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Патент USA US2405231

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Aug» 6, w45
R. c. NEwHoUsE
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' .2,405,231
Filed March 51, 1942
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Filed March 31, 1942
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Patented Aug. 6, 1946
Russell C. Newhouse, Millburn, N. J., assigner to
Bell Telephone Laboratories, Incorporated, New
York, N. Y., a corporation of New York
Application March 31, 1942, Serial No. 437,013
12 Claims.
(Cl. Z50-11)
This invention relates to blind landing systems
for aircraft. More particularly, it relates to im
proved methods and systems for presenting dis~
ploying an electronic switching or commutating
Fig. 6 illustrates an improved frequency meter
ing circuit suitable for converting frequency ín
tance, direction, and altitude indications simul
taneously on a single indicator and so correlated
as to facilitate the navigation of an aircraft along
any one of a plurality of landing paths.
In the preferred illustrative embodiments of
systems of the invention to be described herein~
after, altitude, distance and direction indications
are presented simultaneously on a single cathode
ray oscilloscope screen, the altitude indication
being in the form of a horizontal line, Whose
position above a preñxed line is a function of the
altitude; the distance indication being in the form
of a vertical line, whose position to the right of
a prefixed point is a function of distance,- and
the direction left or right (or on) a particular
beacon course being indicated by the position of
dications into direct current voltages for use in
systems of the invention;
Fig. 6a is a voltage graph relating to the opera
tion of the circuit of Fig. 6; and
Fig. '7 illustrates types of critical altitude and
no-signal alarms which can advantageously be
employed with blind landing systems.
The general arrangement of systems embody
ing the principles of the invention will be under
stood from a description of Fig. 1 which shows
in block schematic form, an embodiment of the
invention. In that figure, lll, l2 and I ll, repre
sent, respectively, radio distance indicating ap
paratus, a radio altimeter and direction indicat
ing apparatus. These apparatus units are con
an auxiliary indication with respect to an index 20 nected to a switching system i8, various forms
mark at the top center of the indicator target.
of which are illustrated in Figs. 3, 4 and 5. The
Switching means, which may take the form
switching system is in turn connected to an in
of a rotating commutator or of an electronic
dicator IS capable of compositing several in
device, repeatedly present successive voltages rep
dependent indications, such as a cathode ray
resenting the three indications desired, the fre 25 oscilloscope. All of the aforesaid apparatus is
quency of repetition being sufficient to provide for
located upon the aircraft, the navigation of which
is to be aided thereby. Cooperative apparatus
retention of the three resulting indications on
may or may not be required at known reference
the cathode ray tube target without perceptible
points on the earth’s surface as will presently be
Indications of the three types desired may be
obtained by any of the numerous well-known
systems for providing indications of altitude, di
rection and distance, provided the systems can be
conveniently modified to furnish voltages (pref
erably direct current) proportional to the mag
nitudes of the quantities involved over the re
spective desired ranges of indications.
This invention will be readily understood from
the following description, when read in connec
tion with the attached drawings in which
Fig. 1 indicates in block schematic diagram
form the general arrangement of systems of the
apparent. The radio distance indicating appara
tus IE can, for example, be of the general type
described in the patent to H. T. Budenbom, No.
2,248,215, issued July 8, 1941. The radio altim
eter can be of the general type described in the
patent to W. H. C. Higgins et al., No. 2,206,896,
issued July 9, 1940, modified in accordance with
Fig. 6 of the accompanying drawings, or the pat
ent to J. G, Chaiïee, Reissue No. 21,955, issued
November 25, 1941, similarly modified. The di
rection indicating apparatus IG can be of the
type described in the patent to J. W. Greig, No.
2,003,932, issued June 4, 1935. The indicating
voltages that are created in each of the aforesaid
apparatus units are successively impressed upon
Fig. 2 illustrates a typical composite indication 45
a compositing indicator such as a cathode ray
of altitude, distance and direction as afforded by
oscilloscope by means of the switching appara
systems of the invention;
tus I6.
Fig. 3 illustrates a system of the invention e'm
As shown in Fig. 2, the screen or target of the
ploying a simple rotary commutator switching
arrangement ;
Fig. 4 illustrates a system of the invention em
indicator or oscilloscope has associated with it
50 a horizontal scale representing the distance from
the aircraft to a ñxed point such as a particular
ploying a plurality of ampliiiers in conjunction
with a rotary commutator switching arrange
` Fig. 5 illustrates a system of the invention em
position on a landing field; a vertical scale repre
senting the altitude of the craft above the terrain;
and at the top of the target an index mark in
55 dicating the “on course” heading of the craft
with respect to a fixed point or beacon station
at the landing field. The distances represented
on the scales are, of course, purely illustrative
and are not a limitation upon the scope of the
invention. They may be in feet, yards, meters
or other convenient units of distance. The point
28 upon the target represents the point of zero
distance and zero altitude.
The altitude of the' craft, in ñight, is repre
sented by a'horizontal line such as 32 which is
parallel to the ground line 26 upon the target.
The distance of the craft from the fixed point
is represented by a vertical line such as 34,‘and
sistances R1 and R2. The cathode 2 is connected
between the potentiometers P1 and P2, and the
focusing grid 4 and tube |82 are connected to the
potentiometer P2 as shown.
The direct current, altimeter, voltage from
Vsource I2, which should be of the type described
above, is applied to the brush I1 of the commu
tator 62 through the switch S3. The brush i9
of that commutator is connected to the poten
10 tiometer P5 to which is attached the battery Bs,
as shown, and that brush is also connected to
the source of audio frequency oscillations 2i
through the resistance R5 and the condenser C1.
