US2048828A

US2048828A - Radio and wire broadcasting system

Info

Publication number: US2048828A
Application number: US672077A
Authority: US
Inventors: Warren H Tidd
Original assignee: American Telephone and Telegraph Co Inc
Current assignee: AT&T Corp
Priority date: 1933-05-20
Filing date: 1933-05-20
Publication date: 1936-07-28
Anticipated expiration: 1953-07-28

Description

July 28, 1936. w. H. TlDD RADIO AND WIRE BROADCASTING' SYSTEM Filed May 20, 1935 5 Sheets-Sheet 1 SSN@ lNvENToR ATTORNEY f July 28, 1936. w. H. TlDD RADIO AND WIRE BROADCASTING SYSTEM Filed May 20, 193:5

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SSS KWF .SNALS wg July 28, 1936. w. H. TIDD RADIO AND WIRE BROADCASTING SYSTEM 3 Sheets-Sheet 5 Filed May 20, 1933 ATTORNEY INVENTOR Patented July 28, 1936 STA-EES?.

RADIO AND WIRE BROADCASTVINGV SYSTEM Warren H. Tidd; White Plains, N. Y., ass'gnor-to American Telephone and; Telegrapl- Company'. a corporation of New York Application May 20, 1933,. SeriaLNo. 67`2l077 18- Claims.

wire distributing systems, and more particularly to a receiver having common amplifying and frequency translating circuits for the reception of both wire transmitted and radio broadcast programs.

The distribution of programs for entertainment or instruction by means of radio broadcasting has become well established. Systems have also been developed for distributing programs by means of wire circuits, such as those employed for telephone service or power distribution. With the further development of these latter systems and particularly systems using carrier frequencies for the transmission of program.

material over wire circuits, it will be desirable to have a receiver capable of receiving programs distributed by either radio or wire systems. Such an arrangement avoids the duplication of appa- 2O ratus which would occur if separate receivers were used for the reception of programs distributed by the two systems. purpose of this invention to provide a receiver of the superheterodyne type which is capable of receiving both radio programs and programs transmitted over wire circuits at carrier frequencies,. said receiver having amplifying, frequency translating and sound reproducing` apparatus common to both the radio and the wire circuits. 30 The superheterodyne receiver is the type most generally used at the present time for the recaption of radio programs. principles of the invention there may be incorporated in such receivers apparatus to enablel them to receive also carrier frequency wire programs.

Another object of the invention is to eliminate,

50 al radio receiver of the superheterodyne type.

which receives only a carrier frequency and single sideband.

In the patent to EspenschiedV and' Fetter, NoQ

1,853,117, which.Y also relates. to ar system for the reception of space and vvred radio programs,

It is, therefore, a.

In accordance with the.

- (Cl.A 179`Z.5)

This invention relates to radio broadcast and' thereV is disclosed anv arrangement (Fig. 3') in. which the band of frequencies;V passedby the intermediate frequency amplifier is wide enough to admit any of thecarrier-f-requency Wire. program channels, as well as the translated' radio-fre- 51 quency. signals. This necessitatesthat all ofthe selectivity for radio reception musti be includedv in the radio-frequency amplier. Alsolters are used to select the carrier-frequency wire programs before impressing. themen the intermedi.- 10\ ate frequency amplifier. In the. present ,invention an intermediate frequency amplifier is',contem plated. which. passes, a band. of. frequencies. only wide enough. to accept. asingle. program channel, either` wire or radio,. the program frequencies be? l5' ing, suitably translated to. thisband'. InA this way the, adjacent channel. selectivity is entirely accomplished by the intermediate frequency amplienforeitherwire or the radio reception. The radio-frequency amplifier, therefore need only suppress. Slo-called image interference, a much less severe requirement. Also no lters 4are necessary for` selecting. the wire programs.

These. aswell as other objects and features of' the invention will now be. apparent/from the following description whenread in connection with the accompanying diagrams. of which Figure 1 shows. an. arrangementA of. apparatus forv av receiver ofthe superheterodyne type capabler of re,-

ceiving both radio broadcast. and? Wire distributed programs, and Fig..2l shows in.. greater. detail a... circuit. arrangement which. might be. employed for. sucha receiver; Figs. 3 andl4 illustrate. adapters or converters. which might be connected to a.

radioA receiver to. permit. the reception. of Wired'. 35

` ceiver of' the superheterodyne type might .be used.

