US2235339A - Transmitter - Google Patents

Description

March 18, 194i. J C. STEWART 2,235,339

TRANSMITTER Filed May 24, 1957 2 Sheets-Sheet l w l e 70k/fe 6MP/Plyl EA- Mmh 18, 1941. J STEWART 2,235,339

TRANSMITTER .Filed May 24, 1937 2 Sheets-Sheet 2 C. Sula/o /y ua/fdyes;

'www UNITED STATES' PATENT OFFICE TRANSMITTER James Charles Stewart, Mount Eden, near Auckland, New Zealand Application May 24, 1937, Serial No. 144,526 In New Zealand June 6, 1936 Claims. (Cl. Z50-17) This invention relates to electric wave signal- In achieving the/,maximum reduction of unling systems Such as amplitude modulated car- Wanted signal handling ability a variable plate rier Wave transmitters, audio or programme fresupply voltage in the nal circuit is used in quency apparatus and the like. combination with a variable-carrier output volt- 5 The object of the invention is to provide elecage, preferably of the type just specified. Oi 5 tric wave signalling arrangements in which, comcourse, other supply voltages will generally repared to arrangements commonly used, a subquire variation in order to achieve the required stantal Saving 0f DOWer is eieoted Without afcarrier output voltage and the required plate fecting detrimentally the quality and other char- Supply voltage simumaneously,

l() ECGISCS 0f the Signals. A further ObjeCi, S In the preferred method for supplying a, Var- 1() to provide arrangements 0f this type ih Which iable voltage, a constant source is connected in apparatus of reduced rating compared 130 that series with a variable source, and in some forms, usually employed may be used Without edu-img the variable source has the usual filtering cirthe eective range or of System. A cuits or l still further object of the invention is to proone particular novel variable Voltage Source 15 Vide apparatus whereby When n0 Programme 0r comprises abank of rectiers fed from an A. C.

signal is being handled, the supply voltages or mains throughva regulating means Comprising ln any of them are other than the values necestandem with each leg of a polyphase Supply a Sary for fun Output (for exemple' m en eudle transmission network some of Whose elements amphi-1er plete Voltage and plate current are are pairs of iron cored reactors. Each reactor 0 reduced) but whereby when e' programme er has a reactive Winding and also a saturating signal is being handled, the said supply voltages Winding these two windings having the greatest or er?, ofbteem etiae ehedemeludlletng Ugg possible mutual coupling. The reactive Windvana mn eme s s 1 y m ep p ings of each pair are connected in parallel; While the strength or voltage of the signals. Further unable means with rectnying properties objects and advantages of the invention will be geel connected to receive from the two saturatgnsllonn the appended descnptlon of its ing windings of each pair saturatingcurrents In apparatus arranged in accordance with the met?. et' Iees'. a D fo' clmpeeerirhe two St invention the signal handling `ability of any stage 1.1m mg Wm lees le; eef; peu el g Cenlec e 30 is varied substantially in dependence upon the m Such. pelenty t et t e aeynlleme-s of the two voltage or strength of the signals. In the best setuea'tmg currents are elsp eeed ney el? e forms, the signal handling ability increases from eyele' The Voltage output from t e reet-'leer substantially zero to just suiieient extent to bank 1s Vened by the e'p-Dheetlon te' ehe een' handle the Signals momentarily present. trollable means of energy (generally rectied) at 35 One particular example of apparatus arranged petentle'ls varylrtg m dependence upon the according to the invention is the amplitude modserength of the slgnal and under control ef the ulated carrier wave transmitter in which the sigslgna'l Waves' nal handling ability is varied by means of var- Tee aeeemp'a'nylflg dra'Wmgs Show d -lagram' lo iations of anode, carrier and other voltages, and maeleauy theappheatlon, of the mventlon t0 a' 40 which is hereinafter described in detail. From milo transmite? 0f the amplltude modulated this particular example the methods and prin- '0i/'Pa ciple of the invention can be understood; and so Y IQ these drawmgs: l other embodiments of the invention not given Flgl 1S a Schematlc dilglmv 0f the trans' will readily be apparent. t mltter; 45

In the substantial absence of signals, the carl E1s- 2 1s a curve showlng the manner 1n Whlch rier output voltage is given an initial or nothe Carrier Output is Verled; signal value; and therefrom the carrier output Fig- 3 is a diagram Showing the derlvatlon 0f voltage is decreased in dependence upon increasprogramme frequency voltages for control During strength of the signals until the signals reach Doses, 5o an arbitrary strength Within the volume-level. Fig. 4 is an alternative arrangement for regu- Thereafter, with further increase in the strength lating the voltage supplies of the transmitter.

