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ec. 31, 1946.
‘ 2,413,62Q I
Filed June 19,’ 1940
4 Sheets-Sheet 1
Dec. 31, 1946.
Filed June 19, 1940
4 Sheets-Sheet 2
Dec. 31, 1946.
G, GuANE|_|_A ‘
2,413,62Q '
Filed June 19,. 1940
4 Sheets-Sheet z
BY 61/5 my GUAA/ELLA
e'c. 31, 146.
Filed June 19, 1940
4 Sheets-Sheet 4
A427 ?e‘;
Patented Dec. 31, 1946
Gustav Guanella, Zurich, Switzerland, assignor,
by mesne assignments, to Patents Research
Corporation, New York, N. Y., a corporation of
New York
Application June 19, 1940, Serial No. 341,225
In Switzerland October 1.6, 1939
6 Claims.
(Cl. 250-911)
The present invention relates to a system for
and a method of direction ?nding by means of
manipulations or adjustments on the part, of the
radiant energy such as acoustic, electro-magnetic
or other waves to serve as a navigational aid for
guiding moving craft such as ships or airplanes
and for other uses.
More speci?cally, although not limitatively, the
or reading substantially without requiring any
Further objects. and aspects. of the invention will
become more apparent from the following detailed
description taken. with reference to the accom
panying‘ drawings forming part of this speci?ca
invention is concerned with directional systems
tion and wherein:
located at a ?rst preferably ?xed point and en
Figure 1 is a. block diagram showing a basic di
abling the use of a simple receiver at a distant 10 rection ?nding system embodying the principle
preferably moving point for determining the di
of the invention,
rection between and/or the relative position of
Figures 2 and .3 are theoretical diagrams.» ex.
said points. Thus, the transmitter may be a
planatory- of the .fHnciiQn and operation of the
ground station and the receiver located on a ship
or an airplane in ?ight.
Figures 4a and 4b; are circuit diagrams of a
According to a known method of direction ?nd~
transmitting and receiving- system, respectively,
ing of the above general character, the direction
il1ustration one form of practical embodiment of
between a ?rst point and a distant point whose
a direction ?nding system according to the in
position it is desired to determine may be found
by determining the direction of incidence of ra 20
Figures 5a and 5b are circuit diagrams showing
diant energy transmitted by the distant point and
a modi?cation of a transmitting and receiving
by communicating this information to the distant
system, respectively,
point by special transmitting means, This meth
Figures 6a and‘ ,6b show further-modi?cations of
od is widely used for position and direction ?nd
a transmitting and receiving system,
ing on board ships and airplanes. A major dis 25 Figure 7 is a block diagram illustrating a, sim
advantage of this method is the fact that special
pli?ed direction; finding system according to the
transmitting means are required, to communicate
the results of the direction determination to the
Figure 8' shows in block diagram form a direc
tion ?nding system constructed according to the
distant point. A further disadvantage is the fact
that it is impossible to carry out more thanv one 30 principle of the invention especially suited for
_direction determination at the same time,
guiding an airplane in effecting a blind landing,
According to another method known in the art
Figure 9 is a block diagram illustrating a di@
of radio direction ?nding, a rotating directional
rection ?nding system suited to serve as a hom
beam is transmitted from a ?rst reference point
ing-beacon and a distance. indicator for guiding
and the transmitting direction determined at the 35 the course of aircraft or other moving vehicle,
Figure 10. shows in block diagram form a simple
receiver from the instant of arrival of the signal
impulse received during a short time intervals or
system for position ?nding utilizing the principle
any other characteristic of the transmitting beam
of the invention‘,
varying according to a pro-arranged schedule as
Figures 11 and 12' are block diagrams illustrat
a function of the transmitting direction. This 40 ing an improved feature of theinvention to elimi
method involves the use of complicated trans—
nate ambiguity of the direction indication.
mitting- apparatus including mechanically mov
Like reference characters identify like parts
ing antenna systems and furthermore requires eX
throughout the different views of the drawings.
act calibration and synchronous operation of the
With the. aforementionedlandi other objects in
receiver. Since the transmitted. energy is re 45 view the invention contemplates the provision of
ceived during a short time interval only, the sys
special transmitting means adapted to transmit
tem is- subject to substantial interference while
radiant-energy waves such as radio Waves whose
its accuracy is limited due to the limited concen
frequency varies periodically according to, a pre
tration or sharpness of the directional beam es
arranged schedule. The waves are caused, to
pecially in the case of radio waves.
50 travel to a distant receiver over at. least two paths,
Accordingly, it is an object. of the present in
vention to substantially overcome the di?iculties
and shortcomings of the above and other direc
tional methods known in the prior art and to pro-r
vide a novel method of’ and system for direction 55
and positioni?nding-enabling a direct indication
the di?erence between which is. proportional. to
the directional angle between the transmitter and
receiver with respect-to a. chosen. reference line.
