US3792357A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Pre-emphasis loop filter for improved fm demodulator noise threshold performance
Assignee: Northrop Grumman Systems Corp
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Filing: 1972-05-24
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Granted: 1974-02-12
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Expires: 1992-05-24
Abstract
Abstract The performance of a noise threshold extension circuit for an FM demodulator is substantially improved by the incorporation of a pre-emphasis-type filter in the control loop of the circuit, which filter ''''matches'''' the frequency response characteristic of the loop to that of the modulating signal. The threshold extension circuit preferably includes a steerable, narrowband tracking filter which tracks the FM signal so that extraneous noise is filtered out.
Inventors
- 👤 N Hekimian
- 👤 W Mack
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 13:54
CPC Classifications
H; H03; H03D; H03D3/00; H03D3/001; H03D3/003; H03D3/005
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
129 words
An improved frequency modulation communication system comprising, a transmitter including a modulator and means including a preemphasis network for producing a modulating signal, and a receiver including a tracking filter circuit means and a demodulator, said tracking filter circuit means including a control loop for regulating the filter characteristic of the tracking filter therein said control loop beginning at a point intermediate said tracking filter and said demodulator and terminating at one input of said tracking filter, the improvement comprising a pre-emphasis type filter connected in said control loop, said control loop further including means for adjusting the gain of said control loop to provide optimum noise threshold response, and wherein the frequency response characteristic of said control loop substantially matches the frequency response characteristic of said modulating signal.
Claim 2
Dependent Claim
129 words
An improved frequency modulation communication system comprising, a transmitter including a modulator and means including a preemphasis network for producing a modulating signal, and a receiver including a tracking filter circuit means and a demodulator, said tracking filter circuit means including a control loop for regulating the filter characteristic of the tracking filter therein said control loop beginning at a point intermediate said tracking filter and said demodulator and terminating at one input of said tracking filter, the improvement comprising a pre-emphasis type filter connected in said control loop, said control loop further including means for adjusting the gain of said control loop to provide optimum noise threshold response, and wherein the frequency response characteristic of said control loop substantially matches the frequency response characteristic of said modulating signal.
Claim 3
Dependent Claim
19 words
A system as claimed in claim 1 wherein said pre-emphasis type filter is topologically identical to said pre-emphasis network.
Claim 4
Dependent Claim
111 words
The system as claimed in claim 1 wherein the tracking filter includes a first and second input means and an output means, said first input means being connected to receive an intermediate frequency input as a reference, said second input means being connected to said pre-emphasis type filter, said closed loop further including a phase detector having a first and second input means and one output means, said phase detector output means being connected as an input to said pre-emphasis type filter, said first phase detector input means being connected to said tracking filter output means, and said second phase detector input means being connected to receive said intermediate frequency input.
Claim 5
Dependent Claim
28 words
The system as claimed in claim 3 wherein said first tracking filter input means furthEr includes a resistive network for controlling the band width of said tracking filter.
Claim 6
Dependent Claim
178 words
A system as claimed in claim 4 wherein said tracking filter circuit means includes a first emitter follower circuit connected to the output of said tracking filter, an amplitude limiter circuit connected to the output of said emitter follower circuit, a buffer amplifier connected to the output of said amplitude limiter circuit and including an output terminal to be connected to said demodulator, a second emitter follower circuit having the input thereof connected to the output of said amplitude limiter circuit and the output thereof connected to said first input means of said phase detector, and wherein said second phase detector input means includes a third emitter follower circuit connected to said intermediate frequency input, a 90* phase shifter connected to the output of said third emitter follower circuit, an amplitude limiter connected to the output of said phase shifter, a fourth emitter follower circuit having the input thereto connected to the output of said limiter and the output thereof connected to a second input of said phase detector, said phase detector output means further including an amplifier.
Claim 7
Dependent Claim
40 words
The system as claimed in claim 2 wherein said pre-emphasis type filter network comprises an inductance means and a capacitance means connected in a series network, said inductance and capacitance series network being connected in parallel with a resistance means.
Claim 8
Independent Claim
139 words
A method for improving the signal-to-noise ratio in a frequency modulation communication system comprising, a transmitter including a pre-emphasis network for producing a modulating signal and a modulator, and a receiver including a tracking filter circuit and a demodulator, said tracking filter circuit including a control loop for regulating the filter characteristic of the tracking filter therein, said control loop beginning at a point intermediate said tracking filter and said demodulator and terminating at one input of said tracking filter, the improved method comprising the steps of: substantially matching the frequency response characteristic of the control loop to the frequency response characteristic of said modulating signal, said matching being accomplished through the use of a pre-emphasis type filter located in said control loop, and adjusting the gain of the control loop so as to provide optimum noise threshold performance.
Claim 9
Independent Claim
139 words
A method for improving the signal-to-noise ratio in a frequency modulation communication system comprising, a transmitter including a pre-emphasis network for producing a modulating signal and a modulator, and a receiver including a tracking filter circuit and a demodulator, said tracking filter circuit including a control loop for regulating the filter characteristic of the tracking filter therein, said control loop beginning at a point intermediate said tracking filter and said demodulator and terminating at one input of said tracking filter, the improved method comprising the steps of: substantially matching the frequency response characteristic of the control loop to the frequency response characteristic of said modulating signal, said matching being accomplished through the use of a pre-emphasis type filter located in said control loop, and adjusting the gain of the control loop so as to provide optimum noise threshold performance.
Claim 10
Independent Claim
158 words
A method for improving the signal-to-noise ratio of a frequency modulation communication system including the steps of, generating an input signal, passing said signal through a pre-emphasis circuit thereby generating a modulating signal, modulating another signal with said modulating signal thereby producing a modulated signal output, transmitting said modulated signal to a remote point, receiving the transmitted signal, filtering the received signal by means of a tracking filter network, demodulating the filtered signal and passing said demodulated signal to other stages of the receiver, the improved method further comprising the steps of, feeding part of said filtered signal back to said tracking filter network, said feedback signal passing through a pre-emphasis type loop filter, substantially matching the frequency response characteristic of said modulating signal, said matching being accomplished through the use of said pre-emphasis type loop filter located in said control loop, and adjusting the gain of the control loop so as to provide optimum noise threshold performance.
Claim 11
Independent Claim
158 words
A method for improving the signal-to-noise ratio of a frequency modulation communication system including the steps of, generating an input signal, passing said signal through a pre-emphasis circuit thereby generating a modulating signal, modulating another signal with said modulating signal thereby producing a modulated signal output, transmitting said modulated signal to a remote point, receiving the transmitted signal, filtering the received signal by means of a tracking filter network, demodulating the filtered signal and passing said demodulated signal to other stages of the receiver, the improved method further comprising the steps of, feeding part of said filtered signal back to said tracking filter network, said feedback signal passing through a pre-emphasis type loop filter, substantially matching the frequency response characteristic of said modulating signal, said matching being accomplished through the use of said pre-emphasis type loop filter located in said control loop, and adjusting the gain of the control loop so as to provide optimum noise threshold performance.
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) | 1977-02-11 | 1977-08-13 | 1978-02-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-02-11 | 1981-08-13 | 1982-02-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-02-11 | 1985-08-13 | 1986-02-12 | $7700.00 | Window Closed / Lapsed |