US1674505A - Telegraphic transmitter - Google Patents

Description

June 19, 1928.

E. W. ENGSTROM 'PBLEGRAPHIC TRANSMITTER Filed Feb. 11, 1927 Patented June 19 1928.

UNITED STATES 1,674,505 PATENT OFFICE.

mm W. nnos'rnou, or SCHENECTAIDY, NEW YORK, ASSIGNOB r0 ennnm unc- TRIG COMPANY, A CORPORATION OF NEW YORK.

TELEGBAPHIC TRANSMITTER.

Application filed February 11, 1927. Serial No. 167,568.

My invention relates to telegraphic transmitters employing vacuum tube oscillatlon generators in which theanode potential for the generator is supplied from any su1table source through appropriate smoothing means.

' In systems of this type and particularly where the anode potentlal is supplied through rectifying valves, it is common to employ as a smoothing means, condensers connected in shunt with the circuit and reactors connected in series with the circuit. Because ofthe useof shunt condensers in the smoothin system and because of the vary-- ing impe ance of the oscillation generator with keying, and particularly 1n high speed telegraphic transmitters where the anode current of the oscillation generator rapidly varies with keying, conditions for oscillatory transients exist and such transients occur at the points of changing current. The use of smoothing reactors in these systems is 11mited in that they delay the flow of direct current to the oscillation generator and'ln that they are conducive to the transient condition mentioned. This is particularly true if the smoothing reactor be connected on the load side of the last shunt condenser. In telegraphic transmitters of the type to be described, it is common to have the last element of the smoothin system consist of a shunt condenser and requently shunt condensers are relied upon altogether for the necessary smoothing. This, however, does not remedy the situation since a transient condition upon closing the signal key remains preventing satisfactory operation of the system, particularly at high speeds.

The object of my invention is to overcome the above mentioned disadvantages and to provide a transmitting system which, among other things, may be operated at high speeds, in which the transmitted signal is of desirable wave shape and in which the anode supply is substantially free from transient conditions.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 represents a transmitting circuit to which my invention has been applied and Figs. 2 and 3 show the effect of my invention upon the anode current characteristic of the oscillation enerator.

With reference to ig. 1 of the drawing, 1 indicates the usual three element electron discharge device which is employed as an oscillation generator having its anode and grid connected through condensers 2 to the oscillatory circuit 3 which is associated with the antenna or other load circuit 4. Connected to the grid circuit of this device is the circuit 5 in which is connected the keying device one side of which is' connected to ground or to cathode potential. This keying device is represented as made u of a condenser" with a contact making nected in shunt thereto, although any of the well-known keying devices may be employed.

The anode potential for the device 1 is' supplied from the alternating current source 7 through a transformer 8 and rectifyi valves 9. and 10, these valves being associafi in the circuit in a well-known manner. 11 represents a smoothing means such as a condenser which is connected directly across the direct current lines leading from the rectifying valves. Itfwill be understood, however, that my invention is not limited to this particular arrangement since it applies equally to other systems where smoothing means are employed. 12 is the usual radio frequency choke. Connected in the circuit between the smoothing means 11, and the oscillation generatorI empoy a reactance 14 for the purpose of eliminating transient or surge conditions. This reactance is made up of comparatively few turns of conducting wire wound upon an iron core having alow re: luctance flux path. With such a construction at the frequency of the usual ripple which exists in this circuit the device will have substantially no smooth effect but when a transient or surge con ition arises the inductance will diminish the amplitude of the transient as to substantially eliminate its undesirable effects u on the circuit.

The a vantages of a reactance of this typev may best be understood by reference to 2 and 3. In Fig. '2 I have shown a curve representing the characteristic of the plate current in the anode circuit of the device 1 before my reactance is inserted and Fig. 8

be sufiiciently great tosoey 6 conrepresents this same characteristic in a circuit in which my reactance is employed. In Fig.- 2, it will be noted that the'direct current upon the initial closing of the key 6 is several times greater than that of the normal current flowing when the contact is closed. This transient is usually of an oscillatory nature and of high frequency. It produces anunsatisfactory wave shape in the signal which is transmitted to the antenna andmay result in injury to the equipment. By the use of a reactance constructed as "above :I have found that it is' possible to eliminate this transient condition as is apparent from the characteristic shown in Fig; 3, and at the same time not incur the undesirable effects incident to the use of the usual smoothing reactors, as for example, transients in the circuit upon opening the key 6 andretardation in the flow of current to the anode of the device 1 upon the closing of the key. I 'prefer to term this reactance a surge reactor since by virtue of its construction its only effect in the circuit is during surge conditions.

Due to the capacity effect of this reactance it is desirable to connect it in the circuit between the radio frequency choke 12 and the potential source, thereby isolating it from the high frequency currents of the oscillation generator. For the same reason it may also be preferable to connectit in the grounded side of the circuit.v f

While I have illustrated and described a single embodiment of myinvention,- I do 'not wish to bellimited to the specific circuit arrangement shown, as it will be "apparent that many variations may be made in the circuit arrangement and the apparatus em-' .ployed without departing from the scope of my invention as set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent of theUnited States, is

1. In a telegraphic transmitter employing a vacuum tube oscillation generator having an anode, a source of potential for said anode, a smoothing system associated with said-source, of potential and a surge reactor connected between said 's'moothing system and said oscillation generator, said surge reactor comprising a coil of lowinductance wound upon a core of low reluctance, said inductance and reluctance being such as to produce no appreciable retarding effect upon the initiation of normal anode current,

whereby surges will be substantially eliminated. 4

2. In a telegraphic transmitter employ- ,ing a vacuum tube oscillation generator havc0 ing an anode a source of potential for said anode, smoothing means associated with said source of potential including shunt capacity and a surge reactor, connected in the circuit between said smoothin means and said os- 05 cillation generator, sai surge reactor compI'iSlllg a coil of low inductance wound upon a core of low reluctance, said inductance and reluctance bein such as to produce no appreciable retar 'ng effect upon the initiation of normal anode currentwhereby surges willv be substantially. eliminated 3. In a telegraphic transmitter employing a vacuum tube oscillation generator having an anode, a source of direct current potential for said anode comprising an alternating current source and rectifying means associated with said alternating current source, a smoothing condenser connected across the circuit of said rectifying means, and a surge reactor connected between said smoothing condenser and said oscillation generator, sa d surge reactor comprismg a coil of low Inductance wound upon a core of low reluctance, said inductance and s5 reluctance being such as toproduce no appreciable retarding effect upon the initiation of normal anode current, whereby surges will be substantiall eliminated.

4; In a telegrap ic transmitter em loy- 9ov ing a vacuum tube'oscillation generator ving an anode circuit and a grid 'circuit, a means in said grid circuit for keying said transmitter, a source of direct current potential for said anode circuit comprising an alternating current source and rectifying ,means associated w1th said alternating current source, a smoothing condenser connected across the circuit Of said rectifying means and a surge reactor con- 10o inductance andreluctance being such as to 108 produce no appreciable retarding efl'ectupon the intiation of normal 1 anode current,

whereby surges will be substantially elimi-. nated.

In witness whereof, I have hereunto set 1 10 my hand this 10th day of February, 1927.

ELDER W. ENGSTBOM I

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