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Patented Sept. 20, 1938 i UNITED STATES PATENT OFFICE 2,130,421 TRANSMISSION AND RECEPTION OF INTELLIGENCE Samuel G. Frantz and Brunson S. McCutchen, Princeton, N. J., assignors to Radio Corpora tion of America, a corporation of Delaware Original application April 23, 1935, Serial No. 17,775. Divided and this application April 17, 1963, Serial No. 74,834 7 Claims.? (01. v179-1) This invention relates generally to the transmission and reception of intelligence and is speci?cally directed towards improving the quality of the received intelligence. 5 The present application is a division of copending application Serial Number 17,775 ?led April 23,? 1935, entitled ?Transmission and reception of intelligence? which in turn is a continuation in part of application Serial Number 496,595 now means are provided to re-eXpend the intensity range to that existing in the Original signal These means at the receiver must be so] arranged as to work in correspondence with the compres 10 U. S. Patent No. 2,006,989. receiver. More speci?cally, the present invention relates to systems and methods for maintaining the relations between the various increments of the intelligence issuing from an electrical energy trans15 lating device at a receiving point substantially The measure of the e?ect of atmospheric dis turbances or other interference on'the quality of reception is the ratio of interference intensity to signal intensity, and this e?eet Will therefore .be most pronounced when the signal intensity is 15 proportional to the relations between the various corresponding increments of the original intelligenee- . sion effected at the transmission station. At this point we desire to emphasize the?fact that one of the bene?ts that will be derived from the use of our system will be the lessening of the effect of atmospheric disturbances upon the . I always be greater than it would be were there no compression of intensity range before transmis sion, and therefore the effect of interference is minimized. In other words, when weak signals are being transmitted the energy Will be more ampli?ed before it is used [for modulation with the result that ordinary atmospheric disturb ances will not obscure the signal. This invention relates to and comprises the above described compression and expansion of intensity range, and means for accomplishing the compression and expansion. In applicants? parent applications there are PTODOSed for this purpose three Ways of inform ing the receiving apparatus as to what amount of in the microphone circuit is made to su??er a expansion is necessary. The three cases may be smaller percentage variation than the latter. 35 This may be called range compression or subproportional modulation. Thus, in this system a weak signal 'will be more amplified before it is classi?ed as follows: 1. Separate wire or radio channel. lation percentage itself as the signal which com feature of our invention is then that the intensity municetes t0 the receiving apparatus how much 40 range or the ratio between maximum and minlmum percentage of modulation of the transmit- ted radio signal is less than the intensity range of the original signal. The extent or degree of this compression of intensity range may in practice 45 result in about the same ratio of maximum to minimum percentage of modulation as is at pres- transmitted modulation. 55 at constant ' percentage In general, in the present system super-proportional range expansion at the re ceiver. Expressed mathematically we have:-? ' 30 35 45 _ 3 �u_kkI _ 3f 2 2 If� 1 2 1 Where I1=皉1g1na1 Intensity Iz=transmitted intensity of modulation _ _ _ 50 I3=rece1ver output intensity I , 751 and 752 are constants obliterated, and a=a constant <1 At the receiving end of the present system ' 1 the intensity range will be compressed but not ' 25 rithmic sub-proportional range compression at the transmitter wlth corresponding logarithmic ent obtained by manual control at broadcasting much further even to the limit at which there is ' the signal should be empll?ed_ 40 The simplest case of the latter would be logaY stations; or, the compression may be carried 50 a total obliteration of intensity range and the 20 ' 2. Variation of carrier frequency. 3. The use of the residual variation of modu used for modulation than will a strong signal. A is 10 low. With the present system. during weak orig-_ inal signals, the transmitted signal intensity Will An object of the invention is to provide a novel -.:o and e?icient method of transmission and reception of signals. Another object of the present invention is the achieving of clear ?delity of reproduction at the receiving end of radio signals and in particular 2-3 music, by partial or total compression of the intensity range, or range of modulation at the transmitting end and corresponding expansion of? the intensity range at~the receiving end. In the proposed system the degree or percent30 age of modulation applied to the carrier wave at the transmitting end instead of being made dil?eetly proportional to the intensity of the signal signal 5 In?usingthe system described in the third sub- 55' 2 2,130,421 division it is obvious, of course, that the intensity range must not be completely obliterated. An object of the present invention is to pro vide a specially constructed bridge arrangement for effecting the desired compression at the trans mitter and expansion at the receiver. Another object of the invention is the pro vision of a plurality of said specially constructed resistance bridges arranged in cascade. Still other objects of the invention will be ap parent from the following description of typical points 22 and 23 of the bridge l8 are connected 10 by conductors 24 and 25 respectively to two di circuits according to our invention illustrated in agonally