US 2025190 A
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DeC 24, i935- H. H. BEVERAGE 2,025,190
MULTIPLEX S IGNALING Filed March 21, 1953 5 sheets-sheet 1 JF f par f2 muy .-ff M45/l ,92 A,94 Rf SCH INVENTOR H. H. BEVERAGE BY 'MnM/L/ ATTORNEY Dec. 24, '1935. H. H. BEVERAGE 2,025,190
MULTKIPLEX SIGNALING l Filed March 2l, 1933 5 Sheets-Sheet 2 INVENToR H. /ERAGE Mu/M/ ATTORNEY H. H. BEVERAGE r2,025,190
MULTIPLEX SIGNALING Y FiledMaroh 21, 1933 5 sheets-sheet 5 Dec. 24, 1935.
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Dec. 24, 1935. H. H. BEVERAGE MULTIPLEX SIGNALING Filed March 2l, 1935 5 Sheets-Sheet 4 INVENTOR EVEIRAGE C I C: N M 1k I C mx mw N /w-zH/L/ ATTORNEY Dec. 24, 1935. H. H. BEVERAGE 2,025,190l MULTIPLEX SIGNALINGv Filed March 2l, 1933 5 Sheets-Sheet 5 lNvENToR H H. Ev RAGE BY /l/OL/ ATTORNEY Patented Dec. 24, 193s UNITED STATES PATENT OFFICE Radio Corporation of Delaware of America, a corporation Application March 21,1933, semina. 661,947
` 12c1aims. (ci. 17a- 51) This invention relates to a method of and system for multiplex signaling. Multiplex systems of various types have beenknown in the telegraphy and telephony arts, both radio and wired, heretofore. Some of these systems involve the use of a commutator for time separation of the elements at the transmitter, and ia receiver with a similar commutator for separation of the signal elements at `the receiver. Systems of this type are in some cases unsatisfactory, due to the diiiiculty of synchronizing the commutators at the transmitter and at the receiver.
In another type of system the difficulties attending synchronization are overcome by using a commutator for time separation of the signals at the transmitter and modulation frequency separation at the receiver. Any system'which depends upon modulating a carrier withl a multiplicity of audio frequencies for obtaining different channels has been found by experience to be relatively inefficient, since it is necessary to keep the side band power relatively low as compared with the carrier power. If this is not done, intermodulation or interference between the channels resuits. A system of this type is sound in theory but in practice is undesirable, due to the fact that the ratio of noise level to signal level is extremely high, and due to the relatively -small amount of power available in the sidebands. In tests made by me it was found that the wave modulated with the different frequencies characteristic of the signal elements could only be read through about ve percent as much noise as interrupted continuous wave signals where all of the transmitter power was available on a single frequency. 4
The most efficient multiplexing systems known heretofore involve the use of continuous wave oscillations at the transmitter with a commutator for time separation of the continuous wave, and a receiver with a similar commutator for selecting the signal elements which are received. The commutators at the transmitter and at the receiver are driven by synchronous motors. The motors may be synchronized by a signal impulse sent out from the transmitter. 'Ihis system is again su'bject to the disadvantage of synchronizing vthe motors at the receiver and the transmitter.
The primary object of appllcant's invention is to provide a new and novel method'of and means for multiplexing signals, which method and means eliminates all, or substantially all, of the material disadvantages noted-v above.
The above -object of applicants invention is accomplishedby a -novel multiplexing system in which time separation of the oscillations into elements characteristic of the signal elements is accomplished at the transmitter by a `commutator. The time separation of the oscillations at the transmitter is accompanied by 5 changes in frequency of the continuous wave. 'I'he resultant transmitted frequencies are Vcharp acteristic of the signal elements. The changes in frequency of the continuous Waves which accompany the time separation thereof may be accomplished in any manner. Preferably, it is accomplished by the use'of a control current, the intensity of which changes in accordance with the signal element to be transmitted. `The changes in current intensity control the saturation of a magnetic modulating device, which may be connected in any desirable manner with any stage in the transmitter to accomplish frequency shift of the oscillations thereof. l
Any signaling code may be used. Preferably, the Morse cable code is used, and'in using the Morse cable code, dots and dashes are of equal length, but are distinguished in transmission and in reception, that is, after demodulation of the high frequency oscillations has been accomplished, by their frequency. For example, the letter A might be represented by a dot on 1500 cyclesfollowed by a dot on 1000 cycles, while the letter B would be a dot on 1000 cycles followed by three dots on 1500 cycles. In this example, the 1500 cycle dot corresponds to a Morse code dot, while the 1000 cycle dot corresponds to a Morse code dash. No signal corresponds to intervals between elements or between words. Of course, thewpresent invention contemplates the use of three frequencies, one of which represents a dot, the second of which represents a dash, and
a third which represents spaces or intervals.
