US1452064A - Radiotransmitter - Google Patents

Description

Apr. 17, 1923. 1,452,,Q64

V. BUSH RADIOTRANSMITTER Filed Nov 22 1918 :C A G Cane/77 in r/man/ J; (Wren/#7 an/nna Patented Apr. 17, 1923.

UNITED STATES earsur creme.

VANNEVAR BUSH, OF CHELSEA, MASSACHUSETTS, ASSIG-NOR TO AMERICAN RADIO &; RESEARCH CORPORATION, OF MEDFORD, MASSACHUSETTS, A CORPORATION OF DELAWARE.

RADIOTRANSMITTER.

Application filed November To all whom it may concern:

Be it known that I, .VANNEVAR BUsH, a citizen of the United States, residing at Chelsea, in the county of Suifolk and State of Massachusetts, have invented certain new and useful Improvements in Radiotransmitters; and I do hereby declare the following to be a full, clear, and exact description of the invention such as will-enable others skilled in the art to which it appertainsto make and use the same.

The present invention relates to radio transmitters having a primary or closed circuit of the impact type in which a series of unidirectional pulses are produced.

The best known types of commercial I transmitting apparatus embody an oscillating primary circuit having a spark gap and a secondary or antenna circuit tuned in resonance with the primary circuit and giving ofl' group trains of waves. The eficient operation of this type of transmitter is dependent directly upon an accurate tuning of the two circuits, as otherwise the transference of a substantial amount of energy to the antenna circuit is precluded and the radiated energy from this latter circuit de creases rapidly. This accurate tuning of the two circuits is diflicult to obtain under ordinary conditions, and this difficulty is more particularly evident in connection with ship, aeroplane, or portable installations where the antenna capacity changes rapidly.

The resurgence of current in a persistently oscillating primary circuit, moreover,tends to heat the gap and dissipate. the useful energy in the circuit, and attempts have been made to overcome these objectionable features by the'provision of a form of gap which quenches or damps the oscillation, and also by providing means for artificially dissipating the heat which is generated in the gap, However, the interposition of this quenched type of gap in the primary circuit renders even more acute the difliculties due to a de-tuning of the two circuits which causes an irregular quenching action and a variation from the desired smooth tune.

The ideal condition for a primary circuit is that in which a single loop of unidirectional current passes through the gap at each discharge of the condenser, thus ensuring the utilization of the maximum amount or energy and. permitting theefwient cow 22, 1918. Serial No. 263,757.

pling of two circuits which are not in resonance.

Repeated attempts have been made to secure a rectifying spark gap of this character which would cause the flow of a'unidirectional current in the primary circuit, but these constructions have universally failed to attain the desired result, either because of the complicated and intricate nature of the constructions employed and the extremely delicate adjustments required to cause the tapparatus to function in the desired manner, or because of a misunderstanding of the principles involved.

According to the present invention a flow of current is permitted when the gap initially breaks down and the condenser discharges, but thereafter the gap opens and a return flow of induced current is prevented. This object is accomplished by providing a primary circuit with a gap of high sparking length as compared with the potential employed and connecting in circuit therewith impedance which renders the potential gradient across the gap-highly nonuniform when this potential is slowly raised, but which does not affect the normal uniform gradient when the potential across the gap is raised with sufiicient rapidity. This impedance, which may be due either to resistance, inductance, capacity or a combination' of these in the circuit, has a time constant when. considered in connection with the capacity of the gap of such length that the resurgence of current through the gap at radio period is prevented and a pulsating unidirectional current produced. This pulsation of current in the primary circuit produces true impact excitation as distinguished from the operation of the quenched gap which merely serves to damp the oscillations in the primary circuit. In the present invention the primary and second ary circuits are closely coupled and detuned. that is. the two circuits do not have the same natural period of frequency. The free wave lengths of the primary and secondary circuits, however, may have a definite numerical relation so that the pulses in the primary circuit produce the maximum possible effect upon the secondary circuit.

A further feature of the invention consists in producing impact vexcitation in the primary circuit of a radi transmitter by first bringing a portion of the unit gaps of a series spark gap to the same potential and thereafter repeating the operation until all of the gaps of the series have been brought to v the same potential, breaking down the entire gap.