. Fig. 1 shows. an antenna. AN and ground GD for intercept'ng, radio signals. from. a transmit.-

ting station. Also, two wires, l and-.2`, areshown V which maybelany; typeof wirey circuit over whichV carrier-frequency signals` arereceived from some program distributingpoint. A switch SW is providedv to connect the apparatusfor reception oi.n either the radio or the Wire program.. When` switch SW is closedlto the'left',tradi`o programsV may be received, and' when. close'dto the. rightr the carrier-frequency wire. programs may be. heard; Y

With the switch SVV-closed t`o the left'the oper- '55...

may be made to differ from therfrequency of the incoming radio carrier by an amount equal -to the frequency to which the intermediate frequency amplifier is tuned, so that `the band of incoming radio frequencies representingthe desired program may be translated in frequency to the band passed by the intermediate frequency amplifier IA. A single control SC varies the frequency generated by the radio-frequency oscillator RO and the tuning of the selective circuits in the` radio-frequency amplifier RA so that the desired program may be selected.

` With the switchSW in Fig. 1 closed tothe right the carrier frequencies from the wire line l, 2 are passed by the transformer TR to the first detector'FD by contacts 5, 6, I and 8 of the switch SW." Contacts II, I2, I3 and I4 pass aV signal generated bythe carrier-frequency oscillator CO tothe modulator FD;` The frequency of this signaldiffers from that ofthe incoming wire carrier by such an amount that a frequency band representing' a carrierefrequency program` may be translated in frequency so that it will be transmitted and amplified by the intermediate fre- 'quencyjampliiier IA. A program selector PS 'quencyamplifier IA contains tuned circuits which are'adjusted to pass a fixed band of frequencies just wide enough to accepta single program, and to reject all'other frequencies. This amplifier IA selects from the modulation products produced in the first detector FD asingle band of frequencies which represents, inthe case of radio reception, the two sidebands and carrier frequency translated to the intermediate frequency band and in the case of wire program reception, the carrier frequency and either one or two sidebands, also translated in frequency to the same intermediate frequency' band. lSuiiicient discrimination is p'rovided'in the intermediate frequency amplifier IA to prevent any undesired signals from being amplified, so that a single program may be received from eitherthe wire program distributing center or the radio broadcasting station without interference from adjacent frequencies.

A'tuning indicator TI is shown connected to the intermediate frequency amplifier. This is to indicate to the'person operating the receiver the position of the selection 'controls for optimum reception. This vcomprises chiefly a sharply se- .,.lectiye tuned circuit, possibly including a piezo'- "`el`ectric"resonator', a rectifier which maybe a vacuum tube or some passive device, and a visual indicator, such as a meter or variable light source. The resonant frequency of this tuned circuit is that frequency in the intermediate frequency band to which the carrier frequency of the received program signals should be translated for optimum reception. When the tuning controls have been adjusted so that the translated carrier frequency equals the resonant frequency of the tuned circuit, some of this frequency is diverted.

This portion of the carrier is rectified and utilized y to actuate the meter or other indicating device.

The demodulator or second detector SD in Fig. 1 demodulates the signals which have been amplified in the intermediate frequency amplifier IA' and delivers the resulting audible frequencies to the audio-frequency amplifier AA. These are further amplified and delivered to a sound reproducer whichV may be the loudspeaker LS shown in Fig. 1. Y

In the usual'receiver of this type the intermediate frequency amplifier will pass a band of frequencies about 10 kilocycles wide. If two sidebandsare received the maximum audible modulating frequency is limited to 5 kilocycles. How# ever, in accordance with the invention it is proposed to translate the incoming frequencies from the wire line so that only the carrier and a single sideband occupy the band passed by the intermediate frequency amplier.

Y10 kilocycles may be received.

' Fig; 2 shows in greater detail a possible circuit arrangement which might be employed for a receiver of the type described in connection with Fig." 1. The radio signals from a broadcasting station are intercepted by the antenna AN and ground 1GB. A variable resistance VR1 may be shunted across the input transformer of the radio-frequency amplifier RA to control the strength of the signal applied to it. This ampli fier RA is tuned by means of tuned circuits TCi and TG2 to discriminate in favor of signals corresponding to the desired program. Amplification of these signals is accomplished by means of vacuum tube VTrwith its4 associated circuits. The radio-frequency amplifier may be of any suitable type and may comprise more than the one vacuum tube shown.

The switch SW1 is closed to the left when radio reception is desired.

