US2258599A

US2258599A - Frequency-modulation receiving system

Info

Publication number: US2258599A
Application number: US343109A
Authority: US
Inventors: Wendell L Carlson
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1940-06-29
Filing date: 1940-06-29
Publication date: 1941-10-14
Anticipated expiration: 1958-10-14

Description

Oct. 14, 1941. w. L. cALSON 1 2,258,599

FREQUENCY-MODULATION RECEIVING SYSTEM Filed June 29, 1940 nvenlor v Homey Patented Oct. 14, 1941 FREQUENCY-MODULATION RECEIVING SYSTEM Wendell L. Carlson, Haddoniield, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application June 29, 1940, Serial No. 343,109

(Cl. Z50-20) 7 Claims.

ceiving system having a frequency-discriminator network adapted for the reception and demodulation of amplitude modulated signals.

A further object of the present invention is to provide an improved frequency-discriminator network for the reception and conversion or demodulation of ultra high-frequency amplitude and frequency-modulated signals selectively, and

lof relatively low frequency amplitude-modulated signals, with a minmium of circuit changes.

It is a further object of the present invention to provide an improved frequency-discriminator network for the reception of both amplitude and frequency-modulated signals and for tuning indication, with a minimum of vcircuit changes;

The invention will further be understood from the following description, when considered in connection with the accompanying drawing, and its scope is pointed out in the appended claims.

In the drawing,

Figure 1 is a schematic circuit diagram of a combined amplitude and frequency-modulation receiving system embodying the invention;

Figure 2 is a similar schematic circuit diagram of a modification of a portion oi the circuit of Fig. 1; and

Figure 3 shows curves illustrating certain oper- `ating characteristics of the circuit of Fig. 1.

Referring to Fig. 1, the circuit 5 is a frequency discriminator network for the reception of frequency modulated signals, provided with a pair of balanced rectiers 6 and 1 preferably of the diode type as shown, from which ,converted signals are applied through suitable volume control means 8 to an audio frequency ampliiier system 9 and output device or loudspeaker I8.

The discriminator network is preceded by suitable intermediate frequency amplier means Arepresented by the amplifier stage comprising the tube I I and the input portion of a multiple band receiving system indicated at I2, through which signals are selected from any suitable signal source such as an antenna circuit I3.

The receiving system is of the multiple wave band type for receiving signals in a plurality of differing wave bands, such as an ultra high frequency amplitude and frequency modulated signal band and the normal broadcast and short wave bands at present in use for entertainment programs. The wave band change means is indicated at I4, and variable tuning means for each band is indicated at I5. As such wave band tuning and selecting systems are known and as any suitable system may be provided at I2, further description is unnecessary.

The discriminator network 5 includes a tuned secondary inductance I6 having terminals connected with the diode rectifier anodes I1 and I8 and having an electrical center tap I9 connected to a similar center tap20 on the balanced rectifier output impedance or resistor network 2|22, each half of which is provided with a suitable bypass capacitor 23. The diode cathodes 24-25 are connected with the terminals of the impedance 2I--22, the cathode 25 preferably being grounded as indicated at 26. The cathode 24 is connected to a switch 21 having a contact 28 providing a connection with the ungrounded terminal of the output impedance and having a second contact 29 connected to the grounded or rst named output impedance terminal preferably through a ground connection as indicated at 30.

The volume control device 8 is connected in shunt with the output impedance 2 I--22 through a coupling capacitor 3l and is preferably of relatively high resistance, thereby to provide a relatively light load on the rectifier circuit and output impedance.

In accordance `with the invention theuse of a choke coil between the secondary terminal I9 and the terminal 20 on the output 'impedance is obviated by interposing in the circuit ordinarily occupied by the choke coil one or more serially connected intermediate secondary windings such as a high frequency winding 35 and a low frequency winding 36, in series, the lower frequency winding being more adjacent to the terminal 28.

The main secondary I6 and the intermediate secondary 35 are each tuned to the same high intermediate frequency, such as 5 mc., for example, by suitable shunt capacitors 3l and 38, respectively, the exact tuning adjustment being ellected preferably by means of movable ferromagnetic tuning cores indicated at 39 and 40.

The secondary winding 35 is coupled to a primary winding 4I which is connected in the output circuit 42 of the amplifier stage II and is contacts 2 9Aand Vis; completed;

tuned by a shunt capacitor 43 to the same intermediate frequency of 5 mc., the final tuning adjustment also being effected preferably by a suitable ferro-magnetic tuning core indicated at 44.

