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Патент USA US2408775

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@CL 3, 1946.
w. M. GooDALL
2,408,773 '
Filed March 31, 1942
IES. l1»
Ii @
¿f2/_ M. 600ML;
Patented Get. 8, 1946
William M. Goodall, Oakhurst, N. J .,v assìgnor to
Bell Telephone Laboratories, Incorporated, Newl
York, N. Y., a corporation of New York
Application March 31, 1942, Serial No. 436,995
10 Claims.
(Cl. Z50-11)
rI'his invention relates to radio position-deter
mining methods and systems and particularly to
methods and means for ascertaining the position
of a mobile body relative to one or more ground
As disclosed in German Patent 546,000, M.
Harms, March 8, 1932; United States Patents
2,148,267, E. A. I-I. Honore, February 21, 1939,
1,995,285, W, Al-bersheim etal., March 26, 1935,
and 2,198,113, P. J. Holmes, Ap`ril 23 1940, the 10
change in location of a mobile body such as an
airplane relative to a pair of spaced ground sta
It is another object of this invention to elimi
nate in a system utilizing a relay or repeater
transmitter, interaction between the incoming
and outgoing energies.
It is still another object of this invention to
secure and maintain, in a phase-integration posi
tion-determining method and system, the proper
frequency relations and the proper initial or
absolute phase angle relations among the radio
frequency waves transmitted from the ground
In accordance with the preferred embodiment
of the invention, the various radio frequencies
tions may be determined at the mobile body by
emitted from the three ground stations in a posi
integrating, during the entire travel or move
tion-determining phase-integration system are
ment of said body, the changes in phase angle of
all derived only from a single source of energy;
a detected low frequency “signal” current hav
ing a non-uniformly changing phase angle rep
and, in accordance with a modification, the above
mentioned radio frequency and also the inter
resenting at each instant the position of said
mediate or low frequencies supplied to the phase
body with respect to said stations. In at least
one of the above-mentioned systems, the integra 20 integrators are all derived only from a single
osciilator having a high frequency stability and
tion is effected by continuously comparing the
located at one of the ground stations. More par
signal current phase angle with that of a “ref
ticularly, the primary ground station A comprises
erence” current having the same low frequency
a crystal-controlled oscillator generating a fre
and a uniformly changing phase angle which is
independent, or substantially independent, of the 25 quency F equal, for example, of three megacycles,
and thisstation emits a Wave nF, where n equals
position of the body. The signal current is de
any integer lbut preferably a large integer such
rived from two waves having different frequencies
as 8. At each of the relay ground stations B1
and received from different ground stations, one
and B2, the wave nF is received, and waves are
of which may be a relay station; and the refer
ence current is obtained from a local low fre 30 obtained therefrom having frequencies (nfl-DF
and (1L-DF which are emitted, respectively, by
quency reference oscillator on the mobile body
these secondary stations. The receiver C at the
or from one of said incoming waves and a third
aircraft includes separate detecting channels for
wave of still another frequency emitted by one
obtaining from waves 'nF and (n+1) F a iirst high
of the ground stations or Áby an auxiliary ground
station. For the purpose of securing a geograph 35 frequency signal current, from waves nF and
ical position determination, a second relay station
may be utilized.
As is apparent, for successful operation of the
system using the local low frequency reference
(1l-DF a second high frequency signal current
and from wave nF a reference high frequency
current. The phase angle of the first signal cur
rent contains a component or factor representing
oscillator, the frequency of the reference current 40 the difference in distances between the aircraft
must lbe maintained in exact synchronism with
that of the received signal current and, in the
other arrangements, the proper frequency rela
tions and the absolute phase relations of the sev
eral emitted beacon waves must -be preserved. ï
Heretofore, completely satisfactory results have
and stations A and B1 and another component
representing the dis-tance between the aircraft
and station A. Similarly, the phase angle of the
second signal current contains two components,
one representative of the difference in the dis
tances of the mobile receiver from stations A and
B2 and the other=representative of only the dis
tance between the receiver and station A. The
phase angle of the reference current includes a
not been attained in practice in using the above
systems primarily because of the difñculty of se
curing a local reference low frequency oscillator
which is highly stable as to frequency and also 50 component which yrepresents the distance between
the aircraft and station A. At the mobile re
in View of the difficulty of synchronizing or ex
ceiver, a 100-k`ilocycle wave isobtained from a
actly relating the frequencies of the various trans
local beat oscillator and combined with the afore
mitted waves.
