Патент USA US3022514код для вставки
Feb. 20, 1962 v. D. STROUD EI'AL 3,022,504 TWO-WAY RADIO TELEPHONE svs'rm UTILIZING FREQUENCY SUBBANDS TO PROVIDE TRANSMITTER-RECEIVER ISOLATION Filed Nov. 18, 1960 “ITQ Q ..L r . V . w\\ . Q/E NIVI /.\ RN JKQ . __ _bkmUhkix-IR TWW .a.5 . IHT a!_Q.25“wkI 1. N.EQCEW aINTI}5 rmm.\\\S\_\_ k Vi \ INVENTORS V/NCE/Vf P. STROl/P l/AROLP 6'. BY RANT 3,022,504 United States Patent 0 Patented Feb. 20, 1962 1 2 provide a two-wire to four-wire terminating circuit for 3,022,504 use in a radio telephone system which is at the same time TWO-WAY RADIO TELEPHONE SYSTEM UTILIZ lNG FREQUENCY SUBBANDS TO PROVIDE relatively insensitive to changes in the telephone line char acteristics, line length and the number of units used on TRANSMITTER-RECEIVER ISOLATION Vincent D. Stroud, 3915 Weller Road, Wheaton, Md., and Harold S. Grant, 2414 Fairlawn St., Washington, any particular line. Other objects and many of the attendant advantages of this invention will be readily appreciated as the same be comes better understood by reference to the following de tailed description when considered in connection with the D.C. Filed Nov. 18, 1960, Ser. No. 70,292 5 Claims. (Cl. 343-178) 10 accompanying drawing, the single ?gure of which is a schematic diagram of a two-station system constructed The present invention relates generally to communica tions systems and more particularly to a terminating net work for providing signal isolation between the transmit- 1 in accordance with a preferred embodiment of the present invention. . Brie?y and in general terms, the above objects of the ting and receiving components of a radio telephone sys 15 invention are realized, according to the present invention, tem connected to a standard commercial two-wire tele by utilizing interleaved comb ?lters to separate the sig phone line. nals in the audio portions of the system into two series The terminating network employed in most radio tele of mutually exclusive but complementary subbands which phone communication systems usually includes, a mutual together ?ll the complete audio spectrum. By means of inductance bridge or a voice operated gain adjusting de 20 this technique, the voice signals coupled, for example, to vice (VOGAD). To achieve the required amount of the radio transmitter from the subscriber’s telephone at isolation between the receiving radio path and the trans one station have missing therefrom a particular series of mitting radio path, it is necessary to maintain a precise audio subbands, which subbands correspond to those balance of the mutual inductance bridge. These adjust which are coupled to the transmitter at the second station ments, to minimize signal feedover, must be repeated 25 from the subscriber’s telephone located thereat. Thus. every time a different telephone line is connected to the in effect, mutually exclusive but complementary audio terminating network. The VOGAD system attempts to subbands modulate the transmitters at the two different solve the problem by the use of voice operated switching stations. Although the signals supplied to the listener are relays to prevent feedback. This leaves much to be de incomplete and have missing therefrom certain frequency sired; however, since the relays being voice operated must 30 subbands, nevertheless, it has been found that such signals often make a compromise when one party interrupts the will convey intelligible speech with little or no change in other. What is worse, to add to the confusion, the inter rupting party does not realize that he is not being heard. the natural sound of the subscriber’s voice as transmitted over a telephone line. Furthermore, by employing com In addition, because of the sensitivity limitations imposed plementary subbands which fall completely within the by the circuit parameters and speech characteristics, the 35 audio spectrum, the bandwidth of the radio transmission ?rst syllable of each word is frequently unheard or lost. system is kept within normal limits. The problem is threefold: (a) Feedback is encountered Referring now to the drawing, the single ?gure of which in long distance two-way radio voice circuits when termi schematically illustrates a two-station radio telephone nated on a two-wire standard telephone line at each end communication system utilizing the present invention in conjunction with a hybrid unit, the subscriber’s telephone because of inadequate isolation between the receiving path and the transmitting path. Since it is necessary to run the radio paths at approximately unity gain, the sys tem will be on the verge of oscillation if no effective iso lation between the receiving and transmitting paths is vset 1 at station A is connected via a two-wire sending line, represented in simpli?ed form by reference charac ter 2, to a ?rst bank of parallelly connected audio band pass ?lters 3. These ?lters are in the input circuit of a maintained. (b) Insu?icient isolation results in the noise 45 conventional» audio ampli?er 4 which supplies the modu being enhanced by the cumulative effect of feedback. lation signal for radio frequency transmitter 5 having a This, in effect, increases the radio path noise which results radiating antenna 6. in a very poor signal-to-noise ratio. (0) The nominal Telephone set 1 is also connected via a two-wire receiv level established by one standard prior art system‘ for a ing line, represented in simpli?ed form by reference voice transmission at the receive side of a two-wire tele 60 character 7, to the output of an audio ampli?er 8 which phone line is —25 db. The high noise level brought has in its input circuit a second bank of parallelly con about by the lack of isolation mentioned above frequent nected audio band-pass ?lters 9. These ?lters are sup ly exceeds the nominal level present in this system. Fur plied with signal energy from the audio output of radio ther, modulating the radio transmitter with this low level frequency receiver 10 associated with detecting antenna 11. voice signal (-25 db) results in an effective decrease of Filters F1, F3, F5, F7 and F, of ?lter bank 3 in the the signal-to-noise ratio at the distant receiver station. transmitting portion of the system are tuned to different It is accordingly a primary object of the present inven frequencies within the audio band. As an example, these, tion to provide a two-wire to four-wire terminating net frequencies could be spaced one from the other by twice work for use in a radio telephone communication system. the frequency spread of the band-pass ?lters. Thus, if all Another object of the present invention is to provide a 60 the above ?lters have a band-pass width of 200 cycles, two-wire to four-wire radio telephone terminating unit ?lter F1 may be tuned to 200 cycles, F3, to 600 cycles, which utilizes interleaved comb ?lters to divide the audio band between the transmitting and receiving circuits. Each link has a comb of (n) ?lters for its use spaced across F5, to 1,000 cycles, F7, to ‘1,400 cycles and F9, to 1,800 cycles. Likewise, ?lters F2,’ F4, F6, F8 and F10 of ?lter the audio band. The second set of (n) ?lters is conq 65 bank 9, associated with the receiving part of the system, are tuned to different frequencies within the audio band, structed to ?t between the pass-bands of the ?rst set. with the separation between adjacent frequencies again A still further object of the present invention is to pro vide a radio telephone terminating network which, by it self or with complementary apparatus, improves the sig nal path isolation between the receiving and transmittin 70 components of the system. > A yet still further object of the present invention is to being twice the band-pass spread of these ?lters. How ever, these last-mentioned frequencies are midway be tween those to which the individual ?lters in band 3 are , tuned. Thus, for example, if the receiving ?lters each have a band-pass width of 200 cycles, F2 may be tuned 8,022,604 4 to 400 cycles, F4, to 800 cycles, F6, to 1600 cycles and ever, in order to provide a greater degree of signal iso F10, to 2000 cycles. lation in the system, a hybrid transformer can be inserted at the junction formed by the above two lines and the ' It would be pointed out at this time that the particular number of ?lters employed in each bank and the band width and center frequency of each ?lter is purely a matter of design. Two speci?c requirements should be con common subscriber line. It would also be pointed out that in the modi?cation above described audio ampli?ers were inserted in the transmitting lines before each of the transmitters 5 and sidered in the above design. One, the pass-bandyof all 21. These ampli?ers are present to permit the operator the ?lters stay within the limits of the audio spectrum to adjust the line level to that required by the transmitter. which may be considered as extending from 200 to 3,000 cycles. Two, in order to preserve the naturalness of the 10 Furthermore, in order to prevent complete dropout of the groups of frequencies between the ?lters in either the voice transmission, it has been determined by experiments transmitting or receiving circuit, a frequency admittance that the band-pass of the individual ?lters should not be level ampli?er may be connected in parallel with each equal and the center frequencies not equally spaced. ?lter bank. These ampli?ers 25, 26 of station A and 27, The ?lters at the low frequency end of the audio spectrum should be designed with narrow band-pass and center fre 15 28 of station B permit the isolation ?gure of the ?lter system to be controlled. quencies closely spaced. As the frequency of the ?lters It would also be mentioned that instead of using a single increases, the band-pass of the ?lters can be wider and telephone set at each station a multiplicity of such sets the center frequencies can be spaced farther apart. It may be connected to the common subscriber line without would also be mentioned that the various ?lters should be designed to provide from 50 db to 60 db attenuation at 20 unbalancing or otherwise disturbing the operation of the system. the ?lter characteristic crossover point between adjacent Obviously many modi?cations and variations of the ?lters, such as F3 in bank 3 and F4 in bank 9. present invention are possible in the light of the above It will be seen from an examination of the construction teachings. ‘It is therefore to be understood that within the of station A that, when a subscriber speaks into telephone set 1, his voice signals will pass to the ?lter bank 3, and 25 scope of the appended claims the invention may be prac ticed otherwise than as speci?cally described. these ?lters will effectively sample the signal at a number What is claimed is: of discrete frequency bands corresponding to the band 1. A two-station radio telephone communication sys pass frequencies of the individual ?lters making up this tem comprising, in combination, means at said ?rst station array. These frequency components will thus pass with out any appreciable attenuation to the input of audio 30 for radiating a radio frequency carrier wave which is mod ulated with a locally generated subscriber’s voice signal ampli?er 4, modulate radio transmitter 5 and be sent out from which a ?rst series of audio subbands have been to remote station B by antenna 6. suppressed, means at said second station for radiating a The modulator carrier wave radiated from antenna 6 radio frequency carrier wave which is modulated with a when station A is sending is detected by antenna 13 at locally generated subscriber’s voice signal from which a station B, and these RF signals are supplied to a conven second series of spaced audio subbands have been sup tional receiver 14 whose audio output feeds a bank of pressed, the subbands of said ?rst and second series oc parallelly connected audio band-pass ?lters 15. These cupying mutually exclusive but complementary portions ?lters, it will be appreciated, are counterparts of those of of the complete audio frequency spectrum, and means at bank 3 located in the transmitting line of station A, being each station for detecting and converting the modulated tuned to the same band-pass characteristics. Consequent ly, these ?lters present little impedance to the incoming radio frequency carrier wave radiated by the other station to an audio signal. audio signals, and they pass via audio ampli?er 16 to the subscriber’s telephone set 17. 2. A two-station radio communication system compris Station B also includes a transmitting bank of ?lters ing, in combination, means at said ?rst station for radi ating a radio frequency carrier wave which is modulated 18 which are counterparts of those located in the receiv ing line of station A, being tuned to the same frequencies with a locally generated subscriber’s voice signal from and having the same band-pass characteristics. This bank which a ?rst series of audio subbands have been sup of ?lters is energized with audio signals from telephone pressed, means at said second station for radiating a radio set 17 via two-wire sending line 19 and feeds audio am frequency carrier wave which is modulated with a locally pli?er 20 which provides the modulating signal for radio generated subscriber’s voice signal from which a second frequency transmitter 21 coupled to radiating antenna series of spaced audio subbands have-been suppressed, the 22. From a comparison of station A and station B, it audio subbands of said second series occurring at those will be seen that the operating equipment located at each‘ portions of the audio spectrum which are not occupied station is essentially the same, the only difference being in by said ?rst subbands, said ?rst and second series of sub the location of the similar banks of ?lters in the trans bands substantially occupying the complete audio spec mitting and receiving lines. trum, and means at each station for detecting the modu The procedure, whereby a subscriber speaking into lated radio frequency carrier wave radiated by the other telephone set 17 at station B communicates with a party station and for converting it to an audio signal. attending telephone set 1 at station A, is similar to that 3. In a two-station radio telephone communication sys previously described. However, the voice signals now 60 tem, the combination of an “A” set of parallelly connected modulating transmitter 21 contain a different set of audio audio band-pass ?lters at each station, the band-passes of subbands, which subbands correspond to those deleted the various ?lters of each “A” set extending from F1 to vfrom the voice