US2536509A

US2536509A - Radio aid to navigation

Info

Publication number: US2536509A
Application number: US718219A
Authority: US
Inventors: David G C Luck
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1946-12-24
Filing date: 1946-12-24
Publication date: 1951-01-02
Anticipated expiration: 1968-01-02

Description

G. C. LUCK RADIO AID TO NAVIGATION Filed Dec. 24, 1946 2 Sheets-Sheet 1 l L SINGLE MOD. 8/05 541w MOD. l l r MOD L H f F 05c. 05c. IKC. aon/ 37 [37 F/LTER REC! L (B45353 ULATOR um) 4 PHASE 47 L 1 MTER PHASE F/LTEI? 0:72am? Assj-s ADJ 47 1 51 PHASE SH/FTEI? I Inventor DavJJ G. OLuck (Ittorncg Jan. 2, 1951 N D. e. c. LUCK 2,536,509

RADIO AID TO NAVIGATION Filed Dec. 24, 1946 2 Sheets-Sheet 2 LOWER UPPER 5/05 BAA/D FREQ M00 5/05 BAND M00. M00. M00.

JUMP

3nventor DavfdGZ Cluck Gttorneg Patented Jan. 2, 1951 UNITED STATES PATENT OFFICE RADIO AID T NAVIGATION David G. C. Luck, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 24,1946, Serial No. 718,219

6 Claims.

This invention relates to radio aids to navigation, and more particularly to improvements in to provide an omnidirectional radio range system 'aflording a higher degree of sensitivity or sharpness of bearing indication than has been achieved heretofore by omnidirectional ranges.

Another object of the invention is to provide a system of the described type which is readily adapted for direct visual indications of bearing, using substantially the same equipment ordinarily employed with conventional omnidirectional radio ranges.

The invention will be described with reference to the accompanying drawing, wherein:

Figure 1 is a schematic block diagram of a range transmitter system embodying the invention; Figures 2, 3, 4 and 5 are polar graphs showing typical radiation patterns produced in the operation of the system of Fig. 1; Figure 6 is a schematic block diagram of a typical omnidirectional radio range receiver which may be used in conjunction with the system of Fig. 1; and Figure '7 is a schematic diagram of a modification of the system of Fig. 1.

Refer to Figure 1. Two antennas I and 3, each by itself having a substantially circular directive pattern in the horizontal plane, are spaced horizontally apart by a distance nl, substantially greater than one wavelength A at the frequency at which the range is to operate. The antennas I and 3 may be in the form of vertical towers, as high as is structurally and economically feasible, and a ty ical spacing between them may be two wavelengths. For long-range operation, a low carrier frequency. of the order of 100 kilocycles per second, is preferred.

A radio frequency oscillator 5 is coupled to the antenna I through a modulator I, and to the antenna 3 through a single sideband modulator 9; The single sideband modulator 9 may comprise a balanced modulator and sideband filter, or anyother known apparatus providing suppression of the carrier and one sideband of a modulated radio frequency signal.

The modulation input terminals of the modulator 9 are connected to an oscillator I! which provides an output of alow audio frequency, for example 30 cycles per second. The oscillator II is also coupled to the modulation input termina of a third modulator I3. An oscillator I5, operating at an intermediate audio frequency such as 1000 cycles per second, is coupled through the modulator I3 to the modulation input terminals of the modulator I.

In the operation of the system of Figure 1, the antenna I radiates a signal comprising a kilocycle carrier modulated by a 1000 cycle subcarrier which is in turn modulated at 30 cycles per second. Both sidebands of the 100 kilocycle carrier are present, each including components differing from the carrier frequency by 1000 cycles per second, 1030 cycles per second, and 970 cycles per second.

The antenna 3 radiates only one sideband of the 100 kilocycle carrier modulated at 30 cycles per second. Assuming the lower sideband to be suppressed with the carrier in the modulator 9, the antenna 3 radiates a signal comprising a single component whose frequency is 100,030

cycles per second. This may be regarded as, and in fact is, the same thing as a 100 kilocycle signal which is being advanced in phase continuously at the rate of 10,800 per second or 360' degrees per cycle of the low frequency oscillator II.

The 100 kilocycle carrier signal radiated from the antenna I combines with the signal radiated from the antenna 3 to provide a space pattern which varies cyclically at 30 cycles per second. Referring to Figure 2, two antennas spaced two j wavelengths apart along the line 0--0 and excited in phase with each other will produce a radiation pattern substantially as illustrated,

comprising a broad lobe I7, three approximately evenly spaced narrow lobes I9, 2| and 23, another broad lobe 25 extending opposite the lobe I1, and

three

further lobes

21, 29 and 3! similar to and symmetrically disposed with respect to the lobes 23, 2| and I9 respectively.