mentioned reference current toproduce a result
It is one object of this invention to determine
ant current, which is separately «combined or
accurately the position of a mobile body.
modulator' 8, filter 9, power amplifier it? and non
directional transmitting aerial II.
rent for the purpose of obtaining a first detected
Referring to Fig. 2, the receiving apparatus at
signal current and a second detected signal cur
the mobile station C comprises a non-directional
rent corresponding, respectively, to the first and
second high frequency signal currents. The in receiving antenna 5, common to the three receiv«
ing branches or channels L, M, and N. Channels
phase angle of each detected signal current in
L and N each comprise a first detector I2, a ñlter
cludes the component representing the difference
i3, -a second detector I4. Channel M includes a
in distances of the aircraft from the associated
radio frequency amplifier I'5, the output of which
stations A and B1 or B2, but does not` include the
is connected to the input of the first detectors I2
component representing the distance between the
in channels L and N, a subharmonic generator
receiver C and station A, since the components
i6, an intermediate frequency local beat oscillator
representative of this variable distance mutually
il, an auxiliary modulator-filter I8 having its
cancel in the modulation process. Each of the
input terminals connected to the subharmonic
detected signals is supplied, together with an un
`generator I6 and to the local oscillator Il and its
modulated 100-kilocycle reference wave from the ~
output connected t0 the input of the second de
beat oscillator, to a different combined phase
modulated with each high frequency signal cur
comparator-integrator. Each ‘comparator-inte
tectors i4 in channels L and N.
grator functions to determine during movement
of the plane the total phase angle change in the
signal current supplied thereto, the total change
meral I9 kdenotes a phase comparator-integrator
including a cycle counter, the integrator being
connected between the output terminals of the
intermediate frequency oscillator i-'l and the sec
ond-detector It in channel L‘; and numeral 29
designates a simi-lar comparator-integrator con
nected between the output terminals of oscillator
I 'I and detector i4 in channel N. The compa
rator-integrators each comprise a phase angle
being a, measure of the change of position, both
asr regards sense and amount, of the aircraft
relative to the two associated stations. ThelOO
kilocycle oscillator is not necessarily of a high
frequency stability type.
If desired, for economical or other reasons, the
Reference nu
meter equipped with a counter and may be of the
above-described system may be modified to omit
the 100-kilocycle oscillator and associated appa
ratus. In the modiñed larrangement the ñrst
electrical type illustrated by Patent 1,934,460,
J. H. Bollrnan, November 7, i933, the gearbox 3E
in the Bcllman system being replaced by a counter
for counting the number of c'ycles of phase angle
change. Alternatively, 'the integrator may be of
high frequency signal current and a portion of .
the high frequency reference current are sup
plied to one combined phase comparator-inte«
grator and the second high frequency signal cur
rent and another portion of the reference high
frequency are supplied to the other comparator
integrator. In the case of each comparator
integrator the phase angle components of the
wave supplied thereto and representing the dis
tance of the aircraft from station A cancel each
other so that the integrated phase angle indica 40
a mechanical type comprising a differential gear
assembly, such as illustrated by Patent 1,907,132,
G. M. Thurston, May 2, 1933, a counter being
attached to the crown gear 6I of the Thurston
In operation, the crystal-controlled oscillator I
at primary station A generates and Isupplies a
wave having a constant frequency F equal, for
tion represents the net change in the difference
of the distances separating the aircraft from the
associated stations A and B1 0r lâz. The arrange
example, to three 'megacycles to the harmonic
generator-amplifier 2, which functions to pro
ment comprising the 100-kilocycle oscillator is
more accurate than the modified embodiment
since the integrated phase angle change in each
quency nF where n «is any integer but preferably
duce a wave having a large intensity and a fre
- isy a large integer "such as 8.
The wave nF is ra
diated by aerial 3 and intercepted by receiving
signal current is transferred or impressed upon
antennas 5 at stations B1 and B2.
t each of
relay stations B1 and B2 the received wave 11F
is supplied over different -paths to the input of
>The invention will be more fully understood
from a perusal of the following specification, taken 50 the subharmonic generator-amplifier 6 and the
ampliñer ’.I. The subharmonic generator fi func
in conjunction with the drawing on which like
a lower frequency.
