US1955095A - Telephony and telegraphy signaling device - Google Patents

Description

A ril 17, 1934. w. RUNGE TELEPHONY AND TELEGRAPHY SIGNALING DEVICE Filed March 15, 1933 AMPZF/[R 7 0/4 INVENTOR W/LHfLM 81/4 65 ATTORNEY Patented Apr. 17, 1934 PATENT OFFICE TELEPHONY AND TELEGRAPHY SIGNALING DEVICE Wilhelm Runge, Berlin, Germany, assignor to Telcfunken Gesellschaft fiir Drahtlose Telegraphic m. b. H., Berlin, Germany, a corporation of Germany Application March 15,

In Germany 3 Claims.

This invention relates to transmitting circuits for telegraphy and telephony operation which includes means for changing from one operation to the other without the use of switches and for increasing the bias on the grid of the power amplifier when telephony signals are to be used to decrease the poweroutput and permit full modulation to be obtained. When the device is again used for telegraphy the bias on the power amplifier is changed to a value which gives maximum power output for telegraphy signals.

The present invention also relates to a transmitting circuit for telephony with automatic means for automatically blocking the master oscillator and thereby interrupting transmission when no voice currents appear in the modulation transformer. This is accomplished by the use of a novel speech current rectifier connected with the modulation transformer and in the biasing circuit for the control grid of the master oscillator.

The novel features of my invention have been pointed out in the claims appended hereto.

The nature of the invention and the operation thereof will be better understood by reference to the drawing, in which:

Figure 1 shows an oscillator and amplifier connected in accordance with my novel invention to permit telegraphy or telephony signaling to be accomplished therein, and to change the output of the amplifier when the nature of the signaling is changed; while,

Figure 2 shows a novel circuit arrangement for biasing the oscillator to cut-off when no voice currents appear in the modulating frequency transformer.

For telephony operation the transmitter is adjusted in such a manner that during the unmodulated state the antenna current is equal to onehalf of the maximum antenna current, deliverable by the transmitter, so that during the modulation process the carrier may be varied between zero and twice its value. However, it is desirable, in the case of telegraphic transmission, to utilize the full power of the transmitter.

Transmitters intended for both telephonic and telegraphic transmission hitherto were equipped with a switch, so that in the one case the transmitter delivers full power, when the key is closed, whereas in the other case the transmitting current is only one-half of the full current. In case of a separately controlled transmitter with grid modulated master oscillator, this is obtained in that for telegraphy the grid bias of the power amplifier is adjusted for the maximum power 1933, Serial No. 660,877 March 4, 1932 output, whereas for telephony the grid bias is increased to such an extent, that only half the output current is produced.

In transmitters with automatic connection and disconnection of the carrier by the speech currents (carrier suppressor), it is possible in the manner described in the following, to produce a carrier of half the amplitude, when the transmitter is modulated by speech, whereas when the key is pressed, the maximum carrier current occurs, without the necessity of any additional switching-over arrangements from telephony to telegraphy operations respectively.

For this purpose the grid bias of the master oscillator 4 is supplied from a voltage divider 2, having a total potential difference which is higher than the biasing voltage (a to b) of the power amplifier 1, required for telephony operation. A small biasing voltage (0 to b) is supplied from the voltage divider 2 and applied to the grid 10 of the master oscillator 4 through the relay contact 3, whereby, when the contact of the relay 3 is closed, the tube 4 is blocked by the negative potential applied to its grid from 2. The winding 11 of relay 3 is energized by current from the modulation transformer 5 which serves for supplying a low frequency grid alternating voltage to the power amplifier 1 for the modulation of the transmitter, and to the rectifier 6 connected with the winding of 3. With no speech currents being applied, the relay contact 3 is closed in its zero position, such that negative potential on the grid of 4 blocks the oscillator 4. On the other hand, the relay key will be opened by the speech current, rectified by the rectifier 6, thus removing the negative potential from the grid of the master oscillator 4. The potential on the grid of 4 is now'determined by the resistance 8 and the direct current in the grid circuit. In this operating condition the transmitter operates as a telephony transmitter. The oscillations are of a value such that 1 supplies half the maximum antenna current, serving as a mean value to which it is demodulated by the speech voltage. The transmitter is modulated by speech currents from 5. a

In order to permit telegraphy keying of the full antenna current of the transmitter without switching operation, the key '7 is connected between the terminal of the voltage divider 2 connected to the cathode and the tap point supplying the biasing voltage for the relay 3. Closing of the key 7 shorts the portion 0 b of the divider 2. When no speech currents are applied, the closing of the key 7 has a double efiect:

(1) It short circuits the resistance 8 and part of 2 and removes the biasing voltage applied to the tube 4 across the closed relay 3 in such a manner that even with the relay being closed, the blocking of tube 4 is removed, and'the tube may start to oscillate.

(2) The grid biasing voltage of the master oscillator is decreased by the short circuiting of a portion of the voltage divider.

