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Патент USA US2406358

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Aug. 27, 1946.
S. DOBA, JR
yGROUND SPEED METER
Filed March 2l, 1944
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2,406,358
5 Sheets-Sheet 1
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/N VEN TOR
BY S. 008A, JR.
AGENT
Aug. 27, ì946.«
2,406,358
S. DOBA, JR
GROUND lSPEED METER `
Filed March 21, 1944
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5 Sheets-Sheet 2
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S. 008A, JR.
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Aug. 27, 1946..V
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s, DQBA, JR
2,495,358
GROUND SPEED METER
Filed March 21, 1944
5 Sheets-Sheet 3
/N VEN TOR
S. DOB/I, JR. A
@r1
AGENT'
Àug. 27, 1946.
s. DoBA, JR
GROUND SPEED METER
\ Filed March 21, 1944
2,406,353
1
s sheets-sheet 4
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Aug. 27, 1946.’
s.- DoBA, JR
(3,406,358
GROUND SPEED METER
v Filed March 21, m44
5 sheets-sheet 5
„VvE/WOR
¿I DOBA, JR
Patented Aug. 27, 1946
2,4%,358
2,406,358
GROUND SPEED METER
Stephen Doha, Jr., Long llsland City, N. Y., as
signor to Bell Telephone Laboratories, Incor
porated, New York, N. Y., a corporation of New
York
Application March 21, 1944, Serial No. 527,459
4 Claims. (Cl. Z50-1)
l
MB, video amplifier l'lû and vertical sweep am
pliñer 20G of Fig. 1; and
This invention relates to an improved method
and apparatus for measuring the relative speed
Figs. 9A and 9B illustrate the patterns on oscil
loscope screen 2 produced when switch S is closed
of an observer and an observed object visible or
invisible. The invention while particularly use
ful in a military airplane ñying to-ward a target
ahead, has a field of use including all cases of
relative movement in the air, at sea or on land~
upward and downward, respectively.
In all figures like numerals and letters indicate
like elements.
The invention will be described with reference
The general object of the invention, therefore,
to its use in an airplane which will be understood
is to provide a method and means for measuring
the relative speed at which an observer ap
proaches an observed position.
The invention makes use of known electrical
object locating and ranging means which are in
to be provided with the usual altimeter and air
speed meter. For simplicity, it will be assumed
that the plane is flying directly, without leeway,
toward a target ahead.
Referring now to Fig. 1, the radar system gen
dependent of weather and light, making such
means an element in a novel system of appara
15 erally indicated by numeral l, not itself a part of
the present invention but here briefly described
to facilitate understanding of the complete sys
tus for measuring the rate of change of range
of a selected object. The invention thus achieves
another object, namely, to provide speed meas
tem, serves to detect the presence of a target
uring means useful in all conditions of observa
ahead and represent that target by a luminous
tion.
In bombing an enemy target from an airplane,
it is obviously important to know the relative
speed of target and bombing plane. Hence an
20 spot T on screen 2 of cathode ray oscilloscope 3.
The location of spot T on screen 2 corresponds as
later explained to the range and bearing, at a
given instant, of the target represented.
System l includes a pulse transmitting circuit
other object of the invention is to facilitate the
prosecution or war in the air, as well as to pro
vide a navigational aid universally useful in time
25 4 and a pulse receiving circuit 5 connected
through duplexing unit 6 to a common antenna
'l which is preferably of the highly directive type
consisting of a small polarized dipole 8 at the
The invention enables the pilot of an airplane
focus of a, parabolic reflector 9. Antenna 'i is
to measure his absolute speed with respect to a
point ahead. If that point is fixed on the earth’s 30 connected by a coaxial link Ill through duplexing
unit 6 to the circuits ¿i and 5, with a rotary joint
surface and its initial distance is large compared
Il in link lil. The portion of link iû above joint
with the plane’s altitude, the absolute speed
H is provided with gearing l2 through which mo
measured is substantially the ground speed of
tor i3 is enabled to rotate antenna 'l at a con
the plane, For example, ii the altitude is 10,000
feet and the distance on the earth’s surface is 35 stant speed in the horizontal plane. Rotation of
antenna ’I in a vertical plane may be accom
50,000 feet between the point of reference and a
plished by a like arrangement of motor and gear
point vertically beneath the plane, the speed
ing which is omitted here as unnecessary to the
measured is 98 per cent of the ground speed. For
oi peace.
present description. The pulse generator i4 sup
a surface craft the measurement requires no cor
rection. In neither case does a head or a tail 40 plies a positive square top pulse of very short du
ration to control radio modulator i5 to supply at
wind or ocean current affect the measurement of
a convenient repetition rate extremely short and
intense pulses of radio frequency energy to an
tenna ‘l by which these pulses are directively ra
diated into space. Duplexing unit 6, which may
speed, Therefore, another object of the inven
tion is to provide navigators with means for
measuring ground speed regardless of wind or
current.