tions to derive from the Ywave nF a wave of fre
reference characters denote elements of a similar
q_uency F which is combined inthe modulator 8
function, and on which:
with the wave nF' from amplifier 'I for the pur
Fig, l illustrates the transmitting apparatus
used at the primary and relay ¿ground stations;
55 pose of producing among other components the
side-band Yfrequencies nF-ì-F and 11F-F. The
Fig. 2 illustrates the preferred receiving equip
ñlter 9 connected to the output of the modulator
ment used at the mobile station;
8 at station B1 passes only the upper side-band
Fig. 3 illustrates the space patterns established
frequency (1i-I- 1)F, whereas the corresponding
‘oy the transmitting stations; Vand
filter at station B2 passes only vthe lower side«band
Fig. 4 illustrates amodiñed receiver which may 60 frequency (n4-DF. At each relay station the
be lused in place of the apparatus of Fig. 2.
selected side-band is amplified by amplifier it!
Referring to Fig. l, reference character A de
and vradiated 'non-directionally by antenna II.
notes a Vmain 0r primary ground transmitting
As radiated, the phase angle of the waves emitted
station and reference ycharacters B1 ‘and B2 desig 65 by antenna 3 and the two relay antennas I I may
nate relayorre'peater ground stations each spaced
ordinarily a distance of’25-50, or even 1D0-500
miles, from station A. The primary station A
be represented as follows:
From antenna 3,~s'tati'on A
cos 21r(nF) (t+a1)
includes a frequency Vstabilized crystal-controlled
oscillator I which _is connectedthrough a com
bined ¿harmonic ¿generator-'amplifier 2Y to a non
from antenna n, station B1
eos 21r<a+1>F<t+a2>
directional antenna system comprising ’the aerial
3 and the Vgroundw'll. Each of relay stations B1
from antenna Il, station -Bz
and B2 includes a receiving aerial 5, -a combined
cos 21r(TL-1)F(t-I-a3)
where t denotes time in seconds, and on, a2 and
amplifier-subharmonic generator 6, ‘amplifier l,
From Equation 15 itis apparent that the phase
as are time factors which diiîer from each other.
The diiîerences among a1, a2 and ce and the phase
angle `variation is dependent on , two factors,
namely, the distance h of station C from station
A and the difference h-g between the> distances
of station C from station-s A and B1.
Similarly, in channel N, the filter £3 passes
only the lower side-band current obtained by
subtracting Equation 6 from Equation e and rep
variations introduced in the equipment at relay
stations B1 and B2, may be compensated if desired
in accordance with the teaching of Patent
1,926,169, El. Nyquist, September l1, 1933.
At the mobile station C the waves nF, {rt-HMP
and (1t-'DF ir-oin stations A, B1 and B2, respec
tively, are intercepted by antenna 5. Assuming
resented by the following equation:
a1, a2 and as have been compensated and, in et
fect, eliminated by proper adjustments at sta
tions B1 and B2, the phase angle of the waves, as
received, may be represented as follows:
Considering channel M, the subharmonic gen»
erator i6 connected to the output or amplifier
~ From antenna 3, station A
l5 functions to derive from the incoming wave,
@es 2mF<i-%)
from antenna l l, station B1 ,
cos 21r(7L-l~1)F<t--%)
and this wave is combined in the auxiliary mod»
ulator nlter i8 with a heat wave
from antenna al, station B2
cos 21r(n~ DFG-â)
a wave
Cos 21rft
from the 10û-kilocycle oscillator to produce the
where c is the velocity of propagation in space
of the Wave and, as shown in Fig. 3, h, o, and y'
are distances, respectively, at any given instant
cos 211-[E (t--ë > -l-ft]
separating the mobile station C from the ground
stations A, B1 and B2. The factor “cos 2W” in
The wave represented by Equation 20 is coin
the phase angle expressions given above is a con~ 30
bined in detectors lll in channels L and N with
stant and hereafter will be omitted for the salse
the side-band currents represented, respectively,
of clarity.
by Equations 15 and 16 to produce in the output
of the detector I4, channel L, the signal current,
The received waves are supplied directly to the
detectors l2 in channels L and N and are also
supplied to these detectors through the ampliñer bij
i5 in channel M. Of the various modulation
products present in the output of each of the
and in the output of detector lil, channel N, the
detectors l2 only one of the side-band currents
obtained by combining the waves received from
station A, Equation 4, and from station B1,
Equation 5, and represented by Equation i5, given
below is passed through the lilter i3 in channel
L. The sum and diiîerence currents obtained by
combining Equations ¿l
5 may be repre
The signal current from channel L and a por
tion of the reference current from oscillator Vl
are supplied to the cornparator~integrator I9,
and the signal current from channel N and an
other portion of the reference current from os
cillator Il are supplied to the comparator-inte
the lower side-band or difference frequency being:
grator 2e.