The audio frequency source 2l Ais also connected
to the’ brush 23 of the commutator @2 and to
mitted from the ground station is represented by 15 the brush 25 of the commutator 64.
a short line such as 3S, which will be to 'the left
The direct current direction indicating voltage
or right of the “on course” indication at the top
from source i4 is applied to the brush 21 of the
of the target if the heading of the craft is to the
commutator 64 through the switch S5 and the
left or the right, respectively, of the on course
potentiometer?PaV with itsassociated battery Bi.
The direct current distance indicating voltage is
Extending upward and toward the right from
applied through the switch S4 to the brush 29 of
' the ground contact point 23, are a plurality of
the commutator Gâ. The commutators, as pre
inclined reference lines 36 and £38 which facili
viously mentioned, are all driven by4 the motor 3l
tate the landing of the aircraft. By maneuvering
having a source of power B5 associated there
the craft to keep the intersection of the altitude
with. While the speed of the motor need not be
indicating line and the distance indicating line
constant it should be sufficiently high, for ex
upon one of the inclined lines, Si! or 13B, a par
ample, 900 revolutions per minute or more, in
the deviation of the craft from the beam trans
ticular gliding angle may be readily maintained
order to prevent pattern flicker. The commuta
or a particular landing path may be followed
tors are designed, as shown, so that the brushes
until contact is made with the field. The in 30 8 and Il, respectively, are connected for a few
clined line or path to be chosen as a guide de
degrees in each revolution to each of the three
pends upon the optimum glide angle of the par
other brushes of the respective commutators.
ticular craft for the wind velocity and similar
Brush I5 connects to brush t2 for a few de
conditions prevailing at the time of landing.
grecs at each of three points on commutator E56.
Fig. 3 shows schematically a system of the in
as shown, the three points corresponding with
vention employing three oommutators 6G, 62 and
the positions of the three outer brushes _of the
64 fixed to a common motor-driven shaft GS for
other two commutators. ‘
applying rapidly in succession to an oscilloscope
As clearly shown on the drawing, the> commu
the voltages representing distance, altitude and
60 is preferably arranged so that the dura
direction, together with appropriate positioning 40 tator
tion of contact between the brush l5 and the
and defiecting voltages to be described presently.
brush 42 of that commutator, is less than the
The cathode ray oscilloscope 180 is of conven
duration of contact between brushes of the com
tional type having a heater l, a cathode 2, a con
mutators 62 and 64. Furthermore, in the case
trol grid 3, a focusing grid l5, a focusing tube |82
of the commutator 60, contact begins later and
and two pairs of deflecting plates 5 and 6, re
ends earlier than in the case of commutators 62
spectively, the plates 5 moving the beam hori
and 64.
zontally and the plates S moving it vertically.
As will now be apparent, the commutator Gi!
Throughout this specification the deflecting
controls the voltage applied to the control grid
plates that move the beam horizontally will be
3 of the cathode ray tube I8. When this com
referred to as the horizontal deflecting plates and 50 mutator circuit is open the beam of the cathode
those that move the beam vertically as the verti
ray tube is cut off by the negative voltage applied
cal defiecting plates. One of the horizontal de
torcontrol grid 3 of the tube by source B14 through
fleeting plates is connected to the potentiometer
resistance R1. When the circuit is completed
P41 to which is connected the battery B2 as shown.
through the commutator 60 and brushes l5 and
The other horizontal deñecting plate is .connected r 42, Vthe voltage on control grid 3 is reduced to
by conductor 'i to a brush 8 of the commutator,
that at the intermediate or brush contact point of
M, the connection including the switch S2.' A
potentiometer P1, and the beam is then permitted
resistance R4 is connected between the conductor
to strike the screen of the cathode ray tube. The
'l and ground for the purpose of controlling the
potentiometer P1 permits adjustment of the volt
voltage applied to the horizontal defiecting plates
age'on the grid during the intervals that the ray
5. One of the vertical deñecting plates 6 is con
is on :the target, or screen, of the cathode ray tube
nected to the potentiometer Ps to which the bat
for the purpose of adjusting the brightness of
tery B1 is connected as shown. The other vertical
the cathode ray spot. The resistance R1 is large
deñecting plate is connected by conductor 9 to
compared to R2 and its purpose isto prevent an
the brush il of the commutator 62, the connec
open grid circuit when the commutator circuit is
tion including the switch S1. A resistance R3 is
open. The beam focus is adjusted by the poten
connected between conductor 9 and ground'for
tial applied through the potentiometer P2 to the
the purpose of `controlling the voltage applied to
grid 4.
the vertical deflecting plates ‘6.
The manner in which the apparatus is adjusted
The control grid 3 is connected by conductor 70 for providing the composite indication of dis
I3 to the brush l5 of the commutator B0. The
tance, altitude and direction is as follows: With
other brush t2 of the commutator El] is connected
the motor operating and the switches S1 andSz
to a point upon the resistance R2 of the poten
open, the potentiometers P3 and P4 are adjusted
tiometer P1. A source of negative high voltage
to position the spot of the beam of light at a
B14 is connected to terminal E8 between the re
point upon the target represented by point 28
of Fig. 2. Thereupon, switches S1 and S2 are
The potentiometer Ps and the battery B4 per
mit the centering of the zero line of the direction
closed and switches S3 and S4 are opened, and
indication as described above.
