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Патент USA US2108827

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Feb. 22,- 1938.
F?ed July 7. 1950
a Sheeté-Sheet 1
A/exander MELmH Mrs/son.
Feb. 22, 1938.
2,108,827 '
Filed July '7. 1930
3 Sheets-Sheet 2
His-.- E
\ \
Feb; 22,_ 1938.-
Filed July 7. 1930
3 Sheets-Sheet 3
"7.515.. E
A/exdna’er MQLean Abba/$017.
Patented Feb. 22, 1938
amass? .
Alexander McLean NicolsomNew York, 7N. Y.,ias
signor to, Communication Patents, Inc., New
York, N. Y., a corporation of Delaware
Application July 7, 1930, Serial No. 466,079
24 Claims. (o1.17s_7_.,2)
' This , invention relates to television systems,
the cathode is not uniformly illuminated. This
andparticularly to the scanning apparatus em
ployed in such systems.
An object of the invention is to more e?iciently
5 transmit pictures by wire or wireless means vfrom
fact, coupled with the fact that the emissivity is
not directly proportional to the illumination,
one station to another, so that a complete elec
trical image is formed in-a fraction of a second,
permitting the transmission of motion pictures
between stations.
Another object of this invention is to facilitate.
the scanning of scenes at a considerable distance
from the transmitting apparatus.
' I
The point of operation on the photocell char
acteristic curve is determined by the total re
- flected light falling on the cathode, and this point
may be‘changed and controlled by the insertion‘
of light ?ltersofsmokedglass and the like‘be
tween the object and the cathode of thecell. 10,
This action is analogous to the biasing of the
A further object of'the invention is to utilize
the non-linear characteristic of a photoelectric
15 cell for obtaining differential illuminating cur»
rents in accordance with the light and shade
intensities of objects.
forms the basis of this invention. -
control grid of a-vacuum tube.
With the; image on the cathode itself, a Search
ing ray of light, produced in any well known
manner, but preferably, in the form of an elec- 1;.5
trodynamic are along electrode rails in a mag
netic ?eld, may be employed for scanning the
A still further object of the invention is to in
crease the ef?ciency of scanning apparatus by re-,
20 generation.
in the electrical transmission‘of the images, of
objects or pictures thereof from a transmitting
station to a receiving station in the form of elec
trical impulses characterized by the light and
5 dark intensities of the objects or pictures, the
Such scanning systems are disclosed in
my co-pending. applications Ser. No. 397,826,
?led October '7, 1929 and. Ser. No. 450,025, ?led 20
May 5, 1930.
Since the intensity of the light of
the searching ray is substantially constant, varié
ations in the current output of the cell are ob
tained through the non-linear characteristic of
the photoelectric cell. For example, when the 25
common manner in which the impulses are ob
tained is the projection of a searching or scan~
scanning ray is projected upon the portion of the
hing ray'of light on the objects or pictures. The
varying intensities of the reflectedlight are in
30 tercepted by a photoelectric cell or plurality
light from the object originating from the sun or
, thereof, to effect the transformation into electri
cal vibrations, which are transmitted from station
It is well known that the intensity of light de~
creases rapidly with distance from the source.
t is obvious, therefore, that if objects are to be
successfully scanned in the usual manner from a
considerable distance, an extremely high power
light source is required in order to obtain a su?i
,19 cient variation‘ in the intensity of the reflected
light upon a photoelectric, cell positioned approx
imately the same distance from the object. Even
' with such a light source, this method is not desir
able, from the convenience standpoint.
In the present invention, a distant or near
scene is scanned by obtaining an image of the
scene upon the cathode of a photoelectric cell
focusing of the image on the cathode of thecell
50 will produce a steady total emission of electrons
to the anode of the cell, and produce a steady
electric current in the input circuit of the photo
electric current ampli?er. Although total emis
sion remains substantially constant, the emission
is not uniform over, the entire cathode, because
cell which is least illuminated by the re?ected
an arti?cial lighting'system, a certain increase'in
the steady value of ‘the photocell current is ob- 3O
tained. The amount of this increase is entirely
dependent upon the amount of light originally
falling upon this area. Now, ‘if the scanning ray
moves to another portion or unit area of the im
age having brighter illuminationpan increase'of .35
photocell current will occur, having a value
greater than that caused by the ray falling on
the ?rst portion. This variation in current in
accordance with the light and dark intensities of
the image will reproduce the image at a receiv- 40~
ing station.
