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Патент USA US2399661

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May 7, 1946.
R. M. BowlE
Filed May 26, 1943
5 Sheets-Sheet 1
May 7, 1946.
R. M. BowlE
Filed May 26, 1945
5 Sheets-Sheet 2
May 7, 1946.
Filed May 26, 1943
5 Sheets-Sheet 3
?’oef/P-r /7 ,50W/¿
May 7, 1946»
R. M. BoWlE
Filed May 26, 1945
5 Sheets-Sheet 4
BY ¿agé
May 7, 1946.
R. M. BowlE-
Filed May 26, 1945
5 Sheets-Sheet 5
/ñßf/Pr /7 50W/f:
2,399,561 Í
Patented May 7, 1946
Unirse stares ea‘raur _ortica
Robert M. Bowie, Emporium, Pa., assigner to
Sylvania Electric Products Inc., Emporium, Pa.,
a corporation of Massachusetts
Application May ze, 1943, serial Nn. «issues
4s claims. (ci. 35-1)
This invention refers to electrical signaling cir
cuits including electron discharge tubes, and in
particular, to tubes and circuits for detecting and
adjusting the coincidence of a plurality of pairs
of electrical quantities such as voltages, currents,
and phase differences. One aspect of this inven
tion refers to cathode ray tubes; another to the
generation and detection of electrical signals and
their interpretation as angles and distances.
'Signals of this type are received and decoded 10
by a certain class of radio locators known as
, radars, in which angles (as azimuth and eleva
tive only after signals which tend to produce an
arbitrarily given deflection of the cathode ray
beam in two mutually perpendicular directions
are compensated-by similar separately control
lable signals. The first named signals may be
two voltages applied to one plate in each of two
pairs of deiiection plates. The second named
signals may be two voltages applied to the other
plates in each pair.
It is therefore an object yof the invention to
provide a tube capable of detecting a double co
tion of an object) are directly read by adjusting
It is another object of the invention to pro
1 the angles of directive antennae to maximum re
vide means for transmitting and detecting in
ception, and distances are obtained by adjusting 15 fomation referring to an angle.
lthe phase angle between periodically transmitted
According to a further object of the invention,
and reflected signals.
means’ are provided for simulating to a student
Speed and accuracy are of utmost importance
the type of infomation normally provided by a
in the detection and location of fast moving
radar regarding distances to, and azimuth. of,
enemy aircraft, as this information is of no value 20 each of several objects and the effects of Various
>if obtained with undue delay. Radar operators
spurious signals.
must therefore be highly trained before attain
Another feature refers to the ease with which
ing the necessary degree of speed and accuracy
the new equipment can be adaptedto the simu
for this purpose.
This training can be carried
lation of multiple echoes and ofarbitrary noise
out with the help of training unit, in which sig 25 eiîects similar to those occurring in actual radio
nals of arbitrarily chosen values, similar to those
locating devices.
received by the actual radio locator, are produced
It is still further an object of the invention to
at will and are injected into a student’s operating
provide means whereby the student can manipu
unit on which the student performs the same
late angular adjustments and obtain the eñ’ect
manipulations as on the actual locating device 30 of the reception of a directional antenna array.
and seesV the same kind of display. Itv is, of
A feature of the invention refers to means for
course, desirable that a large number of pupils
simulating to a student the eiïects obtained by
be trained simultaneously from a single signal
equalizlng two echo responses received by a pair
source and that the nature of the signals be as
of antennae which bear a slight angular dis
realistic as possible.
35 placement with respect to each other.
The devices so far available for this purpose do
A further feature refers to a cathode ray tube
not fulfill these requirements, in that the num
~ for double coincidence detection in Awhich means'
ber of student stations operable from the same
are provided for correcting errors which may re
master or generating unit, and the number of
sult from the earth magnetic field or from other `
effects attainable by the signal generator are very 40 accidental ilelds existing in the vicinity of the
limited, particularly as to the simulation of re
detector tube, or from misalignment of the tube
flections from several objects at diñerent appar
ent azimuth and range positions. This is sub
According to one feature of the invention, the
stantially due to the fact that these prior train
external field correcting means consists in the
ing units are almost entirely mechanical in their 45 addition of two supplementary pairs of deñection
action. The invention avoids these disadvan
A plates.
tages by the use of a completely electrical signal
According to another feature, the external field
ing equipment, which incorporates only those
may be compensated by locating a masked photo
mechanical parts which correspond to the ones
cell in the proper position on the ñuorescent
provided in the actual radio locators, such as the 50 screen of an ordinary cathode ray tube which
dials and knobs for rotating directive antennae
may be used as a detector.
and for adjusting phase differences.
While one aspect of my invention covers the
One important circuit element in my new
detection and 'generation of information con
training unit is a cathode ray tube which is so
cerning an angle in a radar trainer by means of
deslgnedthat one of its circuits becomes conduc 55 D. C. voltages applied to the deflection plates of
which can be used for manipulating an ordinary
cathode ray tubes, it is also intended to cover al
ternate means for accomplishing those purposes
iin conjunction with the training elements for
cathode ray tube with :fluorescent screen as a
double coincidence detector in cooperation with
a movable masked photocell whose position on
the screen may be adjusted for correcting the ef
determining the distances of remote objects) _
These alternate means provide for the match
ing of phases of two waves fed over two or more
different paths from a common source of high
fect of external fields.`
Figs. l0, 11 and l2 refer to another embodi
ment of the invention in which the simulation
i‘requeucy oscillations, by use of circuits contain
of the azimuth operation is carried out by circuits
ing various known types of radio tubes and phas
10 using conventional radio tubes in place of the
ing means to be described.
special cathode ray tube described in connection
Several embodiments of this part of the inven
with Figs. 1 and 7. In Fig. 10, a basic azimuth
tion will be discussed in connection with Figs. 10,
circuit is shown which may be used in place of
11 and 12. One of these embodiments refers to
that used in Fig. 1. In Fig. 11, details are shown
the type of signal received with a single rotating
antenna as explained in the discussion of Figs. 15 of the master phasing circuit used in the circuit
of Fig. 12. Fig. 12 shows a circuit diagram of an
2 and 4. The other one is especially adapted to
azimuth trainer with double peaks corresponding
the reception oi signals of the type referred to in
to the circuit explained in connection with the
Figs. 3 and 5.
Figs. 3, 5 and 6. In place of the special cathode
The principal objects of this portion of the in
vention may therefore be summarized by the fol 20 .ray tube shown in these earlier figures, various
types of standard radio tubes are shown in Fig.
lowing features.
