US3801911A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Synchronous fm-modem
Assignee: US Philips Corp
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Filing: 1972-02-08
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Granted: 1974-04-02
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Expires: 1992-02-08
Abstract
Abstract A synchronous in-plant FM modem for data transmission through local cables or internal telephony lines by means of FSKmodulation. The in-plant modem, when being used in a multi-drop arrangement, may be adapted in a simple manner to the various transmission characteristics by selectively subtracting a delayed version of the modulated carrier from the modulated carrier in the transmitter section thereby selectively producing either binary FSK or pseudoternary FSK and by adjusting in the receiver section the value of a coupling capacitor between line output and receiver filter.
Inventors
- 👤 Horsten H Von
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 23:10
CPC Classifications
H; H04; H04L; H04L27/00; H04L27/10; H04L25/00; H04L25/38; H04L25/40; H04L25/49
Claims Analysis
Total Claims: 3
Claim 1
Independent Claim
198 words
A synchronous modem for transmission of data signals through local cables, comprising a transmitter section; and a receiver section; a frequency modulator in the transmitter section for converting binary coded data signals into frequency shift-keyed signals with continuous phase, a main generator in the transmitting section for providing clock frequencies for the binary coded data signals and for providing carrier frequencies for the modulator, means dividing the modulator output into a first and a second channel, means in the second channel for providing a phase delay between the first and second channels equal to one-half the period of the highest carrier frequency, summing means for selectively subtracting the delayed modulated output in the second channel from the modulated output in the first channel, means connecting the output of the summing means to the local cables, a low pass filter in the receiving section, a variable capacitor in the receiving section, means in the receiver connecting the filter to the local cables through the variable capacitor for adjusting by means of the variable capacitor the proportion of high to low frequencies to the filter, a demodulator in the receiver section, and means for connecting the filter to the demodulator.
Claim 2
Dependent Claim
198 words
A synchronous modem for transmission of data signals through local cables, comprising a transmitter section; and a receiver section; a frequency modulator in the transmitter section for converting binary coded data signals into frequency shift-keyed signals with continuous phase, a main generator in the transmitting section for providing clock frequencies for the binary coded data signals and for providing carrier frequencies for the modulator, means dividing the modulator output into a first and a second channel, means in the second channel for providing a phase delay between the first and second channels equal to one-half the period of the highest carrier frequency, summing means for selectively subtracting the delayed modulated output in the second channel from the modulated output in the first channel, means connecting the output of the summing means to the local cables, a low pass filter in the receiving section, a variable capacitor in the receiving section, means in the receiver connecting the filter to the local cables through the variable capacitor for adjusting by means of the variable capacitor the proportion of high to low frequencies to the filter, a demodulator in the receiver section, and means for connecting the filter to the demodulator.
Claim 3
Dependent Claim
92 words
A synchronous modem as claimed in claim 1, wherein the summing means comprises operational amplifier operating as an adder, and having a first and second adder inputs, means connecting the first adder input of the operational amplifier to the first channel, a signal inverter connected in series with the phase delay providing means in the second channel, and means for selectively connecting the modulated data signals in the first channel or the phase delayed and signal inverted modulated data signals from the second channel to the second input of the operational amplifier.
References Cited (Backward Citations)
US3139615A
Cited
US3230310A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-04-01 | 1977-10-01 | 1978-04-02 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-04-01 | 1981-10-01 | 1982-04-02 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-04-01 | 1985-10-01 | 1986-04-02 | $7700.00 | Window Closed / Lapsed |