Thus,‘ the two received‘ waves-will- be of different
frequency duetothe distanceinlength of the path
over whichthe two wavesltravel, this .diii'erence in
the frequency difference It will be constant except
for short transition periods at the instants when
the transmitting frequency passes through its
frequency being due to the change in frequency
at the receiving station during the time interval
between the arrival of the ?rst wave travelling
over the shorter path and the arrival of the sec
ond wave travelling over the longer path. This
difference in frequency will constitute an index of
maximum and minimum, respectively.
If the
transmitting frequency is varied n times during
a second and over a range of F1 cycles embracing
the directional angle of the line connecting the _ _ a lower and upper limit, then the frequency varia
tion during unit time will be expressed as follows:
transmitter and receiver with respect to a ?xed reference line as Will become further apparent _- ~
g=JJZ=2-n-FI cycles
as the description proceeds.
Referring more particularly to Figure'Lrecl- -_ ..
tangles S1 and S2 represent afpair of transmitters , -_
that'is, the'beatfrequency produced by the oscil
lati‘onsles and :24 received with a time difference
T=(tz—t1)- in this case is determined by the fol
I lowingequation in view of Formula 5:
or radiators spaced at a distance ‘b and radiating =
waves such as electro-magnetic oscillations e1 and
c2, respectively. The frequencyjof these oscillae _
tions is varied simultaneously according. to: the . .
quency of the oscillationsei and e2 being radiated "
, j
The waves transmitted arrive at a distant re
ceiver E by way of two paths s1 and s2, respective
quency swing F1, the frequency n of the varia
tions, the known velocity of propagation c and
the known distance of the base line 1) between the
_ transmitters or radiators.
ly, which are‘ of unequal length if the receiver is
at a point to the right or left of the bi-secting line
at right angle to the baseline b of the transmit
rection indication.
is determined by the following formula:
7 to linear variation of the transmitting frequency
30 which may be varied according to any desired
periodic schedule. Thus, the. transmitting fre-v
quency may be varied or modulated sinusoidally.
about a mean value in as shown in Figure 3. In
this case the momentary frequency is determined
by the following equation:
. f=fo+F2 sin ti
and the derivative will be as follows:
- The difference between‘ the transmitting pe
riods t1 and t2 of the oscillations er; and c4 arriv
ing at the receiver E is then given by the follow
As is understood, the invention is not limited
wherein.“ is the angle subtended by the line con
necting the center of the base lineb with the re
ceiver E and a line at right angle to the base line b.
Thus, by measuring.
the beat frequency h by means of a suitable fre
quency meter I the latter may be calibrated in
directional angles on to affordv a‘ direct reading di-.
ters. The difference between the paths s1 and s2
wherein the constant K1 is dependent merely
upon the maximum frequency deviation or fre
may be expressed mathematically as follows: _
' _ _'
——-sin a=K1-sin a
same pre-arranged schedule; that is, the fre- . .
_ f
wherein ‘c represents'the'velocity of propagation
g=g=Fw cos rt
of the waves radiated from the transmitters.
The frequencies is and ft of ‘the received oscil
The beat frequency produced in the receiver in
this case is determined as follows in accordance
lations es and er differ from each other on ac
' "
count of the varying transmitting frequency f(t)
and the difference of the transmitting periods. 45
This difference in frequency is expressed as fol
with Equations5 and 9:
that is, in other words, the beatfrequency varies
between zero and the following limit valuez'vv
; h=fa_—fi=(t2—t1)-di;=g-T -§ ,
wherein the derivative
-cos vt-sin a
wherein the constant K2 again is dependent upon
the known frequency deviation Fa, the modulaté
riod may be regarded as a constant which will be 55 ing frequency 1;, the velocity of propagation c,
and the base line 1) between the radiators. Since
the case in practically carrying out the invention.
beat frequency hz Varies periodically in the
By combining Equations 3 and 4 the'frequency
rhythm of the constant modulating frequency v;
difference is obtained as follows:
a component as may be derived from this beat fre4
(5) 60 quency by selective means whose amplitude varies
of the frequency?t) during the transmitting pe
in direct proportion to the'frequency deviation of
the beat frequency; that is, in turn in proportion
The simultaneously received oscillations es and er
are recti?ed to obtain abeat oscillation having a‘
to the directional angle a to be determined. Due
to the selective reception of this component which
frequency which corresponds to the difference
frequency h.‘ This beat frequency is proportional 65 after rectification may serve to energize an-indi
cator the effect of interfering and disturbing sig;
to the, directional angle or according to Equation
nals is substantially eliminated thereby-greatly
5 and accordingly maybe utilized to effect a di
increasing the accuracy and reliability of the dil
rect indication by‘_ measurement by means of a
suitable instrument I.
