US2032208A - Transmitting system - Google Patents

Description

Feb. 25, R936. c. W. HANSELL TRANSMITTING SYSTEM Filed March 25, 1931 6 Sheets-Sheet l INVENTOR CLARENCE w. HANSELL BY Mgg@ ATTORNEY Feb, 25, 39%. c. W. HANSELL 2,@3220@ TRANSMITTING SYSTEM Filed March 26, 1931 6 Sheets-Sheet 2 CLARENCE w. HANSELL BY Q g ATTORNEY @eh 25, 319936. Q W` HANSELL B@ TRANSMITTING SYSTEM Filed March 26, 1931 6 Sheets-Sheet '3 INVENTOR mmcsvmmsm Bv g ATTORNEY "@@c 25, H936. C. W HANSELL v 2,932,298

TRANSMITTING SYSTEM Filed March 25, 1931 6 Sheets-Sheet 4 INVENTOR CLARENCE W. HANSELL BYNbQ/WW ATTORNEY Feb.. 259 i936. Q W HANSELL 2,@32,28

TRANSMITTING SYSTEM Filed March 25, 1951 6 Sheets-Sheet 5 INVENTOR CLARENCE w HANSELL ATTORNEY Feb 25, E936. l Q w HANSELL 2,632,208

TRANSMITTING SYSTEM Filed March 2a, 1951 e sheetsheet e INVENTOR 'CLARENCE HH. HNSELL /wwF/L/ ATTORNEY Cil Patented Feb. 25, 1936 STS TRANSMITTER* G SYSTEM Clarence W. Hansell, kPort efferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application March 26, 1931, Serial N0. 525,419

15 Claims. (Cl. 250-17) It has been common practice prior to my present invention to control the frequency of radio frequency transmitters by means of relatively low power, lightly loaded master oscillators, the outputs of which were amplied through a chain of radio frequency ampiiers to the power desired for transmission. In this previously developed system the conditions for holding the frequency of the master oscillators constant could be obtained more easily and economically than would be the case if the oscillations were developed directly in the vacuum tubes which produce the power to be radiated from antenna. A system of the latter kind has been developed for high frequencies by the British Marconi Company and is known as the British Beam System.

In the United States a method for maintaining master oscillators much more constant in frequency than had been possible previously was invented by W. G. Cady and is disclosed in his United States Patent 1,472,583. This method of Cadys employs a piezo-electric crystal and results in a great improvement in frequency control. I-Iowever, it is subject to limitations in that its constancy is diminished at the higher frequencies and the amount of power obtainable from the crystal oscillator is small.

rst limitation is removed by operating the crystal oscillator at relatively low frequency and increasing this frequency by vacuum tube frequency multipliers. A method for doing this is disclosed in U. S. Patent 1,771,375 of I. F. Byrnes. At the beginning of the development of high frequency transmitters the method described by Byrnes was extended to the use of several similar stages of vacuum tubes each operating as a frequency multiplier and resulting in a final output at one of the higher harmonics of the crystal frequency. This resulted in a great improvement in frequency stability through the use of a relatively low frequency crystal even though the outfrequency of the transmitter was much higher any previously used for high power, long distance, communication.

In this type of transmitter the frequency multipliers were all low power tubes. of the same size and type so that there was no increase of power in the successive frequency multiplier stages. The output from the last frequency multiplier was amplied' by a chain of vacuum tube all operating at the same frequency, to the final power level required for the antenna. In case the amplifying system followed the previously established practice used in master osciilator-amplifier transmitters. of the type used in the British Beam System. The main difference was that the conventional master oscillator was replaced by the combined crystal oscillator and requency multipliers.

Although this method of constructing and operating a transmitter was an improvement over any previously used methods, yet, at high frequencies, the circulating currents through the dielectric capacities of the tubes caused losses which reduced the amplification and troubles were experienced from undesired spurious oscillations. These spurious or parasitic oscillations were caused by energy feed back from output to input circuits or amplifier stages and from high power stages to lower power stages. The adjustments required to eliminate these undesired oscillations were critical at high frequencies and difficult to maintain over long periods.

To eliminate these difiioulties while at the same time reducing the number of stages required for a given output is one of the more important objects of my present invention.

In accordance with my invention I change the transmitter, previously mentioned, to eliminate most of the low power frequency multiplying stages and I use a new system in which the successive intermediate stages of amplification work at successively higher power levels, and, most important, the amplifier stages act as frequency multipliers. Thus, I combine amplification and' frequency multiplication in the successive stages of an amplifier system.

After this is done the earlier stages of the am plifier work at lower frequencies where they are more efficient. Also the input and output cir- .si

cuits of each intermediate amplifier stage are tuned to different frequencies so that the feed back from output to input circuits causes little current in the input circuit because of its lack of tuning to the frequency of the energy fed back. Likewise the feed back of radio frequency energy from any stage of amplifier to previous stages is very greatly reduced because of the wide differences in frequencies to which the amplifier circuits are tuned. Consequently, there is a marked freedom from parasitic oscillations and an ease of control and operation borne out in transmitters actually built incorporating the present invention never before approached in an amplifier` system for high radio frequencies.

In my present system of frequency multiplication at increasing power and also in the system of frequency multiplication at substantially constant power, I have obtained a still further improvement in operation by the use of capacity neutralization and harmonic regeneration as previously described in my'U. S. application, Serial Number 177,505, filed March 23, 1927, which resulted in U. S. Patent 1,878,308.