It is apparent that Equation 2l represents a
family or set of hyperbolic isophase curves for
each of which the factor
is a constant and that Equation 22 represents
another set of hyperbolic curves for each' of
which the factor
is constant. Referring to Fig. 3, the curves 33
represent several of the hyperbolic courses cor
responding to Equation 21 and the curves 3l il
lustrate several of the hyperbolic lines corre
sponding to Equation 22, the
being at stations A and B1 and
3l being at stations A and B2.
adjacent hyperbolic curves Si)
foci of curves 3Q
the foci of curves
Considering two
(or 3i) the dif
70 ference between the values of the factor
so that the phase angle of the current in the out
put of the iilter I3 in channel L is
for the two curves mayV for convenience be taken
as one wave-length.
The phase angle given by Equation 21 and ln
tegrated during the movement of the mobile body
or airplane does not change when the airplaneV
subharmonic generator *l5 >and ,the ñlter i3 in
channel L; and integrator 20 ,is connected to the
moves along a path coinciding with one of the
outputs of the subharmonic generator I6 and a
filter I3 in channel N. Considering the receiv
curves 30, but does change when the ,movement Ul ing system of Fig. 4, the high frequency current
is not along oneof these paths. Similarly, the
phase angle given by Equation 22 changes onlil
when the airplane moves in a direction making
an angle with the curves 3l. Considering the
hyperbolic system established by stations A and
B1 and assuming the airplane is at a location
such as P1, Fig. 3, on the particular curve 3!) rep
resenting the condition h-g=0, the rotation or
angular speed of the vector Yof the detected sig
nal current supplied ‘to the integrator 19,'which
vector rotates in a counter-clockwise direction,
is constant. As the plane moves toward the po
sition P2 located farther away from station A and
nearer to station B1, the factor
assumes a positive value and it increases'as the
Equation 18, becomes the reference current. The
high frequency signal currents utilized for inte
gration in channels L and N are given by Equa
tions 15 and 16, respectively. In the modiñed
system the phase angles are measured and
integrated at the very high radio frequency
F(3,000,000), whereas in the system including
the 100-kilocycle oscillator I'I the integration oc
curs at the relatively 10W or intermediate fre
quency of 100 kilocycles. Inasmuch as the in
stantaneous phase angle change may be meas
ured and integrated more easily and more accu
rately at the intermediate frequency f=100 kilo
cycles than at the radio frequency F='3,000,000
cycles, and since integrators designed to oper
ate at intermediate frequencies are more easily
plane moves toward position P2. Hence, the
phase angle as given by Equation 21 continues 25 manufactured and maintained than those de
signed to operate at a radio frequency, the sys
to increase with movement of the mobile body
tem of Fig. 2 comprising the auxiliary oscillator
toward position P2. Since the phase angle of
il, and in which the phase angle changes in the
the reference current from beat oscillator l1 is
radio frequency received wave are transferred to
independent of the movement of the mobile body
and impressed upon the intermediate frequency
the counter in the integrator i9 records every
100-kilocycle wave, is >preferred over the modiñed
S60-degree phase angle change. On the other
arrangement-,of Fig. 4.
hand, if the plane moves from position P1 tov/ard
Referring again to Fig. 1, it will be observed
P3 located near to station A and farther away
that at relay stations B1 .and B2 the received and
from station B1 than P1 the factor
retransmitted waves differ by a multiple of the
fundamental frequency F=3 megacycles. Thus
at stationBi the received and transmitted >fre
changes from a Zero to a `negative value and it
quencies are 24 megacycles and 2'7 megacycles, re
spectively, and at station B2 the received Yand
40 transmitted frequencies are 24 megacyc‘les and 21
gained or lost, as a result of the movement of
megacycles, respectively. Because of the differ
the mobile body and counted ,by the integrator
ence in the order of several million cycles in the
19 is an indication, not of th'e actual distance
received and transmitted frequencies at each re
traveled, but of the change of location with re
lay station, singing and =other interference phe
spect to stations A andk B1. 'The indication is not
nomena are, in accordance with one feature of
in any Way affected by, cr related to, the speed 45 the invention, avoided at the relay station.
of transit of the airplane or ,the timeconsumed
Moreover, as already pointed out, since all fre
in making a night or the geometrical nature,
quencies utilized at the -three transmitted sta
linear or tortuous, of the path or course followed
tions, including the frequencies received andre
by the mobile body. In a similar manner, the
transmitted at ,each relay station, are derived
continues to decrease until position P3 is reached.
