CA1050139A

CA1050139A - Method of and system for locating a position

Info

Publication number: CA1050139A
Application number: CA220,866A
Authority: CA
Inventors: Albert A. Elwood
Original assignee: Individual
Current assignee: Individual
Priority date: 1974-03-08
Filing date: 1975-02-25
Publication date: 1979-03-06
Also published as: GB1506904A; JPS50127592A; CH607853A5; AU7892675A; FR2263525B1; ZA751431B; NO750769L; DE2510120A1; FR2263525A1

Abstract

ABSTRACT OF THE DISCLOSURE
A method of and system for locating a position in which a plurality of frequency standard devices (atomic clocks) based on the action of the natural frequencies associated with transitions between energy states in atoms and/or molecules are synchronized or phase compared at the same initial location.
Two of three frequency standard devices, in a two-dimensional embodiment, are placed at transmitting stations on a known baseline. The third device is at a third station, a receiving station, which receives signals from the two transmitting sta-tions. At each transmitting station, means are provided for producing and transmitting a radio frequency carrier signal of fixed frequency and of fixed phase under the control of the frequency standard device associated with the respective station.
The radio frequency carrier signals produced at the different transmitting stations differ in frequency. The radio frequency carrier signal produced at each transmitting station is modulated with a single, low frequency signal produced under the control of the same frequency standard device which controls the means which produce the radio frequency carrier. At the receiving station, means are provided for producing a reference signal, corresponding, in frequency, to the low frequency modulating signal and two local radio frequency signals corresponding, in frequency, to the radio frequency carrier signals transmitted.
These signal producing means at the receiving station are con-trolled by a frequency standard device (atomic clock) associated with the receiving station. The phase of the reference signal is compared, at the receiving station, with the phase of the modulating signals recovered from the radio frequency carriers to determine respective phase differences, the differences rep-resenting coarse position data from which the total number of phase rotations (full lanes) the receiving station is from each of the transmitting stations are determined. The phase relation-ships between each of the received radio frequency carrier signals and the respective one of the two radio frequency signals produced at the receiving station are determined, the relation-ships representing fine position data which are measurements of the receiving station position within a given phase rotation (lane).

Description

``iO5(~13~
Reference is made to my prior United States patents No, 3,613,095 dated October 12, 1971, ~o. 3,797,015 dated March 12, 1974, No. 3,816,832 dated June 11, 1974, and ~o.

3,839,719 dated October 1, 1974.
BACKGROU~D OF THE_ INVENTIO~
FIEI,D OF THE INVE~q~IO~I
mis invention relates in ~eneral to position locating and in more particulaxity to a method and s~stem for accurately locating a specific posltion.
10~ Although both the method and the system are of general ; utility they are especlally useful in offshore oil surveys where it is important that a specific location be accurately and precisely identified. In an operation such as an offshore oil survey two transmitting stations would be land~based whereas a receiving station would be located on an offshore vessel which can be moved to an exact location which is being sought.
DESCRIPTIO~ OF THE PRIOR ART
Many phase or time comparison systems have been deve-loped for locating a position and are in use today. There are those based on the radar principle in which an echo or return of signal technique i~ used, there are those based on the use of transponders where receipt and retransmission of a signal are utilized, and there are those based on the Loran principle where time difference in the receipt of two transmitted pulses define a hyperbolic line of position.
: ~ :
A method of and a system for locating a position are disclosed in the United States patent to Elwood, ~o. 3,613,095.
A plurality of frequency standards (atomic clocks) are synchron-ized or phase compared at~the same location. Two of the frequency standards are respectively placed at radio transmit~

ting stations located on a known baseline, a third one of the : ~ .

frequency standards being positioned at a receiving station.
The transmitting stations broadcast respective intermittently pulse amplitude modulated radio frequency signals of different frequencies. The phase o the radio signals, the frequencies of the radio signals and the particular points in time during which modulation is applied are all determined under the control of the respective frequency standards at the transmitting stations.
The frequency standard (atomic clock) at the receiving station, which has an unknown position, is used to effect con-trol of the phase and frequencies o-f respective first and second locally produced radio frequency signals and of a locally pro-duced timing pulse signal. The frequencies of the two locally produced radio frequency signals correspond respectively to the frequencies of ~he signals received from the transmitting stations. The receiving station is provided with means to de-modulate the signals received from the two transmitting stations so as to recover the intermittent pulses. Pulse time comparators are used to compare the relative positions of the locally pro-duced timing pulses with those pulses recovered ~rom the received radio frequency signals as measures of the respective coarse ranges ~lane identifications) the receiving station is from the two transmitting stations. The phases of the received radio frequency signals are compared respectively to the phases of the locally produced radio fre~uency signal~ of corresponding frequency as measures of fine range (position within a lane) the receiving station is from the two transmitting stations.
A computer is used to calculate the actual range the receiving station is from each of the two transmitting stations, thus its position is determined in two dimensions.
The method and apparatus disclosed in the United States Patent No, 3,613,095 have a number of drawbacks. Firstly, an ' excessive transmission bandwidth is required due -to the fact that the carriers are required to be intermittently amplitude moduLated with pulses which must have steep leading and/or trailing edges. Secondly, the need to modulate intermittently at precise points in time is very difficult to achieve and requires considerable expense.
SUMMARY OF THE INVENTION
Due to the high stability of atomic clocks, which are accurate on the order of one part in 1012 or 1013, no continuous synchronization between stations is required once the initial synchronization among three atomic clocks is performed or the initial phase/time relationships among the three atomic clocks are established.
The frec~uency of an atomic clock is determined by atomic particLe or molecular vibrations and thereby remains constant. Its accuracy is about one hundred to one thousand times as great as that of the quartz clock in which the vibration frequency changes in the course of time. Due to the constancy of the frequency of an atomic clock a new and novel system of position locating has been discovered.
Coarse range is defined as the total number of phase rotations at the carrier or r.f. frequency (wavelengths~ over the distance between each transmitking station and the receiv-ing station, measured to the nearest full phase rotation in a direction along the transmitting station radials toward each transmltting statlon. Full phase rotations (wavelengths) or even fractions thereof may be further defined as lanes~
Fine range is defined as the position of the receiving station within a given phase rotation, or lane, measured in a direction along the transmitting station radials toward each transmitting station, Coarse and fine ranges are combined in a computer to ~05C~39 determine the distance in lanes and fractlons of a lane to each transmitting station from the receivin~ station. secause of this, the system may be defined as a range-range system. The computer may be an appropriately programmed sophisticated com-puter used to convert the ranges into position with respect to any grid or geographic reference that may be desired.
It is the principal object o the invention to provide a method of and a system for locating a position in which fre-quency standard devices are used and only very small transmission bandwidths are required.
It is a further object of the invention to provide a method of and a system for locating a position in which frequency standard devices are used and no need to modulate intermittently at precise points in time exists.
It is another ob]ect of the invention to provide a method of and a system for locating a position in which frequency standard devices are used and modulation is effected continuously.
It is an additional object of the invention to provide a transmitting station particularly use-ful in conjunction with a method of and a system for locating a position in which very small transmission bandwidths are required, no need to modulate intermittently exists and modulation is effected continuously.
It is a still further object o.E the i.n~ention to pro-vide a receiving station particularly useful in conjunction with a method ~or locating a position in which very small transmission bandwidths are required, no need to demodulate intermittently modulated signals exists and demodulation of continuously modulated signals is accomplished by conventional demodulators.
It is still another object o-f the present invention to provide a method oE and a system for locating a position in which frequency standard devices are used in conjunction with single side band techniques.
: _ 4 -,~, .

