US2253832A - Signaling - Google Patents

Description

J. N. WHITAKER SIGNALING Filed oct. 14, 1939 Aug. 26, 19141,

INVENTOR. Jff .N. WH/TAKER ATTORNEY.

.nim

TN, .E l

Patented Aug. 26, 1941 A'UNITED [STATES PATENT ofFFIcE;

J ames N. Whitaker, Weehawken, N. J assignor to -Radio Corporation of America, a corporation of Delaware Appliation otober 14,1953, serial No. 2.99421 vio claims. (c1. 25e-2o) This invention relates toa radio signaling systern and particularly to the switching of a circuit from one signal to another, depending upon which signal `is the stronger. More specifically, it relates to a vacuum tube and gas filled tube network wherein a means is provided for automatically switching from a standard or primary signalfto an alternative or secondary signal at such times asthe primaryl signal maybe below a usable level, but only if the level of the secondary signal is of a usable value. Y

'This invention, although especially useful in connection with the sub-carrier frequency modulation system described in the U. S. patent application of James E. Smith et al., Serial No. 270,332, filed April 27, 1939, is not restricted thereto.

In the above mentioned application Serial No. 270,332, the use of the switch was shown in block diagram form in Figure 2, and a schematic diagram of the switch Was shown in Figure 5. The operation `of the switch was described in the body of the specification. This Vswitch was arranged to transfer the control of the system from the primary or fundamental input to the secondary or harmonic input at any time when the lfundamental input was reduced in level to a predetermined value, and to again restore the control to the fundamental input when the level of said fundamental input was restored to its original usable level. This switching took place automatically and irrespective of the level of the signal in the secondary (or harmonic) channel.

"Experience has proven that the energy present in the secondary (or harmonic) channel was not always of a usable value when the signal in the fundamentalchannel had dropped below the predetermined level. Therefore, when the switch transferred the control to the harmonic channel, the only signal present was often radio circuit noise, and the prime purpose of the switch (that of filling in a missing portion of the' received intelligence) was defeated.

, The purpose of the present inventiony is to improve the operation of the switch Vand `to provide a differential operation in order that the switching may only take place after t'he fundamental signal has been reduced in amplitude below a predetermined level, and then only providing the signal in the harmonic channel is of a greater amplitude than the signal remaining inthe fundamental channel; f

Having thus described the purpose of the present invention, reference is made to the figure in the drawing and the following description.v

nal intoy the input 2 of amplifier tube 3. The circuit of this amplifier is conventional and will be understood from the drawing withoutI further description. The output circuit 4 introducesthe signal into full wave rectifier 5. AThe positive terminal 6 of ,this rectifier isconnected to one end of resistance l Yand the center tap of transformer 4 (which represents the negative terminal of the rectifier system), is connected tothe other end of the resistor. A smoothing condenser 8 is"ccnnected'acrossthese teri'nin'als.vr o

Control lines Ia'introduce the harmonic signal into the input 2a o-f amplifiertube 3d;YY The circuit of this amplifier, like that of amplifiers is conventional and merits no further description. The output circuit 4c introduces the signal vinto full wave rectier 5a. They positive ter-v minal 5a. of this rectifier is connected to posi-tive terminalA 15, of the fundamental rectifier and therefore also to one end ofV resistance V'1. The center tap of transformer da (which'represents the 'negative terminal of this secondv rectifier system), is connected to`one 'end of'resistance The other end of resistance 9 connects to one end ofresistancel.y A'smoothing'c'ondenser (la. is ccnnected across resistor 9, and an adjustfaible tap on this resistor is grounded.l

The elements thus far described constitute the didveren'tial arrangement used inconnection with the electronic switch. This'diier'e'ntial arrangement asshown inthe drawing is' set apart from the reniainiei` ofthe switch by a dashed line t'o'assist in the' explanation, which covers the operation of the entire system. A y,

The negativeend of resistance 9v is connected @TW-,gh @n a'QPlQPf-'lte 1e5t0` vl!) 'll grid 'H 0f triode The positive end yof resistor 9 is connected thnoughf an vaulipropriate 'negative grid biasing ource I3 grid resistorv I4 to grid il gas ,triode I6. These gas triodes are also` as' Vthyratrons,` grid glow tubes,et,c`.`, andV usually'haye a potential drop of approximately `15 volts across theirv anodes and cathodes when conducting'.VVV The anodes I9 and?? of gas triodes v,IZ and A,lli are connected @garner andro the/positive terminal 41 of' a suitable power source,Y of which the negative terminal is indicated as 42. Terminal ,42 is also connected to ground. The cathodes ll-'l and I8 y of the gas triodes are connected together through connected `through resistance 22' to one end of resistance g3, which end is also connected to the cathddes of push-pullamplifijer tubes 24and 25.

