US1464565A - Call system for radiotelephony - Google Patents

Description

Aug. 141, 1923.

- 11,464,565 L. ESPENSCHIED ET AL CALL SYSTEM FOR RADIOTELEIHONY 3 Sheets-Sheet 1 Filed April 13 gmw e awk 8140244 tow Aug. 14}, 11-923.

L. ESPENSCHIED ET AL CALL SYSTEM FOR RADIOTELEPHONY Filed April '13 1921 3 Sheets-Sheet 2 I ave/Mom wmg mw L. ESPENSCHIED ET AIL.

CALL SYSTEM FOR RADIOTELEPHONY Filed April 13 1921 '3 Sheets-Sheet is amen wow v a fizaiw abtoma Paar-meal Au M, was. llsdddfitd warren grams rarest caste-a new JERSEY, ASSIGNORS :ro AM RICAN TELEPHONE mm rntneaern COMPANY,

- a ooaromrron or new roan.

CALL SYSTEM FOR RADIOTELEPEONY.

Applieationfiled April 13, 1921. Serial 190. 460,869.

To all whom it mag concern: ing apparatus is made selective, the selec- Be it known that we, LLoYnEsPEnsoHiED tivity of such receiving apparatus being car- 55 and RALPH BowN, residing at Queens and ried to an extreme. In this way, the amount I East Ora'nge,in the counties .of Queens and of interfering energy obtained in the .very

v Essex and States of New Yorlrand New narrow band of a'few cycles per second, for Jersey, respectively, have invented certain example, is made very small, and by concen- Improvements in-Call Systems for Radiotrating all of the transmitter energy in this '60 telephony, of which the following is a sp'ecivery :narrow band, the ratio of desired to Ifi ati n' undesired energy is made very large.

0, This invention relates to a'system for the This introduces an undesirable factor,

4 remote control of mechanism by radio-transdue to the difficulty encountered in main mission, and more-particularly to the applitaining frequency agreement between the 65 cation of such remote control to signaling transmitted energy and the frequency ador' ringing systems for usei-n connection mitted by the receiving system. Thisvdifiiwith radio telephony," r culty is overcome in accordance with the In accordance with the present invention, present invention by continually varying the devices to beremotely controlled are up and down in the frequency range over a 70 made extremely selective for the purpose of band lying within the corresponding transpreventing;interference due tostatic or mitted telephone band, either the transmit- 2 other vvdisturbances, and in order to insureting frequency or the beating frequency at the uniformity of operation of the remotely the receiving station. This results in bringcontrolled devices, special means are -proing the two'- frequencies into periodic agree- 75 vided to prevent uncertainty. of operation ment and the circuit may be so arranged that [due to the extreme selectivity-employed. each time frequency agreement is obtained,

In practicing the invention as applied to energy isapplied to the receiving ringing a signaling o'r. 'ringing system ,for radio apparatus or other remotely controlled telephony, for example, a signal frequency device. v I 1 is generated at the transmitting-station and" A further degree of selectivity and insurtransmitted to the; receiving station, at ance'against interference is obtained by renwhich point it'coacts with alocally gen dering the operation of the receiving syserated frequency. The ringing mechanism tem reliant upon a certain predetermined at the receiving station is operatedonly in time element, such .as a certain number of the event the difference between the local successive impulses. This predetermined and incoming frequencies is less than a. few .time element may also be utilized in conas cycles per second. In order to insure that nection with coding and code selecting terthis condition will be realized, one of the minal'apparatus for selective signaling of frequencies is caused to vary slowly over a any one of a number of receiving stations range sufficient to include any. variations I from a given transmitting station. which may occur in the'other frequency. The invention may now be more fully '4 One difficulty encountered in the. pracunderstood by reference to the following tical development of a suitable ringing sysdetailed description, when read in connec tem. forradio telephony resides in the fact tion with the accompanying drawing.