The tuned secondary 36, for low frequency broadcast and short wave signals, for example, is tuned to a low intermediate frequency such as 455 kc., by a suitable shunt capacitor indicated at 45 and is provided with a primary 46 coupled thereto as indicated and tuned by a similar shunt capacitor 41. Both primary and secondary are provided with suitable ferro-magnetic tuning cores indicated at 48 for the purpose of exact tun-I ing to the desired intermediate frequency.

With this arrangement, the tuned primary or primaries in the discriminator'network provide coupling between the intermediate'frequency output circuit and the balanced or push pull secondary I6 and one or more additional secondary windings 35 and 36 which are connected-,through the secondary I6 of the diode rectiers 6 and 'I in parallel, that is, serially between 'substantially the" electrical centers 'of' the' main secondary I6 Vand of the rectifier output impedance 2 I-22. 'In' the present example, the connection between the lowest frequency intermediate' secondary and the'output resistor or impedance .center tap is provided by a lead indicated at 50 -fr'om' which A. V. C. potentials may be derived with' respect to ground through a lead 5I for the input portion of the receiving system' as indicated, in which case the I.F. amplifier I I is preferably operated without appreciable signal limiter characteristics-` Y `With this arrangement, whether operating in response to'amplitude or frequency-modulated signals, the A. V. C'. potential is derived from the 're'si'stor section 22 of therectifler output'circuit is provided in which the rectiiiers are connected with themain secondary I6 Aand the output impedance 2I-22 in balanced or push-pull relation thereby to provide voltages in phase quadrature at resonance and to convert the frequency modulation on'V the carrier to audio signals in the In order to receive amplitude-modulated signals 'at 'either the high Yintermediate frequency of 5 mc., or the low intermediate frequency of 455 kc., switch 21 is moved to the contact 29 vthereby placing the dioderectiiiers in parallel -withrespect to either of the tuned secondaries -35'and 36 with the cathodes connected to ground.

4-The impedance of the low induc'tance, high frequency secondary I6 in circuit with the secondaries 35 and 36 and the impedance 'of' the relatively low Ainductance 'high' frequency secondary 35 in circuit with Ythe low freequency high "indu'ctance primary 36 is substantially negligible.

'For' tuningv indication,` either for amplitudemodulated orA frequency-modulated signals, a

4timing indicator device indicated at 55, may be 'connectedwith the lead, 50 through a switch 56 `hai/'fing a contact`5l'connected with the tuning' 'dev ic'and thence to ground,` as indicated at 58,

wherebythe tuning indicator is placed in parallel -with the output resistor section 22. Y

' :Forffrequencymodulation reception, it is desirable to provide' tuning indication during the- Ytuning operation. In'the present system this is provided by closing the switches 2'I and 56 to the 51, respectively, until the tuning Where a circuit of the Conrad type is used, the discriminator network may be modified as shown in Fig. 2 to which attention is now directed, and in which like reference numerals refer to the same circuit elements as in Fig. 1.

Referring to Fig. 2, the intermediate frequency amplifier stage II is provided with an output circuit 42 including a pair of series connected primary windings 60 and 6I and a third primary winding 62 to the low intermediate frequency by a shunt capacitor 63 together with a ferro-magnetic tuning core 64.

The primaries 6I) and 6I are coupled to

secondaries

65 and 66, respectively, one being tuned above and the other being tuned below the midfrequency or carrier, of the frequency modulated signal, by suitable shunt capacitors 6'I and 68, respectively, together with ferro-magnetic tuning cores 'II and l2. The rectiiiers 6 and 'I are connected with the mistuned input circuits and are differentially coupled to the output impedance 2 I-22 as in the preceding modification.

In the present circuit, however, the center tap for the input circuit is located between the

secondaries

65 and 66, as indicated at 13, and the low frequency secondary 'I4 is included serially in circuit between the center tap I3 and the center tap 20 on the output impedance, through the lead 50. In the present example, the switch 56 connected with the lead 50 is arranged to connect the tuning indicator circuit and A. V. C. lead 5I simultaneously to the lead 50 through the contactV 5'I for amplitude modulation reception only, and tuning indication with amplitude modulation reception, the switch 2I being moved to the contact 29 to connect the rectifiers in parallel. Therefore, these switches may be arranged to be operated jointlyas indicated by the dotted connection '15.

`As in the preceding embodiment, the secondary 'I4 of the low intermediate frequencyV transformer is tuned by a capacitor I6 in conjunction with the variable tuning core indicated at TI.

The invention is applicable to any frequency discriminator network wherein the series secondary circuit may be connected with a balanced secondary circuit to provide push-pull or balanced operation of the rectifiers for frequencymodulation reception and parallel operation for amplitude-modulation reception. This circuit arrangement furthermore permits the use of 'a rectifier output impedance and simplified switching means for connecting the diode output electrodes to the terminals of the output impedance in balanced relation and to the same terminal of said impedance for parallel operation.

