USRE24891E

USRE24891E - Palmer

Info

Publication number: USRE24891E
Authority: US
Priority date: 1947-10-28
Publication date: 1960-10-25
Also published as: GB671037A

Description

Oct. 25, 1960 w. PALMER Re. 24,891

CONTINUOUS WAVE NAVIGATION SYSTEM Original Filed Oct. 28, 1947 6 Sheets-Sheet 1 osc/LbqToR fr y 1p-19.1.

HE/z/VE fffz ,L /TER l-ll I 3 2 f 4 ff asc/LLAMA' fz @ZISTR f2 f2 #Wn l/l//NsLow PALMER Hf/fm A TTORNE Y Oct; 25, 1960 w. PALMER Re. 24,891

CONTINUOUS wAvE NAVIGATION SYSTEM Original Filed 001'.. 28, 1947 6 Sheets-Sheet 2 #fc5/VER I 56 PHHJE mTK Raf/vga gig-5M Z 2/ 7 um fg SENO I I I I I #uw T i? g Mom/410x f f3 RECEIVER @(5)- j 25 26 mm 27 #2.5mm (S-y) wifx-y) mm 26 71% W/X'Z) 535755? 211 2.9

1 I Y /Z) wf-T) OZ Wr X-z) L., F/L7 j #f my) Riff/YER 2 Y (1X1/)(2) "5mm" INVENTOR.

/NsLow PALMER Zw 5717EA' ATTORNEY Oct. 25, 1960 w. PALMER CONTINUOUS wAvx: NAvxGATIoN SYSTEM 6 Sheets-Sheet 3 Original Filed Oct. 28, 194'? fIL NQQQQ n Nk.,

Oct. 25, 1960 w. PALMER CONTINUOUS WAVE NAVIGATION SYSTEM Original Filed Oct. 28, 194'? 6 Sheets-Sheet 4 .mk uuml m. MR EE VM mM P WH o L 5 N MW Y B mm md wlww ATTORNEY Oct. 25, 1960 w. PALMER Re. 24,891

CONTINUOUS wAvE NAVIGATION SYSTEM INVENTOR. VV//VJL 0W PALME/e iwf/w.

A TTORNEY Oct. 25, 1960 w. PALMER Re. 24,891

' CONTINUOUS wAvE NAvIGA'rmN SYSTEM Original Filed Oct. 2B, 194'? 6 Sheets-Sheet 6 o MPL/HER P//HSL' T0 BE MIARS'URED f4 NVENTOR. W//vsLow PALMER 4 TTORNEY United States Patent O 24,891 CONTINUOUS WAVE NAVIGATION SYSTEM Winslow Palmer, West Hempstead, N.Y., assignor, by

mesne assignments, to Seismograph Service Corporation, Tulsa, Okla., a corporation of Delaware Original No. 2,611,127, dated Sept. 16, 1952, Ser.. No. 782,529, Oct. 28, 1947. Application for reissue July 9, 1953, Ser. No. 367,125

41 Claims. (Cl. 343-105) Matter enclosed in heavy brackets E appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

This invention relates to continuous wave radio position determining systems and more particularly to the elimination of cyclic ambiguity in such systems.

Radio navigation systems of the hyperbolic type, such as loran are well-known. In `these systems, a master and a slave station transmit pulses having a denite time relationship, and the difference of time of reception of the pulses is measured at the receiving location thereby establishing a hyperbo-lic locus of receiving positions relative to the location of the transmitter stations. Another combination of transmitting stations is utilized to provide an intersecting hyperbolic locus of positions and thereby a navigational tix.

Continuous Wave hyperbolic radio navigation systems `are also Well-known. In this type of system, the continuous wave signals have Ia denite phase relationship at the transmitting locations and the difference in phase at the receiving location is utilized to determine a. hyperbolic locus of positions relative to the transmitting loc-ations.

A serious diliiculty encountered with continuouswave systems is cyclic ambiguity. It is relatively easy to measure a difference in phase of less than one cycle but it is difficult to keep track of full cycle of phase dierence. In practical operation, it is quite necessary to resolve this cyclic ambiguit For example, at 2,000 kilocycles the Wavelength is 150 meters, a 'distance which is rapidly traversed by a fast moving aircraft.

Several methods have been proposed for resolving the cyclic ambiguity and they are as follows:

(l) Start from a known point and keep a continuous record of the change of position.

This method is practical and useful only for such purposes as surveying or reconnaissance where a minimum of receiving equipment is advantageous and a continuous record is kept. lt is also useful for low velocity travel such as marine navigation. In this method the calibrated instrument is set at the known starting position and is operated continuously and counts full cycle changes of phase. It is not suitable Where the operation is not continuous, and it may not be used for intermittent operation or where there is a probability of interruption of lthe use of the equipment.

(2) Limit the base lines between the transmitted locations to a half Wavelength.

This makes the total phase shift on going from one Station to another to be but one full cycle so that the system is substantially unambiguous. However, the short base line seriously reduces the accuracy and area of coverage of the system.

In this invention, the ambiguity is resolved by utilizing two channels slightly separated in frequency. The difference frequency between the channels may be etectively utilized as a second system Whose wavelength is long enough so that its phase shift is substantially unambigu- ICC ous. This longer wavelength system is used as a medium reading to resolve ambiguity in the fine high frequency readings. A further extension of the non-ambiguous range is obtained by using synchronized low frequency modulation signals on the above-mentioned pair of carrier channels in a manner that will be explained hereafter. These modulation frequencies may be utilized `as.' a third coarse system having a Wavelength long enough to resolve ambiguities in the medium system.

Accordingly, a principal object of the invention is to provide a continuous wave radio navigation system without cyclic ambiguity.

Another object of the invention is to provide a oon- Itinuous Wave radio hyperbolic navigation System without cyclic ambiguity, which may be operated intermittently.

Another object of the invention is to provide a continuous Wave, radio navigation system utilizing phase comparison of radio frequencies.

The invention also relates to the novel features or principles of the instrument-edities described herein, whether or not such are used for the stated objects, or in the stated elds or combinations, wherein Figs. l and 2 are diagrams illustrative of the principles of operation of the invention;

Fig. 3 is a schematic diagram illustrative of a continuous wave hyperbolic navigation system;

Figs. 4, 5 and 6 are schematic black diagrams illustrative of continuous [waves] wave hyperbolic navigation system;

Fig. 7 is a schematic block diagram illustrative of a continuous [waves] wave hyperbolic navigation system, without cyclic ambiguity;

Figs, 8 and 8A are schematic block diagrams of a continuous [waves] wave hyperbolic navigation system, without cyclic ambiguity;

Fig. 9 is an embodiment of phase meter apparatus adapted for use in the invention.

Figs. l0 and ll are vector diagrams illustrative of the operation of the phase meter of Fig. 9.

The operation of the system of this invention may best be understood by considering three basic principles, as follows:

PRINCIPLE I Given a transmitter at one location, radiating a Wave ea=e sin 21rft (1) the wave at the receiver is then es=e sin 21rf (t-R/v) (2) where R is the distance from the transmitter to the receiver and v is the propagation velocity of the Waves.

The wavelength (A) is given by Hence, the wave at the receiver lags the Wave at the transmitter by an angle equal to 21rR/)t radians.

PRINCIPLE II therefore When two Waves are mixed and the heterodyne beat is extracted, if either of the component waves is shifted in'phase through a certain angle, the beat frequency Will shift in phase through the same angle.

This may be proved as follows:

Consider a system as shown in Fig. 1. It consists of two oscillators, 1 and 2, generating different frequencies (f1.) and (f2). The wave from oscillator 1 may be representedy by a` vector El as,- in Fig; 2. The wave from oscilltor 2 may be considered to have the same frequency as the wave'from oscillator 1 with an additional continuous'change in phase at a rate equal to the diiference in frequency, or angular rate of 21r(f1f2) radians per second. The wavemay be represented by the vector Fm which rotates continuously relative to vector F1, as indicated by the arrow. v

The angular position of; vector. F2 in addition to the Steady mtatgn dueto thsffrefiuency d iierene, may be shifted an additional vamount kpb'y phase shifter 3 as indicated byy F2.