The invention is to be understood from the fol
lowing description, read with reference to the ac
companying drawings in which:
be an automatic transmitter-receiver switch of
any known type, eiîectively short-circuits the in
put to receiving circuit 5 while antenna ‘i is emit
ting but allows free passage to circuit 5 of the low
level echo received by antenna 1 from a reflect
ing target. The interval between successive
emissions by antenna 'i is made longer than
Fig. l is a block schematic diagram of the ma
jor components of the invention;
Figs. 2 to 8 are circuit diagrams representing,
respectively, time base generator 2d, range sweep
generator El), rate sweep generator 8%, range dii
ferential amplifier lill, video mixing amplifier
, enough to include the reception of radio echoes
55
from the most distant target to be attached.
A portion of the energy radiated by antenna
2,406,358
3
Y
4
adjustable initial value and at an adjustable rate
of decrease. This sweep voltageoccupies from
100 to 400 seconds to decrease through a range
received by antenna l and 'transformed into an
of 100 volts, so that throughout any 100 micro
electrical pulse which passes through duplexing
second interval it may be considered constant.
unit 6 to radio receiver iii in circuit 5 where it is
The output of generator d@ is likewise applied to
ampliiied and detected. The detected pulse is
range differential amplifier l lil. Obviously, the
further ampliiied by video ainpliñer Il’ and is
initial value of the decreasing .output voltage oi
thus available to produce intensity modulation
generator Sli may be chosen less than the maxi~
of the cathode ray beam of oscilloscope 3. Os
cilloscope 3 may be of the Well-known magnetic 10 mum value reached by the rising voltage of genn
erator E@ so that in each lo() microsecond intern
deflection type and is not shown in detail in Fig.
val there will be an instant of equality oi the
1 beyond intensity grid i8, cathode i9, ñuorescent
two voltages on the input of
differential
screen 2 and deiiecting coils HDC‘ and VDC for
ampliñer lle. As the voltage from generator ílâì
horizontal and vertical beam deflection, respec
-slowly decreases this instant of equality will oc~
tively.
cur progressively nearer to the start of the lo()
vShaft 2E, through which motor i3 drives gear
microsecond interval, that is to say, nearer to
l2, carries a pair of potentiometer wipers 2l and
the moment Of emission of
object ranging pulse
2|’ insulated from each other and from Vshaft 2l)
from
antenna
l.
Y
on which they are mounted radially opposite each
To anticipate the later description, it may here
other. Wipers 2i and 2i’ traverse potentiometer
be said that the voltage from generator Si? is so
22 fixed in the airplane. Battery 23 is connected
chosen that at a given time the instant of equa-1
across diametrically opposite points of potentiom
ity of the sweep voltages from generators d@ and
eter 22. The rotation with shaft 2li of wipers 2l
85B occurs simultaneously with the reception by
and ‘2l’ selects a fraction of the voltage of bat
tery 23 ranging from zero when the pointing of 25 antenna 'l of an echo reflected from a chosen
target and the rate of decrease of the voltage
antenna 'l is directly ahead to a maximum when
from generator 8@ is so adjusted that this in
antenna l points abeam. The polarity oi the
. stant continues to occur simultaneously with the
selected voltage depends on the left or right
reiiected echo as the range of the target decreases.
pointing of antenna l and the voltage so selected
is applied to produce a current in horizontal de~ 30 Clearly, the means which so sets the rate of volt
'l is intercepted and reflected, usually diffusely, by
the target. A part of this reflected portion is
age decrease affords a measure of the rate o_i
iiecting coil HDC of oscilloscope 3. Auxiliary
change of range of the target, that is to say, of
means, not shown, are provided for horizontal
the relative speed of target and plane. If the
centering
when wipers
of 2l
theand
cathode
2l’ select
ray zero
beamvoltage.
on screen
target is stationary and the plane’s altitude is
When the echo pulse from the reilecting target 35 not a large fraction of the plane to target dis»
tance,. the speed so measured is the ground speed
is available on grid is to produce intensity rnodu
of the airplane.
lation of the cathode ray beam a luminous spot
Before continuing the functional description oi
T representing the target will appear on screen
the system of Fig. l it is proper here to describe
2 located vertically thereon at a position corre
the circuits so far involved.
sponding to the target range provided a vertical
eferring new to Fig. 2 a short positive trigger
sweep current, synchronized with the emission of
pulse from pulse generator if: is applied to grid
energy from antenna l, is caused to flow in ver
tical deîlecting coil VDC. The horizontal sweep
'differentiation
of the tube V1,
bywhich
the circuit
is suitably
comprising
SSTL‘E'Z, con
current in coil HRC insures that the target spot
will appear displaced left or right on screen 2
according to the bearing of the target left or right.
For the present purpose, it is assumed that the
target is directly ahead.
It is convenient to describe functionally the op
eration of some of the major components of the
system of Fig. l., postponing the detailed descrip
tion of the involved circuits.