The operation of the tuning indicator system in response to frequency modulation and amplitude modulation signals will be readily understood by reference to the curves of Fig. 3, in which the curve86-'8I shows a resonance dip at 82 showing that the sound output for frequency 'modula- -tion signals falls olf at resonance, while the tunattesta that the tuning indicator may be used for frequency modulation tuning indication providing silent tuning at the resonance point which is a desirable feature of the tuning indication system shown and described.

It is obvious that the switching control for the tuning indicator and detector may be incorporated with the tuning system in any suitable manner other than that shown and described herein by way of example.

I claim as my invention:

1. A radio signal receiving system comprising in combination, tunable signal receiving and selecting means, a frequency discriminator network for multiple wave band reception coupled to said first-named means, rectifier means in said network including a pair of rectifier elements, means for connecting said elements in balanced relation to each other for frequency-modulation reception in one wave band, and means for connecting said elements in parallel relation to each other through said last named means for amplitudemodulation reception in another wave band, and tuning indication means connected to said rectiers in said parallel relation for tuning said system to frequency-modulated signals.

2. A radio signal receiving system comprising in combination, tunable signal receiving and selecting means, a frequency discriminator network for multiple wave band reception coupled to said first-named means, rectifier means in said network including a pair of rectifier elements, means for selectively connecting said elements in balanced relation to each other for frequency-modulation reception in one wave band and in parallel relation to each other for amplitude-modulation reception in another wave band, and means for producing a peak signal indication for tuning to resonance with a frequency modulated signal with substantially Zero output.V Y

3. A radio signal receiving system comprising incombination, amplifying means for selected signals having an output circuit, a frequency discriminator network including a plurality of primary windings connected with said last-named circuit, a plurality of secondary windings coupled to said primary windings, rectifier means connected in balanced relation to one of said secondary windings, means providing a circuit through said one winding and others of said secondary windings in series for operating said rectifier means in parallel, an output circuit for said network including output impedance means, and means for connecting said rectifier means selectively in balanced rel-ation and in parallel relation to each other through said output impedance means.

1l. A radio signal receiving system comprising in combination, amplifying means for selected signals having an output circuit, a frequency discrimin-ator network including a plurality of primary windings connected with said last-named circuit, a plurality of secondary windings coupled to said primary windings, rectifier means connected in balanced relation to one of said secondary windings, means providing a circuit through said one winding and others of said secondary windings in series for operating said rectiiier means in parallel, an output circuit for said network including output impedance means, means for connecting said rectiner means selectively in balanced relation and in parallel relation to eaolh other through said output impedance means, and means for deriving a tuning indication from said output circuit when said rectifier means are connected in said parallel relation to each other.

5. In a multiple waveband signal receiving system, the combination of a frequency discriminatory network comprising a plurality of primary windings, a plurality of secondary windings coupled to said primary windings, and tuned one to a relatively high intermediate frequency and another to a relatively low intermediate frequency, rectifier means connected in .balanced relation to one of said secondary windings, a circuit through said one winding and others of said secondary windings in series for operating said rectiiier means in parallel, an output circuit for said network including output impedance means, means for connecting said rectifier means selectively in balanced relation and in parallel relation to each other through said output impedance means, and means coupled to said output impedance for deriving a converted signal therefrom.

6.111 a frequency-modulation receiving system, a frequency discriminator network comprising a plurality of tuned inductances, rectifier means comprising a pair of rectifier elements, a rectier output circuit including an output impedance, a circuit connecting said rectifier elements in balanced relation between said inductances and said output impedance, said circuit including at least two of said inductances in series, means for tuning one of said seriesconnected inductances to signals one at a relatively low frequency and another at a relatively high frequency, and selective switching means for connecting said rectifier elements in parallel relation with each other to said output impedance for response to signals at one of said frequencies.

7. In a frequency-modulation receiving system, a frequency discriminator network comprising a plurality of tuned inductances, rectifier means comprising a pair of rectifier elements, a rectier output circuit includingWan output impedance, a circuit connecting said rectifier elements in balanced relation between said inductances and said output impedance, said circuit including at least two of said inductances in series, means for tuning one of said series-connected inductances to signals one at a relatively low frequency and another at a differing `frequency, selective switching means for connecting said rectifier elements in parallel relation with each other to said output impedance for response to signals at one of said frequencies, and means for deriving a tuning indication from said output impedance in response to parallel operation of said rectifier elements.

WENDELL L. CARLSON