Contacts

3 and 5 of SW1 transmit the amplified radio signals from RA to the grid of vacuum tube VTs in the first detector FD. These signals comprise frequencies corresponding to the desired program and other relatively attenuated frequencies which were intercepted by the antenna AN. Contacts 6 and I2, 'I and I3, 8 and I4 of the switch SW1 connect the local oscillator circuit OS so that it can generate a range ofV frequencies suitable 'for translating bands of signals, representing radio-frequency programs, to the band passed by the intermediate frequency amplifier IA. The beat frequency is adjusted by the control SC which varies the value of variable condenser VC; in the tuned circuit TG3 of the oscillator OS. This control also adjusts the frequency band to which the radio-frequency amplifier RA is tuned by simultaneously varying condensers VC1 and V02. The band to which the amplifier RA is tuned bears a fixed relation to the frequency generated by the local oscillator, such that said band is translated in frequency to the band passed by the intermediate frequency amplifier by intermodulation with said locally generated frequency.

In this way a modulating frequency of the wire program as high as The modulator FD is shown asa vacuum tube VTa which is so operated that it performs as a second order modulator. Instead of a vacuum tube any suitable type of modulator might be used, such as the cuprous oxide or thyrite units. The radio frequencies representing the desired program and other radio frequencies somewhat attenuated present on the control grid of vacuum tube VTs are intermodulated with the signal from the local oscillator OS, which is applied to the screen grid. The output of the first detector FD contains principally, therefore, the sum and difference of the locally generated frequency with the received radio frequencies.

The intermediate frequency amplifier is essentially a high-gain amplier with a band-pass characteristic, cutting off unwanted frequencies very sharply. As Vshown in Fig. 2, the intermediate frequency amplifier IA comprises two vacuurn tubes of the screen-grid type, VT4 and VT5, coupled by tuned transformers. The tuning of these circuits may be so adjusted that the desired band-pass characteristic will be obtained. This amplifier may, of course, have any number of stages of amplification and employ any of several well-known circuit arrangements. The grid bias of the tubes in this amplifier isV adjustable by varying the resistance VRz, which alters the gain of the amplifier. Thus, resistance VRz may be used in conjunction with VR1 across the input to control the volume level of the audible-frequency output. These may be adjusted by a single eX- ternal control if desired.

The demodulator or second detector SD comprising the vacuum tube VTS may be of any suitable type and the circuit arrangements are well known in the art. The function of the detector is to demodulate the signals passed by the intermediate frequency amplifier IA and deliver to the audio-frequency amplifier AA the resulting frequencies in the audible range. The D. C. component of the rectified current from the second detector SD may be utilized to control the gain of some other part of the receiver, usually the intermediate frequency amplifier IA, so that the volume level of the output is independent of the magnitude of the incoming carrier.

The low frequencies produced in the second detector SD are further amplified by the audiofrequency amplifier AA to a suitable level and impressed on the sound reproducing unit or loudspeaker LS.

' The circuit arrangement for the reception of wire programs is substantially the same. Signals coming over the wires l, 2 from the central distributing point are impressed on the potentiometer PT which controls the signal voltage applied to the first detector FD through the transformer TR1. Switch SW1 is, of course, closed to the right, and

contacts

4 and 5 connect the wire program signals to the grid of vacuum tube VT3. Contacts S and l2, l and I3, H and lll connect tuned circuit TC4 into the oscillator circuit.- The frequency generated by VTz in the oscillator OS is now controlled by this tuned circuit' TC4. Switches SW2 and SW3 change its resonantfrequency by adding condensers FCz and FC3 to FC1. These three frequencies must bear such a relation to the frequency bands representing the three programs, which are assumed present in the wire circuit, that these latter may be translated in frequency by intermodulation to the band passed by the intermediate frequency amplifier. Any number of programs may, of course, be transmitted, and the tuned circuit TCi must be capable of producing a corresponding number of frequencies.

The program signals are intermodulated in FD with the frequency generated in the local oscillator OS. As in the case of radio reception, the intermediate frequency amplifier IA selects and amplifies the frequency band corresponding to the desired program, produced in FD by the intermodulation of the carrier frequencies fro-m line l, 2 with the signal from the local oscillator OS.