It is a further object of my present invention to combine the use of tubes with four or more electrodes with my system of multiplying frequency and increasing power in the same succes-rsive stages of an amplifier system; for, I have found that tubes with more than three electrodes may be used in my frequency multiplier-amplifiers to excellent advantage. Transmitters are now in use employing tubes with two grids in which one grid serves to shield` the control grid from the anode and, the addition of the screen Y grid, which may be kept substantially at zero radio frequency potential, together with appropriate circuit shielding, serves some of the purposes of the capacity neutralization in my Patent 1,878,308 with the advantage that no neutralizing adjustment need be made by an operator and theV probability of ineliiciency due to human error is greatly reduced.

In my transmitting system it is possible toy use any or all stages of amplifiers as frequency multipliers but where expediency in design makes it desirable, I prefer` to use some stages as ampli- Vfiers without change'of frequency. Thus I nor- Vmally prefer to make at least the last stage an ordinary amplifier since the last stage amplifier power output and eliicency. I may use the last stage for amplification only without much danger of parasitic oscillations, if Iemploy screen grid tubes in the last stage or three electrode tubes with capacity neutralization together with other features essential to good electrical and mechanical construction. I have found it expedient in fulfilling certain requirements to make one or more of the earlier stages act as amplifiers without'freq'uency multiplication.V Y .For example I have used an ordinary amplifier immediately after the crystal because by doing so I could lighten the load on the crystal circuit to obtain greater constancy ofv frequency.

In some cases I have provided switching and tuning means to permit changing vario-us stages to make them operate as amplifiers or frequency multipliers of various ratios for the'purpose of changing frequency and a number of transmitters which I made embodying this feature are now in commercial service. For a more detailed description of the method reference may be had to my U. S. application, Serial Number 189,162, filedMay 5,1927.V Y

I have also found that it is undesirable to operate a number of tubes in parallel because of practical difficulties in arranging them so that all willhave like conditions. At high frequencies, for example, it is very difficult to obtain equal effective inductances in the grid leads, a condition which must be obtained'to make each tube take its proper share of load. Parallel tubes are also subject to the possibility of very high frequency parasitic oscillations through the effective inductances of the connections to thetubes.

any stages, their grid bias falls to zero.

from any stage of amplier. At the same time, for purposes of economy, I prefer touse a single tube in all stages where the type of tube and the required power level permit it. Consequently it is a further object of the present invention to provide a method and means for coupling single tube stages to pushpull stages and pushpull stages to single tube stages as may be required for greatest economy when particular4 types of tubes must be used to meet particular requirements of construction. Preferably, according to my invention, I use single tube frequency multipliers and amplifiers followed by pushpull amplifiers.Y

A still further object of my invention is to improve the stability of operation of vacuum tube amplifier and frequency multiplier systems to make them less Subj ect to the effects of power supply voltage variations and at the same time I proy tect the vacuum tubes from destructive currents.

Briefly, I do this by employing the combination, .i

rectified grid current through a grid leak're-V sistance.

It is characteristic of vacuum tube frequency multipliers and high eiciency VamplifiersA that the relative. values of grid bias and radio frequency excitation potential must berather critically adjusted. If anY operator, while making adjustments, ofthe power supply voltage causesa variation above or below normal in radio frequency output from anystage then ,theV excitation and the efficiency andoutputY of the next succeeding stage is adversely affected. I may make the biasing potential increase and decrease in accordance .with the excitation in a manner to hold relatively constant output and efficiency by employing grid leak bias.

, However, when this is done, if for any reason the master oscillator, or any intermediate stage fails .to function, so that there is no excitation on In this case the tubes are subject to excessively high and destructive anode currents and losses which endanger the lives of the tubes. tection on the power supply will not entirely remove this danger because theinput currents,

controlling overload protective devices, under thisV condition may not exceed the normal input while the energy dissipation in the tubes is greatly in- Q;

To remove this danger of tube failure while still Y Overload prois increased in retaining most of the advantages of grid leak bias, is a further object of my present invention and to fulfill it I employ sufficient fixed bias to protect the tubes in case their excitation fails and obtain the remainder of the required biasing potential from grid leak resistances in series with the fixed bias.

amplification, more Vindependent of power supply variation is 'to obtain both the anode and grid bias direct current potentials from rectiflers deriving f their powerfrom the same supply. I also use sufficient excitation on each stage to cause powerV conditions a change in power voltage causes f changes in anode and grid potentials which tend to compensate one another and the unbalanced part of the variation is still further reduced by the limiting.

In accordance with United States Patent Oflice procedure my invention is defined in the appended claims. However, it may best be understood, both as to its structural organization and mode of operation, by referring to the accompanying drawings, wherein,

Figure 1 is a .block diagram of a commercial transmitter built in accordance with my present invention,

Figure 2 is a schematic circuit diagram of the apparatus used in Figure 1,

Figure 3 is a block diagram of another transmitter adapted for commercial use built in accordance with my present invention,

Figures 4 and 4a, schematically illustrate a circuit arrangement used in the apparatus sho-wn in Figure 3,

Figure 5 is a block diagram of another form of commercial transmitter embodying my invention,

Figure 5a is a diagram or table indicating a few of the many combinations of an amplifier and a frequency multiplier amplifier which may be used in the arrangement shown in Figure 5,

Figure 6 is a circuit diagram of the apparatus blocked out in Figure 5, and,

Figures 7 and 8 are schematic wiring diagrams of transmitters devised in accordance with the present invention.

Referring to Figure 1 I have blocked out a transmitter wherein a crystal controlled oscillator 2 supplies energy toan amplier and frequency doubler 4. Both the crystal controlled oscillator and amplifier frequency multiplier 4 are placed within a shielding compartment 5.