~OS~39 It is still an additional object of the present inven-tion to provide a method of and a system for locating a position in which frequency standard devices are used in conjunction with double side band suppressed carrier techniques.
It is yet a further object of the present invention to provide a transmitting station, particularly useful in con-]unction with a method of and a system for locating a position, in which a frequency standard device controls the production of a single side tone radio frequency signal.
It is yet another object of the present invention to provide a transmitting sta~tion, particularly useful in conjunction with a method of and a system for locating a position, in which a frequency standard device controls the production of a sup-pressed carrier double side tone radio frequency signal.
It is yet an additional object of the present invention to provide a receiving station, particularly useful in conjun-ction with a method of and a system for locatin~ a position which includes a frequency standard device and is responsive to a single side;tone radio frequency signal.
20 ~ It is another object of the;present invention to pro-;
vide a receiving station,~particularly useful in conjunction with a method of and a system for locating a position, which includes a frequency standard device and is responsive to a carrier suppressed double side tone radio frequency signal, It is still another object of the invention to provide a method of and a system for locating a position in which fre-quency standard devices are used and phase comparison techniques are used to provide both coarse and fine position data, which represent respectively coarse and fine ranges.
It ls still an additional object of the invention to provlde a method of and a system for locating a position ln , ~ .
:

lOS0~39 which frequency standard devices at transmitter locations are used to produce radio frequency carrier waves which are phase compared with signals produced at a receiving station, under the control of a frequency standard devica, to provide -fine position data, and single frequency modulatlon signals, under the control of the frequency standard devices at the transmitter locations, are placed on the radio frequency carriers, recovered at the receiving station and phase compared with a corresponding signal produced at the receiving station, under the control of the frequency standard device at the receiving station, to pro-vide coarse position data.
It is another o~ject of the invention to provide a position locating system in which atomic clocks or the like are utilized to provide a plurality of signals havin~ known phase relationships with one another and a plurality of single tone modulating signals, and local single tone reference siynal having known phase relationships with one another to develop respectively fine and coarse position information.
It is still a further object of the invention to pro-vide a method of and a system for locating a position in threedimensions using three transmitting stations, controlled by frequency standard devices, and a receiving station which also uses a frequency standard device to provide signals for compari-son with signals received from the transmitting stations.
It is still another object oE the invention to provide a method of and a system for locating a position in three dimen-sions using three transmitting stations, controlled by frequency standard devices, and a receiving station which also uses a frequency standard device to provide signals -for comparison with signals received from the transmitting stations, at least one of the transmitting stations being carried by a satellite.

~d ,f ~OS()~39 In its method and system aspects, the invention involves generating at each of a plurality of transmitting stations respective radio frequency signals modulated by res-pective low, single frequency signals. The low frequency signal and the radio frequency signal, in each case, are produced under the control of a frequency standard device, an atomic clock.
At the receiving station, a low frequency signal, corresponding to the modulation low frequency signal and signals, correspond-ing to the radio frequency signals produced at each transmitting station, are produced under the control of a frequency standard device, an atomic clock. The modulati.on signal is recovered from each received radio frequency signal and phase compared with the low frequency signal produced at the receiving station to produce coarse range data. The phase o~ each oE the received radio ~requency signals, or either their upper or lower side tone, or I.F. signals derived therefrom are phase compared with the corresponding radio fre~uency signals produced at the receiver to produce fine range data, In its transmitting station aspect, the invention involves modulating a radio frequency carrier with a low single frequency modulating signal. The modulator used may be a phase modulator, a frequency modulator or an amplitude modulator. The modulator i9 most preferably a balanced modulator which produces a carrier suppressed double side tone signal. The modulator preferably is a modulator which produces a single side tone signal.
In its receiving station aspect, the present invention involves phase comparison circuit means which compares the phase of recovered modulation signals, which in the case of reception of suppressed carrier wave signals is a signal having twice the ; frequency of the actual modulating signal, with a locally pro-, duced corresponding low frequency signal to produce coarse range data. The phase of each of the received radio frequency signals, or either their upper or lower side tones, or I.F. signals derived therefrom are phase compared with corresponding radio frequency signals locally generated to produce fine range data.
In a still further object of the present invention there is provided a position locating system comprising, in combination: ~a) a first frequency standard course of a signalof given frequency and glven phase, (b) a second frequency standard source of a signal of said given frequency and a predetermined phase relationshlp with said given phasej ~c) a third frequency standard source of a~signal of said given frequency and a pre- -determined phase relationship with said given phase; (d) means controlled by said first source for transmitting a first radio signal from a first point including first modulating means con-trolled by said first source for modulating said first radio signal with at least one first, single frequency signal, (e) means controlled by aaid second source for transmitting a second radio slgnal from~a second point lncluding second modul-ating means controlled~by said second source for modulating said second radio signal with at least one second, single frequency signal, (f) means controlled by said third source for generating a signal having a frequency related to that of said first radio signal and a signal having a frequency related to that of said second radio signal at a third point, (g) means controlled by said third source for producing respective at least one first reference signal and at least one second reference signal having respective frequencies related to those of said at least one first, single frequency signal and to said at least one second, single frequency signal; (h) means for receiving said -first radio signal and said second radio signal at said third point which -., , ~05~139 develop therefrom respective signals respectively iden-tical in frequency to those signals produced at said third point related respectively to said first radio signal and to said second radio frequency signal, (i) first phase comparing means at said third point for comparing the phase of the signal developed which relates to said first radio signal with that of said signaL gen-generated at said third point having a frequency identical thereto, (j) second phase comparing means at said third point for comparing the phase of the signal developed which relates to said second radio signal with that of said signal generated at said third point having a frequency identical thereto, (k) means at said third point for demodulating signals to recover respectiveLy signals corresponding to said at least one first, singLe frequency signal and said at least one second, singLe frequency signaL and having respective Erequencies identical to those of said at Least one first reference signal and said at least one second reference signal, (1) and means for comparing respectively the phase of the recovered signals corresponding to said at Least one first, singLe frequency signaL and said at least one second, single frequency signal with the respective phases of said at Least one first and said at Least one second reference signals.
In a still further object of the present invention there is provided a position locating method comprising: pro-viding a first frequency standard signal o-f given frequency and phase, providing a second frequency standard signal of said given frequency and a predetermined phase relationship to said given phase, providing a third frequency standard signal of said given frequency and a predetermined phase reLationship to said given phase, moduLating a first radio signal related to and : controlled by said first standard signal with at least one first, C