The operation of the receiver for the reception of both radio and wire programs will now be explained using definite frequencies for purposes of illustration. The frequency band between 550 and 1500 kilocycles is at present used for radio broadcasting. The carrier frequencies of broadcasting stations are allocated at -kc. intervals, allowing a theoretical maximum modulating frequency of 5 kilocycles. An intermediate frequency, that is, the mid-band frequency of the intermediate frequency amplifier, IA in Fig. 2, of 175 kilocycles, will be assumed. This means that the intermediate frequency amplifier IA should pass a band of frequencies from 170 to 180 kilocycles, attentuating considerable frequencies outside of this band. The frequency generated by the local oscillator OS for radio reception must be such that it will change the frequency of the incoming program to pass the intermediate frequency amplifier. If the frequency generated by the local oscillator OS is always kep-t higher than the radio signals being received, the resonant fr-equency of TG3 must be variable between 725 and 1675 kilocycles.

In order to receive a radio broadcast program on a carrier frequency of 1000 kilocycles, for instance, the tuned circuits TC1 and TG2 must be adjusted so that the radio-frequency amplifier RA discriminates in favor of the band of frequencies between 995 and 1005 kilocycles. Tuned circuit TG3 must be tuned so that the local oscillator OS will at the same time generate a frequency of 1175 kilocycles. In the first detector FD, which will be assumed a second order device, the frequencies from the radio-frequency amplifier will be intermodulated with the frequency of 1175 kilocycles from the local oscillator. The desired program will be represented by two frequency bands-one, 2170 to 2180 kilocycles, and the other, 170 to 180 kilocycles. Obviously, the higher frequency band will be excluded by the intermediate frequency amplifier IA, as will be products of the modulation other than the 1'70 to ISO-kc. band which now represents the desired program. This consists of a carrier frequency of 175 kilocycles, and the original modulating frequencies up to 5 kilocycles represented as sidebands. This band of frequencies is further selected and amplified in the intermediate frequency amplifier IA, demodulated in SD and the resulting low frequencies amplified and reproduced by the loudspeaker LS.

In the carrier-frequency program system carrier frequencies of 25, 60 and 90 kilocycles will be assumed with only the lower sidebands present. If it is desired to locate the carrier frequency in the center of the band passed by the intermediate frequency amplifier IA, the local oscillator OS should generate frequencies of 200, 235 and 26,5 kilocycles, respectively. However, in order to obtain a better quality program it is proposed in this invention to adjust tuned circuit T04 to frequencies of 195,230 and 260 kilocycles, respectively. This would place the translated carrier frequenciesv at, one side of the frequency band passed by IA, that is, at 170 kilocycles. The

Y sideband could now extend from 170 to 180 kilocycles. Thus the highest modulating frequency that could b-e received would be 10 kilocycles. In order to effectively vaccomplish this result the frequency characteristic of the intermediate frequency amplifier IAniust be quite flat in the passed band. Also, the audio system and sound reproducer must be capable of responding to frequencies upto 10 kilocycl-es. In this way a program band 10 kilocycles wide may be handled without any major changes in the design of the intermediate frequency amplifier, as it is used in many present day radio receivers.

With a receiver of this type it might also be desirable to improve the quality of received radio programs. Radio broadcasting stations could be equipped to transmit a band of program frequencies up to 8 or 10 kilocyclesiin fact many transmitters are so equipped already. In order to receive such high quality transmissions with a receiver such as has been described, it will be necessary to receive only a single side band and carrier, rather than both sidebands as has been customary heretofore. The frequency band favored by the radio-frequency amplier, RA in Fig. l, is theoretically at least v10 kilocycles wide and should accept the radio carri-er and one 10-kc. sideband. Its frequency response should be quite uniform over the lil-kc. band, to avoid distortion.. The frequency generated by the local oscillator, RO in Fig. 1, will now be changed by 5 kilocycles since the tuning and oscillator controls are coupled together. This will place the translated radio carrier at one edge of the frequency band passed by the intermediate frequency amplifier, and one sideband, 10 kilocycles wide, will be accepted and'amplified by it.

In order to indicate when the tuning controls are properly set to enable reception of a single sideband in the manner just described a special sharply tuned circuit may be connected to some point in the intermediate frequency amplifier. This circuit might include a piezo-electric resonator to improve the sharpness of tuning. The resonant frequency of this tuned circuit would be that frequency in the intermediate frequency band to which the radio carrier frequency should be `translated for reception in. they mann-er desired.

