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Патент USA US2411520

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Nov. 26, 194e.
Filed Dec. 22, 1959
3 Sheets-Sheet l
Nov. 26, 194e.
Filed DSC. 22, 1959
_ 2,411,520 ,
5 Shee‘lZS-Sheet 2 _
Nov. 26, 1946.
l l
AIVD @54m/V
Patented Nov. 26, 1946
signor to International Standardv` Electric *Gore
poration, New York, N. Y.,- a corporation of
Application December 22, 1939;» seriaiffnó.` 3ra-51a
9 Claims. (c1. 25o-1)
ted.' from a‘ moving station for rendering a» trans'
My inventi'cm'A relates to distance' and position
determining systemsrand- more particularly to sys
tems andQmethods for» determining the distance
mitter at the4 fixed station operative.
e _ u
It is' a' still further object of my invention to
provideî a further signalling arrangement for in-v
andi position of a` movingl objectV by means of
Ul ~ dicating the identity of the repeating receiving
radi'o waves».
Known ra’diodistanc‘e¿determining systems gen
retransmitting» station.
It is a still further object of my invention to
provide a lateral guiding beacon which in con
junction with said retransmitting station will pro-`
erally depend# upon measurements of the angle
athtwo‘separate transmitting/points, or upon ar
rangements' for~ givingA an approximate indication
f vide an' indication on the, craft of the location
of distance by means of signal strength-measure
with respect to a` particular point of the earth’s
in a'certain type ofdistanceindicatory partie
Other advantages and objects of. my invention
u'larlyusedv forI altimeter purposes, a continuously
willfbe apparent from the particular descriptiçn
varied frequency-wave is transmitted to a reflect 1511 ofia few embodiments thereof,.made in connection
ing* Objectand the distance tothe reñecting ob
with*> the.V accompanying drawings inr which
jectifs-determined* bye means of l a comparison» of
Fig.v 1 is a diagram'illustrating the arrange
thei frequency‘of the reflected wave- with that
ment infaccordancewithmy invention;
of? the wave being transmitted towardsV the re
_ 4
*_ e
Fig. 2 isfal curve used for illustrating the Voper
20" ation'of thefreceiving station >on the movingl ob
This-type" of altix'neter'hasL been found t0 be
quite satisfactory as it does not depend uponl
measurement offamplitude-of waves nor thecom
Fig. Sis a diagram of a retransmitting; station.
operating in'accordance» with my invention;vr
parisonn ofí relative amplitudesv thereof, but/"only"y
Fig;` ‘iA is a‘diagram0 illustrating an arrange
upon? a; measurement'E of the frequency difference 25 ment for preventing feedback and consequent
which“ depends -1J'.pon`the~'flength of the' transmit
singing of the amplifier at the _receiving station;
l ting path.
Imaccordan'ce‘ with “my invention“ Il provide ~ a"
Fig, 5 is a modiñed‘retransmitting station in
accordance.: with my invention, including anar
distance determining system-utilizing a frequency
ran'gement" for transmitting staticnidentifying
varied transmitted'wave andïprovide at the point 30 signals;
fromî‘which’ the distance is to be determined, Aa
transmitterl arrangement responsive to receipt -oi
Fig.k ö‘is'lone. form of systemio'r use onY an air
plane in the combination of my invention;Y
the” frequency varied waves" for transmitting an*
otlierffrequency varied wave which may ’ be> com
part-id:L at' the ‘receiver‘ with' reference’ waveL for "
determining receiver arrangement in accordance
indicating the> distance.
Itis a> principal object'of my' invention toA pro-l
vide‘a radio distance determining means which
is` sin'cplel in constructionV` and' positive' in oper'
Itf‘isA a - still further“ object of my Yinvention to
provideV in" a radio Vdistance ' determining system ’
means’ior simultaneously observingV the direction
ofthe distance point, so that the position of the
receivingstation' maybe determined.
It is a still further object‘of my'i'nv‘en'tion' to
prc'ivi'de` an" arrangement wherein frequency ' mod;
ulatëd'~wa'ves are transmitted from `a` first point"
to a» secondv point and are receivedlv attheïsee
ondfpointl andï'retransmitted to. the ñrst‘ point, I
whereby. the- distance. between. the . two pointsfmay
be dëtemineal...
