US2416327A - Transmitter system - Google Patents

Description

Feb. 25, 1947. E. LABlN TRANSMITTER SYSTEM Filed June 30, 1942 OSC L 4470B 6 m w Y @WW E 4 m3 5 I500 A MBB P M 7 a w 0 s 6 W w 0 L B n Q CONTEOL 1 2 2 F w R mm 4 AL Wu C fiw INVENTOR ATTORNEY Patented Feb. 25, 1947 TRANSMITTER SYSTEM Emile Labin, New York, N. Y., assignor to Federal Telephone and Radio Corporation, a corporation of Delaware Application June 30, 1942, Serial No. 449,091

13 Claims.

This application relates to transmitter systems and more particularly to a transmitter system designed to interfere with or jam undesired transmitting stations.

In the production of so-called jamming signals for the purpose of interfering with or blanketing out enemy transmissions, it is desirable that the transmitting signals completely blanket the range of audio signals so that no holes in the frequency spectrum remain which may be used for communication. In previously proposed systems, a certain regularity or rhythm of repetition of the signals tends to occur and in such systems is is quite likely that holes will be left in the spectrum through which communications can be carried on.

It is a principal object of my invention to provide an arrangement for producing variable audio frequency signals which will cover a broad band of frequencies and will be of such irregularity as to leave substantially no gap or holes in the transmission.

It is a further object of my invention to key a transmitter into oscillation by means of more or less randomly produced impulses to substantially blanket or jam the entire spectrum at this frequency range.

With these objects in view, my invention features a first relaxation oscillation generator having a predetermined time constant which is used to key a second relaxation oscillation generator having a much shorter time constant to produce impulses at varying rates over the desired audio frequency range. These varying impulses may then be used to key into operation a transmitter so that carrier frequency impulses of substantially the same rate of reproduction may be broadcast. I v

A better understanding of my invention as well as the objects and the features thereof may be had from the particular description thereof made with reference to the accompanying drawing in which:

Fig. 1 is a simplified circuit diagram of a system operating in accordance with my invention;

7 Fig. 2 is a set of curves used in explaining the operation of the system; and

Fig. 3 is a block illustration of a third oscillator which may be incorporated in the circuit of Fig. 1.-

Turning to Fig. 1, represents a transmitter orpower oscillator normally biased below the os-- cillation point. From this oscillator energy may be transmitted by antenna shown at l I. Transmitter -Ill is preferably tunable by means of the manual controlling means 12 so that it may be tuned to the carrier frequency or frequencies of the station or stations it is desired to jam. Transmitter I0 is arranged so that any signal voltage applied thereto will cause it to oscillate.

For producing the noise signals used to modulate oscillator I0, I provide a first relaxation oscillation generator comprising a gas tube l3, resistance R2 and condenser C2. A voltage is applied at terminals I4, l5. Current caused by this voltage flowing through resistance R2 charges condenser C2 until the potential on C2 is sufilcient to break down gas tube l3. This arrangement thus produces a saw-tooth wave form such as shown at 20 in Fig. 2. For the purposes of my invention other wave forms which have a sloping output voltage characteristic may be used as well as the saw-tooth waves. This saw-tooth wave form is generally quite regular in recurrence but since it is used for generating noise impulses in a manner to be later described, the voltage applied at l4, l5 may vary considerably and as a consequence produce variations in the recurrence rate without adversely affecting the final operation in any way. Preferably the periodicity of recurrence of the sloped wave impulses 20 is made in the order of between 2 and 5 repetitions per second.

A second relaxation oscillation generator comprising tube l6, resistance RI and a portion of resistance R2 and condenser Cl is supplied with voltage from the output of the first oscillation generator. The portion of resistance R2 is included so that immediately the condenser C2 is discharged, a small voltage is applied across Cl. Thus, the operation of the second relaxation oscillator is immediately started. RI, Cl and the tapped portion of resistance R2 which determine the time constant of the second oscillation generator are made much lower than the time constant of the first oscillation generator. Furthermore, tube I6 must be biased to break down at a much lower potential difference than tube l3 so that the oscillation generator produces impulses under the influence of the applied sloped voltage at a rate much higher than the periodicity of first relaxation oscillator. Preferably, the second relaxation oscillation generator is so constituted that the rate of production of saw tooth waves varies over a wide audio frequency range during the period of operation corresponding to a single period of curve 20. The range may suitably be such that the second oscillator varies between 300 and 1200 repetitions per second. Curve 2| of Fig. 2 illustrates the principle of operation a1- though, of course, in this curve the frequency of repetition of impulses has been greatly reduced in order to facilitate illustration. It should further be understood that in the various curves of Fig. 2 no attempt has been made to show relative magnitudes of the wave but merely to illustrate the principles of operation of my system. I

The impulses in the output of the second oscillator are applied to transmitter In so that this transmitter breaks into oscillation periodically at periods determined by the varying impulses. Thus, bursts of radio frequency energy are transmitted at audio frequency rates. It is clear that the keying impulses produced in the second oscillation generator are rich in harmonics so that a' repetition frequency varying between 300 and 1200 per second will serve to completely blanket the entire audio frequency band. Of course, it is possible if found necessary, to make these repetitions of signals cover a different frequency range, for example, up to 2000 to 10,000 cycles per second if the purpose of the equipment is to jam a signal which frequency components are in this spectrum. It can readily be seen that with this system as described substantially complete jamming of stations within the frequency range of the transmitter II! will be accomplished.