In accordance with the present invention, if it is desired to use higher frequency energy than that supplied by the frequency multiplier 4, an additional amplifier and frequency multiplier 8 is provided. The amplifier and frequency multiplier 8, as indicated, is of larger size and rating than the frequency multiplier and amplifier 4 so that substantial amplification besides frequency multiplication occurs in apparatus 8. If the output of apparatus is of the correct frequency, it may be further amplified by a suitable amplifier ill preferably of the pushpull type placed within a shielded compartment l?. with frequency multiplier-amplifier 8, and the output of amplifier l may be further amplified by an additional amplifier l2 placed in a shielding compartment I4, the output of the latter being fed, as indicated, to an antenna or other suitable utilization circuit.

As shown more fully in Figure 2, the crystal controlled oscillator or electron discharge device has coupled to its input electrodes a frequency controlling crystal l and has a tunable circuit I8 in its output circuit adjusted substantially to resonate at the fundamental frequency of the crystal. Energy from the output circuit of electron discharge device 2 is fed through a suitable blocking condenser 252 to frequency multiplier and amplifier 4 having an output circuit 22 tuned to a harmonic of the input frequency and, as indicated, tuned to the second harmonic (2f) of the fundamental (f).

Energy from the output circuit 22 is fed through blocking condenser 24 to frequency multiplier and amplifier 8 of larger size and rating than tube 4, thc tube 8 having in its output circuit, a tunable circuit 2S tuned to the fourth harmonic (4f) of the fundamental, from which energy is fed to the pushpull amplifier l through the tunable input circuit 28 thereof tuned to the fourth harmonic. I prefer to use a single tube frequency multiplier and amplifier followed by a pushpull amplifier stage for amplifying the output of the frequency multiplier, as a single tube frequency multiplier is more readily adjusted than a frequency multiplier of the pushpull type such as disclosed in Patent 1,873,308, although, if desired, a pushpull frequency multiplier may be used in place of a single tube frequency multiplier.

In any event the grid electrode of each tube acting as a combined amplifier and frequency multiplier is operated at a certain predetermined negative voltage such that when optimum anode potential is applied, plate current iiows only during a bri-ef portion of the duration of the positive cycle of input potential. Under these conditions the power output of the tube is almost as great at the lower harmonic frequencies as at the fundamental frequency. This operation has been pointed out in considerable detail in my Patent #1,878,308, mentioned above, and the brief description given above is believed to suffice for this application.

Trie output circuit 39 of amplifier i0 is tuned referably to the fourth harmonic, and, the amplier itself is neutralized as shown to prevent parasitic oscillation generation.

Output energy from the output circuit 3D may then be fed through blocking ccndensers 32 to the tunable input circuit 34 of pushpull connected amplifier i2, also neutralized and also having a tunable output circuit 3S from which energy may be fed through suitable transmission lines 38 to a radiating antenna 40.

The action and use of chokes 42 and high frequency ley-passing condensers 44 are well known in the art and need not be discussed in detail here. 43, voltage dropping resistor 4l, and by-passing condensers 49, are sufficiently well known in the art so as not to warrant, as already indicated, added comment.

In practice, it is preferred that the transmitter l be divided into, as shown, three separate compartments 6, i3, i4, properly shielded to reduce feed back of radio frequency energy. For this purpose it is preferable that no more than a single amplifier, that is, an amplifier in which there is no frequency multiplication, be placed in any single compartment of the shielding.

The cathode energizing sources of the various electron discharge devices or tubes have been omitted for the sake of simplicity but they may be of the alternating or direct current type, or a combination of the two. Thus, for example, it may be found desirable to supply unidirectional current to the cathodes of the oscillator and first frequency multiplier and amplifier 4, and, for the ci remaining tubes of the system, alternating currents may be supplied to their respective cathodes for energization piuiposes.

The grid potentials for tubes 2, 4, 8 and I!! may be derived from potentiometer 52 grounded in- Similarly, the use of such chokes, as chokes Anode biasing i alternating currents through lines B4 from source 6D. Preferably, a separate rectier 66 also energized from source V6i] is used to supply anode potential to pushpull connected amplifier I 2.

It is to be noted, that deriving the biasing and anode potentials from a single source 60 renders the amplification of the entire system more nearly constant and independent of power supply fluctuations. For, with variations in voltage from source Si) there will be corresponding variations of gridand anode biasing potentials in all of the tubes, and consequently, in the event of say, increased voltage for some reason or other from source Gt, negative grid bias as well as; positive anode bias will be increased thereby tending to keep the relative potentials adjusted for optimum eiiiciency at all times.

it is to Vbe noted that grid leak arrangements in the form of condensers 50 and resistances 48 are used for the tubes. This is advantageous for the reason that should, for any reason, the radio frequency output from anyV stage vary above or below normal during operation, the bias on the succeeding stage is correspondingiy altered to maintain output from the succeeding stage more nearly constant. However, to depend upon condenser and grid leak bias alone for the tubes would be dangerous to the tubes in the event of failure Yof radio frequency input. Under such conditions, there would be a tendency,r for a strong unidirectional anode current iiowpand this would tend to cause rapid destruction of the tube due to high anode currents. Simple overload protective devices placed in the unidirectional energy leads will not prevent ruin of the tubes under such circumstances inasmuch as the unidirectional current drawn may not exceed. that during normai operation of the apparatus, but, the energy dissipation in the tubes is greatly increased due to the loss of high frequency output. Therefore, the loss of radio frequency input to one of the stages and, the iiow of normal unidirectional current therethrough, would require a high energy dissipation in the tubes because of the loss of output.