of the signals, the carrier output voltage is in- Fig. 5 is vafschernatic diagram of an alternative creased in dependence upon increasing strength arrangement for deriving controlling potentials,

of the signals. l and i 55 tive grid bias in series with means RM for providing a negative b-ias proportional to the enve- The means RM may be of any known type s'u-ch as a rec-tier lope value of the signal voltage.

fed with signal energy at a suitable level at X. The components of the means RM and their time constants are so chosen that the buildingr up. of

the bias voltage is substantially complete within one cycle of the highest modulating frequency at which appreciable rapid variation of programme or signal energy occurs and so that the time of decay of the bias voltage is longer th-an one cycle of the lowest modulating frequency to be handled. Modulating potentials are supplied in any convenient and known manner at M to the grid of the modulating valve. s

The modulating Astage MA is supplied with high tension voltage through the line J from :a constant voltage source EC and a variable Voltage source EV. The constant voltage source is of usual low impedance and good regulation and comprises any known and suitable arrangement of components designed to produce a steady smooth D. C. output. Its output is fed to MA through the variable voltage source EV which comprises a bank of rectiers of suitable capacity arranged to deliver a uni-directional output of voltage variable in value with its input voltage. The source EV has no smoothing means. The source EV is fed' with polyphase A. C. energy from the mains AC through voltage regulating means ER. In this regulator each leg of the mains has a transmission network of iron cored inductors LI and L2 connected therein. s Ea-ch inductor has a secondary winding (LSI and LS2) associated therewith. The secondary windings LSI and LSZ as shown are connected to rectiers VI and V2 in series with which are the cathode-anode paths of the valves V3 and V4. The control grids of these valves are supplied with controlling voltages from the driver stage DS which in turn is controlled by the phase reversing D. C. amplier stage DCA. The biassed rectifier RVR is supplied at Y with programme energy at a suitable level. A voltage derived by known means such as the potentiometer R and proportional to the excess of plate -supply voltage over idling plate supply voltage is applied in series with andin opposition to the output voltage of RVR to DCA. The stages RVR, DCA and DS are of any suitable and known type. The time constants of RVRv are chosen according to the same plan as those of RM. When programme energy is supplied-at Y the control grids of V3 and V4 are influenced in accordance with the envelope voltage thereof. By reason of the biassingof the stage RVR, the output of rectiiied programme energy from the stage remains zero until a predetermined volume level of programme depending upon the relative magnitudes of biassing voltage and of applied programme level has been reached. After this volume level of programme has" -beenexceeded and the applied programme voltage has overstepped the threshold value constituted byfrom the windings LSI and LS2. of unidirectional current saturates more the inthe bias, then the voltage output of rectied prol gramme energy from the stage RVR increases in the grids of V3 and V4 more posi-tive in dependence upon increase of programme voltage, and the impedances of the valves V3 and V4 are varied.

They are made more -conductive so that the rectied currents in the circuits of,VI, V4 and V2, V3 are increased, said currents being derived This increase ductors LI and L2 so that the voltage input to EV is increased. The increased A. C. components in these secondaries also have voltage increasing effects by lowering the equivalent shunting impedances coupled across LI and L2. Thus, in accordance with rise of programme voltage above the predetermined level, the voltage applied to EV and hence to the stage MA and VM in series is increased. The voltage of the source EC is less than that whichl would be norm-ally required for operation of the-stage MA and VM at full output. The ratio of the voltage supplied by the constant source EC to the full capacity voltage depends upon the degree of suppression of the idling carrier below full output and also upon the characteristics of the modulator valve VM.

The high tension plate supply for the stage PA is supplied from two sources in series, a constant source ECZ and a variable source EV2, the

general characteristics of which are similar to those of EC and EV with appropriate differences in output Voltage and capacity to suit the greater requirementsof the stage PA. The ratio of the voltage supplied by the source ECZ to the full capacity voltage depends upon the degree of suppression of the idling carrier below full output. Grid bias for the stage PA is supplied from a constant source EC3 and a variable source EVS. The two variable sources EV2 and EVS have their input voltages regulated by means ER2 (including means RVR2) and R2 which are similar to the regulating means ER, RVR and R and which are supplied with controlling programme voltages at a suitable level at Z.

Splitting methods are well known in the prior art whereby the controlling signal voltages fed to X, Y, and Z may be derived from the one source of sign-als whence cornes the modulating signal voltage fed to M. A circuit which may be used is shown in Fig. 3. Signal voltages are supplied through the line PL to gain control means G and thence to splitting means SI. Part o-f the output of SI proceeds through line ML to modulating amplifier means MAM, thence to' strength in accordance with the known operation' of so-called series modulation circuits and consequently reduces the power'input in the modulator plate and to the linear power amplifier plate. The combined peak of carrier voltage and modulation sideband voltages impressed on the carrier is kept substantially constant until a predetermined critical modulation signal voltage is reached. This is accomplished by suitably adjusted gains from the source of signals to RM and to M. When this arbitrary voltage, which is determined by the setting of the bias of the rectier RVR, is exceeded the plate supply voltage fed to the modulator stage MA increases with further increase of programme voltage, because of the saturation and the effectively coupled shunting of `the inductors L'l and L2 as previously explained. At or about this point of programme voltage the plate supply voltage and also th-e grid bias ci the linear power amplifier PA increase with further rise of programme voltage.