In the above example'it is assumed vthat one channel only is being used. The present inven- 40 tion, which relates to multiplexing, contemplates the use of 2. 3, or more, channels. Furthermore, each channel may use two frequencies and no signal for spacing, or two frequencies for marking andy a third frequency for spacing. In the prior example, four frequencies will be necessary v for two channels since no current for intervals and spacing suilices for both channels. If, an interval or spacing frequency is used then live 50 frequencies will be necessary, the additional spacing or interval frequency suiilcing for both ere three channels are used six frequencies, with no,l signal forintervals and spacing, may vbe used, or seven frequencies where a distinct frequency is used for spacing and intervals.
Signaling speed is increased by coordinating the commutators for the time separation of the continuous wave and the automatic keyers vfor keying the transmitter by way of the magnetic modulator so that the spacing intervals on one channel are utilized for marking intervals on other channels and vice versa. This coordination of the time separation commutator with the automatic keyers increases the speed of keying in a manner analogous to the manner in which the speed of keying is increased by the invention disclosed in Briggs Patent No. 1,781,361.
The magnetic modulator, the saturation of the core of which is varied by currents of different intensity, is of a type to accomplish linear frequency shift in the continuous waves. 'Ihe transmitter itself is of the type in which the carrier is radiated at maximum power at all times, and signaling on the different channels is made Aselective by taking into account the amount by which the carrier is shifted in frequency by the various signaling elements.
The time separated frequency shifted signals may be received on a crystal controlled radio frequency receiver. The crystal may be adjusted to match the frequency of the transmitter so that by using heterodyne reception the local oscillator beats the received signal to obtain a beat note whichA is zero or substantially zero during intervals or spacing periods when no signals are being transmitted onk either channel.
The heterodyne receiver feeds into a high pass filter circuit which may include the necessary amplifiers. The high pass fllter circuit supplies the frequency, if any, to a plurality of lter circuits, there being a illtercircuit foreach differkdrawings in which:
Figure 1 illustrates diagrammatically the manner in which time separation of the oscillations is accomplished and the manner in which currents of different intensity are supplied to the magnetic modulator, which may be connected to any suitable transmitter, and shows also the relation of the marking impulses on the individual lchannels and the resultant frequency shift enveloperesulting from the coordination of two channels;
Figure 2 shows diagrammatically the essential elements of my mutiplexing system at the transmitting end; and Figure 2a illustrates in boxl form the manner in which the transmitters AT #I and AT #2 are controlled by a tape in which the -signal characters to be transmitted are punched.
Figure 3 illustrates diagrammatically a receiver of the heterodyne type which feeds the beat notes through a high pass lter to the frequency separation circuit and from thence to the recorders;
Figure 4 illustrates the characteristics of the.