The characteristic of a photocell is comparable
to the grid voltage-plate current characteristic
of a three element vacuum tube, that is, it has a
double in?ection. In the present system the 45
lower bend of this curve is employed similarly to
the portion used in a grid leak detector for radio
When the scanning ray falls on por
tions of the cathode having small illumination,
small increases in photoelectric current are ob‘- 50
tained, while proportionally larger increases 00
our from scanning the brighter portions of the
image.- This relation is the same as that found
whenan. object is directly scanned by the search
ing ray.
This invention also contemplates the impres
sion of a portion of the generated photoelectric
which, after ampli?cation, are transmitted to
cell currents after ampli?cation upon the scan
ning ray producing means to intensify the ray
Referring now to Fig. 3, a portion of a char
acteristic curve of the photoelectric cell is shown,
the co-ordinates of which are light intensity in
proportionally to the light and shade of the
image, thereby amplifying and emphasizing the
non-linear emission characteristic of the cell.
The details of the invention will be more fully
' understood. by. reference to the accompanying '
drawings, irrwhich:v
Figure 1 is a perspective diagrammatic ar
rangement of a single cathodeésingle anode
photoelectric cell scanning system;
Fig. 2 is a cross~sectional view of another em
15 bodiment of scanning apparatus, in which a dou
lumens and photoelectric cell current in micro
amperes. The complete curve may be found in
any treatise on photoelectric cells, and if car- .
ried to the saturation point, will be found to
have a second in?ection in the, reverse direction.
Only the lower portion of this curve is utilized
in the present invention, this portion being com
parablelto the lower inflection of the grid volt
age-plate current characteristic of a vacuum tube.
Of course, the upper bend can be employed in
‘ole anode tube is employed, the cathode of which
the same manner as in detection with vacuum
has a de?nite curvature.
tubeshaving a-positive bias.
Figs. 3, 4 and 5 are curves representing the op
receiving apparatus.
erating characteristics of the photoelectric cell.
Referring to Fig. 1 speci?cally, a photoelectric
cell is shown diagrammatically in the form of a
The cell has a cathode 5 and an anode
6, the cathode beingof an opaque material, coated
with a light sensitive material such as potassium
25 or the like, well known in the art, while the anode
is a metallic ring shown in the form of a square,
but which may have any con?guration. , These
elements of the tube which in practice are con
tained in an evacuated or gas ?lled transparent
envelope, are shown connected in the input cir
cuit of an amplifier system comprising a vacu
Assuming an im~
age has been projected on the cathode of a cell
of the character shown, a steady flow of cur~
rent will occur between the elements thereof, 20
depending upon the total amount of light re
ceived from the scene to be transmitted. On the
curve, the least illuminated area may be rep
resented by the point 3i which will produce a
certain amount of photoelectric cell current. An 25
other element of the cathode receiving the high
est illumination is shown by the point 32, pro
ducingv another value of photoelectric cell cur
rent. The integration over this curveprovides
the steady'current value of thecell output.
In Fig. 4, another representation of this phe
with a potential from a source 8, while the ele
ments in the tube are shunted by a resistance
nomenon of the tube is illustrated. The heavy
line 34 on the left hand side of the drawings rep
resents the cathode, while the heavy line 35 on
35 Q for varying the impedance of the input to the
vacuum tube 1. The vacuum tube is energized
the anode, the drawings being a cross-section
um tube 7.
The photoelectric cell is provided
from a ?lament battery 5 l and a plate potential
battery Hi. The output of the battery is con;
nected through output transformer £3 to an am
40 pli?er M, which in turn is connected to trans
mitting apparatus 45 for transmission of the
photoelectric cell currents. The transmission
may be either over an antenna system H or wire
conductors l8 chosen by the operation of a switch
45 E9.
Connected to the transmitter is also a scan
ning generator 22 for producing a scanning ray
the right hand side of the drawings represents 35
of these elements.
The varying density lines
represent the number of electrons ?owing from
particular points on the cathode, the drawings
illustrating the non-uniformity of emission from 40
the cathodes as the light is projected thereon in
different intensities. The total amount of cur
rent generated by the cell, however, is a substan
tially steady value in spite of any changing
scenes, the changing scenes causing only a re
distribution of activity.
In Fig. 5, these relations are shown by a curve
for a scanning screen 23. The impulses from
plotted between time and photoelectric cell cur
the scanning generator are transmitted along rent. The dotted line 3% represents thesteady
with the photoelectric cell currents for synchro . value of current obtained by the focussing of the
nizing the receiving screen with the transmitter. scene on the cathode, while the wavy line 3?