j Control HDSS l .intfoduceihs fundamental 51g.- 55 Tile other .engl of lresstarwe 23 is grounded and CII resistance 39 and to the cathodes of push-pull;

amplifier tubes 3| and 32. The opposite end of resistor 3D is connected to ground and also to the center of the secondary windingof transformer 33, which is fed by input lines 34. The opposite ends of the secondary of transformer 33 are connected to the grids of amplifier tubes 3l and 32. The anodes of these tubes are connected to the outside ends of the primary winding of transformer 35. The center tap of this winding is connected to cathode Il of gas triode I 6.

The secondary of transformer 35 is connected between the grid of amplifier tube 36 and ground. The secondary of transformer 28 is connected between the grid of amplifier tube 31 and ground. The anodes of tubes 36 and 31 connect to opposite ends of the primary Winding of output transformer 38, the center tap of which is connected to positive terminal 4I of the power supply. The anodes of amplifiers 36 and 31 might also be connected in parallel and to one side of the primary winding of transformer 38, if desired. In that case, the opposite side of the winding would then -be connected to terminal 4I of the power supply. The cathodes of these tubes are connected in parallel through biasing resistor 39 to ground. A by-pass :condenser 40 is connected across resistor 39. The secondary of transformer 38 is connected to the utilization circuit which may be a limiter as shown in Figure 2 of Smith et al., application Serial No. 270,332, filed April 27, 1939.

The action of the complete differentially operated electronic switch is described as follows. Two separate operations are performed in the operation of the switch. First, the control of the switching by the two signals through a differential arrangement and, second, the actual transfer between two signals by means of the electronic switch proper. The two signals which are switched may be the saine two signals that act differentially to operate the switch.

The differentiation between the two signals is a function independent of the operation of the switch. The operation of the switch, however, is dependent upon the differential between the two controlling signals. Therefore, it is found convenient and less confusing to first describe the action of the differential arrangement and then to describe the operation of the electronic switch, resulting from the differential currentsrderved from the two signals.

The action of the fundamental and harmonic signal amplifiers and rectifiers incorporating elements I to 6 and Ia to 6a inclusive and respectively is conventional and will be understood by reference to the circuit diagram -without further description.

Let us assume for the moment that there is a fundamental signal input to I. This signal is amplified and rectified and produces an IR drop across resistor 1. The end of I which connects to elements 6 and 6a of rectifiers 5 and 5a will be positive with respect to the opposite end oi this resistor. Let us say that the Potential cl-"- veloped across resistor 'I by the fundamental signal is X volts. Let us also assume that a signal is also present at Ia of the harmonic channel. This harmonic signal will be amplified, but rectifier a cannot pass current unless the harmonic signal reaches a higher value than the fundamental signal. This is due to the biasing action on rectifier 5a due to the IR drop across Vresistor 1 caused by the fundamental signal. If

the level of the fundamental signal is reduced, or

if the signal level in the harmonic channel is lncreased so that the signal as rectified by 5a is greater than X volts, current will fiow through resistors 9 and I from rectifier 5a. This current flow will cause a potential to appear across resistor 'I which will be greater than X volts and rectifier 5 will cease to pass signal currents for the same reason as previously described for rectifier 5a. Thus, it will be understood that the only rectifier which may pass current is the one receiving the stronger signal.

In actual practice the fundamental signal is always considerably stronger than the harmonic signal except under conditions where the R.-F. carrier fades out and permits the two sidebands to beat together and generate a strong second harmonic. For this reason it is apparent that rectifier 5a will operate only during these abnormal conditions.

The combined elements of the fundamental channel operate to produce an 1R drop across resistor 'I only, and `only acts to prevent the operation of rectifier 5a.

The elements of the harmonic channel operate to produce an IR drop across both resistors 7 and 9. Resistor 9 also forms a part of the electronic switch. Therefore, the signal applied to the harmonic channel not only acts to block the signal output of the fundamental channel, but also operates the electronic switch.