switch S5 thrown to the ground position. This
The output of the field localizer beacon receiver
will serve to apply the voltage of the audio fre Ci
is a voltage whose polarity depends on the direc
quency oscillator 2| alternately to the pairs of
tion of departure from the true course, and the
deflecting plates 5 and 6 of the oscilloscope. This
magnitude depends upon the amount of such
will cause to appear upon the target the hori
departure. The application of this voltage
zontal line 2S and a short vertical line near the
through the commutator causes a deflection to
top and cenlter of the target, the vertical length
the right or left of the index line 38 shown in
of which is adjusted by potentiometer P5 as will
Fig. 2 unless the craft is on course. In order
appear hereinafter and which should be adjusted
to prevent the line 38 extending from the top
by potentiometer Ps to coincide with the index
to the bottom of the target, the audio frequency
mark 38 corresponding to an on course or zero
voltage applied to the vertical plants 6 is re
deviation directional signa. Line 26 represents
duced by the drop in potential through the re
zero altitude. Zero distance is represented by .
sistance Rsand the center of the mark is shifted
Vits left end, point 28. The switches last men
upwards by the adjustment of the potentiometer
tioned are preferably ganged so that they may be
P5. In that way confusion that may otherwise
thrown simultaneously to the positions last stated
result with a vertical line representing distance,
and in that way the zeros of the respective scales
such as line 34, is thereby avoided.
may be checked quickly at any time.
Fig. 4 shows schematically a form of the inven
When the switches S3, S4 and S5 are thrown
tion employing amplifiers by means of which
to their operating positions, the direct current
relatively lower voltages from the distance, direc
voltages of the altimeter source i2, the distance
tion and altitude measuring apparatus may be
indicator source l0 and the direction indicator
employed. The arrangement employs six ampli
source I 4 will be impressed in succession upon the
fiers designated A1 to As, inclusive. Those am
oscilloscopev and will produce deflections of the
pliiiers are in turn arranged in groups of three,
beam in order t0 indicate altitude, distance and
each of which groups has its plates connected
direction, respectively, the said indications being
in parallel and A1 to A3 are directly connected
presented with such rapidity as to appear upon
30 to one of the horizontal deñecting plates 5 of
the screen simultaneously.
the cathode tube. The plates of the other group
This is effedted in the following manner. With
of tubes, namely, A4 to A6, inclusive, are con
the commutators in the position shown in Fig. 3,
nected to one of the Vertical deilecting plates
the direct current voltage from the altimeter will
6 of the said tube. The battery B5, shown to the
be impressed upon the vertical de?lecting plates
right of the tube A1, furnishes the plate voltage
t0 the tubes A1 to A3, inclusive, through the
resistance R10. Resistances R11, R12 and R13 are
tator 64 to the horizontal deflecting plates 5.
connected in series with the battery B6, and the
There will, accordingly, be traced upon the screen
or target 2€), a horizontal lines the vertical posi 40 voltage drop through resistances R11 and R12,
when applied to the grid of that tube, is suiiicient
tion of which indicates the altitude of the aircraft
above the terrain.
to cut off the plate current of the tube. Now
it will be seen that the junction between resist
Assuming the connnutators to rotate in the
6 and, simultaneously, the audio frequency from
ithe source 2| will be applied through the commu
direction of the arrows the commutator S2 will
nent close the circuit between brushes || and I9
which will apply the audio frequency to the ver
tical deñecting plates `6. At the same instant the
commutator 64 will close the circuit between the
brushes 8 and 2l thus connecting the direction
ances R11 and R12 is connected by conductor 5S
to the brush 5| of the commutator 65| of the
group of commutators that provides the switch
ing arrangement for this form of the invention.
Since the brush 52 of the commutator 64 is
grounded, the resistance R11 will be short
indicator to the horizontal deiiecting plates 5. 50 circuited whenever the circuit is closed through
the brushes 5| and 52 which occurs approxi
That will produce a short vertical line such as 35
of Fig. 2 representing the deviation, if any, of the
mately one-third of the operating time. During
craft from a iixed radio beam or like ñxed direc
the period in which resistance R11 is short
circuited, space current will ñow through the
tive guide.
As the commutaltci's continue to rotate, the
distance indicating voltage will be applied
through brushes 8 and 29 to the horizontal de
flecting plates 5 simultaneous with the applica
tion of the audio frequency through brushes Il
and 23 of commuta‘tor G2 to the vertical deiiect
ing plates. That will produce a vertical line such
as 3d of Fig. 2, the horizontal position of which
will indicate the distance 0f the craft from the
tube A1 and the drop in potential across the re
sistance R10 will cause a deflection of the beam
of the cathode ray oscilloscope.
The ampliñers A1, A3 and As are Connected by
the switches S1, S2 and S3, respectively, to the
distance indicating device I0, the direction in
dicating device Ill, and the altimeter l2, re
That apparatus which is the same or
similar to the apparatus described in connection
with Fig. 1 is adapted to apply a direct cur‘ent
fixed reference station.
It is to be noted »that the electron stream of the 65 voltage to the grids of the respective amplifier
tubes. The amplifiers A2, A4 and A6 are con
oscilloscope that produces those traces upon the
nected to a source of audio frequency 2|, and
target 2B is permitted to strike the target only
the output of all amplifying tubes is adapted
during the period in which the brush I5 of the
to lbe applied by means of the commutators to
commutator 60 is conductively connected to the
the deiiecting plates of the cathode ray oscillo
other brush 42 of that commutator and, as has 70 scope.
been previously pointed out, the duration of con
As in the case of the apparatus shown in Fig.
tact of 'the brush I5 with its coacting brush is
3, adjustment must be made for zero altitude,
shorter than the 4duration of Contact of corre
distance and deviation. To adjust for zero dis
sponding brushes upon the commutators 62
and 64.
tance the switch S1 is opened, and with the corn
mutators rotating, the trace of light produced
the corresponding segments of the other com
by the oscilloscope Ybeam is positioned at the
mutators upon the same shaft.
point 28 of the target shown on Fig. 2. This is
accomplished by adjustment of resistance R13.
Then, with the switch S2 open, the trace of light
produced by the beam is positioned centrally in
the upper segment of the target by adjusting
resistance R23.
