US1921859A - Elimination of key shocks - Google Patents

Description

Aug. 8, 1933. H. RODER ELIMINATION OF KEY SHOCKS Filed Sept. 9, 1950 INVENTOR HANS RODE R BY ATTORNEY Patented Aug. 8, 1933 UNITED STATES PATENT FFICE ELIMINATION OF KEY SHOCKS Hans Roder, Scotia, N. Y., assignor to Tele funken Gesellsohaft fur Drahtlose Telegraphic m. b. H.,-Berlin, Germany, a Corporation of Germany Application September 9, 1930, Serial No. 480,714, and in Germany September 17, 1929 10 Claims.

means for eliminating key shocks which areproduced principally by the key operation of the plate circuit in transmitter tubes.

It-is known that when a receiver is mounted in the vicinity of a transmitter reception will be more or less seriously disturbed by the transmitter for each key signal in the latter, or each rise and fall of the signal will be audible in the ;receiver set in the form of a cracking noise Whichhas come to be known as key shocks. When the transmitter {and the receiver equipments are installed in one and the same room, and if furthermore the sending and the receiving antennae are mounted at relatively great proximity to each other, or even underneath each other, then reception will become practically impossible so long as the transmitter operates.

An attempt to obviate such key shocks by the provision of radio frequency stoppers in the receiver set is practically hopeless inasmuch as the rapid start of the oscillation phenomenon contains a practically continuous frequency spece trum. Hence, it is necessary to evolve ways and means for the transmitter which are adapted to limit this frequency spectrum. This result is attainable by so regulating the rise and fall of the key signals that the .signals are'rounded. V

The present invention has as its principal aim and object that of disclosing a method with this end in view which will be useful in connec-' tion with transmitter tube outfits which are imodulated by the interruption of the plate direct current lead.

The invention has been illustrated in several of its preferred forms by the accompanying drawing wherein:

Fig. 1 illustrates a self-excited tube set;

Fig. 2 illustrates a connection of resistors in the self-excited transmitter set; and,

Fig. 3 illustrates a modification of-Fig. 2 using the generator of Fig. 2 as a pilot for another generator tube which is connected with the transmitting antenna.

If in a self-excited transmitter set, as shown, for instance, by Fig. 1, the plate potential is broken, it is found that the ratio between plate direct current potential and plate direct current remains practically constant until the oscillations eventually break oil when voltage E assumes very low values. Hence, the generator tube could be conceived as being replaced by transmitter sharp edges of the.

the constant resistance RX. What logically follows from this consideration is this: when the current J is interrupted by the agency of the key T the condenser C which has been charged up to potential E will be discharged by way of the resistance RX. Hence, amplitude of the radio frequency oscillation falls oil in direct proportion to voltage E until it finally breaks off suddenly as soon as E has attained a certain low value. Now, this interruption would conceivably be audible in the receiver apparatus in the form of a key shock; but the fact is that in practice this stopping of the oscillation is free from any disturbing effect inasmuch as it happens in the presence of a very small radio frequency amplitude. But when closing or depressing the key T, the capacity C is charged up almost instantaneously, in other words, the oscillations are started with great precision. For the above purpose, the arrangement is unserviceable inasmuch as the rise is too hard, and the drop is too soft, considering the fact that Ex is a very high resistance.

The circuit scheme shown in Fig.2 illustrates one suitable system to carry out the aim and object of this invention. When closing the key T of the system shown by Fig. 2 a retarded charging up of the condenser C by way of resistance R takes place, or, in other words, the initiation of the oscillations is smooth. When opening or releasing the key, resistance R is cut in the circuit and the capacity C is discharged by wayof the resistances 'R'+Rx so that the discharge proceeds at a much faster rate than previously. The softness or smoothness with which the signals set in can be governed by the convenient selection of the value of resistances R and R and the capacity C.

In parallel connection to resistance R in the key circuit is a choke coil L adapted to avoid the fall 'of potential which otherwise would permanently occur across the terminals of the resistor R, without precluding the retarding influence of resistor B when closing the circuit. The choke L is so dimensioned that the system comprising R, L, C and BK will'remain aperiodic.

The above keying scheme, of course, could just as readily be connected in the plate lead of a separately or pilot exicted transmitter or else be included in the input stages of a separately-excited transmitter.

Using the generator tube connected in a Way as shown in Fig. 2 as a pilot generator for another "generator tube as shown in Fig. 3, then any sudden change in the antenna current is avoidable by imparting and applying to the grid of the output stage a negative grid biasing potential Ev. To be sure, the pilot tube breaks off suddenly and abruptly whenever the values of E and therefore also of Eg and Ev are low; but it can be so adjusted that the antenna curr nt will already have died down to zero value when the sudden change of Eg occurs.