While the programme voltage is below the cri-tical value the rate of lowering of the carrier voltage with increase of programme voltage is adjusted by the gain control means regulating the input alt X so that plate signal saturation on outwards modulation peaks does not occur in the linear power amplifier.

lWhen the programme volume level exceeds the critical value the gain control means regulating the input lto Y is adjusted to vary the rate of increase of the modulator plate supply voltage so that inwards over-modulation does not occur. Also when the programme volume level exceeds the critical value the rate of increase of the linear power ampliiier plate supply voltage compared with .programme voltage is adjusted by gain control means regulating the input to Z so that the outwards modulation peaks will be free from plate signal saturation.

Without limiting the invention, the following are suggested as desirable values to which to adjust the transmitter performance for a programme exten-ding 40 fdb. and having an average volume level 14 db. below full capacity:

Carrier at full output Zero level Idling carrier .Minus 1.9 db. Carrier at critical volume level Minus 6 db. Critical audio volume level .lVIinus 10 db. Voltage of sources ECZ and 'ECS .40 percent of the respective full capacity voltages.

The manner in which the carrier volt-age may change in .the apparatus described land adjusted in Iaccord-ance with the above table, is shown by the line COV in Fig. 2. It i-s assumed that the modulating signal strength ranges from Zerolevel (written 0 db.) to minus 40 db. At full modulation (zero level) it is assumed that the carrier output is 1.0 land that in the idling condition (no modulation) the carrier output is 0.8. As modul-ation is increased the carrier output falls, due to increased bias upon the modulating valve VM pro-duced by RM under the Iiniiuence of increasing programme voltage. The decrease is preferably effected so that as the modulation increases towards a critical value, say minus l0 db., the modulation peaks are approximately equal -to the carrier level at no modulation. As modulation increases and the carrier level decreases, the stage of over-modulation is lapproached but before this stage is reached, due to the effect of increasing programme voltages upon the voltage regulating means ER and ERZ, increased voltages are applied to the stages MA and PA and the carrier is expanded from` the minimum value (of say, 0.5) to its full value so that the higher modulation voltages may be handled without distortion. The change in carrier voltage is shown by the full line COV. Clonsideralble power is therefore saved as, except'at the highest modulation levels, the carrier is always at a relatively lo-W value. A comparatively high idling value of carrier say 0.8, is chosen so that in receivers having A. V. C. fthe. noise level is kept down when the modulation is low or absent.

At or about the arbitrary programme level chosen, say minus 10 db., the units ER and ERZ begin to increase the voltages lapplied to the stages MA and PA so that they vary as shown in Fig. 2 by the dotted lines MAI or MAZ for the stage MA, and by the dotted line PA flor the stage PA. The sources EC and E02 supply the approximately constant voltages indicated by the horizontal porti-ons of the lines and the units EV and EV2 produce the increase indicated by the sloped portions. The voltage of ECG plus EV3 is of the same pattern as the voltage of ECZ .plus EV2 but of appropriate difference in magnitude. The two lines MAI and MAZ are shown in Fig. 2 in order to represent the fact mentioned earlier that the ratio of the volt-age vfrom EC to the voltage at full modulation from EC plus EV depends also on the characteristics of the valve VM, and so Will naturally vary from type to type. l

In Fig. 4 there is shown a modification of the method of controlling the input voltage to any of the variablesources EV, EVZ or EV3. Each lead of the polyphase `circuit from the regulator ER to the source EV, for example, has included therein two windings which are respectively the secondaries of transformers TI and T2, the primaries olf which are connected to the mains. These secondaries deliver voltages respectively in quadrature and the magnitudes of the voltages in the secondaries of TI and T2 are adjusted so that the idling voltages in the polvpha-ses yconnections J2 are any arbitrary value. Preferably, these voltages are zero. In operation the output voltages from .TJ and T2 subtract veotorially from 'the output voltage of ER so that in the idling conditi-on residual voltage from ER can be substantially cancelled.

In the above descriptions the means R and RVR, and the like, have been described as one means for controlling the operation of the means ER and the like.

An alternative arrangement, illustrated in Fig. 5, consists in bringing the connection from the means RVR, or the like, .to a bias source B suitable for the means DCA, or the like, instead of (as shown in Fig. 1) to the output of the means R, or the like.

In operation, signal vpower applied at Y gencrates controlling potentials which are transmitted through DOA and which control the means ER, as already described in reference to Fig. 1.