Now, using the in-phase condition of Figure 2 as a starting point, let us advance the phase of the excitation of one of the antennas. As this is done, the lobes I9, 2I and 23 move counterclockwise and the

lobes

21, 29 and 3| move clockwise. The broad lobe I I gradually splits into two lobes I'! and I1" which move counterclockwise respectively, as indicated in Figure 3 and Fig-1 ure 4. Figure 3 shows the pattern obtained when the phase has advanced 90, and Figure 4 shows the condition.

As the right hand lobe II expands and splits, thelobe 25 contracts and disappears. Withcon- 'tiiiued advance in phase, the lobes 23 and 21 pattern which varies through the fonegoing: second, A radio receiver cycle 30- timesper within range of' the transmitter and at some definite azimuth with respect thereto (say along the dash line 35) will receive a signal. which.

varies cyclically in amplitude. This is caused by the passage of successive lobesthroughthe-lin-e 35;

Referring to Figures 2, 3 and 4, it isseen that the lobe 23 passes through the line 35, and will be followed by the lobes 2|, l9 and; I;T,, and. other subsequent lobes which develop from the right as. the phase advances. With a phase rotation, frequency of 30 cycles per second, the frequency of variationin. signal: amplitude. along: the line 35. (or other radial line from. the midpoint be tween the antennas if. and. 3-); i's:3Q-; oyclespci! SEC? and; It: may be: noted that: this: frequency of modulation caused.v by rotation. is not; a function of the antenna spacing.

Beferring'to Figure 6., a. suitable receiver-- and indicator system is; shown. This; is; substantially the; same as that commonly" used; with conven tionalomnidirectional radio: ranges except; for thecalibrations. Azreceivert -l.=,.tuned.inthepIese cnt: ejxamp-e; to; respond to 1:00. kilocyclesr has its. audio output circuit connected; to; two. narrow band passfiiters 3.91 and 4.1-... The filter; ca passes: the one kilocycle subcarrier, with: its 30, cycle modulation, which is; impressed on the-carrier radiated'by thetransm-itter anterma. t. Thefilter 4. I.-

4 lation depends on the bearing of the receiver from the transmitter. Thus, if the line 35 is moved clockwise from its illustrated position, the modulation phase will advance. However, the phase of the 30 cycle modulation of the 1000 cycle subcarrier is independent of azimuth. The difference in phase between the output of the filter H and the; output of; the rectifier 5,3 is accordingly 2; measure of the angle of the bearing line 35.

Suppose, for example, that the two modulations are in phase when the bearing line 35 coincides withthe, line 35 in Figure 2. Then, as the line 35 moves clockwise, the phase of one modulation passes. the; 30. cycle rotation; frequency module tion produced by the cyclical slipping of radiationl lobes across the line; between transmitter andreceiyer, as. described above.

The. modulated 1.0.00 cycle: output. of the filter 39.is.app1ied:to a demodulator lthwhichldemoduvlates the.- subcarrierto provide. a. constant. phase:

' 3.0. cycle output. This: is. applied to one pair of.

terminals of. av phase; meter 4.5., which m y hoof-f the wattmeter type or any other known, type, The. 3.0, cycle outputv of the. filter M. is, applied to the other. pair of termi-nalsoi. the. phase. meter. 45..

In addition. to. the phase meter. 45,. a. phase deviation indicator. may be; provided, compris ing. aphase detector 4.1 oonnectedto the, demodw later 4.3. and through. an. adjustable. phase. shifter. 49. to. the. filter Al. The. phase. detector 41' may; be. of. the. balanced. rectifier type, which provides. a D..-C.. output whose. magnitude. and polarity depends on the difference.- in. phase. between. the two. inputs. The output is. applied to. a. zero.- center D..-C... meter 51,. marked L-Rlike. the. visual course indicator. of a conventional radio. range.

The operation of the systemof. Figure. 6. in response. to. signals. of. the. type. transmitted by the system. of Figure 1 has follows I The. receiver and. indicator. system. is. carried. aboard an airplane or. other mobile; craft- .The. hearing from the. transmitter. must. be known. ap.-- proximately, or determined by auxiliary means such. as a. direction. finder, with an accuracy corresponding to or better than. the width. of. one. lobe (say ten degreesl.v Suppose. the mobile crait. to. be. on a line within five. degrees either way from the line 35 of Figures 2, 3,. 4 and. 5.

