US3571713A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Low frequency wide band fm demodulators
Assignee: Individual
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Filing: 1968-05-27
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Granted: 1971-03-23
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Expires: 1988-05-27
Abstract
Abstract The disclosure concerns a demodulator for demodulating frequency modulated subcarriers. The demodulator is used in combination with a conventional FM receiver detector and is designed to demodulate SCA broadcasts. The SCA intelligence is introduced as FM signals to the modulator of an FM transmitter along with normal audiofrequency intelligence. The demodulator, connected to the output of the FM receiver detector, converts the FM intelligence of the SCA broadcast to audiofrequency intelligence using a two-stage active band-pass filter network and a ratio detector. The components of the demodulator are mounted on a printed circuit board in a manner to achieve compact size and a low profile.
Inventors
- 👤 James D Zachary
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-04 00:26
CPC Classifications
H; H04; H04B; H04B1/00; H04B1/06; H04B1/16; H04B1/1646
Claims Analysis
Total Claims: 18
Claim 1
Independent Claim
194 words
An FM demodulator adapted for selective connection to the detector output of an FM receIver and operable to demodulate an FM subcarrier above the audiofrequency range appearing thereat, said demodulator comprising, in combination: A. an input terminal for connection to the detector output of an FM receiver; B. a first amplifier connected to said input terminal; C. a second amplifier; D. a first RF transformer having: 1. a primary winding connected to said first amplifier, and 2. a secondary winding connected to said second amplifier; E. capacitors connected in circuit with said primary and secondary windings of said first RF transformer to form a stagger-tuned, magnetically coupled band-pass filter having a center pass frequency corresponding to the frequency of the FM subcarrier; F. a second RF transformer having: 1. a primary winding tuned to the FM subcarrier frequency and connected to said second amplifier, and 2. a secondary winding tuned to the FM subcarrier frequency; G. FM detection means connected in circuit with said secondary winding of said second RF transformer; and H. an output terminal connected to said FM detection means and adapted for connection to the audio section of the FM receiver.
Claim 2
Dependent Claim
194 words
An FM demodulator adapted for selective connection to the detector output of an FM receIver and operable to demodulate an FM subcarrier above the audiofrequency range appearing thereat, said demodulator comprising, in combination: A. an input terminal for connection to the detector output of an FM receiver; B. a first amplifier connected to said input terminal; C. a second amplifier; D. a first RF transformer having: 1. a primary winding connected to said first amplifier, and 2. a secondary winding connected to said second amplifier; E. capacitors connected in circuit with said primary and secondary windings of said first RF transformer to form a stagger-tuned, magnetically coupled band-pass filter having a center pass frequency corresponding to the frequency of the FM subcarrier; F. a second RF transformer having: 1. a primary winding tuned to the FM subcarrier frequency and connected to said second amplifier, and 2. a secondary winding tuned to the FM subcarrier frequency; G. FM detection means connected in circuit with said secondary winding of said second RF transformer; and H. an output terminal connected to said FM detection means and adapted for connection to the audio section of the FM receiver.
Claim 3
Dependent Claim
51 words
a secondary winding connected to said second amplifier; E. capacitors connected in circuit with said primary and secondary windings of said first RF transformer to form a stagger-tuned, magnetically coupled band-pass filter having a center pass frequency corresponding to the frequency of the FM subcarrier; F. a second RF transformer having:
Claim 4
Dependent Claim
51 words
a secondary winding connected to said second amplifier; E. capacitors connected in circuit with said primary and secondary windings of said first RF transformer to form a stagger-tuned, magnetically coupled band-pass filter having a center pass frequency corresponding to the frequency of the FM subcarrier; F. a second RF transformer having:
Claim 5
Dependent Claim
48 words
a secondary winding tuned to the FM subcarrier frequency; G. FM detection means connected in circuit with said secondary winding of said second RF transformer; and H. an output terminal connected to said FM detection means and adapted for connection to the audio section of the FM receiver.
Claim 6
Dependent Claim
48 words
a secondary winding tuned to the FM subcarrier frequency; G. FM detection means connected in circuit with said secondary winding of said second RF transformer; and H. an output terminal connected to said FM detection means and adapted for connection to the audio section of the FM receiver.
Claim 7
Dependent Claim
12 words
the spacing therebetween being manually adjustable to vary the magnetic coupling therebetween.
Claim 8
Dependent Claim
12 words
the spacing therebetween being manually adjustable to vary the magnetic coupling therebetween.
Claim 9
Dependent Claim
32 words
The demodulator defined in claim 1 which further includes switching means for connecting said input terminal to the detector output and said output terminal to the audio section of the FM receiver.
Claim 10
Dependent Claim
20 words
The demodulator defined in claim 1 wherein the windings of said first and second RF transformers are ferrite core inductors.
Claim 11
Dependent Claim
19 words
The combination defined in claim 3 which further includes: A. a printed circuit board mounting the circuit components thereof;
Claim 12
Dependent Claim
23 words
The combination defined in clam 4, and epoxy encasing said transformers to preserve the established spacing between said primary and secondary windings thereof.
Claim 13
Dependent Claim
23 words
The combination defined in clam 4, and epoxy encasing said transformers to preserve the established spacing between said primary and secondary windings thereof.
Claim 14
Dependent Claim
37 words
The combination defined in claim 4 wherein said FM detector is a ratio detector which includes an inductor disposed in closely spaced, insulated relation to said primary winding of said second transformer and tightly magnetically coupled thereto.
Claim 15
Dependent Claim
14 words
The demodulator defined in claim 1 wherein said FM detector is a ratio detector.
Claim 16
Dependent Claim
31 words
The demodulator defined in claim 1 wherein said first and second amplifiers are transistors, said transistors being provided with incomplete emitter bypassing at audiofrequencies to reduce transistor gain for audiofrequency signals.
Claim 17
Dependent Claim
24 words
The demodulator defined in claim 1 wherein said band-pass filter has a center pass frequency in the range from 24 kc. to delta kc.
Claim 18
Dependent Claim
24 words
The demodulator defined in claim 9 wherein said band-pass filter has a bandwidth of + or - 8 kc. about its center pass 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) | 1974-03-22 | 1974-09-21 | 1975-03-23 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-03-22 | 1978-09-21 | 1979-03-23 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-03-22 | 1982-09-21 | 1983-03-23 | $7700.00 | Window Closed / Lapsed |