band pass filters shown schematically in Figure 3;
Figure 5 is the same as Figure 1, except that in Figuresignalingonthree channelsbytheuse of six frequencies is accomplished; while i Figure 6 is similar to Figure 2, except that it shows a multiplexing system in which'signals may be sent out on three channels. The method of multiplexing signals in accordance with my invention vwill be understood by reference to Figure l of the drawings. The squares designated by the numerals I and 2 represent commutator segments. 'Ihe shaded 10 squares, which are marked No. I, are all connected together and to a slip ring shown schematically at SR1. In like manner, all of the No. 2 squares, or commutator segments, are connected together to a second slip ring, shown sche- 15 matically at SR2. A single brush 1 bears on the commutator so that when the commutator is rotated the brush l makes contact with the segments I and 2 alternately. The magnetic modulator MM has its saturating winding 6 connected 20 with the brush 1, with a source of potential 9, and by way of a plurality of resistances R1, Rz, R: and R4 to a plurality of contacts K1, K2, Ka and K4. Closing of the contacts completes the circuit `of the l magnetic modulator winding 6 25 through the battery by way of one of the -segmentsl or 2 and the slip rings SR1 or'SRz. As
. the commutator revolves it connects the transmittcr alternately to the two channels by way o! the contacts K1, Ka, K1 and K4. The 'frequency 30 of the transmitter T, which is connected by way of the winding I0, with the magnetic modulator,
,is controlled by the current flowing through the tensities flow through the winding 6 of the magnetic modulator. Each slip ring is associated 40 with a channel and the current is adjusted to four different values for two channels. This is accomplished by .adjusting 'the resistances R1, Rz, R3 and R4 connected with the keys K1, K2, Ks and K4 of the keying relays. For purposes of il- 45 lustration, I have assumed that when K1 is closed a current I1 will flow in channel 2 and this current will represent a dash; current of intensity I-i will flow in channel 2 when K4 is closed and this will represent a dot; current of intensity I; 50 will ilow in channel I when Ka is closed and this will represent a dot; current of intensity Izwill flow in channel I when Kn is closed and this will represent a dash; while, current of zero intensity will ilow when spaces or intervals ap- 55 pear in the signal. 'Ihe keying ,relays may be separably, biased polar relays, such that a positive line current operates one relay while a negative line current operates the other. With no line current the bias will pull both relays to the 60 "off" side so that no current will flow to the commutator during the idle time on that channel. These keying` relays may be modified in a number of ways, such as usinga lzero center relay, tube relays,- etc. It is also possible toput a fixed 65 current on the modulator and key straight from the line with positive and negative impulses. .A preferred form of relayhas lbeen shown in Figure 2, which will be discussed in detail hereinafter.
A positive'impulse corresponds to a dot, and a 7o negativev impulse corresponds to a dash in the Morse cable code. The currents I1, Ia, IJ and I4, referred to above as flowing in the circuits when the contacts K1, Ks, Ks and K4 close, reprent the currents flowing in the commutator segment corresponding to the characters represented. The little sketch at the bottom of Figure 1 represents the relation between these control currents and the transmitter frequency.` With this in mind it is easy to draw out the combined frequency envelopes of the transmitter, as shown. The frequency envelope of the combined chan nels, that is, channels I and 2, has been shown in line I. 'I'he envelope of the control current sent out over channel No. has been shown separately in line 2 and the envelope of the control current sent out over channel No. 2 has been shown separately in line 3. These envelopes will be referred to again hereinafter. The manner in which magnetic modulation is accomplished and the nature of the receiver will be` described first.
Referring to Figure-2, the commutator having the segments I, 2 on its periphery may be mounted on a shaft S rotating in a bearing I2.
The shaft S may be driven by a motor |4 at the desired. speed. Slip rings SR1 and SR2 for channels I and 2 may be fastened to a face of the commutator for rotation therewith.` Brushes B1 and B1 may cooperate with the slip rings to complete circui/ts by way of magnetic relays MR1 and MRz with automatic keying devices AT1 and ATz. The automatic keying devices are driven in synchronism with the commutator by way of bevelled gears I4' and I4" by the motor I4, as shown. 'I'he Wheatstone transmitters AT1 and ATz may be of the automatic type and are driven insynchronism at'the same rate of speed through the gears I4' and I4". 'I'he connection between the automatic transmitters AT1 and ATZ and lthe gearing I4 and I4 respectively on the shaft I5 is such that the spacing intervals of one transmitter coincide with the marking intervals of the other transmitter, and vice versa, that is, the plunger contacts of automatic transmitter AT1 for channel I are always up when the plungers on the automatic transmitter ATZ for channel 2 are down, and vice versa. The automatic transmitters AT1 .and ATz are connected by wires I6, |8 and 20, 22 respectively with relay windings I1, I9 and 2|, 23 respectively of magnetic relays MB1 and MR: respectively. The contacts K3 and K2' are closed under certain conditions by the armatures associated with magnetic relay windings |1 and |9 respectively. The contacts K1 and K1 are closed under certain conditions by current in the windings 2| and 23 respectively of magnetic relay MR2. windings I1, |9, 2| and 23 are connected by way of resistances R3, R1, R4 and R1 respectively to the source of potential 9, which is in turn ,connected with the winding 6 of the magnetic modulator MM. 