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Патент USA US3047797

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July 31, 1962
c. w. WANDREY ET AL
3,047,737
TUNERDRIVEAPPARATUS
Filed Nov. 9. 1959
2 Sheets-Sheet 1
98.9909/6'8
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ATTORNEY
July 31, 1962
c. w. WANDREY ET AL
3,047,787
TUNER DRIVE APPARATUS
Filed Nov. 9, 1959
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United States Patent O?lice
1
3,047,787
Patented July 31, 1962
2
FIGURE 1 illustrates a television receiver 10 having a
cabinet 11, a picture screen 12, a combination on-off
and volume-control knob 13, and a station selector con
trol knob 14. The structural and electrical characteristics
3,047,787
TUNER DRIVE APPARATUS
Clarence W. Wandrey, Wheaton, and Howard C. Grosser!
heider, Deer?eld, 111., assignors to Zenith Radio Cor
poration, a corporation of Delaware
of the television receiver may be entirely conventional
and will not be described in detail. In the particular
receiver illustrated, the usual station selector or tuner
Filed Nov. 9, 1959, Ser. No. 851,780
1 Claim. (Cl. 318—265)
15 is mounted at the rear of cabinet 11 land is me
This invention is directed to a new and improved sta
chanically coupled to selection knob 14 'by means of a
tion selector apparatus. The apparatus is particularly 10 shaft 16. Tuner 15 is preferably of the turret or band
useful in adjusting the operating characteristics of a
switch types, although it may ‘also comprise a continuous
television receiver, and will be described in that connec
ly variable tuning device, in which case it is preferably
tion, although it may also be used with other devices.
provided with a mechanical detenting arrangement to
Many different remote control ‘arrangements have been
identify particular station positions. ‘In addition to sta
proposed vfor both radio and television receivers, some
tion selector 15, receiver 11} also includes the usual audio
of which have been exploited commercially. Many of
circuits coupled to the station selector circuit and con
these remote control systems require physical intercon
trolled from knob 13 ‘as well as conventional power sup
nection between a remote control station and the re
ply circuits which are also controlled from knob 13; these
ceiver, usually by a conductive wire or multi-conductor
circuits are not shown in FIGURE 1. The power sup
cable. Remote control systems in which receiver char 20 ply circuits, are, of course, coupled to both the audio
acteristics are varied in response to signals from a portable
and station selector circuits in accordance with the usual
practice.
miniature radio transmitter have also been developed.
It is a primary object of this invention to provide a
The remote control system incorporated in receiver
new and improved station selector mechanism capable
10 comprises four photo-sensitive switching devices 17,
of being employed advantageously with a remote con 25 18, 19 and Ztl mounted behind individual recessed open
trol system.
ings in cabinet 11 around the periphery of viewing screen
12. The position of these photo-sensitive devices, which
may comprises simple cadmium sul?de photocells or other
' It is another object of the present invention to provide
a tuner drive mechanism for a television receiver which
assures positive and accurate control of the tuner opera
conventional photo-electric switching devices, is not
critical, although they should be spaced from each other
tion but yet which is simple and economical to produce
and which is durable and rugged.
by a sufficient distance to ‘ ermit individual actuation.
The apparatus of the invention thus is utilized for con
trolling a wave signal receiver of the type including a
station selector having a shaft rotatable sequentially
Photocells 17-20 are electrically coupled by means of a
plurality of conductors 22 to a control circuit mounted
on an auxiliary chassis 21. A series of switches 23, 24,
through a predetermined plurality of circuniferentially 35 25 and 26 are mounted on cabinet 11 in positions closely
spaced positions to select different received signals. The
associated with photocells 1'7, 18, 19 and 20 respectively
apparatus includes means coupling an electric motor to
the station selector shaft to rotate the latter through the
and are electrically connected to the photocells in a man
ner to be described more completely in connection with
different positions. A disc is coupled to the shaft to
‘FIGURE 2. The electrical circuits mounted on chassis
rotate therewith. The disc has a like plurality of notches 40 221 are also coupled to a motor-control apparatus 27
peripherally spaced in correspondence with the aforemen
tioned circu'm-ferentially ‘spaced positions.
which is mechanically coupled to shaft 16 of station selec
nism ‘further includes cam follower means successively
tor 15. The electrical control circuits mounted on chassis
21 are also provided with a master control switch 28
engageable in each of the notches and moveable thereby
and a master sensitivity control 29 preferably made
The mecha-
'
transversely between ?rst and second positions during 45 readily accessible from outside cabinet 11; master switch
rotation of the disc in response to energization of the
motor following a control action. Finally, the appara
tus comprises means responsive to movement of the cam
follower means between the first and second positions for
28 may be employed to energize or to disable the remote '
control system, whereas sensitivity control 29 is utilized
to compensate ‘for variations in ambient illumination in
the room where receiver lil is located, and as will be
maintaining energizati-on of the motor when the shaft 50 more completely explained in connection with FIF
URE 2.
is between any of the circumferentially spaced positions.
