US2253958A

US2253958A - Rotating radio beacon

Info

Publication number: US2253958A
Application number: US215102A
Authority: US
Inventors: David G C Luck
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1938-06-22
Filing date: 1938-06-22
Publication date: 1941-08-26
Anticipated expiration: 1958-08-26
Also published as: NL62090C

Description

Aug. 26, A1941.

n. G. c. LUCK MICROF/[UNE ROTATING RADIO BEACGN sPzscH Filed June 22, 193s PHE@ w n I 'f TED Po w51? bsc/LL/Wan F'mw. ,6

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[ILE/ER 1751775 Enom/Lara )ry/LIER (Aira F/L'rsn Las PHH'SE' IMD/61770)? David C. L aofi Bnuentor Cttorneg Patented Aug. 26, 1941 UNITED STATES PATENT OFFICE ROTATING RADIO BEACON David G. C. Luck, Haddon Heights, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June 22, 1938, Serial No. l215,102

(Cl. Z50-11) -6 Claims.

I, modulation. A non-directive wave is radiated from an antenna at the central point. The rotating wave and the non-directive wave combine to` establish a substantially cardioid eld -which rotates about the central point. 4The rotating field induces signal currents in a receiving antenna within the iield. The signal currents havev substantially a sinelwave form. with phase vary-v ing directly with received azimuth.

If the phase o'f the sine wave is determined, the bearing of the receiver with respect to the transmitter can be determined.y In order to make such determinations, it is proposed, intheabove mentioned` patent, to key olf both fields at the instant when the maximum of the cardioid passes through due North. In order to have a sharply defined reference signal the keyingshould be of very short duration. In some lnstallations abrupt keying is disadvantageous because the steep wave front of the reference'impulse corresponds to a wide. band-of frequencies, and a Wide bandv is either not available or may interfere with speech'modulations which may be applied to the carrier wave.

In the instant invention, it is proposed to vavoid the aforementioned diiiiculties .by establishing a double' modulation of the carrier `wave. The double modulation is equivalent to sub-carriers and their side bands which are arranged slightly beyond vthe speech frequency bands of the main carrier. The method of generating the reference phase'by `double modulation and receiving and demodulating will be morev fully discussed hereinafter.

Onel of the objects of this invention is to provide'means for double modulation in a rotating radio beacon transmitter wherebyy waves of varying andiixed` phases are established. 'An' other objectsisvv to provide means for receiving double modulation signals from a rotating beacon transmitter,l and to, derive therefrom currents of Y. t iixed and variable phases. Another object is to f Vprovidefmeans for establishing in a rotating radio fieldv a fixed reference phase by means of subcarriers which arelmodulated. A further ob.

ject is to provide means for receiving a wave of variable phase and a carrier wave including a sub-carrier which includes la reference phase. A still further object is to provide improved means for transmitting from a rotating beacon station Waves including speech, fixed phaseandvariable phase signals, and for receiving and separating said signals. l

'I'he invention will be described by referring to the accompanying drawing in which Figure 1 is a block diagram illustrating one i embodiment of the invention;

vFigure 2 is an illustration ofthe carrier and sub-carrier; and

Figure 3 is a block diagram of one form of receiver embodied in the invention.

Referring to Fig. 1, an oscillator l is connected to a modulated power amplifier 3, which is coupled to an antenna 5. The oscillator is also connected to a pair of balanced'modulators 1, 9.

The balanced modulators are coupled to pairs of Adcock or other directive antennas Il, I3. The

' pliiier 3.

' w-i-(i-a) are established. The currents. alongv A second oscillator I5 is connected to a modulated amplifier Il which is connected to the modulated power amplifier 3. Speech signals may be applied to the microphone I9 and, through the speech amplifier 2|, to the modulated power am- A rthird oscillator 23 is connected through a phase shifter 22 to the modulated amplifier i 1, directly to the first balanced modulator l, and through the phase shifter 25 to the second balanced modulator 9,. The phase shifter 22 is adjusted to obtain a reference phase, corresponding, for example, to North.

The operation of the transmitter is as follows:

-The oscillator l generates carrier frequency currents of frequency'w which are amplified and modulated by currents from the second and third oscillators l5, 23 to thereby establish radio fre- The secondl and third oscilwith the carrier and the carrier i speech frequency currents, are applied to the central antenna 5 from ywhich non-directive fields are radiated. The third oscillator, which generates cur- 'There-- l modulators,

rents of frequency e, applies these currents in phase quadrature to the pairs of balanced modulators. The balanced modulators 1. 9 apply the currents of side band frequency wie: and

wia/90 and the speech frequencyside bands are illustrated in Fig. 2. It may be observed that the frequencies a are made lower than speech frequencies and the sub-carriers are higher than the frequencies required for speech transmission. The arrangement makes it practical to apply the rotating beacon and telephonie transmission to a single channel of comparatively narrow range.