To illustrate the reception of a single sid-eband a radio broadcasting station having a carrier frequency of 1000 kilocycles will again be assumed. However, the side-bands will now extend from 990 to 1010 kilocycles, since modulating frequencies up to 10 kilocycles are assumed. The intermediate frequency amplifier will be assumed to pass the frequency band from 170 to 180 kilocycles. In order to receive the lower sideband, 990-1060 kilocycles, the radio-frequency amplifier must be tuned to this band, and the beat frequency oscillator must at the same time generate a frequency of 1170 kilocycles. Thus, by intermodulation, the radio carrier would be translated to 170 kilocycles and the lower sideband to the l'-lo-kc. band passed by the intermediate frequency ampliiier. The upper sideband, 1000- 1010 kilocycles, would be translated to 17o-160 kilccycl-es, and this band would be rejected by the intermediate frequency amplifier. The resonant circuit in the tuning indicator would be tuned to 1'70 kilocycles, so that when the carrier is translated to this frequency, proper tuning will be indicated.

In order to receive the upper sideband of the radio-frequency transmission, 100G-1010 kilocycles, the local oscillator must generate 1180 kilocycles. The radio carrier frequency will now be translated to 180 kilocycles, and the sideband to the 180-170-kc. band. The unwanted side band, 990-1000 kilocycles, will be translated to 180-190 kilocycles and will thus be eliminated. The tuning indicator will be adjusted to 18() kilocycles.

In accordance with the present invention a radio receiver of the superheterodyne type may be adapted so that it will also receive carrier frequency programs transmitted by Wire, by the use of an adapter such as is shown in Fig. 3. Two terminals, l and 2, are provided to which the wire circuit transmitting the carrier frequency programs is connected. The potentiometer PT for volume control is connected to these terminals. A transformer -TR similar to that in Fig. 2 is included. From this transformer one wire 2l transmits the carrier-frequencies to the grid of the modulator of the first detector of the radio set, the connection including the contacts of a switch, as in Fig. 2, by which the radio program circuit could be, at that time, disconnected from the said grid. Another wire 26 completes the circuit to the ground of the radio receiver.

The tuned circuit TC of the beat frequency. oscillator for wire program reception is shown the same as that in Fig. 2 and proper connections are made through contacts 9, Ill and Il of a suitable switching arrangement to the grid and plate circuits of the vacuum tube in the radio receiver local oscillator, the radio frequency tuning circuits being disconnected at that instant. The switching arrangement could be` similar to the switch SW1 in Fig. 2 inserted in the circuits of the radio receiver to accomplish the changeover from radio reception to wire program reception.

Another possible arrangement for adapting a superheterodyne radio receiver for the reception of carrier frequency wire programs is shown in Fig. 4. This adapter includes a vacuum tube VT to generate the beat frequency instead of utilizing the one associated with the radio receiver. The tuned circuit TC for determining the three beat frequencies is the same as shown in Figs. 2 and 3. Filament and plate voltages are supplied by the radio receiver by means of wires 23, 24 and 22. A resistance R2 is connected in the plate supply lead to prevent the possible short circuiting of the local oscillator output. As in Fig. 3 the wire circuit is connected to the terminals l, 2 of the input circuit which includes the potentometerPT and the transformer TR. The incoming carrier frequencies and the local oscillator beat frequency are impressed on the grid of the first detector by means of lead 2|. A lead 25 provides a connection to the receiver ground. A condenser C1 is provided to exclude the plate voltage from the grid circuit. A resistance R1 is inserted to regulate the amplitude of the beat frequency. Only one switch Contact is necessary with this arrangement to connect the grid of the first detector to either the radio-frequency input and radio-frequency beat oscillator or the carrier frequency program adapter.

Other arrangements similar to those shown in Figs. 3 and 4 are obviously possible and are included in the scope of the invention. Such arrangements should make it possible to adapt most Within the cabinet of the radio receiver. How-.75V

ever, this apparatus could be mounted separately if necessary.

The operation of the adapters shown in Figs. 3 and 4 together with a radio receiver of the superheterodyne type is the same as that described in detail in connection with the combined receiver shown in Fig. 2. The controls necessary are a volume control such as PT and a program selector such as switches SW2 and SW3 associated with a tun-ed circuit TC.

Fig. 5 shows an arrangement which might be used to distribute carrier frequency programs to subscribers overwire circuits. Among the features of this system are the separate amplification of sidebands and carrier frequencies at distribution points and the arrangement whereby three programs may always be present 0n the wire circuit with other optional programs available. The wires used for the program service may be separate circuits or those used for regular telephone service. The receiver may be Acombined space radio and' carrier frequency wire program receiver such as previously described herein but is not necessarily limited to this type.

