Patent US3824470A successfully refreshed from Google Patents.
US3824470A
Expired / Lapsed
US
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Communications system and method for transmitting over a limited bandwidth transmission link
Assignee: Motorola Solutions Inc
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Filing: 1973-02-20
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Granted: 1974-07-16
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Expires: 1993-02-20
Abstract
Abstract A communications system, including portable transmitters and several remote receivers connected to a base station by means of a limited bandwidth transmission link (such as a telephone line), wherein the receivers include an encoder for transmitting the information over the transmission link and removing a small band of the information and inserting a carrier frequency, amplitude and frequency modulated by the coded squelch signals and the information signal strength signals, and the base station includes a decoder.
Inventors
- 👤 B Eastmond
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 09:21
CPC Classifications
H; H04; H04B; H04B7/00; H04B7/02; H04B7/04; H04B7/08; H04B7/0837; H04B7/084
Claims Analysis
Total Claims: 32
Claim 1
Independent Claim
260 words
A communications receiver for use in a communications system including a base station, connected to said receiver by a limited bandwidth transmission link, and at least one remote transmitter for providing information signals lying within the limited bandwidth of the transmission link and coded squelch signals at a frequency different than the information signals, said receiver comprising: a. receiving means for receiving and amplifying signals from the portable transmitter; b. means connected to said receiving means for passing at least the information signals in the received signals to an output; c. bandpass filter means connected to the receiving means for passing the coded squelch signals contained in the signals received by said receiving means; d. signal strength indicating means connected to the receiving means for providing a signal indicative of the signal strength of the information signals in said receiving means; e. oscillator means providing a carrier frequency lying within the limited bandwidth of the transmission link and including means for frequency and amplitude modulating the carrier frequencY; f. means connecting said bandpass filter means and said signal strength indicating means to said oscillator means for frequency modulating the carrier frequency in accordance with one of the information signals and the signal strength indicating signal and for amplitude modulating the carrier frequency in accordance with the other of the information signals and the signal strength indicating signal; and g. means connected to said means for passing the information signals and said oscillator means for coupling the information signals and the frequency and amplitude modulated carrier frequency to the transmission link.
Claim 2
Dependent Claim
260 words
A communications receiver for use in a communications system including a base station, connected to said receiver by a limited bandwidth transmission link, and at least one remote transmitter for providing information signals lying within the limited bandwidth of the transmission link and coded squelch signals at a frequency different than the information signals, said receiver comprising: a. receiving means for receiving and amplifying signals from the portable transmitter; b. means connected to said receiving means for passing at least the information signals in the received signals to an output; c. bandpass filter means connected to the receiving means for passing the coded squelch signals contained in the signals received by said receiving means; d. signal strength indicating means connected to the receiving means for providing a signal indicative of the signal strength of the information signals in said receiving means; e. oscillator means providing a carrier frequency lying within the limited bandwidth of the transmission link and including means for frequency and amplitude modulating the carrier frequencY; f. means connecting said bandpass filter means and said signal strength indicating means to said oscillator means for frequency modulating the carrier frequency in accordance with one of the information signals and the signal strength indicating signal and for amplitude modulating the carrier frequency in accordance with the other of the information signals and the signal strength indicating signal; and g. means connected to said means for passing the information signals and said oscillator means for coupling the information signals and the frequency and amplitude modulated carrier frequency to the transmission link.
Claim 3
Dependent Claim
59 words
A communications receiver as claimed in claim 1 wherein the carrier frequency lies within the range of frequencies of the information signals and the means connected to said receiving means for passing the information signals includes band reject filter means for removing information signals at frequencies approximately equal to the frequencies of the frequency and amplitude modulated carrier frequency.
Claim 4
Dependent Claim
28 words
first filter means coupled to the output of said gain control means for passing the information signals and rejecting substantially all other siGnals from said gain control means,
Claim 5
Dependent Claim
28 words
first filter means coupled to the output of said gain control means for passing the information signals and rejecting substantially all other siGnals from said gain control means,
Claim 6
Dependent Claim
24 words
frequency demodulator means coupled to the output of said gain control means for receiving the modulated carrier frequency and demodulating the frequency variations thereof,
Claim 7
Dependent Claim
24 words
frequency demodulator means coupled to the output of said gain control means for receiving the modulated carrier frequency and demodulating the frequency variations thereof,
Claim 8
Dependent Claim
41 words
A communications receiver as claimed in claim 1 wherein the transmission link includes telephone lines and the means connected to said receiving means for passing the information signals includes a low pass filter capable of passing frequencies below approximately 3 KHz.
Claim 9
Dependent Claim
38 words
A communications receiver as claimed in claim 3 wherein the coded squelch signals are in a range below approximately 300 Hz and the bandpass filter means includes a low pass filter capable of passing frequencies in the range.
Claim 10
Dependent Claim
24 words
amplitude demodulator means coupled to the output of said gain control means for receiving the modulated carrier frequency and demodulating the amplitude variations thereof,
Claim 11
Dependent Claim
24 words
amplitude demodulator means coupled to the output of said gain control means for receiving the modulated carrier frequency and demodulating the amplitude variations thereof,
Claim 12
Dependent Claim
24 words
averaging means connected to said amplitude demodulator means for providing an average signal in response to the demodulated amplitude variations of the carrier frequency,
Claim 13
Dependent Claim
24 words
averaging means connected to said amplitude demodulator means for providing an average signal in response to the demodulated amplitude variations of the carrier frequency,
Claim 14
Dependent Claim
38 words
A communications receiver as claimed in claim 1 wherein the oscillator means includes a voltage controlled oscillator having an input for controlling the frequency of said oscillator in accordance with variations of a voltage applied to the input.