'I‘he number of net degrees, radians, or cycles
integrator 2li indicates the change of position of
the plane relative to the line connecting .sta
tions A and B2.
By observing the registration on both indica
tors at a known starting point P1, at which each
counter has a predetermined reading, and ob
serving the registrations on ‘Lboth counters ,at
any given subsequent time, the position of ¿the
plane with respect to the three stations A, B1
and B2 may be ascertained and the straight line
distance separating the starting and termination
points ,may be determined. If desired, a mech
anism which may be set or yadjusted at t'h‘eiknown
starting point prior to Vthe 'beginning `of travel
may be utilized to operate a camera, bomb `re
lease, etc., whenever one counter gives a pre
determined registration and similarly the other
counter gives another predetermined registra
tion. If desired, the transmission from each sta
tion may be camouflaged by voice broadcast
50 from the oscillator l at station A, the frequency
difference at each relay station `between the re
ceived and transmitted waves is maintained.
Although the invention has been explained in
connection with certain embodiments Yincluding
a modified receiving arrangement, it should be
vunderstood that it is not tto be limited to the em
bodiment described inasmuch as other apparatus
may be employed in successfully practicing _the
invention. As is believed to be app-arent, the
position of the mobile body may, in -accordance
with the invention, be determined in a plane
other than the azimuthal plane as, for example,
a vertical plane.
What is claimed is:
l l. In a phase integration position determin
ing system, means for transmitting from two
spaced geographical points waves of different
frequencies, means at a mobile body for securing
modulation of the emitted radio frequency waves.
a reference current having a constant phase
angle and for obtaining from said ’waves a signal
Referring to Fig. 4, the 100-kilocyc1e oscillator
l1, auxiliary modulator 'i8 and the detectors I4,
employed in the arrangement of Fig. 2, are in
the modified receiving circuit. ‘In Fig. 4, -inte
current having a vphase ¿angle variation 4depend
ent upon only the Vdifference vin the distances of
said body Ato said points, and a phase integrator
at said mobile body for .comparing said currents.
2. In a phase integration position determining
grator I9 is included between'the `outputs of the ‘
system, means for transmitting from spaced geo
graphical points a pair of waves of different fre
quencies, receiving means at a mobile body for
obtaining from both of said waves a ñrst cur
rent and from only one of said waves a second
current, said currents having equal frequencies,
signal current having vsaid given frequency„the
instantaneous diñerence in the phase angle varia
tions of vsaidsecond signal current and said ref
erence current being related to the'instantaneous
change of position ~of said body with respectï to
said first station and said second relay station,
and a second measuring means .actuated bysaid
last-mentioned currents for integrating the last
the phase angle of the first current being repre
sentative of the difference in the distances be
tween said mobile receiver and said stations and
mentioned instantaneous differences , during
the phase angle of the second 'current being in 10
dep'endent of said difference, and means con
'7.' In combination, a first transmittingstation
trolled by said currents for integrating during
for radiating a vwa've'of a given carrier'frequency,
movement of said body the relative phase Hangle
a relay'sta'tion lspaced from the'ñrst stationV for
travel of said body.
changes in said currents.
3. In combination, a pair of spaced ground sta
tions for radiating harmonically related frequen
radiating ,a .waveof Vdi'iferent frequency, the ì fre
quency of the last-mentioned wave being derived
from the first wave and the frequency difference
cies, a receiver on a mobile body for receiving said
between said waves being a submultiple of each
waves, said receiver including means for obtain
radiated wave, and means at a mobile station for
ing from said waves a signal current having a
obtaining from the transmitted wave a signal cur
frequency equal to a submultiple of each of said 20 rent having a phase angle related to the position
waves and a phase angle representative of the
of mobile station and a reference current having
a substantially constant phase angle, and means
distance between said mobile body and one of said
stations andthe difference in the distances be
controlled by said currents for integrating the
relative changes in phase angle of said currents
tween said body and both stations, means for ob
taining from one of the received waves a reference 25 during the travel of said mobile station.
current having the same submultiple frequency
8. In combination, a primary station, and two
and a phase angle representative of the first
relay stations spaced therefrom for radiating
three different harmonics of a fundamental radio
mentioned distance, and means connected to both
frequency, receiving means atV a mobile body com
of said means for integrating the phase angle
change of the signal current during travel of said 30 prising a first channel for deriving from the har
_ body.