It is to be understood that any type of scan
is the variation in the photocell currentv caused
ning system which provides a sharp exploring by the scanning thereof by the scanning appa~
ray of substantially constant intensity, may be ratus. The addition of the scanning ray will
used to scan the image.
increase the photoelectric cell current, and a min 55
There isalso shown in Fig. l a camera 25 with
imum will always be above that of the steady
its pinhole 26, for producing a scanning beam value caused by the re?ected light from the
of light, and a focusing lens 28 which may be
adjusted to properly focus an object on the
Returning now to Fig. 3, which shows how
o'athode. A light intensity controlling screen the wavy line 31 of
5 is obtained, we may 60
is interposed between the lens 28 and the assume that the light intensity of the scanning
anode B, but the screen may also be placed be
ray is equal to‘ the distance a between the ver
tween the scene and the lens.
tical parallel lines. That is, the illumination of
An object positioned at O for instance, which all. unit areas of the cathode is increased by a
may be a near or far scene, may have light pro
consecutively by the ray passing over them.
iected upon it from either the sun or arti?cial
sources. A portion of this projected light is re
When the arc is projected, therefore, on a dark
?ected through the focusing lens 28, the screen
28, the anode 5 onto the photoelectric cell cath
5, as shown at I. This image is then scanned
by the ray of light produced by the screen 28
and projected through the pinhole 26 of the
camera 25.
Because of they non-linear char
acteristic of the cell, varying currents are set
75 up in the input circuit of the vacuum tube 1,
portion of the image on the cathode, the increase
in photoelectric cell current may be considered
as the distance between the ?rst set of horizon
tal lines I). As the ray shifts to a portion which 70
has abrighter illumination, for instance as shown
by the middle set of vertical lines, the increase
in photoelectric current will be that shown by
the distance between the middle set of horizon
tal lines 0. When the are again advances to a 75
still more illuminated portion of the‘ cathode,
the increase in photoelectric cell current is that
' shown by the distance d betweenthe upper set
of horizontal lines. It is seen, therefore, ‘that
although the scanning ray has a constant in
tensity, the increase in photoelectric cell cur
rent is dependent upon the illumination of the
cathode by the light re?ected from the scene.
As the ray is projected over the cathode in any
desired con?guration, it illuminates the light and
dark areas with light of constant intensity, but
produces a. variation in the photoelectric cell
output current, in accordance withthe light and
dark portions of the image on the cathode.
The operation of this circuit is identical with
that of a direct scanning system in which the
increase in photoelectric cell current is deter
mined by the intensity of the re?ected light from
a directly scanned object, that is, the lightpor
.20 tions of the object will re?ect morelight and
produce a higher value of photoelectric cell cur
rent. The present system, however, instead of
projecting the light to great distances with the
extreme loss in intensity through distance, has
25 a substantially constant scanning range with no
lossoi scanning power due to the ‘varying length
of the light projection paths. In- this way the
system is extremely efficient for the scanning of 1
or a singleitube with a double anode, as shown.
For instance, the grid ?ll is connected to the oath
ode 45 of the photoelectric cell, while the anode
M of the cell, is connected through a variable
inductance 6,! to an anode 62 of the vacuum tube.
Similarly, the anodeélé of the cell is connected
through a variableinductance 63 to the anode M
of- thevacuum ‘tube, ‘ A resistance 65 is connected
in shunt to these elements for controlling the
operation of the cell. A plate potential ‘66 for 10
the vacuum tube, supplies also the operating
voltage for photoelectric cell through the primary
of the output transformer 61, chokes 68 and 69,
in parallel, variable inductances BI and 63‘ in
parallel, anodes (it? and $5 in parallel, cathode 15
Q3, and grid (it. An increase in emission of the
cathode to either of the anode-s of the cell will
produce an increase in the voltage on the input
circuit of the tube, which will be transmitted
through the output transformer _61 to an ampli 29
?er ‘Hi.
The output circuit has a variable in
ductance ll connected therein which is employed
for feed-back purposes. The inductances, there
fore, El and 6t and ‘El may be used to produce
a certain amount of regeneration. The scanning 2.5
arc is supplied from a scanning generator 15
through conductors‘lt. The output of the am
pli?er ‘is is alsoconnected to conductors 176, for
distant scenes, and this e?iciency is maintained ' the purpose of increasing the intensity of the
arc asv the photoelectric, cell ‘currents are in 30
30 in the scanningof near objects. The direct scan—
ning of an image on an ordinary screen does
not produce the photocell current contrast values.
by‘ increasing the intensity of the scanning ray
in proportion to- the increase in photoelectric'cell
current. That is, should the current be consid
erably increased by the scanning ray falling on 3.5
as will the present system...
