US2425020A

US2425020A - Interference reducing radio system

Info

Publication number: US2425020A
Application number: US483360A
Authority: US
Inventors: Jr Norman H Young
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC; Federal Telephone and Radio Corp
Priority date: 1943-04-16
Filing date: 1943-04-16
Publication date: 1947-08-05
Anticipated expiration: 1964-08-05
Also published as: ES182136A1

Description

, ug 5 w?. N. H. YOUNG, JR

INTERFERENCE REDUCING RADIO SYSTEM Filed April 16,' 1943 2 Sheets-Sheet IN VEN TOR /vo/wA/v H. You/v6, Je.

Aug. 5, E947. N. H. YOUNG, JR 2,425,020

INTERFERENCE REDUGING RADIO sYsTEM fFiled April 1e, 194s 2 sneetssneet 2 Patented Aug. 5, 1947 DJ'IERFERENCE RE SYS signor to Federal ration, Newark, N. J.

DUCING RADIO TEM Norman H. Young, Jr., Jackson Telephone Heights,` N. Y., asand Radio Corpoa corporation of Delaware Application April 16, v194.3, Serial No. 483,360

12 Claims.

The present sion and with audio-frequency signals.

It is desirable to reduce the amplitude of any interfering or jamming waves which are received mixed with audio-freqency signals. The present invention provides a system whereby the audiofrequency signals are chopped up prior to transmission, and then restored at the receiving station to approximately their original form. However, any jamming waves also received are versing the phase of an audio-frequency signal and then transmitting this periodically phase-reversed signal.r

Another object of theinvention is to provide a method andfmeans for receiving a periodically phase-reversed signal and restoring the signal to its original form.

A further object of. the invention is to synchronize the. phase-reversing apparatus at the receiving. station with thephase-reversing apparatusV at the sending station through the use; of means controlled by the frequency of'phase reversal in the signal itself.

The invention has` asa still further object a method not periodically reversed in phase synchronously with the transmitted audio-frequency signal will be rendered ineffective to jam or interfere to any appreciable degree with such reversed audio signal.

Other-objects and advantages of the invention will be apparent from the following description of one embodiment ofthe invention and from the drawings, in which:

Fig. 1 is a block diagram of a transmitting and receiving circuit embodying one form of the present invention ;V

Fig. 2 is a set vof 'curves'illustrating the operation of the circuit of-Fig. 1;

Fig. 3 sagraph showing the operating characteristics ofone of the elements-of Fig. 1.

In thecircuit of Fig. 1, voice-frequency signals from a source 2 are applied over a normal audio-frequency amplier l to a phase-reversing devceicomposed of a phase` splitter Sand an electronic switch 7. The phase-splitter 3 is designed to produce two output waves, one of which is in phase` with-1 the input and the-other 180Pr out of phase, as shown in Fig. 2 (B).

Anoscillator 5 having afrequencyof, say 2 kc. is provided, `operating a square wave generator 6. The output waveforms of the oscillator and generator are shown in Fig. 2 (A).

The square wave output A from the generator S is used to control the operation ofthe electronic swtioh l.

When the square wave output A from generator 6 (having a 2 kc. frequency is applied to operate the electronic switch l, the switch will operate at the 2 kc, frequency to select alternately one of the two output waves from the phase splitter 3. In Fig. 2 the effect or control wave A on A. F. waves B is shown at C.

Thus due to wave A the phase of the audiofrequency signal from source 2 is reversed at the 2 kc. frequency of the oscillator 5 to result substantially in the waveform of Fig. 2 (C).

In Fig. Y2 (B) an audio wave of fairly low frequency has been illustrated, resulting in a rather high number of phase-reversals per cycle by the 2 kc. square wave A. If a higher frequency audio signal is taken as an example, then the numberv of phase reversals per cycle will lower. Nevertheless, if the the audio signal inv phase at least once each reversing wave.

cycle by the 2000 cycle This chopped wave is then apused to control a square wave generator I2 similar-` to the square wave-*generator 6 in the transmitter. The desired signals from the receiver detector l 'are appliedto an amplifier I4 consisting obviously be audio-frequency band hasa maximum of say, 3000 cycles, then will be chopped or reversedA 'the output of the relI8 so that the phase-reversed wave portions appearing there will be transposed into normal portions like those appearing on the lead I9. In order to make the average potential of the outputs the same, the condensers Ci and C2 and the resistors R1 and R2 are so dimensioned that the time constants of C1, R1 and C2, R2 of the output network are sufficiently long.

The electronic switch Il is similar in construction to the eelctronic switch 'i of the transmitter arrangement. The square wave output from generator I2 is applied to the electronic switch il to operate the switch synchronously with the frequency of phase-reversal of the transmitted signals, since the operating control frequency for the switch is derived from the transmitted signal itself.

Thus the switch il passes the output of lead I9 when the normally phased Wave portions are appearing thereon, while it passes the output of lead 20 when the phase-reversed portions, now transposed to normal phase portions, are appearing thereon. A phase control i3 may be inserted as shown between the square Wave generator l2 and the electronic switch l? for the purpose of properly phasing the square wave with respect to the transmitted reversals. The output of the electronic switch Il is then applied over a filter I5 to a sound reproducing device iS.

The wave received at l and partly reversed by the amplifier i6 and electronic switch I1 has the form shown in Fig. 2 (D), being substantially the form of the original wave before modification by the phase splitter 3 and electronic switch of the transmitter.

