US2123727A - Modulation circuit for retarding field generators - Google Patents

Description

July 12, 1938.

H. E. HOLLMANN MODULATION CIRCUIT FOR RETARDING FIELD GENERATORS Filed Oct. 25, 1934 MON/LA T/OA/ P07 5' N T/ALS MODULATION POTENTIALS INVENTOR HANS ERICH' HOLLMANN ATTO R N EY UNITED STATES PATENT OFFICE MODULATION CIRCUIT FOR RETARDING FIELD GENERATORS Hans Erich Hollmann, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Tclcgraphie m. b. H., Berlin, Germany, a corporation of Germany Application October 23, 1934, Serial No. 749,535 In Germany November 3, 1933 Claims. (c1..179 171);

It is known, in the prior art, that a generator notes the retarding field tube which excites a connected in a Barkhausen-Kurz type of retard- Lecher wire system L united with the grid and ing-field circuit arrangement is modulable with the anode in well-known manner. M denotes the relatively low alternating voltages and that the modulation transformer whose winding S1, as

5 modulator potential em is superposed upon the reabove pointed out, is included in the lead brought 5 tarding electrode potential Eb. While this method to the retarding field electrode so that apure insures satisfactory modulation, it nevertheless alternating voltage em becomes superposed upon involves the drawback thatthe modulating voltthe biasing voltage Eb of the retarding field elecage works upon the internal retarding resistance trode.. In order that the modulation potential em,

0f the retarding field generator; in other words, pursuant to the idea underlying this invention, 1 upon the resistance acting between the cathode may also be fed to the grid, a second secondary and the retarding field electrode. Since the latwinding S2 of the modulation transformer may be ter resistance amounts toabout 1000 ohms, this included in the grid lead. Transfer of current means a severe load for the source of the modulafor the modulation frequency may then be equaltion voltage which, in the majority of cases, conized and maintained constant by Virtue of the 15 sists of a transformer. In other words, although mutual inductance of the two windings S1 and S2, the voltages are inherently low, a considerable without any action being brought upon the priamount of modulation power must be provided. mary winding.

This drawback is obviated entirely by the pres- Another circuit scheme is shown in Fig. 3, in

ent invention. By the mere adoption of certain which the modulation potential em is imparted to 20 means and ways in the circuit organization, the grid by way of a suitable condenser C and is perfectly non-dissipative modulation of a retardprevented from leaking or draining away to the ing field generator is obtainable. The invention grid voltage source by the aid of the choke coil D is based upon the fact that the oscillator tube contained in the grid lead. In this circuit arof a retarding field generator operates inside the rangement the transfer of current is equalized 25 saturation region, so that the total electron emisbetween grid and retarding field electrode by way sion current is=i +ib, distributed over the reof C, and for this reason the bridging condenser tarding field electrode and the grid, is constant. must be chosen so large that it will still constitute Consequently, in the state of oscillation, the rea short-circuit even for the lowest modulation tarding field characteristic ib=f (eb), having an frequency. Hence, in audio frequency modula- 30 inverted image pattern, is transferred to the grid tion a condenser of a few microfarads will be reend in the very same manner as in the static charquired, whereas for radio frequency modulation, acteristics of the retading field tube. For insay with one intermediate carrier frequency, the stance, Fig. 1 shows the two statically plotted capacity of the turning bridge piece B will gencurrent characteristics of an oscillating retarding erally be suificient. In this instance, all that will 35 field transmitter, it and 21, being observed as a be necessary is the connection of the choke-coil D. function of the biasing retarding field voltage eb. What is claimed is:

According to this invention, the modulator volt- 1. An oscillation generator comprising an elecage cm is impressed not only upon the retarding tron discharge device having an anode, cathode field electrode, but, at the same time, also upon and a grid, means for supplying a positive po- 40 the grid. This means that operation takes place tential to said grid and a less positive potential not only upon the retarding field characteristic to said anode relative to said cathode, whereby ib=f (6b), but, at the same time, also on the grid there is obtained pendulum motion of electrons current characteristic ig=f (8b). In this case it about said grid, and means for supplying moduand i become added, resulting in the constant l-ating potentials co-phasally to said anode and 45 saturation current is, and the modulation voltage grid, the last said means comprising means for em, as a consequence, works upon the pure saturacausing a constant saturation electron fio-w from tion resistance of the tube. said cathode.

Fig. 1 shows curves explanatory of the com- 2. In a modulation circuit for a retarding field 0 ponent currents forming the total emission curtype generator, an electron discharge tube havrent. Figs. 2 and 3 show, schematically, two eming a cathode, an anode and a grid, means for bodiments of the invention. impressing a highly positive charge on said grid A circuit organization adapted to carry the relative to the charges on said cathode and said basic idea of the invention into practice is illusanode respectively, means for impressing simul- 5 trated in Fig. 2. Referring to the same, R detaneously upon said grid and upon said anode,

respectively, modulation voltages which are comaintaining a constant saturation electron flow from said cathode.

3. An oscillation generator comprising an electron discharge tube having a plate, a cathode and a grid, means for rendering the charge on said grid highly positive with respect to said cathode, means for maintaining a relatively small difierence of direct current potential between the cathode and the plate, means for producing a constant saturation electron flow from said cathode, and means for impressing modulation voltages co-phasally upon said grid and upon said plate while facilitating the operation of the next previously mentioned means.

4. A generator in accordance with claim 3 and having electrostatic coupling means between the grid and the plate for the transfer of modulating potentials to said grid, said coupling means having a low impedance to the band of frequencies of said modulating potentials.

5. An oscillation generator comprising an electron discharge tube having a cathode, a grid and a retarding electrode, means for maintaining a highly positive charge on said grid with respect to said cathode, means for maintaining a relatively small difference of direct current potential between the cathode and the retarding electrode, a transformer having a primary winding upon which modulation potentials may be impressed, and two secondary windings, one of said secondary windings being in circuit between the oathode and the grid and the other of said secondary windings being in circuit between the cathode and the retarding electrode, and a capacitor intercoupling the grid and the retarding electrode, said transformer in combination with said capacitor constituting means for maintaining a. constant amplitude of electronic emission from said cathode while impressing said modulation potentials co-phasally upon the electrodes of said tube.

HANS ERICH HOLLMANN.

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