In Fig. 2 of the drawings, a cross section of a
television camera is illustrated, with its external
regeneration circuits. In this ?gure, a casing 40
encloses a photoelectric cell 4|, a scanning arc
screen 122 with respective lenses .43 and 44a. The
photoelectric cell 4| is shown with a curved cath
40 ode 46 and anodes 4,4 and 45, arrangedon oppo
site sides of the cathode, and conforming to the
curvature of the cathode. The cathode in this
cell is translucent, and will transmit light through
This action will produce regeneration -
a highly illuminated area of the cathode, this
increase will be augmented hythe‘substantially
simultaneous increase in the scanning ray in
tensity. When the ray falls on a less illuminated
area, 'the contrast will be much greater than 40
with the normal scanning ray.
The photoelectric cell currents and the are
producing currents are segregated by a ?lter
it as well as being able to hold the image of a
I? in the output circuit of the system. The output
scene projected thereon intercepting sufficient
light for this purpose. The advantage. of the
curved cathode is that the projection path of the
ray of light from the rails 41 of the scanning
terminals ‘it may be connected to transmission ap
paratus such as shown at H5 in Fig. l. With the
scanning generator a direct current source, it is
unnecessary to employ a ?lter.
system 42 is always a constant distance from the
cathode and image thereon. In this manner the
intensity of the normal light is maintained con
stant at the image. Thedouble anode arrange
ment of this system provides a more efficient
The above described television scanning system
is particularly adaptable to the transmission of 50
distant scenes, but it is also particularly e?icient
photocell, since the cathodeqmay be made‘ trans
cut image can be formed on the cathode of the
for the transmission of details of near objects.
By using a special focus lens, an extremely clear
55 lucent with active material on both sides thereof.
celLwhich when scanned by an arc of constant 55
intensity with regeneration, will produce espe
cially ?ne definition, in a reproduced image. In
the scanning ray of the screen 41 is projected on
cell currents caused by the varying length of pro 60
jection path for the scanning ray, such as exists
This arrangement is also advantageous from the
mechanical point of View. ,An object O is pro
jected on the left hand side of the cathode’, while
the right hand side.
The photoelectric cell is mounted on. an ad
justable stand 58, while the scanning apparatus
is mounted on a. similar stand 5|, the adjustment
of the elements of which is controlled by the
thumb locking screws 52 and 53, respectively.
The scanning apparatus is shown with a cooling
jacket having a ?uid passage 54 and heat dis
sipating material 55 such as steel wool and the
like, surrounding the jacket.
Heat conveying
70 fluids pass through the ?uid channel to maintain
the screen electrode rails ill’ at a constant tem
perature. A ?eld winding in series with the rail
electrodes ill is also cooled by the jacket system.
The external circuits of this system include a
.75 photoelectric cell ampli?er having either two tubes
this system there is no distortion in the photo
when objects are scanned directly.
The non-linear characteristic of a photoelec
tric cell is adaptable for other uses outside the art
of television, and the invention is to be limited 65
only by the scope of the appended claims.
What is claimed is:
1. In a television system, a light sensitive de
vice having a cathode, means for focusing an
optical image of a scene to be transmitted on said 70
cathode, and means for scanning with a ray of
light said optical image while it is focused on
said cathode.
2. In a television system, ‘a photoelectric cell,
an electrodynamic arc screen, an ampli?er for 75
the currents generated by said photoelectric cell,
and means for feeding a portion of said photo‘
electric cell currents to said are screen.
3. In a television system, a camera, a photo
electric cell having its cathode placed at the
14. In a television transmission system, a light
sensitive device having a cathode, means for
focusing re?ected light from a scene to be trans
focus of said camera, means for scanning an ob
mitted on said cathode of said device'to produce a
ject focused on said cathode with a light ray, and
de?nite electron emission, and means for simul~
means for transmitting the varying electric. cur
rents transmitted by said photoelectric cell.
taneously scanning with a ray of light an optical
4. In an electrical transmission system, a tele
vision’ camera, said camera including a light
sensitive device and a scanning screen, and means
for simultaneously focusing the light from said
scanning screen, and the re?ected light external
of said camera on said light sensitive device.
5. In an electrical transmission system, a
photoelectric cell, and an electrodynamic arc
V scanning screen for scanning said cell, said photo
electric cell having a curved cathode to maintain
20 the projection path of light from said scanning
screen constant for every position of said scan—
ning light.
