US2099294A - Carrier wave modulation and suppression - Google Patents

Description

Nov. 16, 1937.

W. BUSCHBECK CARRIER WAVE MODULATION AND SUPPRESSION Filed 001:. 8, 1936 WAVE ENE/Q6) SOURCE SIDE BAA/D 01/ P r MODUMf/IVG T U POTENTIAL E SOURCE s/oE BAND 7 I 1 007/ 07 ENERGY l SOURCE E wwwv- MODUMT/IVG POTENTIAL 01/RCE\ {1/ .N 1 SIDE 1 -BAND c I our/ 07 WAVE ENERGY INVENTR SOURCE WERNER BUSCHBECK ATTORNEY I PatentedN 93 PATENT OFFICE CARRIER WAVE MODULATION AND v V SUPPRESSION ill-3 .Werner'Bu schbeck. Berlin, Germany, assignor to Telefunkcn 'Gesellschaft fur Drahtlose" Telegraphic m. b. H., Berlin, Germany, a corporation of Germany I 7 "Application October's, 1936, semi No. 104.631

In Germany September 30, 1935 a 5 Claims. "(01. 179- 171) The known and often used method of Carson for the suppression of the carrier wavein a modulated transmitter, which method provides .for differential p g. of twotubeswhich'are ,con-

5 .trolled cophasal for highfrequency and in phase opposition for low frequency (see Zenneck-Ru kop, Figure 645, page 708) whereby said tubes influence a common outputcircuit, presents great 7 difiiculties, due to; this latter point, concerning 10 the insuring of rectilinear modulation characteristics. It is knownthat there is required above all for the purpose of obtaining grid or plate modulation characteristics having a linear course, a constant external resistance having a high value 16 compared to the limiting resistance of the tube. But these requirements cannotbe realized in the type of construction known in the prior art for the reason that the external resistances vary.

back and forth from practicallyze'ro (in un- 20 modulated state) to the maximum value possi- 'ble (in the case of great modulation. depth) due to the coupling caused bythe output circuit common to both tubes which work in opposite relationship; The external resistance is equal 5 to zero in the un-modulated state since a current flows in the oscillation circuitwithout creating an ohmic counter-electromotive.force therein.

In line with this invention this condition is remedied by providing means whereby the two differential tubes or tube groups,'modulated in phase opposition, are de-coupled from each other in their plate connections as to this external resistive effect. To obtain twin-circuit arrangements, mutually uninfluenced, per tube I use separate plate oscillating circuits and a common bridge oscillating circuit the transmission of the side band frequencies being established by means of suitable coupling with the bridge wherein constant circuit attenuation is maintained.

The de-coupling of the circuits issuitably accomplished' through a bridge arrangement. As is'known', in double-fed bridge circuit schemes,

7 the bridge branches (arms) located opposite each other carry either the sum or difference of the currents. The next following stage is now connected or coupled to one of the two bridge 7 branches which carries the difference of the currents produced by the two tubes. Just which able because a symmetrical load is placed on the 1 control stage. H In describing my invention reference will be made to the attached drawing wherein Figures 1, 2, and3-each show modifications of my 'sup- 5 pressed carrier modulator. Figures 1 and 2 use the bridge arrangement to decouple the modulator'outputs while Figure 3 accomplishes this result without the bridge circuit. f

Figurel shows an embodiment by way of ex- 10 ample of the idea of the invention for grid potential modulation. Unessential details have been omitted. The two tubes I and II are excited cophasally by high frequency energy from a source of control potential such as an oscillator. The 15 grids'of I and II can also be modulated in phase opposition bylow frequency from a transformer T1. The output electrodes of the tubes I and II each feed independent oscillation circuits K1 and K2 respectively which in turn are coupled to a bridge arrangement Br the arms of which may for instance consist of capacities S and D. It is assumed that the coupling ofKi and K2 tothe bridge is adjusted for cophasal operation. In that case, for any instant the direction of the 25 currentsproduced by the two tube groups can be indicated, as shown by arrows. The next following stage is coupled to the bridge arm carrying the difference currents flowing in the arms D. Dissymmetries, for instance of the secondary side 30 of transformer Tr or of the characteristics of the two tubes may be equalized easily by the coupling adjustment of the bridge to the oscillation circuits K1 and K2, small phase errors may be eliminated in all cases by a subsequent tuning of the 35 output circuits. Thus, the carrier wave may be removed in an exact manner. which represents a great improvement in the one-side-band telephony as far as'subsequent filter circuits are concerned. 7

Since the output resistance of the modulated *tubes I and II is constant and of exactly measurutilized to a great extent. Furthermore, insuring actually rectilinear modulation characteristic curves means that the carrier wave vanishes not only in non-modulated state or for any exactly established degree of modulation, but in fact for I any desired degree of modulation below the allowable m'aximum limit the carrier output still remainsnegligibly small.

Particularly rectilinear modulation characteristics are insured in case of plate modulation of 5 7 screen grid tubes with simultaneous modulation of the screen grid. Figure 2 shows such an arrangement which otherwise corresponds to Figure 1.

It is also feasible to make use of other know types of modulation.

Figure 3 illustrates an arrangement wherein the de-coupling is accomplished without the use of a bridge. II is supplied with a separate plate oscillation circuit K1, K2. The circuits are so arranged thatno appreciable current flows in the coupled circuit S. v

This is especially the case in long waves since. in that case only a small wattless current flows through the grid to filament capacity of the output tube. In Figure 3 the input circuits may be formed exactly the same as in Figures 1 or 2.

I claim:

1. In a modulation system of the carrier wave suppression type comprising a pair of electron discharge-tubes of the multiple-electrode type and means for impressing wave energy to be modulated on like electrodes thereof'and'modulating energy -'on like electrodes thereo-fla bridge circuit having four arms, a couplingbetween the output electrodes of one of said tubes and pposed points on said bridge, a coupling between the output electrodes of the other of said tubes and other opposed points on said bridge and an output circuit coupled to one arm of said bridge.

2. In a modulation system of the carrier wave suppression type comprising a pair of electron In this modification each tube I and discharge tubes each having a control grid, a cathode, an anode, and auxiliary electrode and means for impressing wave energy to be modulated on said control grids and modulating energy on said anodes and auxiliary electrodes, a bridge circuit having 'four arms, a coupling between the anode and cathode of one of said tubes and opposing points on said bridge, a coupling between the anode and cathode of the other of said tubes and other opposed points on said bridge, and a utilization circuit coupled to one arm of said bridge.

3. In a modulation system of the carrier wave suppression type comprising a pair of electron discharge tubes each having input and output electrodes and means for impressing wave energy to be modulated on the input electrodes thereof and modulating energy on like electrodes thereof tuned circuits" connected with the output electrodes of each of said tubes, a bridge circuit having four arms, means coupling one of said tuned circuits to opposed points on said bridge, means coupling the other of said tuned circuits to other opposed points on -said bridge, and an output circuit coupled to one arm of said bridge. 7

4. A system as recited in claim 1 wherein the arms of said bridge each include capacitive reactance.

5. A system as recited in claim 2 wherein each arm of said bridge circuit includes capacitive reactance.

WERNER BUSCH-BECK'.

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