'I'he winding 6 is connected with the brush 'I bearing on the periphery of the commutator. The automatic transmitters are coordinated to each other so that one is marking when the other is olf, and vice versa. The operating time ls divided up equally between each transmitter.v This necessitates the use of signal elements of like time duration. Both transmitters are coordinated with the commutator so that a segment is under the brush 'l when the automatic transmitter AT1 is marking and a segment 2 isunder the brush 'I when the automatic transmitter AT: is marking. Thus the time of operation is divided up equally between the two chan# nels. The current owing in the winding 6 varies the intensity of the ux in the core of the magnetic modulator. This in turn varies the permeability of the iron -core which causes the induc- The armatures of theA tance of windlngIll to vary in accordance with the current variations. The winding I is shunted across a portion of the inductance 2l, which, in commotion with the condenser 29, determines the frequency o f oscillation of vacuum tube 3|. When current flows in winding 6 the inductance of winding I0 decreases. This decreases the total inductance in the oscillating circuit and causes vacuum tube 3| to oscillate at a higher frequency. 'I'he amount of frequency 10 shift is governed by the value of the control current in the winding 6. Choke coils 3l and 39 are inserted in series with control winding to keep radio frequency from owing in the control circult. A
As an example to further illustrate the operation of this circuit, assume that with no control current flowing in winding 6 of the frequency shifting device MM the transmitter sends out a frequency of 10,000,000 cycles, and that the oscillator associated with the receiver at the other end of the circuit is also adjusted to 10,000,000 cycles, so that the beat note is substantially zero. Now assume that the intensity of the current flowing in resistance R4 is such as to decrease the in- 25 ductance of MM to such an extent that the transmitter frequency is increased to 10,000,000 cycles. At the receiver the transmitter frequency. beats with the local oscillations, which results in a beat of 2000 cycles; the resistance R3 permits a cur- 30 rent to ow through the winding 6, which vdecreases the frequency of the oscillations transmitted suiiiciently to result in a beat note of 1500 cycles when the transmitted oscillation beats with the local oscillations at the receiver; the resistance R2 permits sulcient current to iiow through the winding 6 to lower the transmitted frequency to such a value that a beat note of 1000 cycles results at the receiver; while, the resistance R1 allows sumc'ient current to flow through the 40 winding 6 to produce a beat note at the receiver of 500 cycles. Thus, the letter A" on channel I might be represented by a dot on 1500 cycles (Morse dot) followed by a dot on 1000 cycles (Morse clash); while, the letter B might be represented by a dot on 1000 cycles followed by three dots on 1500 cycles. Of course, where two channels are used the elements of one letter on one channel should be alternated with elements of another letter on the other channel, as illustrated in line I of Figure 1. The frequency modulated oscillations may be amplified by power amplifier 25 and radiated or utilized in any desired manner.
While I have described one means for shifting the frequency of the transmittter, many methods are known to the art, and any of them could readily be adapted for use with my invention.
At the receiver, see Figure 3, the signals are picked up on an antenna system 40 and supplied to a radio frequency amplifier 4i!l followed by a de- 60 tector 44 with associated oscillator 46. The audio frequencies are amplified in amplifier 48. Oscillations of a frequency substantially equal to the frequency of the incoming signal are supplied from oscillator 46. The oscillator 46 is prefer- 65 ably of the crystal controlled type, so that the frequency supplied at the receiver matches the frequency of the transmitter and a zero or substantially zero beat note results when none of the channels are marking. 'Ihis beat note, if any, 70 may be further amplified in 48 after passing through high pass filter 50. This high pass filter blocks out4 beat notes below a certain frequency `and passes beat notes between this frequency this high pass .filter is to eliminate harmonics which might be of such frequency as to pass through one or more ofthe band pass filters. The beat notes resulting are supplied to the filter circuits 52, 54, 56 and 58 and from thence-by way of rectiers 60, 62, 64, and 66 to the recorder coils 68 and 02;'
At the receiver the transmitter comes in at or near zero beat when both channels are oiI. This low frequency beat note is cut off by the high pass :filter 50 so that nothing is heard. As soon as the brush 1 touches segments No. I on the commutator, the transmitter is keyed to a frequency F3, see line I of Figure 1. A beat note of frequency Fs-Fo, or 1500 cycles, in this case, is in the output of the receiver and may be heard. This beat note is passed through the filter 52 and by way of the rectier 60 to the coil68 of recorder No. I where it pulls up the pen 14. When the segment No. 2 reaches the brush 1 the beat note instantly changes to Fi-Fo, or 500 cycles. This pulls down the pen 88 on recorder 2. Simultaneously the pen of recorder I has dropped back to zero since the frequency F3 has disappeared. When the third segments, that is, the second segment No. I, reaches the brush 'I the frequency Fn appears since contact K2 has been closed by the automatic transmitter AT1. This beat note Fz-Fo, which is equal to 1000 cycles, passes through filter 5I of channel No. I and pulls down the recording peri of' recorder I to complete the letter A on channel I in its original form, as shown in lines I and 2 of Figure l. In this manner the letter B is keyed by the automatic transmitter AT1 on channel I, while automatic transmitter AT: is completing the letter X and starting on letter Y over channel 2, as shown in Figure 1. The receiver has four band pass filters corresponding to the four frequencies necessary for two channels when no signal onzero -beat is used for spacing.
