US2392672A - Program control receiver - Google Patents

Description

Jan. 8, 1946. w. R. KoH

PROGRAM CONTROL RECEIVER Filed July 24, 1942 Para@ Jee-@194,6 t

Winfield R. Koch, Haddoniieid, N. J., signor to I Radio Corporation of America, a corporation of Delaware A I Application July 24, 1942, Serial No. 452.5173

(CL 25o-20) i claim.

My present invention relates to program control systems, and more particularly .to a frequency j modulation communication system bemploying program-selective control tones.

It is often desired on the part of the receiver operator, especially in the broadcast band, to cut out receiver reproduction during announcement periods. This type of program control is of especial desirability during music program transmission. Further, the broadcast listener often objects to the fact that speech-music control 1 switches, such as acoustic compensation and fidelity control switches, must be operated manually and at the receiver control panel. It would be highly desirable to provide a method of automatically monitoring the program arriving at the broadcast `receiver so as to secure the aforementioned characteristics. Frequently modulation of the present day type lends itselfI to such monitormg It may be stated to be one of the main objects of my present invention to provide a radio communication systemwhereln a control, or monitor, tone is transmitted along with modulation del aired to be discriminated against at the receiver,

and the control tone being utilized at the receiver to eiiect one or more control functions with respect to the modulation on the received carrier.

Another important object of this invention is to provide a method of automatically preventing receiver response during -announcement periods .of a program broadcast; a special monitor tone being included on the carrier during such periods.

' Another object of my invention is to providev a broadcast -receiver wherein the listener lis permitted to hearonly announcements, such as news bulletins, and not the musical program. l

Another object of my invention is `to provide automatic acoustic'compensation control and/or fidelity control at a broadcast receiver in response to the reception of aspecial monitor tone of superaudible frequency. v

Yet another object of my invention is to providel a frequency modulation system ,wherein a super-audible monitor tone is included inthe modulation during such periods of transmission when a particular type of program control is de- Stili' other lobjects are.`to improve generally the mciency and reliability of program control sys,-

tems. and more `especially to provide such control systems 'in frequency modulation receivers.

The novel features which I believe tob'e characteristic of my invention areset forth with particularityin the appended claims; the invention `tions whereby my itself. however, as to'both its organization and method of operation will best be understood by 'reference to the following description taken in connection with the drawing in` which I have indicated diagrammaticaliy several circuit organizaeect. l In the drawing: Fig. 1 schematically shows an FM (frequency modulated carrier wave) transmitter system embodyingthe invention; and

, Fig. 2 shows an FM receiver employing the irlvention.

Referring now to Fig. l, there is showna transmitting system of the FM type. The generic term angular velocity-modulated carrier wave is used herein to denote that either frequency, or phase, modulation may be employed. The present system of control with a super-audible monitor tone lends itself particularly to high deviation range FM communication. lIn the latter the master oscillator l operates at some carrier frequency in the assigned ultrahigh frequency band of 42 to 50 megacycles (ma). The frequency modulator 2 is usually an electronic reactancedevice which is connected across the oscillator tank circuit .to vary the oscillator frequency with respect to a center frequency which is the unmodulated car-l rier frequency value. Themagnitude of the elec-H tronic reactance is varied bythe applied modulation.

Thus, the program microphone 3` feeds the modulation amplifier 4 with the usual music or other audible program material. The switch 6-5 being closed. the amplified modulation energy is fed through a. furtherlampliie'r l to the reactance tube 2. The latter is so constructed that the carrier frequency is deviatedk in accordance with the modulation amplitude; the rate of deviation is a function of the ymodulation frequencies per se. In the presently-assigned FM band the channel width is 200 kilocycles (ka), but the transmitter actually deviates the carrier a maximum of kc.

. either side of the transmitter mean frequency.

During the course of a program, such as music. there will be announcing. periods. Usually the announcers microphone 8 feeds an amplifier, which is connected in turn to the contact III of switch arm 6. Thus, closurel of switch 6-I0 permits the modulation appledto modulator 2 to be from solely source 8,' while source 3 is concurrently cut oir. A control tone is fed into amplifier 9 from pilot tone oscillator Il. The latter operaies at a super-audible frequency, say 22 kc. Both oscillators ,il and Il. operate with constant aminvention may be carried into ing current components by condenser 3|.