opposite points 21 and 26 respectively temperature bridge; of a second temperature bridge device I9. The other two points of said last named bridge, namely, 28 and 29 may be connected either to an other similar bridge arrangement or to the modu Figure 2 illustrates diagrammatically a meth od by which two or more temperature bridges by Figure 1 through the medium of conductors Ill Figure 1 illustrates a transmitter arrangement may be cascaded; and, Figure 3 illustrates diagrammatically a receiver in accordance with our invention employing a temperature bridge arrangement for receiving an appropriately expanding signal transmitted from a system such as shown in Figure 1. Referring to Figure 1 a microphone circuit is shown composed of microphone 5, transformer ?I and the usual source of current 6. An ampli?er for the current generated in the microphone cir cuit is shown generally at 8 coupled to the micro 30 phone circuit by means of the transformer 1. The output of the ampli?er 8 is connected to a temperature bridge 9 by means of conductors l3 and I2 connected to diagonally opposite points l4 and I5 respectively of the bridge 9. The 35 other two diagonally opposite points of the bridge 9, namely, i6 and H are connected by conductors II and I0 respectively, to a modulator and radio frequency energy source circuit of any well known design. Referring more particularly to the tem perature bridge I, 2, 3 and 4 compose the four elements thereof. Elements | and 4 are of the same material and elements 2 and 3 are of some lator and radio frequency energy source as shown and II. It will thus be evident that in the ar rangement shown any number of temperature 20 bridges may be connected in cascade for obtain ing any results desired. Attention is now directed to Figure 3 which shows a receiver adapted to properly expand the signals which were compressed by the trans 25 mitter shown in Figure 1. In Figure 3, 3|! rep resents generally a stage of audio frequency am pli?cation in an ordinary radio receiver. Con pled to the output of said stage by means of transformer 3| is a temperature bridge 32 in ac 30 cordance with our invention. It will be noted that the secondary of the transformer 3| is connected by conductors 33 and 45 to two diag onally opposite points of said bridge 32. The other two diagonally opposite points of the bridge 35 are connected by means of conductors 35 and 36 to the input of an amplifier generally shown at 31. The output of this ampli?er 31 is connected by means of conductors 39 and 38 to a receiving instrument shown generally as a telephone re ceiver 40. The bridge 32 is made up of elements I, 2, 3 and 4 which operate in a somewhat simi other material having a different temperature coefficient of resistance than said ?rst material. The wires it will be evident are appreciably heat ed by the passage of the currents due to the signal lar manner to that described above in connection with Figure 1 except that in the case of the re voltage applied from the ampli?er output. With maximum signal voltage the bridge is hottest greater the applied electromotive force across the secondary of the transformer 3| the greaterv and the resistances are so proportioned that under this condition the bridge is almost bal anced; that is, the ratio of bridge output volt age to bridge input voltage is a minimum. .With very low input voltage the bridge is comparative ly cold and has a maximum of unbalance and 55 hence the ratio of output to input voltage is a maximum. Thus the bridge acts as a non-pro portional attenuator, attenuating strong sig nals more than weak ones. While we do not in tend to limit ourselves to any particular construc tion of the bridge one way in which the bridge could be constructed would be of small wires about the size of ?ash-light bulb ?laments. 65 coe?icient of resistance. Attention is now directed to Figure 2. In said ?gure conductors l2 and I3 correspond to the conductors l2 and I3 leading from the output of the ampli?er 8 of Figure 1. Conductors I2 and I3 are connected to diagonally opposite points 2| and 20 respectively of the temperature bridge l8. rI'he other two diagonally opposite the accompanying drawing, in which of one form of our invention utilizing a so-called 20 elements 2 and 3 comparatively low temperature - Either I and 4 or 2 and 3 may be resistances so designed as to heat but little. Broadly, the term ?temperature bridge? as used herein in cludes any network with input and output con nections in which the ratio of output to input voltage varies according to the input voltage 70 as a result of change of resistance of any of the elements of the network due to heating by the current passing through it. In Figure 1 the arrangement? could be such that the elements I and 4 have comparatively high temperature coefficient of resistance and ceiver, the bridge will be in approximate balance 45 for minimum signal, so that in Figure 3 the will be the resistance of elements I and 4 com pared to the resistance of elements 2 and 3. This 50 condition causes an increased unbalance of the bridge and an increased output current. It is to be distinctly understood that while we have shown only one bridge arrangement in the re ceiver shown in Figure 3 two or more such bridge 55 arrangements may be arranged in cascade as shown in Figure 2. We claim: 1. In a radio receiving system including means for connecting the input of the system to a 60 source of variable intensity signal energy and means for connecting the output of the system to a utilizing circuit, a four-arm resistance bridge interposed between said two means, opposite arms of said bridge being constructed so as to 65 have substantially the same temperature coef ?cient of resistance but one pair of said arms having different temperature coefficient of re sistance than the other thereof, said bridge be ing adjusted so as to be approximately balanced 70 for minimum signal intensity and to become more and more unbalanced as the average intensity of the signal energy increases, the ratio of out put to input voltage varying according to the input voltage as a resultvof change of resistance 75 2,130,421 of any of the elements of the network due to heating by current passing therethrough. 