Tlczsumfof; the twcvcctors. F1 and F'z isv a vector whose magnitude may be found by the Iw of COSines:

of the variations of the magnitude of the sum vector Fl-{TFZ due to the rotation and shiftin phase of f'g relathe phase of `the heter-odyne beat tive to fll' Therefore, q varies by they angle @exactly asthe phase of Fz varies bythe angle 95 relativeto F2 and F1.

PRINCIPLE III @modulated wave is. transmitted, the phase of` the modulation frequency wave, when demodulated at the reeeiver,V lags themodula-tion frequency wave at the transmitter, byan` angle equal to the number of,wave lengths of the modulation frequency between thetrans mitter and the receiver.`

Thismay beshown asV follows:

A modulated wave may be represented by the equation where.

fc is lthe carrier radliofrequency and fili'. is fllfsdilat'ifl' ff'saueacy At the receiver the waves will be retarded by the time of travel (R/v) between: transmitter and receiver what@ R=,t1 1, distance, and

v=the velocity of propagation. Hansa .at th@ receiver.

e,=E,r11-m sin 21rfm(t-R/v)] sin frzfcu--Rf/v)` (7) A linear detector is not affected by the phaseV of the carrier, hence, the -demodulated wave em will have the ffml.

clpv=rnEr` ,sinv [21rfmt-21rR/m] since mT-V/fm (9) Hence, the phase ,of ther, modulation frequency at the receiver will be retarded by 21rR/ radians relative to the phase, of the ,modulation at the transmitter.

Referring to Fig..3 there is shown an embodiment of area they are ),toserve, define lines of position as contours` of constantL ph,ase,differene between the, beatr frequency',

waves directly'obtaned, :mining thesignalsyfrom Jthe from (a) by only a fraction of a percent.

A-t station A there is a4 receiver 12 that receives both frequency (a) and frequency (b), beats them together, extracts the beat lfrequency (a-lb)` and modulates a third transmitter D, with the beat frequency, by means of modulator 13. Transmitters A and D are coupled together and, to antenna 1L by means of coupler 9.

The. receiver apparatus, at Sf, the position to be determined, contains two radio frequency receivers. Receiver 16 receives frequencies (a)A and (b), beats them together and extracts the beat frequency Wave. Receiver llreceives the carrier frequency (d) and its modulation and extracts the modulation frequency. A phase detector 18 then measures the phase angle between the directly derived beat frequency, and the reference modulation heat,l frequency..` The phase angle may be automatically indicated as follo-ws: the phase detector 18 generates a voltage proportionalto the cosine of the phase diierencg andfthis `voltage isv fed toservo 19 which turns the phase shifter. 20 in` such a manner as to reduce the phase difference to Calibrated indicator 21, which may be a, mechanical counter device, is geared to the- Shaft ofy servo 1,9, and thereby indicates continuously and automatically the phase difference.

The phase,v angle difference is a function of the positionoi the receiver, and depends upon the diierence of thefdstanees from thereceiver at S, to the transmitters `at A and B', respectively. Thiscan be shown as follsvs.

` The waves received` at arelresp'ectively en andl eb where e.,=e,l sin 21ra(t-Ra/C) (10) and;

where R.,L andA Rb areA the` respective distances to A B Thephase .angle 9 is measured :at the phase detector 18..`

between..themodulation. frequency and the beat frequency. and is obtained bytaking the difference of theV arguments in EquationslZ and 15.

This @duss-S10 Equation 17 shows that the phase angle 0 between the beaefrequeney andmodulationfrequency at the receiver dependsu upontheadiiferenceoffthe distances to thetwo transmitters plusy @constant thaV distance betweenLthetransmitters thatsfherphasetansis,is independent@ thafrequeuiss S from transmitters A andvB.

t is determinedv yby .theE Itshould be notedA It is convenient to convert the phase angle units to cycles and the distances to wavelengths. When this is done, Equation 17 becomes Tb=M-l(Rs-Rb) (18) where Tb is in cycles of phase angle and Ra, Rb and M are in wavelengths of frequency (b).

Since Ra and Rb are the distances of S from two fixed points, Fig. 3, Equation 18 represents a family of hyperbolae of constant phase difference such as the line T, about the stations A and B as foci. For each value of Tb there is associated a unique hyperbola.

Fig. 4 illustrates a system for determining a navigational x. There are three transmitters X, Y and Z, suitably separated, and the position to be determined is designated as R. The transmitters Y and Z are continuous wave transmitters of ordinary crystal controlled stability, transmitting frequencies (y) and (z) respectively.

Located at transmitter X station, there is a receiver 40 which is adapted to receive the three frequencies (x), (y) and (z) and its output is fed to detector 41. The detector 41 output is fed to

filters

44 and 45, their outputs being respectively difference frequencies (x-y) and (x-z). These diiference frequencies are fed to a fourth transmitter W which transmits a carrier frequency (w) modulated with the two dierence frequencies.

The receiving apparatus at R comprises two

radio frequency amplifiers

21 and 25. Amplifier 21 receives frequencies (x), (y) and (z). These three frequencies are mixed in detector 22 and the desired beat frequency (1r-y), iS extracted by filter 24 and the desired beat frequency (X-z) is extracted by lter 23. The R.F. amplifier 25 receives (w) and its modulation frequencies (x-y) and (x-z) which are demodulated in detector 26, and the modulation frequencies are separated in

lters

27 and 28. The separately derived (x-y) frequencies are compared in phase meter 29 and separately derived (1r-z) frequencies are compared in phase meter 30. The reading of each [phasemeter] phase meter determines one of the intersecting hyperbolic loci of positions one in range (y-x) and the other in range (y-z) thereby determining a navigational fix of the position R relative to the location of the three transmitting stations.

The frequency (w) was suggested as the most direct means for obtaining the reference modulation frequency (x-y) and (x-z) at the receiver. This frequency (w) may be eliminated by providing that the beat frequencies generated in

mixers

44 and 45 be modulated upon transmitter X. To do this the beat frequencies are divided by some small integer (p) in order that they may be later separated.

Fig. shows the equipment required at transmitter X location in order to accomplish this result. In this case, the three frequencies (x), (y) and (z) are all received as before in receiver 40, mixed in detector 46, and then fed to filters -47 and 48 which extract the proper beat frequencies (x-y) and (X-z). Each of these frequencies is divided by the same divisor P in the frequency dividers 49 and 49', thus providing s? and aga which modulate transmitter X by means of modulator 50.

The cooperating equipment at the receiving location R is illustrated in Fig. 6 and comprises a radio frequency amplifier 51 which receives the three carrier frequencies (x), (y) and (z), plus the frequencies modulated upon the carrier frequency x, namely (X-lgy) and (X1-DZ) All of these frequencies are mixed in detector 52, the output of which is connected to four filters which extract the modulated beat frequencies, and the directly derived beat frequencies as follows; iilter `53 extracts frequency (x-y), filter 54 extracts frequency (x-y) P filter 59 extracts frequency (x--z) and filter 57 extracts frequency (X-z) P The frequency (x-y) P is fed from filter l54 to multiplier 55 which multiplies by the same factor P and thereby restores it to the original frequency (x-y). It is then fed to phase meter 56 in which it is compared with the directly derived beat frequency (x-y) thereby giving an indication of the phase difference and determines a hyperbolic locus of position in the range (y-x). The frequency is fed from filter 57 to multiplier 58 where it is multiplied by the same factor P and restored to its original frequency (x-z). It is then fed to phase meter 60 where it is compared with the directly derived frequency (x-z) obtained from lter 59 and provides a reading of the phase difference, and determines a hyperbolic locus of position in the range (y-z) which intersects the first hyperbolic line of position.