Each trigger pulse from pulse generator i4 ini
tiates the emission of a pulse of radio frequency
energy from antenna l and at the saine time is ’
supplied to actuate time base generator 24. Gen
erator 2s produces a pair of voltage pulses oi op
posite polarity and lasting for approximately 10€)
microseconds, which are both supplied to range
sweep generator 5B, the negative pulse serving to f
excite in generator 5E! a positive sweep voltage
rising through a voltage range of about 10G volts
linearly with time at a predetermined rate
throughout the 100 rnicrosecond interval, the
positive pulse producing a positive pedestal volt~
age on which is superposed the rising sweep volt
age, This sweep voltage on a pedestal recurs with
each radar emission and starts simultaneously
therewith. ït is supplied by range sweep genera~
tor El? at all times to range differential ampliñer
Hf! and when switch S is closed upwards it is
fractionally supplied also to vertical sweep am
denser ”¿5 and resistance E?. Grid 225i
tube V1
~ is negatively biased by battery 28 so that tube
Vi is normally not conducting. Differcntiating
circuitv CZSRZ'E produces a positive pip at the
leading edge of the trigger pulse, an instant here~
inafter designated as to. _fi
-Á
trailing edge on the trigger pulse is disregarded.
Prior to the arrival of the positive pip on grid
25 no anode current flows in tube V1 and there is
no voltage drop across the resistor 29 through
which anode 3B of V1 is connected to 300 Volt
battery 3l. Battery 3| is also connected through
resistor 32 to-anode 33 of tube V2, a double triode
such as a 6N?, through resistor 3s to grid 35 and
through resistor 29 to anode 35 of V2. Cathodes
38 and 39 are electrically connected together and
through resistors ¿l0 and di in series to ground.
The junction of resistors lll) and 4l is connected
to grid 42 through resistor ¿i3 while grid ‘d2 is
shunted to ground by condenser dit. Cathode
45 of V1 is likewise grounded. ïn all circuits
cathode heating power is understood to be sup
plied though not shown. Between ground and
cathode 39 of V2 are connected condenser ¿l5 and
resistance ¿il in series, from the junction of
which, through condenser 4S shunted by resistor
¿59, a square topped voltage pulse negative to
ground of itil microseconds duration is fed to
range sweep generator 5U. Also to generator 5S
plifier 2m).
a square topped voltage pulse, positive to ground,
Rate sweep generator 30 produces a sweep volt»
ageslowly decreasing linearly with time from an 75 is fed from anode 3,3 oi V2. Of these voltage
2,406,358
5
pulses, the former excites the rising sweep volt
age produced by generator 50 while the latter
4provides the pedestal which the sweep voltage
overlies.
In the circuit of Fig. 2, grid 25 of V1 is normally
.biased to cut-off by battery 28. Grid 42 of tube
V2 is biased to cut-off by the voltage developed
tive, square topped, pulse across resistors 40 and
4| due to the abrupt drop and succeeding rise of
current therein, a negative pulse which is taken
olf between cathode 39 and ground and is used
as above stated to produce the sweep voltage in
generator 50.
Here the terminal distortion is
harmful and is removed by the ñlter circuit com
across resistors 40 and 4| in series by the flow
of current in the right half of V2 from anode 33
prising condenser 46, resistor 4,1 and condenser
48 shunted by resistor 49.
to cathode 38. Since grid 35 is connected through 10
The input terminals of the circuit of Fig. 2
1.5 megohm resistor 34 to battery 3|, its voltage is
are A and ground G, across which the trigger
pulse from generator I4 is applied. The output
slightly higher than that of cathode 38, namely,
about 20 volts positive to ground and the right
terminals are B1, C1 and ground G1, the sweep
producing pulse being taken between C1 and
half of V2 is normally conducting. Condenser 31
is connected between grid 35 and anode 36.
15 ground, the pedestal pulse between B1 and ground.
n A positive voltage pip drives grid 25 positive,
Time base generator 24, which the circuit of Fig. 2V Y,
so that V1 becomes conducting and its anode volt
constitutes, defines the duration of the voltage
rise in range sweep generator 58 and thus the
age falls. Anode 136 of V2 is connected directly
range of the most distant target to be considered.
to anode 30 of V1 and through condenser 31 to grid
35 of V2. The fall of voltage at anode 30 thus is 20 The 100 microsecond interval, corresponding to
a target distance of about 10 miles, is fixed by the
coupled through condenser 31 to grid 35 to cut-off
choice of condenser 31 and resistor 34, in the case
the right half of V2, and the consequent disap
described 200 micromiorofarads and 1.5 megohms.
pearance of current from resistors 48 and 4| per
respectively. The sweep interval is in any case
mits the left half of V2 to become conducting.
Initially, V1 is not conducting, anodes 30 of V1 25 preferably somewhat shorter than the interval
and 36 of V2 are 300 volts positive to ground. In
between successive signals from antenna 1 which
in some radar installations may be long enough
V2 cathodes 38 and 3B as well as grid 35 are
for a 100 mile range to be dealt with.