10S(~13~ .
single frequency signal also related to and controlled by said first standard signal: transmitting the first radio signal from a first point; modulating a second radio signal related to and controlled by said second standard signaL with at least one second, single frequency signal also related to and controlled by said second standard signal; transmitting the second radio signal from a second point; generating at a third point under control of said third frequency standard signal at least one first, reference signal related in frequency to said at least one first, single frequency signal and at least one second reference signal related in frequency to said at least one second, single frequency signal; generating at said third point, also under control of said third frequency standard signal, a third reference signal and a fourth reference signal respectively related in frequency to said first radio signal and to said second radio si.gnal, recovering at said third point signals corresponding to said at least one first, single frequency signal and said at least one second, single frequency signal and havin~
respective frequencies identical to those of said at least one first reference signal and said at least one second reference signal; comparing the phase of the signal corresponding to said at least one first, single frequency signal recovered at said third point with that of said at least one first reference signal; comparing the phase of the signal corresponding to said at least one second, single frequency signal recovered at said third point with that of said at least one second reference signal; developing respectively from said first and said second radio signals received at said third point a first and a second signal identical respectively in frequency to said third reference signal and to said fourth reference signal; comparing the phase of said third reference signal with that of said signal .~ ' 1 ~
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~50139 identical in frequency thereto which is developed from said first radio signal at said third point' and comparing the phase of said fourth reference signal with that oE said signal iden-tical in frequency thereto which is developed from said second radio signal received at said third point.
In a still further object of the present invention there is provided a position locating system comprising a plura-lity of frequency standard sources of signals of given frequency and predetermined phase relationships, means controlled respect-ively by each of said plurality of sources for transmitting fromrespective points respective radio signals, thesç means including respective modulating means controlled respectively by respective ones of said plurality of frequency standard sources for modulat-ing each of said respective radio signals with at least one respective single frequency signal derived from respective ones of said frequency standard sources, a further frequency standard source of signaL at an additional point having the same given frequency as said plurality of frequency standard sources and a predetermined phase relationship; means controlled by said further frequency standard source of signals for generating at : said additional point a first plurality of reference signals related respectively to said respective radio siynals, means controlled by said further frequency standard source of signal at said additional point for producing a second plurality of reference signals having respective frequencies related respec-tively to the frequencies of said single frequency signals, means for receiving said respective radio signals at said additional point, means at said additional point for deriving from said radio signals received at said additional point a further plur-ality of signals respectively identical in frequency to said first plurality of reference signals, phase comparing means at said additional point for compari.ng respectively the phase of each signal of said further plurality signals derived from said radio signals with the phase of respec~ive signals of said first plurality of reference signals, means at said additional point for recovering an additional plurality of signals corresponding respectively to respective ones of said single fre~uency signals and having respective fre~uencies identical to the frequencies of respective ones of said second plurality of reference signals, and phase comparing means for comparing respectively the phase of each recovered signal of said addltional plurality of signals with the phase of respective signals of said second plurality of reference signals.
In a still further object of the present invention there is provided a radio receiving station comprising a stahle source of oscillations, means receiving a plurality of radio frequency signals modulated respectively with at least a respec-tive one of a plurality of single frequency signals, means cont-rolled by said stable source of oscillations for developing a flrst plurality of reference signals corresponding respectively to said plurality of radio frequency signals, means controlled by said stable source of oscillations or developing a second plurality of reference signals corresponding respectively to said plurality of single frequency signals, means for developing from said plurality of radio signals a further plurality of signals identical in frequency to respective ones of said first plurality of reference signals, first phase comparing means for comparing the phase of each of said further plurality of signals with respective ones of said first plurality of reference signals, means for recovering an additional plurality of signals corres-ponding respectively to respective ones of said plurality of single frequency signals and having respective frequencies identical to respective ones of said second plurality of reference ~D
, ~050~39 signals, and second phase comparing means for comparing the phase of each signal of said additional plurality of signals with the phase of respective ones of said second plurality of reference signals.
Further eatures, objects, and advantages will either be speci~ically pointed out or become apparent when, ~or a better understanding of the invention, reference is made to the following written description ta~en in conjunction with the accompanying drawings.
BRIEF DESCRIPTIO~ OF THE D~AWI~GS
Figure lA is a diagrammatic view illustrating the use of a method and system, in a~two-dimensional arrangement, according to the invention, Figure lB is a diagrammatic pictorial view illustrat-ing the use of a method and system, in a three-dimensional arrangement, according to the invention in which three trans-mitting stations are used, Figure lC is a diagrammatic pictorial view illustrat-ing the use of a method and system, in a three-dimensional arrangement, according to the present invention in which two transmitting stations are used in conjunction with an altimeter which can be carried on an aircraft or the like, Figure lD is a diagrammatic pictorial view illustrat-ing the use of a method and s~stem, in a three-dimensional arrangement, according to the present invention in which three transmitting stations are used, one of them being carried by a satellite, Figure 2 is a block diagram of an illustrative embodi-ment of a transmitting station according to the invention, Figure 3 is a block diagram of an illustrative embodi-ment of a transmitting station which produces a single side tone signal according to the invention .~

Figure 4 is a bloc]c diagram of a preferred embodiment of a transmitting station which produces a carrier suppressed double side tone signal according to the invention' Figure 5 is a block diagram of a preferred transmitting station which produces a burst modulated carrier according to the invention, Fi~ure 6 is a block diagram of an illustrative embodi-ment of a receiving station according to the invention' Figure 7 is a block diagram in greater detail of part o~ a typical receiving station, the two sheets of the drawing containing Figure 7 are to be placed end-to-end to illustrate a complete station inluding a computer, and Figure 8 is a block diagram of part of a receiver which may be used in a receiving station according to the inveI~-tion, the receiver being a superheterodyne receiver.

DESCRI PTION OF PREFERRED EMBODIMENTS
Referring now to Figure LA of the drawings, a system according to the invention will include a transmitting station A which lS placed:at a known positlon, a transmitting station B
which is placed at a known position, with A and B placed on a known baseline Rb , and a receiving station C which is at an unknown position and becomes the measured or located position.
As .illustrated in Figure lB, a three-dimensi.onal system according to the i.nvention may include a transmitting station A, a transmitting station B and a transmitting sta*ion D each placed at a respective location, spaced from one another. Stations A
and B are placed on a known baseline RbaSe l and stations B and D are placed on a known baseline RbaSe 2 A receiving station C, illustrated as being carried by a moving aircraft, is at an unknown position and becomes the measured or located position.