When receiver it? is placed in operation ‘with master
The features of the invention which are believed to
be novel are set forth with particularity in the appended
switch 2% positioned to disable the remote control system,
claims. The organization and manner of operation of
the receiver operates in a completely conventional man
the invention, together with further objects and advan 55 ner. Station selection is achieved by means of control
tagesv thereof, may best be understood by reference to
knob 14, and the receiver is turned on and off and sound
the following description taken in conjunction with the
volume is controlled by means of knob 13. When master
accompanying drawings, in which like elements are identi
switch 28 is thrown to the position in which the remote
?ed by like numerals in each of the ?gures, and in which:
control system is energized, control knobs 13 and 14 may
FIGURE 1 is a perspective view of a television receiver
'still be employed to vary the operating characteristics of
in which a tuner drive apparatus constructed in accord
ance with the invention is incorporated; a portion of the
receiver cabinet has been cut away to show various corn~
ponents of the receiver and control system;
FIGURE 2 is a schematic diagram of ‘an electrical cir
cuit for a control system with which the inventive ap
paratus may be utilized;
receiver 10‘; at the same time, however, the remote con
trol system enabled to control operation of the receiver
in response to light impulses from an external controllable
light sorce, here represented as a ?ashlight 30.
‘ With the receiver in operation, ?ashlight 30 may be
employed to focus a beam of light upon photocell 19 and
turn the receiver off without turning control knob 13 to its
‘FIGURE 3 is a perspective view of a portion of the
off position. The control system is so arranged that only
control system of FIGURES l and 2, showing apparatus
a brief impulse of light need be supplied to the photocell
constructed in accordance with the invention; and
70 to de-energize the receiver; a much longer light impulse
’ FIGURE 4 is a fragmentary perspective view of ‘a por
has the same eifect. A second discrete impulse of light
tion of FIGURE 3.
a
directed to photocell 19 from ?ashlight 30 may be em
4
3
ployed to bring receiver 19 back into operation; again,
duration of the light impulse does not affect the sequence
of operation.
Flashlight 31) may also be employed to direct ‘a beam of
light to impinge upon either of photocells 17 and 18.
When the beam is focused upon photocell 17, a motor
control apparatus 27 is energized to rotate tuner shaft 16
in a clockwise direction, thereby changing the signal-trans
lating condition of station selector 15' in accordance with
a predetermined station sequence.
prising an indirectly heated cathode 43, a control electrode
44, and a shield electrode 45 in addition to anode 39; the
commercially available type 2D2l thyratron may be em
ployed. Shield elect-rode 45 is connected through a bias
resistor 46 to a tap 47 on transformer 38; the ?lament ‘for
cathode 43 is directly connected to the same transformer
tap. Cathode 43 is connected to ground and control elec
trode 44 is coupled through a series-connected circuit
comprising an input resistor 48 and photocell 19‘ to the
As long as the light 10 variable tap on potentiometer 29.
An auxiliary or manu
al-control circuit comprising switch 25 and a resistor 49‘
beam is focused upon photocell 17, motor apparatus 27
is connected in parallel with photocell 19 and the photo
continues in operation and continues to change the station
cell is connected to ground through a potentiometer 50
setting; when the desired station position is reached, the
and a resistor 51. Resistor 51 forms a part of a voltage
light beam is extinguished or de?ected away from the
photocell cell and rotation of the tuner is interrupted. 15 divider including a second resistor ‘52., the other terminal
of resistor 52 being connected through a recti?er 53 to a
Thus, the e?e‘ctive signal-translating condition of station
second tap
on transformer 33‘. A capacitor 55 is con
selector 15 is determined by the duration of the light im
nected in parallel with voltage divider 51, 52.