-As already described, the received. signal s modulated. in amplitude owing to. the. rotation of the directive pattern. The. hase of. this. modu x the advances-with respectt'o the other. The advance will baapproximately, though not necessarily exactly, roportional to the angle a. between the lines. 35.! and. When the line 35 reaches the line 35", the phase angle has advanced 360. Further clockwise motion of the line 35 will cause further phase rotation.

It; will? be evident: that the low: frequency: phase reference signal may be; impressed on. the.

carrier as a. frequency modulation, ratherthan. as; amplitude modulation. Thiszmay-afford somgre-L duction in crosstalk between the. two low fre.-. quency channels in thereceiyer system. Itisalso feasible to frequency-modulate the radio ire-e quency carrier with the modulated subcarpi'er. With such modulation, the pattern lobes will wobb e. ata 1600 cyce rateaboutzmean positions which move at 30- cycl'es as: described. This: will not affect the accuracy of the system, since the detector will integrate to provide 30: cycle output corresponding to the mean positions of the pattern lobes.

Since a change in bearing through an angle-ct 0' degrees will cause a change in phase through anangleof na d'egrees, where nis a constant. de-- pending on the spacing of the transmitter-antem has; theaecuracy of bearing determination within any sector (such as that between the lines 35'" and 35 may be approximatelyn times that which would be obtained with the usual single lobedpattern of prior art omnidirectional ranges. This results from the fact that the instrumental errors of the system are about the same in both cases, while the change in phase in response to a change in bearing is n times as great in the present-system as in previously used systems;

The price of increased accuracy in this caseis loss of uniqueness of indioation since the phase relations; appearing in the sector between the lines 3 5," and 35- of Figure 2 are, duplicated along corresponding bearin-glines in various'other similar sectors; The scale 45 may be. calibrated in terms of bearing angle, rather than in terms of" phaseangle, In this event, the scale must be replaced. with another when the desired course lies in a different, sector. Sectoridentification may be made by means of a direction finder on themobile. craft, as mentioned above, or by means of an auxiliary omnidirectional range of the single-lobed pattern. type- The, course deviation in ic t r s used. as. n. ordinary radio. range. sy tems to ctandmainr' tam. a prescribed radial. course. to r. rom. the

transmitter. station, The. phase. shifter 59.. is. ads iusted so. hat. the. ou p t. of. the. phase. d tector 41 is zero when the. craf s. on the. desired course! Deviation from course will cause the outputoi'. the. phase shifter 49, to, advancev or retreat in phase. with. respect. to the. output. of, the rectifier. 6'3... Thephase. detec or. will accordin ly provid an output whose polarity and. magnitude depends.

5 on the direcuii' fidtntfidiiiit '61 deviation, andthe deviation is indicated on the meter 5|.

The described transmitter system. does not-prO-" vide bearing information in all directions. Thus, along the line ---0- in Figures- 2 through 5, there is no rotary motion of the pattern lobes, but only expansion and contraction. Complete gangular cgverage through 360 degrees, if it is required, may be; obtained by providing another transrnitter system like that shown in Figure .l, but withthe antennas inaline at right angles .to fireme For clarity of description andsimplicity of i 1- lustration, it has been assumed that the antennas I and 3 are energized equally, causing the radiation patterns of Figures 2 through to go to zero between lobes. In actual practice, this would be undesirable because the percentage modulation of the reference phase signal would become infinite (i. e. the carrier would disappear) each time a pattern null swept through the position line 35. This difficulty is avoided very simply by supplying one antenna, for example the antenna 3, with less power than the other. The resulting radiation patterns will be similar to those shown, except that the minima, will be partial rather than complete.

With the two antenna systems of Figure 1 there is in addition to the above-described effects, an undesired amplitude modulation at 30 cycles of the 1000 cycle subcarrier. This may tend to introduce crosstalk between the two 30 cycle channels in the receiver-indicator system and cause error unless the

detectors

43 and 41 are completely non-responsive to amplitude variations.

Amplitude modulation of the subcarrier may be prevented by providing a third antenna and an additional single sideband modulator, as shown in Figure 7. As in the system of Figure 1, the antenna l is excited by the carrier oscillator 5 through the modulator 1, which impresses on the carrier at 1000 cycle subcarrier frequenc modulated at 30 cycles per second. Instead of the single antenna 3 of Figure 1, two

antennas

53 and 51 are provided, one on each side of the antenna l. The antenna 53 is energized by the 100 kilocycle source 5 through a single sideband modulator 59 controlled by the 30 cycle oscillator II, and transmits only the lower sideband, whose frequency is 99,970 cycles per second. The antenna 51 is similarly energized through a single sideband modulator 6| to transmit only the upper sideband of 100,030 cycles per second.

