequency AM stereophonic broadcast and receiving apparatus
Assignee: Magnavox Consumer Electronics Co
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Filing: 1980-04-23
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Granted: 1982-06-01
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Expires: 2000-04-23
Abstract
Abstract Apparatus is described for transmitting and receiving stereophonic broadcasts in the low frequency commercial AM broadcast band. A transmitter is described which modulates the phase and amplitude of a broadcast signal with separate information signals. A pilot tone may also be included to identify the transmission as stereophonic. Receiving means for detecting the PM and AM components to derive separate signals for stereophonic reception are included.
Inventors
- 👤 Robert D. Streeter
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 20:08
CPC Classifications
H; H04; H04H; H04H20/00; H04H20/44; H04H20/46; H04H20/47; H04H20/49
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
223 words
In a system for broadcasting stereophonic related signals L(t) and R(t), wherein said signals modulate a broadcast signal in amplitude as a summation signal L(t)+R(t) and in phase as a difference signal L(t)-R(t), said broadcast signal being further frequency modulated with a low frequency signal tone, a receiving apparatus comprising: (a) a mixer; (b) a local oscillator connected to said mixer; (c) means for supplying said broadcast signal to said mixer; (d) means for amplifying the signal from said mixer, said means having automatic gain control for providing a signal having a substantially constant level; (e) means for removing amplitude modulation components from said constant signal, whereby a first audio signal proportional to said summation signal L(t)+R(t) is formed; (f) phase and frequency detector means connected to receive a portion of the signal supplied by said means for amplifying, said detector means supplying an indicator signal proportional to said low frequency signal tone, and a second audio signal proportional to said difference signal L(t)-R(t); (g) means for combining said first audio signal with said second audio signal to form a pair of stereophonic related signals; and (h) means for applying said pair of related signals to a speaker system in response to said indicator signal, said means applying said first audio signal to said speaker system in the absence of said indication signal.
Claim 2
Dependent Claim
223 words
In a system for broadcasting stereophonic related signals L(t) and R(t), wherein said signals modulate a broadcast signal in amplitude as a summation signal L(t)+R(t) and in phase as a difference signal L(t)-R(t), said broadcast signal being further frequency modulated with a low frequency signal tone, a receiving apparatus comprising: (a) a mixer; (b) a local oscillator connected to said mixer; (c) means for supplying said broadcast signal to said mixer; (d) means for amplifying the signal from said mixer, said means having automatic gain control for providing a signal having a substantially constant level; (e) means for removing amplitude modulation components from said constant signal, whereby a first audio signal proportional to said summation signal L(t)+R(t) is formed; (f) phase and frequency detector means connected to receive a portion of the signal supplied by said means for amplifying, said detector means supplying an indicator signal proportional to said low frequency signal tone, and a second audio signal proportional to said difference signal L(t)-R(t); (g) means for combining said first audio signal with said second audio signal to form a pair of stereophonic related signals; and (h) means for applying said pair of related signals to a speaker system in response to said indicator signal, said means applying said first audio signal to said speaker system in the absence of said indication signal.
Claim 3
Dependent Claim
17 words
The receiver of claim 1, further comprising an indicator for indicating the presence of said indication signal.
Claim 4
Dependent Claim
107 words
The receiver of claim 2, wherein said phase and frequency detector means comprises: (a) a voltage controlled oscillator; (b) a phase detector connected to receive a signal from said oscillator and a signal from said means for amplifying, said detector providing an output voltage proportional to the difference in phase between received signals constituting said second audio signal; (c) a low pass filter connected to receive an output voltage from said phase detector, said low pass filter providing a control voltage to said voltage controlled oscillator proportional to said low frequency signal tone; and (d) means for filtering said control voltage whereby an indicator signal is derived.
Claim 5
Independent Claim
187 words
A system for broadcasting and receiving first and second stereophonic related signals comprising: (a) a transmitter having means for combining said stereophonic related signals to produce a summation signal; means for subtracting said stereophonic related signals to produce a difference signal; means for frequency modulating a broadcast signal with a low frequency identifying signal; means for linearly phase modulating said broadcast signal with said difference signal; means for amplitude modulating said broadcast signal with said summation signal, whereby a broadcast signal is produced; (b) a receiver coupled to said transmitter having a local oscillator; means for mixing a portion of said broadcast signal with a local oscillator signal whereby an intermediate frequency signal is produced; an amplitude detector means for forming a signal from amplitude variations in said intermediate frequency signal; phase detector means for forming a signal proportional to the variation in phase of said intermediate signal; means for combining a signal from said amplitude detector means and said phase detector means for producing first and second stereophonically related signals; and means for providing a signal proportional to frequency modulation components in said intermediate frequency signal.
Claim 6
Independent Claim
187 words
A system for broadcasting and receiving first and second stereophonic related signals comprising: (a) a transmitter having means for combining said stereophonic related signals to produce a summation signal; means for subtracting said stereophonic related signals to produce a difference signal; means for frequency modulating a broadcast signal with a low frequency identifying signal; means for linearly phase modulating said broadcast signal with said difference signal; means for amplitude modulating said broadcast signal with said summation signal, whereby a broadcast signal is produced; (b) a receiver coupled to said transmitter having a local oscillator; means for mixing a portion of said broadcast signal with a local oscillator signal whereby an intermediate frequency signal is produced; an amplitude detector means for forming a signal from amplitude variations in said intermediate frequency signal; phase detector means for forming a signal proportional to the variation in phase of said intermediate signal; means for combining a signal from said amplitude detector means and said phase detector means for producing first and second stereophonically related signals; and means for providing a signal proportional to frequency modulation components in said intermediate frequency signal.