‘If the transmitting frequency ,f(t) varies linear.-v 70
ly about a mean value it such as shown in Fig
ure 2, the frequencies is‘ and ii of the received os
cillations es and er delayed'in accordance with the
transmitting periods tsj anduti; respectively, will
also vary according to a linear function whereby
rection indication.
' f5 '
Referring to Figure 4a there is shown a trans
mitting system for radio waves for practicing the
invention comprising a pair of radiators Si and
_ S2 which may be in the form of dipoleantennyae
' or the like serving to radiate oscillations e1 sneer
and energized through feeding lines Z1 and Z2
from a common generating system. The latter
quency f varies in a similar manner. As is under-g
comprises a feedback master oscillator V3 in the
form of a vacuum tube having a tuned plate cir
stood, the acceptance band Width or frequency
pass range of all the tuned circuits of the trans
mitter should be designed to be su?iciently wide
to prevent suppression or weakening of the ex»
cult C3—Ls regeneratively coupled with the grid
circuit to generate sustained high frequency os
cillations in a manner well understood by those
skilled'in the art.
treme transmiting frequencies.
Item B3 is a source of space
In Figure 41) there is shown a receiving system
current Connected to the anode of the tube. The
suited for cooperation with the transmitter de
scribed in Figure 4a. The received oscillations
high frequency oscillations produced by this os
cillator are ampli?ed in a known manner by
means of a .power ampli?er comprising in the ex
ex and or are combined and ampli?ed by means
of an ampli?er A0 thus yielding a high fre
quency oscillation e5 whose amplitude varies in
ample shown two push~pull stages comprising
amplifying tubes V4—-V5 and Vs—V7, respectively.
the rhythm ofv the beat frequency h. This oscil
lation is impressed by way of a transformer L9
upon a double diode recti?er circuit comprising
diodes Va and V9 of known design to produce a
low frequency potential 66 across the condenser
C9 and resistance R4 corresponding at all times
The common tuned input circuit Lil-C4 and the
tubes V4-—V5 is suitably coupled with the oscil
lating circuit C3-—L3 and the output circuit of
the ?rst stage of the power ampli?er is coupled
to the input of the second stage by way of a
push-pull transformer L5 tuned by means of a
condenser C5 shunted across its secondary.
The '
output of the power ampli?er is impressed upon
the feeder lines Z1 and Z2 by way of a further
push-pull transformer Ls having its secondary
to the instantaneous high frequency amplitude
and varying in the rhythm of the beat frequency
h. The potential e6 is applied by way of‘ coupling
condenser C10 and grid leak resistance R5 to the
grid of a low frequency ampli?er and limiter V10.
tuned by means of a condenser C6. The radiating
An additional resistance is connected between
antennae are coupled with the feeder lines :5 the grid of the ampli?er V10 and the coupling
through transformers L7 and L8 tuned by means
condenser C10 whereby this ampli?er acts as a
of condensers C7 and Cs, respectively. Items B3
limiter to convert the impressed sinusoidal po
and B4 are the space current sources for the
tential into a substantially rectangular potential
push-pull stages connected between the cathodes
as understood more clearly from the following.
and the center tap of the coupling transformers 50 Since the grid of the tube V10 due to the grid
in a manner well known. If the feeding lines Z1
current passing through the resistance Re and
and Z2 are of equal length, the frequencies of the
the voltage drop developed across this resistance
oscillations 61 and c2 radiated by the antennae
is never allowed to become positive, and since
will also be equal to and in synchronism with
furthermore the anode current is completely
each other.
In order to effect a periodic variation of the
transmitting frequency .the tuning of the master
oscillator is varied continuously and periodically.
In the example illustrated there is provided for
this purpose a variable reactance electron tube
V2 effectively shunted across the tuning con
denser C3 of the oscillating tank circuit. The
anode and cathode of this tube are connected
through a condenser C2 and a resistance R2 in
0; Ci
blocked when the grid becomes highly negative,
the anode current ?ow is restricted by upper and
lower limits; that is, the potential impressed
from the plate to the primary of the output
transformer L10 by way of coupling condenser C11
and having a frequency corresponding with the
frequency h of co, will assume .a rectangular
shape with constant positive and negative limit
values substantially independently of any inci
dent amplitude variations of the input potential
series with the grid of the tube connected to the 45 86. The potential 6': converted from a sinusoidal
junction point of this condenser and resistance.
to a rectangular shape is impressed upon a suit
In this manner by proper design of the circuit
able frequency variation response circuit to pro
constants the potential applied to the grid of the
duce a current i varying in proportion to the
tube from the oscillating circuit will be in quad
beat frequency h to energize a suitable measuring
rature to the potential at the plate whereby the 50 instrument for direct indication of the direction
tube will act as an effective reactance deter
angle a to be determined. In the example shown
mined by the ampli?cation factor of the tube.