that, owing to he extreme "sensitivity of In the drawing, Figure 1 is a simplified the receiving'ringing apparatus to be emoircuit'arrangement of a transmitting sta- 5 ployed, the apparatus is liable tov produce tion, illustrating three forms of transmitfalse alarms, due to staticor other interferting channels which may be employed, Fig. ence s.-- In order to meet the requirement of 2 is a. corresponding receiving clrcult freedom of. interference, it is proposed to, illustrating three forms of receiving appatakeadvantage of the slow speed nature ratus; Fig. 3 illustrates a transmltting sta- 50 of the callingor ringing channel 'by working tion adapted for selectively calling any one near the limit of this condition.-- This is acof a number of receiving stations; Fig. i

complished by reducing to a minimum the is a transmitting circuit arrangement simifrequency ban d to which the receiving ringlar tothat of Fig. 1, but difiering therefrom in that successive modulating steps are utilized in generating the signaling frequencies; Figs. 5 and 6 are'silnplified diagrams of transmitting and receiving stations arranged for radio telephonic transmission and for the transmisslon of ringing-signals in connection with the telephone system;

Figs. 7 and 8 are similar diagrams but differing from Figs. 5 and 6 in that a mechanically selective calling-device is. employed. I

Referring to Figs. 1 and2, TA is'a transmitting antenna with which are associated. three transmitting channels I, II and III, while RA represents a corresponding receiv. ing antenna having associated therewith cor responding receiving channels I, II and III".

I The simplest form of transmitting -appa- .for purposes of illustration, is shown as a vacuum tube detector. A local source of beating energy G .,is provided, said source being associated with the input circuit of thedetector D. This source may have any desired frequency so chosenthat the differerence between the received frequency and the local frequency will be comparatively small. In the case illustrated, the beating frequency is 690,000 cycles. -An amplifier A, of any well-known type, is associated with the output circuit of the detector D, this amplifier being, in the case illustrated, a vacuum tube amplifier. vThe output circuit of this amplifier is associated with the severalselective receiving channels.

The receiving channel I, corresponding to the transmitting channel I, includes a band filter BF]; for selecting the difference frequencies in the neighborhoodof 10,000 cycles, said filter being associated'with the input circuit of a detector 1),. The detector D, may" also be supplied with energy from a local source G,', the frequency of which will also be in the neighborhoodof 10,000 cycles. The frequency of the generator G, may be caused to vary over a narrow range,

sufiicient to includeanypossible variation of the generator'G, at the transmitting station. This is accomplished, for example,'by

means of an adjustable capacity C,, arranged to determine the frequency of the generator (which may be of the well-known vacuum tube type) in a well-known manner.

The capacityC, may be periodically varied by mechanically rotatin its plates with respect to each other, as indicated schematically in the drawing. The detector D, detects a frequency corresponding to thedifference between the step-down receiving frequency passed through the .band filter BF, and the frequency supplied by the generator G,, and this difference may be made quite small if thetransmitting and receiving frequencies are properly adjusted.- In the output circuit of the detector D a band filter BF," is rovided, this band filter being rendered se ective'to an extremely narrow band of frequencies, extending for example, from zero to 10 cycles per second. Each time the frequency of the generator G, is cyclically .varied, the received and locally generated frequencies will be periodically brought into harmony, so that a frequency variation extending from zero to 10 cycles per second will be passed through the filter BF,". A receiving relay. R, is provided on the output side of the filter, this relay being slow-acting sothat its armature will be held up so long as its-windingis energized by successive pulses corresponding to the cyclic variation of thefrequency of the generator Gf. The relay B, may be made to operate any desired form of translating device.

In the case of the transmitting and receiving channels just described, the cyclic frequency variation is introduced at the receiving station. In many instances it may be preferable to introduce this variation at the transmitting station, and the channels II and II are accordingly so arranged. The transmitting channel II includes a vacuum tube generator G having a vario'meter' V in' its plate circuit for controlling the frequency supplied-by the generator. The variometcr V comprises two windings, one of which may be mechanically rotated with respect to the other, thereby changing the in ducta-nce in the plate circuit. If the movable winding be mechanically rotated at a given speed, a corresponding cyclic variation will;

be produced in the frequency generated by the generator G The corresponding receiving;channel includes a band filter. BF-