Claim 7
Dependent Claim
17 words
The stereophonic broadcast system of claim 4, wherein said identifying signal comprises a low frequency data signal.
Claim 8
Dependent Claim
24 words
The stereophonic broadcast system of claim 5, wherein said low frequency data signal contains data for identifying call letters of a particular broadcast station.
Claim 9
Dependent Claim
18 words
The system of claim 4, wherein said low frequency identifying signal has a frequency of substantially 5 Hz.
Claim 10
Dependent Claim
18 words
The system of claim 7, wherein the peak frequency deviation of the broadcast signal is substantially 20 Hz.
Claim 11
Dependent Claim
30 words
The system of claim 4, wherein said broadcast signal has a frequency modulation index resulting from said identifying signal different from the phase modulation index resulting from said difference signal.
Claim 12
Independent Claim
250 words
A system for broadcasting and receiving first and second stereophonic related signals comprising: (a) a transmitter having means for combining said stereophonic related signals to produce a summation signal L(t)+R(t); means for subtracting said stereophonic related signals to produce a difference signal L(t)-R(t); means for frequency modulating a broadcast signal having a frequency of W c with a low frequency signal tone having a frequency W o ; whereby a frequency modulated signal proportional to COS (W c t+A COS W o t) is produced; means for linearly phase modulating said broadcast signal at a modulation index B with said difference signal, whereby a signal COS (W c t+B(L(t)-R(t))+A COS W o t) is produced; means for amplitude modulating said broadcast signal with said summation signal at a modulation index M, whereby a broadcast signal [1+M(L(t)+R(t)] COS (W c t+B(L(t)-R(t))+A COS W o t) is produced; (b) a receiver coupled to said transmitter having a local oscillator; means for mixing a portion of said broadcast signal with a local oscillator signal whereby an intermediate frequency signal is produced; an amplitude detector means for forming a signal from amplitude variations in said intermediate frequency signal; phase detector means for forming a signal proportional to the variation in phase of said intermediate signal; means for combining a signal from said amplitude detector means and said phase detector means for producing first and second stereophonically related signals; and means for providing a signal proportional to frequency modulation components in said intermediate frequency signal.
Claim 13
Independent Claim
250 words
A system for broadcasting and receiving first and second stereophonic related signals comprising: (a) a transmitter having means for combining said stereophonic related signals to produce a summation signal L(t)+R(t); means for subtracting said stereophonic related signals to produce a difference signal L(t)-R(t); means for frequency modulating a broadcast signal having a frequency of W c with a low frequency signal tone having a frequency W o ; whereby a frequency modulated signal proportional to COS (W c t+A COS W o t) is produced; means for linearly phase modulating said broadcast signal at a modulation index B with said difference signal, whereby a signal COS (W c t+B(L(t)-R(t))+A COS W o t) is produced; means for amplitude modulating said broadcast signal with said summation signal at a modulation index M, whereby a broadcast signal [1+M(L(t)+R(t)] COS (W c t+B(L(t)-R(t))+A COS W o t) is produced; (b) a receiver coupled to said transmitter having a local oscillator; means for mixing a portion of said broadcast signal with a local oscillator signal whereby an intermediate frequency signal is produced; an amplitude detector means for forming a signal from amplitude variations in said intermediate frequency signal; phase detector means for forming a signal proportional to the variation in phase of said intermediate signal; means for combining a signal from said amplitude detector means and said phase detector means for producing first and second stereophonically related signals; and means for providing a signal proportional to frequency modulation components in said intermediate frequency signal.
Claim 14
Dependent Claim
144 words
A receiver for detecting a broadcast signal, said signal containing first and second stereophonic related signals modulated thereon, comprising: means for detecting amplitude variations of said broadcast signal, said means providing a signal representing the summation of said stereophonic related signals; means for detecting phase variations of said broadcast signal, said phase variation detecting means providing a signal representing the difference of said stereophonic related signals; squelch detector means for detecting the loss of said broadcast signal, said squelch detector means providing a switching signal during said loss of broadcast signal; means for combining said signal representing said difference between stereophonic related signals and said signal representing said summation of stereophonic related signals, whereby first and second stereophonic signals are produced, said means for combining including means for inhibiting the production of first and second stereophonic related signals in response to said switching signal.
Claim 15
Dependent Claim
144 words
A receiver for detecting a broadcast signal, said signal containing first and second stereophonic related signals modulated thereon, comprising: means for detecting amplitude variations of said broadcast signal, said means providing a signal representing the summation of said stereophonic related signals; means for detecting phase variations of said broadcast signal, said phase variation detecting means providing a signal representing the difference of said stereophonic related signals; squelch detector means for detecting the loss of said broadcast signal, said squelch detector means providing a switching signal during said loss of broadcast signal; means for combining said signal representing said difference between stereophonic related signals and said signal representing said summation of stereophonic related signals, whereby first and second stereophonic signals are produced, said means for combining including means for inhibiting the production of first and second stereophonic related signals in response to said switching signal.
Claim 16
Dependent Claim
37 words
The receiver of claim 11, wherein said means for combining produces said signal representing the summation of said stereophonic related signals when said squelch detector means provides a switching signal indicating the loss of said broadcast signal.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1985-05-31 | 1985-11-30 | 1986-06-01 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1989-05-31 | 1989-11-30 | 1990-06-01 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1993-05-31 | 1993-11-30 | 1994-06-01 | $7700.00 | Window Closed / Lapsed |