ItÍÍisè> a=still'..iùrther» object offmyl invention! toy
provide- controlmeans at .at-.iiked repeater station
respçnisiye«to»V variable .frequency Waves transmit#
Figs '7 is'a'lf'urther modified 4form of distance"v
withimy invention, and
Figs. 8 and 9 illustrate anA embodiment of my
invention wherein 'beacon guidingv is »used , in-V con
junction with a distance determiningvsystem.
Infaccordance-with my invention I provide,_as
shown in Fig. 1, onf-af moving craft such as air
planeY l0, an arrangement comprising a transmit
ter Il, a receiver l2~,`and an indicating meter I3.V
Transmitter llv emitsv a wave-which isV continu
ously cyclically varied betweentwoiixed values.A
vThe transmitter is- generally operated only at.,
intervalswhen distance indication is ‘desiredand
inl the »caseotlregular air lines may» bev used‘only,y
after permissionis.. given. This transmitted-wave '
is~received- at aiiXed. point on» a receiving an
tenna I4.' Receivingantenna Mïisfcoupledatova;
receiving-and retransmitting device |55, the 'out
put of which is coupled to a- transmitting antenna
I6, so that a wave varyingin4 >frequency in «a
manner similar to- the received wave willbe trans
, mitted therefrom.-`
The wave transmitted from antenna I6 is re
ceived on craft I0 by receiver I2. This received
wave is then conveyed to indicator I3 and simul
taneously a small part of the energy being gen
erated in the transmitter II is also conveyed to
indicator I3. Indicator I3 is a frequency meter
which indicates the frequency difference between
the wave received at I 2 and the Wave' being trans
mitted from I I. Since the frequency transmitted
is continuously varying, the frequency difference
is a function of time required for the wave to
means 34 is coupled to an oscillator 35 to vary the
frequency of this oscillator in a manner similar
to the frequency of the received wave signal.
The output of oscillator 35 is then amplified in anV
amplifier 33 and is transmitted from antenna 31.
A portion of the received signal is transmitted
over line 33, to rectifier 39 and used to'control a
trigger tube arrangement 40.
Accordingly, when signals are received on an
10 tenna 30, they are rectified at 39 operating tube
travel to its respective station and back, plus the
time delay of apparatus I4, I5, I6, it is clear that
the frequency difference between these waves will
indicate the length of the path. The meter I3
may be calibrated directly in distance to provide
on the craft a direct indication of its position
» 43, which is in series between the oscillator out
put and the amplifier arrangement. Thus the
transmitter 35 is rendered effective upon receipt
of signals. The frequency modulation of these
retransmitted signals is controlled by means of
the portion of the signals rectified at 33 by means
of control means 34.
In order that the energy transmitted from an»
tenna 37 does not interfere with that received at
relative to the receiving and transmitting sta
The function of the indicator may be more
33, that is, is not fed back to the amplifier over
antenna 36 to build up;singing oscillations, it is
clearly understood by reference to Fig. 2. In this
figure the solid line curve 2I represents the fre~
necessary to provide some arrangement whereby
quency of the wave transmitted from transmit
such feedback cannot occur. This may be ac
ter Ii with respect to time, and the broken line
complished by,transmitting from antenna 31 a
22 represents the variation in frequency with re 25 frequency different from that received at 30 and
spect to time of the wave received at receiver I2.
reconverting the energy after receipt on the craft
Consequently the distance may be readily ob
back to the same frequency as that of the craft
tained from the frequency difference a, b, shown
on' the curve, allowing for the constant frequency
difference due to the fixed time delay by the re
peating station, The calibration ofk the meter
Thus the frequency range of the
retransmitted waves may be made to vary cor
respondingly with the aircraft transmitter but
at a frequency range differing therefrom. Feed
back may accordingly be prevented by tuning the
circuit of receiver 3| to reject the band of fre
quencies in the range transmitted at 31.
can be so made that this is taken care of.