I-Iaving thus described the operation of the signal differentiating means, I will proceed to describe the action of the electronic switch with reference to the schematic diagram shown in the figure of the drawing.

We will again assume that the fundamental signal is usable; and rectifier 5a is blocked off by a drop of X volts across resistor 1. Grid bias I3 places a sufiicient negative bias on the grid I5 of gas triode I6 to prevent conduction in this tube. No bias is applied to grid II of gas triode I2, which is now conducting. Current is flowing through this tube and resistors 29 and 39 to ground. The entire power supply voltage (minus the l5 volt tube drop) will now appear across these two resistors. Cathode I8 will be at a positive potential with respect to ground. Cathode I8 also connects to the center tap of transformer 28. By means of this connection, a positive potential is applied to the plates of amplifier tubes 24 and 25 through the transformer. The IR drop across resistor 23 due to the plate current of these amplifiers will provide a normal cathode bias for class A operation. Therefore, the fundamental (or doubled fundamental) signal will be amplified and passed on to the utilization circuit.

Let us now assume the .second condition. The fundamental signal has been reduced until the IR drop across resistor 'I is substantially lower As the input to the I3 begins to conduct.

creased rectifier 5a will 'pass current, through resistors 9 and 1.. .A negative .bias is applied through .resistor HlA to grid Il .of gas triode I2 because-of the IR. drop Aacross resistor 9. Likewise, a positive potential will be applied to .grid 45 of gas triode t6 through bias. I3 andY resistor I4. (This is due tothe division .of the potential appearing across resistor 9 by the variable tap, which is grounded.) As this positive potential is increased, bias lwis overcome, and gas triode (This conduction isoften spoken of as firing To say such a tube is fired means that the Vconduction is started.)

When gas triode i6 .is fired, it raises the potential at the terminal .of .condenser :2.4 by the amount of drop across resistors V22 and 2.3. The potential of cathode .i8 is momentarily raised above the potential of anode 2E). The. ycur-rent through tube i2 is thus .interrupted and the tube ceases to ldraw current, or is extinguished t The time constant .of .condenser 2l is such that `it vcannot .discharge sufficiently fast to lower the cathode .to 'its operating voltage .before de.- ionizat'lon occurs in `tube 1.2. Therefore, grid H kresumes control. .Since grid H is now made negative by the signal drop in resistance 9, tube `l2 cannot restrike at .this .time after vde-ionization takes place. YCi'mclenser 2l thereafter dis.- charges thr-ough resistors 2.9 and 36 and recharges in the opposite direction.

When tube I6 was fired and tube t2 wasextinguished, plate voltage was removed from arnplifier tubes 24 and 2.5. Blocking bias was simultanecusly removed from tubes .3| and 32. Blocking bias was also applied to tubes 24 and 25 due to the IR dropacross resistor .23. fore, amplifiers .24 and 25 became inoperative. Likewise, amplifiers .3i and 32 became operative, and the harmonic or secondary signal was passed on to the output..

When thefundamental signal again returns vto normal, or if the harmonic signal drops below a predetermined value, the bias .on grid Il of the .tube i2 is reduced and this' tube fires, and the opposite of the above action occurs, returning the .switch to the first operating condition.

Although :primarily intended for use in connection with sub-carrier frequency modulation systems, this invention should not .be limited thereto.

For instance, any two signals vmay be .switched by any other two signals. Additional elements may be added to provide a vmeans for controlling the selection of any one of `three or more signals fro-mas many inputs, etc.

Also, it may be found desirable to use such a device to switch .between .tivo signals by a .prearranged tone signaling device, such as, for

instance, a time clock.

The system may .also vbe. adapted to double frequency keying wherein one signal of a given frequency would be transmittedfor marking and another signal of a .dierent frequency'transmitt'ed for spacing. n

It may conceivably be ,used in a secrecy. sys- .tem where part of the elements of a letter were to be transmitted on one frequency and a vpart on the other.

I also do not wish to be limited to gas triodes, as any gas lled tube containing two or more elements could conceivably be used. This applies particularly to gas filled pentode tubes.