this frequency conversion means comprises a pair
The latter is controlled by a potential eo im
of triodes V11 and V12 having both .their grids
pressed by way of a high frequency choke coil
excited by the potential e": by means of separate
L1 from a low frequency relaxation oscillator'in 55 secondary windings of coupling transformer L10.
such a manner as to vary the tuning of the oscil
The cathodes of the tubes are connected through
lating circuit C3—L4 and in turn the transmitting
a condenser C12, the anode of tube V12 is con
frequency fin the rhythm and in accordance with
nected to the cathode of the tube V11 through a
the shape of the relaxation oscillations. The lat
current source Be, and the anode of tube V11 is
ter in the example shown are produced by the 60 connected to the cathode of the tube V12 through
aid of a gas ?lled triode V1 shunted on the one
hand by a condenser C1 and on the other hand
by battery B1 in series with a resistance R1. In
a suitable current indicator I shunted by a con
denser C13. The operation of this conversion and
indicating system is as follows: With the poten
tial 67 becoming negative the grid of tube V12
operation, the condenser Cl is periodically
charged to a potential equal to the ?ring poten 65 will become positive thus rendering this tube con
tial of the tube V1 and thereafter discharge
ductive and causing a charging of the condenser
through the tube. During each discharge period
C12 by the battery Be. During the next half
the grid of the tube receives a negative impulse
cycle of 8? tube V11 becomes conductive whereby
through the condenser Cu connected across the
the condenser C12 will be discharge through the
tube in series with a further resistance R0 where 70 instrument I. Thus, during each period of the
by the‘ extinction of the-tube is accelerated and
rectangular potential 67 a de?nite electric charge
premature ignition is avoided. The thus obtained
passes through the indicating instrument. The
relaxation potential increases linearly and there
condenser C13 serves to smooth or equalize the
after decreases rapidly in accordance with a saw
currents and tosteady the movement
tooth pattern whereby the transmitting fre 75 of the pointer
of .the indicating instrument. Ac
e‘ord'ingly, the average current i passing through
nected ahead of the network N by, means of
the instrument will be proportional to the fre
quency h of the potentials er and es; that is, in
turn to the difference between the travelling
vided it falls within the audible range. ,
which the beat frequency may be ascertained pro--_,
According to a further modi?cation, the high.
frequency oscillations er and c2 may be generated
paths of the received oscillations ea and er, re
by separate transmitters at the radiating points
spectively. Thus, by suitable calibration of the
as shown in Figure 6a.. The tuning of the high
generators G1 and G2 in this case is
stantly ascertained by a direct indication.
varied simultaneously in accordance with a con:
If very high frequencies are used difficulties
may be encountered in feeding the energies to ll) trol potential at produced by a low frequency gen
instrument I the directional angle a can be in
erator G3 in such a manner that the frequencies
of both oscillations ei and e2 which are further»
ampli?ed by means of ampli?ers A1 and A2, re
theradiators S1 and S2. In such cases a low fre
quency potential e0 may be utilized produced by
a common generator Go as shown in Figure 5a
and transmitted to the radiating stations. At the
latter the low frequency potential is stepped up to
the desired high frequency by means of frequency
multipliers M1 and M2 of any known type and
construction, additionally ampli?ed by means of
ampli?ers A1 and A2 and then radiated in the
form of high frequency oscillations er and ez in 20
spectively, are constantly varied periodically and
in an equal manner. The control potential ‘at
may serve to excite the grid of a variable react-_
ance tube in a manner similar as shown in Figure
4a to effect a corresponding variation“v of the
transmitting frequency or any other suitable tuning control may be employed. Since the trans
mission of the low frequency potential uo to the
a manner similar to that described hereinbefore.
radiating points does not offer any practical
The periodic frequency variation may be effected
difficulties, arrangements of this type are special
by varying the frequency 6a of the common oscil
.ly suited in cases where the radiators are spaced
lator in any suitable manner purely electrically as
described or by continuously rotating a variable 25 by a comparatively large distance or base line b.
Thus, if the auxiliary potential uo, varies accord-;
tuning element (condenser) by means of a motor
ing to a sinusoidal function the transmitting fre
P as indicated schematically in the drawings.
quencies will also vary sinusoidally about a mean
By suitably matching the transmitting channels,
value and in turn the beat frequency obtained in
frequency multipliers and ampli?ers, the vari
able frequencies f1 and j: of the radiated oscil 30 the receiver will vary between zero and-a maxi
mum he in accordance with Formula 10 as shown
lations e1 and e2 Will be in exact synchronism with
in Figure 3.