20 volts positive while anode 33 is about 257 volts
In Fig. 3 is shown the circuit of range sweep
positive to ground, the right half of V2 being
conducting while the left half of that tube is 30 generator 50. Input terminals for generator 50
are B2 and C2 on which are impressed positive
blocked. Grid 42 of V2 is thus 20 volts negative
and negative pulses from terminals B1 and C1
with respect to cathode 39 and condenser 31 is
respectively, of Fig. 2, and ground G. The nega
thus across a potential difference of 280 volts be
tive square topped voltage pulse at terminal C1.
tween anode 36 and grid 35. The positive volt
age pip from differentiating circuit C26R21 makes 35 of Fig. 2 is applied at terminal C2 of Fig. 3 to
V1 conducting and the potential at anodes 30 and
grid 5| of tube Vs, a 6AC7, for example, initially
conducting and rendered inactive when a nega
36 falls to about 165 volts. This drop of 135 volts
tive pulse arrives at grid 5|. Screen grid 52 of
at anode 36 is communicated through condenser
V3 is supplied through resistor 55 from battery
31 to grid 35 which accordingly falls to 115 volts
negative to ground cutting oiï the right half of V2 40 3 i ’ which may be the same as battery 3| serving
to supply all voltages of the system of Fig. 1.
so that the potential of anode 33 rises to 300 volts.
Grid 52 is shunted to ground by condensery 56
The current in resistors 40 and 4| becomes mo
mentarily zero, thus removing the 20 volt nega
while suppressor grid 53 and cathode 54 are
grounded. Anode 51 is supplied through re
tive bias on grid 42 so that the left half of V2
becomes conducting, its anode 36 remaining 165 45 sistor 58 and bias control tube V5, a diode such
volts positive to ground. A small current now
as one-half of a 6H6, from the junction of resistors
ñows in cathode resistors 40 and 4| and conden
59 and 60, these resistors constitute a voltage
ser 31 starts to readjust its charge to the new
divider between battery 3| and ground whereby
anode 6| of Vs is supplied with 50 volts. Cathode
voltage difference about 146 volts, between anode
36 and grid 35. This involves a rise in poten
62 of V5 is connected through resistor 58 to
tial of grid 35 which on reaching the cut-01T po
anode 51 of V2. Condenser 63 shunting resistor
tential -10 volts allows the right half of V2
53 is connected between anode 51 of V3 and grid
to conduct. Now the flow of current of resistors
64 of tube V1 which is suitably one-half of a
40 and 4| results in cut-01T of the left half of V2
GSN'TGT. Anode 65 of V1 is supplied directly from
and the initial conditions are restored. The re 55 battery 3| while between cathode 66 and ground
adjustment of the charge of condenser 31 is by a
are connected resistors 61 and 68 in series.
partial discharge through resistor 34 and the left
Resistor R, preferably 200,000 ohms, is con
half of V2. The time constant C31R34 is 300
nected between cathode 66 and the junction of
microseconds and the rise in potential at grid 35
condenser 63 with anode 51. Between anode 51
of V2 from 1~115 volts to -10 volts requires 100 60 and input terminal B2 are connected condensei~
microseconds. During this interval the potential
C about 200 micromicrofarads, and condenser C',
of anode 33 is 300 Volts rising abruptly from 267
which may be 1,000 micromicrofarads, in series.
volts at the instant V1 becomes conducting and
Shunting this connection of condensers C and C’
falling rapidly 100 microseconds later. This fur
are condensers 69 and 10 in series serving as a
nishes a 33-volt positive square topped pulse. At 65 trimming capacitance. Condenser 69 is suitably
the end of the 100 microsecond interval the po
an air condenser, while condenser 10 may have a
tentia1 of anode 33 falls slightly below the initial
capacitance of 1,000 micromicrofarads. Resistor
value of 267 volts because of a small flow of cur
R1. about 330,000 ohms, is inserted between
rent from grid 35 to cathode 38. The 33-volt
cathode 66 and the junction of condensers C
positive pulse is used as pedestal voltage in range 70 and C'.
sweep generator 50 and the terminal distortion is
It will be observed that the positive pedestal
unimportant. Condenser 44 of capacitance .006
voltage pulses from time base generator 24 applied
microfarad holds grid 42 at constant voltage with
to input terminal B2 is interposed between ground
respect to ground. Simultaneously with the posi
and the circuit of Fig. 3 to the right of tube V3.
tive pulse at anode 33, there is produced a nega 75 Further, those acquainted with sweep voltage
2,406,358
7
generators, well described, for example, in “Time
Bases” by O. S. Puckle, published in London in
1943, will recognize that the circuit of Fig. 3
is such a generator, inactive while tube V3 is con
10,000 ohms resistance, on ‘which tap 82 selects a
fractional voltage adjusted, as later described,
to be proportional to the speed of the airplane
relative to the target. This fractional voltage
appears across resistor 93, about 1/2‘ megohm, and
ducting but generating a rapidly rising voltage
from a fixed point 80 thereon about île of the
starting from the instant when V3 is blocked by
voltage selected by tap 82 is applied through 3
the negative pulse applied to grid 5i from gen
megohm resistor 85 to grid 80 of tube V6. Cathode
erator 24. .This rapidly rising voltage rises sub
81 is connected through resistor 88 to the posi
stantially linearly with time and continues so
to rise until the negative pulse from generator 24 10' tive terminal of battery 3| and to ground through
the 300 ohms of resistors 89 and 90 in series.
has passed from grid 5|. The rate of voltage rise,
Variable resistor 89 is so adjusted that when tap
controlled by the ratio of the voltage across con
82 _is at ground no current iiows in resistor 85.