To remove the danger of this possibility while retaining the advantages of grid leak bias. it is to be noted that the various grids are connected through conductors such as conductors 68, 'IU and 'i2 to potentiometer 52 wherefrom sucient Xed bias is obtained to protect the tubes involved in the event that their input excitation fails. During high frequency operation, of course, the added negative biasing potential required is supplied by the grid leak and condenser arrangements 4B, 50.

In order to transmit code signals on the transmitter shown in Figure 2, a remotely controlled electromagnetic relay 14 having a movable armature 'I6 is provided. In the upper position of the armature 16, the grid'bias leads of tubes VIIJ are connected toa reiatively low negative potential Vpoint on potentiometer 52, thereby rendering the pushpull connected amplifiers conductive and thereby causing radiation of high frequency energy from the antenna 40. ,For stopping the signal energy, the armature 'i6 is moved to its lower position whereby the grids of tubes il) are connected to a high negative point on the potentiometer 52 through resistance 13 and their anode currents are stopped, preventing amplification and delivery of power to the antenna. In this manner the oscillator 2 is allowed to oscillate continuously, and, the interposition of tubes 4, 8 prevents the varying loads from making themselves manifest upon the oscillator, thereby assisting in constant frequency operation of the oscillator tube 2.

. Of course, if desired, the system shown in Figure 2 may be modulated by telephone signals, in which case, various known arrangements may be used. Moreover, it is not necessary that rectifier 56 be of the three phase type, but, if found suitable, a single phase rectifier may be used, and connected across a single phase of the supply source B.

If desired, the anode potential of tubes l may be simultaneously reduced with the increased bias on the gridsthereof in a manner similar to the modulation scheme involving tubes 232 andresistance 236 of Figure 6, a similar relay suchas 14 appropriately controlling the grid potentials on the tubes 232. It is to be understod, of course, that any combination of modulation schemes may be used such as the simultaneous variation in grid bias on tubes l0, and for example, the simul- These various combinations Will,.

are Wiring diagrams of the more important ele- Y ments of the transmitter shown schematicallyin Figure 3. As shown in Figure 3, the transmitter comprises a crystal controlled oscillator 80 followed by buffer or shock absorbing amplifier 82, two frequency multiplier stages B4, 86, Vthe latter also being used as a modulator and both multif pliers being used preferably as frequency doublers. Another stage 8S adapted to be used as a simple amplifier or, as indicated as a frequency tripler, and, a final amplifier stage 90 are provided. As indicated, the crystal controlled osciliator 80, buiier amplifier 82, and first frequency multiplier 84, may be placed safely within a single shielding compartment 92 without fear of parastage 90 should, of course, be placed with an in-VV dividual shielded compartment 93. Inasmuch as shielding is well known in the art, a further de,- scription of it is unnecessary here.Y

The tube vsizes indicated in Figure 3, and'also' in Figure l, are given merely by wayof example and are'not to be construed in any way limitative of the present invention. Attention is directed in particular to the second frequency multiplier same size and rating, such as that of stage 84 for example. And similarly, the frequency multiplier stage 88 is made considerably larger in size and rating than the prior stage 86 so that within the frequency multiplier 38 a considerable amount of amplification ensues.

a long chain of amplifiers, subject to parasitic oscillation and costly maintenance, for building up the energy to a value suiiicient to operate power amplifier 90, is eliminated.

By the use of amplicat Y tion within the stages 8S, 83, as already indicated,

The arrangement shown in Figure 3 is illustrated in greater detail in Figure 4. Regeneratively coupled electron discharge device oscillator is frequency controlled by either crystal 98 or i by suitable actuation of coupling or switching arrangement |92 which couples either crystal capacitively to the input electrodes of oscillator 8B. The purpose of using two crystals is, of course, to provide a space crystal or to vary the final output of the transmitter.

The crystals preferably are temperature controlled by any suitable temperature controlling apparatus diagrammatically indicated within rectangle ||l4 energized with heating energy from a suitable source |05.

The output circuit 03 is tuned substantially to the fundamental of the crystal placed in circuit with oscillator SB, and energy therein is fed through a blocking condenser lili to a buffer amplier 82 having a tunable output circuit H2 tuned also to substantially the fundamental frequency. To prevent parasitic oscillation generation or self oscillation, the buffer oscillator may be neutralized by the use of a suitable neutralizing condenser H as indicated, or, as illustrated in the transmitter shown in Figures 6 and 7 for example, tubes for that purpose may be made of the screen grid type. Similarly, for better control the crystal oscillator tube 8@ may be of the screen grid type or' of any multi-electrode type. The buffer amplifier, of course, acts to maintain constant load on the crystal oscillator preventing variations in load from making themselves felt upon the electrodes of the oscillator 86.

Output energy appearing in tunable circuit 5 I2 is fed to the input side of a first frequency multiplier, here indicated as a frequency doubler and amplifier 89, having a tunable output circuit H6 tuned to the second harmonic of the fundamental. As described in my Patent 1,878,308, frequency multiplier and amplifier Sil may be regeneratively coupled by means of a condenser H8 for energy of harmonic frequencies, but degeneratively coupled for energy of the fundamental frequency so that presence of energy of the fundamental frequency in the output circuit of tube 3d is effectively eliminated or reduced to a negligible value.

Output energy from the frequency doubler and amplifier de is fed through conductor a to frequency multiplier-amplifier modulator 86 shown in Figure lid. rIhe output circuit of tube Sii is tuned substantially to the fourth harmonic of the fundamental and -as illustrated is regeneratively connected for energy of the harmonic frequency 4f.