pulse supplied -to photocell 17 from source 30. In the
The circuit of FIGURE l2 includes a second thyratron
event that the desired station setting is passed, the light
beam from source 30 may be shifted to photocell 18', which 20 switching stage which is substantially identical in con
struction with the stage just described. It comprises a
energizes motor apparatus 27 for rotation in the opposite
second thyratron 56 including an anode 57, a shield elec
or counter-clockwise direction. The station setting may
trode 58, a control electrode 59, and an indirectly heated
thus be corrected or a dilferent station setting selected by ,
cathode 6t). Shield electrode 58 and the cathode ?lament
counter-clockwise rotation of tuner shaft ‘16; as before,
the ultimate station selected is determined by the duration 25 are connected through a second terminal of relay 33 to tap
47 of transformer 38, a biasing resistor 61 being interposed
of the light impulse from ?ashlight 30.
in the shield electrode circuit. Cathode 60 is grounded
The light beam from ?ashlight 30 may also be directed
and control electrode 59 is connected to potentiometer
to photocell 25), which is coupled to the audio system of
29 through an input resistor 62 and photocell 20. Photo
receiver 10 through the electrical control circuit mounted
on chassis 21. The connection to the audio system may 30 cell 20 is shunted by a series circuit comprising switch 26
and resistor 49; as before, the photocell is connected back
comprise a motor or other variable drive for the volume
to voltage divider 51, ‘52 through a variable resistor 64-‘.
control of receiver 10 or may comprise a simple muting
Anode 57 of thyratron 56 is connected to power supply
arrangement coupled to the audio system, as will be de
conductor 35 through the solenoid operating coil 65 of a
scribed in connection with the circuit of FIGURE 2.
Thus, when ‘the viewer desires to maintain a conversation 35 single-pole sequence switch 66.
The electrical control system also includes an addi
without losing track of the ‘general program continuity,
tional control stage comprising two triode sections 67
the light beam from ?ashlight 30 is focused upon photo
and 68; the triode sections may comprise the two elec~
cell 20 to mute the audio system of the receiver. When
trode systems of a 6BX7 or similar double triode. Tri
it is again desired to receive the sound portions of the pro
gram in addition to the image version thereof, a second 40 ode 67 includes a ‘grounded indirectly-heated cathode 69
and a control electrode 70; the control electrode is con
light mpulse is applied to photocell 2t) to re-energize the
nected to recti?er 53 through a variable bias resistor 71.
audio system and restore it to its operative signal-translat
The anode 72‘ of triode 67 is connected through a coil 73
ing condition. As in the case of the on-off portion of the
and a pair of normally-closed contacts on ‘a single-pole
control system, the photo-sensitive switching mechanism
comprising cell 120 is coupled to receiver 10 through a 45 double-throw switch 74 to power conductor 35. Coil 73
comprises the operating coil of a solenoid~operated single
stepping relay or other similar means to establish a se
pole double-throw switch 75 which is substantially iden
quence of actuation which is independent of the duration
tical with switch 74.
of light impulses from ?ashlight 30.
The indirectly-heated cathode 76 of tube 68 is ground
FIGURE 2 illustrates an electrical control system suit
able for use in the remote control system described in con 50 ed and the control electrode 77 is coupled to recti?er
53 through a variable bias resistor 78. The anode 79
nection with \FIGURE 1. It includes the master control
of triode 68 is coupled to power conductor 35 through
switch 28, here shown as a double-pole double-throw
the operating coil 80‘ of switch 74 and through the nor
switch. One of the internal terminals 32 of switch 28 is
mally-closed contacts of switch 75. Control electrode
connected to one terminal of an external power source 31,
which may comprise the usual 60 cycle 110-120 volt 55 77 is coupled to potentiometer 29 through photocell 17
and control electrode 70‘ of tube 67 is similarly coupled
household power supply; the other terminal of the power
source, which in this instance is grounded, is connected
directly to the power-supply circuits of the receiver (not
shown). Master switch terminal 32 is connected through
one pole of a double-pole single-throw solenoid-operated
to the potentiometer through photocell ‘18. A bridging
circuit comprising a resistor 81 and manual control switch
23 is connected in shunt with photocell 17, and a similar
circuit comprising resistor *81 and switch 24 is connected
in shunt with photocell 18.