a detector D a band filter BF, in' the output circuit of the detector and a receiving. relay R The'detector D is supplied with a. locally generated frequency from a source (ir,. The channel II differs from'the re ceiving channel I in that-the generator G i this instance is-not cyclically varied. '-As indicated, the receiving"relay.-.R,- is utilized r to operate alamp S or a'ringe'r S Assuming that 'the generator G is'- designed to generate frequencies in the neighborhood of 710,000 cycles, each time the key K is closed, the generator will become act ve and will generate oscillations whose free-f neeaeee quency will undergo a cyclical chan e determined by the variometer V,. At t e receiving station, the cyclically-varying frequency will beat with the locally generated frequency of 690,000 cycles to produce a 'diflerence frequency in the neighborhood of 20,000 cycles. The cyclically varied diilerence frequency will be selected by the band filter BF, and applied to the detector D,. By beating with the locally generated lire-- quency of 20,000 cycles, a difierence trequency varying from zero to a few cycles per second will appear in the output circuit the detector D, and successive pulses of current corresponding to the cyclical variations of the ire uency transmitted through the band filter T," will energizethe sluggish relay R to close and maintain closed the signaling circuit as long as the hey K is operated.

Transmitting channel TH and receiving I channel Hll'- illustrate the use of a mechanical selecting device in connection-with the general type of signaling channel previously described. The channel TH includes an oscillator G which may be of the vacuum tube type and is arranged to generate any desirable carrier frequency. In the case illustrated, the frequency generated is in the neighborhood of 720,000 cycles but may be periodically varied by means of an adjustable condenser C, so arranged that its capacity may be periodically varied by some suitable mechanical means. The circuit of the generator G, is arranged so' that code signals may be transmitted under the control of a relay 21, which is in turn controlled by a code sending apparatus of some wellmown type. For purposes of illustration, a code sender of the type illustrated in the patent to rl ield, No. 1,343,256, of June 15, 1920, is schematically indicated in the drawing. As the mechanical details of this code sender are somewhat complicated and an understanding of these details is not necessary to a complete understanding of the present invention, the apparatus is not illus trated in detail and will not be described in detail. The code sender comprises a transmitting disc TS having a toothed periphery adapted to engage with contact springs whereby a battery controlling relay-22 and a pole changing relay 23 may be operated. The relays 22 and 23 are arranged to transmit positive and negative impulses to lar relay 24 under the control of the disc TS.

When the disc is in normal position, the con-. tact 25 is disengaged therefrom and contacts 26 and 27 are opened so that relays 22 and 23 are deenergized. As soon as the disc is rotated in a counter-clockwise direction, the spring 25 rides upon the periphery of the disc, thereby completing a circuit through the spring 25 andthe body of the disc to energize the relay 22. The circuit'ot the relay 22 remains closed throughout the retation of the disc until the disc again assumes its normal position, when the circuit will be again opened. During the time that the relay 22 is energized, it connects battery to the circuit of the polar relay 2%. The

springs 26 and 27 control the circuit of the pole changing relay 23 and these springs are so set that when the spring 25 is riding over the surface of the disc, springs 26 and 27 will be maintained open, except during the times that the spring 25 ridin over i the upper surtace of the toothed port1on oi? the periphery of the disc. Consequently,the springs 26 and 27 open and close the circuit of the relay 23 as the spring 25 rides up and down over the teeth in the periphery of the disc.