$`

10S~139 As shown in Figure lC, a three-dimensional system according to the invention may comprise a transmitting station A
which is placed at a known position, a transmitting station B
which is placed at a known position, stations A and B being positioned on a known baseline ~ , and a receiving station C
shown as being carried by a moving aircra~t which is at an un-~nown position. The aircraft carries as part of its equipment an altimeter.
As illustrated in Figure lD, a further three~dimensional system according to the invention may include a transmitting station A a transmitting station B and a transmittiny station D
` each positioned at respective locations, spaced apart from one another. Stations A and B are placed on a known fixed baseline RbaSe 1 and stations B and D are placed on a known baseline RbaSe 2' As illustrated, station D is carried by a satellite ; which may be either a synchronized satellite or an unsynchron-ized satellite having a predictable orbit and known position at a given time. A receiving station C, illustrated as being carried by a movlng alrcraft, is at an unknown position and becomes~ the measured or located position.
The two transmltting stations lllustrated here as shore-based stations ~ and B (Figures lA and lC) and transmitting stations A, B and D (Figures lB and lD) may be constructed as illustrated in greater detail in any one of Figures 2-5, The station is duplicated at A and B or A, B and D with the only essential difference being that different RF frequencies are ; transmitted from respective stations.
Referring to Figure 2, the transmitter includes an atomic clock 10 which provides a high frequency signal, for example 9 GHz, which is utilized in two ways, The high frequency signal is fed to frequency synthesizer 11 where it is reduced in C~, ~ 050139 frequency to a selected frequency in a range suitable for trans-mission over distances o~ up to about 100 miles, in an exemplary system, and for accuracy of phase determination. The range may be, for example, from about 1.0 to about 5.0 MHz, The frequency synthesizer 11 converts the high ~requency signal, from clock 10 to one in the lower range (1.0 - 5.0 MHz) while maintainlny the stability of the primary standard from clock 10. The output of frequency synthesizer 11 which is extremely accurate in its phase and frequency characteristics is fed to a driver syn-thesizer 12 wherein it is amplified to a level sufficient todrive highly stable radio transmitter 13. The radio transmitter 13 is provided with an antenna 15 from which a radio frequency signal of given frequency is transmitted, Thus, the stability and accuracy of clock 10 is preserved and reflected in the radiated signal.
The high frequency signal from clock 10 is also fed to a frequency synthesizer 14 wherein it is converted into a given low frequency signal, which is useful as a single frequency modulating signal. The modulating signal may have a frequency ZO of, for example, SOO Hz. The synthesizer 14, like the synthesizer 11, preserves the accuracy and stability o the clock 10 and reflects the accuracy thereof in its own output which is coupled to a modulator 16 which may be either a frequency modulator, a phase modulator or an amplitude modulator.
The modulations appearing on carrier signals from trans-mitting stations A, B and D (Figures lB and lD~ or A and B
(Figures lA and lC) are utilized at a moving recelving station C
(Figures lA-lD) to produce coarse position information data, and the phase relationships of the radio frequency signals from the transmitting stations are utilized to produce fine position information, 1050~39 In Figure 3 a further transmitting station, which may be used in place o~ the transmitting station shown in Figure 2, also includes an atomic clock 10, frequency syn~hesizers 11, 12 and 14, a modulator 16, constructed as an amplitude modulator which is preferably a balanced modulator with a side tone filter, and an antenna 15. A single side band radio transmitting linear r,f, amplifier 113 is provided in place of the radio transmitter 13 (Figure 2), differ~ing from the transmitter 13 in that one of its possible side bands, preferably its upper side band, is eliminated. The modulator 16 receives its carrier signal input from the driver synthesizer 12 and its modulating signal from the frequency synthesizer 1~.
In Figure 4 a preferred transmitting station, which may be used in place of the transmitting station shown in Figure

2, also includes an atomic clock 10, frequency synthesizers 11, 12 and 14, and an antenna 15. A balanced modulator 116, which receives its carrier signal input from the driver synthe~ zer 12, is used instead of the modulator 16 tFigure 2) and a radio transmitting linear r.f, amplifier 213, fed from the modulator 2~ 116 supplies a double side band suppressed carrier signal to the antenna 15. The linear r.f. amplifier 213 is used in place of the radio transmitter 13 (Figure 2). The single side band fun-ctions are performed by the balanced modulator and sidetone filter.
It is to be appreciated that the transmitting station illustrated in Figure 3 has the distinct advantage of extremely low transmission bandwidth requirements. It is also to be appreciated that the single side tones transmitted from the trans-mitting station illustrated in Figure 4 contain considerably more power than those produced and transmitted with an unsup-pressed carrier, Since all necessary information is present in the upper and lower side tones for producing coarse and fine - 17 _ .~ .

range data at a receiving station, improved signal-to-noise characteristics are realized for the locating system.
It i9 not necessary to modulate the radio transmitters continuously for it is seldom necessary to determine the coarse position of a receiving station on a continuous basis, the most recent lane identification as displayed being accurate. It is desirable, however, to provide a carrier signal which is as strong as possible to determine the fine position within a lane.
The preferred embodiment of a transmittiny station illustrated in Figure 5 is constructed to provide for burst modulation, thereby allowing an unmodulated radio ~requency carrier to be radiated at full power during given periods having, for example, nine second durations, the modulation signal being supplied in bursts having, for example, three second durations, As illustrated in Figure 5, the transmittin~ station includes an atomic clock 10 which provides a high frequency signal, for example ~ GHz, which is fed to frequency synthesizers 11, 14 and 218.
The high frequency signal is reduced in the frequency synthesizer 11 to a selected frequency in a range suitable for transmlssion over distances up to about 100 rniles, in an exem-plary system, and for accuracy of phase determination. The range may be from about 1.0 to ahout 5.0 MHz. The output of the frequency synthesizer 11 which is extremely accurate i.n its phase and frequency characteristics is fed to a driver synthesizer 12 where it is amplified to a level sufficient to drive a highly stable radio transmitter 13 provided with an antenna 15.
The high frequency signal from the clock 10 fed to the frequency synthesizer 14 is converted into a given low frequency signal which is to be used as a single frequency modulation sig-nal. The modulating signal may have a frequency, for example, ~OS0139 of 500 Hz, The output from the frequency syn-thesizer 14 is fed to a modulator 216 via a gate circuit 217. The modulator 216 may be an amplitude modulator, a phase modulator or a frequency modulator, as shown ln Figure 2. The modulator 216 may be a balanced modulator corresponding to the balanced modulator 116 shown in Figure 4. In this case the transmitter 13 would be a transmitting linear r.f. amplifier which receives a double side band suppressed carrier signal from the modulator 216, arranged as illustrated in Figure 4. The radio transmitter 13 could, if desired, be a linear r.f. amplifier which receives a single side band signal from a balanced modulator and side tone filter, arranged as shown in Figure 3.
: The high frequency signal from the clock 10 fed to the synthesizer 218 is reduced to a low frequency signal which con-trols and synchronizes a pulse timer 219 which produces, for example, a pulse of three seconds duration every twelve seconds.
The train of pulses from the pulse timer 219 is fed as an enabling pulse to the gate circuit 217.
Thus, the transmitter 13 produces a burst modulated radio signal~which is radiated from the antenna 15, the modulation ~eing present during three second intervals separated by nine second intervals during which the carrier is present a~ full strength.
The signal from the radio transmitter 13 (Figure 2 or 5~ or 113 (Figure 3) or 213 (Fi~ure 4) at station A (Figure lA) is received by the receiver 17 (Figure 6) while the signal from a corresponding radio transmitter at station B (Figure lA) is received by the receiver 18 (Figure 6). Radio frequenc~ output signals from receivers 17 and 18 are fed to phase determining 39 units 20 and 21, respectively, each of which compares the phase of respective radio frequency signals with the phase of the radio frequency slgnals -from frequency synthesizers 29 and 31 which have their respective inputs coupled to an atomic clock 19.
The phase differences translated into digital signals ~ phase A
and ~ phase B representative of phase differences are fed into a range computer 24 of the~computer 27 of the system and converted into two range signals indicating fine position information within a particular lane which may be, for example, 720 feet wide Each degree o~ relative phase rotation in the example represents two feet~ Of course, the outputs of the phase deter-mining units 20 and 21 do not provide lane identification, Each of the receivers 17 and 1~ is provided with appro-priate demodulators (not shown) which may be amplitude demodula-tors, phase demodulators or frequency demodulators depending on the nature o-f the modulation type selected for use at the trans-mitting stations. In the event sin~le side tone/carrier signals are received, it is most practical to use balanced demodulators.
In the case double side tone/carrier suppressed signals are received, the demodulators must be balanced demodulators. Out-puts from the demodulators are fed to phase comparators 23 and 22, respectively. The phase comparators 22 and 23 compare the phase of respective demodulated signals from the receivers 17 and 18 with that of a signal from a frequency synthesizer 41 which has its input coupled to the atomic cloc]c l9. I~.e phase comparators 22 an~ 23 provide output coarse range digital signals RBC and RAC which are also fed into the range computer 24, the output of which is coupled to a position computer 2S
which provides output signals ReA and R~B representing the accurate distance station C is from each of the stations A and B, as illustrated in Figure lA, In the case phase modulation is used, it is to be understood that phase determining units 20 and 21 could advisably .

