US1801870A - Radio transmitting system - Google Patents

Description

April 21, l931 D. G. 1T|| E RADIO TRANSMITTING SYSTEM Filed Aug. l1, 1927 ATTRNEY Patented pr. 21, 1931 l u PATENT OFFICE .noNALn of. L rr'rLE, or nnenwoon', PENNSYLVANIA, AssIGNoR To WEs'rrNGfHoUsnV Y nrnernrea MANUrnorUnrNer commits, A coaronArroN ori-PENNSYLVANIA y .mimo rRANsMrrrING SYSTEM i v- Application filed August 11,.-1927. Serial No. 212,153.

i My invention'relates to radio transmitting systems, and it has particular relation to` systems in `v'vhich `transmission is effected byV utilizing carrier-currents of extremely high -l, frequencies of the order of 3,000 kilocycles or higher. K f

It has been quite denitely established that less energy is required for communication over long distances if high frequencies are used, than is required for low frequencies. It is not. feasible, however, in the case of commercial transmitting stations, to reduce the power to the point whereV fadin-g, static, etc., tend to interfere with the messages being sent, and all of such stations must of necessity-make use of a plurality of highpower, water-cooled tubes in order that an adequate amount of energy shall beradiated.

By reason of the large size of the electrodes in high-power, water-cooled amplifying tubes, their inter-electrode capacity isl high, and when a plurality of them are connected in parallel, as is customary if large power-output is imperative, the total capacitance is so great that it is substantially impossible to'tune the output circuit associated therewith toV Wave-lengths below 100,1neters. The amount of energy radiated at high fre'- quencies therefore, has been limited by the Y number of power-tubes that could be connectedgin parallel without le-tuning theL output circuit from the desired transmission frequency, the most powerful short-wave'transmitter withwhich I was acquainted previous to the present invention `being capable of radiating only l'kilowattsat 20 meters, and having an effective commercial range of only- 500 miles.` j c v Y It is accordingly an Vob] ect of my "invention 40 to provide a radio transmitting system that is capable of radiating 4 a larger amount of power at high frequenciesv than lsimilar systems known to theprior art. f* *l Another object of my invention is 'to prowhich high-power, water-cooled tubes may be successfully utilized. ,i 4

Another object of my invention isto .provde a lnovel .circuitI network for, a radio *.50 1 transmitting'j system, whereby the effectgof vide a4 short-wavetransmitting system in the inter-electrode capacity ofthe requisite number of high-power water-cooled amplifying tubes is minimized.

1I attain the aforementioned objects by sub- Vdividing into a plurality of groups the poweramplifying tubes necessary to provide the requisite amount of radiated power, and vby so limiting' the number of tubes in each parallel-connected group that the total inter-electrode capacity thereof is less than the capacity necessary to tune the output circuitv to the `desired frequency., Each group of power-amplifying tubesv has itsl output circuit coupled to a radiating structure in series-aiding relation, and is energized from a masteroscillator common to all the groups, through an individual intermediate amplifier. Y I have also found it feasible to utilize a single intermediate amplifier for two or more groups of powerlamplifiers, and to 4control all of the intermediate amplifiers lfrom another amplifier of lower' power which is directly energized froml the master oscillator.

. Among vthe novel features of'my invention are..those particularly setforth in the appended claims. The ,invention itself, however, bothf as to its organization and its method of operation, together withfurther objects and advantages thereof, will best be understood from a consideration of the following description of a specific embodiment, taken in connection with the accompanying drawing. Y

The single figure ofthe drawing is andiswitches, etc., thathave no bearingon the invention, being omitted for sake ofclarity.

Referring specifically to the drawing, a master oscillator l, which may comprise a piezo-electric crystal-controlled thermionic device or other appropriate oscillation generator, is connected in parallel by conductors 2, 3, l' and 5 to a plurality of intermediate amplifiers 6, 7v and 8.- Each of 'the intermediate amplifiers may comprise a plurality of low-power thermionic devices coupled t0- gether 1n "cascade, either by'transformers,

resistor-condenser networks or impedances untuned or tuned to the frequency generated by the master oscillator.

The intermediate amplifier 6 is connected to a second intermediate amplifier 10, the output of which is applied to the input circuit of a. plurality of high-power water-cooled thermionic devices 11, 12, 13 and 14 connected in parallel. A. radio frequency transformer 15 may be utilized for coupling thev second intermediate amplifier 10 to the power amplifier stage as illustrated, or an impedance coupling device of any well known type may be used if desirable. For examples of coupling devices, reference may be mace to the patent to Curtis, 1,648,811.

The anodes of the power amplifier thermionie devices 11, 12, 13 and 1li are connected in parallelby a conductor 16 to a tunable output or tank-circuit comprising an inductor 17 and a variable condenser 18. The inductor 17 is coupled to an inductor 2O included in a radiating structure which may comprise an antenna 21 and ground connection 22, or the ground ccnnection may be replaced by a counterpoise. In the latter case, the inductor 2O in the antenna circuit need not be in inductive relation to the output inductor 17, a single lead conductively connected therebetween sufiicing to transfer energy from the output circuit to the antenna.

The anodcs of the power amplifier the 1mionic devices are supplied from a source of high voltage (not shown), and the cathodes thereof may be supplied from the saine source (not shown) Vthat supplies the cathodes of the thermionic devices Vcomprised in the intermediate amplifiers and the master oscillator.