In the accompanying drawings illustrating the invention, Figure 1 illustrates diagrammatically a circuit provided with a resistance shunt acrossa portion or the unit gaps of a series gap; Fig. 2 illustrates a gap employing such a shunt in which the capacity between the plates has been increased by the connection of an auxiliary condenser; Fig. 3 shows a circuit having inductance shunted across a portion of the unit or aseries gap; Fig. 4- represcnts diagrammatically the current which flows in the primary circuit due to this form of gap upon each'discharge of the condenser; and Fig. 5

represents the character of current flow, in

the antenna circuit which is induced by each loop of current in the primary circuit. l The illustrated embodiment of the invention is shown in connection with a transmitting set having a generator D, a condenser C, the primary P of an oscillation trans former, and the secondary S of the oscillation transformer. The primary circuit is. provided'with a series gap G which, as shown in Fig. 1, may consist of eight unit gaps, and is preferably a gap which rapidly deionizes after the discharge of the spark. The potential supplied by the generator l) is insufficientto break down all of the unit gaps comprising the series, but is sufficient to break down part of these gaps A resistance r is accordingly shown connecting; middle plate of the series gap with one ,end, and in consequence the plates 1- and 5 are brought to approximately the same potential almost immediately after potential. is applied to the circuit, the length of time required for this depending upon the value of the resistance r and also upon the value of capacity between the difi'erent plates of the quenched gap. When the plates 1 to 5 Teach thesame potential the full. potential the generator D is applied across the reinaining four gaps 5 to 9, and since this pot'eiitial is sufficient to break down four gaps in the series a spark will then pass from plates 5 to 9. Thereupon the full potential is brought to bear across plates 1. to 5 by tin tue oi the fact that plates 5 to 9 have now been reduced to the same potential by the passage of the spark and the remainder of the gap willthen break down. thus causing: the passage of a spark across all of the gaps oi the series. When this occurs the condenser C discharges through the primanv P, of the oscillation transformer and the transmitter operates.

The flpw of the current thro this type of gap" is illustrated uiagrarniaatically in secondary circuit.

Fig. 4 andas indicated is confined to substantially a single loop of unidirectional current. This action creates a series of unidirectional pulses in the primary circuit and permits close coupling with the transference of a maximum amount ofenergy to the In order to accomplish this new and important result it is necessary, as stated previously that the time constant of the resistance 1 in connection with the capacity of the gap plates be small as compared with the tone period and large compared with the radio period of the circuit. During the comparatively long time which elapses :tor the charging'o't'the condenser U at audio frequency there will be suflicient leakage through the resistance r to properly distribute the potential gradient across the gap so that break-'dowu'will occur. After the break-down has occurred, however, and V the condenser C discharges through the primary P there is not sullicicnt time during the radio period for a similar break-down to take place in the reverse directioinowing to the fact that in this short interval there is an inappreciable tlowoft current throng the shunted mpedance which is entirely insuflicient to charge the capacity and de til ill]

wise cause a reverse'fio'w oi current encoun- I ters the full dielectric strength of the gap at uniform gradient. Since this reverse potential cannot possibly exceed the potential which was on the primary condenser just before break-down, tl1e gap will hence not break down in therever'se direction, and the primary current will bepulsating and unidirectional.

This action should not. be confused with that which would occurifthe shunt 2' were chosen at random and without reference to the gap capacity, gap of negl' ible capacity between plates isusecl, or it the shunt r is chosen too si'nallwith'reference to the gap capacity, the gradient across the gap will be non-uniform even when the potential across the gap rises at a rate determined by the radiot' equency. The gap will then break down again in the reverse direction ai tcr the initial pulse. and the t' marycurrent will be oscillstory and no I eating: The effect of introducii of this latter sort, which is not correctlated to the gap capacity and the audio and radio frequencies usechvcill hence be "1 ply to cause somewhat more rn iiid quench iii-i without essentially changing the urethral operation of the apparatus. i

The following illustrates one method cl estimating the resistance r for p roperopera lif of capacity of plates 1 to 5 in Fig. 1, and if .the tone period is 10* second'corresponding to a tone ire uenc otone thousand c cles then r must be designed so that the product middle plate shall follow the potential of the end plat-e with tone frequencies but at radio frequencies this action does not take place, rendering impossible a break-clown of the gap after the initial loop of primary current has passed therethrough and thus securing an impact excitation.