As a typical example of the frequencies in
volved, assume a normal carrier of 100 mc. and
use a frequency variation of 2 me., i. e., the car,
„ It is clear that if instead of reconverting the ‘
rier varies from minimum of 98 mc. to a maXl
mum 102 mc. Assume this variation occurs with
repeated signal after reception on lthe aircraft,
the aircraft oscillator may be provided with
a period of 1/5 of second for a complete cycle, i. e.,
the carrier varies from 98-102 mc. in 1/5 second.
means to generate in a wave in the same fre
quency range as that received from therepeater
for providing the comparison to determine the
Then as radio waves travel 186,000 miles per sec
ond a round trip to the ground station and re~
turn will be 2/186000 second per mile away from
station. Assume 10 miles distance, then time of
travel will be 20/185000 second and carrier differ
ence as received at moving object will be
A further and simpler arrangement for pre
venting feedback action is disclosed in Fig. 4.
According to this figure an arrangement is pro-_
vided so that the energy received on antennae 4I,
42 is supplied to an amplifier 43 over branch lines
(2O/186000) X4 X 10(i X 5
gives 2,150 cycles. For 100 miles the carrier fre
quency difference will be 21,500 cycles.
44, 45. The output circuit of amplifier 43 is cou
pled to transmitting antenna 46. If the path be
tween the antenna including the coupling lines
ing objects as airplanes the so-called Doppler ef
that the distance from point 47 to antenna 46 is
as carrier varies 4 mc. in 1/5 of a second.
- On account of the very high speed of such mov - 50 44, and 45, and point 4l is made of such length,
substantially the same electrically in both direc
tions, except for a 180° phase shift, then energy
received on receiving antennae 4I, 42, from any
fect on the frequency of the carrier as received
at the moving object is not negligible. For a
plane moving 200 miles per hour directly towards
or away from the ground station the Doppler ef
fect will change the 'received frequency by 331/3
cycles per second if the carrier is 100. mc. This is
55-tenna 46 will neutralize at point 41, so that there v
can be no feed into amplifier 43 therefrom. The
type of arrangement is explained more in detail
in the U. S. Patent 2,134,278, issued October 25,
only approximately 11/2% error at a distance of
10 miles and for the conditions used in the ex
ample given immediately above and consequent
ly does not introduce too great an error.
1938, in the name of Andrew Alford.
While the antenna arrangement of Fig. 4 may
be utilized, together with a repeater system such
as that shown in Fig. 3, itis also clear that if
A suitable arrangement for the frequency var
desired, the amplifier arrangement 43, instead of
iable retransmitter or repeater arrangement is
the various control elements shown in
shown in Fig. 3. In this arrangement the receiv
65 Fig. 3, may be simply an amplifier which will as
ing antenna is indicated at 30 coupled to an au
sume operation upon receipt of signals and re
tomatic volume controlled receiving amplifier 3l.
transmit the same signal from antenna 46 as am.. l
The output of amplifier 3| is coupled to a net
plified waves.`
work 32 so designed that with constant voltage
It is often desirable that with any transmitting
output the voltage impressed on rectifier 33 »is
70 system, such as the retransmit-.ting arrangement
proportional to the received frequency. As is
in accordance with this invention, a means may
apparent to those skilled in the art, such a net
be provided for indicating the identity of the sta
work may be readily designed for a predeter
mined frequency band. as is common in high
Such an arrangement is disclosed in Fig. 5.
According to this system the rtransmitting an
fidelity receiver circuits. This frequency control 75 tenna 46 is shown coupled to a switching arrange
busy the pilot may try another by changing the
ment äûïand' a receiving ampliñer 5|-, to-the re
frequency range of-this-transmitter.ceiving antenna; In the- position Shown receiv
In- Fig.> 6- is-disclosed--one-form of stationl suit
ing >ampliiier - 5 l*
able forusevv on the movable craft lin accordance
tacts- of switch 56',~ directlyy to the- transmitting
with my invention. In this system a variable
amplifier 15 to provide a retransmitting system. C7 frequency transmitter TI-«ls- provided connected to
Switch- 50i-is controlled by a cam 52 driven from
the transmitting antenna 12.- A-rotatable‘ loop
a- motor 53 through gears 513-, 55 andfäß‘. When
antenna 13ïmay-b`e-used for'receiving thesi'gnals,