All of the systems previously described are subject to cyclic ambiguity of phase shift. This problem is solved in the present invention by operationg two systems similar to those already described, side by side, simultaneously, on dilferent frequencies. The two systems, in addition to their own indications, then cooperate to provide a third system based upon a wavelength corresponding to the difference frequency between the two systems. The ambiguous regions of this longer system difference wavelength are fewer in number. This system difference concept may be visualized by considering two rotating vectors of different frequencies. Assume they both start from a zero position at zero time and therefore the higher frequency vector immediately starts to lead the lower frequency vector. At a certain time T the higher frequency vector will overtake the lower frequency vector, and this time T is equal to the period of their difference frequency. In other words, the difference frequency has been phase shifted one full cycle in this time T. By measuring a phase shift of this system difference frequency, of less than one full cycle, we may resolve cfyclic ambiguity in the phase shift readings of the higher frequencies. In addition the system may be so arranged that the modulation frequency of one [ssytem] system is transmitted in one station and the modulation frequency of the other system is transmitted in the other station. If now, the modulation frequencies of the two system are synchronized, then the phase comparison of the modulation frequencies at the receiving location will form a third system based upon wavelengths of the modulation frequencies. This will be explained in detail hereinafter.

If the frequency difference between the systems is between 2% and 5% of the carrier frequencies and the modulation frequency is between 2% and 5% of the difference frequency, then the resolution of the difference frequency system will be less than the wavelength of the carrier frequencies, and the resolution of the modulation frequency system will be less than the wavelength of the difference frequency system, so that the entire `(at) by a few percent.

group of systems operating together have an accuracy prportinal fte the carrier frequency system Yand an nnlbigds `fange proportional to "the m'odulation Wavelength.

Fig. 7 is a block diagram of atwo station system which can define lines of position without cyclic ambiguity. A third station is required yfor a navigational fix but it has been omitted as it is not required in the illustration of how the cyclic `-ambiguity is resolved. v

At station B there is a transmitter 72 which :transmits a frequency (b). At station A there is a transmitter 61 that transmits a carrier frequency (a) which differs from (b) by a low beat frequency (a-b). Receiver 62 at location A' receives frequencies (a) fand Cb), ampliiies them and extracts lthe beat frequency (a-b). Frequency divider 64 divides this frequency by a factor K and modulates the transmitter 61 through modulator 65 with the divided beat frequency. n At the position to be determined S, an RF. amplifier 77 picks up the Vfrequencies (a) and (b) plus the modulation on frequency (a). =Filters 79 'and 80 extract Vthe 'frequencies (a-b) and a divided "frequency The divided frequency is then fed to a multiplier 83 which multiplies by the same factor K thus restoring the original frequency (a-b). These ktwo frequencies `are then compared in a phase meter 85 giving aphase angle difference 01,

v-At -station lA' there is another transmitter k66 which transmits a frequency `(d) which differs from frequency At station B', a transmitter 67 transmits a frequency (e), and a receiver 68 `receives frequencies (d) and (e) and generates a low beat frequency (d-e) which is equal to (a-b). A frequency divider 70 connected to receiver 68 generates the modulation frequency (d-e) K -is also fed from the frequency divider 70-to the phase detector 75. The frequency (aj-b) is'also supplied to the phase detector 75 from'the receiver 73. These two divided frequencies are compared in f phase by the phase detector 75 which provides an error -voltage proportional tothe phase diiference to the `frequency controller 76 which changes thefrequency (b) lof transmitter 72 proportionally to the error signal in order to reduce the phase diiferenceat phase detector 75 to zero. Therefore, this operation synchronizes the modulation frequencies of thetwo different systems.

At the' position to be-determined, 'S, radio lfrequency amplifier 78 receives frequencies (d) and (e) and the Amodulation frequency vThe amplifier 78 is connected to'two iilters 8'1 and 82 which-extract the frequencies (d-a'e) and Y (dr-) respectively. The frequency an c similarly, lthe phase difference 0.2 measured by phase meter 87 equals 0= (M-l-Ra-RQ (19) a2=2-tM+Rb-na 20 Equation 19 shows that 61 is proportional to a constant term M plus the difference between distances Ra and Rb in terms of the vlI 'wave-length] wavelength of frequency (b).

Similarly Equation 20fshows -that 02 lis proportional to aconstant term M plus the difference between the dis- -tances YR., and Rb in terms of the wavelength of frequency=(d).

Accordingly, therefore, 01 or zrnay be read and this reading vwill deline a hyperbola of constant phase difference betw'een Ra :and Rb, exactly as in standard loran procedure wherein avconstant time difference is measured. This measurement lis in terms of the wavelength of the carrier frequency used, and the accuracy of the measurement is approximately one-hundredth of a wavelength ofthe carrier frequency, as that amount kof phase difference may be conveniently measured.

However, in order to `avoid ycyclic ambiguity in the above fine measurement, coarse and medium measurements at lower frequencies are provided as will be shown in 'the .following discussion.

If H1 and 02 are added we have the following:

YEquation 2l shows that `@rl-02 is equal to a constant term plus the difference `between Raand Rb in terms of the `wavelengths of the system difference frequency (b-d). Therefore, `the readingof 01+H2-in indicator 88 will enable theresolution of cyclic ambiguity in the carrier frequency 1 reading 61.

The phase angle 03'between'the two [modulation] low beat frequencies which is determined by phase meter 86 is likewise-dependent upon the difference of the distances'to the two transmitting stations A and B. This can be shown as follows:

From Equation l5 we see that the [modulation] lo-w beatffrequency; ie., the output of the multiplier 8.3; derived in the-navigation receiverat S from the modulation component of the wave received from station A, is:

Likewise the [modulation] low beat frequency; Le.,

V'the 'output of the multiplier 84; derived' from the modulation component of the 'carrier e received from station 'B [upon carrier e] is:

Remembering that the frequency control 7 '6 at station B makes the beat frequencies synchronous, so that the phase angle between the [modulation] low beat frequencies from the multipliers 8.3 and 84 at the receiver is 03, where Equation 24 shows that the phase angle 93 between the modulation frequencies is likewise dependent upo-n the difference of the distances to the two stations, with the indication in terms of wavelengths of the [modulation] low beat frequency (a-b). The reading of this phase angle 03, obtained from phase detector 86, provides a coarse reading at the longer modulation wavelength which resolves the cyclic ambiguity in the higher frequency medium reading, (614-02).

In developing the equations for the phase angles, all of the delays, including fixed delays such as those due to the time of transit of the various waves between stations, were included. However, the zero refe-rence for the phase angles may be shifted to the line where R,=`Rb, apd the

Equations

19, 20 and 24 `for the phase angles 01, 02 and 63 would become i- E) AAE gir-(C AR- Ab where 01 is proportional to AR in terms of the wavelength of frequency b Where 02 is proportional to AR in terms of the wavelength of frequency d ab AR= AR where 63 is proportional to AR in terms of the wavelength [rnodulation] low beat frequency (a-b) where and 7( represents the wavelength of the subscript frequency. Also; from Equation 2l, dropping the constant term we have 211 Arb-a) and a preferable ratio is 400:20:l.

The phase Shifters can be expected to measure to about 1% of a cycle, hence 03 will indicate AR to about which is less than ?\(b-d), a-nd 014-02 will indicate AR to about .OlMb-d) which is less than )((b).

Therefore the system will resolve all ambiguities in up to full wavelengths of the modulation frequency.

In a specific instance the carrier frequencies may be approximately 78 kc. and 82 kc., the system difference frequency about 4 kc., and the [modulation] low bea't frequency about 200 cycles. A Wavelength at 200 cycles is 932 miles. Since the maximum phase shift is twice the baseline, in wavelengths, a system with a 450 mile baseline between stations would have no ambiguities with a carrier frequency approximately of kc.