Claim 15
Dependent Claim
36 words
A communications receiver as claimed in claim 5 wherein the bandpass filter means is connected to the input of the voltage controlled oscillator for varying the frequency of said oscillator in accordance with coded squelch signals.
Claim 16
Dependent Claim
21 words
reference means providing a reference voltage of an amplitude sufficient to maintain the gain control means at a desired value, and
Claim 17
Dependent Claim
21 words
reference means providing a reference voltage of an amplitude sufficient to maintain the gain control means at a desired value, and
Claim 18
Dependent Claim
63 words
comparing means having a first input connected to receive the average signal from said averaging means, a second input having the reference voltage applied thereto from said reference means, and an output coupled to the second input of said gain control means for adjusting said gain control means in accordance with the value of the average signal with respect to the reference voltage.
Claim 19
Dependent Claim
63 words
comparing means having a first input connected to receive the average signal from said averaging means, a second input having the reference voltage applied thereto from said reference means, and an output coupled to the second input of said gain control means for adjusting said gain control means in accordance with the value of the average signal with respect to the reference voltage.
Claim 20
Dependent Claim
32 words
A communications receiver as claimed in claim 1 wherein the connecting means includes means for converting a DC signal to pulses having a frequency proportional to the amplitude of said DC signal.
Claim 21
Dependent Claim
45 words
A communications receiver as claimed in claim 7 wherein the connecting means further includes a bistable circuit connected to receive the pulses from the converting means for converting the pulses to a square wave having a repetition rate one half the frequency of the pulses.
Claim 22
Dependent Claim
63 words
A communications receiver as claimed in claim 8 wherein the connecting means further includes wave shaping circuitry connected to receive the square wave from the bistable circuit for generating a wave having the same repetition rate but a substantially lower harmonic content than a square wave, said wave shaping circuitry being connected to the oscillator means for amplitude modulating the carrier frequency therefrom.
Claim 23
Dependent Claim
84 words
A communications system utilizing a limited bandwidth transmission link comprising: a. a communications receiver providing information signals and a carrier frequency amplitude and frequency modulated by coded squelch signals and signals indicative of information signal strength at said receiver, said information signals and modulated carrier frequency lying within the limited bandwidth of the transmission link; b. a base station coupled to said communications receiver by means of the transmission link for receiving the information signals and the modulated carrier frequency, said base station including
Claim 24
Dependent Claim
84 words
A communications system utilizing a limited bandwidth transmission link comprising: a. a communications receiver providing information signals and a carrier frequency amplitude and frequency modulated by coded squelch signals and signals indicative of information signal strength at said receiver, said information signals and modulated carrier frequency lying within the limited bandwidth of the transmission link; b. a base station coupled to said communications receiver by means of the transmission link for receiving the information signals and the modulated carrier frequency, said base station including
Claim 25
Dependent Claim
100 words
A communications system as claimed in claim 10 wherein the amplitude variations of the carrier frequency include a wave having relatively low harmonic content, the amplitude demodulator means of the system including envelope detector means and second comparing means having two inputs and an output with one of said inputs coupled to said envelope detector means for receiving the low harmonic wave therefrom and the other of said inputs coupled to said averaging means for providing a reference DC signal and indicating the crossing thereof by the low harmonic wave in the form of a square wave at the output.
Claim 26
Dependent Claim
68 words
A communications system as claimed in claim 11 having in addition means attached to the output of the second comparing means for converting the square wave output to a wave having twice the repetition rate of the square wave and means attached to the doubling means for converting the output wave to a DC signal representative of one of the information signal strength signal and coded squelch signals.
Claim 27
Independent Claim
109 words
A method of transmitting information signals, coded squelch signals and information signal strength signals over a transmission link having a bandwidth approximately equal to the bandwidth of the information signal, including the steps of: a. passing the information signal through a band reject filter to form a notch in the bandwidth having substantially no signals; b. providing a carrier frequency lying within the notch in the bandwidth; c. amplitude and frequency modulating said carrier frequency in accordance with the coded squelch signals and the information signal strength signals; and d. mixing the amplitude and frequency modulated carrier frequency with the information signals and applying them to the transmission link.
Claim 28
Independent Claim
109 words
A method of transmitting information signals, coded squelch signals and information signal strength signals over a transmission link having a bandwidth approximately equal to the bandwidth of the information signal, including the steps of: a. passing the information signal through a band reject filter to form a notch in the bandwidth having substantially no signals; b. providing a carrier frequency lying within the notch in the bandwidth; c. amplitude and frequency modulating said carrier frequency in accordance with the coded squelch signals and the information signal strength signals; and d. mixing the amplitude and frequency modulated carrier frequency with the information signals and applying them to the transmission link.
Claim 29
Dependent Claim
38 words
A method as claimed in claim 13 including in addition the steps of receiving the information signals and coded squelch signals from a remote transmitter and developing an information signal strength signal upon reception of the information signals.
Claim 30
Dependent Claim
25 words
A method as claimed in claim 13 including in addition the step of limiting the amplitude modulation to allow continuous transmission of the carrier frequency.
Claim 31
Dependent Claim
33 words
A method as claimed in claim 13 wherein the deviation of the signal frequency modulating the carrier frequency is limited so that second and third order sidebands of the carrier frequency are insignificant.
Claim 32
Dependent Claim
34 words
A method as claimed in claim 13 wherein the coded squelch signals are used to frequency modulate the carrier frequency and the information signal strength signals are used to amplitude modulate the carrier frequency.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-07-15 | 1978-01-14 | 1978-07-16 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-07-15 | 1982-01-14 | 1982-07-16 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-07-15 | 1986-01-14 | 1986-07-16 | $7700.00 | Window Closed / Lapsed |