Three carrier frequency channels are utilized in the program system shown in Fig. 5. At the program center three carrier frequencies, 25, 60 and 90 kilocycles, are generated by oscillators OSi, OS2 and OSs. The 25kc. carrier is introduced to modulators MDi, MD2 and MDs, Where it is modulated with

programs

1, 2 and 3. Program 4 is modulated to the 60-kc. channel in MDi and program 5 is modulated to the 90-kc. channel in MD5. i The program material may be produced in studios at the program center or transmitted thereto from some outside pick-up point. Program material may also be produced by some process of electrical transcription.

The modulators are so arranged that the carrier frequency is suppressed. The bandV lters BFi, BF2, BFs, B111 and B135 suppress in each case the upper sideband, passing only the lower sideband. There are, of course, other arrangements for obtaining a single sideband, -.any of which would be suitable. It might be desirable, rather than to suppress completely one sideband, to transmit vestiges of the carrier frequency and lower modulating frequencies. The modulators MB1, M132 and MD3, therefore, produce sidebands from 15-25 kilocycles, modulator MDi. 50-60 kilocycles and modulator MD5, -90 kilocycles. sidebands corresponding to programe l, 2 and 3 are amplified in AM1, AM2 and AM3, respectively. The sidebands corresponding to

programs

4 and 5 are amplied in a common amplifier, AM4. The three carrier frequencies are amplified in a single-amplifier AMs. All of these amplifiers are designed to furnish power sumcient to feed a large number of lines.

The trunks L1, L2, Ls'and L4 transmit the five program sidebands from the programv center to a central office and the trunk Ls transmits the threecarrier frequencies to the same point. Additional lines'transmit the programs to other central oihces. AtI theY central office shown in Fig. 5 ampliers AMG, AMY, AMS, AMQ and AMio, respectively, amplify the incoming program frequencies. Each of these is also capable of furnishing power for-a large number of lines which,

in this case, are subscribers circuits.

One'such subscriber circuit Le is shown vin Fi 5. In this case the line Ls is the subscribers regular telephone loop connecting thesubscribers telephone set TS with the voice-frequency equipment at the central office. However, a separate Wire circuit might be used. vIn order to prevent interference between' the program service and voice-frequen-cy message service, low-pass filters, LPi and LP2, are necessary at'the central office and at the subscribers station, as shown. These permittelephone conversation at voice frequencies and exclude the program frequencies from the telephone apparatus. At the central office the programs at carrier frequencies are applied tothe line Le; through a high-pass filter HP1 from the program bus PB. This busPB islconnected tojthe output of the amplifier AMs'which suppliesthe sidebands'for the 60 and 90-kc. channels corresponding to

programs

4 and 5 and the amplifier AMio which furnishesthe three carrierfrequencies. Programs l, 2 and 3 all o f `which occupy the same carrier frequency band; 15-725 kilocycles, are supplied bythe amplifiers AM6,-AM7 and AMa to the three: jack vmultiples JAi, JA2 and JAs. A plug'PL is connected to the subscribers line through resistances R2 and by plugging `it into a jack in the multiple one of the three programs may be transmitted to the subscriber. The 25-kc. carrier is present in the line beingobtained from the program bus PB.V Therefore, only the sideband corresponding to the desired program is required andl this is obtained from onek of the amplifiers AMS, AMY o r AMS through the jack multiple JA1, JA2 0r JAa and the plug PL. l

Since all of the subscribers lines are connected to the common bus PB, transmission between'the subscribers lines on the 25-kc. channel must be prevented in order to prevent interference of the three programs in this channel. Forv this purpose resistances R1 have been inserted in series with each line. These must have high enough values s o that the attenuation ofthe network of four of th'emitwoin each of two lines) with the low ybus impedance shunted between them will prevent crosstalk between individual circuits.

Similarresistances R2 are placedin lthe circuit of the .plug PL to ,prevent' currentsfrom the program bus PB from entering the jack multiples JAi, JAz and JAa.

At the subscribers station ahigh-pass filter HP2 admits the carrier program'Y frequencies and excludes the voice frequencies. The program receiver PR isconnectedjto the output of the high-pass filterI-IPg. Thisv receiver contains selecting circuits for choosing oneof the three carrier frequency channels, amplifying circuits and demodulating circuits. vThe audible freiquency output from the receiver PR, amplified to a suitable volume le vel,"is appliedto the sound reproducing unit or loudspeaker L S. This receiver PRmay well be one of the type previously described herein, in which the carrier program frequencies are translated in frequency to pass through an intermediate frequencyy amplier which is also used for the reception of radio programs.` Y