Fig. 8 is a block diagram of a three station system, which is the required number of stations to provide a navigational fix. This system is similar to that yof Fig. 7 with the addition of a third station C, which is essentially similar to station B. Station B is identical with station B of Fig. 7 and cooperates with station A, as described in connection with Fig. 7, to define the hyperbola O of constant phase difference in the range AB.

Station C cooperates with station A in a similar manner to dene a hyperbole. P in the range AC. This is done with the same technique as described in detail in connection with Fig. 7. However, different frequencies must be used in order to differentiate the signals at the receiving location.

Station C generates a frequency (c) in transmitter 72 and a frequency y'(f) in transmitter 67. Receiver 68 receives frequencies (d) a-nd (f) and receiver 73 receives frequencies (a) and (c). Frequencies (la-c) and (d-f) are compared in phase detector '75' and synchronized through the operation of frequency controller 76' which controls the frequency (c) of transmitter 72'. The difference frequency (d-f) is also modulated on carrier (f) of transmitter 67. All of the iabove mentioned units of station C are the same `as those of station B with the exception that different frequencies are used.

Station A is the same as in lFig. 7 except that a second filter divider 64 has been added to the output of receiver [61] 62 to extract the frequency.

(a-G) K from the output of receiver [61] 62 in addition to the signal extracted by the filter divider 64 at frequency.

(2l-b) K azbSa-I) and eig-gi)- The output of this R.F. amplifier is applied to four

filters

91, 92, 93 and 94 which extract respectively frequencies (af-JD): K

y (ade) and (2L-C) K ei-Me) (e-f) K K and fj;

The output of RJ?. amplier 102 is connected to four 1l filters; 103., 104,` 105 and 1,06,

which extract respectively frequencies (d e), (fm) and LK@ The, two divided frequencies are multiplied by a factor of K in the

multipliers

107 and 108 to restore the original frequencies. The separately derived (d-e) frequencies are compared in phase meter 109, providing la measurement of 92 for the AB range; and separately derived (fd) frequencies are compared in phase meter 110, providing a measurement of 02 in the AC range.

The [modulation] low beat frequencies (a`b) and (d-e) from

multipliers

95 and 108 are applied' to phase meter 111 Where they are compared to give the coarse measurement 03 of the phase difference in the AB range. As previously explained, this coarse position is based upon the long and therefore unambiguous wavelength of the [modulation] low beat frequency (a-b).

The (a-c) [modulation] low beat frequency and the ('f-d) [modulation] low beat frequency are similarly compared in the phase meter 112 to provide a measure ment of 03 in the AC range.

The readings in the AB range are combined in indicator 113 to thereby provide a coarse, a medium and a line reading which will identify hyperbola O.

The 0 readings in the AC range are combined in indicator 114 to thereby provide a coarse, a medium and a fine reading which will define hyperbola P.

In the AB range indicator 113 the coarse reading is provided by indicator 1,40 which merely repeats the reading 93 of phase detector 111. The medium reading is provided 'by indicator 141 which adds the 01 reading from phase detector 100, and the 02 reading from phase detector 109. This addition may be done mechanically as by a differential. The line reading is provided by indicator 142 which repeats the 02 reading of phase detector 109.

In the AC range indicator 114 the coarse provided by indicator 143 which repeats the 03 reading of phase meter 1112. The medium reading is provided by indicator 144 which adds 01 reading from phase detector 101 and the 02 reading from phase detector 110. The line reading is provided by indicator 145 which repeats H2 reading which is derived by phase detector 110.

The readings from

indicators

113 and 114 may be referred to a previously prepared chart such as` used with standard loran, in order to determine the navigational fix.

One method of combining the three dial readings in

indicators

113 and 114 to get a composite reading, may be illustrated in a typical example as follows:

Assume we have two transmitting stations M and N separated by l/m of the (modulation) frequency. Then as a receiver is moved from M to N, remembering the frequency ratio of carrierzsystem diiferencmmodulation is 400:20: l, the values are chosen so that:

reading is The coarse dial (03) will turn l revolution,

The medium dial (014-02) will turn 20 revolutions,

and

The tine dial (01) will turn 400 revolutions.

It must be noted that as a receiver is moved V2A from one station, it also moves V2A closer to the other station, so that the total phase difference is Ik.

The, dials may be conveniently calibrated in arbitrary distance units, the total distance being 400 units such that:

lrevolution of the line dial=1k unit l revolution of the medium dial=20 units l revolution of the coarse dia1=400 units Suppose the receiver is put at the location to be determined, which is in fact, .632 of the total distance, or

12 252.8 distance units along the line joining the. twoy stations. The phase angle difference 01 will be cycles, i.c., if the receiver had been movedy from the point of zero distance, the fine dial would have turned 252.8 revolutions. The number of complete cycles are not indicated on the dial, and therefore, the fine dial reading is .8 revolution which is equal to .8 units.

Similarly, if the receiver had been moved from zero the medium dial would have turned 20X.63,2=12.64 revolutions. As the full cycles are not indicated, the only significant portion is .64 revolutions which, as the dial has 20 distance -units per revolution is equal to 12+ units.

Similarly, if the receiver had been moved lfrom zero position, the coarse dial would have turned .632 revolutions. As this dial is calibrated with 400 distance units the reading to its allowable tolerance will be 240+ units.

The operator may add the readings to obtain the posi tion in distance units equal to 252.8 units.

Alternatively, an additive mechanism might easily be provided to furnish the final reading without any computation on the operators part.

The dial markings must be chosen to be read with an accuracy, proportional to the allowable tolerance in that particular part of the system. The lower frequency dials resolve cyclic .ambiguity of phase shift of the highest frequency, without regard to the previous history of motion of the receiver. The receiver does not have to be set at a known location and kept in continuous operation, which would be the case if the medium and coarse dials were merely cycle counters of the fine dial. The equipment may be turned on, at the unknown location without any pre-setting and will immediately give the correct reading.

Fig. 9 illustrates apparatus to indicate phase difference which may be used in the phase meters such as 85, 86 and 87 of Fig. 7. The reference phase voltage is connected to the input transformer 150, the secondary of which is connected to a phase-splitting network for the purpose of dividing the single phase input into a three phase volt-age to energize the

stator windings

151, 152 and \153 of self-synchronous transformer or Selsyn 160. The phase-splitting circuit, comprising adjustable condenser 155 and adjustable resistor 156, is connected across

stator arms

151 and 152. The values of

condenseris

155 and 156 are chosen so as to provide a balanced three phase voltage across the three stator arms when a single phase voltage is applied to the input.

The rotor 157 of the Selsyn 160 is adapted to be turned by motor 158 and shaft 169 t-o thereby produce a phase shifted Selsyn output voltage across the rotor 157 winding. The beat frequency phase voltage to be COmPICd with the reference phase voltage is applied to the primary of transformer 16-1, and each end of the secondary of the transformer 161 is connected to the plates of a pair of

diodes

162 and 163. The cathodes of the diodes are connected to a balanced resistor-capacitance network 165. The reference phase voltage (ER) output from the rotor 157 is connected between the center tap of the secondary of transformer 161 and the center of the balanced out,- put network 165.

When the two signals are in phase, the zero position of rotor 157 is chosen so that ER is 90 out of phase with EA and EB as `shown in Fig. 10. The resulting voltage vectorsy Ec and ED, are -equal in amplitude and their rectiiied outputs balance each other in the network providing zero output.

lf there is a phase shift in one direction as illustrated in Fig. l1,l the amplitude o-f ED becomes larger vand the amplitude of EC becomes smaller. If the phase yshift had been in the opposite direction EC would have become assai larger and ED smaller. These two voltages EC and En are rectified in the diodes 16-2 and 163 and these rectified voltages are opposed in network 165, thereby providing a D C. error voltage Whose amplitude and polarity is proportional to the magnitude and sense of the phase difference.