`anode end of resistor 3l is connected to a conplitude. It will now be seen that when the announcing switch 3+-I0 is closed the speech and control tone me utilized as composite modulation. 'Ihe `reacts-nce device at 2 is varied in accordance with output of amplifier 9.v Since the channel is at least 150 kc. wide, the super-audible control tone is readily utilized in thev transmission. The

- F. M. wave energy is amplified by power amplifier I2, and radiated by the antenna I3. y

f course, the sources 3 and 8 may be respectively music and speech kfor different sequences oi! a long broadcast schedule. The sources may be located in separate studios. and the switch deasoaova c J end connected to the anode of diode rectifier 32, L

while the opposite end is connectedto the lower end of load resistor 33. The latter is bypassed by alternating current components by condenser 34. 'Ihe lower end of resistor-33 is connected to the negative terminal of a source of high negative biasing potential 35 whose positive terminal is grounded. The cathode end or resistor 33 is vice IIi--Ii--Ili maythenbe used as a change-over switch from one program to another. At the receiver the collector I4, which may be a dipole, feeds the collected FM wave energy to a radio frequency amplifier I5. The latter may include lone or more selector circuits each tuned to the mean, or carrier, frequency of the collected wave energy. The converter I6 reduces the 'center frequency to an operating I. F. value, and the latter may be 4.3 mc. After intermediate frequency (I. F.) amplification at I1, thel energy is subjected to the action of an amplitude limiter I8. The latter functions to eliminate any amplitude modulation effects which may arise in the receiving system.

The FM detector I9 may be of any welll known form, and the function of the detector is to derive from the FM wave energy the modulation which was applied to the master oscillator at the connected by lead 50 to a contact 31.

The audio frequency amplifier 2l may have a gain control electrode thereof, such as the signal input grid, connected to the adjustable control switch arm 39. Thev contact' 38 is provided in spaced, intermediate relation to contacts 33` and 31. Contact 38 is connected to the negative terminal of negative biasing source 40, the latter having its positive terminal grounded. Switch arm 33 is adjustable, and can be connected in electrical contact with point 38, point 38 or point v 31. Switch 39 is, therefore, the announcement control switch." Assuming that switch arm 39 is in contact with point 38, then the audio amplifier 2| will be operating in normal fashion since 1 the source 40 applies normal bias to the amplithereafter. In this way the super-audible control n tone is prevented from passing through to the audio amplifier 2I. 22 and 23 may be arranged in cascade with the output terminals of amplier '2l'. The output transformer of amplifier 23 may be connected to any desired type of reproducer. Those skilled in constructing networks I I to 23 inclusive, and, therefore, they are schematically represented.

l The monitoring circuit comprises the bandpass filter 25 having its input terminals connected to the output terminals of detector I9 by a path 2l. In other words when the 22 irc.v control energy exists in the output of the detector I9, the energy is transmitted over path 24 to nlter 25. The nlter 25 may have a passband width which is relatively narrow so that only the energy of superaudible frequency will pass to the amplifier 26. After amplification the super-audible control energy is applied to a pair of transformers 21 and 28.

The primary windings of the two transformers may be arranged in series in the Plate Circuit 0f amplier 26. The secondary of transformer 21 has one side connected to the cathode of diode rectier 29, while its Opposite end is connected to one end of load resistor 30, which is also connected to the negative terminal of bias source 40. The load resistor 30 is bypassed for alternattact 33. The secondary of transformer 28 has one Successive audio amplifiersy Theiler. In that case the modulation from either of sources 3 or 8 will be heard. This follows because there is nocontrol applied to amplifier 2i, even though the control tone exists, on the carrier when the switch B-IIJ is closed.

If, now, the switch arm 39 is adjusted topolnt n 36, only. the 'program modulation from source 3 will be heard and announcements from source 8 will be deleted. 'I'his occurs because when switch 5-10 is closed, the control tone is super- -posed on the carrier. At the receiver the recti 4iler 29 recties the control tone energy, and provides a direct current voltage across resistor 30 whose magnitude is suillciently high vto bias audio amplifier 2| to cut-off. vAs'soon as the switch 6-I0 is open, and switch -3-5 is closed, the program from source 3 is received, but no control action is'applied to amplier 2| from rectifier l 29, since vno control tone is applied to the carrier. In other words, when-switch 39-36 is closed, the receiver automatically will be non-responsive to that modulation source which is applied to the carrier concurrently with the monitor tone.