The intermediate amplifier 7 is coupled to an intermediate amplifier 23 which may comprise a plurality of thermionic devices of slightly higher power, though not of the water-cooled type, and the output circuit of the intermediate amplifier 23 is coupled to the common input'circuit of a plurality of highpower water-cooled thermionie devices 2l. 25, 26 and 27 connected in parallel. rEhe anodes of the thermionic devices 211, 25, 26 and 27 are connected in parallel by a conductor 2S to a tunable output circuit comprising an inductor 3() shuntedby a variable condenser 31. The inductor 30 is coupled to a second inductor 32 serially comprised in the radiating structure. The anodes of the devices 24, 25, 26 and 2T, are supplied from theY same high-potential source that supplies the anodes for the first described group of power amplifiers.

The intermediate amplifier 8 is coupled to an amplifier 33 of slightly higher power, having an output circuitwhich in turn is coupled to the common input ci\.uit of a plurality of high-power water-cooled tubes 34, 35, 36 'and 37, the corresponding elements of which 'are connected in parallel. Thepower tubes 341,

35, 36 and 37 are connected by a conductor 38 to an individual output circuit comprising an inductor 40 shunted by a tuning condenser 41, and the inductor is coupled to an inductor 12 comprised in the radiating structure. The third group of power tubes is supplied with anode potential from the common source which supplies the first and second mentioned groups.

In addition to the elements thus far described, a complete radio transmitting station would comprise modulating devices, additional potential sources, various switching and control devices, and numerous other circuit connections which have been omitted from the drawing in order that applicants invention shall not be needlessly obscured. The omission of these elements detracts in no way from the completeness of the present disclosure.

In the operation of a radio system arranged according to my invention, the intermediate frequency amplifiers which control the several groups of power amplifiers are energized exactly in phase by the master oscillator, which is so arranged that the frequency supplied therefrom is the same frequency to which the output circuits of the several groups are tuned. Accordingly, the power amplifiers transmit energy to the radiating structure at a definite predetermined frequency and exactly in phase.

The number of power amplifier tubes included in each group is governed by the platefilament capacity of the individual tubes. The plate-filament paths of the several tubes in each group are connected in shunt to the output-circuit timing condenser and the total capacity thereof must not be greater than the total capacity required to tune the output circuit to the predetermined frequency. Such capacity is largely determined by the inductance necessary in order that the coupling between the output circuit and the antenna shall be suflicient to insure an eflicicnt transfer of energy therebetween. In other words, it is not feasible to reduce the inductance of the output inductor below a certain definite value for each and every transmission frequency,

and consequently, the maximum value of the timing condenser associated therewith is rather sharply determined.

Assuming, for example, in the system illustrated, that it is desired to transmit on a wave length of 100 meters, corresponding to a frequency yof 3,000 lrilocycles, and that a vpower output of kilowatts is necessary to satisfactorily cover the desired ytransmission range, it may bev determined by calculations familia-r to those skilled in the art, that a cerdefinite number of high-power watercooled tubes is necessary. The number chosen for purposes of illustration, namely 12, Vis `merely an arbitrary number and vbears no relation to the actual number required in the ice hypothetical case. If these 12 tubes were connected in parallel to a single output circuit having the required amount of inductance,

' the total plate-filament capacity would be so much greater than the capacity necessary to tune such output circuit that it would beimpossible to transmit on the frequency desired, namely 10,0 meters. By distributing the-power tubes in groups as shown, however, the total capacity of any one group may be made much less than the required tuning capacity and cach output or tank circuit may accordingly be accurately tuned by thevariablecon- -densers shown. v

The total amount of powery transferredv from the several groups of amplifiers tothe radiating structure is substantially the same when the system is arranged accordingpto my invention as when all of the tubesare connected in parallel to a singlet output circuit, the losses in the two additional tuning condensers, in the output inductors and the losses in the connecting wiring, being substantially negligible.

It is also feasible to further sub-divide the power-amplifiers, if desirable, and to energize two or more of the groups from a single intermediate amplier. In such event, all of the intermediate ampliers may in turn be energized in parallel from a single intermediate amplifier coupled directly to a master oscillator.

Various other systems of sub-dividing the apparatus between the power amplifier groups and the master oscillator may be employed, all falling within the scope of my invention, which is mainly directed tothe Y subdivision of the power-amplifiers proper, into separate groups of parallel-connected devices, in order that the total inter-electrode capacity of the devices in any one group shall not prevent proper tuningV of an output circuit energized thereby. l

My invention is particularly advantageous,

when it is desired to radiate a relatively large amount of power at frequencies above 3,000

kilocycles. I haveestablished, by experiment, that when the power'ampliflers are sub-divided properly, a transmitting system can be provided which will radiate many times more power than' systems known to the prior art, wherein all of the power amplifier tubes were connected in parallel. Although described in connection with space-radio, my invention is not to be restricted thereto,'but is equally applicable to short-wave type wherein it is desired to trans- Y v mit a larger power output at higher radio frequency than is normally feasible with all the power amplifying devices in parallel con Vnectionto a single output circuit, a plurality of groups of power-amplifying thermionic n dev ices connected in parallel, means for applying varying potentials in phase across the input-circuits of the groups, a tuned out- Vput circuit foreach group, the said output circuits being coupled to a single work circuit, the total inter-electrode capacity'of the thermionic devices in each Vgroup being of such value as to permit the output circuit individual theretoV to be tuned to high frequencies of the order of three thousand kilocycles.

In testimony whereof, I have hereunto subscribed my name this 3rd day of August,

' l.DONALD e. LITTLE.

roo

carrier-current transmission over wires when- Y ever the transmission frequency is so high that tube capacity must be taken into account in the tuning of the output circuit, or in` other situations where large power-output at i high frequency is necessary.

Although I have shown anddescribed aV single specific embodiment of my invention,

4 numerous modificationsthereof will be ,ap-

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