2. In a radio communication system, a source of variable intensity signal voltage and a utiliz ing circuit, a four-arm resistance bridge, a pair of diagonally opposite terminals of said bridge comprising input terminals therefor, the other pair of diagonally opposite terminals of the bridge comprising output terminals therefor, means for connecting the source of signal volt age between the input terminals of the bridge and means connecting the utilizing circuit in a balanced condition for substantially maxi mum ?average value of signal intensity and to become more and more unbalanced as the av erage intensity of the signal energy decreases, the ratio of output to input voltage of said bridge circuit varying according to the input voltage as the result of changes in the resistance of any of the elements of the bridge circuit due to heat ing thereof by current passing? therethrough. 5. A volume range compressor comprising a 10 resistance bridge having input terminals and out put terminals, means for connecting a source of between the output terminals of the bridge, varying intensity voltage to said input termi each of a pair of opposite arms of said bridge in nals, a utilizing circuit connected to said output terminals, means connected in the arms of said 15 bridge for attenuating electrical energy applied to the input terminals thereof to a greater or cluding means having a, high temperature coef ?cient'of resistance, the other pair of opposite arms including means having a comparatively low temperature coe?icient of resistance, said bridge less extent depending upon the average intensity ' being adjusted so as to be approximately in a of the electrical energy applied to the input ter minals of the bridge, said means attenuating 20 high intensity energy to a greater extent than low intensity energy whereby the ratio between? balanced condition for a predetermined value of average signal voltage and to become more and more unbalanced as the average intensity of the signal voltage departs from said value in one direction, the ratio of output to input voltage of said bridge circuit varying according to the aver age value of signal voltage as the result of change of resistance of any of the means provided in the arms of said resistance bridge due to heating by the lowest average intensity of the energy ap plied to the input of the bridge to the highest average intensity applied thereat is substantially current passing therethrough. greater than the ratio of the lowest average in tensity of the voltage appearing across the out put terminals of the bridge to the highest aver age intensity voltage applied thereat. 3. ?In a radio communication system, a source of variable intensity signal energy and a utiliz sistance bridge having' input terminals and ing circuit, ?a four-arm resistance bridge inter posed between said source and the utilizing cir cuit, opposite arms of said bridge including means 6. A volume range expander comprising a re 30 output terminals, means for connecting a source ture coemcient of resistance than the other pair thereof, said bridge being adjusted so as to be of varying intensity electrical energy to said input terminals, 3, utilizing circuit connect ed to said output terminals, said bridge including 35 means for attenuating electrical energy applied to the input terminals thereof to a greater or less extent depending upon the average intensity of the electrical energy applied to the input ter approximately in a balanced condition for a pre minals of the source, said means acting to at determined average value of signal intensity and tenuate high average intensity energy less than having substantially the same temperature co efficient of resistance but the means provided for one pair of said arms having different tempera 40 to become more and more unbalanced as the av low average intensity energy, whereby the ratio erage intensity of the signal energy departs from said value, the'ratio of output to input voltage of said bridge circuit varying according to the input voltage as the result of change of resist ance of any of the elements of the network due to heating thereof by current passing there between'the lowest average intensity energy ap plied to the input terminals of the bridge and through. est average intensity energy applied thereat. 7. A volume range expander device comprising, 50. 4. In a radio communication system, a source of variable intensity signal energy and a utiliz ing circuit, a four-arm resistance bridge circuit interposed between said source and the utilizing circuit, opposite arms of said bridge including means having substantially the same tempera ture coe?icient of resistance but the means pro vided for one pair of said arms having di?erent temperature coe?icient of resistance than the means provided for the other pair of arms,,said bridge being adjusted so as to be approximately the highest average intensity applied thereat is 45 substantially smaller than the ratio of the low est average intensity energy appearing across the output terminals of the bridge andthe high a four-arm bridge circuit, substantially equal ?xed resistance means having'a low temperature coe??icient of resistance connected in each of two opposite arms of the bridge and substantially similar resistance means having a high tempera 55 ture coe?lcient of resistance connected in each of the other two opposite arms of the bridge. SAMUEL G.v FRANTZ. BRUNSON S. MCCUTCHEN.