Deviation from the true course
will be indicated by departure of the trace of
light from that initial position. With the switch
S3 open, the trace of light isthen positioned for
zero altitude by the adjustment of the resistance
Thereupon the switches are closed and the
direct current voltages from the several pieces
of indicating apparatus will be applied tothe
oscilloscope, that is to say, the voltage fromeach
l indicating device will be applied to one set of
The arrangement shown in Fig. 5 represents a
form of embodiment of the invention which is
free from a mechanically operated commutating
device such as that which characterized the ar
rangements of Figs. 3 and 4. This is accom
plished by the use of a plurality of square-topped
waves which are applied in such phase relation
to the amplifiers as to produce the same effect
in the oscilloscope as that produced by the com
mutators of the preceding figures.
In Fig. 5 an oscillator or an alternating current
generator |00 is connected to a plurality of shap
ing amplifiers A10, A11, A12 and A13.
The connection to A11 includes a phase shifter
|0| and that to A12 a phase shifter |02.
The connection to the amplifier A13 includes
deflecting plates simultaneous with the applica
a tripling- device |03 by means of which the fre
tion of the audio frequency to the other set of
plates. Specifically, the voltage from the dis
quency of the oscillator |00 is tripled before being
applied through the phase -shifter |04 to the
tance indicator l0 will be applied to the hori
zontal plates 5 simultaneously with the applica
amplifier A13.
tion of the audio frequency through the ampli
ByY methods well known in the television art
it is possible in an amplifier by controlling the
fier A4 to the vertical plates 6. This is obviously
amount of overloading, to generate square-topped
effected by the joint action of the several com 25 or rectangular waves, and by controlling the
mutators 60, 62 and B4. As shown in Fig. 4,
input amplitude to control the duration of the
the brushes 5|, 52 of the commutator 64 are
positive and negative portions of such a wave.
conductively connected and the resistance R11 is
For the purpose fof the present invention it is
thereby shunted which permits the flow of cur
desired that the wave generated by such an am
rent through the amplifier A1; and at the same
„plifiershall have a positive duration not less than
time the conductive connection of the brushes |'|
two-thirds of the cycle of the wave.
and || of the commutator 012 shunts the resist
This is represented by the graphs
ance R21 thus permitting the flow of plate cur
|01 which represent the output' of the amplifiers
rent through the ampliñer A4. Furthermore, the
A10, A11 and A12. It will be seen that the positive
brushes 42 and |5 of the commutator 60 are
portion of each of those waves is in length equal
then also upon conductive segments which re
duces the negative charge upon the control grid
of the oscilloscope and permits the beam of elec
trons to strike the target 20.
As the commutators continue to rotate, in the
direction of the arrows, the voltage from the
to 240 degrees or more, and the negative portion
120 degrees or less. It will further be seen that
the phase difference between waves |06 and |05
is equal to one-half of the length of the positive
portion of |05; and, in like manner, wave |01
is phased to lag behind |05 by an amount equal
to one-half of the length of the positive portion
of |06.
The output of amplifier A13 is represented by
direction indicator I4 will be applied through
the amplifier A3 to the horizontal plates 5 and,
simultaneously therewith, the audio frequency
from oscillator `2| will be applied through the 45 the wave |08 which in frequency is three times
amplifier Ae to the verticalA plates 5 thus pro
that of waves |05, |06 and |01. The negative
ducing a vertical trace on the target at a position
portion of this wave should have not more than
to right or left of the “on course” line of the
one-half of a cycle in duration. The phase of
plane unless, of course, the craft heading is on
50 this VWave should be adjusted so that the centers
the beam when the trace will fall on the index
of the negative portions of each cycle coincide
mark. ‘Further rotation of the commutators
will apply the voltage from the altimeter to the
with the centers of the negative portions of waves
|05 to |01, inclusive. Thus, it will be seen that
vertical plates and, simultaneously, the audio
the center line m of the first negative portion of
frequency to the horizontal plates to produce a
wave |08 corresponds rin time with the center
trace indicative of the altitude of the plane above 55 of the negative portion of wave’l06; in like man
the zero line previously established. In this
ner, the center y of Vthe next .negative portion of
connection it should be noted that the audio
|08 corresponds with the center y of wave |01,
frequency applied to Ae is reduced by the setting
and the center z of wave |08 corresponds to the
of potentiometer P10 in order to limit the length
center 2 of wave |05, the purpose of all of which
of the line traced in the upper part- of the 60 will be clearly understood from later description
of the invention.
It should be pointed out that in order to offset
The tubes of the amplifiers A10 to A13 are con
the direct current voltages on the deflecting
nected to the amplifiers shown at the right-hand
plates, two potentiometers lE’s’V and P4’ and the 65 side of the figure. Thus, the output of A10 is con
battery B2’ have been provided which function
nected to the amplifiers A211 and A23; the output
in the same way as similar apparatus described
of amplifier A11 to amplifiers A21 and A21, and
in connection with Fig. 3. Focusing of the beam
the output of amplifier -A12 to amplifiers A22 and
ofthe tube is controlled by the voltage on the
A25. The outputV of amplifier A13 is connected to
grid 4 and the brightness of the beam by the
ampliñer A32.
voltage on the grid 3. The dimensions of the 70
During the application of the positive voltage
segments of the commutator 00 of Fig. 4 are
to the grids of tubes A20 and'A23 'for a period rep
similar to the corresponding segments of the
resenting 240 degrees or more of wave |05, the
commutator 50 of Fig. 3 so that contact of the
said amplifiers become conductive and plate cur
brushes with’those segments begins Vlater. and
rent will flow through those tubes from the bat
ends earlier than the Contact of the brushes upon 75
tery B10. During the negative portion of the
cycle of wave |65 the plate current through the
tubes A20 and A23 will be cut olf. Tubes A21 and
A24 and tubes A22 and A25 operate in similar
fashion. The result of this is that the pairs of
rent which occur during a particular predeter
mined interval which is long with respect to the
duration of one cycle of the lowest alternating
current to be translated, and then determining
the voltage which has been established on the
tubes mentioned hereinabove, namely, A20 and
condenser during the particular predetermined
A23, A21 and A24, and A22 and A25, are each cut off
long interval. As applied to modify the system
during one-third of the time in rotation.