105~)139 be constructed so as to reject from the}r outputs any signals having a time variation above about 50 cycles, that is, about 1./10 of the modulation ~requency, This could be accomplished by a digital filter.
The position computer 25 operates a position keeper and display 26 which converts the two ranges from the shore stations and B into precision position in any selected coordinate sys-tem. Signals R~A and R~B may be either digital or analog signals and the position keeper and display 26 may be either digital or analog or both. The atomic clock 19 is provided with a timing output signal tl which is used to synchronize the computer 27 as illustrated generally by timing inputs t which are provided by count-down circuits (not shown) which are driven by the tim-ing signal tl. Alternatively, the timing signal tl could be directly fed i.nto the computer 27 provided that the computer 27 contained suitable count-down circuits.
It is to be appreciated that in the event the receiv-ing station shown in Figure 6 is used in conjunction with trans-mitting statlons of the type shown in any one of Figures 2-5, the phase determining units 20 and 21 are responsive to the carrier or side tone frequencies received by the receivers 17 and 18 and the phase comparators 22 and 23 respond to the actual modulation signals, for example 500 ~I , or 1000 H in the carrier suppressed case, recovered from the signals received by the receivers 17 and 18.
In the event the receiving station shown in Figure 6 is used in conjunction with transmitting stations of the type shown in Figure 4, the phase determining units 20 and 21 are responsive to either the upper or lower side tone signals, pre-ferably the lower side tone signal, and the frequency synthe-sizers 29, 31 and designed to produce signals having the same i~i frequencies of the particular side tone signals selected. In this case the frequency synthesizer 41 is operatively arranged and designed to produce a reference signal which has a fre~uency twice as high as the frequency produced in the frequency syn-thesizer 14 (Figure 4) as the moaulating signal at the trans-mitters, Thus, the signal produced by ~he frequency synthesizer 41 would be 1000 ~ in the event the signal produced by the synthesizer 14 (Figure 4~ at each transmitting station were 500 Hz, as suggested above.
Figure 7 illustrates in greater detail the instrument-ation used in the offshore station when the system is being used to locate an offshore position.
The phase determining unit 20 of Figure 6 is shown, in Figure 7, as comprised of a phase comparator 30. The phase determining unit 21 of Figure 6 is shown in Figure 7 as comprised of a phase comparator 32.
Frequency synthesizers 33 shown in Figure 7 correspond to the frequency synthesizers 29 and 31 shown in Figure 6 and the frequency syntheslzer 42 corresponds to the frequency synthesizer 41 shown in Figure 6.
In the embodiment illustrated in Figure 7, the function of the two phase comparators 22 and 23, illustrated in Figure 6, is performed by a singIe phase comparator 34 which has its inputs, from the receivers 17 and 18, provided via a multiplexer 43, and its outputs representative of coarse ranges A and B fed to the computer 27 via de-multiplexer 44.
Digital outputs from phase comparators 30 and 32 are fed respectively to digital range computers 35 and 36 as fine position data, while outputs from phase comparator 34 are fed respectively, to the digital range computers 35 and 36 as coarse position data, via the de-multiplexer 44.

The two digital range computers 35 and 36 process their respective data inputs to provide output siynals represent-ing the accurate (fine plus coarse) range of station C rom stations A and B iespectively, The outputs from the digital range computers 35 and 36 are fed to a digital position computer 37 associated with a data storage apparatus 39 which provides baseline and shore base station information. Using stored information from the storage apparatus 39, the digital positlon computer 37 translates the accurate position data supplied from the range computers 35 and 36 into position signals R~A and ReB which are fed to a digital/
analog storage generation and display device 31, the output of which is fed to a position display 40.
The device 31 is provided with storage means which contains phase correction data reflecting the initial absolute phase differences, if any, between three atomic clocks. Addi-tional stored information, as desired, may be provided or developed within -the device 31 such as bearing, range, course, and known distance to the desired position within an offshore lease, for example, as shown in Figure lA. In some applications, such as a fast moving station C, Doppler correction data could be developed or stored within the device 31. In the embodiment illustrated in Figure 7, the atomic clock 19 provides a timing output signal tl which is used to develop, in circultry not illustrated, timing signals generally designated t which synchronize the computer 27, the position keeper 28, the multi-plexer ~3 and the de-multiplexer 44. The phase cornparator 34 is provided with two gating outputs A and B which are used to gate the radio receivers 17 and 18.
While the foregoing discussion is concerned principally with description of the method and system of the invention and its operation in a two-dimensional arrangement, it will be clear 10~013~
that the invention may be applied equally well in t~ree-dimensional arrangements. It is suitable, ~or example, -for locating the position of an aircraft or other object which moves in three dimensions. Figures lB, lC and lD show three exemplary three-dimensional arrangements.
Referring to Figure lB, a three-dimensional system according to the method and system may include a transmitting station A, a transmitting station B and a transmitting station D
each placed at a known position and spaced from one another. A
receiving station C, carried by an aircra-ft, is at an unknown position and becomes the measured or located position in three dimenslons. The three transmitting stations A, B and D (Figure lB) may be constructed as the transmitting station illustrated in Figure 2 or the one illustrated in Figure 3 or the one illus-trated in Figure 4, or the one illustrated in Figure 5, the only essential difference among the transmitting stations A, B and D
being that different RF frequencies are transmitted from res-pective transmitting stations. As illustrated in Figure lB, the xeceiving station C is carried by an aircraft. The receiving station C (Figure lB) may be constructed similarly, for example, to either the receiving station shown in Figure 6 or the receiv-ing station shown in Figure 7, it being understood, in either case, that an additional radio receiver suitable for receiving signals from the transmitting station D would be provided at receiving station C as well as instrumentalities for developing a phase D and RDC signals which would be fed to the computer 27 in addition to the ~ phase A, a phase B, RAC and RBC signals.
The frequency synthesizer 41 (Figure 6j or 42 (Figure 7) would, of course, produce a local signal having the same frequency as produced by the frequency synthesizer 14 ~Figures 2, 3 and 5) or twice the frequency of the frequency synthesizer 14 (Figure 4).