each other. In order to obtain a desired variation
In the latter case, that is where the transmit
of the frequency such as a sinusoidal variation,
ting frequency is varied according to a sinusoidal
the plates of the tuning condenser rotated by the
motor P may be suitably shaped as is readily un
35 or any other non-linear periodic function a re
In Figure 5b there is shown a modi?ed receiv
ing system wherein the received oscillations es
and e; are combined in a receiver or ampli?er
ceiver may be used as shown in Figure 611-.y In
the latter, the received high frequency 'oscillae
tions as and 24 after ampli?cation by1means-of
ampli?er A0 yield a combined high frequency
A0 with a constant local oscillation en generated 40 oscillation e5 applied to a ?rst detector D1 in va
manner similar as described in Figure 5b result-‘
by a local oscillator O to obtain a combined in
ing in a low (intermediate) frequency oscillation
termediate frequency oscillation e5 having an am
e6 whose frequency corresponds to the beat free
plitude varying in the rhythm of the beat'fre
quency. In order to maintain the amplitude of
quency h. This intermediate frequency potential
is recti?ed by means of a recti?er Di. In order 4 Or the potential es substantially constant the direct
current component of era is applied through an
to render the reception independent of the am
channel including a suitable smoothing ?lter
plitude or strength of the received oscillations,
N: to a gain control element of the ampli?er An
there is provided an AVC system connected be
in a manner substantially similar to that de
tween the detector D1 and the ampli?er A0 where
by a control potential proportional to the am 50 scribed hereinabove. The potential as of varying
frequency is impressed upon a frequency responé
plitude of the received oscillations is impressed
sive network Ni comprising in the example shown
upon a gain control element of the ampli?er A0
in such a manner as to maintain a constant aver
age amplitude of the potential es supplied by the
output of the detector D1. The potential 66
Whose frequency in case of linear variation of the
transmitting frequency according to Equation 7
is proportional to the sine of the transmitting
angle on is applied to a frequency conversion or
response network N comprising in the example
shown a series resistance R11 and a parallel in
ductance L11. By proper design of the latter there
is obtained at the output of the network N an
alternating potential as having an amplitude
proportional to the frequency of es. By recti?ca
tion of this potential in adetector D2 there is ob
tained a direct potential e» which is proportional
to the frequency h of the potential es, i. e. in turn
to the directional angle 0:. This potential is suit
ably measured by an instrument I which may be
directly calibrated in angles a to a?ord an in
stantaneous direction indication.
In many cases a simultaneous subjective re
ception of the beat frequency is desired. For
a series
condenser and a parallel ; resistance
whereby there is obtained at the output of this
C1 or network a low frequency potential ea whose am
plitude is an index for the frequency h; of ca.
Since this frequency according to Formula‘ 10
varies periodically in the rhythm of the modu
lating frequency v the potential e9 derived
from ea by further recti?cation by means of de_.
tector D2 varies periodically in the same'rhythm
in such a manner that the maximumlamplitude
of eg increases in proportion to an increase of
the beat frequency h. The potential e9 is imi
pressed upon a selective network N2 comprising
in the example shown a series resonant'circuit
L15--C15 and a parallel tuned circuit‘ Ll6—'-C16.
The network N2 is suitably designed in such’ a
manner as to obtain'a variable component "eifo
at its output which in turn is recti?ed in -a- dei
tector'Da to yield a ?nal potential'en' ‘energizing
an ordinary current indicator 'I.' The. latter in:
dicates the amplitude of thefpotentialr-em corree
sponding to the ‘maximum Ivalues ea‘i'. vefrto the
this purpose a pair ‘of headphones may be con- 75 maximum beat frequencies he.‘ .Bysuitablyicalr
brating the instrument, the transmission angle a
can be read directly on the scale of the instru
ment. Due to the selective transmission of the
potential e9 through the ?lter N2 all disturbing
frequencies and interfering components are sub
stantially suppressed whereby this system be
the same frequency range may be used for all
transmitters by alternately and successively con
necting the transmitters in rotation. In the lat
ter case only a single receiver is required which
alternately indicates the separate directional
angles on and 002, etc. 'In order to identify the
comes highly selective and accurate with com
separate transmitters it is advantageous to use
paratively small receiving signals. As is under
unequal transmitting periods in such a manner
stood a selective measurement of the component
that transmitter S10 may be connected during a
e9 may be effected by other means well known 10 lOnger interval than the transmitter S20 and any
in the art. I
additional transmitters used are connected dur
Referring to Figure 7 there is shown a simplié
ing still shorter transmitting periods.