(1a) The development of two sinusoidal volt
Referring to Fig. 1, the tube I is in the form of
ages, the phases of which-are under the control
an elongated glass bulb or envelope having an
of master and student respectively.
(2a) The addition and subsequent rectification 25 electron gun mounted at one end for developing
a beam of electrons. This gunv may be of any
of said sinusoidal voltage in such a way that a
construction well-known in the cathode-ray tube
rectified sign-a1 is obtained which is a minimum,
art and comprises, for example, an electron-emit
preferably zero, when a predetermined phase re
ting cathode 2, control electrode 3, ñrst acceler
lationship exists between the two sinusoidal
waves. This predetermined phase relationship 30 ating and focussing anode 4, and a second accel
may be 180°.
(3a) The control of the gain of a stage of am
plification through which another signal is passed
such that the strength of that output signal may
be maximized by shifting the phase of one sinus- ^
oidal signal with respect to the other.
(1b) The simultaneous development of two
D. C. voltages in the manner just described under
(1a) and (2a) above, either of which may be 40
maximized separately -by the control of the phase
of one sinusoidal voltage with reference to the
phase of one of two other sinusoidal voltages
whose phases differ by a predetermined amount.
(2b) The control of the gain of two stages of
amplification through- which another signal
passes in parallel, these stages also being provided
with means which alternately paralyze one or
another of them, since their outputs are in par
My invention will be best understood by a de
tailed description in connection with the draw
ings in which:
erating and focussing anode 5. Supported on the
sealed-in wires 6 and 1 are the two'spaced elec
trostatic beam deflector plates 8 and 9; and sup
ported on the sealed-in wires I0, II, are the ad
ditional set of beam deñector plates I2, I3.
Plates 8 and 9 are mounted in planes at right an
gles to the planes of plates I2 and I3, in the wellknown manner. Mounted at the opposite end
of tube I is a centrally perforated metal plate or
baille I4, and a hollow cylindrical metal cup or
collector electrode I5. Electrodes 2 to 5, I4 and
I5, are mounted so that they are in axial align
ment, with the aperture I6 in line with the gun
aperture I1, and with the plates 8, 9, and I2, I3,
symmetrically positioned with respect to the axial
line between the said apertures.
When the tube is in operation, the focussed l
electron beam B emerging from gun aperture
I1 passes between the deflector plates and strikes
50 either the plate I4 or collector I5. When the
potential on deflection plate 8 with reference
to the second anode of the gun is equal to that
of plate 9, the beam passing between them will
remain undeflected. In like manner when the «
Fig. 1 is a perspective View of one type of dou
ble coincidence detecting tube with part of the 65 potential of the electrode I2 is equal to that of
electrode I3, the beam continues undeiiected in
envelope broken away to show the electrode ar
a straight line and passes through the aperture
rangement and a schematic diagram of the cir
I6, thus causing an output signal from collector
cuits associated with the tube elements.
I5. Therefore, the described tube is capable of
Figs. 2 and 3 show response curves obtained
60 use as a double coincidence detector. yIf the
from two kinds of directional antennae,
potential of deñection plate 8 is not equal to
Figs. 4 and 5 show the forms of the correspond
that of plate 9 or if that of I2 is_ not equal to
ing kinds of signals appearing on an oscilloscope
that of I3, no output signal is released from col-v
screen as a result of the response diagrams of
lector I5. It should be further notedfthat when
Figs. 2 and 3.
Fig. 6 is a circuit diagram, partly schematic, of 65 the beam B is passing through the aperture I6,
it is possible to transmit intelligence along the
beam B to the collector I5 under control of grid A
signals received by two directional >antennae
a trainer unit which is capable of simulating the
3. The beam may, for instance, be modulated by
code or by impulses of any desired shape.
The tube as just described, when associated
of Fig. 6.
with certain circuits, may be used to indicate the
Fig. 8 shows a double coincidence detector tube
coincidence of an angle setting on the controlin which compensating deflection electrodes are
whose response curve is given in Fig. 3.
Fig. 'l is a more detailed circuit diagram of part
provided for correcting errors due to external
Fig. 9 ‘shows another arrangement of tubes
dial of one circuit, with an angle setting _on the f
control dial of another circuit. For this pur-4
pose, any arrangement may be used which auto
matically produces pairs of voltages in response
` mark 39 of the oscilloscope.
to an angular dial setting, which are proportional
to the sin and cos of that angle.- In the embodi
' azimuth knob 21 he may then bring the shorter
ment of Fig. 1, this is _accomplished by impress
ing the voltage from battery I1M across the
potentiometers IBM and ISM. A crank arrange
ment 20M actuated from the master azimuth
knob 2IM, causes contacts on the two poten
tiometers to be .positioned according to the sin
By rotating the .
echo pulse 34 to a maximum on his oscilloscope
screen. and thus determine the azimuth angle.
Finally, by rotating the range knob 38 until the
echo pulse coincides with the index mark, he
can determine the range.
Although the-description given in connection' i
with Fig. 1 refers to a single student unit con
and cos of the angle set von the azimuth knob. 10 nected to the master unit and the circuit shown
In this way, the two desired voltages with refer
in Fig. 1 provides only a single echo, it is obvious
ence to the second anode of the gun are sup
that a large number of student units could be op
plied to deñection plates 9 and I3. At the
erated from a single master unit. The master
student’s position, indicated by the dotted line
unit comprises all parts marked with an M, phase
I, a similar arrangement of battery 23, poten 15 delay circuit 32 and the attenuator 33. All other
tiometers 24 and 25, and crank 26 is provided.
components, including the double coincidence
For obtaining the desired double coincidence,
detecting’tube, must be duplicated at each stu
the student rotates his azimuth knob 21 until the
dent unit. In order to simulate multiple echoes,
potentials on plates 8 and l2 are equal to those
itis, of course, necessary to duplicate the master
supplied by the master to plates 1 and I3. At
echo equipment for each additional echo.
this setting of the angle of the student’s azimuth
knob beam, B will pass through the aperture I6.