denser 83 to the product RC, is in the present
Anode 9| of Vs is directly connected to cathode
circuit about l volt per microsecond. This sweep
voltage appears as a voltage positive to ground 1,5 92 of V7 of which grid 93 is positively biased from
the junction of resistors 94 and 95 to a potential
at cathode 60 to which output terminal D1 is
of about 45 volts. Anode 98 of V7 is supplied from
connected. Tube V4 is an ampliiier tube supply
battery 3| through lO-megohm resistor 91. Sweep
ing negative feedback to linearize this voltage
wave as a function of time while the circuit R1C’
condenser C”, 4 microfarads, together with re
is an integrating circuit further contributing to 20 sistor 85 constitutes the sweep circuit controlled
by the voltage taken between point 84 and ground.
the desired linearity.
The output voltage from the circuit of Fig. 3 is
Effectively condenser C" is connected between
taken between terminal D1 and ground, or a
grid 80 of Ve and anode 96 of V7, which tubes
desired fraction of it may be taken between
constitute a direct coupled direct current am
Terminal D1 is used 25 plifier supplying negative feedback to linearize
with time the variation in voltage across conwhen switch S, Fig. l,_ is closed downward,
denser C”. Actually, instead of being directly
terminal E1 when S is closed upward.
Resistors 55, 559 and 00 are respectively about
joined to anode 98, condenser C" is connected to
cathode 98 of tube V8, of which grid 99 is joined
68,000, 20,000 and 100,000 ohms >while resistor 58
is 2.2 inegohrns. Resistors El' and 08 are about 30 through resistor |00 to anode 98 of V7. Anode |02
of Vs is directly supplied from battery 3|, the
250,000 and 50,000 ohms, respectively, so that the
pedestal and sweep voltages at terminal E1 are
load resistor of Vs being composed of voltage
regulator tube V9 in series with resistor |03.
each about one-sixth those at terminal D1.
It will be clear from the foregoing description
Across tube V9 is shunted resistor |94 which may
that in the circuit of Fig. 2 tube V2 is a single~ I.
be of 100,000 ohms resistance and is tapped to
shot multivibrator synchronized by tube V1 with
furnish at terminal F1 a desired fraction of the
the trigger pulse which simultaneously actuates
constant voltage across tube V9, plus the decreas
terminal E1 and ground.
radar system l. The output negative pulse from
ing voltage across resistor |03. Battery |05, de
terminal C1 controls the conductance of tubel
rived from battery 3 | , provides a negative voltage
V3 in the circuit of Fig. 3, and the duration of 40 to stabilize tube V9. Grid 99 of Vs is shunted to
the voltage rise at terminals D1 and E1 of Fig. 3.
ground by condenser |08, which with resistor
This voltage rise is linearized by negative feed
|00 serves to prevent oscillations of voltage at
back from tube V4 and further improved in
grid 99. Tube Vs functions as a cathode follower
linearity by the integrating circuit R’C’, for
tube so that condenser C” when connected be
which values of resistance and capacity are chosen
tween cathode 98 of Vs and grid 80 of V6 is effec
with. regard to the values of R and C and the
tively connected between that grid and anode 9S
amplification factor of tube V4. Diode V5 is so
of V1. To increase the amplification positive
inserted that in the intervals between successive
feedback is provided by resistor |07 between cath
sweeps condenser 53, of .006 microfarad capaci
ode 98 of Vs and cathode 81 of Ve, thereby raising
tance, may be rapidly charged by diode V5 through 50 the amplification factor ofthe ampliñer circuit
tube V3, which is during such intervals con
to 5,000.
ducting, and so be at a fixed potential at the
Switch S’ is closed as shown in Fig. 4, when
start of each successive pulse from tube V2. The»
switch S of Fig. 1 is closed upward. Closing
circuit of Fig. 3 is not itself a part of the present
switch S’ connects battery 3| through 5,000 ohm
invention but is disclosed and claimed in the co 55 resistor |08 to one plate of condenser C”, the
pending application of J . lV. Rieke, filed March
other plate thereof being connected to grid 86,
21, 1044, Serial No. 527,457, assigned to the same
assignee as the present application.
The voltage at terminal D varies from about
100 to about 200 volts, starting with about 65
volts during the interval between sweeps, to which
a 433-volt pedestal is added at the start 0f the
which is at ground potential and only about 2
volts negative to cathode 8l. Condenser C” ac
cordingly charges to about 195 volts (battery |05
opposing battery 3|) positive to ground at cath
ode 98, through resistor |08 and the grid-cathode
circuit of Ve. This voltage also appears across
tube V9 and resistor |83, 75'Volts being across
The rate sweep generator, of which the circuit
tube V9. Thus, the tap |09 on resistor |04 makes
is shown in Fig. 4, provides a voltage slowly de 65 available at terminal F1 120 volts plus a desired
creasing between terminal F1 and ground from
fraction of '75 volts. This is a steady state Volt
age independent of the operation of the sweep
about 200 to about 100 volts over a time interval
circuit of Fig. 3. The equality of this voltage
varying from 11/2 to 6 minutes. The circuit of
with the sweep voltage from range sweep gen
Fig. 4 includes vacuum tubes Vs, V1 and Vs and
voltage regulator tube V9. Suitably tubes Ve 70 erator 50 can be set by adjustment of tap |09 to
occur at any desired instant in the 100 micro
and V7 are respectively, the two triodes contained
sweep.
in a GSL'T, Va is one-half of a 6SN7GT while V9 is
second interval between near its end and near its
a VR75. Battery 3| supplies the voltage re
quired in the circuit of Fig. 4. Across this bat
beginning.