A reversible motor 82 is included in the control appa
ratus of FIGURE 2; the motor illustrated is of the type
sequence switch 33 to the on-off switch 34 of the television
receiver by means of an electrical conductor 35. One of
the external terminals 36 of master switch 28 is also con
employing a single center-tapped ?eld winding 83 with
nected to power conductor 35, by-passing switch 33 for
65 the usual phase-shifting capacitor connected across the
manual operation A second external terminal 37
winding. The center tap on winding 83 is connected to
adapted to be electrically interconnected with terminal 32
ground and one terminal of the winding is connected to
is connected to an auto-transformer 38, the other terminal
a normally-open terminal of switch 75, the other termi
of transformer 38 being coupled back to the ground ter
minal of external power source 31.
nal of winding 83 being coupled to a normally open
Switch terminal 37 70 contact on switch 74. The motor circuit also includes
is also connected through the solenoid coil 41 of relay 33
a carry-over switch 84 which will be more completely
to the anode 39 of a ?rst thyratron 40 ‘and is further con
described in connection with FIGURE 3.
nected to ground through a potentiometer comprising mas
The circuit diagram of FIGURE 2 also shows a por
ter sensitivity control 29.
tion of the audio circuit of the receiver of FIGURE 1,
Thyratron 46 may be of the four-electrode type com 75 here illustrated as a triode ampli?er 85'. The control
6
electrode 86’ of tube 85’ is coupled to tuner 15 through
rendering thyratron 56 conductive and energizing coil
a conventional volume-control potentiometer 87' con
trolled by knob 13; potentiometer 87' is also connected
65 to open switch 66. Normal audio reproduction may
also, of course, be obtained by employing switch 26 to
to one terminal of sequence switch 66. The other ter
minal of sequence switch 66 is connected to an external
operate the sequence switch circuit. Thus, the second
photo-sensitive switching mechanism of the control sys
terminal 88’ of master switch 28; when switch 28 is in
its automatic position as illustrated, terminal 88’ is con
nected to ground through the internal switch terminal
89'. The remaining external terminal 90' of switch 28
tem comprising thyratron 56, sequence switch 66, photo
sensitive device 20 and switch 26, sequentially actuates
audio circuit 85’ between‘its normal operative signal
is left as an open circuit.
translating condition and a muted signal-translating
10 condition.
In order for the electrical control system shown in
Tuning of the receiver is quite similar to the muting
FIGURE 2 to be effective, the power supply switch 34
and energizing operation in many respects. ‘For exam
of the receiver must be actuated by knob 13‘ to its closed
ple, photocell 17 may be illuminated to reduce the im
position. In addition, it is necessary for master switch
pedance thereof to a very small value as compared with
28 to be moved to its “automatic” position, since when 15 its unilluminated impedance, thereby rendering triode 68
it is placed in its “manual” position the control system
conductive. The current drawn by triode 68 also ?ows
is effectively by-passed and cannot change the opera
through solenoid 80, closing the normally-open contacts
tional characteristics of the receiver. With switch 28
of switch 74. When switch 74 closes, motor 82 is en?
in its automatic position, as shown, the system eifectively
ergized for rotation in a clockwise direction and thus
controls station selection and audio reproduction and in 20 drives tuner shaft 16 (FIGURE 1) in that direction.
addition can be employed to turn the receiver on and off.
Motor 82 is continuously energized and continues to drive
With the illustrated circuit, thyratron 40 is always
the tuner shaft as long as photocell 17 is illuminated.
energized and ready for operation whenever switch 28
is in the ‘automatic position. Consequently, if sequence
switch 33 happens to be open at the time when opera
tion of the receiver is desired, it is only necessary to
illuminate photocell 19. A light impulse applied to this
photocell sharply reduces the impedance of the cell
thereby effectively raising the voltage on control grid
44 and ?ring thyratron 40. The current conducted by
the thyratron ?ows through solenoid 41 and moves switch
33 to its closed position. The sequence switch remains
in this position independently of the duration of the light
impulse applied to photocell 19. To disable the receiver,
it is only necessary to apply light to photocell 19 a second
time to again energize thyratron 40‘ and solenoid 41 and
return switch 33 to its open-circuit position.
The same
effect can be achieved by closing switch 25; consequently,
the manual control switch effectively simulates the func
When the light impulse applied to the photocell ends,
switch 74 returns to its normally open position and mo
tor 82 is de-energized, e?ectively determining the station
setting of the receiver. Complete rotation of the station
selector to the next station setting in sequence is assured
by means of carry-over switch 84, as will be more com
completely described in connection with FIGURE 3.