The >current collected-by. catcher I5 may be in
In operating the trainer unit described above,
the student determines the azimuth by adjusting
the response of the echo 34 upon the oscilloscope
dicated on an oscilloscope 28 as shown in Fig.
screen to a maximum'. This adjustment is ob
l, or by a microammeter or other indicating 25 tained by rotating the azimuth knob 21 back and
forth about the maximum position. This opera
Inasmuch as the diameter of beam B and the
tion corresponds to the determination of azimuth
diameter of the aperture I6 are of iinite size,
used in one type of radar. In other types of
there is a range of angles over which current may
radars a more accurate method is used for the
be collected at collector I5. If this current is 30 determination of the azimuth. Instead of a sin
plotted as a function of the student’s azimuth
gle antenna with a response such as shown in
setting, a diagram as shown in Fig. 2 is obtained
Fig. 2,-the more accurate method provides two
when the azimuth of the master dial is ñxed at
antennae displaced from each other by a small
the value indicated by 29 in Fig. 2.
angleand rotatable as a unit. The response dia
In view of the similarity between the.curve 35 gram of this arrangement is 'shownin Figs. 3 and
just described in connection with Fig. 2, and that
obtained from a directional antenna of a radar,
the usefulness of this tube and circuit arrange
ment in training radar operators becomes clear.
5. The intensity response of one antenna is given
-by curve A, that of the other one by curve B of
Fig. 3. In this type of reception, it is customary
to receive alternately upon one antenna and then „
The azimuth of a fictitious object can be set on 40 upon the other. Assume that an object in the
the master azimuth dial 2IM and may be de
direction indicated by line 29 in Fig. 3 has» been
tected by the student by rotating his azimuth
knob 21.
at a certain instant an echo is ‘received on an
In the operation of radars, usually brief pe
Following the wave pulse transmitted
tenna A corresponding to a point on lobe curve
riodic pulses of radio Waves are transmitted, 45 B. The relative sizes of the two responses -are
whose echoes from the ñeld of view are received
then compared by the operator by the means de
together with the originally transmitted signal.
scribed in connection with Figs. 5 and '1. By ro
The range of each object is determined> by the
tating the assemblyas a unit, it is possible to
echo time. To simulate the eiîect of range, it is
equalize the responses received by the two an
therefore only necessary to produce a pulse wave 50 tennae A and B. For equal response on the two
30 from a suitable master oscillator 3| and apply
antennae, the object lies along the line bisecting
it to a phase delay circuit 32, the delay of which
the angle deñned by the maxima of the lobe
is under control of the master. The output 'of
curves A and B in Fig. 3. For determining the
phase circuit 32 is then fed to a Suitable at
equality of the two responses, reference is now
tenuator 33 and from there to the grid 3 of the 55 made to Fig. 5 -which represents a view of the
electron gun as shown. Thus, the pulses 3,4 ap
oscilloscope screen. Consider the instant of
plied to grid 3 are of smaller amplitude and
time when a signal is received on antenna A, vand
phase delayed with relation to pulses 30. Pulses
assume that the corresponding scan on the cath
30 are also fed to another phase delay circuit 36
which isunder the control of the student. The 60 ode ray tube screen started at the point marked
“A start” and progressed towards the right, pro
output of phase delay circuit 36 is used for ini
ducing the peak mark A in Fig. 5 when the echo
tiating the horizontalvscan on oscilloscope 28 by
is received. When the antenna switch is shifted
any well-known means. The vertical scan of the
to receive from antenna B, a small Afixed D. C.
oscilloscope is derived by adding the signal reach
ing collector I5 to the original signal 30 thus 65 voltage is applied to the horizontal deflection
plates in the oscilloscope so that the correspond
producing a composite signal 35.` The tall pulses
ing scan starts a “B start” and progresses to the
are those produced by signal 30 and represent
right giving the slightly displaced peak mark B
the directly received transmitter pulses. The
interspersed smaller pulses 34 are derived from
when the echo is received on antenna B. This
collector I5 and are variable in amplitude and 70 process of switching antennae repeats itself in
position relative to the tall ones. They repre
deñnltely. Accordingly, the two peak marks, A
sent echoes. The student can now adjust the
and B, appear stationary and close to each other
zero setting of his range scale on the oscilloscope
on the screen and their relative height may be
screen by adjusting the range knob 38 so as to
changed by merely rotating the antenna assem-locate the unattenuated pulses 30 on the index 75 bly. When the heights of A and B appear equal
on the oscilloscope screen, the antenna assembly
is directed towards the object.
To achieve this effect in a radar trainer ac
cordin'g to the invention, it is necessary to devise
means for quickly changing the two voltages
which are applied to the electrodes 8 and I2 of
the tube shown in Fig. 1. One way of doing this
would be to use, at the student unit, two sets of
sinusoidal potentiometers ganged together but
displaced by a slight angle with respect to each
other and to provide rapidly operating mechani
cal switches. This, however, is impractical'be
cause the rate of switching is too high for me
the tube I signals represented by :A0 c'os an as
well as the'direct signal sin au. The resultant
signal on plate I3 is therefore sin (suino). The
resultant signals applied to plates 8 and I3 as
above described reproduce the conditions corre
spending to a shifting of an angle of a pair of
directional antennae4 of a radar,device as de- .
scribed above in connection with Figs. 3 and 5.
Fig. 7 shows in somewhat more detail the cir
cuit connections for controlling the pair of elec
tronic switches 44 and 48 under control of the
_“sin” potentiometer IBM with its crank 26. The
crank 26 in addition to varying the main “sin”
and “cos” arms 22M and 28M also varies an
other pair of arms 40 and 4I. The arm 48 is
connected to a high resistance potentiometer 42
obtain the desired effect by a method based Yon
and from thence through potentiometer arm 43
certain properties of the sin and cos of the sum
to the control grid of a pentode 44 which acts
and difference of two angles. Take the well
as one of the electronic switches. This applies
known relation:
20 a voltage sin 0 to the control grid of tube 44.