" ~0S~139:
In Figure lC, a three dimensional system for locating the position according to the invention may include a transmit-ting station A, which is placed at a known position, a transmit-ting station B, which is placed at a known position, with stations A and B being on a known baseline ~ ase' and a receiving station C, illustrated as being carried by an aircraft which is at an un]cnown position and becomes the located or measured position. In the arrangement shown in Figure lC, the two trans-mitting stations A and B may be constructed as the transmltting station illustrated in Figure 2 or in Figure 3 or in Figure 4 or in Figure 5, and the receiving station C may be constructed, for example, similarly to either the receiving station shown in Figure 6 or the receiving station shown in Figure 7. In the system illustrated in Figure lC, however, the receiviny station C, which is carried by the aircra~t, includes an altimeter (not shown) of known construction which develops height data which is fed to the computer 27 (Fi~ures 6 and 7) thereby enabling the computer 27 to determine the position of station C
in three dimensions, the computer 27 being capable of deter-mining distances RA and RB in accordance with the system asshown in Figure lA.
Turning now to Figure lD, a three-dimensional system similar to that shown in Figure lB is shown, the only essential difference being that transmitting station D is carried by a satellite. The satellite may be either a synchronous satellite or a non-synchronous satellite. If the satellite is synchronous, its position is fixed relative to transmitting stations A and B
(Figure lD) and the system operates identically to the system shown in Figure lB. If the satellite is non-synchronous, its position is constantly changing relative to the positions o~
transmitting stations A and B (Figure lD) in a predetermined pattern. In the latter case, the computer 27 (Figures 6 and 7) _ 25 -)139 is provided with a data store which supplies a signal indicative of the instantaneous position of the non-synchronous satellite at any given ~ime. Thus, the computer 27 (Fi~ures 6 and 7) may determine from signals representative of a phase A, ~ phase B, phase D, ~AC~ RBC, RDC, as in Figure lB, and the signal re~
presenting the instantaneous position of the non-synchronous satellite, the position of the receiving station C.
The foregoing description, particularly as it reLates to the receiving stations illustrated in Figures 6 and 7, as thus ar described by way of examples involves the use as ~uned radio frequency receivers at the receiving stations. The noise rejection characteristics of the receivers can be considerably improved by use of superheterodyne receivers, particularly super-heterodyne receivers which involve double conversion. Since the stages in the receivers desirably have low gains and broad band-widths i.e. 2-3 KHz, in order to avoid injecting any unwanted phase shifts, it is desirable to use superheterodyne receivers which tend to re~ect noise signals while maintaining the phase relationships of the signals sought to be amplified. Such a superheterodyne receiver, which may be used as the receiver 17 (Figures 6 and 7), for example, and similarly for other receivers to be used at a receiving station location, is illustrated in Figure 8~
As shown in Figure 8, each of the receivers 17 and 18 at a receiving station includes, in cascade, an R.F. amplifier 71, a first mixer 72, a first I,F. strip 73, a second mixer 74 and a second I.F. strip 75. The receiver includes a frequency synthesizer 76 and a frequency synthesizer 77 which are provided with respective inputs from the atomic clock 19 (Figure 6~, the frequency synthesizers producing signals of appropriate fre-quencies or local oscillators suitable for supplying the locally generated signals to the mixers 72 and 74.

- 1050~39 The I.F. strips 73 and 75 are carefully designed not to distort the signals which are amplified therein, so far as the phase information present on the I.F. signals is concerned, that is, the strips operate on phase locked ampliFiers by virtue of their associated local oscillators, which are fed from syn-thesizers connected to the atomic clock. Since the mixers 72 and 74 are provided with inputs controlled by the atomic clock 19 (Figure 6), the phase information in the signals passed through the receiver and the modulation information is not dis-torted or aestroyed, The I.F. output slgnal from the second I.F, amplifier is fed to a demodulator 78 which, in turn, feeds one input of the phase comparator 23 (Figure 6) which receives a correspond ing signal from the frequency synthesizer 41.
The I.F. ou-tput from the second I.F. amplifier is also fed to one input of the phase determining unit 20 (Figure 6), the other input being supplied from the frequency synthesizer 29 (Figure 6). Tbe frequency synthesizer 29 supplies a signal having the same frequency as the I.F. signal, in the event the receiving station receives a double side band unsuppressed carrier signal or a single side band unsuppressed carrier signal.
In the case the receiving station receives a double side tone suppressed carrier signal, the frequency supplied to the phase determining unit 20 ~Figure 6) from the atomic clock 19 (Figure 6) would correspond to the I.F. signal plus or minus the modula-tion frequency supplied at the transmitting station. Thus, the phase of one of the side tones is used to determine the coarse position rather than the phase of the carrier. Preferably, the lower side tone is used.
Although the present invention has been illustrated as involving a moving receiving station and two or three transmit-~050139 tin~ stations, it is to be appreciated that the receiving station could be fixed and one of the transmitting stations moving, In some special applications all of the stations could be moving.
While the present invention has been illustrated, in general, as one in which the signal outputs from phase compara-tors are digital, the outputs from these units cauld, if desired, be made analog in which case the analog outputs could be com-bined in a network, servo system, or the li~e. For the sake o-f accuracy, however, the outputs from the phase comparators are desirably dig1tal.
The present invention is highly accurate and serves to eliminate lane ambiguity without the need to be operating at all times or accumulating lanes as, for example, when a vessel carrying the receiving station leaves shore and proceeds to sea.
The atomic clocks used in the present invention may be provided by cesium beam tubes such as the tube forming part of a Hewlett-Packard* cesium beam frequency standard sold under model number 5061A, The transm1tters and receivers may be of various constructions, and should be extremely stable. The com-puter used may be, for example, a Control Data Corporation 5103A
system or a Contral Data Corporation 469 system, the latter being particularly suitable for use in aircraft.
It will be appreciated that many variations of the present invention are possible, and the foregoing detailed des-cription relates only to illustrative embodiments. It is to be understood that various changes may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

* trade mark _ 28 -,~:

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A position locating system comprising, in combination:
(a) a first frequency standard source of a signal of given frequency and given phase;
(b) a second frequency standard source of a signal of said given frequency and a predetermined phase relationship with said given phase;
(c) a third frequency standard source of a signal of said given frequency and a predetermined phase relationship with said given phase;
(d) means controlled by said first source for trans-mitting a first radio signal from a first point including first modulating means controlled by said first source for modulating said first radio signal with at least one first, single frequency signal;
(e) means controlled by said second source for trans-mitting a second radio signal from a second point including second modulating means controlled by said second source for modulating said second radio signal with at least one second, single frequency signal;
(f) means controlled by said third source for generat-ing a signal having a frequency related to that of said first radio signal and a signal having a frequency related to that of said second radio signal at a third point;
(g) means controlled by said third source for produc-ing respective at least one first reference signal and at least one second reference signal having respective frequencies related to those of said at least one first, single frequency signal and to said at Least one second, single frequency signal;
(h) means for receiving said first radio signal and said second radio signal at said third point which develop there-from respective signals respectively identical in frequency to those signals produced at said third point related respectively to said first radio signal and to said second radio frequency signal;
(i) first phase comparing means at said third point for comparing the phase of the signal developed which relates to said first radio signal with that of said signal generated at said third point having a frequency identical thereto;
(j) second phase comparing means at said third point for comparing the phase of the signal developed which relates to said second radio signal with that of said signal generated at said third point having a frequency identical thereto:
(k) means at said third point for demodulating signals to recover respectively signals corresponding to said at least one first, single frequency signal and said at least one second, single frequency signal and having respective frequencies identical to those of said at least one first reference signal and said at least one second reference signal;
(l) and means for comparing respectively the phase of the recovered signals corresponding to said at least one first;
single frequency signal and said at least one second, single frequency signal with the respective phases of said at least one first and said at least one second reference signals.

2. A position locating system according to claim 1 wherein said first frequency standard source, said second frequency standard source and said third frequency standard source are respectively first, second and third atomic clocks.

3. A position locating system as claimed in claim 1 in-cluding computer means receiving output signals from said first phase comparing means, from said second phase comparing means and from said means for comparing respectively the phase of the recovered signal corresponding to said first single frequency signal and the recovered signal corresponding to said second single frequency signal with the respective phases of said first and second reference signals for providing output signal data representative of the distance the third point is from the first and second points.

4. A position locating system as claimed in claim 3 in-cluding means controlled by said computer means for storing and displaying said output signal data.

5. A position locating system according to claim 1 wherein said first modulating means is a first amplitude modulating means for amplitude modulating said first radio signal with said first single frequency signal, said second modulating means is a second amplitude modulating means for amplitude modulating said second radio signal with said second single frequency signal, and said means at said third point for demodulating are means for detecting amplitude modulation to recover signals corresponding to said first single frequency signal and said second single frequency signal.