In Fig. 6 there is shown an alternative :arrangement for producing saturation in the reactors Ill and L2 of Fig. 1. Grid controlled gas discharge tubes (or thyratnons) Thi and Th2 have their grids connected to known grid controlling devices GCDI and GCDZ respectively, and these are in turn connected to DS which is .identical with DS of Fig. 1. The plate circuits of Thi and Th2 are connected in series respectively with IiSI and LSZ which are identical with LSI and LSZ of Fig. 1.

In operation, as described previously, when the strength of the signal rises, voltage proportional .to the streng-th of signal is transmitted through DS, and this iniluences the ring of Thl and .Th2 through the action of GCDI and GCDZ. The magnitude of the currents in LSI and LS2 is thus inuenced in well known way by .Th'l and Th2, and so, as described previously, the saturation of the reactors Ll and L2 is oontrolled.

In the above description and in the claims appended hereto certain terms have been used. These terms as used have the meanings set out hereunder.

Supply voltage means any voltage excepting a signal wave Voltage or a modulation sideband voltage which may be required to be incorporated in the circuit of an electric wave signal handling arrangement for the standard operation thereof, and will include carrier wave input voltage.

In dependence upon" used in reference to a varied or controlled voltage or the like means existence (as understood in physics) of a singlevalue-d function substantially defining the pattern of variation. Despite the fact that the function may define the time pattern of .the dependent from the time pattern of the independent variable, strictly only in the case of indefinitely slow variation rates, except when time delays or the like are specifically referred to, the variation is still described as in dependence upon.

Final circui of an electric wave signal handling arrangement means that electrical loop in the said arrangement wherein power associated with one or more of the operating or supply voltages is converted to the power iiow which constitutes the output wave of the arrangement.

Signal handling ability means the peak voltage of that sustained wave which can be generated Without substantial distortion being int-roduced vby voltage overload. Thus in a plate circuit, the signal handling ability may for example be different for an audio wave :and for a single side band.

I claim:

1. In a variable-carrier signalling arrangement,

apparatus generating carrier-frequency output vol-tage .and amplitude-modulation sideband waves originating from signal frequency waves, in combination with a first means eiective in the presence of and actuated by energy under the control of signal waves of less than an arbitrary strength within the volume-range of the said signals, said rst means changing the said carrrier output voltage to values substantially in dependence upon values of the strength of the said signal waves and less than the Value of said carrier output voltage in lthe substantial absence -of signal, and with a second means effective in the presence of and actuated by energy under the control of signal waves of greater than said arbitrary strength, said second means changing said carrier output voltage to values substantially in dependence upon values oi the strength of the said signal waves and greater than the Value of the said carrier output voltage in the presence of signal Waves of said arbitrary strength.

2. In 1a variable-carrier signalling arrangement, apparatus according to claim 1 and having a Afinal circuit and a supply voltage for said nal circuit, in combination with a third means effective in `the presence of and actuated by energy under the con-trol of the said signal waves, sai-d :third means changing the Value of the said supply voltage .to values substantially in dependence upon values of the strength of the said signals.

3. dn a variable-:carrier electric wave signalling arrangement, a final circuit in which may occur electric waves comprising both carrier-frequency output voltage and valso amplitude-modulation sideband waves originating from signalfrequency waves, a substantially un-modulated supply voltage source for said final circuit, and a modulation circuit distinct from said final circuit, in combination with a first means effective in the presence of and actuated .by energy under the control of said signal waves, said `first means changing the Value of said .carrier output voltage to values substantially in dependence upon values of the strength of the said signals, and with a second means effective inthe presence of and actuated by energy under .the control of the said signal waves, said second means changing the value of .the said supply volt-age to values y.substantially in dependence upon values of the strength of the said signals.

4. In a variable-carrier signalling arrangement, apparatus as claimed in claim 3, and in which during any substantially short moment, for the instantaneous peak envelope `voltage of signal waves which is occurring, the signal handling ability afforded in the said final circuit by the said supply voltage is substantially equal to the peak voltage of ythe electric wave which is occurring in the said final circuit 5. In an electric wave signal handling arrangement incorporating a. supply Vol-tage source, an iron cored reactor circuit for varying said supply voltage in response to saturation of said iron, and means for saturating said iron in response to controlling potentials, means for generating controlling potentials which vary substantially in dependence upon values oi the strength of the signals, comprising, in combination, a first means for deriving voltage proportional :to the difference between said supply voltage in the absence of signals and said supply voltage whilst varied, avsecond means for deriving voltage which is uni-directional and is in substantially linear dependence upon the envelo-pe voltage of the said signals, and a third interconnecting means for deriving the difference constituting the said controlling potentials, between the voltages from said first and said seco-nd deriving means.

J Alt/EES CHARLES STIiVV-AJEtT.v

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