cam _52 is rotated- so that the lower portion there
loop 1-3--b‘ei-ng- coupled-to- receiver 'M'. The fre
of i's--opposite- switch 5i), the switch contacts' in the
quency--variable signals received may then- be
lower' position are closed. Preferably the lower 10 transmitted from receiver Tdt-to indicator-15 and
cam portion is shorter than the-raised portion
a-l small- part-of the energy from 1l may loe-trans*
so that the distance indicating transmission is
mitted to 15 -to-provide‘ a distance indication-by
effective for the maior portieri> of- the-time.- Mo
frequency comparison. Simultaneously loop-13
tor-".’?iìlsimultaneously drives-by means of gear 55
may be adjusted directively so- as to produce ya
a- record- ‘disc Se, which may-'be madeof transpar
directive indication in indicator' 16.- By this ar-ent material and> have on- its--periphery- a` signal
rangement bothV the distance and direction of
indicating the identity of the station. Immedi
the transmitting stat‘on may be determined; thus
ately- behind dise 60- is providedY a lamp-6| which
enabling an airplane to iind its exact» position
shines-«through the» disc onto photocell 62 con
with reference to the transmitting'station. This
nected: to a voice- frequency ampliiier 63;. The 20 may be desirable in scme'cases where a limited
output of voicefrequency-amplifier S3 is modu
landing area is- provided and crafts leave‘thi‘s
lated in 64 with high frequency oscillations gen#
area and must return thereto. For example, on
erated iti-oscillator vE5. « In this position modu
an aircraftcarrier it is vital» that the'planesbe
lator ßliïhas‘? its output connected through the
enabled to return-to the carrier, but itis- prefer
lower contacts ofswitch 50 tothe transmitting
able that they be enabled to fly asia-r as possible
amplifier 1li-'and antenna lili»y` and so- transmits
so as to make ful-l use ofthe gasoline carried».
intermittently distance indicating signals and
By use of a system in accordance with my inven
signals indicating the identity of the station.
tion, this may be accomplished since the pilot 'of
Preferably the oscillator @5l operates at a» fre
the aircraft will at. all times know' the distance
quency such that signals may be received on the
from ther transmitting- source and may therefore
regular receiving apparatus, or on- the distance
determine if sufficient gasoline remains so- that he ,
determining receiver. The identifying.Y radio
may stay -out awhile longer. In addition- tothe
waves may-bereceivedfon» the- airplane by a-suit
direction` finding feature 'the aircraft may then
ablev auxiliary-receivery tuned to the frequencyV of
head-directly for-the-transmitting station. `
` `
oscillator 65.
In Fig. 7' an` aircraft equipment suitable-‘forde
Since the retransmitting station may» not be
termining direction and distance, and‘ïin' addition
required to operate during a- large portion of the
receiving signalsidentifying the relaystation'is
time, it may be-preferaloleto-havey the povverl am
illustrated. Inl this> arrangement parts similar 'to
pliiier> of the transmitter disconnected at times
Fig. 6-l are provided with'th'ev same-reference char
that the signals are not desired.- I accomplish
acters. At the-receiver, in addition to the rotat
this result according to-onesystenz-i»,Y by providing
able loop 73, I have shown an auxiliary'non-di
a relay 65 controlled from` the output of receiver
rectional sensing antenna 18; Of course, ii’- the
amplifier 5i over rectifier-61 -tof close switch 68
direction indication is not desiredv any type of
connected to- the high tension power supply 69
aerial maybe used. In the output of receiver
for» >the-»radio frequency power ampliñer T9;
amplifier 'i4 I provide a detector '19.V The output
When- ncl-signals are being received on- the receiv
of> this detector is connected to an indicating
ing antenna,> relayA 66 is deenergized and- connec
arrangement such as shown by heady phone'- 80
tions are opened at 68.- Upon- receipt of signals,
for indicating the ridentity of` the station.A Also;
however,~ the high tension supply B9 is connected 50 in the output of detector 'i9 is branched the rec-->
to amplifier-61- over contact B8; It is-clear- that
tiñer unit 8| which serves to furnish energy for
other contacts may be provided' under control of
thedirection indicator 15'.
relay 66- to- energize motor 53- and the auxiliary
It is sometimesr desirable that an aircraft- be
apparatus 63', 64, 65ionly during receipt of signals
able to fly from a given station a» particular
in receiver-5l` to provide further saving in power.