6. A position locating system according to claim 1 wherein said first modulating means is a first frequency modulating means for frequency modulating said first radio signal with said first single frequency signal, said second modulating means is a second frequency modulating means for frequency modulating said second radio signal with said second single frequency signal, and said means at said third point for demodulating are frequency demodulating means for detecting frequency modulation to recover signals corresponding to said first single frequency signal and said second single frequency signal.

7, A position locating system according to claim 1 wherein said first modulating means is a first phase modulating means for phase modulating said first radio signal with said first single frequency signal, said second modulating means is a second phase modulating means for phase modulating said second radio signal with said second single frequency signal, and said means at said third point for demodulating are means for detecting phase modulations to recover signals corresponding to said first single frequency signal and said second single frequency signal.

8. A position locating system according to claim 1 com-prising a fourth frequency standard source of signal of said given frequency and a predetermined phase relationship with said given phase, means controlled by said fourth source for transmitting a third radio signal from a fourth point including third modulating means controlled by said fourth source for modulating said third radio signal with a third single frequency signal, means for receiving said third radio signal at said third point, means controlled by said third source for generating a third reference signal having a frequency related to that of said third single frequency signal, means controlled by said third source for generating a signal having a frequency related to that of said third radio signal, means for receiving the third radio signal at said third point which develops a signal identical in frequency to that of the signal generated at said third point related to the third radio signal, third phase com-paring means at said third point for comparing the phase of the signal developed which relates to said third radio signal with that of said signal generated at said third point having a frequency identical thereto, means at said third point for de-modulating to recover a signal corresponding to said third single frequency signal and having a frequency identical to that of said third reference signal, and means for comparing the phase of said signal corresponding to said third single frequency signal with the phase of said third reference signal.

9. A position locating system according to claim 8 wherein said third modulating means is a third modulating means for amplitude modulating said third radio signal with said third single frequency signal, said means at said third point for demodulating to recover said signal corresponding to said third single frequency signal is a means for detecting amplitude modulation, said first modulating means is a first modulating means for amplitude modulating said first radio signal with said first single frequency signal, and said second modulating means is a second modulating means for amplitude modulating said second radio signal with said second single frequency signal, and said means at said third point for demodulating to recover signals corresponding to said first single frequency signal and said second single frequency signal are means for detecting amplitude modulation.

10. A position locating system according to claim 8 wherein said third modulating means is a third modulating means for frequency modulating said third radio signal with said third single frequency signal, said means at said third point for demodulating to recover a signal corresponding to said third single frequency signal is a means for detecting frequency modulation, said first modulating means is a first frequency modulating means for frequency modulating said first radio signal with said first single frequency signal, said second modulating means is a second modulating means for frequency modulating said second radio signal with said second single frequency signal, and said means at said third point for demod-ulating to recover signals corresponding to said first single frequency signal and said second single frequency signal are means for detecting frequency modulation.

11. A position locating system according to claim 8 wherein said third modulating means is a third modulating means for phase modulating said third radio signal with said third single fre-quency signal, said means at said third point for demodulating to recover a signal corresponding to said third single frequency signal is a means for detecting phase modulation, said first modulating means is a first modulating means for phase modulating said first radio signal with said first single frequency signal, said second modulating means is a second modulating means for phase modulating said second radio signal with said second single frequency signal, and said means at said third point for demodu-lating to recover signals corresponding to said first single frequency signal and said second single frequency signal are means for detecting phase modulation.

12. A position locating system according to claim 8 in-cluding computer means receiving output signals from (1) said first phase comparing means, (2) from said second phase compar-ing means, (3) from said third phase comparing means, (4) from said means for comparing respectively the phase of the recovered signal corresponding to said first single frequency signal and the recovered signal corresponding to said second single fre-quency signal with the respective first and second reference signals and (5) from said means for comparing the recovered signal corresponding to said third single frequency signal with said third reference signal for providing output signal data representative of distance said third point is from the first, second and fourth points.

13. A position locating system as claimed in claim 12 including means controlled by said computer means for storing and displaying said output signal data.

14. A position locating method comprising:
providing a first frequency standard signal of given frequency and phase, providing a second frequency standard signal of said given frequency and a predetermined phase relationship to said given phase, providing a third frequency standard signal of said given frequency and a predetermined phase relationship to said given phase; modulating a first radio signal related to and controlled by said first standard signal with at least one first, single frequency signal also related to and controlled by said first standard signal, transmitting the first radio signal from a first point, modulating a second radio signal related to and controlled by said second standard signal with at least one second, single frequency signal also related to and controlled by said second standard signal; transmitting the second radio signal from a second point, generating at a third point under control of said third frequency standard signal at least one first, reference signal related in frequency to said at least one first, single frequency signal and at least one second reference signal related in frequency to said at least one second, single frequency signal; generating at said third point, also under control of said third frequency standard signal, a third reference signal and a fourth reference signal respectively related in frequency to said first radio signal and to said second radio signal, recovering at said third point signals corresponding to said at least one first, single frequency signal and said at least one second, single frequency signal and having respective frequencies identical to those of said at least one first reference signal and said at least one second reference signal; comparing the phase of the signal corresponding to said at least one first, single frequency signal recovered at said third point with that of said at least one first reference signal; comparing the phase of the signal corresponding to said at least one second, single frequency signal recovered at said third point with that of said at least one second reference signal; developing respectively from said first and said second radio signals received at said third point a first and a second signal identical respectively in frequency to said third refer-ence signal and to said fourth reference signal, comparing the phase of said third reference signal with that of said signal identical in frequency thereto which is developed from said first radio signal at said third point, and comparing the phase of said fourth reference signal with that of said signal identical in frequency thereto which is developed from said second radio signal received at said third point.

15. A position locating method according to claim 14 wherein said first frequency standard signal, said second frequency standard signal and said third frequency signal are provided respectively from first, second and third atomic clocks.

16. A position locating method according to claim 14 wherein the step of modulating said first radio signal is the step of amplitude modulating said first radio signal with said first single frequency signal, the step of modulating said second radio signal is the step of amplitude modulating said second radio signal with said second single frequency signal, and the step of recovering signals corresponding to said first single frequency signal and said second single frequency signal com-prises steps of amplitude demodulating.

17. A position locating method according to claim 14 wherein the step of modulating said first radio signal is the step of frequency modulating said first radio signal with said first single frequency signal, the step of modulating said second radio signal is the step of frequency modulating said second radio signal with said second single frequency signal, and the step of recovering signals corresponding to said first single frequency signal and said second single frequency signal comprises frequency demodulating.

18. A position locating method according to claim 14 wherein the step of modulating said first radio signal is the step of phase modulating said first radio signal with said first single frequency signal, the step of modulating said second radio signal is the step of phase modulating said second radio signal with said second single frequency signal, and the step of re-covering signals corresponding to said first single frequency signal and said second single frequency signal comprises steps of phase demodulating.