The code transmitted may consist of a series of groups of positive and negative impulses, each group being separated by impulses of longer duration. Various combinations of the groups of impulses may be made. The particular disc illustrated is designed to transmit a code consisting of a group comprising a positive impulse, a negative impulse and a positive impulse followed bya prolonged negative impulse, another group comprising a positive, a negative, a positive, a negative, a positive and a negative followed by a prolonged positive impulse, and the final group comprising a negative, a positive, a negative, at positive, a negative and a positive followed by a prolonged negative impulse. The purpose of the last prolongednegative impulse is to provide a ringing interval at the receiving station, as will be described later. 'At the end of the ringing interval another positive impulse is transmitted to restore the selected selector at a distant receiving station. The polar relay 24=-responds to the positive and negative impulses transmitted to open the circuit of the relay 21 for a negative impulse and to close the circuit for a positive impulse. Consequently, the gen erator G, will transmit groups of high frequency oscillations during the continuance of each positive impulse and each group of high frequency oscillations will cyclically "ill vary'in frequency under the control of the ranged to respond to the groups of oscillations in a manner similar to the relays previously described. The relay R controls a mechanical receiving selector RS, which may be of any well-known type, but as schematically illustrated, comprises a selec- 'tor of the type illustrated and described in the patent to Field, previously referred to. This type of selector includes a rotatable disc adapted to be stepped by a polar magnet 28. The polar magnet controls an apparatus whereby the disc of the receiving selector is stepped forward one step for each positive and each negative impulse, regardless of its length. The mechanical details whereby this result is accomplished are not illustrated, but are fully described in the patent to Field above referred to. The armature of the polar magnet 28 has a normal neutral position and'when the armature is in the neutral position, the disc will be free to return to its normal position under the influence of a spring (not shown) unless the disc is maintained in the position to which it is stepped by the engagement of a latch 29 with one of the pins 30, 31 or 32, located by the periphery of the disc. A condenser 33 is included in the circuit of the polar magnet 28, which circuit is controlled by the receiving relay R Consequently, the polar magtive impulse to step the disc one step. When a prolonged impulse, either positive or negative, occurs, however, the condenser 33, which is charged at the beginning of the prolongedv impulse, permits current to flow through the windings of the polar magnet and causes the disc to take a corresponding step, but the condenser discharges before the end of the prolonged impulse and camequently, the armature of the polar magnet will be permitted to resume its neutral position. The pins 30, 31 and 32 will be differ- 'ently arranged about the peripheries of the various selecting discs at different stations so that during the prolonged impulse following the first group of impulses all of the discswill be permitted to return to normal except those having pins 30 so arranged as to engage with the latch 29. In response to another group of positive and negative impulses followed by a prolonged impulse, the various selecting discs will be further advanced and of those which are advanced, only those will. remain in advanced position whlch have pins 31 engaging with latches such as 29 during the prolonged impulses. This results in certain of the discs, which had previously remained advanced, being restored to normal; At the end of the last group of impulses followed by a prolonged lm-pulse, only one disc will remain advanced, as only one disc will have a pin 32 so situated as to engage with the latch 29. Each .disc carries a contact arm 34 so arranged as i to make a contact with the segment 35 when that particular disc is advanced the right messes number of steps, and when a disc is advanced so that its pin 32 is in'engagement with the latch 29, a transmitting circuit to actuate some receiving or other device will be closed. The disc illustrated in Fig. 2 has its pins 30, 31 and 32 so arranged that it will be selected when the transmitter TS all of the discs will be restored. The selected disc will obviously be restored by reason of the fact that there will be no pin in position to engage'with the latch 29 while the armature of themagnet 28 is in neutral position.

The operation is as follows: When the transmitting disc TS is rotated, the spring 21 rides up over the periphery of the disc, which energizes relay 22 to connect battery to the polar relay 24 during the complete he springs 26 and 27 will be opened until the first tooth is reached, and consequently,

during this period the relay 23 will be deenergized so that the polar relay 24 will shift its armature in the positive direction, thereby energizing the relay 21 over a circuit including the contact of the polar relay and the lower make contact of the relay 22. The

circuit of the generator Gr is, therefore, closed, and during the continuance of this impulse a group of cyclically varying high frequency oscillations are transmitted to the receiving station. At the receiving station, the high frequency group of oscillations is stepped down by means of the detector D to a frequency in the neighborhood of 30,000 cycles, which is selected by the band filter BF, and applied to the detector D to beat with. the oscillations from the local source G, of 30,000 cycles frequency. During each cyclic variation a low frequenc pulse is transmitted to the receiving relay 8 as already described, and a number of these pulses will be transmitted for each direct current si nal impulse transmitted by the disc TS. The relay R being sluggish, remains energized during the continuance rotation of the disc as previously described. net 28 responds to each positive and nega- T of this pulse and sends a positive pulse 1,4. -,eee

transmit a negative impulse through the step ing magnet 28 to advance the disc RS anot er step. -Another positive impulse is now transmitted, stepping the disc RS a third step, this pulse being followed by a prolon ed negative impulse due to the disc TS. uring the prolonged negative impulse, no oscillations are transmitted and the relay R remains deenergized, so that a negative impulse is transmitted to the -magnet 28 and the disc RS advances a fourth step. During the continuance of this negative impulse, the magnet 28 is deenergized, due to the discharge of the condenser 33, and its armature assumes its neutral position. The disc RS at the desired station, however, will remain in its advanced position for the reason that pin will be so positioned as to en age with the latch 29 at this time.