chanical contacts. It is possible, however, to
avoid mechanical switching altogether, and to
cos (ûiAß) = (cos 0. cos A0) :(sin 0. sin A0)
Another voltage tapped ofi by contact 22M and
vIf A0 is a small angle, the above formula yields
proportional to -sin 6 is divided by a high re
sistance potentiometer 45 and is fed to the con
trol grid of pentode 46. Either one or the other
cos (eiAû) :cos [email protected] sin 0
In like manner, it can be shown that
sinwino) :sin @i0 cos 0
25 of these tubes is caused to become conducting by
the application of the square waves 54, 55, (Fig. 6)
to their respective suppressor grids. Fixed max
imum potentials of the suppressor grids (with
Therefore, in order to achieve the desired shift
respect to the cathode) are determined by means
ing of angle, it is only necessary to add to and 30 of resistors 41 and 48, condensers 49, and double
then to subtract from the voltage representing
diode 50. When tube 46 is conducting, a small
cos 0 a small voltage which is proportional to
voltage proportional to sin 0 is added through
sin 0, as A0 is a small constant. The sine volt
condenser 51 to the undivided voltage propor
age applied to the other plate is manipulated
tional to cos 0 from arm 4I, as a result of the
correspondingly. One arrangement for achiev 35 action of resistors 52 and 53. When the tube 44
ing these results is shown in Fig. 6, wherein parts
is conducting, the added voltage is proportional
corresponding in function to those in Fig. 1, bear
to _sin 0. The square waves 54 and 55 which
the same designation numerals. In addition to
alternately energize tubes 44 and 46 are derived
the parts of Fig. 1, there are shown in schematic
from'the same source 3| but are 180 degrees out
form, 4apparatus and circuit connections for add 40 of phase. Both are synchronized with the signal
ing to the voltage applied to _the plates 8, 9, I2
supplied to the terminal "H-scan” >on the oscillo
and I3 of tube I, two other small voltages, name
scope of Fig. 1 but at half its frequency as de
ly i-Ao cos 0M and [email protected] sin 0M. For this latter
scribed in connection with Fig. 6. It is this half
purpose, the crank 26 also controls a movable
frequency synchronizing signal which also in
tap 40 which supplies a voltage sin 0 to the elec
troduces the small D.I C. voltage referred to in
tronic switch 44. At thesarne time, there is de
connection with Fig. 9. Thus the shifting of the
livered over contact arm 22M a voltage _sin s
angle coincides in time with the initiation of the
to the electronic switch 46. The switches 44 and
scan.` It will be understood that while Fig. 7
46 are controlled by respective square-Wave sig
has been described in detail for producing the
nals 54, 55, derived from the same master oscil 60 oscillation about cos o, the oscillation about sin 0
lator source 3| -but are 180 degrees out of phase.
is likewise effected and the corresponding por
For this latter purpose, a portion of the output
tions of the circuit bear the same numerals with
of the phase adjuster 36 is changed in frequency
the added letter a.
by a frequency divider D to one-half the input
Fig. 8 shows a tube whose construction is sub
frequency as described for example in applica 55 stantially the same as that of the tube shown
in Fig. 1, but in addition to the double part of
tion Serial No. 453,367, filed August 3, 1942.
These divided frequency waves are then passed
plates 18, 19, and 82, 83, which correspond to
through a wave Shaper SH to convert them into
square waves as indicated. A portion of the out
the previously discusseddeflection plates 8, 9, I2
and I3, two additional pairs of deflection plates
put of device SH is applied to switch 44. An 60 88, 89, and 92, 93, are incorporated in the tube
of Fig. 8. The second set of deflector plates 88,
other’ portion is applied to an inverter 1N Where
by the output Waves of the inverter are displaced
89, 82, 93, is used to compensate for errors due
to misalignment of the tube electrodes or due to
180 degrees with respect to the input waves. As
weak magnetic iields such as that of the earth.
a result, the switches 44 and 46 are alternately
conductive and produce a series of waves corre 65 If all deiiection plates in either Fig. 1 or Fig. 8
were grounded, it is quite possible that the elec
sponding respectively to [email protected] sin 0 and _A0 sin 6.
tron beam would not strike exactly the center of
These latter signals are then impressed upon the
baille electrode I4 or 84 because of the possible
plate 9 of the tube I together with the cos 0M
slight misalignment of the tube electrodes or as
waves directly from the potentiometer ISM so
that the resultant voltage applied to_ plate 9 is 70 a result of external ñelds. While in the descrip
tion made in connection -with Fig. l, no means
cos (0M-LM). Likewise, the potentiometer ISM
have been mentioned for correct centering of the
feeds another pair of electronic switches 44a, 46a,
beam, attention should now be called to the fact
similar to‘switches 44 and 46, switches 44a and
that in practical operation it is necessary to
46a being also fed with signals 54 and 55, with
the result that there is applied t0 the plate I3 of 75 employ external correcting means in connection
2,399,661 -
with the tube of Fig. 1. They may consist of a
permanent magnet or of two'sets of orthogonal
coils, each provided with a separate current ad
justment. In the special tube shown in Fig. 8,
the necessary corrections yfor misalignment and
external ñelds are made by means of the aux
in the ñgure is controlled by the student and it is
by means of this control that he attempts to
match the setting of the master operator.
The output signals of the two phasers maybe
added in any of several different ways. I have
chosen two parallel triodes |03 and |04 which are
operated on the linear portion of their character
istics. When the signal on the grid of tube |03
Centering of the beam of the tube shown in
is 180 degrees out of phase with that on the grid
Fig. 8 is obtained as follows: With the plates 18,
19, 82, and 83 grounded to the second anode, 10 of tube |04, no alternating current passes
through the combined load circuit |05 and hence
potentiometers 90 and 9| are adjusted simulta
no Voltage is developed. For all other phasing
neously until the current collected by catcher 85
conditions, however, the currents through tubes
reaches a maximum. No further adjustments of
|03 and |04 do not cancel but will result in a
potentiometers 90 and 9| are necessary so long
as the external- fields do not vary appreciably. 15 finite current of an amount depending upon _the
phase difference which produces an alternating
Instead of using the arrangement of the tube
voltage across load circuit |05. This alternating
shown’in Figs. l and 8, a double coincidence
voltage is rectified by tube |06 and is smoothed
>detector arrangement can also be obtained by
by the RCv circuit made up of condenser |01 and
using a standard cathode-ray tube of the type
used, for instance, in television, in conjunction 20 resistor |08. The direction or poling of therecti
ñer is such that with increased A. C. voltage
with a photocell. This arrangement will now be
across load circuit |05, the bias on the grid of
explained in connection with Fig. 9 in which
tube |09 is increased. . A fixed bias of a suitable
'numeral 94 indicates an ordinary cathode-ray
value is applied to the grid of tube |09_by means
tube provided with two dimensional or coordinate
iliary electrostatic deflection plates 88, 89, 92, 93.
scanning means and preferably with means for
modulating the electron beam. As can readily
be understood, in the absence of scanning poten
tials, the fluorescent' signal appearing on the
screen of the cathode-ray tube in response to the
stationary electron beam will be located at a' 30
ñxed point near the center of the screen when
the deflection plates of each pair are at the same
D. C. potential. In the absence of external ñelds,
and if the electrodes of the tubes are perfectly
aligned, the spot will appear exactly at the center
of the screen. The aperture 96 of housing 95
which is made of opaque material, is now placed
on the center of the ñuorescent screen, where
of battery ||0. The pulse signal |34 corresponds
to the signal 34 in Fig. 1. It can readily be seen
that the gain of tube |09 is a function of the bias
which is applied to it by the action of diode |06
and load circuit |05. Hence, the amplitude of l
the output pulse signal ||| is controlled by the
angular setting of the student shaft S relative
to that of the` master shaft M. It is readily un
derstood, of course, that the tube |09 may be a '
remote cut-off pentode or any other desired type
of amplifier tube. By suitable selection of this
tube and of bias | I0, it is possible to have output
' signal only when the student shaft is within say
x20 degrees of the setting of .the mastershaft
M. The amplitude of the output signal plotted
the bright spot appears` The light penetrates
from the bright spot through aperture 96 and is 40 against student phaser shaft angle can thus be
made to resemble closely the response curve of
received by the photocell 91 whose electric re
y sponse may be used to release a relay or to give
Fig. 2.