- 6. In a television transmitting apparatus, a
photoelectric cell having a translucent cathode,
25 anodes positioned on opposite sides thereof, means
for scanning one side of said cathode with a
visible light beam, and means for focusing on the
other side of said cathode the scene to be trans~
, mitted over said television system.
7. In a television transmission apparatus, a
photoelectric cell, scanning means for scanning
one side of the cathode of said cell, means for
focusing an object to be transmitted on the other
side of said cathode, means for amplifying the
35 currents generated by said scanning means, and
means for impressing a portion of said generated
currents on the light producing means for said
scanning system.
ampli?er having its input connected to said
cathode and anode, means for focusing an image
on said cathode to generate a certain value of
current in said cell, and means for producing
45 variations in said current value, said means in—
cluding a constant light ray source.
9. An electrical generator system in accordance
with claim 8, in which said last mentioned means
comprises an electrodynamic are light scanning
50 system.
10. In
a television
image of said scene formed on said cathode by
said focused reflected light while said optical 10
image is on said cathode to cause actuation of said’
cathode approximately in accordance with the
square law.
15. In a television transmission system, a light
sensitive device, means for focusing the image of a
scene to be transmitted on said device, said image
generating electrons at a point on the charac
teristic curve of said device which is non-linear,
and means for scanning with a ray of light the
optical image of said scene while it is focused on
said device to increase and decrease the output
therefrom non-uniformly in unit areas during the
projection thereon of equal light intensities.
16. A television transmission system in ac
cordance with claim 15, in which said scanning
means comprises a self-luminous, self-propelling
electrical discharge.
17. The method of transforming the light
densities of the unit areas of an image into elec
trical currents proportional thereto with a light- ''
sensitive device, comprising combining the cur
rents produced by the light from‘the entire image
projected on said device with the current pro
duced by a unit area scanning beam scanning said
image, the total current being determined by the
light intensity-output current characteristic of
said device.
18. In a television system, a photosensitive de
8. In an electrical generator system, a photo
40 electric cell having a cathode and an anode, an
transmission system, a
photoelectric cell, means for focusing the re?ect
ed light from a scene to be transmitted on said cell
to produce a definiteelectron emission in said cell,
55 and means for Varying said emission in different
proportions in accordance with the variations in
light intensities on said cell, said means includ
ing a luminous electrical discharge source of con
stant intensity.
nels positioned adjacent said electrodes for hous
ing a circulatory heat conveyor.
11. In combination, an electronic device hav
ing an electron emissive surface activated by
light, means for projecting on said surface non
uniformly distributed light of a substantially con
stant value, and means for uniformly increasing
65 the light on consecutive unit areas of said surface.
12. A combination in accordance with claim 11,
in which said last mentioned means comprises a
television scanning system including an electro
dynamic discharge screen.
13. In a television system, a photoelectric cell,
a scanning device for generating activating light
for said cell, said device comprising an electro
dynamic arc in a magnetic ?eld electrodes for
determining the path of said arc, and means for
75 cooling said device, said means including chan
vice, means for projecting an optical image on
said device, means for simultaneously scanning 40
with a ray of light said optical image while it is
projected on said device to produce electrical
currents proportional to the light densities of the
unit areas of said image, the variations in said
currents being determined by the characteristic 45
of said device and means for biasing each unit
area of said device with light producing said
19. A method of television which comprises ?rst
energizing the photoelectric surface of a limited 50
area, then sensitizing the said photoelectric "sur
face with an image of a View, simultaneously
traversing said surface with a scanning beam of
strong illumination and causing the photoelectric
values to be impressed upon a transmitting
medium and repeating these steps in the trans
mission of each individual image.
20. In a television system, a light sensitive de
vice, means for projecting an optical image of an
object on said device, and means for scanning
with a ray of light said optical image while it is
projected on said device.
21. The method of transmissing images of ob
jects electrically with a light sensitive device,
comprising projecting an optical image of said ob 65
ject upon said device and scanning with a ray of
light said optical image while it is projected on
said light sensitive device.
22. The method of transmitting pictures of
objects electrically, comprising obtaining an opti 70
cal image of said object on the cathode of a
photoelectric cell, scanning with a ray of light
said optical image while it is obtained on said cell,
and transmitting the variations in current pro
duced in said cell by said scanning ray.
23. In a television system, a light sensitive de
vice, means for obtaining an optical image of an
object on said device, and means for scanning
with a ray of light said optical image While it is
5 obtained on said light sensitive device.
24. The method of transmitting images of ob
jects electrically with a light sensitive device,
comprising obtaining an optical image of said ob
ject upon said device and scanning with a ray
of light said optical image While it is obtained
on said light sensitive device.
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