monic received from the primary station a ref
erence current of the fundamental frequency, a
4. In combination, means for radiating from
two spaced geographical points different har
second channel for deriving from the last-men
tioned harmonic and the harmonic received from
monic waves derived from a given fundamental
frequency, receiving means on a mobile body for 35 one of the relay stations a first signal current of
said fundamental frequency, a third channel for
obtaining from said waves a signal current and a
deriving from the first-mentioned harmonic and
reference current both of said said fundamental
frequency, the phase angle of the signal current
the harmonic received from the other relay sta
being representative of the position of said body
tion a second signal current of fundamental fre
with respect to said points and the phase angle 40 quency, said first signal current having a phase
angle variation related to both the change in the
of the reference current being representative of
distance between said body and the primary sta
the position of said body with respect to only one
tion and the change in the difference in the dis
of said points. and an integrator controlled by
tances between said body and said primary sta
said currents for ascertaining the net change in
phase angle of the signal current relative to the ' tion and the first-mentioned relay station, said
second signal current having a phase angle varia
change in phase angle of the reference current
tion related to both the change in the first-men
resulting from travel of said body. said integrator
being responsive to every instantaneous change
tioned distance and the change in the difference
in the distances between said body and the pri
in phase angle. and a counter controlled by said
integrator for indicating the net number of cycles 50 mary station and the second-mentioned relay
station, said reference current having a phase
of phase angle change.
angle variation related to the change in said first
5. In combination. means at a first station for
mentioned distance, means including a beat oscil
securing a wave of a given frequency _F and
lator for deriving from the reference current and
transmitting a harmonic nF of said frequency
to a relay station and to a mobile body, means at 55 the first signal current a ñrst intermediate fre
said relay station for deriving from the received
wave the harmonic (n+1) F of said frequency and
transmitting said wave to said mobile body, and
quency signal current having a phase angle varia
tion representing the first-mentioned difference
and for deriving from said reference current and
the second signal current a second intermediate
means on said mobile body for obtaining from
said waves a reference current and a signal cur 60 frequency current having a phase angle variation
representing the second-mentioned difference, a
rent having` the same given frequency and an in
stantaneous difference in their phase angle vari
ations related to the instantaneous change of
position of said body with respect to said stations`
ñrst phase integrator actuated by the ñrst inter
wave a harmonic (1L-1) F of said given frequency
ting from one station a wave having a frequency
mediate frequency signal current and an inter
mediate frequency reference current of constant
and a measuring means actuated by said cur 6 Ul phase angle from said beat oscillator, and a sec
ond phase integrator actuated by the second in
rents for integrating the instantaneous differ
termediate frequency current and another inter
ences during travel of said body.
mediate frequency reference current of constant
6. A combination in accordance with claim 5.
phase angle from said beat oscillator.
a second relay station for receiving the wave
emitted by the first station and means at said 70 9. A method of position determination utiliz
ing two spaced stations which comprise transmit
second station for deriving from the received
nF, where n is any integer, obtaining at the sec
ond station from said wave another wave having
taining from the 'nF and (1t-DF waves a second 75 a frequency (ni 1) F and transmitting said wave,
and transmitting said (fri-DF harmonic to the
mobile body, means at said mobile body for ob
obtaining at a mobilev receiver from both trans
mitted waves a signal current F having a, varia
tion related to the change in the difference. of the
distances between said mobile receiver and said
stations, obtaining from the first-mentioned wave
nF' a'reference current F having a phase angle
independent of said change, and continuously
having one of the frequencies (niDF and trans
mitting said last-mentioned Wave, obtaining‘at a
mobile receiver for both transmitted Waves a, sig
nal` current F having a phase angle Variation rep~
resentative of the change in the difference of
the distances between said mobile receiver and
comparing and integrating the phase differences
Wave nF a, reference currentv F having a phase
between said waves during travel` of the mobile
angle variation independent of said change,
changing the frequency of the reîerence and sig
l0; 1A method of position determination utiliz
ingv two spacedv stations which comprises trans
saìdlstations, obtaining- from the ñrst-mentioned
nal currents each to the same intermediate fre
quency, and integrating the phase differences
between said Waves during travel of the mobile
lflîulttingV from one station a Wave having a fre
quency 12F, Where n is any integer, obtaining at
the second station from said wave another wave 15
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