. the art are fully acquainted with the manner of If now the switch arm 39 is shifted so as to close switch 39-31 onlyfthe announcements from lmicrophone 8 will be heard, andthe receiver will not be responsive when switch 6-5 is closed at the transmitter to apply modulation from microphone 3 on the carrier. This follows from the fact that normally the negative biasing source 35 cuts off amplifier 2|. When, however, modulation is applied from source 8 concurrently with the pilot tone, then diode rectifier 32will develop direct current voltage across resistor 33which will be applied in a polarity sense such as to oppose the biasing source 35. The amplier'ZI is, therefore, rendered operative. However, the receiver will only be reproducing the modulation from source 8. Hence, the receiver now automatically responds solely to modulation source-8, but does not respond to the other of the modulationv sources. From a generic viewpoint, therey fore, there has been provided a selective switching mechanism which enables the same monitor tone of super-audible frequency selectively to permit response to one modulation source while prevent response to the modulation source combined with the control -tone while permitting reannouncements may be provided, instead of complete elimination of either. In that way,vfor example, the speech sequences could be at very low level, while the music periods would be of normal level, orr the reverse could be had.

The super-audible control tone energy may, also, be utilized to provide acoustic compensation control and/or fidelity control. For either of these functions the direct current voltage developed across resistor 33 by rectifier 32 may be used. Acoustic compensation control is readily provided by connecting the plate circuit of a control tube 4| to the grid circuito! audio amplifier 22 through a path including condenser 42 and coil 43 in series. The plate of tube 4i may be connected to any desired source of positive potential through a proper choke coil. The cathode of tube 4| may be connected to ground through any desired biasing means, such asf shown.

The plate to cathode impedance of tube 4I is regulated by connecting the control grid thereof to lead 50 through a switch 4544. The choke coil 43 has a low impedance to low audio frequencies, while condenser 42 has a low impedance to high audio frequencies. Hence, when switch 45-44 is closed, high negative bias from source 35 biases tube 4| to cut-off; This is the condition when no modulation is being transmitted from source 8. However, when switch E-IU is closed and modulation from sources 8 and Il are applied to the carrier, rectifier 32 will function to render tube 4i conductive. means that the low and high audio notes are bypasse-d from the grid circuit of ampliiier 22. Of course, when the switch 45 is adjusted to the free contact, no control is applied to tube 22.

The fidelity control is provided by a tube 41 which is constructed in the same manner as the acoustic compensation control. Therey is this difference: the condenser 46, which has a low impedance to high audio frequencies, is arranged in series between the plate of tube 41 and the grid circuit of amplifier tube 23. Switch arm 49 is connected to lead 50, while the contact 48 is connected to the control grid of tube l4'1. When switch 49-48 is closed, and no control tone energy exists on the carrier, the tube 41 is cut oil.

Thisl v However, when speech from source 8 is applied to the carrier, the control tone energy is rectified and overcomes the biasing source 3B. This results in bypassing of the higher audio frequencies. Accordingly, fidelity of reproduction is limited on speech so that stray noise is reduced. It will be understood that the switch arms 39, 45 and 49 are to be adjusted in any desired manner, or sequence. In such case where the microphone 8 is located in a studio where speech programs are constantly delivered, the switch 49-48 is closed so that when themicrophone 8 is active in delivering speech to the carrier, there will automatically be developed a limited fidelity of reproduction for the receiver.

WhileI have indicated and described several systems for carrying my invention into eiect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention.

What I claim is:

In a frequency modulation receiver oi' the type adapted to receive frequency modulated carrier waves provided with a special control frequency modulation component representative of a desired conditioning of the receiver; lthe improvement comprising a detector at the receiver -to produce the modulation signals ofthe received waves, means for filtering from the signals current of the special control frequency, means for utilizing the modulation signals, a source of volt age for rendering said utilizing means operative, a rectifier coupled to said filtering means, and responsive to said special control frequency current, to overcome the eil'ect of said voltage source, a second voltage source capable of rendering said utilizing means ineiiective, a second rectifier coupled to said filtering means for deriving from the control current a voltage to overcome the effect of said second voltage source, and means for selectively connecting in circuit Iwith the utilizing means either of said rectiiiers and its associated one of said two voltage sources.

WINFIELDR Kocr'r.

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