The characteristicsof the band pass lters which were illustrated diagrammatically in Figure 3, have been shown in Figure 4. The high pass filter eliminates all beat notes below about 200 cycles and thereby overcomes any diiilculties that might be encountered from harmonics' of the spacing frequency. Forexample, if the spacing frequency should overload the audio amplifier, harmonies would be generated which might pass through the band pass filters and produce false marking on the recorders. By placing the high pass filter 50 (Figure 3) ahead of the audio amplifier, this dimculty is eliminated.
The four filters are centered at 500, 1000, 1500, and 2000 cycles, and are made as wide as possible in order to allow some drifty between the transmitter frequency and the local oscillator frequency at the receiver. The signals may be kept centered in the filters by slight 'adjustment of the oscillator at the receiver.` K y.
When it is desired to transmit on three channels the commutator may lbe as illustrated in Figure 5. Heze the segments run in sequence, I to 3 and repeated. Three slip rings are necessary and three automatic transmitters of the type similar to the two shown in Figure 2 will be necessary. In view of the fact that the system in which three channels are used will be clearly understood from the prior description of the system, in which two channels have been used, it is thought unnecessary to describe in detail the system in which multiplexing on three channels is accomplished. 'I'he system has, however, been illustrated in Figure 6.
In Figure 6 parts which correspond to the similar parts in Figure 2 have been designated by-like reference symbols.
In Figure 2 the automatic transmitters may be considered as spaced 180 degrees apart so that 5 -when one is marking the other is spacing, and vice versa. In the three channel system of Figure 6 the automatic transmitters are spaced by the gearing I4', Il" and I4", 120 degrees apart so that when one is marking the others are 10 spacing. l
In drawing the envelopes of the frequencies sent out by the transmitter over the three channels, in Figure 5, the off signal has been placed intermediate the three signaling frequencies for convenience and to facilitate understanding of the invention.
In some cases it is desirable to interrupt or cut oi the carrier frequency oscillations when spacing occurs on. all channels. This may be accomplishedv as indicated in Figures 2 and 6. When all channels happen to be spacing the control current in winding 6 of modulator MM falls to zero because all of the circuits in series with thev modulator are interrupted. Relay 4I is adjusted 25 so that the minimum current I1, that is, the minimum current which produces a signaling frequency, will hold the relay closed, thereby putting lnormal bias on oscillator grid 5I through relay contact 41 from battery I5. As soon as the ccn- 30 trol current drops to zero (when all channels are spacing) relay contact 41 is pulled over by a spring S and puts a high negative bias from batteries 45 and I3 in series on the grid 5I of oscillator 3l. 'Ihis negative bias interrupts the oscil- 35 lations being generated by said tube so that no radiation takes place during intervals on all channels.
While the oscillation interrupting means has been shown connected with the oscillation generator, it will be understood that this interrupting means may also be connected with any stage subsequent to the oscillation generator. For example, it may be connected with any succeeding amplifier, frequency multiplier, or other relaying stage included in the circuit between the oscillation generator and the radiating system.