19. The position locating method according to claim 14 including providing a fourth frequency standard signal of the given frequency and a predetermined phase relationship with said given phase, modulating a third radio signal related to and controlled by said fourth standard signal with a third single frequency signal also related to and controlled by said fourth standard signal, transmitting the third radio signal from a fourth point, receiving said third radio signal at said third point, generating at said third point under control of said third standard signal a fifth reference signal having a frequency related to that of said third radio signal, generating at said third point a sixth reference signal having a frequency related to that of said third single frequency signal, recovering at said third point a signal corresponding to said third single frequency signal and having a frequency identical to that of said sixth reference signal, developing from said third radio signal received at said third point a signal identical in fre-quency to said fifth reference signal, comparing the phase of said fifth reference signal with that of said signal identical in frequency thereto which is developed from said third radio signal received at said third point; and comparing the phase of the recovered signal corresponding to said third single frequency signal with said sixth reference signal.

20. The position locating method according to claim 19 wherein the step of modulating said third radio signal is the step of amplitude modulating said third radio signal with said third single frequency signal, the step of recovering a signal corresponding to said third single frequency signal is a step of amplitude demodulating, the step of modulating said first radio signal is the step of amplitude modulating said first radio signal with said first single frequency signal, the step of modulating said second radio signal is the step of amplitude modulating said second radio signal with said second single frequency signal, and the step of recovering signals correspond-ing to said first single frequency signal and said second single frequency signal comprises steps of amplitude demodulating,

21. The position locating method according to claim 19 wherein the step of modulating said third radio signal is the step of frequency modulating said third radio signal with said third single frequency signal, the step of recovering a signal corresponding to said third single frequency signal is a step of frequency demodulating, the step of modulating said first radio signal is the step of frequency modulating said first radio signal with said first single frequency signal, the step of modulating said second radio signal is the step of frequency modulating said second radio signal with said second single frequency signal, and the step of recovering signals correspond-ing to said first single frequency signal and said second single frequency signal comprises steps of frequency demodulating.

22. The position locating method according to claim 19 wherein the step of modulating said third radio signal is the step of phase modulating said third radio signal with said third single frequency signal, and the step of recovering a signal corresponding to said third single frequency signal is a step of phase demodulating, the step of modulating said first radio signal is the step of phase modulating said first radio signal with said first single frequency signal, the step of modulating said second radio signal is the step of phase modulating said second radio signal with said second single frequency signal, and the step of recovering signals corresponding to said first single frequency signal and said second single frequency signal comprises steps of phase demodulating,

23. A position locating system comprising a plurality of frequency standard sources of signals of given frequency and predetermined phase relationships; means controlled respectively by each of said plurality of sources for transmitting from res-pective points respective radio signals, these means including respective modulating means controlled respectively by respective ones of said plurality of frequency standard sources for modul-ating each of said respective radio signals with at least one respective single frequency signal derived from respective ones of said frequency standard sources, a further frequency standard source of signal at an additional point having the same given frequency as said plurality of frequency standard sources and a predetermined phase relationship; means controlled by said further frequency standard source of signals for generating at said additional point a first plurality of reference signals related respectively to said respective radio signals; means controlled by said further frequency standard source of signal at said additional point for producing a second plurality of reference signals having respective frequencies related respec-tively to the frequencies of said single frequency signals; means for receiving said respective radio signals at said additional point, means at said additional point for deriving from said radio signals received at said additional point a further plural-ity of signals respectively identical in frequency to said first plurality of reference signals; phase comparing means at said additional point for comparing respectively the phase of each signal of said further plurality signals derived from said radio signals with the phase of respective signals of said first plura-lity of reference signals, means at said additional point for recovering an additional plurality of signals corresponding respectively to respective ones of said single frequency signals and having respective frequencies identical to the frequencies of respective ones of said second plurality of reference signals;
and phase comparing means for comparing respectively the phase of each recovered signal of said additional plurality of signals with the phase of respective signals of said second plurality of reference signals.

24. A position locating system according to claim 23 wherein said plurality of frequency standard sources of signals are two sources of signals and the respective points are two points.

25. A position locating system according to claim 23 wherein said plurality of frequency standard sources of signals are three sources of signals and the respective points are three points.

26. A position locating system according to claim 25 wherein at least one of said plurality of frequency standard sources of signals is carried by a satellite.

27. A position locating system according to claim 25 wherein said source of signal at said additional point is carried by an aircraft.

28. A position locating system according to claim 24 wherein said source of signal at said additional point is carried by an aircraft, said aircraft having an altimeter,

29. A position locating system according to claim 23 wherein each modulating means is an amplitude modulating means.

30. A position locating system according to claim 23 wherein each modulating means is a frequency modulating means.

31. A position locating system according to claim 23 wherein each modulating means is a phase modulating means.

32. A position locating system according to claim 23 wherein said means for receiving said radio signals includes superheterodyne receiver means having mixer means controlled by said additional frequency standard source of signal at said additional point for reducing the frequency of the respective radio signals received.

33. A position locating system according to claim 23, wherein said modulator means comprise respective balanced modulators, the respective radio signals being double side tone suppressed carrier signals.

34. A position locating system according to claim 23, wherein said means for transmitting comprise respective single side band transmitter means.

35. A position locating system according to claim 23, wherein said respective modulating means include means for modulating with bursts of respective ones of said single frequency signals.

36. A radio receiving station comprising a stable source of oscillations, means receiving a plurality of radio fre-quency signals modulated respectively with at least a respective one of a plurality of single frequency signals, means control-led by said stable source of oscillations for developing a first plurality of reference signals corresponding respect-ively to said plurality of radio frequency signals, means con-trolled by said stable source of oscillations for developing a second plurality of reference signals corresponding respect-ively to said plurality of single frequency signals, means for developing from said plurality of radio signals a further plurality of signals identical in frequency to respective ones of said first plurality of reference signals, first phase comparing means for comparing the phase of each of said further plurality of signals with respective ones of said first plurality of reference signals, means for recovering an additional plurality of signals corresponding respectively to respective ones of said plurality of single frequency signals and having respective frequencies identical to respective ones of said second plurality of reference signals, and second phase com-paring means for comparing the phase of each signal of said additional plurality of signals with the phase of respective ones of said second plurality of reference signals.

37. A radio receiving station as claimed in claim 36, wherein said stable source of oscillations comprises an atomic clock.

38. A radio receiving station as claimed in claim 36, wherein said means for receiving said plurality of signals comprises means for receiving two signals.

39. A radio receiving station as claimed in claim 36, wherein said means for receiving said plurality of signals comprises means for receiving three signals.

40. A radio receiving station as claimed in claim 36, wherein said means for recovering an additional plurality of signals comprises amplitude modulation detecting means.

41. A radio receiving station as claimed in claim 36, wherein said means for recovering an additional plurality of signals comprises frequency modulation detecting means.

42. A radio receiving station as claimed in claim 36, wherein said means for recovering an additional plurality of signals comprises phase modulation detecting means.

43. A radio receiving station as claimed in claim 36, including mixer means responsive to signals derived from said source of oscillations and to each of said plurality of radio frequency signals for reducing the frequency of each of said plurality of radio frequency signals to a plurality of signals of lower frequency.

44. A radio receiving station as claimed in claim 38, wherein said receiving station is carried on a vehicle.

45. A radio receiving station as claimed in claim 38, wherein said vehicle is a ship.

46. A radio receiving station as claimed in claim 39, wherein said receiving station is carried on a device movable in three dimensions.

47. A radio receiving station as claimed in claim 46, wherein said device is an aircraft.

48. A receiving station as claimed in claim 36, including a computer means responsive to output signals from said first phase comparing means and from said second phase comparing means for determining the distance the receiving station is from each of a plurality of transmitting stations and the position of the receiving station located.

49. A receiving station as claimed in claim 48, including means responsive to said output signal data from said computer means for storing and displaying said output signal data.