This error voltage generated across the output network 165 is applied to the `input of amplifier 166 which energizes motor 158 so as to turn rotor 157 in a direction which will reduce the phase difference to zero. When this is done the desired phase reading 01, 02, or 63 may be read from dial 170.

Thus it is seen that cyclic ambiguity is resolved by utilizing two channels slightly separated in frequency. The difference frequency between the channels may be effectively utilized as a second system whose wavelength is long enough so that its phase shift is substantially unambiguous. This lo-nger wavelength system is used as a medium reading to resolve ambiguity in the fine high frequency readings. A further extension of the non-ambiguous range is obtained by using synchronized low frequency modulation signals on the above-mentioned pair of carrier channels. These modulation frequencies are utilized as a third coarse system having a [wave length] wavelength long enough to resolve ambiguities in the medium system.

These various frequencies must be suitably chosen to obtain the best coverage. A ratio of approximately 20 to l between the carrier frequency and the difference frequency between the carrier channels, and `a similar ratio of `approximately 20 to l between the system difference frequency and the law baat signal used to develop the modulation frequency has been 'found preferable in one embodiment of the invention. The actual choice of frequencies must -be governed by design considerations such as, coverage desired, length of available baseline, frequencies available and propagation and other factors.

Since many changes could be made in the above construction iand many apparent-ly widely different embodiments of this invention could be made without departure from the scope thereof, it is intended that all matter contained in the above-description or shown in the accompanying drawings shall be interpreted as illustrative `and not in a limiting sense.

What is claimed is:

[l. In a radio navigation system of the type wherein continuous wave signals are transmitted from three separate locations, and first and second beat frequency waves derived from said three signals are transmitted separately from -said transmitting locations; a receiver, comprising first receiving means adapted to receive said first three signals, second receiving means adapted to receive said first and second beat frequencies, detecting means. responsive to said first receiving means to obtain said first and second beat frequencies directly from said first three signals, filter means responsive to said second receiving means to separate said first and second beat frequencies, first phase comparison means responsive to said filter means and said detecting means to compare in phase said separately received first beat frequencies, second phase comparison means responsive to said filter means and said detecting means to compare in phase said separately received second beat frequencies] [2. In a radio navigation system of the type wherein continuous wave signals are transmitted from three separate locations, and first and second beat frequency waves derived from `said three signals are transmitted as a modulation from said transmitting locations; a receiver comprising means to receive said three continuous wave signails, means responsive to said receiving means to obtain said first `and second beat frequencies by mixing said three continuous wave signals, filter means responsive to said receiving means to obtain said first and second beat frequency modulations, and first phase comparison means to compare in phase said first lbeat frequency and said first 14 beat frequency modul-ation signals, and second phase coniparison means to compare in phase said second beat frequency and said second beat frequency modulation signals] [3. ln a radio navigation system of the type wherein continuous wave signals are transmitted from three separated locations, and first and second beat frequency waves derived from .said three signals `are transm-itted as a modulation from said transmitting locations; a receiver comprising means to receive said three continuous wave signais including said modulations, detecting means responsive to said receiving means, first filter means responsive to said detecting means to obtain said first beat frequency, second filter means responsive to said detector means to obtain said first beat frequency modulation, phase comparison means responsive to said first and second filter means to compare the phase thereof, third filter means responsive to said detecting means to obtain said `second beat frequency, fourth filter means responsive to said detector means to obtain said second ybeat frequency modulation and phase comparison means responsive to said third and fourth lter means to compare the phase thereof; to thereby determine the position of said receiving location with reference to predetermined hyperbolic lines of position relative to said three transmitting locations] 4. Means to `obtain navigational position by radio means without cyclic ambiguity comprising means to transmit a first continuous wave signal from a first location, means to transmit a second continuous wave signal from a second location, means to receive said first and second signal at said first location and means connected to said receiving means to mix said first and second signals to thereby obtain abeat frequency, means to divide said beat frequency, means to modulate said first signal with said divided beat frequency, means t-o transmit a third continuous wave signal from said first location, means to transmit a fourth continuous wave signal from said second location, means to receive `said third and fourth continuous wave signals at said second location, means to mix said third and fourth received signal and to divide the resultant beat frequency, means to modulate said fourth continuous Wave signal with said divided beat frequency, receiving means at said second loc-ation iadapted to receive said first and second signals, means to mix said first and second signals to obtain a beat frequency including means to divide said beat frequency, phase comparison means connected to said third receiving means and to said modulating means and adopted to measure the phase difference between the divided beat frequency of said first and second signals :and the divided beat frequency of said third and fourth signals, -frequency control means responsive to said phase detecting means adapted to vary the frequency of said second signal transmitting -means to reduce said phase difference to zero, receiving means at `a third location adapted to receive said first and second signals, filter means connected to said receiving means adapted to obtain the lbeat frequency between said first and second signals, second filter means connected to said receiving means adapted to obtain said divided beat frequency of said first and second signals first multiplication means connected to said divided filter adopted to multiply said divided frequency to its original value, first phase detecting means connected to said multiplication means and said first filter means, second receiving means at said third location `adapted to receive said third yand Ifourth signals, third filter means connected to said second receiving means `adapted to obtain the beat frequency of said third yand fourth signals, fourth filter means connected to said receiving means and adapted to obtain the -divided beat frequency, of said third and `fourth signals, second multiplication means connected to said divided Afrequency filter means, to restore said divided beat frequency to its original value, second phase detecting means connected to said third filter means and said second multiplication means to measure the phase difference therebetween, and third phase detecting means connected to said first and second multiplication means to measure the phase difference therebetween.

5. Means for yobtaining a locus of navigational position by radio means Without cyclic ambiguity, comprising means for obtaining a beat frequency at the receiving location from a pair of signals received `from separate transmitting locations, means for obtaining said beat frequency at the, first of said transmitting locations and separately transmitting it to said receiving location as a modulation, means for obtaining a second beat frequency at said receiving location `from a second pair of signals received from said separate transmitting locations, means for obtaining said second beat frequency at the second of said transmitting locations and transmitting it to said receiving location as a modulation, means for compairing the phase of said separately received first beat frequencies at said receiving location, means for comparing the phase of said separately received second beat frequencies at said receiving location and means for comparing the phase of said separately received modulation frequencies at said receiving location to thereby determine the hyperbolic locus of positions of said receiving location relative to said transmitting locations with accuracy proportional to the highest frequency and without cyclic ambiguity.

6. Means for resolving cyclic ambiguity in continuous wave navigation systems, comprising means for obtaining a beat frequency at a receiving location from a pair of signals received from separate transmitting locations, means for deriving said beat frequency separately at the first of said transmitting locations and transmitting it to said receiving location as a modulation, means for obtaining a second beat frequency at said receiving location from a second pair of signals received from said separate transmitting locations, means for deriving said second beat frequency at the second of said transmitting locations and transmitting it to said receiving location, means for obtaining said first beat frequency at said second location, means for comparing the phase at said second location of said first and second beat frequencies and means for controlling the frequency of the signal of said first pair of signals transmitted from said second location to reduce the phase difference to zero, and means at said receiving location means for comparing the phase of said first beat frequencies, means for comparing the phase of said second beat frequencies and means for comparing the phase of said modulation beat frequencies.

7. Means for obtaining a navigational fix by radio means without cyclic ambiguity, comprising means for obtaining a beat frequency :at a receiving location from a pair of signals received from separate transmitting locations, means for deriving said beat frequency separately at the iirst of said transmitting locations and transmitting it lto said receiving location as a modulation, means for obtaining a second beat frequency at said receiving location from a second pair of signals received from said separate transmitting locations, means for deriving said second beat frequency at the second of said transmitting locations and transmitting it to said receiving location, means for obtaining said first beat frequency at said second location, means for comparing the phase at said ysecond location of said first and second beat frequencies and controlling the frequency of the signal of said first pair of signals transmitted from said second location to reduce the phase difference to zero, means for comparing the phase of said first beat frequencies, means for comparing the phase of said second beat frequencies and means for comparing the phase of said modulation beat frequencies at said receiving location.