To obtain an .overall ,picture of mypresent invention it may be restated briefly as follows: g As v.ezvrplained in the .copending application lof There- James E. Smith et jal., Serial blo-270,332, filed April V27,v 1939,.variab1e. light impulsesy picked up by a scanning device vare employed to produce corresponding electrical currents. .These .cur-

rents are employed to amplitude modulate an Y alternating current `of constant frequency. The amplitude modulated currents are rectified and the rectified currents or Waves are employed to yfrequency modulate a sub-.carrier alternating current wave. This frequency modulated subi-carrier, which may be of an audible or super-audible frequency, in turn is employed to amplitude modulate a high frequency.v or radio vfrequency carrier wave. The carrierV wave is vtransmitted to the .receiver and picked up, as shown in the circuit diagram, by the receiving antenna RA.

The picked up waves are fed into a superheterodyne receiver SI-IR whose output is the fre.- quency modulated sub-carrier wave. AIn the .event that the carrier wave fades, the super-heterodyne receiver will produce a second harmonic output effectively caused by the beating together .of the sidebands received by the receiving antenna RA.

When the carrier is present and the super-- heterodyne receiver reproduces vin its output .a strong fundamental frequency modulated .subcarrier, the filter FF passes the fundamental Asubcarrier with its frequency modulations on to a limiter L and also.. as .explained previously, tothe transformer 2 through line l. The output of limiter L is fed through a low pass filter LPF, then to a frequency doubler FD, as explained in the copend-ing application referred to, to transformer 26 through lines v2l.

As explained, when .the radio frequency carrier is strong and a strong fundamental subcarrier is produced, this `sub-carrier of doubled frequency as .obtained from frequency' doubler FD 4is fed through transformer 26, amplifiers 24 and 25 and amplier 31 to the utilization or output circuit .indicated at 38.

When the radio frequency carrier fades so .that a strong second harmonic of the sub-carrier is produced in the output of the super-heterodyne receiver SHR, this harmonic energy passes by way vof the band passy filter BPF tothe harmonic transmission lines I a.. As explained hereinabove, With the strong second harmonic and a weak fundamental sub-carrier switching takes place so that the utilization circuit 38 is supplied with the harmonic energy through circuit la, conductors 34, transformer 33, amplifiers 3|, 32 and amplier 36. n f Y It should be clearly understood thatthe frequency modulated sub-carrier `'at the transmitter shown in Figure 1 of the copending application of Smith, et al., referred to above, may be employed to frequency modulate the radio frequency carrier generated at the transmitter. In that event, -the super-heterodyne receiver'r SHR should be Vof thetype adapted to receive `and translate the frequency modulatedy radio frequency waves into the frequency modulated Ysub-carrier. Also, rif. desired at the transmitter, the frequency moclu lated sub-carrier may be Vemployed to 'phase modulate the radio frequency carrier, in which event the receiver SHR lshould be a phase modulation receiver. Also, if desired at the transmitter, the sub-carrier may be phase ymodulated and this phase modulated sub-carrier `employed to phase modulate the radio frequency carrier Wave, in which event, as 1before,'the `.receiving systern SHR should be a phase modulation receiver. Also, .if a. phase *modulated sub-carrier 'is employed yat the .transmitter .thisphase modulated sub-carrier may be employed to amplitude modulate the radio frequency carrier, in which event the receiver SHR should be a simple amplitude modulation receiver.

When the phase modulated sub-carrier is employed, the second harmonic of the phase modulated sub-carrier which appears in the output circuit at 38 may be translated by any suitable phase modulation translator. Thus, for example, the phase modulated sub-carrier may be fed to a detector through a lter which passes only one sideband of the doubled sub-carrier and the doubled carrier frequency of the sub-carrier. The detected output in this case would be a replica of the modulating envelope referred to hereinbefore.

Having thus described my invention, what I claim is:

1. A receiving system for receiving a carrier modulated by a sub-carrier comprising means for deriving from the modulated carrier sub-carrier wave energy, means for filtering out fundamental sub-carrier energy from the derived energy, additional means for filtering harmonic energy from the derived sub-carrier energy, means for raising the filtered fundamental energy to a harmonic frequency, and means including trigger-acting discharge tubes for selectively controlling the transfer of the raised energy or the directly derived harmonic frequency energy to a translating device, said ,selectively controlling means being adapted to favor one of said energies when both are of substantially equal value.