When it is desired to rotate tuner shaft 16- [counter
clockwise, a beam of light is focused on photocell 18.
Triode 67 is then rendered conductive and energizes sole
noid 73, closing switch 75 to connect motor 82 to the
power supply for counterclockwise rotation. In this in
stance, as with the switching mechanism including pho
tocell 17, triode 68 and switch 74, the motor remains in
operation as long as the photocell is illuminated, the ?nal
signal-translating condition of the station selector being
determined ‘by the duration of the light impulse. Coun
tion of photocell 19 and may be employed to either ener
terclockwise rotation of motor 82 and of the station se
gize or de-energize the receiver. Thus, operation of the
power supply circuits of the receiver is effectively con
lector may also be achieved by closing switch 24 and
clockwise movement of the tuning mechanism may be
obtained by closing switch 23. It should be noted that
trolled by the remote control system; at the same time,
the ?rst photo-sensitive switching mechanism of the con
the two motor switches 74 and 75 are electrically inter
trol system, comprising thyratron 40, sequence switch 33, 45 locked so that they cannot be closed at the same time,
photocell 19 and switch 25 is employed to energize or
thereby preventing simultaneous actuation of the two
de-energize the remainder of the control system along
tuning-control switching mechanisms and protecting mo—
tor 82.
with the receiver.
Sensitivity of all of the photocell-actuated switching
With switch 33 closed, as shown, all of the remaining
circuits of the control system are energized. Light im 50 circuits may be adjusted 'by varying the setting of master
pulses may then be applied to photocell 20 to open and
control 29, thereby adjusting the control electrode oper
close sequence switch 66 in the same manner as sequence
switch 33 is operated by photo-sensitive switching device
19. For normal operation of the receiver, with complete
audio reproduction, switch 66 is opened and the signal
translating conditions in the audio system represented
by ampli?er tube 85’ are controlled by potentiometer
87’ from knob 13. When it is desired to mute the audio
ating potentials. Individual adjustment is provided by
varying the effective resistance of elements 50, 64, 71,
and 78 to vary the operating voltages on control elec
trodes 44, 59, 70 and 77 respectively. Thus, the system
may be adjusted for proper operation over a wide range
of ambient illumination levels.
FIGURES 3 and 4 show a preferred form of the mo
system, light is applied to photocell 20, thus ?ring thyra
tor driving apparatus 27 including motor 82 and carry
tron 56 and energizing solenoid 65 to close switch 66. 60 over switch 84. Apparatus 27 includes a gearing arrange
Closing switch 66 effectively shunts the input circuit of
ment, not shown in detail, coupling the shaft of motor
82 to tuner shaft 16. A serrated ‘cam disc 85 is mounted
the audio ampli?er to ground and thereby mutes the
on tuner shaft 16 for rotation therewith and includes a
audio circuit completely. If only a reduced level of
series of indexing indentations or notches 86 spaced
audio reproduction is desired, some resistance 94 may
around ‘its periphery at positions corresponding to the
be incorporated in the muting circuit so that audio circuit
different station or signal-translating settings for tuner 15.
85' is not completely disabled. Thyratron 56 may also
One of the indentations 86a is shown in engagement with
be energized by closing switch 26 instead of by applying
a cam-follower 87 which is affixed to the principal contact
a light impulse to photocell 20 to achieve the same effect.
element 88 of carry-over switch 84; the cam vfollower
Sequence switch 66 is of the same general type as
switch 33 and is actuated in a sequence independent of 70 extends through slot 86a at an angle of approximately
45° ‘with respect to cam 85 so that rotation of the cam in
the duration of light impulses applied to photocell 20
or of the length of time during which switch 26 is main
either the clockwise or counter-clockwise direction dis~
tained closed. When it is desired to restore audio cir
places the cam follower from the slot as indicated ‘by
cuit 35’ to its normal signal-translating condition, a
arrows C and C’. Usually, either cam follower 87 should
second light impulse is applied to photocell 20, again 75 be of or covered with insulating material (as shown) or
'2’
disc 85 should be of such material. Switch 84 is also
provided with two secondary contact elements 89 and 90
disposed on opposite sides of primary contact member
88; secondary contacts 89 and 90 are connected in the
electrical circuit of motor 82 as shown in FIGURE 2.