?edmodi?cation of the invention requiring only
Referring to Figure 9 there is illustrated a
a single radiator S1 for transmitting the fre—
further embodiment of the invention suited as a
quency modulated oscillations whereby a second
homing-beacon and distance indicator for guid
transmission path S21+s22 different from the
ing a moving vehicle in particular an airplane
direct transmitting path 51 is obtained by the
towards a place of destination, such as an air
provision of a re?ecting surface W. Since the
port. According to this modi?cation there are
angle of incidence in and the re?ecting angle 92
provided two transmission groups S'11-—S12 and
for the oscillation re?ected at the point We are 20 S21——S22, respectively, each provided with a com
equal to each other, the re?ected oscillation will
mon generator Gin-and G20 such as according to
travel over the same path 82 as if it would emanate
Figure 5a or 6a. These transmitter groups are
from a radiating point S2 located at a point
alternately connected by means of a distributor
forming the mirror image of the radiator s2 with
or interrupter U. In an arrangement of this type
respect to the re?ecting surface W as indicated
the beat frequency in the receiver E will be equal
in dotted lines in the drawings. Thus, the differ
for both groups if the receiver is at a point coin
ence in the travelling path s21+s22—s1 determined
ciding with the bi-secting line q between the
by measuring the difference between the fre
transmitters since in this case the angles on and a2
quencies of the received oscillations, in this case
are equal to each other. These angles a1 and a2
too will be proportional to the sine of the trans 30 will decrease as the distance 201 of the receiver
mitting angle a. In arrangements of this type
from the point Q at the intersection of the sym
all problems and di?iculties of a common control
metry lines for the transmitter groups S11—S12
or synchronization of two separate transmitters
and San-S22 between the transmitters becomes
or radiators are substantially avoided and the
less; that is, the distance 101 may be determined
realization of the inventive method is enabled
directly by measuring the average beat frequency.
with a, minimum of apparatus required. In ad
A lateral deviation in from the bi-secting line q
dition to the transmitter S1 whose frequency is
will result in a corresponding difference between
varied periodically, all that is required is a re
the angles 0:1 and 1x2 and in turn a di?erence' be
?ecting surface W which in many cases may be
tween the two beat frequencies whereby such
already existent. The re?ecting surface may
deviation may be at once ascertained and cor
have the form of a metallic layer of suf?cient
rected by the pilot to maintain the course towards
extension or a wire net whose meshes are small
his destination known as a homing ?ight. A
compared with the wave length used. In many
system of this type is further suited for blind
cases natural re?ecting surfaces may be utilized
landing in that in addition to the direction the
such as a water surface or the surface of the
45 average beat frequency, indicated by the instru
earth itself.
ment I, may be used to inform the pilot of his dis
The method and arrangement shown in Figure
tance from the transmitter and in particular to
7 is well suited for guiding a plane above an air
point where to commence a landing operation.
port and as a navigational aid to assist a pilot
The control of the lateral deviation in may be
in e?ecting a landing. Thus, according to Figure , eifected by ascertainingthe difference between
8 the elevational angle on of a plane at the point
the beat frequencies in a head phone receiver I-I
of the receiver E can easily be ascertained by
connected after the ?rst recti?er in the manner
the aid of a transmitter or radiator S10 at a height
as shown in Figure 5b.
In order to discriminate between the two trans
mitter groups, the group S11-S12 may be con
55 nected during a short period while the group
above the landing ?eld in a manner substantially
S21—S22 is connected during longer periods. Al
similar to that described in connection with Fig
ternatively, the connection may be effected in an
ure. 7. A further transmitter S20 also operated
interlocking manner in accordance with the let
with a variable frequency is arranged in front of
ters n and a of the Morse alphabet. In the lat
a vertical re?ecting surface, preferably a wire 60 ter case if the aircraft deviates to the right or
net or wall W2 for indicating the zenithal angle
left from the bi-secting line q, a change of the
“2 which latter decreases rapidly as the airplane
pitch of the beat note is observed in such a man
approaches the wall W2, thus furnishing the pilot
ner that the letter a is heard at a higher pitch
with information as to his position relative to
and the letter n at a lower pitch or vice versa.' If
and above the landing ?eld and enabling him
the plane follows the bi-secting or homing course,
to safely land during conditions of poor visibility
a. continuous note of constant frequency or pitch
or to e?ect, what is known as a blind landing.
is heard. If the instrument I has su?icient inertia
In order to effect a direction determination in
its indicating pointer will not follow the rapid
multiple arrangements of the type shown in Fig
frequency ?uctuations whereby the average beat
ure 8 without‘ ambiguity different frequency 70 frequency indicated will be directly proportional
ranges may be employed for the separate trans
mitters. In this case‘ either separate: specially
tuned receive-rs may be ‘($3901 of a CGm'IhQn re
to the distance P1 from the transmitter thus
enabling a direct calibration of the instrument
in units of distance travelled.
ceiver Whose tuningis adjustedw alternately to
Referringto Figure 10, there is shown an ar
the different transmitting ranges. Alternatively, 75 rangement for position ?nding of a receiving sta
It can be easily seen that this beat frequency
tion E which may be located at an aircraft or
will assume different values for all directional
ship utilizing the principle of the invention.