Having thus described my invention and the operation thereof, what I claim is:
1. In a multiplex telegraph system, the method of communication by means of three element signals which comprises generating high frequency oscillations, producing discrete current impulses of different intensities characteristic of the signal elements to be transmitted over each channel, and producing changes in the frequency of the oscillations which are determined by the changes in intensity of said current impulses, at least two different frequencies being transmitted over each channel.
2. 'I'he method of multiplexing signals over a' plurality of channels which includes the steps of producing current impulses of constant duration and intensity which are characteristic of signal elements, and producing high frequency oscillations, the frequencies of which are determined by the intensity of said current impulses, there being at least two different frequencies for each channel, which frequencies differ from the' frequencies use forthe other channels. 7o
3. The method of multiplexing signals over two channels which comprises producing two current impulses of like duration but of different intensities characteristic of the elements of the signal to be transmitted on one of said channels, mOi-75 ducing two other similar current impulses of still other intensities for said other channel, and generating oscillations whose frequency is deter- -mined by the intensity of the current impulses.
4. The method of multiplexing signals which includes the steps of producing signal impulses of .a predetermined intensity, producing signal imin the Morse code signaling, and producing oscillations,A the frequency of which varies substantially in accordance with the intensity of the impulses.
5. The method offmultiplexing signals which includes signaling on a plurality of channels simultaneously by producing current impulses, the intensities of which are characteristic of the sig-l nal elements to be transmitted, there being an impulse of different intensity for each channel and for each signal elementen each channel, producingl high frequency oscillations characteristic of the intensity of each signal impulse, and 'coordinating said impulses so that the spacing intervals on one channel are utilized for marking intervals on* another channel and vice versa.
6. The combination of an oscillation generator including an electron discharge device having its electrodes coupled by way of a frequency determining lcircuit including, an inductance, and means for keying thel oscillations produced by varying the'value of' said inductance, of a winding coupled to said inductance, a'second winding magnetically related to said flrstnamed Winding,4
a commutator, a plurality of groups of segments on said commutator, a brush bearing on said commutator segments, said brush being connected -.to one terminal of said last named winding. slip rings on said commutator, there being a slip ring a resistance connecting each of said contacts by way of a common source of potential tothe other terminal of said last named winding, magnetic relays associated with said contacts, and automatic keying means in circuit with the magnetic relays, there being a keying means for each group of segments, and a motor for driving said commutator and said keying means in synchronism. 7. l Multiplex receiving meansc'omprising, a re.
' ceiver responsive to a band of frequencies, heterodyne demodulating means coupledto said re-v ceiver, a -high passfllr coupled to Asaid demodui. v
lating means, a plurality of pairs of band pass filters connected with said high pass lter, and a single recording means connected to each pair4 of band pass filters. y
8. Signaling means comprising an-electron dis- 5 charge device having anode, cathode, and control grid electrodes, a reactance couplingsaid anode, cathode and control grid for producing sustained oscillations and for determining the frequency of the same, electrical means for controlling the ef- 10 fe'ctive value of said reactance for varying the frequency of the oscillations produced over a -predetermined range, and means in circuit with said electrical means for applying'a potential to said control grid electrode to render said device 16 inoperative. y A
9. The method of multiplexing which includes thev steps of producing oscillations, interrupting said oscillations to produce impulsesof high frequency oscillatory energy, and simultaneously 20 .changing the frequency of the` time separated the steps of coordinating said channels so that marking intervals on one channel utilize the spacing intervals on another channel, and interrupting said oscillations when spacing intervals appear simultaneously on al1`channels.
1l. A device for multiplexing signals comprising a transmitter,l a modulator connected therewith, a plurality of sources of impulses of different intensity, there being employed a plurality of impulses of different intensity for each channel, and automatic means responsive to signal characters for selectively `associating said sources i with said modulator.
12. A ,multiplex telegraph receiver for receiving a plurality of frequencies each of which is characteristic of a signal impulse element to be transmitted which 'comprises an energy collector, heterodyne demodulating means coupled to s aid collector, a filter coupled to the output of said'45 demodulating means, and a plurality of additional 'nlters in circuit with said rst filter, each of said plurality of lters being individual to oneof the Asignal impulse elements to be received, at least two filters being provided for each channel and a translating device for each channel which is responsive to the signal impulses received over the filters in said channel.
HAROLD H. BEVERAGE. se