US2498731A

US2498731A - Radio jamming device

Info

Publication number: US2498731A
Application number: US574158A
Authority: US
Inventors: Wilkie Harry
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-01-23
Filing date: 1945-01-23
Publication date: 1950-02-28
Anticipated expiration: 1967-02-28

Description

Feb. 28, 1950 H. wlLKlE mno JAMMING DEVICE Filed Jan. 23, 1945 f Ww w W M m W M n mllllll 1m M M m lllll i l\ m .w M L Patented Feb. 28, 1950 UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) 3 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to radio jam'ming transmitters and more particularly to an improved jamming transmitter that provides irregular and unpredictable jamming transmission.

In the past the alteration of transmitted modulation frequencies in radio jamming transmitters has been commonly accomplished through variations, by means of a geared on-off switch, in the speed of an electrical motor that controlled the modulation frequencies of the jamming carrier. Devices of this type are cumbersome and when the motor stops the switches remain open and the device stops functioning.

In the art of jamming, it is a requisite that the interfering signal carrier have irregular characteristics that (a) preclude the forecasting of those characteristics by the enemy and the neutralization of the eifect of the jamming device; and (b) that increase the psychological effectiveness of the jamming, as is well known to the art.

The objects of the present invention comprise the provision of an improved radio energy jammer that provides a continuously and irregularly varying jamming signal carrier that cannot be predicted by the enemy; and a jammer that comprises a thermally actuated switch that is sufciently irregular in its actions to impart a desired irregularity tothe jamming transmission.

With the above and other objects in view which will be apparent to those who are informed in the field of jammers and jamming methods from the following discussion, an illustrative embodiment of the present invention is shown in the accompanying drawing wherein the gure discloses an addition to a known jammer circuit that embodies the present invention.

In the accompanying drawing a jamming radio transmitter I comprises a master oscillator 2 that has, as a part thereof, a continuously variable oscillator tank condenser or capacitor 3, the rotor blades of which are turned by being joined. to a shaft 4 of a motor 5. The motor 5 is energized from a power line 6 that has in series therebetween an irregularly operating, thermally actuated switch 1 of any suitable design for the intended purpose.

The thermally actuated switch l preferably is of the type wherein Contact points 8 and 9 are in engagement when the switch is not carrying current and are making and breaking contact at erratic time intervals when the switch is conducting current. Other devices that are similarly in a state of electrical or mechanical inequilibrium may be used to replace the bimetallic thermo-switch 1. The jamming transmitter l is provided with a sending antenna lll from which the device transmits a frequency modulated car- I'lel.

In operation, when the device is started by the energization of the motor 5, thru the cool contact points 8 and 9 of the switch l, the motor 5 and the rotor blades of the variable condenser 3 part of the oscillator 2 vary the frequency of the carrier that is emitted from the antenna I0. This variation is cyclic with the rotation of the condenser plates, and so in turn with the rotation of the motor. One cycle of modulation is completed in one cycle of rotation of the condenser 3. The assembly is such that the modulation characteristics of the carrier vary with motor speed or with the spinning rate of the rotary plates of the condenser 3. Variation in the spinning rate of the rotary plates of the condenser 3 varies the frequency of modulation of the transmitted carrier.

The motor 5 attains and holds its normal revolution rate momentarily during the period required for the temperature of the bimetallic element of the switch 1 to increase sufciently to cause the withdrawal of the point 8, that is carried by the bimetallic portion of the switch 1, from its mating contact 9. Upon the opening of the electrical connection between the points 8 and 9, the motor speed declines and the spinning rate of the rotors of the condenser 3 drops, thereby varying the frequency of the modulation of the jammer carrier emitted by the antenna l0.

As the bimetallic element of the switch 'l cools, the points 8 and 9 approach each other. When the points 8 and 9 arrive in electrically conductin'g contact, the motor 5 and the rotors of the variable condenser 3, pick up speed and increase the rate of the frequency of modulation cycle impressed on the transmitted carrier. The period of the modulation cycle varies with the varying spinning rate of the rotor plates of the condenser 3 thru a frequency range that is determined by the varying rate of the motor 5.

There is thus impressed an irregular wobbulation on the rate of the frequency modulation of the carrier, which is distracting to listen to and which is too complex to be successfully neutralized. It thus fullls the desired functions of a jamming signal. The frequency modulated output of the jamming transmitter has a modulation frequency that Varies suiliciently so that an 3 enemy cannot use audio lters as countermeasures. The use by an enemy of a filter that would be effective for all frequencies would likewise reject all signals.

The range of the changes in frequency in the output of the present jamming transmitter extends over the frequency coverage of the transmitter and is determined by the design of the rotating condenser 3. The modulation frequency is varied in an erratic manner thru the erratic operation of the thermal switch 1. Irregularities in the operation of the jamming transmitter that is comprehended hereby results from variations in contact operation due to the usual instabilities in operating conditions, such as vibrations, uctuations in power supply, and the like, as well as instabilities that are inherent in the thermal switch 'l itself.

It is to be understood that the particular assemblage of parts of the device that are shown and described herein have been submitted as an embodiment of one form of successfully operating jamming transmitter and that various modifications, substitutions and changes in the parts thereof may be made without departing from the true scope and spirit of this invention.

What I claim is:

1. In a radio transmitter of the character described, comprising in combination means for modulating the radio frequency of transmission, rotatable means for operating said modulating means in a cycle of modulation, and a thermoswitch in an electric input circuit of said rotatable means actuated by the current passing therethru whereby the rate of rotation oi said rotatable means is Varied erratically.

2. In a radio transmitter of the character described, comprising in combination means for varying the frequency of the radio transmission, an electric motor automatically operating said means in a cycle of modulation, and a normally closed thermo-switch in the electric input circuit of said motor actuated by the current passing therethru whereby the rate of rotation of said motor is made erratic.

3. In a radio transmitter of the character described comprising in combination means for frequency modulating the transmitted signal, cyclic means to vary said frequency modulating means and a thermo acting device in the input circuit of said cyclic means actuated by the energy input to said cyclic means, whereby the repetition rate of a cycle of said cyclic means is made erratic.

HARRY WILKIE.

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

UNITED STATES PATENTS Number Name Date 1,607,485 Schmidt Nov. 16, 1926 1,704,821 Brown Mar. 12, 1929 2,218,223 Usselman et al Oct. 15, 1940