nother group of positive and negative impulses will be transmitted by the disc TS followed by a prolonged positive impulse occurring while the spring 25 is riding over the ortion of the periphery of the disc at the bottom thereof. The high frequency oscillations are accordingly transmitted during the continuance of this prolonged positive impulse and the relay 23 will remainenergized during this period, transmitting a positive pulse through the magnet 28.

Owing to the condenser 33, this pulse is only effective upon themagnet 28 for an instant, after which the armature assumes its neu-' tral position. The second group of impulses transmitted, however, results in bringing the in 33 into position to be engaged by the atch 29. During prolonged pulse, other discs, not having pins so situated, will be restored to normal. third group of positive and negative impulses is now transmitted, followed by a prolonged negative impulse. This results in stepping the disc RS to a position where the pin 32 engages with the latch 29 during the prolonged negative impulse, and consequent- 1y, he switch arm 34 is is contact with the and continue the transmission stepping it forward an additional step sothat no pin will be in position to engage the latch 29. At the end of this positive impulse, the spring 25 rides off of the periphof the disc into the notch" illustrated at the top of the disc, and the disc comes to rest.

The circuit of the relay -22 is at once broken and while the armature of the polar relay 24 will remain in its positive position, tending to close the circuit of the relay 21 of high frequency oscillations, this result Thev sender TS, may

the continuance of thisband filter will be defeated by the opening of the circuit of the relay 21 at the lower armature of the relay 22, this armature falling off as soon as the spring 25 falls into the notch at the top of the disc.

' Fig. 3 illustrates a sending station provided with a plurality of selective transmitters for selectively signaling any one of a plurality of receiving stations, each of which may be presumed to have selective receiving signaling channels such as channel III of Fig. 2. ting antenna plurality of transmitting. senders T8,, T8,, TS and T8 all of which, except the sender TS are merely indicated conventionally. be taken as illustrative of all four of the senders and is of the same general character as the sender illustrated in connection with channel III of Fig. 1. The nature of this apparatus and its method of operation will be clear from the precedin description of the apparatus of Fig. 1 and no 'further description is deemed necessary. When it is desired to signal the given receiving station, the selector disc, arranged to transmit the proper combination of im-,

pulses to properly actuate the corresponding receiving selector,- will be rotated and the station having the proper receiving selector will be signaled to the exclusion of all of the otherstations. A plurality of selectors may also be arranged'to transmit at the same carrier frequency by connecting them in parallel in the frequency chan ing circuit as indicated by the multiple lead Fig.- ;.4 illustrates an arrangement havin a plurality of transmitting channels I, II and III, similar to those illustrated in Fig. 1. The arrangement of Fig. 4 differs from that of Fig. 1, however, in that the frequencies initially generated in the three channels will be relatively low and will modulate by means of a modulator M a radio frequency supplied by a generator G. The generator G, for purposes of illustration, may generate frequencies of 690,000 cycles. The channel I is shown as generating 10,000 cycles, which, by modulation with the frequency of the generator G, will produce a sun-1 frequency corresponding to the 700,000 cycles. The correspondin ence frequency will be eliminate BF.- Similarly, the generator of the channel II will generate oscillations in the neighborhood of 20,000 cycles, which,

combined with the, frequency from the generator G, will produce sumfrequencies in the neighborhood of 710,000. cycles. Likewise the generator associated with the channel III is illustrated as transmitting oscilla- In this figure the transmit- TA has associated therewith a or sender T5,.

difierby the I upper side .frequencies in each instance and its cut-off points may, therefore, be so chosen as to be just below 700,000 0 cles and just above 720,000 cycles. It wil be seen that the frequencies radiated by the antenna from the several channels will be the same as those in Fig. 1, and the station will, therefore, co-operate with the receiving apparatus of Fig. 2, and its. operation in such connection will be obvious-without further description.