When switch S’ is opened, condenser C" starts'
tery is connected potentiometer 8| of about 75 to discharge through 3 megohm resistor 85, the
9
2,406,358
discharge rate being controlled by the voltage at
tap 84. From the stated values of capacity of
condenser C” and resistance of resistor 85 time
constant C”R85 appears to be 12 seconds, but
the eifective time constant determining the lin
earity of the sweep is the product of this 12 sec
onds by the amplification factor obtained from
tubes Va, Vv and V0, namely 1,000 minutes. In
the circuit of Fig. 4 enough amplification is pro
10
K the echo signal from video ampliider l1 of Fig.
1. The bias of grid M2 is controlled by tube V17.
The amplified positive pulse at anode E43 of V14
and the amplified echo signal at anode |44 of
V15 are applied on grid M5 of tube Vis, from the
cathode circuit of Which are fed a pair of negative
voltage pips corresponding respectively to the ar
rival of the echo signal at terminal K and the
start of the square-topped pulse applied to ter
vided to make unnecessary an integrating cir 10 minal H2. For a reason later given these voltage
cuit such as R’C’ of Fig. 3. By analysis of the
pips are delayed 5 microseconds by network 25€).
operation of Fig. 4 when switch S' is opened, it
Ground terminals, not shown, are provided for
may be shown that as condenser C" discharges,
the circuits of Figs. 5 and 6 and subsequent
grid 86 of V6 remains substantially at ground po
figures.
'
tential, so that the discharge current through re 15
In Fig. 'Il is shown the circuit of final video
sistor 85 is determined by the voltage at tap 84.
amplifier lïû. Terminal L’ receives from ter
The operation is in eñect a cancellation of the
minal L of Fig. 6 the negative voltage pips, de
charge placed on condenser C” when S’ is closed,
layed 5 microseconds by network 250, and applies
by an opposing sweep charge whereby the voltage
these to grid lll of tube V10 in amplifier H0.
across C” is caused to fall at a rate equal to 20 The amplification and reversal of sign of `these
E’/R85C” volts per second where E’ is the voltage
voltage pulses is accomplished by tubes V18 and
to ground at tap 84. When E’ is 12 volts the
V19 so that corresponding positive voltage pips are
voltage at cathode 98 and so at terminal F1 will
available at terminal N, To permit these volt
fall 1 volt per second, the voltage drop across V0
lages to produce traces on screen 2 of oscilloscope
is constant. Therefore, if initially with S’ closed, 25 3 of Fig. l, the positive pips are superimposed on a
tap |09 is at cathode £8 and E'=12 volts, the in
positive pedestal voltage derived from tube V20
stant of equality of the voltages, from terminal
to grid §13 of which are applied via terminal N
F1 and from terminal D1 of Fig. 3 Will move when
unblanking pulses that are explained in the de
S’ is opened in 100 seconds from near the end to
scription of Fig. 8. It is convenient to provide
near the beginning of the 100 microsecond inter 30 also at terminal Z a blanking voltage, derived in
val prescribed by time base generator 24.
any convenient manner from radar system I to
The rate sweep circuit of Fig. 4 is also nota
blank the oscilloscope trace during the rearward
part of the present invention but is described and
pointing of antenna l. This blanking voltage
claimed in the copending application of J. W.
may be a positive voltage applied to grid i512 of
Rieke above referred to.
35 tube V21 during such rearward pointing and re»
In the system of Fig. 1, the major components
placed by a ground when antenna l points for
following range sweep generator 53 and the rate
ward of the airplane. When present the blank
sweep generator 8l] use known circuit arrange
ing voltage annuls the output voltage at terminal
ments and will be here described chiefly func
N. Thus, only when antenna 1 points forward is
tionally, reference being made to the attached
the negative bias of grid i8, Fig 1, to be over
drawings for the circuit details. Referring to
come and the trace is brightened only when a
Fig. 5, vacuum tubes V10 and V11 of range differ
positive voltage pip appears at terminal N to
ential ampliñer Híl receive on grids lll and H2,
gether with a pedestal voltage from tube V20.
respectively, the voltages appearing at points D1
In Fig. 8, the circuit of vertical sweep ampliñer
of Fig. 3 and F1 of Fig. 4. Of these voltages 45 26€) comprises tubes V22, V23, V24 and V25, Tubes
the first is a rising sweep voltage lasting 100
V22 and V23 are suitably the two triodes of a
microseconds, the second is a voltage slowly de
GSN'IGT. Their respective anodes 2Q! and 2112
creasing over a comparatively long time equaled
are supplied from battery 3l through resistor 2û3.
by the rising voltage at an instant in the 100
Grids 23d and 265 are biased 50 volts negative
microsecond interval depending on the positions 50 by battery 295 through resistors 20T and Zíiß for
of taps 82 and m9 of Fig. 4. Tube V12 is an
grid 28d, 269 and 2li! for grid 205 and further
amplifying tube providing positive feedback to
biased by the voltage drop in common cathode
tube V10 through constant current tube V13 which
resistor 2i l. When switch S, Fig. l, is closed upf
is inserted between ground and joined cathodes
ward the fraction of the output sweep voltage of
range sweep generator 5d appearing at terminal
H3 and H4 of tubes V10 and V12, respectively.