There are provided for this purpose at least two
transmitters or groups of transmitters S11—S12
angles on between 0° and 180° that is, the arm-
E may be determined in a simple manner by find
thereby ful?lling Equations 16, '17 and 18.
biguity inherent in Formulae 5, 'I and 10 is sub-=f
stantially eliminated in this manner. The dif
and s21—-S22 located at points separated from
ference in the transmission periods according to
each other. These transmitters may operate with
Figure 11 may be obtained by feeding the high
separate frequency ranges or intermittently with
frequency oscillations of varying frequency di
the same frequency range. The directional angle
rectly from the generator G to the ampli?er A1
a1 is determined by measuring the beat frequency
between the oscillations transmitted by Si1—-S12 10 of the ?rst transmitting or radiating station while
the second transmitting station is fed through
and the directional angle (:2 is determined by
a Lecher wire system Z0, the length of-which
measuring the beat frequency of the oscillations
with a speed of propagation 00:0 corresponds to
transmitted by 521-822. If the location of the
the base b between the transmitting stations
transmitters is known the position of the receiver
A certain ambiguity still exists in the latter
ing the intersection of the directional lines from
the transmitters (triangulation method).
As is understood, the direction and position
?nding systems according to Figures 9 and 10
case inasmuch as a directional angle a and an
angle 180°-—cx, will result in similar beat fre
quencies. In order to eliminate this ambiguity,
may use a single transmitting or radiators S12 and 20 a plurality of transmitters may be employed ar
ranged in the manner shown in Figure 12 i; e.
S21 in combination with suitable reflecting sur
with the transmitters or radiators located at
faces in place of the double transmission systems
points other than upon a straight line. If the
shown in the drawings. Moreover, the direction
transmitters are energized in the same manner
or position determination according to Figure 8
may be effected without special re?ecting surfaces 5 such as shown in Figure 11, and if the base lines
between the transmitter groups S1—Sz and
by using spaced radiators or transmitters operat
Si-S3 form a right angle, the beat frequencies
ing with the same frequency in accordance with
originating from the ?rst and second transmitter
the invention.
. In the arrangements according to Figures 4 to
group will yield separate measuring results as
6 the frequencies of the oscillations c1 and c2 radi—'
ated by the transmitters are substantially equal
to each other. Since the polarity of the beat
frequency has not practical signi?cance, a posi~
tive and negative directional angle a i. e. on either
which may lie within 0“ and 360° can be posi
side of the bi-secting line which will result in the
tively determined without ambiguity. In order
same direction indication. According to a further
to carry out such a measurement, the trans
feature of the invention, in order to avoid this
mitters S1 and S3 may be operated alternately
ambiguity, the oscillations are transmitted with
a predetermined time delay To. In this case the
While S1 transmits continuously.
As pointed out hereinbefore the radiant energy
total difference in travelling times between the 40
used for direction ?nding purposes according to
received oscillations as expressed by Formula 3
the invention may be of any desired character
will be modi?ed as follows:
=gjsin a
such as in the form of radio waves or acoustic
waves which latter may be within or above the
audible range. The oscillations of varying ire-
whereby in turn the beat frequency will be as
quency may be transmitted directly through a
suitable medium or by the aid of a separate car
rier wave of constant high frequency modulated
in any desired manner.
In the latter case a sep-‘
Thus, in case of linear variation of the frequency,
arate demodulator is required in the input stage
the beat frequency in view of Formula 6 may be 50 of the receiver as is understood by those skilled
expressed as follows: -
in the art.
r The time delay Tn may be effected for instance ,
by transmission over a feeder line having a, length
b0 and a propagation transmission on in which
case the delay will be as follows:
ing vehicle to automatically maintain the vehicle
lowing condition may be ful?lled for a given value
of co:
This is the case for instance when co=c, and if
bo=b in which case Formula 14 is modi?ed as
begins-(Hem 0;)
and in case of linear frequency variation:
at a predetermined course; that is, the invention
may serve for use as an automatic pilot for
guiding a ship, airplane or other moving craft.
According to an alternative’ method, the beat
frequency varying proportionately to the dis
Thus, by a special design of the length 170, the fol
tential may serve for‘opera'ting a control mech
anism such as a steering mechanism of a mov
The method and system proposed by the inven
tion is especially suited for direction and/or dis
tance measurement by direct reading or indica
tion. Alternatively, the output current or po
tance is split into two or more phases in any
suitable manner, such as by a 90° phase shift
ing circuit and the split phases causedto pro
duce a rotary magnetic ‘?eld actuating a rotor
whose speed will be proportionate to' the dis
70 tance tobe determined and may be measured
or indicated in. any suitable manner.