dis-tance. therefroml in a- given direction so that
In the-arrangement described above it is evi
lloy merely reading the instruments the pilo-t‘will
dent that should more than one aircraft attempt
know exactly where he is.> Such a result. can be
to obtain distance indication simultaneously, no
accomplished -loy'use of' a distance finding system
clear reading -could‘ be obtained-by either since
in accordance with my invention in‘ conjunction
the frequencies received on each aircraft would
with a direction finder of Figs. 6 and 7, and. a
be-hopelesslyjumbled and no steady-meter read 60 gym-compass. However, it is-desirable to» have
ing‘co'uld~ be obtained. However, suchv a condi
as little `apparatus-on the craft as possible. This
tion is' not likely to arise asA usually distance- de*
may be accomplished by using on the ground?,
terminations will be madev only at comparatively
equipment to produce direction guiding instead~
long intervals. IfV upon attempt to> obtain a'dis 65 of using a= direction finder on the craft.
tance reading the meter shows that another craft
In Fig. 8 an embodiment of‘ myf invention
isk also trying to get a reading, the navigator need
whereby the pilot may be enabledV to ascertain
only continue trials` until a steady indication is
his position from a given» retransmi-ttingv station
is illustrated. In this arrangement at the trans
Should traffic conditions- be heavy enough to
mitting station 8U, is provided a repeater- station
require it', several repeater stations may be erect 70 of the type above described', whereby thev pilot of
ed at a particular port >each responsive to a dif
the craft 8i may ascertain his distance fromthe
ferent' frequency range andthe aircraft circuit
transmitting station. Also, at station -80 is pro
may be provided with switching means> so that
vided a ’beaconV transmitter ofv any known type
the transmitter may operateselectively at differ
which defines a given' course-'- line. `The pilot
ent‘frequency ranges; If one repeater is' then
then merely need follow the given course line
until his indicator of distance Vd reads the> desired
value. c Then by use of a suitable altimeter, pref
erably’a radio’altimeter, it is possible to fly at
energy in opposite phase so as to overcomewthe
effect of» mutual coupling may be utilized.
Y . »
. While I have disclosed various embodiments of
any desired height h, with respect to the ground
my invention in the Vspecification as Ídescribed
surface at, the particular distance d.
above, it should be distinctly understood that
various modifications and alterations thereof may
be made by those skilled in the art without de
parting froml the spirit of the invention. What
In order
to obtain these indications it is necessary that
the aircraft carry the ordinary beacon receiving
arrangement andinaddition the distance finding
I consider my invention and upon which I desire
system described in the present application and
to secure protection is embodied in the accom
an accurate altimeter to indicate his altitude with 10 panying
claims. '
respect to the earth. Since the altimeter and
What I claim is:
beacon receiver are generally standard equipment
A1. Adistance determining system, compris
only the distance finder represents added appa
ing means for transmitting radio frequency
ratus. With this arrangement it is possible for
apilot of a craft to ascertain his positionr with 15 waves of cyclically varying frequency from a first
station, means at a second station comprising a
outbeing able to sight the ground. While the
repeater for receiving said radio frequency waves
height must be taken into consideration for pre
and transmitting therefrom under control of
cise -calculation of the distance along the ground,
said received waves corresponding radio fre
in practice this generally is not necessary since
the angle included between ground and the line d 20 quency waves cyclically varying in frequency,
means at said first station for receiving the Waves
is so small that this indicated distance is sub
transmitted from said second station and other
stantially equal tothe groundl distance. A
waves varying in frequency corresponding to the
With these systems it is often desirable that
frequency variations of waves from said first
the'v radiations from the beacon be such that it
is’notdetectable at the ground level. Accord 25 named transmitting means, and means at said
first`> station responsive to said received _Waves
ingly, an arrangement as disclosed in Fig. 9 may
and said other waves for comparing the _fre
be used rather than the beacon system produc
quency of said received waves and said energy
ing the field pattern of Fig. 8. In accordance
for determining the distance between said first
with this arrangement of Fig. 9 the transmitter
station may transmit abeacon guiding system at 30 and second stations.
2. A distance determining system according
an _angle to the earth, so that substantially no
to claim 1, further comprising direction finder
radiation »occurs along the earth’s surface it
means at said first station to indicate direction
selfj.` Ii'l the beacon isdesie’ned so as to produce
toward lsaid second station, whereby the position
only a single guide line, for example, by utilizing
fourintersecting patterns instead of two to define 35 of said first station with respect tosaid second
station may be determined.