signal modulating transmitter 5 when F2 cycles, F3 to F4 cycles, F5 to F6 cycles, etc., a “B” set station A is broadcasting to station B. Consequently, of parallelly connected audio pass-band ?lters at each sta when the modulated carrier wave detected by antenna 11 tion, the band-passes of the various ?lters of each “B” set is converted by radio receiver 10 to the audio portion of extending from F2 to F3 cycles, F4 to F5 cycles, F6 to F? the spectrum, the resultant subbands match the band cycles, etc., with the band-passes of the ?lters of both “A” pass characteristics of ?lters F2, F4, F6, etc. Hence, these and “B” sets substantially ?lling the audio spectrum, a signals suffer little attenuation in the receiving line and telephone, a radio transmitter and a radio receiver at each pass via audio ampli?er 8 and two-wire line 7 to the sub 70 station, means for connecting the telephone at each station scriber‘s telephone at this station. to one side of an “A” set and a “B” set of ?lters, means for In the above description, the telephone sets at each connecting the other side of one of the “A” sets of ?lters station were directly connected by two-wire lines, such as to a radio transmitter, means for connecting the other side 2 and 7 of station A, to the transmitting ?lter bank 3 and of the other “A” set of ?lters to a radio receiver, means the output of the audio ampli?er 8, respectively. How 75 for connecting the other side of one of the “B” sets of ?lters 8,022,504 5 6 of said second group of ?lters, and means for connecting the output of said second group of ?lters to said telephone to a radio transmitter, means for connecting the other side of the other set of “B” ?lters to a radio receiver whereby one of said stations radiates a carrier wave mod ulated by a voice signal from which a ?rst series of audio set. 5. In an arrangement as de?ned in claim 4, a third group of parallelly connected audio band-pass ?lters located at said second station, the band-passes of the vari ates a carrier wave modulated with a voice signal from ous ?lters of said third group extending from F1 to F3 which a second series of audio subbands have been sup cycles, F3 to F4 cycles, F5 to F6 cycles, etc., a fourth group pressed. of parallelly connected audio-band-pass ?lters located at 4. In a two-station radio telephone communication sys tem, the combination of a ?rst group of parallelly con 10 said second station, the band-passes of the various ?lters of said fourth group extending from F2 to F3 cycles, F4 to nected audio pass-band ?lters located at said ?rst station, F5 cycles, F6 to F7 cycles, etc., with the band-passes of the band-passes of the various ?lters of said group ex both the third and fourth groups of ?lters covering sub tending from F1 to F, cycles, F3 to F4 cycles, F5 to F6 stantially the complete audio spectrum, a telephone set lo cycles, etc., a second group of parallelly connected audio. band-pass ?lters, the band-passes of the various ?lters of 15 cated at said second station, means for connecting the voice signal generated by said telephone in response to the sub said second group extending from'Fz to F3 cycles, F4 to F5 scriber’s use thereof to the input of said fourth group of ?l cycles, F, to F7 cycles, etc., with the band-passes of both ters, a second radio frequency transmitter, a second radiat groups substantially ?lling the complete audio spectrum, subbands have been suppressed and the other station radi a telephone set located at said ?rst station, means for con in g antenna, means for connecting the output of said fourth response to the subscriber’s use thereof to the input of said ?rst group of ?lters, a ?rst radio transmitter, a ?rst radi ating antenna, means for connecting the output of said ?rst group of ?lters to said ?rst radio frequency trans mitter, thereby to modulate said ?rst transmitter, means 25 means for connecting the output of said second radio fre necting the voice signal generated by said telephone in 20 group of ?lters to said second radio frequency transmitter, for connecting the output of said ?rst transmitter to said ?rst radiating antenna, a ?rst detecting antenna, a ?rst radio frequency receiver, means for connecting the output of said ?rst detecting antenna to the input of said ?rst radio frequency receiver, means for connecting the audio output of said ?rst radio frequency receiver to the input quency transmitter to said second radiating antenna, a sec ond detecting antenna, a second radio frequency receiver, means for connecting the output of said second detecting antenna to the input of said second radio ‘frequency re ceiver, means for coupling the audio output of said second radio receiver to the input of said third group of ?lters, and means for connecting the output of said third group of ?lters to the telephone set located at said second station. 30 No references cited.