The arrangement of Fig. 10 corresponds to that
of Fig, 1 in that in both cases the student deter
in the figure). Photocell 91 will only receive
mines the azimuth by maximizing the height of
light when the spot on the cathode-ray tube 45 the pulse seen on the scope. This maximum
screen is at or very near to its center. If the
height is found by turning the student shaft S
spot is not at the center of the screen, the
back and forth.
photocell will not respond. This will happen if
In order to obtain the type of display described
the voltages applied to the deflection plates of
50 in connection with Figs. 3, 5, 6 and 7, it is possi
a direct signal in an associated circuit (not shown
one or both pairs are not equal. The arrange
ment of Fig. 9 also gives a simple method of com
ble to make use of a circuit such as that shown
in Fig. 12, although of course numerous varia
pensating for external ñelds or for misalignment
tions are within the scope of the invention. The
of the tube elements. 'I‘hisadjustment can sim
sinusoidal oscillations- from source |20 are fed to
ply be carried out by removing all deflection
two phasers |2|, |22. The phaser |22 controlled ‘
signals and then moving the housing 95 over 55 by the student is exactly like those previously re
the face of the cathode-ray tube screen until the
ferred to. 'I'he master phaser |2| is preferably,
current from photocell 91 reaches a maximum.
however, of a modified design about to be de
The housing is then clamped in this position by
scribed in connection with Fig. 1l. The rotating
magnetic ñeld is achieved in exactly the same way
Instead of simulating the azimuth operations 80 as in a standard phaser. .As shown in Fig. 1l, the
by the means of Fig. 1, a modified form is shown
oscillator |55 provides sinusoidal voltage to the
in Fig. l0. Referring now to Fig. 10, sinusoidal
damped resonant circuit comprising resistor |59,
oscillations of any predetermined frequency from
capacitor |58 and inductance |51, which are so
source |00 are fed to two identical phasers ||J|,
adjusted as to give a magnetic field at its center
|02, of the type described, for instance, in my 65 exactly equal to, but in phase quadrature with
copending application Serial No. 435,157, ñled'. that produced by coils |56. These coils are or
March 18, 1942. It is essential that the output
thogonal to each other and thus produce the ro
of the type of phaser employed be of constant
magnetic ñeld The pick up coil |60
amplitude but of phase variable throughout any
number of degrees. The shaft which adjusts the 70 comprises a relatively large number of turns.
Orthogonal to coil |60 there is another center
phase shift of one of these phase shifting devices
tapped coil |6| of a smaller number of turns.
is controlled by the master operator'and its angu
Because of the orthogonal relationship and the
lar position represents the azimuth of an object
nature of the rotating magnetic ñeld, the voltage
on a plane. This shaft is marked M in the fig
ure. The position of a similar shaft marked S 75 developed across coil |60 is 90 degreesout of
means not shown in the figure.
phase against that developed across |6|, so that
the voltage takenbetween'eontacts |62 and |63 is
equal to but slightly phase shifted against that
developed'betweencontacts |62 and |64. ,This
phase difference is determined, of course, by the
relative number of turns in, and the sizes of coils
|60 and |6I. A convenient value may be 15 de
termined path with respect to its path‘before '
passing said deflecting elements.
4. A double coincidence detector according to
, claim 1, in which the last-mentioned means in
cludes an oscillosëöpe which is jointly controlled
by the electron beam after passing said deflecting
elements and by the phase relation between two
sets of pulses which also control the said electron
Returning now to Fig. 12, the output signal of
5. A double coincidence detector according to
the student phaser |22 is added separately to the 10
claim 1, in which the standard source includes
twooutput signals of the master phaser |2| by
mon plate load |35, and tubes |36 and |31, which
have the, common plate load |38. Rectiiiers |39
means for generating two adjustable voltages, one
being a function of the sine of a given angularsetting, and the other being a function of a cosine
signal |43 corresponds to signal`34 in Fig. l.
the potentials tapped off thereby in correlationv
means of tubes |3| and |32, which have a com
and |40 develop separate bias voltages which are 15 of that angular setting, and the comparison
source has siny‘lar means for producing sine and
determined by the plate relationships between
cosine function voltages.
the voltage delivered by the student phaser and
6. A double coincidence detector according to
each of the two voltages provided by the master
claim 1, in which the standard source and the
phaser. These two bias voltages are supplied to
the grids of two pentodes (or similar tubes) |4| 20 comparison source each includes a pair of potentiometers each having an adjustable tapping arm
and |42. nPulse signal |43 is superimposed upon
and a common operating control for simultane
the control grids of both of these tubes and in
ously adjusting the positions of the arms to vary
series with the previously described bias. Pulse
Square waves |44 and |45 modulate the suppres-y 25 with different angular functions of the particular
angular setting of said common control.
sor grids of tubes |4| and |42 in phase opposi
'7. In a double coincidence detector, an elec
tion. Their amplitudes are so chosen as to cut
tron tube having means to develop an electron
off completely the tube to which they are applied
beam, beam deflecting plates arranged in oppo
during their negative cycles. Thus, tubes I 4|
and |42 become alternately conductive. Hence, 30 sitely disposed pairs, means to energize the plates
of one pair under control- of sine functions of the
signals |44 and |45 determine which of the two
angular settings of two independently adjustablev
developed bias voltages shall affect the size of the
control members, and means to energize the plates
output signal. ' As shown in Fig. 12, pulses |46
of the other pair under control of the cosine
are derived from tube |42, the smaller pulses |41,
functions of said angular settings.
from tube |4|. Therefore, the bias developed on
8. A double coincidence detector according to
>tube |4| is greater in this instance than that on.
claim '7, in which the electron beam producing
tube |42, indicating that the angular position of
means is provided with a beam-modulating elec~
the student shaft S is different from that of the
trode, and means are provided to energize said
master shaft M. 'I'he two sets of signals |46 and
|41 may be displayed in the manner described in 40 modulating electrode by pulses which are derived
connection with Fig. 6.