2. In a receiving system for a fundamental carrier wave containing a modulation frequency, means providing separate transfer paths for the fundamental carrier wave per se and for a harmonic component of said wave respectively, a translating device having an input circuit under alternative control of the energy in the two said paths, electronic switching means including gaseous discharge tubes for selecting the transfer path which is appropriate to the stronger of said fundamental and harmonic waves, and means controlled by the stronger of the two said waves for firing the proper gaseous discharge tube to cause the path selection.

3. In a receiving system the combination according to claim 2 and including means effective when one of said gaseous discharge tubes is fired for extinguishing the other of said tubes.

4. In a receiving system, the combination according to claim 2 and including a push-pull amplifier in each of said transfer paths, each of said amplifiers having a grid bias control circuit under the influence of the conductive and non-conductive states of said gaseous discharge tubes.

5. In a receiving system., the combination according to claim 2 and including a push-pull amplifier in each of said transfer paths, each of said amplifiers having an output circuit the source of anode potential for which is supplied through the space discharge path of one of said gaseous discharge tubes respectively.

6. The method of selecting one of two transfer circuits between a radio receiver and a translating device, by means of two alternatively conducting gaseous discharge tubes, which coniprises separately rectifying a modulated subcarrier wave component and a harmonic derivative of the side bands of the same sub-carrier wave, causing a first one of said tubes to be conductive so long as the amplitude of rectified energy from said sub-carrier wave component eX- ceeds a predetermined value, causing a second one of said tubes to become conductive and the first said .tube to be extinguished when the amplitude of said rectified energy falls below said predetermined value, and causing each said tube to control an appropriate one of said transfer circuits in such manner that only the stronger of the signals carried by said sub-carrier wave and its harmonic derivative respectively are passed to said translating device.

7. In a device for switching from one potential source to another, a utilization circuit, a rst and a second gas tube, means whereby each tube at times starts to conduct and substantially simultaneously quenches the other, a first and a second amplifier tube, each amplifier tube having its output circuit connected to said utilization circuit, the input circuit of one amplifier tube being connected to one of said potential sources and the input circuit of the other amplifier tube being connected to the other of said potential sources, means for applying a positive potential to the plate of the first amplifier tube from the output circuit of the first gas tube While it is conducting, and means for applying a positive potential to the plate of the second amplifier tube from the output circuit of the second gas tube While it is conducting.

8. In a device for switching from one potential source to another, a utilization circuit, a first and a second gas tube, means whereby each tube at times starts to conduct and substantially simultaneously quenches the other, a first and a second amplifier tube, each amplifier tube having its output circuit connected to said utilization circuit, the input circuit of one amplifier tube being connected to one of said potential sources and the input circuit of the other amplifier tube being connected to the other of said potential sources, means for applying a positive potential to the plate of the first amplifier tube and a negative blocking potential to the grid of the second amplifier tube from the output circuit of the first gas tube while it is conducting, and means for applying a positive potential to the plate of the second amplifier tube and a negative blocking potential to the grid of the first amplifier tube from the output circuit of the second gas tube while it is conducting.

9. In a device for switching from one potential source to another, a utilization circuit, a first and a second gas tube, means whereby each tube at times starts to conduct and substantially simultaneously quenches the other, a first and a second amplifier tube, each amplifier tube having its output circuit connected to said utilization circuit, the input circuit of one amplifier tube being connected to one of said potential sources and the input circuit of the other amplifier tube being connected to the other of said potential sources, means for applying a positive potential to the plate of the first amplifier tube and a negative potential to the plate of the second amplifier tube from the output circuit of the first gas tube while it is conducting, and means for applying a positive potential to the plate of the second amplifier tube and a negative potential to the plate of the first amplifier tube from the output circuit of tlie second gas tube while it is conducting.

10. In a device for switching from one potential source to another, a utilization circuit, a first and a second gas tube, means whereby each tube at times starts to conduct and substantially simultaneously quenches the other, a first and a second amplifier tube, each amplifier tube having its output circuit connected to said utilization circuit, the input circuit of one ampliiier tube being connected to one of said potential sources and the input circuit of the other amplier tube being connected to the other of said potential sources, means for applying a positive potential to the plate of the first amplifier tube and a negative potential to both the plate and grid of the second amplifier tube from the output circuit of the iirst gas tube While it is conducting, and means for applying a positive potential to the plate of the second amplifier tube and a negative potential vto both the plate and the grid of the rst amplifier tube from the output circuit of the second gas tube while it is conducting.

JAMES N. WHITAKER.

Images