E1 of Fig. 3 is applied via terminal I through con
The cathode current of tubes V10 and V12 is con
trolled by the potential of grid H5 of V13. Tube
denser` 2l2 to grid 29d. dit the same time switch
S” ganged with switch S, is closed upward and
V11 is a buiîer tube protecting rate sweep gener
grounds the junction of resistors 281 and 238
ator 80 from loading due to grid current in tube
V12, while voltage regulator tube V11 controls the 60 thereby removing from grid 266 the bias of bat
screen voltage of V13.
tery 206. As a result, tube V22 becomes conduct
ing, increasingly so as the sweep voltage rises at
It may be shown by analysis of the operation of
terminal I. A correspondingly increasing current
the circuit of Fig. 5 that when the voltages at
terminals D2 and F2 are equal there appears a
flows in resistor 2i I,
At the same time a nega
square-topped positive pulse at anode H6 of V12 85 tive voltage wave appears at anode 2i?! which is
transferred from terminal M' to terminal M of
which continues to the end of the 1GO-microsec
Fig. 7. The bias on grids 2534 and 265 suñìces to
ond intervall This pulse is supplied from ter
cut off the pedestal of the voltage from the range
minal H1 to Video mixing amplifier |40 and from
sweep generator and only a rising voltage appears
terminal H1’ when switch S is closed downward
to vertical sweep ampliiier 200.
70 across resistor 2H to be transferred through
The circuit of video amplifier Mii, of Fig. 1, is
stopping condenser 213 and resistor 2M to
shown in Fig. 6. It comprises pulse amplifying
the junction of resistors 2| 6 and 2H of
tube V14, on grid 14H of which is impressed the
which the other terminals are connected
pulse from terminal H1 of Fig. 5, and video ampli
respectively to grids 218 and 2| 9 of tubes V24
fier tube V15 of which grid |42 receives at terminal 75 and V25. these grids being normally biased to
2,406,358
li
cut off through resistor 220 by battery 22 l. Tubes
V24 and V25 are amplifying tubes in parallel and
at their anodes 222 and 223 there appears the
amplified sweep voltage which produces a vertical
ray deiiecting current in coil VDC of oscilloscope
3. A permanent magnet, not shown, is used to
fix the starting point of the vertical sweep, pref
erably near the bottom of screen 2.
Referring again to video amplifier il@ of Fig. '7
the negative voltage wave arriving at terminal VM
is reversed in sign in tube V20 and ultimately
appears as an unblanking pulse across resistor
H6 in the cathode circuit of tube V19. This pulse
is applied to intensity grid i8 of oscilloscope 3
which thus allows the trace on screen 2 to
brighten when there arrives a negative pulse at
terminal L', Such a pulse, either a radar target
echo or one occurring at the instant of equality
of range sweep and rate sweep voltages produces
a bright spot on screen 2_
12
Fig. 9B shows the appearance of screen 3 when
switches S, S’ and S” are thrown down-wards.
Range line RL appears vertically centered and
stationary on screen 3 since its creating voltage
pip on grid le, although simultaneous with the
equality of voltages starting the sweep, is delayed
a constant 5 microseconds relative to the moment
of such equality. This moment is continually
earlier because the voltage at tap E32 on poten
tiometer Si determines the date of decrease of>
the rate sweep voltage, which accordingly equals
the rising range sweep voltage at a continually
earlier epoch in the time base interval. If tap
t2 is so set that this advance of the moment of
equality is proportional to the rate of decrease
of the range from plane to target, spot T will con
tinue to be intersected by line RL.
It will be noted that delay network 256 serves
the purpose of Yplacing the intersecting range line
and target spot on the screen in a position con
venient for observation. Further, it will be re
alized that it is much simpler to adjust tap 82 to
maintain the coincidence of spot T and line RL
than it is by adjustment of tap H39 to follow the
Referring to Fig. 8, when switches, S, S’ and
S" are thrown downward, tube V23 is rendered
conducting and the positive square-topped pulse
produced by range diiîerential amplifier H0 pro
duces a voltage across cathode resistor 2 ll which 25 moving target spot of Fig. 9A.