In operating jamming stations, it is often desirable to block the operation of the transmitter periodically in order to receive signals or for other purposes. This may be accomplished in the arrangement of my invention by supplying impulses over line H, Fig. 1, to the grid of tube t6. These impulses are of such a value as to bias thetube positively so that the gas tube IE will be conductive and that no substantial volt age can build up across condenser CI, therefore, there will be no output from tube I6 and no radio frequency power will be transmitted from the transmitter. In the proposed system, the transmitter is operated for two-thirds of the time so that the keying signal applied over line I! may berepresented by curve 22 of Fig. 2. When such keying does take place, this keying signal should be in no way synchronized with the sawtoothoscillations. Accordingly, the transmitter may be cut off at any point intermediate the peaks of any of the particular saw-tooth oscillations and may again be cut into surface at a point intermediate such peaks. This keying of thetransmitter may therefore phase shift impulses. In curve 23 is diagrammatically shown the effect that keying signal 22 may have on the peaks of curve 2|. During the first transmitting period, part 3| of curve 23 has substantially the same form as curve 2|, however, since the keying impulse comes intermediate the ends of the third saw-tooth impulse this third saw-tooth will be very small. 7 The second operative period 3| again occurs substantially in line with the impulses shown in curve 2|. However, during the period 32, it is seen that the keying impulse which renders the circuit operative comes intermediate'peaks of curve 2|. As a consequence, the saw tooth generator l6 will have to start from zero at this point. However, the saw-tooth voltage as can be seen from curve is not zero at this point so the first impulse in period 32 will be of a duration intermediate that of the first two impulses of curve 2| and its peak will be completely out of phase with the other impulses. Likewise, the following impulses during this period 32 will be of different length than from those shown in curve 2| and will all be consider- 4 ably out of phase therewith. Part 33 again happens to initiate impulses substantially in line with curve 2| and therefore the impulses are shown as being substantially the same shape and phase position.

It should be distinctly understood that in actual operation the impulses shown in curves 2| and 23 are short compared to those of curve 20. Also, it should be understood that since there is no control between the operation of the keying means I1 and the oscillation generators substantially random production of the impulses as to position and timing may result. Furthermore, if the voltage of the source applied between terminals M and I5 is poorly regulated so that the voltage applied to the first relaxation oscillator varies, then the controlling sloped waves 20 will vary in repetition period and the impulses produced in the second oscillator will be even more randomly spaced in time.

These variations could themselves be controlled by using instead of the D. C. voltage supply |4|5 another relaxation oscillator connected to the terminals |4|5 as shown in Fig. 3. In this manner a still more complex wave form would be generated. By using two time constants R1, C1 and R2, 02 and by interrupting the transmission at another rate with keying, the complexity of the wave obtained has proved to be adequate for speech jamming. In some other cases it could be useful to consider three (or even more) successive oscillators the lowest rate of change being say at 1 or 2 cycles per second, the intermediary at 10 to 30 and the hEhest at 300 to 1200. By choosing the values of preferred frequencies the wave shape generated can be adapted to jam with the maximum efficiency a given type of signal such as speech, telegraphy, facsimile, etc.

While it is considered that the primary use of the circuit of my invention is that of providing jamming signals for interfering with communications, it is clear that the principles of the generator described above may be applied to other purposes. For example, the complex output wave from the second relaxation generator could be used for synchronizing special apparatus for the purpose of maintaining secrecy or the wide band produced might be used in testing special equipment.

While I have-described above a particular apparatus embodying my invention, it should be distinctly understood that this description is made merely by way of example and is not intended as a definition of the scope thereof.

What is claimed is:

1. Means for producing varying impulses comprising a voltage source producing a varying out: put voltage having successive immediately recurring periods of the same predetermined duration during each of which the voltage increases substantially linearly until near the end of said period, an oscillator of the relaxation type having a time constant very short with respect to said predetermined periods, means for applying said output voltageto said oscillator to produce impulses of increasing frequency during each predetermined period, and means for'preventing the normal production of'impulses from said oscillator for a portion of a predetermined period.