Figs. 5 and 6 illustrate respectively transmitting and receiving apparatus for radio telephonic communication and auxiliar apparatus for transmitting a ringing signa At the transmitting station, a modulator M is provided, having a switch SS in its input circuit, whereby the modulator may be connected either to the circuit of a telephone transmitter TT or to the circuit of a ringing transmitter HR. The modulator M is provided with carrier oscillations from a suit able source G and includes an amplifier A. in its output circuit. The apparatus. RR, for transmitting a ringing signal, comprises a generator and variometer similar to those of the channel II of Fig. 1.. The generator of the apparatus RR is preferably arranged to generate a frequency within the audible limit, as for example, a frequency in the neighborhood of 1,000 cycles. At the receiving station, a detector is provided for detecting from the received high frequency oscillations either'the low frequency telephonic signals or the frequency in the neighborhood of 1,000 cycles from the sending station. An amplifier may be associated with the output circuit of the detector and a filter BF provided for the purpose of selecting low frequency signaling currents, either telephonic or ringing, to the exclusion of high frequency currents. A switch SS is associated with the output circuit of the filter for connecting it to either the re ceiving telephone apparatus TT or the receiving ringing or signaling apparatus RR. The signallng apparatus comprises a detector, a low pass filter and a slow-acting relay for" contrelling the ringer or other form of signal {as described in connection with channel II of Fig. 2. The detector has associated with its input circuit a source generating a frequency in the neighborhood of the frequency employed for transmitting ringing signals. In. the case given, this frequency may be 1,000 cycles. V

If the operator at the station of'Fig. 5 desires to telephone to the operator at the station of F ig, 6, the switch SS will first be thrown to its lower position connecting the' ringing apparatus to the input circuit of the modulator M. By throwing the key associated with the generator,'a frequency in the neighborhood of 1,000 cycles will be generated. This frequency will be cyclically varied by the variometer and impressed on the modulator M with the frequency from the generator G. The carrier frequency from the generator G is accordingly modu lated with the signaling frequency and after being amplified is transmitted to the receiving station, where the detector D detects the varying frequency corresponding to that. generated by the generator at the transmitting station. This frequency is amplified by the amplifier A, passed through the filter BF and 'over the switch SS .(which will normally be in its lower position) to the re ceiving signaling apparatus. The cyclically varying frequency in the neighborhood of 1,000 cycles will beat with the locally generated frequency of 1,000 cycles to produce low frequency beats which will operate the receiving relay to in turn actuate the ringer or other responsive device. The operator at the station at Fig. 6, upon perceiving the signal, will throw the switch SS- to its upper position to connect the telephone receiver'to the detector circuit and the operator at the sending station, after having transmitted the ringing signal, will throw the switch SS to its upperposition to connect the telephone transmiter to the modu lator. transmitter, will cause the carrier frequency generated by the generator G to be modulated in accordance with telephonic currents, which will be transmitted to the receiving stationand detected by the detector D. The telephone waves, after being detected, will be amplified and passed through the filter BF to the receiver TT.

- Figs. 7 and 8 illustrate respectively transmitting and receiving radio telephone sets The operator, in speaking into the I no provided with ringing or signaling devices 7 nection with the channel III of Fig. 1, and

the signal will be received by the receiving signal apparatus at the station of Fig. 8 in a manner similar to that described in connection with the channel III of Fig. 2. After the signal has beentransmitted, the switches SS and SS will be thrown to their upper positions and telephone variations may be transmitted by modulatin the carrier frequency supplied to the mo ulator M from the generator G. The receiving operation will be the same as that of Fig. 6. It will be obvious that the general princioperating, the operator will I duce a periodically varying difference freples messes herein disclosed may be embodied in many other organizations widely difierent from those illustrated, without departing from the spirit of the invention as defined in the following claims, i