of Patent 2,206,896, above mentioned, it substi
When the postive portion of wave I 65 is applied
to the grid of amplifier A20 the space current of 10V tutes the apparatus to the right of vacuum tube
V1 (12') in Fig. 6 for the apparatus to the right
that tube flows to ground through resistance R26,
of vacuum tube l2 of Fig. 5 of the patent. In
and the negative potential thereby created is
the arrangement of Fig. 6, which is, viewed in
applied to the grid of tube A26 and is suñicient
one aspect, an improved type of frequency meter,
to block the plate current of that tube. Simul
taneously, a similar eiîect takes place in tubes 15 the Voltage to be rectiñed, designated e1, is ap
plied to the tube V1, this tube having negligible
A23 and A22. The net result of all of which is that
resistance at low plate voltages when its controlV
during the positive portion of the wave | |15, no
grid is at zero potential.
voltage will be applied to the oscilloscope by the
Connected to the plate of the tube V1 is a
distance indicator I0 and its associated oscil
source of potential, battery B12 having a voltage
lator 2|.
However, during the negative portion of the
wave |û5, the space current oi tubes A20 and A23
is blocked and the negative bias on the grids of
tubes A2@l and A29 is so reduced as to permit the
20 E12, the connection including the resistance R.
Connected between the plate and the grounded
side of the tube V1 are the condensers C1 and C2,
the latter being shunt-ed by the diode vacuum
flow of plate current therethrough. Thus the 25 tube V3 as shown. Diode Vs has substantially in
finite impedance -when its anode is negative and
voltages of the distance indicator Ill and oscil
substantially Zero impedance when its anode is
lator 2|, suitably amplified, are applied to the
positive. The voltages across C1 and C2 are rep
plates of the oscilloscope.
resented by E1 and E2, respectively.
The electron beam of the oscilloscope is es
Connected across the condenser C2 also is the
tablished and disestablished in the following 30
input of the tube V4 which in turn feeds into the
manner: The wave |08 when applied to the am
rectifier 'I2 through ampliiier 'lil as shown.
plñer A32 causes it to alternately draw high and
Connected to the junction between condenserp,
low, or cut oil.” values of the plate current. Dur
C1 and C2 is the plate of the tube V2 to the in
ing the positive portion of the cycle of the volt
age applied to the tube A32 the cathode ray beam 35 put of which is connected a circuit containing an
oscillator 74, a phase shifter T6 and a shaping
is cut ofi". During the negative part of the cycle
amplifier and doubler 78. The shape of the wave
of wave |68, when applied to tube A32, the beam
produced by the doubler 'I3 is shown by the graph
of the oscilloscope is established; and since the
associated therewith and designated c2. The fre
center of each negative part oi wave |96 corre
spends with a negative part of waves |85, m6 40 quency of e2 is never greater than the minimum
value of f which represents the variable fre~
and |01, it will be seen that the beam of the os
quency of the voltage e1 shown in graph F. The
cilloscope is “on” and persists during the period
during ’which the volta-ges of the several indicat
ing devices and their associated oscillators are
being applied to the plates of the oscilloscope.
function of the circuit just described, including
oscillator 14, phase shifter 76, doubler 78, and
45 vacuum tube V2 is to periodically discharge con
denser C2 through the plate circuit of tube V2
With the switches S1, S2 and Ss open, the var
when voltage e2 causes the control grid of V2 to
become positive. If the input wave F is of the
type indicated by curve 33 of Fig. 2 of the above
ode ray tube are adjusted to cause the line oi’ 50 mentioned patent to Higgins et al., c2 should be
adjusted to occur at the cross-over or zero fre
zero altitude, the zero distance point and the “on
quency points and the voltage accumulated on
course” direction to be traced. When this ad
Cz will then represent directly the number of
justment has been completed the switches are
(or frequency) of the Wave 33 above men
then thrown to connect the distance, direction
and altitude indicating devices to the tubes A26, 55 tioned between zero points which is, of course,
a measure of the altitude.
A23 and Asn, respectively. Thereafter those dis
During the charging interval for the condenser
tances, directions and altitudes are shown upon
C1, the same total current ñows through both
the screen of the oscilloscope.
condenser C1 and condenser C2. When both con
The operation of the circuits described here
inbeiore, depends upon the ability of the distance, 60 densers start with zero charge and are allowed
to charge for an inñnite time, or a time large
iable resistors Rae, R27, etc., in the circuits of the
tubes A26, A27, etc., and the potentiometers con
nected to two of the deflecting plates of the cath
direction and altitude indicating apparatus to
compared to the time constant RC1, the charges
produce direct currents for application to certain
of both condensers are equal and a steady-state
of the deflecting plates of the oscilloscope as
value is reached represented by the equation
above described.
In the event that the output of such apparatus 65
is an alternating current, it is necessary for the
carrying out of this invention to translate that
In Equation 1 the factor K is the quotient of C2
current into the form of a direct current Volt
divided by C1. This value is represented by the
An apparatus peculiarly lwell adapted for ef 70 graph shown in Fig. 6a, by the first step, e2<1), on
the stair-shaped wave form es.
fecting such translation is shown in Fig. 6. The
When this steady-'state value of E2 has been
basic principle of operation of the circuit of Fig.