Keyed energy appearing in lines |22 may be used to remotely control the electromechanical relay |24 to alter the bias on the grid of tube 8% so that in its contacting position it will shift the grid voltage on tube 25 to such a value as to pass peaks of input current into the output circuit of tube 8G such that it is shock excited at the harmonic frequency as described more fully in my copending application just referred to. That is, in the closed position of relay |2, a less negative potential from conductor i2@ coupled to a suitable source of potential or potentiometer |28, is applied toy the grid of tube 86 through connections iS. In the relay open position, negative tapping point 32 biases the grid of tube 86 through resistance i3d to such an extent that no high frequency energy appears in the output circuit !36 of tube 36. In addition to the relay for controlling the transmitter there is provided switch |23 by means of which the control may be transferred from relay I2@ to the local telegraph key |25 for the use of the transmitter attendant.

Fourth harmonic sign-al modulated high frequency energy is fed inductively, as indicated, to lines 533 to the inout electrodes of pushpull connected frequency amplifier or frequency multiplier and amplifier 8&3 for the complete action of which reference is again made to my Patent #1,878,368. As shown, the stage 88 acts simply as an amplifier, but, when used as a frequency multiplier to produce energy three times that appearing in the input circuit hit or energy of a frequency |212 switches |42, lf'li are moved to their other position by uni-control means |46 so that a higher negative bias is applied to the grids of the pushpull connected tubes 8B and so that the portion of the output circuit |48 to the right of the dotted line lii, is cut out of circuit or short circuited away from the output electrodes of tubes 83. Under such circumstances, the output circuit is composed of inductances 52, |55 and condenser l, tuned to the twelfth harmonic of the fundamental as indicated. With the inclusion of condensers |53 and inductance coil |82, the entire output circuit is, of course, tuned to if and t e tubes 8B act as a simple amplifier.

When acting as a simple amplifier, output enc ergy from the output circuit of tubes 88 is fed through blocking condensers |62 and lines |64 to the input side of the power amplier 9D. When acting as a frequency tripler or multiplier as indicated, output energy from tubes 8S is fed inductively to secondary coil E53, to the lines |58 through blocking condensers im to the input side of the power amplifier 9S.

As described in my Patent Number 1,751,996, it is preferable that the output ends of the transmission lines |38, |56 and |553 are coupled to the respective input circuits such that the lines face a portion of the input circuit equivalent in value to the surge impedance of the line so that standing waves are not set up thereon.

The stage Si! or the tubes therein are almost always used, in order to obtain best overall efficiency for the entire transmitter, as a simple amplifier, provision being made to readily adjust the tuning of the amplifier to either one of the frequencies which it is desired to amplify. Thus, a uni-control switching means |12 is provided which places low frequency coils |90 and |82 in the input and output circuits respectively of tubes 9S, when stage 83 is used as an amplifier for energy of the lower frequency. Under such circumstances also, the transmission line |73 to the short wave or low wave length antenna is grounded by switches |88 as indicated.

A reverse movement of controlling member |12 will act to short circuit the long wave coil |82 out of circuit by switch |853, and, the relatively longer wave antenna transmission line will be grounded by the other position of switches E88. In the input circuit, the longer wave coil l@ will be remove-d from circuit, and, the shorter Wave coil l'/l will be placed in the circuit by the reverse setting of switch i212.

This uni-control arrangement for rapid change-over in amplifier frequency is more fully described and claimed in my co-pending application, Serial Number 189,152, filed May 5, 1927.

To prevent parasitic oscillation generation, the power amplifier tubes are neutralized by condensers i-i cross-connecting the terminals of may be energized by alternating currents.

separate rectiers as found necessary, but, in'

accordance with the present invention it is preferred that the separate rectiiiers be energized from a single alternating current source wheref by there is less tendency for changes in amplification with changes in supplied alternating voltages as would b-e the case where Various rectiners are supplied from different alternating sources.

Figure 5 is arblock diagram of still another form of transmitter, thevsizes ofthe tubes given being merely suggested and not in any way to be considered as limiting or binding the present invention thereto. The table shown in Figure 5a adjoining Figure 5, indicates a few of the many combinations of an ordinary amplifier and frequency multiplier which may be used in the arrangement shown in Figure 5. It is to be noted that wherever frequency multiplication occurs, the size and rating of the frequency multiplier are larger than the size and rating of a preceding amplifier tube. In this manner, as already thoroughly brought out hereinbefore, there is a considerable saving in the number of amplifiers required relative to arrangements heretofore known iny the art, Preferably, in the arrangement shown in Figure 5 screen grid tubes are used rather than resort to neutralization for the prevention of parasitic oscillations. In addition, the use of screen grid tubes allows of better control and especially so in the caseof the frcquency multipliers. In this larrangement also, each stage is separately shielded, and, the circuits may be so arranged that each of the stages may be used for amplification either with or without frequency multiplication.

In practice many combinations of ordinary amplifiers and frequency multipliers may be used depending upon desired constructional requirements and the' final value of frequency desired. Moreover, in'this transmitter any stage may be used as an ordinary amplifier or as a frequency multiplier, and, if from the standpoint of power efficiency, the amount of frequency multiplication in any one stageY is limited to tripling, and the last stage is always used as an ordinary amplifier, there are two-hundred and forty three (243) possible combinations of amplifier and frequency multiplication which may be used in the transmitter shown in Figure 5 without any change in the circuit arrangements.