Other modifications and changes may suggest themselves to those skilled in the art to which the invention relates, and I, therefore, believe myself to be entitled to make and use any and all or" such modifications as fairly fall within the spirit and scope of the hereinafter appended claims.

Having now described my invention, what. I claim and desire to secure by Letters Patent'is the following:

1. In combination with a keying system for avoiding key shocks in transmitter tubes wherein when the plate supply lead to the transmitter tube is opened bykeying the signal amplitude decreases and increases when the lead is closed keying, a resistor in series with the key when the lead is closed for retarding the rise of keyin impulses, a choke coil connected iii-parallel with said resistor for avoiding the drop in potential across the said resistor, a second resistor in series with said key when the plate supply lead is opened by keying for accelerating the decrease in keying impulses during periods when the key is opened, means for connecting the generator tube with a'second transmitting tube;

and means for applying a negative biasing poand inductively con 'cuits connected betvwen said electrodes comtential to the transmitting tube or" such value repeater having input and output electrodes and separated input and output circuits connected with said electrodes comprising, a source of direct current potential having one terminal connected directly to an output electrode, a key connected to the other output electrode, a contact associated with said key, a resistance and inductance connected in parallel between said contact and the other terminal of said source,

and a capacity connected in parallel with the impedance between the output electrodes of said tube.

3. Keying means for a thermionic relay tube having input and output electrodes and separated input and output circuits connected with said electrodes comprising, a source of direct current potential having oneterminal connected to an output electrode, a switch connectedto the other output electrode, a contact associated with said switch, a resistance and inductance connected in parall l between said contact and the other electrode oi aid source, and a second resistance havone terminal connected to one of said output electrodes and the other terminal connected with; a contact adjacent said switch whereby said resistance may be connected in parallel with the output electrodes of said tube;

4. Keying means a thermionic oscillation generator having in ut and output electrodes d input and output cirisiiig, aisource of direct current potential havsaid output electrodes, a capacity connects in parallel with the impedance between said output electrodes, a switch connected with one terg one'terminal connected directly to one of minal of said capacity, a pair of contacts, and means for retarding the rise in the potential applied to said output electrode and the charging rate oi said condenser connected in parallel with the impedance between the output electrodes of said tube including, an inductance and a resistance in parallel connected between one of said contacts and the other terminal or" said source, and means for increasing the disclrargingrateof said capacity comprising a resistance connected between the other of said contacts and the other terminal of said source.

5. Keying means to be used with thermionic repeaters having input and output electrodes and input and output circuits connected between said electrodes comprising, a source of direct current potential having one terminal connected to one of said output electrodes, a capacity connected in parallel with the impedance between said output electrodes, a switch connected with one terminal of said capacity, a pair of contacts, and means for retarding the rise in the potential applied to said output electrode and in the charging rate of said condenser connected in parallel with the impedance between the output electrodes of said tube including, an inductance'and a resistance in parallel connected between one of said contacts and the other terminal of said source, and means for increasing the discharging rate of said capacity comprising a resistance connected between the other of said contacts and the other terminal of said source.

6. Keying means for a thermionic oscillation generator having input and output electrodes and inductively coupled input and output circuits connected between said electrodes comprising, a source of direct current potential having one terminal connected to one of said output electrodes, a capacity connected in parallel with the impedance between said output electrodes, a switch connected with one terminal of said capacity, a pair of contacts, and means for retarding'the rise in the potential applied to said output electrode, and the charging rate of said con denser connected in parallel with the'impedance between the. output electrodes of said tube including, an inductance and- 'a resistance in parallel connected between one of said contacts and the other terminal of said source, means for increasing the discharging rate of said capacity comprising a resistance connected between the other or said contacts and the other terminal or" said source, and a thermionic repeater having its input circuit associated with the output circuit of said generator.

7. Transmitting means comprising, a thermionic oscillation generator; having its anode, cathode and control grid electrodes connected in oscillation circuits, means for interrupting said oscillations at signal frequency comprising a key having a signalling position and a spacing or non-signalling position, a source of direct current potential having one terminal connected to the cathode of saidoscillation generator, a first contact connected to the other terminal ofsaid source,'a connection between said key and the anode of said generator, means for preventing an abrupt increase in direct current potential on said anode when said key is in the, signalling position on said first contact comprising, a resistance connected between said first contact and said source, and means for insuring a rapid falling off of the oscillations generated when said key is in said spacing or non-signalling position comprising, a second resistance havingone terwhich a charging capacity is connected in parr allel with the anode to cathode impedance of said tube in either position of said key.

10. An arrangement as claimed in claim 7 in which an inductance is connected in parallel vwith said first named resistance and in which a charging condenser is connected in parallel with said second named resistance when said key is in the spacing or non-signalling position.

HANS RODER.

Images