What is claimed is:

1. The method of distant control which consists in transmitting high frequency energy from the transmltting station, receiving said high frequency energy at a receivin station, beating the received energy with 'a ocally supplied frequency to produce a difference frequency, and periodically varying at a sub-audible rate one of said frequencies over a range such that th'ehtwo frequencies will coincide at periodic intervals.-

2. The method of distant control which consists ingenerating at a transmitting station energy varying periodically at a subaudiblefrequency, transmitting said energy of said periodically varying frequency to a receiving station, receiving said energy at a receiving station, and beating it at thereceiving station with a locally supplied frequency to produce a periodically varying difference frequency whose variations extend over a very narrow range.

3. The method of distant control, which consists in transmitting high frequency energyfrom a transmitting station, receiving said high frequency energy at a receiving station, beatin said received energy with a locally supp ied frequency to produce a difierence' frequency, periodically varying one of said frequencies at a sub-audible rate over a range such that the two frequencies will periodically coincide, whereby the difference frequency will vary from zero to a low maximum frequency, selecting a narrow band from said difi'erence frequencies including the zero difierence frequency, and impressing said narrowband upon a translating device.

A. The method of distant control which consists in generating at a transmitting station energy of periodically varying frequency, transmitting said energy of perrodically varying frequency to a receiving station, receiving said energy at said receiving station, beating said energy at the receiving station with a locally supplied energy to profrom zero to a low maximum a narrow band from said including the zero dif- I uency varying requency, selecting difference frequenc es ference frequency, and impressingsa itd narrow bandupon a translating device. i

5. The method of distant control which consists in transmitting high frequency energy from a transmitting station, recelving said energy at a 'receivin station, successively beatin the receive energy with 10- cally supplie frequencies, periodically varying one ofthe frequencies at a sub-audible rate whereby the difierence frequencies frequency, selecting a narrow band from said frequencies including the 1 final difference zero difierence frequency, and impressing said narrow band upon a translating device.

7. The method of distant control which consists in generating at a transmitting station energy of periodically varying frequency, transmitting saidenergy of periodically varying frequency to a receiving station, receiving said energy at said receiving station, successively beating the received energy at 'i1h8 receiving station with a locally supplied frequency to produce a final difierence frequency which periodically varies over a narrow range extending from zero to a low maximum frequency.

8. The method of distant control which consists in generating at a transmitting station energy of periodically varying frequency, transmitting said energy of periodically varying frequency to a receiving station, receiving said energy at said receiving station, successively beating the received energy at the receiving station with a locally supplied frequency to produce a final differ-v ence frequency which periodically varies over a narrow range extending from zero to a low maximum frequency, selecting a narrow band from said difference frequencies including the zero frequency, and impressing said narrow band upon a translating device.

9. The method of distant control which consists in generating high frequency energy at a transmitting station, controlling said high frequency energy in accordance with a predetermined code combination, transmitting said energy to a receiving station in accordance with said code combination, subjecting the received energy to abeating action with at least one locally supplied frequency, periodically varying one of said frequencies at a sub-audible rate over a range such that a final difierence frequency will be produced which periodically varies over a narrow range extending from zero to a low maximum frequency, said difference frequencies having impressed thereon the predetermined code combination, and reproducing from the narrow band of difference frequencies the code combination.

10. The method of distant control which consists in generating at a transmitting statil-t tion energy periodically varying at a sub-- audible frequency, controlling the said periodically varying energy in accordance with a predetermined code combination, transcode combination.

' 11. The method of distant control which consists in generating energy periodically varying at a sub-audible frequency within the audible range at a transmitting station, controlling the said periodically varying frequenc energy in' accordance with signals, modu ating carrier frequency energy in ac cordance with said periodically varying frequency energy, transmitting the modulated carrier frequency energy to a receiving station, stepping-down the received frequency at said receiving station to a point within the voice range, and beating the steppeddown periodically varying frequency with a locally supplied frequency energy lying within the limits of said periodic variations, and reproducing'from the resultant difference frequencies the signals imposed upon the periodically varying frequency at the transmitting station.