8. A coarse and [fine hyperbolic navigation system comprising, means at at least two separate :locations vto transmit at least two continuous. wave signals each,

vmeans ,at at kleast one of said locations to receive said signals, means responsive to said receiving means to generatesubharmonic modulation products from Said f l5 signals, and means to retransmit said modulation prod@ ucts to thereby establish coarse and -fine hyperbolic lines of position relative to said locations.

9. Craft receiving means comprising means to receive signals from two separate locations, means responsive to said first means to detect modulation products from said signals, means to receive separate subhanmonic modulation products from at least one of said :loca-tions, means to compare said modulation products `to thereby determine the craft position relative to said locations, and means to resolve ambiguities of said comparison.

10. Navigation apparatus comprising means to receive a plurality of separate frequency signals and a plurality of separate modulations, means to generate a plurality of modulation products from said signals, means to compare in phase said modulations with said generated modulation products, means to indicate said phase difference in terms of two of said signal wavelengths, and means to resolve cyclic ambiguity of each, of said phase differences including means to combine said phase differences.

1l. A coarse and fine navigation system comprising, first and second continuous wave hyperbolic navigation systems of the type transmitting nonsynchronous continuous wave signals `from separate transmitters and transmitting a beat frequency reference modulation from one of the transmitters, first and second receiving means responsive to the frequencies of said first and second transmitting systems to measure distance, means to resolve cyclic ambiguity of measurement of said first and second systems comprising third receiving means responsive to the difference frequency between said first and second transmitting systems.

12. A coarse and fine navigation system comprising, first and second continuous wave hyperbolic navigation systems of the type transmitting nonsynchronous continuous wave signals from separate transmitters, and transmitting a beat frequency reference modulation from one of the transmitters, first and second receiving means responsive to the frequencies of said first and second transmitting systems and having iii-st and second phasemeters to measure distance, means to resolve cyclic ambiguity of measurement of -said first and second systems comprising means for adding the outputs of said .iirst and second phasemeters to provide la distance measurement in terms of the difference frequency between said first and second transmitting systems.

13. A coarse, medium and fine navigation system comprising, first and second continuous wave hyperbolic navigation systems of the type transmitting nonsynchronous modulated continuous wave signals from separate .transmitters and transmitting a beat frequency reference modulation from one of the transmitters, first and second receiving means responsive to the frequencies of said first and second transmitting systems, means to resolve cyclic ambiguity of measurement of said first and s econd systems comprising third receiving means responsive to the difference frequency between said first and second transmitting systems, and means -to resolve cyclim ambiguity of said system difference frequency distance measurement comprising fourth receiving means responsive to said modulation frequency. Y

14. A coarse, medium and fine navigation system comprising, first and second continuous wave hyperbolic navigation systems of the type transmitting nonsynchronous modulated continuous wave signals from separate transmitters and transmitting a beat frequency reference modulation fro-m one of the transmitters, first and second receiving means responsive to the frequencies of said first and second transmitting systems, means to resolve cyclic ambiguity of measurement of said first and second systems comprising third receiving means responsive to the difference `frequency between said `first and second transmitting systems, and means to resolve krcyclic ambiguity of said system difference frequency 17 measurement comprising a -phasemeiet' responsive to said modulation frequency.

15. In a position indicating system, means for translating space radiated signals into p-osition indications comprising, means for obtaining a first beat frequency signal at a receiving location from a first pair of signals received from separate transmitting locations, means for obtaining a second beat frequency signal at said receiving location from a second pair of signals received from said separate transmitting locations, means at one of said transmitting locations for obtaining said first and second beat frequency signals, mea-ns at said one transmitting location jointly responsive to said first and second beat frequency signals for controlling the frequency of at least one of said space radiated signals to maintain the phase difference between said beat frequency signals at a predetermined value and thus maintain the same beat frequency value between said first and second pairs of signals, and means at said receiving location jointly responsive to said first and second beat frequency signals to produce a position indication.

16. A wave signal transmission system comprising, a pair of spaced transmitting units, a plurality of pairs of transmitters for radiating signals of different frequencies, said transmitters of each pair being respectively disposed at dierent transmitting units, means at one of said transmitting units for obtaining a first beat frequency signal from the signals radiated by a first pair of said transmitters, means at said one unit for obtaining a second beat frequency signal from the signals radiated by a second pair of said transmitters, and means at said one unit responsive to at least one of said beat frequency signals for controlling the frequency of at least one of said transmitters to maintain the same beat frequency between said first and second pairs of signals.

17. A wave signal transmission system comprising, a pair of spaced transmitting units, a plurality of pairs of transmitters for radiating signals of different frequencies, said transmitters of each pair being respectively disposed at different transmitting units, means at one of said tran-smitting units for obtaining a first beat frequency signal from the signals radiated by a first pair of said transmitters, means at said one unit for obtaining a second beat frequency signal from the signals radiated by a second pair of said transmitters, and means at said one unit responsive to at least two of said signals for controlling tlie frequency of at least one of said transmitters to maintain a predetermined phase difference between said beat frequency signals.

18. A wave signal transmission system comprising, a pair of spaced transmitting units, a plurality of pairs of transmitters for radiating signals of different frequencies, said transmitters of each pair being respectively disposed at different transmitting units, means at one of said transmitting units for obtaining a first beat frequency signal from the signals radiated by a first pair of said transmitters, means at said one unit for obtaining a second beat frequency signal from the signals radiated by a second pair of said transmitters, means at said one unit for comparing the phase of said beat frequency signals, and means controlled by said phase comparing means for controlling the frequency of at least one of said transmitters to maintain at a predetermined value the phase difference between said beat frequency signals.

19. Means for resolving cyclic ambiguity in continuous wave navigation systems, comprising means for obtaining a beat frequency signal at a receiving location from a pair of signals received from separate transmitting locations, means for obtaining a second beat frequency signal at said receiving location from a second pair of signals received from said separate transmitting locations, means for obtaining said Jirst and second b'eat frequency signals at one of said transmitting locations, means at said one transmitting location jointly responsive to said first and second beat frequency signals for controlling the fre- 18 quency of at least one of said transmitted signals to maintain at a predetermined value the phase difference between said beat frequency signals, and means at said receiving location for obtaining a position indication in response to said first and second beat frequlency signals.

20. In a position indicating system, means for translating space radiated signals into position indications comprising, means for obtaining a first beat frequency signal at a receiving location from a first pair of signals received from separate transmitting locations, means for obtaining a second beat frequency signal at said receiving location from a second pair of signals received from separate transmitting locations, means at one of said transmitting locations for obtaining said first and second beat frequency signals, means at said one transmitting location for transmitting a reference signal derived from at least one of said beat frequency signals to said receiving location as a modulation, means at said one transmitting location jointly responsive to said first and second beat frequency signals for controlling the frequency of one of said transmitted signals to maintain at a predetermined value the phase dierence between said beat frequency signals, means at said receiving location for comparing the phase of said modulation with the corresponding beat frequency signal to produce one position indication, and means at said receiving location jointly responsive to said first and second beat frequency signals for producing another position indication.

21. A wave signal transmission system comprising, a pair of spaced transmitting units, a plurality of pairs of transmitters for radiating signals of dierent frequencies, said transmitters of each pair being respectively disposed at different transmitting units, means at one of said transmitting units for obtaining a first beat frequency signal from the signals radiated by a first pair fo said transmitters, means at said one unit for obtaining a second beat frequency signal from the signals radiated by a second pair of said transmitters, means at said one unit for modulating a reference signal derived from at least one of said beat frequency signals on thle signal radiated by one of said transmitters at said one unit, means at said one unit controlled by the phase relationship between said beat frequency signals for controlling the frequency of the signal radiated by one of said transmitters to maintain the beat frequency between the signals radiated by said Jirst pair of transmitters equal to the beat fnequency between the signals radiated by said second pair of transmitters.