Turning to Figure 6, the circuit diagram for the transmitter blocked out in Figure 5, an electron discharge device crystal controlled oscillator supplies energy from its output circuit 202 of fundamental frequency f to a buffer amplifier 2M preferably of the screen grid type. Fundamental frequency energy f is'fed from the output circuit 2% and buffer amplifier 264 to frequency multiplier and amplifier 208 whose Voutput circuit 2W is tuned to the second harmonic 2f. Energy from output circuit 2|() of second harmonic frequency is fed to a further Vamplifier 2|2 which in turn, supplies amplified By connecting coil 2|6'to the output circuit of tube 2|4, the output circuit willV be tuned to a frequency'f, and, by connecting coil V2| 8 to the output circuit ofthe tube 2M, the output circuit thereof will be tuned to a frequency 8f, in which case a slightly higher negative bias should be imparted to the grid adjacent the cathode of tube 2|4V to cause more eiiicient transformation of energy in its input circuit of the frequency 2f to energy three times that in its output circuit. Y

The pushpull connected screen grid tube stage 2|8 may be used as an ordinary amplier for amplifying the output from frequency multiplier and amplifier |24, or, when supplied with energy at its input side of a frequency 8f, its high frequency output coil 22@ may be placed in the circuit whereby the pushpull connected tubes 2|8 act as a frequency multiplier further multiplying frequency to a value sixteen times the fundamental frequency supplied by the crystal controlled oscillator.v The output of ,stage 2|8 may then be fed to the four tubes 222, 224, tubes 222 and tubes 224i being connected in parallel, and the parallelly connected tubes being connected in pushpull fashion and neutralized as shown for the use of suitable neutralizing condensers 226. Suitable connection may then be made to the output coil 228 by transmissionlines 23D to energize suitable antennae (not shown).

Modula-tion may be accomplished by the use of parallelly connected tubes 232 supplied at their input side with signaling potentials fromV transformer 232. Consequently, by Virtue of the connection of impedance 238 in the anode supply lead furnishing anode potential to tubes 232 and amplifier 2|2, the potential supplied toamplier 2|2 will vary inversely to the current drawn by the modulating tubes 232 as a result of which modulated currents will appear in the output circuit of amplifier 2 l2, which are further acted upon bythe following frequency multipliers and amplifiers before radiation over Ythe antenna. Of course, modulation may be accomplished by connecting conductors 238 to any one of the anode supply leads of the tubes shown, or, to any of the screen grids of the tubes and in practice the stage selected depends chiefly upon the character of the modulation. If the modulation is for telephone purposes it will usually be introduced in the anode or screen grid supply leads to sta-ge 2,!8 in order to obtain more faithful reproduction. If the modulation consists of telegraph keying only, Yor keying and tone modulation, it will usually be introduced in some earlier stage such as 2|4 or 2|2 becauseV ythese early stages require less modulating energy and potential. In the figure no arrangement for keying is shown but it is intended that tubes 232 serve this purpose also by having superimposed upon the alternating current from transformer 234 to the grids, suitable direct current potential variations by means of a relay or vacuum tubes which are not shown in the drawings. If desired the modulation of the grids of the modulator tubes may consist only of direct current fiuctuations in accordance with keying by telegraphic code. This will usually be the case where continuous wave telegraphy is desired. Y

The final power amplifier stage comprising tubes 222 and 224 may, of course, be ofthe screen grid type if desired, and, it should be clearly understood that any of the tubes in any of the systems shown may have a still greater number of electrodes, if found desirable.

Figure 7Vis a circuit diagram of ano-ther transconnected amplifier 256.

mitter which may be built in accordance with the principles of the present invention. Energy of fundamental frequency f is fed from a crystal controlled oscillator 243 to a screen grid electron discharge device frequency multiplier and amplifier 242. Modulation is introduced into its stage by the action of transformer 254 which algebra.- ically adds modulation potentials to the unidirectional potentials sup-plied to the anode of tube 242. Tube 242 is followed by a further frequency multiplier and amplifier 246 of larger size and rating than any of the preceding tubes Zeil, ft2 which supplies energy of multiplied frequency to the pushpull connected screen grid amplifier Ei whose output, as shown, is directly radiated from asuitable antenna 255i.

In Figure 8, modulation is introduced to the screen grid of a frequency multiplier 252 following a crystal controlled oscillator A and pushpull Depending upon signaling potentials introduced by transformer 253, variable currents are drawn by modulator tube 2353 connected across rectifier 252 in series with resistance 254 whereby, the positive potential applied to the screen grid of tube 22 is varied inversely to the current drawn by tube 265i. The modulated frequency multiplied energy from frequency multiplier-amplifier modulator 252, is fed to a pushpull connected amplifier 266 whose output is further frequency multiplied and amplied by a single tube screen grid frequency multiplier tube 263. 'I'he output of the latter tube is further amplified by pushpull connected amplier 2l@ energizing antenna 212 with the amplied frequency multiplied and modulated high frequency energy.

As previously explained in connection with Figure 6 it is to be understood that the modulation scheme shown in Figures 7 and 8 may have many modifications depending upon the character of modulation desired and the characteristics of the various parts brought together to form the coinplete transmitter. Thus the modulation may be introduced on the anodes, screen grids or control grids of any stage depending upon the results desired and telegraphic, facsimile, or other keying may be introduced at the same or different points. The circuits shown are merely examples of a few of the combinations in which my invention may be used.

In the arrangement shown in Figure 8, it should be noted that for the sake of simplicity, the neutralizing connections have been omitted from the pushpull connected amplifiers, if desired, may be made of the screen grid type, and which are alternated with single tube frequency multipliers and amplifiers of sufficient size and rating to introduce appreciable amplification as Well as frequency multiplication of the output of the preceding pushpull connected amplifier.