Figure 2 illustrates an arrangement of gap in which the capacity cot gaps 1 to 5 is increased bygthe condenser of capacity C connected in parallel therewith. The time constant of this gap is now 1" (0 C). This arrangement is sometimes advantageous since it allows a smaller value of resistance r to be used.

To illustrate this effect, suppose that the capacity C of 9 X 10* farads is added to the gap just considered. Then the total capacity (0 C) between 1 and 5 is 10- farads. If the time constant 1" (c O) is to have as before the value 10' second 1" should be given the value 10,000 ohms. It will not be necessary that 1 should have exactly this value, but merely that it should be approximately this value.

Figure 3 illustrates a further modification of a primarycircuit in which impedance 2 is connected in shunt across some of the unit gaps ofthe spark discharger, the time constant of the impedance 2 in connection with the capacity of the unshunted gap plates being so proportioned that a return flow of current may not pass through the gap at radio frequencies.

The drawings illustrate a tone circuit T which is included in the primary circuit when a direct current generator is employed and operates in the usual manner to produce a tone of any desired pitch in the emitted note.

It will be obvious to those skilled in the art that this type of gap may be employed to equal advantage in radio sets transmitting with a sustained oscillation from the antenna circuit as well as with sets which signal by the radiation of train group waves from the antenna circuit. When using the rectifying gap in the first instance, the fre quency of discharge is considerably above audible limits and may bear a predetermined relationship to the natural period of oscillation of the antenna circuit. How

ever, whether or not the discharges in the exciting circuit-do bear a certain definite numerical relation to the time period of the antenna circuit it is a characteristic of the unidirectional pulses set up in-the primary circuit that they invariably boost'the oscillations in the antenna circuit, the oscillations in the antenna circuit apparently triggering off these pulses at the proper time to invariably boost and not retard the oscillations. l Vhen this type of gap is employed in connection with transmitters which radiate waves of train group he quency from the antenna circuit it is necessary to so adjust the constants of the exciting and antenna circuits that they are not in. resonance with one another and have difterent natural periods of frequency.

What is claimed is:

1.. A spark gap for radio transmitting systems comprising a series of unit gaps and means connected therewith and having in conjunction with the capacity of the gap a time constant which is small compared with the audio period of the transmitting system and large compared with radio period of the transmitting system to cause the gap to be broken down by a potential which rises at audio frequencies but to be unaffected by the same potential rising across the gap at radio frequency.

2. A radio transmitter comprising a spark gap and impedance shunted around the gap and having in conjunction with the capacity of the gap 2. time constant which is small compared with the audio period of the transmitting circuit and large compared with the radio period of the circuit.

3. A radio transmitter, comprising a primary circuit including a generator, a primary condenser; a gap of high sparking length compared with the potential of the circuit, an impedance connected with the gap and having in connection with the capacity of the gap a time constant which is small compared to the audio period of the circuit and large compared to the radio period of the circuit to cause the flow of a unidirectional current in the circuit, and an antenna circuit coupled to the primary circuit.

4:. A radio transmitter, comprising a primary circuit which includes a series spark gap of high sparking length compared with the potential of the circuit, and impedance shunted across a portion of the unit gaps of the series gap to render the potential across the gap highly non-uniform, the impedance having in conjunction with the capacity of the gap a time constant which is small compared with the audio period of the circuit and large compared with the radio period.

5. A radio transmitter, comprising a primary circuit which includes agenerator, a

primary condenser, a spark gap of high sparking length compared With the potential of the circuit and consisting of a plurality of unit gaps, and impedance shunted across a portion of the unit gaps tocause the initial breaking down of partof the unitgaps of theseries gap and a final breaking down of all of the gaps in the series gap, the impedance having in conjunction with the capacity of the gap a time constant whichis small 10 compared with the audio period of the circuit and large compared With the radioperiod.

VANNEVAR BUSH.

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