6 is that of adding substantially equal increments
of charge to the charge on a condenser for each
of the positive half cycles of the alternating cur
been reached, the plate circuit of V1, which has
been blocked so far, is made conductive by the
arrival of a positive one-half of a cycle of the
75 input frequency f and the condenser C1 is corn
12 '
pletely discharged through the plate circuit ofv
the tube V1 an'd the diode Vs, leaving the voltage
of condenser C2 unchanged.
When the negative swing of the grid of the
tube V1 occurs, the plate of V1 is again blocked
and condenser C1 recharges through resistance R
and the condenser C2. The charges gained by
both C1 land C2 are equal but the total voltage
available for charging is reduced by the step 10
Em) and is represented by E12-E20).
By continuing for the time interval represented
by the distance between two adjacent pulses of
Voltage e2 that process, the stair-shaped wave ea
is built up. Each step isa little smaller than the 15
previous one so it is evident that a strictly linear
relationship cannot be obtainedY between.> the
operate upon particular current values being
reached corresponding to altitudes'of 1000 and
500 feet, respectively, for example. As explained
in the above patent, an increase of the plate cur
rent occurs at low altitudes. The parameters of
the feedback circuits and its associated control
circuits must of course be adjusted so that the
current in the circuit including relays |20'q and
|30 changes over at least the range within which
alarms are to be actuated, in this instance up to
1000 feet. Across the armature and contact of
relay |20 is connected a low altitude alarm |26
and a source of Voltage |24. The `altitude alarm
|32 is similarly associated with relay |30.
Another relay, designated |22, is connected to
conductor |04' that extends from the plate of
tube |03’ to the screen grid of the tube 85', to
which conductor a source of plate voltage is also
connected. Across the armature and contact of
very much larger than l, a relationship ap
20. relay |22 is connected a circuit that includes the
proaching substantial linearity can be obtained.
source of voltage |24 and an alarm, that indi
By using negative feedback in the» amplifiers.
cates the absence of input signal to the altimeter
including the tube V4 and the later Vtubes, sub
receiver or its falling to a very low value.
stantial constancy and linearity can be obtained.
Reference may be had to the patent to Higgins
Either polarity of direct current can of course 25 and Newhouse, mentioned above, for a detailed
be obtained from the ñnal rectifier 12. _
description of the mode of'ope'ration of the cir
In using the apparatus just described withv an
cuit of Fig. 7 of the drawings accompanying this
oscillator, fas shown in the previous figures, either
specification, which, except for the alarm circuits
the direct current from the rectiñer can be used
and the adjustment of the feedback circuit as
or the stair-step alternating current can be ap-`
30k just described is, ‘as above stated, identical with
plied directly to the oscilloscope, and all steps,
the circuit of Fig. 5 of the patent. For an under
except the highest, can be blanked out if de
standing of the particular improvement being
now described, viz. the addition of alarm devices,
In an altimeter of the type described in the
it is felt that the more general description given
above-mentioned Patent 2,206,896 to Higgins et
i below will suffice.
al., the oscillator shown should be that which
The voltage representing the output of the de
drives the motor to produce the frequency modu
tector of the altimeter is applied to the circuit
of Fig. 7 between contact 59' and ground and
The phase shifter should be yadjusted `as stated
upon amplification by the multistage ampliñer,
above so that the positive portion of the rec
comprising stages 6|', 24’ and 62', is impressed
tangular wave produced by the doubler and the
upon the frequency measuring circuit 25’. The
shaping amplifier occurs at the same point as
said ampliñer i-s given a frequency-gain char
the cross-over points, or the zero frequency
acteristic that rises with frequency but in order
peak value represented by E200 and the Yire
quency ,f unless K is inñnite. If, however, K is
points, in the signal supplied to the tuberVi.
to avoid distortion in the low frequency range an
where that signal is of the type shown in Fig. 2 45 automatically controlled feedback circuit 26’ is
of the patent to Higgins et al. and designated 33.
provided. This cooperates with the network 2|'
Fig. 7 shows the details of arrangements fory
so as to give the ampliiier system a characteristic
operating alarms when the altitude indicated by
that at frequencies above the range of immediate
the altimeterreaches particular low values, such,
interest is constant with frequency. In order to
for example, as 500 feet or 1000 feet, respectively`
do this, the feedback amplifier 26’ must be con
and also for giving an alarm when the signal
trolled according to frequency, and this is accom
strength falls to `a predetermined low value to
plished by the auxiliary frequency measuring cir
serve as a warning that the altitude indications
cuit 21', in which the voltage across the resistor
may not be dependable. The arrangement shown
09’ is negative with respect to ground, and also is
in Fig. '7 is an improvement upon that shown in
proportional to frequency. That voltage is `ap
the above-mentioned patent to Higgins and New
plied to the control grid of the tube 85’ of the
house, No. 2,206,896, specifically in Fig. 5 ofvthat
feedback ampliñer and varies directly the plate
patent, which discloses an altimeter circuit. and
current of that tube. Accordingly, the plate cur
the same reference numerals with prime marks
rent will increase at low altitudes, and the relays
for corresponding pieces of apparatus have been
|20 and |30 may be set to operate their respec
used in Fig. '7 as are shown in the figure of the
tive alarms |26 and |32 at any desired altitudes
patent. As explained above, for use in systems
within the range in which the current increase
of the presentV invention, the apparatus in the
occurs. Alarms |26 and |32 may be signal lamps
anode circuit of vacuum tube 12 of Fig. 5 of the
, or bells or the like.