from a standard source, and an oscilloscope is
provided and connected to said tube and to said
source to produce an indication jointly controlled
factured and used by and for the Government
by the voltages impressed on said pairs of plates
of the United States for governmental purposes,
without payment to me or assigns of any royalty 45 and the pulses impressed on said modulating
The invention described herein may be manu
9. In an apparatus of the character described,
a signal source producing a succession of pairs of
1. A double coincidence detector comprising
impulses, means to delay the phase of one pulse
means to develop an electron beam, a pair of
beam deflector elements for deflecting the _beam 50 of each pair with respect to the other pulse of
the same pair, means to adjust the amount of
in one direction, another pair of beam deñecting
said phase delay, a double coincidence detector
elements for deflecting the beam in a different
tube having means to _develop an electron beam,
direction, means to energize one element of the
beam-modulating means upon which at least
first pair under control of a signal from a stand
ard source, means to energize the other element 55 one of said pairs of pulses is impressed, and an
oscilloscope whose deñecting system is controlled
Iof the first pair under control of a signal from a
What I claim is:
comparison source, means to energize one ele-`
by the signal from said detector tube and by the
said phase delay.
ment of the second pair under control of said
10. Apparatus for teaching the manipulation .
standard source, means to energize the other ele
ment of the second pai'r under control of said 60 and operation of radars and the like, compris
ing a master’s device for producing an electric
comparison, source, and means to detect when the
signal representing azimuth settings, a student’s
signal from the comparison source bears a pre
determined relation to the signal from the stand
device/for producing an electric signal represent
ing azimuth settings, a master’s device for producing electric signals representing range set
2. A double coincidence detector according to->
tings, a student’s device for producing electric
claim l in which the last-mentioned means in
signals representing range settings, and doublecludes a collector electrode for the electron beam.
coincidence detector means connected to all said
and a baille electrode located-between said col“
devices to produce a characteristic indication
lector 'and said deflecting elements.
70 when the student’s azimuth and range settings
3. A double coincidence detector according to
correspond to the master's azimuth and range
claim 1, in which the last-mentioned means
includes an indicating device for producing a
11. Apparatus for teaching the manipulation
ard source.
and operation of radars and the like according
characteristic indication when said beam, after
passing said deflecting elements follows a prede 76 to claim 10, in which the double coincidence de
tector includes an electron tube having two sets
4of control members for the beam, one set being
connected to the master’s azimuth setting device
and the other set being connected to the student’s
azimuth setting device, said tube having addi
tional means for controlling the production of an
output signal only when the eñect of one of said
sets of control members is substantially neu
tralized by the effect of the other set.
12. Apparatus for teaching the manipulation
and operation of radars and the like according
to claim 10, in which the double coincidence de
tector includes an electron beam tube having'
pairs of beam-deñecting members,l one pair be
ing energized under control of the master’s azi
muth signal, and the other pair being'energized
under control oi' the student’s azimuth signal,
a-nd- means responsive to the output of said tube
to produce an indication to show the relation
student’s device, and control means in said tube
upon which the said master pulses are impressed
together with the echo pulses, means controlled
by the output of said tube for producing an in- ‘
dication corresponding to said echo pulses, said
indication being produced only when the master’s
and student’s azimuth settings are substantially
alike, the last-mentioned means being of a type
which also simultaneously indicates when the set
tings of a master’s and student’s range setting de
vice are substantially alike.
16. In a radar training system and the like, a
master’s position, a student’s position, the mas
ter’s position including means to develop electric
signals representing azimuth settings, the stu
dent’s position also including means to develop
electric signals representing azimuth settings,
both the master’s position and the student’s posi
tion each having means to produce a signal rep
between the two signals.
20 presenting range settings, an electron tube hav
13. Apparatus for teaching the manipulation
ing an electron emitter, a control electrode sys
and operation of radars and the like according
>tem and an output electrode, said control elec
to claim 10, in which the double coincidence
trode system being connected to the master’s and
detector includes a tube for developing a beam
student’s positions to cause said tube to pro
of electrons, deiiecting means controlled jointly 25 duce an output signal which is a function of the
by the student’s azimuth signal and the master’s
relative settings of the master’s and student’s
azimuth signal, said beam normally following an
azimuth setting device, means to impress on said
undefiected or axial path when the two signals
control electrode system a plurality of successive
are substantially alike, and means responsive to
pairs of pulses, one pulse of each pair represent
deflection of said beam to determine when said 30 ing a datum signal and the other pulse represent
signals are unlike.
ing a radio echo, and an indicator device which
. .14.. Apparatus for teaching the manipulation
is connected to said electron tube so as to produce
and operation of radars and the like compris
an indication only when the master’s and stu
ing a pair of potentiometers, a master control
dent’s azimuth settings are substantially alike,
device for simultaneously adjusting said poten 35 said indicator device also including means to pro
tiometers in accordance with a master azimuth
duce a characteristic indication when the stu
setting to produce two voltages one correspond
dent’s range setting and the master’s range set
ing to the sine of the azimuth angular setting
the other corresponding to the cosine of that set
ting are substantially alike.
17. A system according to claim 16 in which
ting; an electron tube for developing an elec 40 said control electrode system comprises a pair of
tron beam and having a pair of electrostatic de
horizontal beam deflecting plates, a pair ci ver
iiector plates arranged to deflect said beam in
tical beam deflecting plates and a contrai grid,
two diiîerent coordinate directions; means to ap
said master’s position being connected to a hori
ply said sine and cosine voltages to said plates
zontal deñecting plate and to a vertical. deflect
respectively; another pair of potentiometers, a 45 ing plate, said student’s position being connected
student’s control device for simultaneously ad
to the other horizontal deíiecting plate and to
justing said other pair of potentiometers in ac
the other vertical deiiecting plate, said control
cordance with a student’s azimuth setting to
grid being connected to a source of echo pulses
produce two voltages one corresponding to the
controlled from the master‘s position.
sine of the student’s azimuth angular setting the 50
18. A system for radar training and the like,
other corresponding to the cosine of that setting,
comprising a source of datum pulses, a master’s
another pair of electrostatic deñector plates in
position, ‘a student’s position, means at said mas
said tube also arranged to deilect said beam in
ter’s position to receive said pulses to produce
said coordinate directions, and means to apply
corresponding phase delayed pulses simulating a
the sine and cosine voltages from the student’s
radio echo and representing a range setting.