The operative procedure thus requires that with
now is a square-topped wave, positive to ground,
switches S, S’ and S” thrown upward, tap |89,
beginning at the instant of equality of range and
Fig, e, be set to make line RL, Fig. 9A, intersect
rate sweep voltages and lasting to the end of the
spot T. The ganged switches are thenthrown
100 microseconds time base interval. The cut
01T bias of grids 2W and 2I9 is reduced to zero. 30 downward and tap 82 is adjusted so to control the
rate of decrease of the rate sweep voltage, that in
The voltage at anodes 222 and 223 abruptly drops
Fig. 9B line RL continues tointersect ’spot T. The
at the start of this cathode voltage and rises
setting of tap 62 thusproduces a voltage to ground
proportional to the plane’s velocity relative ‘to
in anode voltage of tubes V24 and V25 results in
a rise in anode current which ñows in coil HDC, 35 the target considered. This velocity, aspre-V
viously stated, is with aA fixed target substan
the inductance of which is so chosen that the
tially the ground speed of the plane. VThis speed
duration of this current is about 11 microseconds.
is thus measured by the system of the invention
It is thus clear that when switches S, S’ and
independently of the conditions of light or
S” are closed upward a vertical sweep starts from
thereafter exponentially.
This exponential rise
the bottom of oscilloscope screen 2 and lasts 100 40
weather.
'
While Vthe invention has been described with
reference
to a situation in which the target range
appears on screen 2 only when there arrives on
is continually decreasing, those skilled in the art
grid i8 either a target echo from radar system l
are acquainted with means for inverting the de
or a pulse from range diiîerential ampliiier l Hi at
the instant range and rate sweep voltages are 45 creasing voltage from the rate sweep generator to
obtain an increasing voltage. This enables them
equal. The azimuth sweep current through coil
to maintainV the range line RL intersecting target
HDC is controlled from potentiometer 22 of radar
spot T as the range increases, thereby adapting
system i, so that a target echo brightens the
the disclosed system to measure Vspeeds of reces
oscilloscope trace at a point corresponding hori
microseconds.
During this sweep a bright spot
zontally to the target bearing, vertically to the
target range.
On the other hand, the voltage
sion as Well as of approach.
What is claimed is:
`
Y
l. The method of measuring the speed of a ves
sel relative to an object at a varying range ahead
of said vessel, said range being determinable,
ness appears as a horizontal line.
Fig. 9A represents the appearance of screen 2 55 which comprises the steps of determining said
range, defining a repetitive timeinterval, estab
under these conditions. T is a target spot hori
lishing a ñrst voltage rising substantially linearly
Zontally centered while RL is a line formed by
with-time during >said repetitive interval, estab
the fusion of spots representing equality of range
vlishing a second voltage decreasing at a controlla
and rate sweep voltages. The vertical position
of spot T represents target range, decreasing as 60 ble rate substantially linearly with time over a
desired interval longer than said repetitive in
the plane iiies onward. Range line RL is made
terval, deñning in said repetitive interval an in
to intersect spot T at an initial instant by proper
stant representative of said range and varying in
setting of tap H39 kof Fig. 4. Spot T appears
accordance therewith, adjusting said second volt
lower and lower as time goes on. While tap m9
age to equality with said iirst voltage at an in
may be manually shifted to maintain coincidence
stant in said repetitive interval coincident with
of RL and T, it is convenient to throw downward
said representative instant at an initial definition
switch S and switches S' and S” ganged with it.
thereof, and controlling the rate of decrease of
Now, as previously described, a vertical sweep ll
said second voltage to maintain the simultaneity
microseconds long starts only at the moment of
equality of range and rate voltages and line RL 70 of occurrence of said equality and said represen
tative instant, whereby said rate of decrease s
appears in a fixed position on the screen, This
controlled is proportional to said speed.
'
position would be at the bottom were it not for
2. Means for measuring the rate of decrease of
delay network 25S which delays the echo pulse
the> range from an airplane to a target ahead of
and the range line pulse each about 5 micro
equality pulseis independent of the rotation of
antenna ‘l and the corresponding trace bright
seconds.
v75 said airplane comprising electrical means for
13
2,406,358
ranging and locating said target including a cath
ode ray oscilloscope provided with a fluorescent
screen on which the Vertical position of a 1u
minous spot moves in accordance With the change
in range of said target, electrical means for pro
ducing on said screen a luminous horizontal line
intersecting said spot in an initial position thereof
and electrical means including a potentiometer
14
spot in an initial position thereof and electrical
means including a potentiometer graduated in ve
locity units for maintaining said spot and said
line stationary on said scree .
`
4. Means for measuring the Speed of a vessel
relative to and in the direction of an observed
target comprising electrical means for ranging
and locating said target including a cathode ray
graduated in velocity units for moving said line
oscilloscope provided with a fluorescent screen
to follow said spot.
10 on which the vertical position of a luminous spot
3. Means for measuring the speed of a Vessel
represents the range of said target, electrical
relative to an object ahead comprising` electrical
means for producing a horizontal luminous line
means for ranging vand locating said object in
on said screen intersecting said spot in an initial
cluding a cathode ray oscilloscope provided with
position thereof and electrical means including
a fluorescent screen on which the vertical position 15 a potentiometer graduated in velocity units for
of a luminous spot represents the range of said
maintaining said line continuously intersecting
object, electrical means for producing a horizon
said spot.
tal luminous line on said screen intersecting said
STEPHEN DOBA, JR.
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