patent should be replaced by the arrangement of 65
To indicate the absence of signal voltage from
Fig. 6 of this application, described in detail
the altimeter receiver, or its fall to an undesired
above. However, as this feature does not affect
minimum, the alarm |28 has been provided which
the alarm circuits now to be described Fig. '7 has
depends upon the operation of the “lock-out”
not been so modified. The general structure of
>circuit 28’. When the voltage applied to the
the circuit of Fig. 7 and its mode of operation,
control grid of tube |03’ is normal, it blocks
ì the,
except for the alarm circuits now added, are the
platecurrent of that ‘tube and no current flows
same `as that of the patent. The exceptions are
in conductor |04’ in which' relay |22, controlling hereinafter noted and described in detail.
alarm |28, is connected. When the received sig
In the lead extending from the source of plate
_nal falls to a predetermined Value the strength
voltage to the plate of the tube 85’ there has been
of the plate current flowing through conductor
inserted the'relays |20 and |30 in series which
|04' will be sufficient to operate relay |22 and
actuate the alarm |28. With the rise of signal
strength to normal, relay |22 will be released
zontal distance from the index mark which is
determined by the heading of the craft with re
and the alarm will cease. Alarm IZB can con
veniently be a signal lamp or bell or like device.
While this invention has been disclosed as em
spect to th'e on course heading` said commutat
l. A radio navigational system to facilitate the
blind landing of aircraft which comprises, means
for 4obtaining a first signal voltage which varies
course heading of the craft.
2. The system of claim 1 the target of said
ing means effecting the said successive presenta
tions of the said three described voltage combina
tions with suflîcient rapidity to establish on the
bodied in certain forms, it is obviously capable
target of the cathode ray indicator simultane
of embodiment in numerous other and diiïerent
ously the indications as described of clearance or
forms without departing from the spirit and scope
altitude, distance and course heading whereby
10 the aircraft navigator may determine at a glance
of the appended claims.
What is claimed is:
the clearance or altitude, the distance and the
cathode ray tube being inscribed with an inclined
directly with the clearance or altitude of fthe 15 line ‘the lower end of said line resting on the point
of said target selected to represent zero clearance
craft above th'e surface of the earth beneath it,
or altitude and zero distance, the line forming
means for obtaining a second signal voltage which
an angle with the lateral horizontal axis of said
varies directly with the distance of the craft
target which corresponds to an appropriate land
from a ñxed point on the earth, means for ob
taining a third signal voltage which varies di
rectly with deviation from a known fixed course.
a cathode ray indicator including horizontal and
vertical deflec‘ting plates, a control anode and a
retentive luminescent target or screen, ñrst, sec
ond and third ray positioning adjustable poten
tial sources, an anode control potential source, a
source of sweep circuit voltage, and circuit and
comrnu‘tating means for successively presenting
ing path angle for said craft whereby the navi
gator of the craft can follow the said appropri
ate landing path by maneuvering the craft so
that the intersection of the horizontal clearance
indicating line and the vertical distance indicat
ing line, described in claim 1, coincides with the
said inclined line at all times during the landing
3. The system of claim 1 the target of said
cathode ray tube being inscribed with a plurality
to the cath'ode ray indicator three different com
binations of a signal voltage, a ray positioning 30 of inclined lines representing a plurality of land
ing paths whereby the navigator of said craft may
voltage, a sweep voltage and an anode control
follow any of the said paths in bringing the craft
voltage, one said voltage combination compris
to a landing, his selection being made in View of
ing the presentation to the deflecting plates of
positioning voltages to position the ray at a
the prevailing conditions at the time of landing.
point on the target representing zero distance and
4. In a blind landing system for aircraft, a
zero clearance or altitude on the target of the
cathode ray indicator including a luminescent
tube, the presentation to the horizontal deflect
target thereon, said target having inscribed on it
ing plates of a sweep voltage to sweep the ray
a plurality of lines including a horizontal scale
horizontally across the target, the presentation
calibrated in terms of distance, a vertical scale
to the Vertical deñecting plates of th'e first said 40 calibrated in terms o-f altitude, and a plurality
signal voltage and the presentation to the control
of lines all terminating at the zero end of the
anode of a voltage permitting the ray to reach the
aforementioned horizontal scale but inclined with
target whereby a horizontal line is traced on the
respect thereto at different angles appropriate
target of said cathode ray indicator at s, verti
for landing aircraft under a like plurality of par
cal distance above the point or line of zero alti
ticular predetermined landing conditions, respec
tude which is determined by the altitude of the
tively, and means for successively deflecting the
craft, a second said voltage combination com
ray of said indicator to trace on said target a
prising th'e presentation to the deilecting plates
vertical line the lateral position of which indi
of positioningr voltages to position the ray at a
cates distance from a particular beacon station
point on the target representing zero distance 50 and a horizontal line the vertical position of
and zero clearance or altitude, the presentation to
which indicates the altitude the the craft, said
the vertical deflecting plates of a sweep voltage
traces recurring at sufficiently frequent intervals
to sweep the ray vertically across the target. the
to appear continuous whereby a glide angle cor
presentation to the horizontal deñecting plates
responding to any one of the said inclined lines
of the second said signal voltage and the presen
may readily be maintained by maneuvering to
tation to the control anode of a voltage permit
keep the intersection of said altitude and said
ting the ray to reach the target whereby a ver
distance indicating lines on the selected inclined
tical line is traced on `the target of said cathode
ray indicator at a horizontal distance from the
5. In a blind landing system for aircraft, the
point of zero distance which is determined by the 60 combination oi means for providing on said craft
distance of the craft from the said fixed point on
two voltages the magnitudes of which represent,
the earth and a 'third said voltage combination
respectively, the distance of said craft from a ref
comprising the presentation to the deñecting
erence point and the altitude of said craft above
plates of positioning voltages to position the ray
earth’s surface, a cathode ray indicator in
at an index mark representing the on course 65 cluding a target therefor, a horizontal scale asso
heading of the craft, the presentation to the
ciated with said target representing distance from
vertical cleñecting plates of a sweep voltage to
said predetermined point, and a vertical scale
sweep the ray vertically across a portion of the
associated with said target representing altitude
target determined by the aforesaid just-men
above the earth, and switching means for suc
tioned positioning voltages. 'the presentation to 70 cessively and repeatedly connecting the said two
the horizontal deflecting plates of the third said
voltages in conjunction with appropriate sweep
signal voltage and the presentation to the control
circuit voltages and bias voltages to the deflect
anode of a voltage permitting the ray t0 reach
ing plates of said indicator to provide intersect
the target whereby a vertical line is traced on the
ing traces on said target whereby a point of
target of said cathode ray indicator at a hori 75
intersection is obtained the position of which in
dicates both the distance from a reference point
and the altitude of said craft.