22. In a position .indicating system, means for translating space radiated signals into position indications comprising receiving means for receiving a plurality of pairs of space radiated signals and for heterodyning said received pairs to produce beat frequency signals having frequencies respectively related to the beat frequencies between the signals of each pair, means for receiving at least one modulated space radiated carrier signal and for developing therefrom reference signals having frequencies respectively equal to said beat frequency signals, means for phase comparing an lequal frequency pair of said beat frequency signals and reference signals to provide at least one position indication, means for mixing said beat frequency signals and said reference signals, and means responsive to the output of said mixing means for producing at least o-ne other position indication.

23. Wave signal receiving apparatus for translating received space radiated signals into position indications comprising, a plurality of receivers for respectively receiving pairs of spalce radiated signals and for heterodyning said received pairs to produce beat frequency signals having frequencies respectively representative of the beat frequencies between the signals of each pair, means for receiving a modulated space radiated carrier signal and for developing from thie modulation components thereof reference signals having frequencies respectively equal to said beat frequency signals, first phase comparison I9 means energized by one of said beatA frequency signals and the corresponding one ofsaid reference signals, second phasecomparison means energized by the otherk beat frequency signal and reference signal, and.` dierential means responsive to the outputs of said phase comparison means for providing position indications.`

24. A fine and coarse position determining system, comprising jrsttand second continuouswave systems of the type transmitting non-synchronizedxwave signals from separate transmitters and prov-iding beat frequency signals used in developing reference signals for transmission, receiving means responsiv'e to the wave signalsand *reference signals of one of said systems to provide a position indication related to the frequency of-` the'wave signals of said one system., and means to resolve the cyclic ambiguity ofsaid position indications comprising means to provide a positionindication in terms of the difference frequency between said first andsecond systems.

25; A system for providing fine and coarse position indications, comprising rstand second continuous wave transmission systems each including spaced non-synchronized transmitters for transmitting continuous wave signals from separate points totA produce beat frequency signals and including means for radiating reference signals derived from said beat frequency signals, receiving means responsive to thle wave signals and reference signals of one of said systems to provide one ofsaid position indications related to the frequencyxof the wave signals of said one system, and means responsive to the wave signals and reference signals. of both 'of said systems to provide the other of said vposition indications related to the relative. values -of the frequencies of said rst and second systems.

26. A system for providing `position indications, comprising first and second continuous wave transmission systems each includingrspacednon-synchronized transmitters for transmitting, continuous wave signals from separate `points to produce beat` frequency signals and including means forv radiatingreference signals derived from saidv beat frequency signals, and receiving means responsive to the` wave signals and reference signals of both of said systems for providing position indications related to the relative valuesof thefvfrequencies of said rst and second systems.

27. A system for providing position indications, comprising )rst and second continuous wave transmission systems eac'h. including spaced non-synchronized transmitters for transmitting continuous wave signals in pairs from at least two separated points, the signal frequencies utilized in said first system being different from the signal frequencies utilized in said second system; and receiving means responsiveto the wave signals of both of saidI systems for.y providing position indications related to the relative values of the signal frequencies utilized in said first and second systems.

28. A fine' and coarse position determining system, comprising first and second continuous wave systems of the type transmitting non-synchronized wave signals from separate transmitters andpro-viding beat frequency signals for use in devel'opingfreferencer signals for transmission, receiving means responsive to the wave signals and reference signals of one of said systems for providing a position indication related to the frequency' of the-wave signals of said one system, and means to resolve the cyclic ambiguity of said position indications including means responsive to thewave signals of both of said systems for providing a second position indication related to the frequency difference between the wave signals of said first and second systems.

29. In a position determining system, a pair of continuous wave systems of the type transmitting non-synchronized wave signals from separate transmitters and providing beat frequency signals forr use in developing reference signals for transmission, `said rsystems operating at.dierent frequencies,` receiver means-for each ofV said systems for receiving said different frequency signals, and means responsive to the outputs of said receiver means for providing a position indication related to the frequency dierence betweenl the wave signals of said pair of systems.

30. Wave signal receiving apparatus comprising means to receive a plurality of pairs of signals radiated from two separate locations, said pairs of signals being of distinguishably different frequencies, and the two signals forming each pair being radiated from different locations and each pair of signals haivng the same frequency separation, said receiving apparatus including means for heterodyning the signals of a rst of said pairs to pr duce a first beat frequency and for heterodyning the signals of a second of said pairs to produce a second beat frequency signal equal in frequency to the first beat frequency signal, and means jointly responsive to said beat frequency signals to provide a position indication related tothe frequency difference between said pairs.

31. In a system for determining the location of a receiving point respective to spaced transmitters by comparing at said receiving poin-t the phases of signals emitted by said transmitters and received at said receiving point, at least two spacedv transmitters for emitting continuously at least three dierent non-synchronized high frequency waves, `the choice of saidL frequencies being limited by the only con-dition which is suyficient and necessary that the algebraic sumof the respective products of said frequencies by any integers, at least one of which is positive and at least one of which is negative, is zero, at said receiving point: a receiver comprising in combination filtering, amplifying and mixing means to receive said waves and deduce therefrom by `means of differing frequency mixtures two currents having the same frequency and phasemetering means jointly responsive to said two currents for providing an indication concerning the location of said receiving point respective to said transmitters.

32. In a systemy for determining the location of a receiving point respective to spaced transmitters by comparing at said receiving point the phases of signals emitted by said transmitters and received at said receiving point, at least two spaced transmitters for emitting at least three different high frequency waves, the choice of said frequencies being limited by the only condition which are suicient and necessary that the algebraic sum of the-respective products of said frequencies by any integers, at least one of which is positive and at least one of which is negative, is at least substantially zero, means for cancelling said algebraic sum and for automatically maintaining it at zero, said means comprising in combination: a receiver comprising in combination ltering, amplifying and mixing means, to receive said waves and to deduce therefrom by means of frequency mixtures two currents the difference between the frequencies of which is equal to said algebraic sum and means responsive to the difference between the frequencies and the difference between the phases of said two currents to act upon the frequency and the phase of one of said emitted waves to cancel said frequency difference and consequently to cancel said algebraic sum, at said receiving point: a receiver comprising in combination filtering, amplifying and mixing means to receive said waves and deduce therefrom by means of differing frequency mixtures two currents having the same frequency and phasemetering means jointly responsive to said two currents for providing an indication concerning the location of said receiving point respective to said transmitters.

33. In a system for determining the location of a receiving point respective to spaced transmitters by comparing at said receiving point the phases of signals' emitted by said transmitters and received at said receiving point, at least two spaced transmitters to emit continuously four dierent continuous, non-synchronized high frequencywaves subject to the only condition that the difference between vtwo of said frequencies is equal to the difference between two other frequencies, a receiver comprising in combination ltering, amplifying and mixing means to receive said waves and deduce therefrom by means of differing frequency mixtures two currents having the same frequency and phasemetering means jointly responsive to said two currents for providing an indication concerning the location of said receiving point respective to said transmitters.