In order to receive one of the alternate programs on the 2 5-kc. channel `arrangements may bev made by telephone with an operator at the central oflice to change the position of the plug PL to a jack in the multiple corresponding to the desired program. It is also possible to accomplish the same result mechanically, using the dial associated with the subscribers telephone to ,select by a special code the 'desiredprogram lection at his receiver. These comprise the programs on the 60 and 90-kc. channelsand one of the Vprograms on the 25-kc. channel.- The subscriber may, by-telephone, request one of the other programs available on this channel. The number of programs available on the 25-kc. channel need not be limited to three, as shown, but any number may be provided. Also, instead of having only one program available on the 60 and 90-kc. channels there might be alternative programs available forY these channels as Well. These could be connected on request by telephone-from the subscriber or mechanically as the result of a dialing operation at the subscribers station. 1 -fWhile this invention has been disclosed as embodied in certain particular forms, it is capable of embodiment in other and different forms without-departing from the spirit and scope of the appended claims.

What is claimed is:

1. The method of receiving either space radio or wire distributed carrier frequency programs on a common receiver, consisting in translating either the space radio or the carrier frequency programs to an intermediate frequency band, selecting and amplifying the band of intermediate frequency, the said frequency translation being so controlled that `the resultant band will be within the frequency range for which the amplifier is selective.

2. In combination, means for collecting space radio signals, a superheterodyne receiver including an intermediate frequency amplifier capable of passing a fixed band of frequencies, a wired radio line delivering signals at carrier frequencies, means for translating in frequency either said space radio signals or said carrier frequency wire transmitted signals to the band passed by the intermediate frequency amplifier.

3. A superheterodyne receiver for radio .broadcast and wire distributed carrierfrequency programs, including a modulator, intermediate frequency amplifier and associated band filter, demodulator, and audio system all common to the radioand wire receiving systems,v and a local oscillator capable Vof generating a plurality of frequencies, said oscillator supplying a frequency to said modulator of such value that the incoming signals representing any single program, either Wire or radio, are translatedl in frequency to the frequency band passed by said intermediate frequency amplifier and its associated band filter.

4. In combination, a collector ofspace radio signals, a receiver of the superheterodyne type including an intermediate frequency amplifier arranged to select a band of frequencies, a wire line delivering programs at carrier frequencies, means for translating in frequency either said Yspace radio signals or said carrier frequency signals, means for connecting either said translated space radio signals or said translated carrier frequency signals to said intermediate frequency amplifier, said intermediate frequency amplifier selecting a band of frequencies corresponding to a single program.

5. A combined space radio and wired radio receiving system comprising, in combination, highfrequency circuits arranged to intercept `space radio signals, a wire line conveying carrier frequency signals, frequency changing apparatus arranged to change the frequencies of either the space radio signals or the wired radio signals, an intermediate frequency amplifiertransmitting a fixed band of frequenciesarranged to select said band of frequencies from the changed frequencies of either the space or the Wire signals, a demodulator,iaudiofrequency amplifier and sound reproducing system arranged to convert to sound Waves the band of frequencies selected by said intermediate frequency amplifier.

6. In a system for the reception of Wire distributed and radio broadcast programs, the combination of a Wire line transmitting a plurality of program channels each based on a carrier frequency differing from the others, a local oscillator capable of generating a plurality of fre-r quencies, a collector of space radio signals, means' for partially selecting and amplifying certain of said signals, a rsecond local oscillator capable of generating a plurality of frequencies, switches toi introduce to a modulator either the incoming carrier frequency signals and a frequency from said first local oscillator 'or said space radio signals partially selected and amplified and a frequency from said second local oscillator, means for selecting from the output of said modulator a fixed band of frequencies in the superaudible frequency range sufiiciently wide to pass one program channel, means for amplifying and demodulating said frequencies, means for varying the frequency of either local oscillator so that a desired program may be selected, means for varying the radio-frequency selecting circuit accordingly, audio-frequency amplifying means and sound reproducing means.

7. Inra combined space radio and wired radio receiver of the superheterodyne type including an intermediate frequency amplifier capable of selecting and passing a fixed band of frequencies, the'method of receiving only a single sideband and carrier frequency of either the space or Wired radio transmission, consisting in translating in frequency said transmission by modulation with a locally generated signal so adjusted that the translated carrier frequency is located at one edge of the band of frequencies passed by said intermediate frequency amplifier and one sideband is included in said band.