It would be impractical to illustrate and describe all of the various modifications of the pre"- ent invention Wlfn'ch would readily suggest themselves to those skilled in the art. Consequently it is to be clearly understood that the present than the discharge device of said oscillator coupled to the output of said oscillator for frequency multiplying and amplifying the oscillations produced thereby, a pair of pushpull connected electron discharge devices coupled to the output of said last named amplifying and frequency multiplying device and arranged to simultaneously frequency multiply and amplify the oscillations of said frequency multiplier, and a second pair of pushpull connected electron discharge devices coupled to the output of said last named pair of tubes and arranged to amplify the output of said pushpull connected frequency multiplier and amplifier arrangement of electron discharge devices, whereby oscillations of considerable frequency and amplitude are obtained with a minimum amount of apparatus.

2. In high frequency signaling apparatus, the combination of a crystal controlled master oscillator of the thermionic type, a single tube combined frequency multiplier and amplifier, a circuit tuned to the frequency of the master oscillator interposed between the master oscillator and the frequency multiplier for coupling the latter to the former, and an output circuit for said amplier and multiplier tuned to some multiple of the frequency of said tuned coupling circuit, whereby said second named tube frequency multiplies and ampiifies the output of said master osciliator, a

second single tube combined frequency multiplier n multiplier and amplifier interposed between said combined frequency multipliers and amplifiers, and an output circuit for said last mentioned combined multiplier and amplifier tuned to a multiple of the frequency of said last named tuned circuit whereby said last named combined multiplier and amplifier multiplies and amplifies the output of said first mentioned frequency multiplier and amplifier, an amplifier for amplifying the output of said last mentioned combined frequency multiplier and amplifier, and, an antenna coupled to said amplifier.

3. In high frequency electrical apparatus, the combination of a master oscillator of the crystal controlled thermionic type, a pushpull amplifier of the thermionic type having its input electrodes coupled to the output electrodes of said oscillator for amplifying the oscillations produced thereby, a single tube combined frequency multiplier and amplier having its input electrodes coupled to the output of said pushpull amplier, a pushpull amplifier of the thermionic type having its input electrodes coupled to the output electrodes of said last named combined frequency multiplier and amplifier for amplifying the oscillations in the output of said combined frequency multiplier and amplifier, a single tube combined frequency multiplier and amplifier of larger size and higher rating than the preceding tubes coupled to the output of said last mentioned pushpull amplier, a pushpull amplifier coupled to the output of said last named tube for amplifying the oscillations in the output of said last mentioned combined frequency multiplier and amplifier, and a load circuit coupled to the output of said last mentioned pushpull amplifier, each of said single tube combined frequency multipliers and amplifiers having an anode, a cathode, a plurality of auxiliary electrodes, an input circuit tuned to a predetermined frequency, and an output circuit tuned to a produced with minimumV apparatusand reaction between successive stages is prevented. Y .Y .4L Irr combination, a high frequencyelectricai Y signaling appaifatus, a master oscillatorof the thermionic type', an efficientY means forincreasingy the amplitude and frequency Yof the oscillations in said oscillator comprising, a plurality of combinedV frequency multipliersV and amplifiers successively coupled togethenjusuccesive combined frequency multipliers and amplifiers being of larger size and rating than piior'combined frequency multipliers and amplifiers, and an output circuit for the last mentioned combined frequency multiplier andamplif'ler, one or more of the tubes of said frequency multipliers and amplifiers having a screen grid therein to insure stable operation of said apparatus.

5. In apparatus foic transmitting high fre-g quency undulatory electrical currents, a control oscillator, an electron discharge device combinedqfrequeney multiplier and amplifier coupled to said Vcontrol oscillator, an electron discharge device amplifier coupled to said combinedY frequency multipiier and amplifier for amplifying energy from said combined frequency multiplier and amplifier, a rectifier for supplying anode potential to said combined frequency multiplier and amp-iifier, another rectifier for supplying anode potential to said electron discharge device amplifier, and af single source of alternating energy for energizing said rectifier, whereby eicient and stable operation with a minimum amount of' apparatus is obtained. 'f f 6. In vapparatus for relaying undulatory high frequency electrical currents, an electron discharge device having within an evacuated container, an anode a cathode and a grid, a potentiometersubjected to substantially unidirectional potentials, a connection between a point on said potentiometer and said cathode, a. connection between a point on said potentiometer, whichris negative relative tosaid first namedV point, and said grid, Varresistarrce in series in one of said connections, wherebym'in the presence of high frequency potentials applied to said grid appreciable grid current flows and said grid is maintained at a desired unidirectional potential, by the drop in potential through said resistance, and, in the absence of .said high frequency potentials and appreciable grid current, the potential derived from said potentiometer is sufcient to prevent unduly highunidirectional currents from flowing to the anode'Y of saidlelectron discharge device, a high frequericy choking inductance in said connection, and a high frequency bypass condenser conaected in shunt with said resistance and that po n of the potentiometer between said cath- Vodeand saidfgrid. f 7.jIn apparatus for undulatory electrical currents, an electron discharge device oscillator; an electron discharge device combined frequency Vmultiplier and amplifier coupled toV said oscillator for simultaneously amplifying and frequency multiplying energy from said oscillator, said electron discharge device frequency multiplier havingY within its evacuated container an anode a cathode a control grid and a screen grid which insures stable operation of Ysaid device, and means for subjecting said screen grid to modulating potentials whereby in the output circuit of said frequency multiplier there appears signal modulated frequency multiplied energy.