It is quite easy to design the voltage divider in such a manner as to produce the proper grid bias necessary for the maximum telegraphic current, when the key is pressed, whereas, with the key being open, the bias at the voltage divider corresponds to half the power output required for telephony transmission. In place of the relay 3 which in the present example is shown as a. contact relay, an electron relay may be substituted.

It is known to connect the carrier current of a telephony transmitter by the speechitself in such a manner that the transmitter is automatically disconnected during the speaking intervals. This arrangement has the advantage, as compared with transmitters with a continuously operating carrier in that reception is possible at the receiving end during the speech intervals without any difficulties and even on the same wave length. The circuits operate mostly in that the speech current is applied to several amplifying stages, parallel to the transmitter, operating upon a rectifier. The rectified current actuates a switching relay, performing the connection and disconnection of the carrier. It is, furthermore, known to substitute an electron tube for this relay. For instance, the discharge path of an additional three-electrode tube is inserted in the anode lead of the master oscillator, and the grid of this additional tube is negatively biased to such an extent as to block the tube. The lead from the anode current source to the master oscillator is thus interrupted. The blocking of thetube is then suspended by the speech current, after having been amplified and rectified, and

\ applied to the grid of the tube in such a manner that the master oscillator receives its anode voltage and isunable to start to oscillate.

This arrangement has a number of serious drawbacks:

(1) The necessary anode voltage is essentially higher than required by the master oscillator.

(2) The additional tube must carry the same anode current as the master tube, and, accordingl'y, must, at least, be of the same size as the master tube.

(3) Remainders of the speech alternating voltage, occurring after the rectifier applied to the additional tube, produce a modulation of the master oscillator besides the desired modulation of the power amplifier, resulting in variations of the frequency and distortions.

(4) The voltage variations applied to the additional tube necessary to effectively block the same, must be of the order of the grid amplitude of the master oscillator, i. e. must be comparatively high.

In the following a circuit will be described for overcoming the above mentioned disadvantages.

Tube 1, see Figure 2, serves as a self-exciting master oscillator, provided with a resistance 2, serving as grid current leak. The anode of the blocking tube 3 is connected with the terminal of the resistance 2. at the grid end. Its cathode is connected to an auxiliary negative voltage of high value, so as to completely block the tube 1.

The direct voltage obtained through rectification of the speech currents by means of rectifier 4 is applied to the grid cathode path of the tube 3 to serve as a negative bias. The operation of this circuit is as follows:

If no speech currents are applied to the rectifier 4, the grid bias of the tube 3 is zero. The tube, thus, has a high conductivity, delivering a sufiiciently negative voltage to the grid end of the resistance 2 so as to completely block the master oscillator 1 and prevent it from oscillating. If, on the other hand, tube 3 is blocked by the rectifier speech currents, the negative bias of tube 1 disappears, and'the master oscillator starts to oscillate. Once tube 3 has been blocked, the value of. the blocking voltage has no longer any influence upon the master oscillator. Thus, the master oscillator cannot be modulated directly by the speech current. The size of the tube 3, furthermore, is dependent only on the value of the grid current of the tube 1, and may, accordingly, be considerably smaller than the tube 1. Furthermore, in view of the small speech current required for the tube 3, a tube of lower anode voltage may be used, so that small voltages will sufiice for blocking tube 3.

Furthermore, this circuit does not require an additional anode voltage, in that the anode voltage for the blocking of tube 3 is supplied from the existing biasing source for the power amplifier 5.

Having thus described my invention, what I claim is:

1. Signaling apparatus comprising a thermionic oscillation generator, a power amplifier connected therewith, and means for operating said oscillator and amplifier at full load for sending out interrupted. continuous waves, or at reduced load for sending out modulated waves comprising a direct current circuit connected with the grid and cathode of said oscillator, a source of biasing potential and a source of modulating potentials connected with the grid and cathode of said amplifier, a normally closed switch connecting the grid and cathode of said oscillator with a portion of said biasing potential source, a key in shunt with said connection, and means actuated by the modulating potentials from said source for opening said normally closed switch.

2; Signaling apparatus comprising, a thermionic oscillation generator having control grid, anode and cathode connected in oscillation producing circuits and coupled to a modulator tube, said modulator tube having anode, cathode and grid electrodes, a direct current circuit connected between the grid and cathode of said thermionic oscillation generator, said circuit including a resistance through which direct current due to grid rectification fiows to produce a bias for said oscillation generator sufiicient to insure production of oscillations of reduced amplitude, a circuit including a normally closed switch and a source of direct current connected with the grid of said ioo oscillator to bias the same to cut-01f, a biasing V source including said first named source connected between the control grid and cathode of said modulator, a key for short-circuiting said first named source to reduce the bias on the grid of said oscillator and said modulator at keying frequency whereby said oscillation generator pro- Q telegraphy including, an oscillation generator tube having anode, cathode and control grid, a modulator tube having anode, cathode and control grid, a source of biasing potential having its positive terminal connected to the cathodes of said tubes and connections between points on said source and the control grids of said tubes, the

control grid of said oscillation generator being biased to cut-off by said source, a circuit for ap-

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