The preferred embodiment of the carry-over switch il
lustrated in FIGURE 3 also includes a pair of damper
elements 91 and 92 disposed on opposite sides of pri
mary contact 88. Damper elements 91 and 92 are pref
erably constructed from resilient material such as Phos~
phor ‘bronze; the primary contact member is also made
from spring material.
In addition, the damper elements
are constructed to have an effective moment of inertia
substantially equal to that of primary contact eiement 88.
When motor 82 is energized 2by the circuit of FIGURE
8
those skilled in the art that changes and modi?cations
may ‘be made without departing from the invention in its
1broader aspects. Accordingly, the aim in the appended
claim is to cover all such changes and modi?cations as
may fall within the true spirit and scope of the invention.
We claim:
In an ‘apparatus for controlling the operation of a
station selector ‘having a shaft rotatable selectively in
either direction sequentially through a predetermined plu
rality of circumferentially spaced positions to select differ
ent stations under ‘the control of a bidirectional drive
mechanism including an electric motor, means coupling
said motor to said station—selector shaft to rotate the latter
sequentially through said positions, a disc coupled to said
2 to drive shaft 16 in a clockwise direction, cam follower
87 is forced out of slot 86a in the direction of arrow C
station~selector shaft to rotate therewith with the periphery
of said disc having a like plurality of portions one of
which is peripherally spaced in correspondence with a re
and moves primary contact element 88 away from damp
er element 92 and into contact with secondary contact
element 89. If the switching mechanism of FIGURE 2
positions, and means responsive to a control action for
energizing said motor to rotate said disc selectively in
comprising cell 17, triode 68 and switch 74 is subsequent
ly de-energized [before the station position is reached,
carry-over switch 84 maintains a complete electrical cir~
cuit to motor 82 until cam follower 87 drops into the
next cam indentation 861). Thus, the carry-over switch
prevents interruption of the tuner drive mechanism at a
point intermediate the station settings. When cam foi~
lower 37 engages in indentation 86b, resilient primary
contact 88 moves back toward its normal open-circuit
position. As the primary contact strikes damper 92,
movement of the primary contact is immediately arrested,
due to the fact that the moment of inertia of the contact
is equal to that of the damper element. Consequently,
the primary contact member cannot make electrical con—
tact with the other secondary element 90. Carry-over
switch '84 therefore permits positive control of the ulti
spective one of each of said circumferentially spaced
either direction, the improvement comprising: means de~
?ning a plurality of notches one each in each of said
portions of said disc; cam-follower ‘means, disposed at an
acute angle to and normally cutting across the plane of
said disc and receivable in said notches, movable trans
versely of the disc out of any given one of said notches
in one direction by one side and in the other direction by
the other side of that notch during rotation of said disc
respectively in one direction or the other in response to
energization of said motor; ‘a ?rst electric contact coupled‘
to ‘and movable in response to movement of said cam
follower means; second ‘and third electric contacts dis
posed respectively on opposite sides of said ?rst contact
with each in a position to be engaged by said ?rst con-tact
upon movement of the latter respectively in one direction
or ‘the other in response to movement of said cam-follower
means from a location in a given notch to a location out
mate position of the tuner by means of the two photo
of and between said notches; and means responsive to
sensitive switching mechanisms shown in FIGURE 2
engagement of said ?rst contact With a respective one of
without creating undesirable transient pulses in the con
trol system due to vibration of the switch contacts.
40 said second and third contacts for maintaining energize
tion of said motor and rotation of said shaft in the cor
The tuner drive apparatus of the invention thus per
responding direction when said shaft is between said cir
mits precise control of the station selector and insures
against false operation and particularly against termina
cumferentially spaced positions.
tion of its ‘function between adjacent channel positions
Which'otherwise might occur should the actuating con
trol signal the of incorrect duration or be improperly
timed. This is accomplished with a physical structure
which is extremely simple and which by reason of its sim
plicity is economical to manufacture and very durable.
While a particular embodiment of the present inven
tion has ‘been shown and described, it will be obvious to
References Cited in the ?le of this patent
UNITED STATES PATENTS
2,116,247
2,146,562
2,758,181
Macdonald ____________ __ May 3, 1938
Cameron et :al. __‘ _______ __ Feb. 7, 1939
‘Crouch _______________ __ Aug. 7, 1956
2,833,976
Kennedy et a1 ____________ __ May 6, 1958
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