V8. In a combined space and wired radio receiver of the superheterodyne type including an intermediate frequency amplifier capable of selecting and passing a fixed band of frequencies, means for translating in `frequency the received signals, either space or Wired radio, so that a carrier frequency and single side band are included vin the band selected and passed by said intermediate frequency amplifier, and means for impressing upon said intermediate frequency amplifier Athe band of frequencies thus translated. Y `9. The method of receiving any desired one of 'a plurality of high quality Wired radio programs with a space radio receiver of the superheterodyne type having an intermediate frequency amplifier passing a fixed band of frequencies, said receiver being so arranged that said intermediate frequency amplifier selects and passes a translated space radio program consisting of a carrier and two symmetrical sidebands, said method consisting in translating said Wired radio program in frequency by an amount such that the translated carrier and one sideband are selected and passed by said intermediate frequency amplifier, the translated carrier being near one edge band of frequencies, any one of a plurality of carrier frequency programs transmitted over a wire line, consisting in translating in frequency the desired carrier frequency program to the fixed frequency band passed by said intermediate frequency amplifier and applying said band to said amplier.

11. In combination with a space radio receiver of the superheterodyne typ-e including therein an intermediate frequency amplifier having connected therewith a band filter passing a fixed band of frequencies substantially equal in Width to that of a carrier program, a Wire line conveying a plurality of programs at carrier frequencies, and frequency translating means connected to said wire line and having means for changing the frequency of any incoming program band to the fixed band passed by said intermediate amplifier and the filter connected thereto.

12. In combination, a radio receiver of the superheterodyne type including an intermediate frequency amplifier and tuned circuits for selecting a fixed band of frequencies, a Wire line delivering a plurality of programs at carrier frequencies, and means for translating the signals from said Wire line in frequency so that they may be selected and amplified by said intermediate frequency amplifier and said tuned circuits.

13. In combination, a radio receiver of the superheterodyne type including an intermediate frequency amplifier, so arranged as to be capable of passing a fixed band of frequencies, a wired radio receiving line conveying a plurality of programs on separate carrier frequency channels, a local oscillator capable of generating a plurality of frequencies, each to be beaten with one of the said carrier channels, a modulator adapted to translate each of said channels to the frequency band passed by the intermediate frequency amplifier when the said channel is beaten with its particular locally generated frequency.

14. In combination With a radio receiver of the superheterodyne type having included therein a local oscillator, a first detector, intermediate frequency amplifier and associated band filter, a wire line conveying signals at carrier frequencies, a second local oscillator of variable frequency, means for introducing into said first detector the incoming carrier frequencies from the Wire line together With a frequency from said second local oscillator, the frequency of said second oscillator being adjusted in such a manner that a band of frequencies produced in the output of the first detector is passed by the intermediate frequency amplifier and associated band filter of said radio receiver.

15. In a system, by means of which wired radio programs may be received With a space radio receiver of the superheterodyne type, the combination with a space radio receiver of the superheterodyne type having a modulator included therein, of an adapter including a generator for producing frequencies suitable to translate in frequency any one of the Wired radio programs to the frequency band passed by the intermediate frequency amplier of said space radio receiver, and means for introducing any one of said frequencies from said generator, together With the Wired radio program frequencies, into the modulator of said space radio receiver.

16. A converter, by means of which Wired radio programs may be received with a space radio receiver of the superheterodyne type, including tuned circuits for controlling the frequency of a local oscillator, means for introducing a frequency from said local oscillator together with the wired radio signals into the modulator of said space radio receiver arranged so that the Wired radio signals are translated in frequency and a band of frequencies representing a single program is selected and passed by the intermediate frequency amplifier of said space radio superheterodyne receiver.

1'7. A receiver for radio broadcast and Wire distributed carrier frequency programs comprising means for impressing upon said receiver either the incoming space radio frequency band or the Wire carrier frequency band, means to change the frequency of those incoming signals to a single fixed superaudible frequency band, a selective amplifier and a detector connected thereto, the said fixed band comprising thatfrequency o range for which the said amplifier is selective.

18. Means for adapting a superheterodyne receiver normally designed for the reception of space-radio programs only, to receive either the space-radio or Wired-radio pro-grams, the said adapting means including a group of tuned circuits designed for substitution, at will, for the space-radio frequency tuned circuit normally connected to the oscillator of the said receiver, and capable, when so substituted, of producing a plurality of .discrete carrier frequencies, and switching means to connect said group of tuned circuits to the said oscillator in place of the space-radio tuned circuit, and to impress the Wired-radio programs upon the said receiver simultaneously with the impression thereon of beating oscillations, the frequency of which is such as to produce that band of frequencies which the intermediate frequency amplifier is designed to pass.

WARREN H. TIDD.