12. In a signaling system, a transmitting station, a receiving station, means for generating high frequency energy at sa1 d transmitting station, means for transmitt ng said high frequency energy to the recelvmg station, means to beat the received energy with atleast one locally supplied frequency at the receiving station, means for periodically varying one of the frequencies at a subaudible rate, thereby producin a final difference frequency whlch perio ically varies over a narrow'ra-nge from zero 'to a low maximum frequency, a responsive device at the receiving station, and a selecting apparatus to prevent the transmission to sald responsive apparatus of final diflerence frequencies exceeding a predetermined low maximum frequency. I

13. In a signaling system, a transmitting station, a receiving station, means to generate energy of periodically varying high fre'quency at the; transmitting station, means to transmitgsaid energy of periodically varying frequency to the receiving station, means at the receiving station to beat the energy of periodically varying received frequency with at least one locally supplied requency to produce a periodically varymeet ing difference frequency extending over a range from zero to a low maximum frequency, a responsive device at the receiving station, and selective means to prevent the transmission to said responsive device of final difference frequencies higher than a pre-assigned low maximum frequency.

14. In a signaling system, a transmitting station, a receiving station, means at said transmitting station for generating high frequency energy, means for controlling the said high frequency energy in accordance with a code combination, means for transmitting said high frequency energy to the receiving station, means at said receiving station for beating the received energy with at least one locally supplied frequency,

means to periodically vary one of said frequencies at a sub-audible rate whereby the final difference frequencies will periodically vary over a narrow range from zero to a low maximum frequency, a responsive device for reproducing from said final diflerence frequencies the code combination originally transmitted at the sending station,

and selective means for preventing the translIllSSlOIl to said responslve device of final difference frequencies higher than a pre-assigned low maximum frequency.

15. In a signaling system, a transmitting station, a receiving station, means for generating high frequency energy periodically varyin at a low frequency rate at said transmitting station, means for controlling the said periodically varying energy in accordance with a code combination, means for transmitting said energy to the receiving station, means at said receiving station to beat the received energy with at least one locally supplied frequency, thereby producing a final difference frequency periodically varying over a narrow range from zero to a low maximum frequency and having superposed thereon the code combination transmitted at the transmitting station, a responsive device at the receiving station for reproducing from the final difference frequencies the code combination superposed thereon, and selective apparatus for preventing the transmission to said responsive device of difference frequencies higher than a pre-assigned low maximum.

16. In a signaling system, a transmitting station, a' plurality of receiving stations, means to produce ener of periodically varying frequency at saiilt ransmitting station,

a plurality of code senders at the transmitof periodically varying frequency to receiving station, means at each re-.

meats a ceiving station to beat the received energy with at least one locally supplied frequency, thereby producing final difi'erence frequencies which periodically vary over a narrow range extending from zero to a low maximum, code selectors at each receiving station, each code selector being responsive to the node combination of a corresponding code transmitter at the receiving station, devices at each receiving station responsive to the final diflerence frequencies'for op-= crating said code selector, and selective means at each receiving station for prevent ing the transmission to said responsive means of final difierence frequencies greater than a pre-assigned low maximum.

15?. In a signaling system, a transmitting station, a receiving station, means at said transmitting station to generate energy of periodically varying frequency within the voice range, means to generate voice waves,

a modulator supplied with carrier frequency energy, means to transmit to said modulator either said energy of periodically varying frequency or said voice waves, whereby the carrier frequency energy may be modulated in accordance with either the periodically varying frequency ener or the voice waves, means to transmit t e modulated carrier frequency energy to the receiving station, means at the receiving station to detect the modulations from said carrier, a telephone receiver, a demodulator, means to apply energy of the detected modulating frequencies to said telephone receiver and to said demodulator, a beating frequency supplied to said modulator, said heating frequency lying within the range of the periodic variations in the audible frequency generated at the transmitting station, a responsive device, and means to prevent the transmission to said responsive device of difference fre quencies appearing in the output circuit of said demodulator and lying above a preassigned low maximum frequency.

In testimony whereof, we have signed our names to this specification this 12th day of April, 1921.

' LLOYD ESPENSCHIED.

RPH BOWN.

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