Y, .
the beacon range, then thecraft 8l need not carry
3. VA distance determining system according to
an Valtimeter but need merely >follow this single
claim l, further comprising means for inter
line until the meter on the plane indicates thaty
mittently interrupting transmission of said fre
the proper distance has been reached. >'I-‘he an
tenna of the repeater station should also be of 40 quency variablewaves at said second station, and
means-for transmitting other signals therefrom
such construction that radiationtherefrom is di
during saidperiod of interruption.
rected away from the earth. This may be ac
4. A'distance determining system according to
complished by the use of properly designed radi
claim 1, further comprising energy supply means
ators or vby various refiectorl arrangements as
known in the art. Since the radiation as exem 45 at said‘second station and means at said second
station responsive to energy received from said
pliñed by the conical patterns say 83, is not per
first station for supplying energizing power to
ceptible at the surface of the earth at the posi
said radio _transmitting means at said second
tion P, it is not possible for those at this posi
tion to know that the beacon is pointed in their 50 station from said energy supply means. '
5. A distance determining system according to
claim 1, wherein said waves transmitted from
If the beacon pattern 83 is not sui’ñciently
said second station are of the same frequency
narrow or if a single guide line is not provided,
range as the vwaves received thereat from said
craft 8l may carry an altimeter for use in con
first station, further .comprising `circuit means
55 for preventing waves transmitted from said
second station from affecting the operation of the
~, While I have described a few embodiments of
nection with the distance finder and beacon for
precisely determining its position.
receiving means at said second station.l ~
my invention in connection with the accompany
6. In an aircraft positionl determining system,
ing drawings, it should be clearly understood that
a transmitting station, means at said station for
these are made merely by way of illustration. It
is clear that each of the various embodiments 60 defining a radio beacon guiding course, means
for determining the distance of said craft from
illustrated in the figures may be modified by
transposing and combining various elements of
the systems illustrated as desired. Furthermore,
'any known type of recording arrangement and 65
reproducing arrangement may be used instead
of the photoelectric control arrangement dis
closed in- connection with Fig. 5. Likewise, it
should -be understood that at the receiving sta
tion, Figs. 6 and '7, various known arrangements
for preventing coupling between antennae such 70
as 'I2 and 'I3 may be provided.
These may con
stitute, for example, shield arrangements to pre
vent any coupling. Other known arrangements
such as systems for feeding over a portion of the
said transmitting station comprising-,a cyclically
variable frequency transmitter carried by- said
aircraft, means at said transmitting station re
sponsive _ to receipt of said variable frequency
waves for retransmitting to said craftr waves
correspondingly variable in frequency, and means
on said aircraft for receiving said retransmitted
Waves and comparing them with said trans
mitted waves to determine distance, and means
on said aircraft responsive to received energy for
indicating when said Vaircraft 'is following said
7. A navigation system for- aircraft` compris
75 ing means for transmitting radio frequency
Waves of cyclically varying frequency from a first
station, means at a second station comprising a
repeater for receiving said radio frequency Waves
and transmitting therefrom under control of
said received waves radio frequency waves cor
respondingly cyclically varying in frequency,
means at said first station for receiving the
first-mentioned transmitted waves are varied,
and means at said ñrst station for comparing the
frequencies of said received waves with the in
stantaneous frequency of said first-mentioned
transmitted Waves.
9. A navigation system for aircraft comprising
means for transmitting radio frequency Waves
of cyclically varying frequency from a ñrst sta
tion, a second station comprising a repeater for
frequencies over which said first-mentioned 10 receiving said transmitted Waves and for re
transmitting said Waves, means at said first sta
transmitted waves are varied and means at said
tion for receiving the waves transmitted from
first station for comparing the frequencies of
said second station and for receiving other Waves
said received waves with the instantaneous fre
Within the range of frequencies over which said
quency of said first-mentioned transmitted
transmitted waves are Varied,
said other Waves including waves transmitted
8. A navigation system for aircraft comprising
from said ñrst -station and reflected by objects
means for transmitting radio frequency Waves
external to said first station, and means at said
of cyclically varying frequency from a first sta
ñrst station for comparing the frequencies of
tion, a second station comprising a repeater for
receiving said transmitted waves and for re 20 said received Waves With the instantaneous fre
quency of said first-mentioned transmitted
transmitting said Waves, means at said first sta
tion for receiving the Waves transmitted from
said second station and for receiving other waves
within the range of frequencies over which said
Waves transmitted from said second station and
for receiving other waves Within the range of
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