It will be evident from the foregoing that the
invention is not limited to the specific circuits,
arrangements of parts and~the steps “described
75 and disclosed herein for illustration, butthat the
novel underlying thought and principle of the
converting said beat signal of varying frequency
invention are susceptible of numerous variations
into a signal current having an amplitude vary
and modi?cations differing from the speci?c em
bodiments shown and disclosed and coming with
in the broader scope and spirit of the invention
as de?ned by the appended claims. The speci
?cation and drawing are accordinglyvto be re
garded in an illustrative rather than a limiting
ing in proportion to the beat frequency, selec
tive means for segregating from said last cur
rent a predetermined frequency component, and
means for utilizing said last component as an
index of said directional angle.
4. In an elevational radio direction ?nding
I claim:
1.,In a direction ?nding system, a radiator
transmitting radiant energy located at a ?rst
point, a re?ecting surface arranged in relatively
?xed spaced relation to said radiator, a receiver
located at a distant point, whereby energy is 15
transmitted to said receiver both over a direct
path from said radiator and over an indirect
system, a radiator relatively ?xedly located above
ground, a receiver located on an aircraft in ?ight
whereby energy is transmitted to 'saidreceiver
both over the direct path from said radiator and
over an indirect path by way of re?ection from
the ground surface, means for periodically vary
ing the frequency of the energy transmitted ac- '
cording to a predetermined schedule, means as
sociated with said receiver for producing beat
path by way of re?ection by said surface, means
energy from the energies received over said sep
for periodically varying the frequency of the en
arate paths, the frequency of said beat energy
ergy transmitted according to a predetermined 20 varying according to the elevational angle of said,
schedule, means associated with said receiver for
receiver, and means for utilizing said beat fre
producing beat energy from the energies received
quency as an index of said elevational angle.
over said separate paths, the frequency of said
_5. A system for navigating an aircraft to
beat energy varying according to the directional
ward a carrier-wave re?ecting surface compris~
angle of the line connecting the point of said 25 ing, a carrier-Wave radiating system relatively
surface directly opposite to said radiator and
?xedly supported in spaced relation above said
said receiver with respect to a ?xed reference
carrier-wave re?ecting surface, means for ap
line, and means for utilizing the beat frequency
plying a frequency-modulated carrier wave to
as an index of said directional angle.
said radiating system for radiation therefrom,
2. In a radio direction ?nding system, a trans 30 means carried by said aircraft and adapted to
mitting antenna, a re?ecting surface arranged
receive the carrier wave radiated by said radiat
ing system and responsive to the difference fre
quency of carrier-wave energy traveling directly
and by re?ection from said carrier-wave re?ect
ing surface to said receiving means for deriving
a control signal, said radiating system having the
in relatively ?xed spaced relation to said antenna,
a receiver located at a distant point, means for
radiating electric waves from said antenna
whereby said waves arrive at said receiver both
over a direct path from said antenna and an in
direct path by way of re?ection by said surface,
means for periodically varying the frequency of
the waves radiated according to a predetermined
schedule, means associated with said receiver for
producing a beat signal from the waves received
over the separate paths, and means for utilizing
characteristic that equal-valued control-signal
loci are represented by geometric surfaces of
the frequency of said beat signal as an index
revolution ?xed relative to said radiating sys~
tem, and means for utilizing said control signal
to aid in the navigation of said aircraft along a
desired course approaching said re?ecting sur
of the directional angle of the line connecting
6. A system for navigating an aircraft toward
the point on said surface directly opposite to 45 a carrier-Wave re?ecting surface comprising, a
said antenna with said distant point with re- ‘
carrier-wave radiating system relatively ?xedly
spect to a ?xed reference line.
supported in spaced relation above said carrier-'
3. In a radio direction ?nding system, a radi
wave reflecting surface, means for applying a
ator located at a ?rst point, a re?ecting surface
arranged in spaced relation to said radiator, a 60
receiver located at a distant point, means for
radiating electric waves from said radiator,
whereby said waves travel to said receiver both
frequency-modulated carrier Wave to said radi
ating system for radiation therefrom, means car
ried by 'said aircraft and adapted to receive the
receiver for producing a beat signal from the
characteristic that equal-valued control-signal
carrier wave radiated by said radiating system
and responsive to the difference frequency of
over a. direct path from said radiator and an in
carrier-Wave energy traveling directly and by
direct path by way of re?ection by said surface, 55 re?ection from said carrier-wave re?ecting sur
means for sinusoidally varying the frequency of
face to said receiving means for deriving a com
the waves radiated, means associated with said
trol signal, said radiating system having the
frequency loci are represented by geometric sur
beat signal having a frequency periodically 60 faces of revolution ?xed relative to said radi
varying between zero and a maximum accord~
ating system, and means for utilizing said con
ing to the directional angle of the line connect
trol signal to aid in the navigation of said air
ing the point on said surface directly opposite to
craft along a desired OOurse approaching said re
?eeting surface.
said radiator with said receiver with respect to
a ?xed direction, frequency response means for 65
Waves received over said separate paths, said -
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