34. In a system for determining the location of a receiving point respective to spaced transmitters by comparing at said receiving point the phases of signals emitted by said transmitters and received at said re'ceiving point, at least two spaced transmitters to emit four different continuous high frequency waves, the choice of these frequencies being limited by the only condition that the difference between two of said frequencies is at least substantially equal to the difference between two other frequencies, means for rendering equal said two differences and for automatically maintaining them equal, said means comprising in combination: a receiver comprising in combination filtering, amplifying and mixing means to receive said waves and deduce therefrom by differing frequency mixtures two currents the dierence between the frequencies of which is equal to the difference of said above mentioned frequency differences, and means responsive to the difference between the frequencies and the difference between the phases of said two currents to control one of said transmitters to regulate the frequency and the phase of the wave emitted thereby to cancel said last mentioned frequency difference and consequently to render equal said two first mentioned frequency differences, a receiver `at said receiving point comprising in combination filtering, amplifying and mixing means to receive said waves and derive therefrom by means of differing frequency mixtures two currents having the same frequency and phasemetering means jointly responsive to said two currents for providing an indication Iconcerning the location of said receiving point respective to said transmitters.

35. In a system for determining the location of a receiving point respective to spaced transmitters by comparing at said receiving point the phases of signals emitted by said transmitters and received at said receiving point, at least two spaced transmitters to emit four continuous high frequency waves, respectively having a first, a second, a third and a fourth frequency which are all different and the choice of which is limited by the onlycondition that the beat between said first and third frequencies on the one hand and between said second and fourth frequencies on the other are equal low frequencies at said receiving point, the first and second frequency waves being radiated from one of said transmitters and the third and fourth frequency waves being radiated from the other transmitter, a receiver comprising in combina tion filtering, amplifying and mixing means to receive through a first channel said first and third frequencies and to detect the beat thereof and to receive through a second channel said second and fourth frequencies and to detect the beat thereof, and phase metering means jointly responsive to said two beats for providing an im dieation concerning the position of said receiving point respective to said transmitters.

36. In a system for determining the location of a receiving point respective to spaced transmitters by coimparing at said receiving point the phases of signals emitted by said transmitters and received at said receiving point, two spaced transmitters to emit a first, a second, a third and a fourth continuous high frequency wave having respectively a first, a second, a third and a fourth frequency, one of said transmitters emitting said first and second waves and the other said third and fourth waves, said frequencies being all different and their choice being subject to the only condition that the difference between said first and third frequencies is equal to the difference of said second and fourth frequencies, at said receiving point: a receiver comprising in combination filtering, amplifying and mixing means to receive said waves and deduce therefrom by means of differing frequency mixtures two currents having the same frequency one of said currents being derived by beating said first and third frequency waves and the other current being derived by beating said second and fourth frequency waves, and phasemetering means jointly responsive to said two currents for providing an indication concerning the loca.- tion of said receiving point respective to said transmitters.

37. In a system` for determining the location of a receiving point relative to spaced transmitters, at least two spaced transmitters emitting continuously at least three different non-synchronized signals having frequencies which are independent of each other except that they satisfy the relation where F1, F2 Fn are said frequencies and K1, K2, Kn are integers at least one of which is positive and at least one of which is negative, whereby two currents of the same frequency can be derivefd from said signals by combination filtering, mixing an'd amplifying means, a receiver at said receiving point incluuding combination amplifying, filtering and mixing means to receive said signals and derive therefrom two currents of the same frequency, and means jointly responsive' to the last-mentioned two currents for providing an indication about the position of said receiving point relative to said transmitters.

38. In a system-for determining the location of a receiving point relative to spaced transmitters by comparing at said receiving point the phases of signals emitted by said transmitters and received at said receiving point, at least two spaced transmitters for emitting at least three different high frequency signals having frequencies which satisfy the relation where F1, F2 F,L are said frequencies and K1, K3, L K7, are integers at least one of which is positive and at least one of which is negative, whereby two currents of equal frequency can be )derived from said signals` by combination filtering, amplifying and mixing means, a receiver of fixed location having filtering, dmplifying and mixing means to rece-ive said signals and derive therefrom two currents having the same frequency when said relation is satisjed, one of said transmitters having a frequency and phase regulating device, means responsive to the difference between the frequencies and the difference between the phases of said two currents derived by said receiver when said relation is not satisfied to actuate said frequency and phase regulating device to cause the frequencies of said signals to again satisfy said relation, a receiver at said receiving point having filtering, amplifying and mixing means to receive said signals and derive therefrom two currents having the same frequency, and phase metering means jointly responsive to the last-mentioned two currents for providing an indication concerning the location of said receiving point relative to said transmitters.

39. In a system for determining the position of a receiving point, at least two spaced transmitters emitting signals of at least three frequencies, means to regulate one of said frequencies so that said frequencies at least substantially satisfy the relation KlFl-l-KZFZ -i-KF=0 where F1, F2 Fn are the frequencies and K1, K2 Kn are integers at least one of which is positive and at least one of which is negative, whereby two currents can be derived from said signals by combination filtering, amplifying and mixing means which currents have the same frequency when said relation is satisfied and have a frequency dyference when said relation is not satisfied, said means including a frequency varying device in one of `said transmitters, means responsive to `all of said signals and having combination amplifying, filtering and mixing means for deriving two currents from said signals and means responsive to any )differences in frequency and phase between the last-mentioned two currents when said relation is not satisfied for actuating said frequency varying device to vary said one frequency to compensate for any lack of stability of the other frequencies "and cause said relation to be a'gain satisfied, a receiver at said receiving point having combined amplifying, filtering and mixing means `for Aderiving two `currents of the same frequency from said signals when said relation is satised, and means jointly .responsive toy the `last-mentioned two currents to provide an indication with respect to the position of said receiving point.

40. A fine .and coarse position determining system, comprising transmitting apparatus for emitting first and second pairs of `wave signals from separate transmitters and also including means forbeatingthe waves of at least one ofthe pairs together to 'develop-beat signals used in deriving reference signals for transmission, `the signals of the rfirst pair being distinguishable from the signals of the second pair, receiving means responsive to the wave signals and reference signals `to provide ya first position indication, and means to resolve the cyclic ambiguity of said rst position :indication comprising lmeans to provide a second position indication in terms `of the difference frequency between the wave signals of the first pair and the wave signals of the second pair.

41. Wave signal receiving apparatus Acomprising means to receive a plurality of pairs of signals radiated from at least two separate locations with at least one signal having modulated thereon reference signals derived from beating the signals of a first of said pairs of signals, said pairs of signals being ofdistinguishably dierent frequencies with the two signals forming each pair being radiated from differenti-locations and with each pair of signals having the same frequency separation, said receiving apparatus including means for reproducing the reference signals, for heterodyning the signals of the first pair to produce a first beat frequency and for Iheterodyning the signals of a second of said pairs to produce a second beat frequency signal equal in frequency to the first beat frequency signal, means jointly responsive to the reproduced reference signals and to the first beat frequency signal for producing a first position irtdication related to the frequencies of the signals of the first pair, and means jointly responsive to said first and second beat frequency signals to provide a position indication related to vthe frequency difference between said pairs.

42. In a position determining system, a pair of continuous wave systems of the type transmitting wave signals from separate transmitters and providing beat frequency signals for use in developing reference signals for transmission, said systems operating at different frequencies, receiver means for each of said systems for receiving said diyerent frequency signals, means responsive to the outputs of the receiver means for providing a yrst position indication related to the frequencies of the wave signals of one of said systems, and means responsive to the outputs of said receiver means for providing a second position indication relatefd to the frequency dierence bet1fveen the wave signals of said pair of systems.

43. A system for providing position indications, comprising rst and second continuous wave transmission systems each including spaced non-synchronized transmitters for continuously transmitting wave signals from separate points arid receiving means responsive to the wave signals radiated by both of said systems for providing position indications related to the relative values of the frequencies of said first and second systems.

44. A system for providing position indications, comprising first and second continuous wave transmission systems each including spaced non-synchronized transmitters for continuously transmitting wave signals fromI separate points and receiving means responsive to the wave signals radiated by both of said systems for providing position indications in terms of the frequency difference between the wave signals of the first and second systems.

4References Cited in the le of this patent or the original patent I UNITED STATES PATENTS Re. 23,050