6. In a navigating system for aircraft, an al
timeter system including a signal amplifier and a
feedback circuit operatively coupled with said
amplifier to produce distinctive modifications in
the response of said amplifier for a plurality of
particular predetermined ranges of altitudes re
spectively and a like plurality of alarm circuits,
operatively coupled with said feedback circuit to
operate a particular distinctive alarm signal for
each of the said respective operative conditions
of said feedback circuit whereby the attention of
the navigator of the aircraft is directed to sig
nificant changes in the altitude of the craft.
resistance, and two capacities C1 and C2, the
negative terminal of said potential source'being
grounded, the positive terminal being connected
to one terminal of said resistance, the other ter
minal of the resistance connecting to one termi
nal of capacity Ci, and to the anode of said first
vacuum tube, the other terminal of C1 connecting
to a terminal of capacity C2, the other terminal
of capacity C2 connecting to the cathode 0f said
first tube and to ground, a unidirectionalcon
ducting device electrically shunted across capacity
C2 said device being poled >to prevent the dis
charge of capacity C2 therethrough, a second uni
directional periodically conducting Vdevice elec
trically shunted across capacity C2, means for
controlling the periods of conductivity of said
'7. In a navigating system for aircraft, an al
last-stated device to discharge capacity C2 at in
timeter system including a signal amplifier, feed
tervals relatively long with respect to the lowest
back means operatively coupled with said ampli
periodicity of the said alternating current the fre
fier to modify the response of said amplifier over
quency of which is an index of distance, and
particular ranges of altitude, a second means op
means for indicating the voltage which is estab
eratively coupled with said amplifier to render
lished across capacity Cz during the charging in
said feedback means inoperative for currents be
tervals thereof.
low a predetermined amplitude, and an alarm cir
ll. In a navigational system the combination
cuit operatively coupled with said second means
of a distance measuring system providing an al
to operate an alarm signal when said second
ternating current the frequency of which vis an
means disables said feedback means whereby the
index of distance, means for deriving from said
attention of the navigator of the aircraft is di
alternating current a direct current voltage pro
rected to the fact that the altimeter system is not
portional to the frequency of said alternating cur
receiving sufñcient signal to provide reliable alti
30 rent which comprises a capacity, means for add
tude indications.
' ing an increment of charge to the charge in said
8. 'I'he system of claim 1, the first-stated means
capacity for each positive half cycle of said alter
thereof comprising an altimeter system which in
nating current occurring during a deñnite pre
cludes a signal amplifier and a feedback circuit
determined time interval, and means for meas
operatively coupled with said amplifier to pro
uring the voltage established across said capacity
duce distinctive modifications inthe response of 35 at the end of said predetermined time interval
said amplifier forl a particular predetermined
whereby a direct current voltage the magnitude
range of altitudes, and an alarm circuit opera
tively coupled with said feedback circuit to oper
of which is a measure of the distance indicated
by said distance measuring circuit current is 0b
ate an alarm signal when said feedback circuit '
operates to produce a particular modification in 40 tained.
12. In a navigational system the combination
the response of the amplifier whereby the aircraft
of a distance measuring system providing lan al
navigator is apprised of the fact that the craft
ternating current, the average frequency of which
has approached within a particular distance of
is an index of distance, the frequency of said cur
the earth’s surface.
passing through zero at regular periodically
9. The system of claim l, the first-stated means 45 recurring intervals which are long with respect
thereof comprising an altimeter system which in
to the duration of a cycle of said alternating
cludes means for modifying the response of the
current, means for deriving from said alternating
altimeter system for currents below a predeter
current a direct current voltage proportional to
mined amplitude and an alarm circuit operatively
the frequency of said alternating current which
connected with the last-stated means to operate
comprises a capacity, means for adding substan
an alarm signal when the last-stated means mod
tially equal increments to the charge in said
ifies the response of the altimeter system whereby
capacity for each positive half cycle of said alter
the navigator of the aircraft is apprised of the
nating current occurring during a definite pre
fact that insufficient signal is being received by
determined time interval, mean's for adjusting
the altimeter system to provide reliable altitude
this predetermined time interval to coincide with
the above-mentioned interval between the zero
10. In a navigational system the combination
points of the said alternating current, and means
of a distance measuring system providing an al
for measuring the voltage established across the
ternating current the frequency of which is an
"said capacity at the end of said predetermined
index of distance and means for converting the cc time intervals, whereby a direct current voltage
said alternating current into a direct current
the magnitude of which is a measure of the dis
voltage the magnitude of which is an index of
tance indicated by said distance measuring circuit
distance said voltage varying in a substantially
is obtained and an indication of distance con
linear manner with distance, said means com
'zu vement-,1y adaptable for use in said navigational
prising a first vacuum tube having negligible re et system can readily be provided.
sistance at low plate voltages when its control
grid is at Zero potential, a source of potential, a
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