potentiometers to said other pair of plates re
means at said student’s position to receive said
spectively, and an output circuit for said tube
pulses and to adjustably phase delay them to
which produces a characteristic signal when the
represent the student’s range setting, an electron
action of the iirst two voltages on said beam is
tube having a control electrode upon which at
neutralized by the action of the second two volt
least. said echos are impressed, an oscilloscope
having a pair of de?lecting systems, one system
15. Apparatus for teaching the manipulation
being controlled by the output of said tube, and
and operation of radars and the like, comprising
the other system being controlled by the student’s
a source of master electric pulses simulating the
phase-delayed pulses.
direct and echo pulse of a radar, a master’s phase 65
19. A system according to claim .1,8 in which
delay device, a student’s phase delay device, said
said tube includes an electron beam deflecting
devices being independently adjustable by the
system for deflecting the beam in one direction
master anad student respectively to simulate
and another electron beam deiiecting system .for
range settings of a radar and the like, the mas
deflecting the beam in the opposite direction, one
ter’s device also including an attenuator for at 70 deflecting system being connected to both the
tenuating certain of said pulses to simulate the
master’s and student’s positions, other deflecting
echo pulses, a double coincidence detector tube
system also being connected to both the master’s
having means which responds to electric sig
and student’s positions, and means to produce a
nals _representing respectively azimuth settings of
characteristic signal in the output of said tube
a master’s device and azimuth settings of a 75 when the control from the master’s position on
said deilecting systems is substantially equaled
phase delayed pulses is the same as. the phase
by the control from the student’s position on said
of said echo pulses. ,
.deíiecting systems,
_ 27. A radio training system according to claim
24 in which the student’s azimuth setting device
20. In a radar training system and the like,
means to produce pulses simulating respectively Cil derives -two_vo1tages for each angular azimuth set
ting, one voltage being a sine function and the
other a cosine function of said setting.
the direct pulse from a radar transmitter an
tenna and the echo pulses, means to-produce
control voltages respresentin'g respectively a
28. A radio training system according to claim
2i in which the student’s azimuth setting device
setting at a student’s position, a cathode-ray tube 10 and the master’s'azimuth setting device each' de
range setting at a master’s position and a range
defiectiug system and a beam modulating sys
rives two voltages for its respective angular set
ting, one voltage being a s_ine function and the
tem, means to energize the modulating system `
other a cosine function of said setting.
double coincidence detector comprising a beam
29. A radar training system according to claim
under control, of at least said echoes, means' to
energize the deiiecting system under joint control 15 24 in which the master’s azimuth setting device
of a master’s azimuth setting device and a stu
derives two voltages for each angular azimuth
dent’s azimuth device, and a cathode-ray tube
setting, one voltage being a sine function and the
oscilloscope connected for joint control by the
other a cosine function of said setting, and means
output signal from said tube and by the setting
are provided to automatically osoillate thesine
of the student’s range device.
2l. A system according to claim 20 in which
said cathode-ray tube detector comprises an ad
ditional beam-deflecting system which is ad
justeu' to centralize the cathode-ray beam to ren
der it independent of external stray ilelds.
22. A system according to claim 20 in which
said cathode~ray tube detector has a fluorescent
screen and the deilecting syst-em is such that an
output signal is produced on said screen only
when said beam is centralized.
23. A system according to claim 20 in which
said cathode~ray tube detector has a fluorescent
screen and is provided with an apertured mask
l' `lit cell combination mounted adjacent the
screen to produce a signal only when the cath
ode~ray beam is centralized.
2a. 'in a radar training system, means to pro
20 and cosine functions about a mean angle to simu
late the effect of oscillation of a radar double
30. In combination, an adjustable device whose
setting represents the angular orientation of an
25 object, means responsive to the setting of said de
vice to produce at least two voltages which are
related by cosine and sine functions of said ori
entation, a switch responsive to at least one volt
age to control the oscillation of the sine voltage
30 about a mean value, another switch responsive to
at least one other voltage for oscillating the cosine
function about a mean value, and a common de
tector circuit connected to both switches for pro
ducing a signal which is controlled jointly by the
35 two oscillated voltages.
pulses representing respectively the
31. The combination according to claim 30 in
which' each of said switches is an electronic
switch, and means are provided to render the
direct pulses from a radar antenna and the echo
switches alternately conductive in predetermined
pulses, and means to simulate the Operation of 40 timed relation.
a radar oi' the type which utilizes the overlap
32. In combination, an adjustable device whose
ping field patterns of two angularly displacedy
setting represents the angular orientation of an
antennae, the last-mentioned means_including
object. a potentiometer for deriving a sine func
a student’s azimuth setting device for deriving
tion voltage of said orientation, another poten
signals representing an azimuth to be deter
tiometer for deriving a cosine function voltage,
mined, a master’s azimuth setting device for de
riving signals representing said azimuth setting
to be determined by the student, a double coin
cidence electron tube detector, means to impress
the said student’s azimuth signals and said mas
ter’s azimuth signals on the electrode system of
said tube, and means to impress at least said
echo pulses also on the electrode system of said
tube, said tube having its electrodes arranged so
that it produces a characteristic signal in its out
put only when the student’s azimuth signal is
substantially the same as the master’s azimuth
both said potentiometers being operated jointly
by said device, electron switch means connected
to the sine function potentiometer for producing
an oscillation in the value of said sine function,
other electron switch means for producing an os
. cillation in the value of said cosine function, a
second adjustable device, a. sine function poten
tiometer and a cosine function potentiometer for
producing sine and cosine voltages corresponding
to the angular setting of said second device. and
a double coincidence detector upon which' the
voltages from all said potentiometers are applied
_ to determine when the setting of the second de
25. A radar training system according to claim
24 in which the master’s azimuth setting device
vice corresponds to the setting of the ñrst device.
33. The combination according to claim 30 in
has means to vary the azimuth signal a prede
termined small amount on either side of a mean
which each of said switches is in the form of a
pair of grid-controlled electron tubes, and a
source of timing waves is connected to each pair
of said tubes whereby the tubes of each pair are
alternately rendered conductive.
34. The combination according to claim 30 in
which each switch comprises a grid-controlled
correspond with the phase delay of said echo
electron tube, means to apply a portion of the sine
pulses, and an oscilloscope indicator is connected 70 function voltage to a grid of said tube to produce
to the output of said double coincidence detector
an output voltage proportional to said sine func«v
tube and to the student’s phase-delay device
tion voltage, and means to combine the said
whereby the student can observe when his azi
cosine function voltage with said output voltage.
muth setting corrsponds to the master’s azimuth
35. In combination, an angularly adjustable de
setting and also when the phase of the student’s
vice, means responsive to a given angular setting
setting to simulate the effect of two directional
radar antennae.