With the above arrangement any jamming signals which are received will be chopped up in the receiver and reduced primarily to a 2 kc. and 4 kc. frequency. This is true because the disclosed system consists essentially of two circuits each designed to reverse the phase of a signal at a predetermined frequency. If the signal reversed by one circuit is then synchronously reversed by the other circuit, the reversals cancel one another and the original signal results. However, any wave applied directly to the second reversing circuit without being previously reversed in phase Will be reversed in phase at the predetermined rate, and by proper filtering can be eliminated from the sound reproducting part of such second reversing circuit. If the normal transmitting band is arranged to run from, say, 200 cycles to 3000 cycles, then the filter l should have approximately the operating characteristics shown in Fig. 3, with a small portion of the band immediately adjacent the 2 kc. frequency being removed. This will not interfere with the intelligibility of the desired signals, but the amplitude of any jamming signals or other interference will be substantially reduced.

While I have described above the principles of my invention in connection with specific apparatus and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of my invention as set forth in the objects of my invention and the accompanying claims.

I claim:

1. In a radio circuit adapted to operate with an audio-frequency signal wave having periods of normally recurring phase reversal, the method which comprises deriving from said signal wave a .control variation synchronized with said periods of normal phase reversal, and controlling the modification of said signal Wave by said variation during said periods.

2. The method of receiving a normally periodically phase-reversed voice-frequencysignal which comprises separating from the received signal a wave indicative of the phase reversal frequency of the signal, and `employing the separated indicative Wave to control a modification of the received signal during the periods of normal phase reversal.

3. The method of receiving a normally periodically phase-reversed voice-frequency signal which comprises separating from the received signal a wave indicative of the phase-reversal frequency of the signal, employing the separated indicative wave to control the operating frequency of a wave generator, and then controlling a modification of the received signal by the output of the wave generator.

4. The method of claim 3, further .comprising controlling the phase of the Wave generator output with respect to the received signal.

5. In an interference-reducing radio circuit, means for receiving a periodically phase-reversed signal, a filter connected to said receiving means for obtaining from said signal a control wave having a frequency corresponding to the frequency of reversal in the phase of said signal, a phasereversing device connected to said receiving means, means for employing said control wave to control the operation of said reversing devlce, a second filter connected to the output of said reversing device, and means for reproducing the signal output of said second filter.

6. Apparatus for receiving a normally periodically phase-reversed audio-frequency signal, comprising a receiver, a filter connected to the output of said receiver, a phase-reversing apparatus connected to the output of said receiver, a wave generator controlled by the output of said filter and controlling said reversing apparatus, a second filter connected to the output of said reversing apparatus, and a sound-reproducing device receiving the output of said second filter.

7. The apparatus of claim 6, further comprising a phase shifter connected between said wave generator and said reversing apparatus.

8. In a radio circuit, a receiver and detector, a phase-reversing amplifier connected to said receiver and detector, a band-pass filter and limiter connected to said receiver and detector, a square- Wave generator, means for controlling said square-Wave generator by the output of said band pass filter and limiter, a phase control in the output of said square-wave generator, means commutating the output of said phase-reversing amplifier by the output of said square-Wave generator, a filter connected to said phase-reversing amplifier, and a sound-reproducing device connected to said filter. Y

9. In a signal system, a source of audio signals, means for periodically reversing the phase of said audio signals, means for controlling the frequency of operation of said phase-reversing means, means for transmitting and receiving said periodically phase-reversed signals, means for separating from said received signals a control variation varying in frequency synchronously with said first-mentioned means, means for periodically reversing the phase of said received signals, means for controlling the periods of operation of said last-mentioned means by said Ycontrol variation, and means for modifying said received and phase-reversed signals to cause them to correspond approximately to those produced by said source.

10. Apparatus for receiving a normally periodically phase-reversed audio-frequency signal, comprising a receiver and detector, a lter connected to the output of said receiver and detector, a multi-stage amplier connected to the output of said receiver and detector, said amplier including an electron discharge device having an anode, a cathode, and a grid in the last stage thereof, means for deriving the normally phased portions of the periodically phase-reversed audiofrequency signal output of said receiver and detector from the anode circuit of said electron discharge device, means for transposing into normally phased portions the phase-reversed portions of said audio-frequency signal appearing in the cathode circuit of said electron discharge device, an electronic switch selectively connected to the anode and cathode circuits of said electron discharge device, a square-wave generator, means for controlling the frequency of operation of said square-wave generator by the output of said lilter, a sound-reproducing device, means for controlling the operation of said electronic switch by the output of said square-wave generator to cause said switch to connect alternately said sound-reproducing device to the anode and cathode circuits of said electron discharge device, and a second lter connected between said sound-reproducing device and said electronic switch.

11. Communication system comprising, an alternating current signal source, means periodically reversing the phase of said signal source, a carrier wave source, a modulator fel by said carrier wave source, an electronic switch for alternatively connecting the outputs of said phase reversing means to said modulator for modulating said carrier, an oscillator, a square Wave generator controlled by said oscillator and keying said electronic switch, means for transmitting said modulated carrier, and receiver means including a demodulator, phase splitting means and a band-pass lter of the frequency characteristic of said oscillator both fed from said demodulator, signal reproducing means, a second electronic switch, alternatively interconnecting the outputs of said phase splitting means with said signal reproducingmeans, a second square wave generator connected to and controlled by the output of said band-pass filter, and means controlling the operation of said second electronic switch by said second square wave generator.

12. The combination according to claim 11, in which said phase splitting means comprises an amplifier, and means deriving signals of opposite phase from the output stage of said amplien NORMAN H. YOUNG, JR.

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

UNITED STATES PATENTS N umber- May 7, 1934