2. Means for producing impulses varying in a substantially irregular manner over a frequency range, comprising a first oscillator of the relaxation type having a circuit with a predetermined time constant whereby the output voltage is of sloped wave form of relatively long period, a second oscillator of the relaxation type having a resistance-condenser circuit with a time constant very short with respect to said predetermined time constant, and means for applying said output voltage to the condenser in the circuit of said second oscillator to cause said condenser to charge and discharge at a constantly increasing rate to result in the production by said second oscillator of impulses having an increase in frequency corresponding to the rate of increase in the charge and discharge of said condenser.

3. Means for producing impulses according to claim 2 wherein said first time constant is such that the repetition of the sloped wave form is in the order of from 2 to 5 per second and the time constant of said second oscillator is such that the rates at which impulses are produced vary over a range of about 300 to 1200 per second.

4. Means for producing impulses according to claim 2 further comprising means for periodically interrupting the operation of said second oscillator.

5. A system for producing disturbances to substantially blanket undesired radio transmission comprising a transmitter tuned substantially to said undesired transmissions, said transmitter being normally biased below its oscillation point, a first oscillator of the relaxation type having a circuit with a predetermined time constant whereby the output voltage is of sloped wave form of relatively long period, a second oscillator of the relaxation type having a time constant very short with respect to said predetermined time constant, and means for applying said output voltage to said second oscillator to produce impulses at varying rates over said frequency range, and means for supplying said impulses to said transmitter to overcome its bias whereby radio frequency impulses corresponding to said impulses are transmitted.

6. A system according to claim 5 further comprising means for periodically interrupting operation of said second oscillator for predetermined periods, whereby transmission of said radio frequency impulses is periodically interrupted.

7. A system according to claim 5 wherein said first time constant is such that the repetition of the sloped wave form is in the order of from 2 to 5 per second and the time constant of said second oscillator is such that the rates at which impulses are produced vary over a range of about 300 to 1200 per second.

8. A system according to claim 5 further comprising means for variably tuning said transmitter to a desired operating frequency.

9. A system according to claim 5 further comprising a third oscillator of the relaxation type having a time constant greater than said first oscillator and means for supplying the output voltage from said third oscillator to said first oscillator to variably control the durations of said relatively long period.

10. In an impulse generator, a voltage source including means for building up voltage over a given period and means for reducing said voltage to a minimum within a very small fraction of said period when a predetermined value of said voltage has been attained for producing a wave output of substantially saw-tooth pattern wherein one edge of each saw-tooth is inclined representing a desired voltage variation and the other edge is substantially vertical representing an abrupt change in voltage, an oscillator of the relaxation type having a time constant very short with respect to a cycle of the said saw-tooth wave, and means for applying the voltage output from said source to said oscillator to produce impulses from said oscillator varying in frequency during each cycle of said saw-tooth wave substantially in proportion to the variation in voltage from said source.

11. In combination, a first gas-filled discharge device having a cathode and an anode, an input circuit therefor serially including said anode and cathode, a first resistance, and a source of direct current, a first condenser shunting said anode and cathode, a second gas-filled discharge device and a second resistance connected serially in the output of said first gas-filled discharge device, said second gas-filled discharge device also having an anode and a cathode, a second condenser shunting the anode and cathode of said second gas-filled discharge device, said second condenser and said second resistance having a time constant appreciably lower than the time constant of said first resistance and said first condenser, and a load in the output circuit of said second gas-filled discharge device.

12. The combination of claim 11 in which said second gas-filled discharge device is a triode, and further means for selectively biasing the grid of said triode positively to render said triode conductive and thus short-circuit said second condenser regardless of the electrical status of such second condenser.

13. A system for transmitting impulses varying in frequency comprising a constant unidirectional source of potential, a first condenser shunting said source and charged thereby, a first resistance in series with said source and said condenser, a first glow discharge tube having a predetermined break-down voltage in parallel with said first condenser, a second glow discharge tube in parallel with said first condenser and a selected portion of said first resistance, a second resistance in series with said tubes, a second condenser in parallel with said second glow discharge tube, said second condenser being of much smaller relative capacity than said first condenser, whereby a completion of the circuit from said source will cause said second condenser to charge to the breakdown voltage of said second tube and discharge therethrough to produce oscillations recurring at an increasing rate due to the concurrent increasing charge on said first condenser from said source, said first condenser charging to the breakdown voltage of said first tube only after a series of oscillations of increasing frequency are produced by said second tube, a transmitter, and means for applying the output of both said tubes to said transmitter.

ElVIILE LABIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,849,679 McCreary Mar. 15, 1932 1,893,029 Hund Jan. 3, 1933 2,230,243 Haffcke Feb. 4, 1941 2,235,667 Blount et a1 Mar. 18, 1941 2,294,411 Lay Sept. 1, 1942

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