The reception is effected by receiving the several signals on a radio receiver 21 which includes a demodulator, and an amplifier. The output of the amplifier is connected to a speech frequency filter 29, a second lter (ia) 3|, and third filter (a) 33. The output from the first filter 29 is applied to telephone receivers 35. The second filter 3| is connected to a demodulator 31 which is connected to a fourth filter (a) 39. The outputs from the third filter 33 and the fourth lter 39 are applied to a phase indicator 4|.

The operation of the receiver is as. follows:

- The received radio signals, after amplification,

demodulation and, if desired, further amplification, include currents of speech, double modulation (ia), and modulation (a) frequencies. The currents of the several frequencies are separated by

filters

29, 3|, 33 of appropriate design. The currents of double modulation (ia) are demodulated to obtain the current of fixed reference phase a, which after filtering is applied to the phase indicator. quency a are obtained from the rotating fields (wl-a) and the current oi.' reference phase is obtained from the non-directive double modulation (ia), it follows that one phase is fixed and the other phase is a function of the bearing of the receiver.

Thus a rotating radio beacon system has been described. The transmitter is characterized by its use of a single channel for transmitting speech, double modulation and a rotating cardioid field. The double modulation includes a component of fixed phase which serves as a reference for determining the phase of the rotating cardioid. Reception is obtained by filtering the several currents after demodulating in the receiver and effecting a second demodulation to derive the reference phase which is compared to the signal phase to determine bearing. The details of the oscillators, modulators, balanced filters and the like have been omitted because these elements are generally well known to those skilled in the art. Furthermore, reference is made tothe above mentioned patent which describes the preferred elements which have been employed in practice.

I claim as my invention:

1. The method of directional transmission which includes radiating a non-directive carrier wave, modulating said carrier with a modulated sub-carrier of frequencies beyond the speech fre- Since the currents of frequency band, further modulating said carrier waveby speech frequencies, and radiating a directive rotating field of the same carrier frequency as the non-directive carrier and rotating at the angular velocity of said sub-carrier modulation frequency.

2. The method of directional transmission which includes generating carrier frequency energy, modulating said energy with energy from a modulated sub-carrier of a frequency higher than speech frequencies, modulating said carrier with speech frequencies, radiating said double modulated carrier energy. deriving two phases of energy. of said sub-carrier modulation frequency, modulating said carrier frequency energy by said two phase energy and separately radiating said last mentioned energy in differently directed patterns.

3. 'Ihe method of`determining bearings by radio which includes radiating a non-directional carrier wave, modulating said wave by a modulated sub-carrier of a frequency higher than speech frequencies, further modulating said carrier wave with speech frequencies, rotating a radiated directional wave of the samevcarrier frequency as said non-directional carrier wave and rotating at the angular velocity of said subcarrier modulation frequency, receiving said non-directional and directional waves of the same carrier frequency, demodulating said waves, deriving from said demodulated waves. currents of speechV frequencies, deriving from said demodulated waves, currents of fixed reference phase, deriving from said demodulated waves, currents whose phase varies as a function of the bearing of the receiver and determining the difference of said phases.

4. In a rotating radio beacon the combination of a carrier frequency generator, means for modulating currents from said generator by modulated sub-carrier currents, said sub-carrier having a frequency higher than speech frequencies, and said modulation being lower than speech frequencies, means for modulating said carrier with speech frequencies, means for radiating said compoundly modulated carrier, means for establishing'currents of two phases of the frequency of said sub-carrier modulation, modulation means for modulating said carrier by said currents of two phases, and antennas for separately and directively radiating the last mentioned modulated carrier.

5. In a rotating radio beacon, a first generator of carrier frequency currents, a second generator of sub-carrier currents. a third generator of modulation frequency currents, a fourth generator of speech frequency currents, means for modulating said sub-carrier currents by said modulation frequency currents, means for modulating said carrier currents by said modulated subcarrier and speech frequency currents, a non-directive antenna, means for applying the .thus modulatedy carrier currents to said nondirective antenna, directive antennas, means for modulating said carrier frequency currents with said modulation frequency currents, and means for applying said last mentioned modulated carrier currents to said directive antennas for radiating therefrom a rotating field.

\ 6. In a beacon of the character of claim 5, a

phase shifter connected between said third generator and saidsub-carrier modulating means.

DAVID G. C. LUCK.