8. In a system for transmitting intelligence sapete fromxlo'ne geographically i situated, point n otherA by propagated electromagnetie wavesq derived from the flow of undulatory high frequency electrical energy operated upon in accordance withgthe, intelligence to be transmitted, amplifyingr apparatus for obtaining improved stability and freedom from parasitic oscillations comprising a chain of successive alternating current arnpliiierV stages, circuits for capacity neutralizing one o-r more of the stages whereby coupling be-` tween input and output circuits thereof is eliminated, means for obtaining frequency multiplication of alternating currents in one or more of the amplifierV stages, and means for protecting said tubes from overload including circuits for applying Va bias between the control grids and cathodes' which is determined in part by a` xed source and in part by the amplitude ofthe signal impressed on the respective control grids. n

9. In a system of the character described having a chain of alternating current electron discharge device amplifiers and combined amplifiers and frequency multipliers, the method Vof improving the stability and freedomrfrom the eects of power supply voltage variations ofsaid apparatus during operation which includes, applying'input energy of such magnitude to one of the stages so that limiting ensues whereby Variations in Ystrength of the 'input energy produces relatively littlefvariation instrength of the output Venergy of thatqstage, vand simultaneously amplifyingv and frequency multiplying the energy rej sulting Vfrom said limiting action.

l0. In apparatus of thecharacter described,

a crystal controlled electron discharge device oscillator producing energy of a fundamental frequency, a singletube electron Vdischarge device frequency multiplier and amplifier for combined frequency multiplying and amplifying the energy from said oscillator of fundamental frequency, a pushpull arrangement of electron discharge devices for simultaneously vfrequency multiplying Y and amplifying t output of said single tube combined frequency multiplier and amplifier, and

a pushpulharrangement of eleotrondischarge def vices coupied to said pushpull frequency multiplier, for VYamplifying the frequency multiplied Y energy from said pushpull connected electron discharge device frequency multiplier.

n11. In high frequency electrical apparatus, the i combined frequency multiplier and amplifier, the

tubes in each of said stages being ofa fsize greater than the tube inpreceding. stages, andV meansV whereby said lastnamed Vstage may be operated as an amplifier as a frequency multiplier including an output circuit comprising tuning reactances coupled to the output electrode of said last named tube, and switching means for changing the reactances in said output circuit.Y .l Y i; Y

12. In high frequency electrcalapparatus, the combination of a mastercscillator of the crystal fr I controlled thermionic type, a thermionic amplifier coupled thereto for amplifying the oscillations produced by said oscillator, a combined frequency multiplier and amplifier including a single tube coupled to said first named amplifier, a second combined frequency multiplier and amplifier including a single tube coupled to said last mentioned combined frequency multiplier and amplifier, an additional thermionic stage including a thermionic tube having an input circuit coupled to the output of said last named combined frequency multiplier and amplifier, the tubes in each of said stages being of a size greater than the tube in preceding stages, means whereby said last named stage may be operated as an amplifier or as a frequency multiplier including, an output circuit comprising tuning reactances coupled to the output electrode of said last named tube and switching means for changing the reactances in said output circuit, means for applying biasing potentials to the control grids of all of said tubes, and switching means for changing the valuei of the biasing potentials applied to the control grid of the tube in said last named stage when the reactance in the output circuit of said stage is changed.

13. In a high frequency electrical apparatus, the combination of a master oscillator of the crystal controlled thermionic type, a thermionic amplifier coupled thereto for amplifying the oscillations produced by said oscillator, a combined frequency multiplier and amplifier including a single tube coupled to said first named amplifier, a third amplifier stage including a single tube coupled to said last mentioned combined frequency multiplier and amplifier, an additional combined frequency multiplier and amplifier stage including a thermionic tube having an input circuit coupled to the output of said last named combined frequency multiplier and amplifier, the tubes in each of said stages being of a size greater than the tube in the preceding stage, a fifth thermionic stage having its input coupled to the output of said additional thermionic stage, said fifth thermionic stage comprising, a pair of thermionic tubes having input electrodes and output electrodes, a plurality of input circuits normally resonant at different frequencies, a plurality of output circuits normally resonant at different frequencies, and switching means for coupling predetermined sets of said input and output circuits to said input and output electrodes, whereby said last named stage amplifies the oscillations impressed on the input of the preceding stage coupled to said last named stage either at the fundamental frequency or a harmonic thereof.

14. In electrical apparatus of the character described, a control oscillator, a combined frequency multiplier and amplifier of the thermionic type coupled to said oscillator for simultaneously amplifying and frequency multiplying energy derived from said oscillator, a pair of pushpull connected electron discharge devices coupled to said amplifier for frequency multiplying and amplifying the frequency multiplied energy derived from said frequency multiplier and amplifier, a source of fixed potential connected between the grid and cathode of each of said tubes, and means for superimposing an additional bias on each of said fixed biases including a resistance in series in each of said connections.

l5. A signalling system including an oscillation generator comprising a thermionic tube having a control grid connected in a frequency determining circuit, including a piezo-electric crystal, said tube also including an anode and a cathode, a circuit connected to said anode and cathode of said tube, means to tune said circuit tothe frequency at which said crystal tends to oscillate due to the stored wave energy therein, an amplifying device comprising a second thermionic tube having anode, cathode and control grid, a reactance coupling said control grid tothe tunable output circuit of said oscillator tube, a tunable circuit coupled between the anode and cathode of said second named tube, an amplifying and frequency multiplying device comprising a third thermionic tube of greater power rating than said second named tube, said third named tube having an anode, cathode and control grid, a device coupling the control grid of said third named tube to the tunable circuit connected to the anode of said second named tube, an amplifier comprising a fourth thermionic tube of greater power rating than said third named tube, said last named tube having anode, cathode and control grid, a reactance coupling the control grid of said fourth named tube to the anode of said third named tube, and a Work circuit coupled to the anode of said fourth named tube.

CLARENCE W. HANSELL.

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