26. A radar training system according to claim
24 in which a student’s phase delay device is pro
vided for receiving and delaying said pulses to
A0 of said‘device to produce a voltage represented
by sin 0 and simultaneously to produce another
voltage represented by cos 0, a pair of electron
switches, means‘to apply the sin 0 voltage to one
of said switches to produce a voltage represented
by :L-Aâ sin 0, means to apply the cos 6 voltage to
the other switch to produce a voltage representedl
voltages, said tube having another electrode for
controlling the output of the tube under control
of the output of the master’s phase shifter, and
a cathode-ray tubel oscilloscope having one de
iiection system controlled by the output of said
detector, and the other deñection system con
trolled _by the output of the student’s phase
by [email protected] cos 0, means to combine the sin -0 voltage
and th'e :4_-A0 cos 0 voltage, means to combine the
41. A radar trainer according to claim 40 :in
cos 0 voltage with the im? sin 0 voltage, and a 10 which the master’s sine and cosine voltages are
double coincidence detector on which both said
varied positively and negatively under control of
sets of combined voltages are applied to deter
a pair of electronic switches, each of said
mine equality or lack of equality with other sets
switches being controlled in synchronism with
of voltages also applied to said detector.
said master oscillator.
36. The combination according to claim 35 in 15
42. A radar trainer according to claim 40 in
which each electron switch comprises a pair of
which the master’s sine and cosine voltages are
grid-controlled tubes which' are alternately ren
varied positively and negatively under control of
dered conductive by connection to a Vsource of
a pair of electronic switches, each of said
timing impulses, one tube of the ñrst pair pro
switches being connected to said master oscil
ducing in its output A0 sin 6 voltage, and the other 20 lator through a frequency subdivider.
tube of said ñrst pair producing -Aa sin 0 voltage,
43. In a phase comparison system, a source
one tube of the second pair producing A0 cos 0
of master oscillations, a standard phaser and a
phaser connected to said source, each
producing _A0 cos 0 Voltage.
phaser having a control shaft, a pair of grid
37. The combination according to claim 30 in 25 controlled electron tubes having their input cir
which the means for producing the sine and
cuits connected respectively to the standard
cosine function voltages comprises a pair of po
phaser and the comparison phaser, a common
tentiometers whose contact arms tap oiï said volt
load device connected to the output electrodes of
ages in response to the setting of said adjustable
said tubes, and means controlled by the current
device, each potentiometer having an additional 30 in said load for producing a signal only when the
arm for tapping 01T negative cosine and negative
shaft of the comparison phaser is within a pre
sine functions of said voltages.
determined angular setting with respect to the
38. In combination, a pair of potentiometers,
shaft of the master phaser.
a pair of slider contacts for each potentiometer,
44. A phase comparison system according to
a common operating device for simultaneously 35 claim 43 in which the said tubes are connected
moving both pairs of contacts to positions repre
to add the outputs from the two phasers, and the
senting the angular settings of an object, the
means for producing said signal comprises a rec
two contacts for one potentiometer deriving re
tiiier for rectifying the load current and another
spectively a voltage sin 0 and -sin 0, the two con
grid-controlled tube whose grid is biassed under
tacts for the other potentiometer deriving respec 40 control of said rectifier.
tively a voltage cos 0 and -cos 0, where 0 repre
45. A phase comparison system according tovv
sents said angular setting, means to combine at
claim 43 in which the said pair of tubes are con
regularly recurrent intervals with the sin 0 volt
nected to the two phasers to add the outputs
age an increment represented by *__-A0 cos 0,
thereof, and the means for producing said signal
means to combine at regularly recurrent inter 45 comprises a rectifier for rectify-ing the load cur
vals with the cos 0 voltage increments represent
rent and a grid-controlled tube whose grid bias
ed by [email protected] sin 0, and a common detector upon
is controlled by the rectified current, the recti
which both said sets of combined voltages are
ñer and grid-controlled tube being designed so
that the output signal simulates the field re
39. The combination according to claim 38 in 50 sponse of a radar antenna or the like.
voltage, and the other tube of the second pair
which said detector comprises a cathode-ray
tube having coordinate beam deflecting systems
upon which said combined voltages are respec
tively impressed.
46. In a phase comparison system, -a source of
master oscillations, a standard phaser, a com
parison phaser, each being connected to said
source of oscillations and each having a control
40. In a radar trainer or the like, a student’s 55 shaft movable to'represent azimuth settings, the
azimuth setting device, a student’s range setting
device, a master’s azimuth setting device, a mas
ter’s range setting device, means responsive to
standard phaser having means to produce two
series of phase-displaced signals, means to com
tube having a set of four electrodes for compar
bear a ñxed phase relation.
bine the signals from the comparison phaser
the student’s azimuth setting device to produce
with the two signals from the standard phaser,
sine and cosine voltages representing said angu 60 a pair of alternately conductive electron switches,
lar setting, means responsive to the master’s azi
and means connecting the control' electrodes of
muth setting device to' produce sine and cosine
said switches to both said phasers to control the
voltages representing angular settings to be as
current through the switches in accordance with
certained-by the student, the master’s sine and
the angular relation between shafts of the two
cosine voltages being aried positively and neg 65 phasers.
atively symmetrically about a mean angular
47. A phase comparison system according to
value at regularly timed intervals, a master os
claim 46, in which the standard phaser comprises
cillator, a pair of phase Shifters fed from said
two stator windings energized at a phase differ
master oscillator, one phase shifter being con
ence of approximately 90 degrees and a pair of
trolled by the student’s range device and the
pick-up windings on the rotor, oriented approxi
other phase shifter being controlled by the mas
mately 90 degrees with respect to each other andl ter’s range device, a double coincidence detector
being so connected as to give two voltages which
ing the student’s and master’s sine and cosine 75
48. A phase comparison system according to
claim 46 in which the means to combine the out
puts from the two phasers includes a, pair of
grid-controlled electron tubes whose control grids
are excited respectively by the two signals from
the standard phaser, and another pair ot grid
controlled electron tubes whose control grids are
excited in phase by the signal from the com
parison phaser, a common output circuit for one
of the ?rst 4pair of tubes and one ot the seœnd
pair of tubes, another common output circuit for
the other tube of the nrst pair and for the 'other
tube~ of the second pair, respective rectiners for
.said common output circuits, and respective elec
tron switch tubes for said recti?ers.
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