The radiation patterns produced bythe system of Figure 7 are substantially identical with those shown in Figures 2 through 5, providing the

antennas

53 and 5! are each two wavelengths from the central antenna I. The signal at the receiver is the same as described with reference to the system of Figure 1, except that the 1000 cycle subcarrier is purely frequency modulated. As in the system of Figure 1, it is preferable to divide the power unevenly between the central antenna I and the

side antennas

53 and 51 to fill in the nulls of the radiation patterns to some extent.

I claim as my invention:

l. A radio range transmitter system, including two omnidirectional antennas spaced horizontally from each other by a distance d, a Source of radio frequency energy of wavelength substantially less than d, means providing a composite modulation signal including a constantphase signal of relatively low audio frequency and a signal of substantially higher frequency r applying the resultant modulated en r y to one 'of said antennas, and means simultaneously'and: continuously changing the phase of another portion of said radio frequency energy at a constant rate of 360 per cycle of said low audio frequency signal and for applying the resultant phase-shifted radio frequency energy to the other of said antennas.

2; A radio range system including means generating in space a multiple-lobed radiation pattern which is substantially symmetrical with respect to a predetermined line and means moving the lobes on one side of said line clockwise continuously at a constant rate and moving the lobes on the other side of said line counterclockwise continuously at said constant rate, and means modulating the radiation in said pattern as a whole to provide a distinguishable phase reference signal of a frequency corresponding to the rate of motion of said lobes.

3. A radio range system including two antennas spaced apart horizontally, a source of radio frequency energy, a modulator connected between the first of said antennas and said source, a second source of A.-C. energy of a frequency substantially lower than that of said first source, a second modulator connected between said source and said first modulator, a third source of A.-C. energy of a frequency substantially lower than that of said second source and means for applying the output of said third source to said second modulator; a single sideband modulator connected between said first source and the second of said antennas, and means for applying the output of said third source to said single sideband modulator.

4. A radio range system including two horizontally spaced antennas, means exciting one of said antennas with a signal including a radio frequency carrier, means modulating said carrier by a subcarrier which is of substantially lower frequency than said carrier and means modulating said subcarrier by a constant frequency signal of still lower frequency, and single sideband modulating means exciting the other of said antennas with a signal sideband signal of radio frequency difl'ering in freouency from said carrier by the frequency of said lowest frequency signal.

5. A radio range system including a central antenna and two side antennas equally distant from said central antenna and on a line including said central antenna, a source of radio frequency signal of wavelength substantially less than the spacing between said antennas, a source of low frequency signal, means modulating said radio frequency signal with said low frequency si nal to provide separately the upper and lower sidebands of said radio frequency signal, means applying said upper and lower sidebands respectively to said two side antennas, a further source of Signal of intermediate frequency, means frequency modulating said last-mentioned signal with said low frequency signal to provide a com osite modulation signal, means modulating said radio frequency signal with said composite modulation signal, and means applying the resultant signal to said central antenna.

6. A radio range system including a central antenna and two side antennas, a source of radio frequency signal, a source of low frequency signal, means modulating said radio frequency signal with said low frequency signal to provide sanamtsly -ohe lower sidebamd "01 saidrasiin :frequency sigml, means applying said up= pier and awe: sidgbands respeetive'ly 11 sa d WQ side. antennas. a iumzhex m1me off'slg Q1 of in: immediate ue1;@y. mean n; said, afirmenti ned si n-a l with said. 21.9w itrequency si nal to "pr vid a om osite mo ulati n sigma}. means medula i g said rad o frequ ncy si n l with salid1comp ite:m du;a;tion Signal, and means app ying the resultant sign l to said central antenna. I

DAVID G. C. LUCK.

r 56? 1mm 13mm:

UNITED m Name 1311: Martin V V May 1, $928 *Campbefl a" me. 11),. "1911p Luck -Aug. 26, 19211 ul er 39311.30, 19;; OBrien Aug. 2-I, I946 Brunner MagrfZS, T9317 Number 116673792 -1 $138,522 2 ,25 3 i958 2 5 36853 1% 2,40 6 ,"BQB 2317.807 '2 5122,1 10

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