close

Вход

Забыли?

вход по аккаунту

?

Патент USA US2109618

код для вставки
March 1, 1938.
R. s. HOLMES
TELEVISION SYSTEM
Filed Deo. l, 1935
' 2,109,618v
2,109,618
Patented Mar. 1, 1938
UNITED STATES -PATENT OFFICE
2,109,618
TELEVISION SYSTEM
Ralph S. Holmes, Haddonñeld, N. J., assignor to
Radio Corporation of America, a corporation
of Delaware
Application December l, 1933, Serial No. 700,478
7 Claims.
i)
My invention relates to improvements in tele
vision systems.
In communication by television, wherein pic
ture signals and synchronizing signals are inter
cepted and supplied to some form of scanning
apparatus which develops an image of the view at
a particular transmitting station, there occur
variations over a substantial range in the ampli
tude or level of the received signals. These varia
il) tions occur, for example, upon tuning the receiv
ing apparatus for reception from different trans
mitting stations of different power and/or dif
ferent distances from the receiving apparatus.
Such variations, also, are attributed to atmos
' pheric disturbances and the phenomenon com
monly referred to as “fading”.
The eiïect of the variations referred to is mani
fested at the receiver by wide variations in the
overall brilliancy of the received picture and,
20 possibly, by overloading of the ampliilers.
With the foregoing in mind, it is one of the
objects of my invention to provide an improved
television system wherein provision is made for
automatic control or adjustment of the same in
vision receiving system including a preferred em
bodiment of my invention;
Fig. 2 is a graphical illustration of the principle
of operation in Fig. 1;
Fig. 3 is a diagrammatic View of an amplifier
stage; and
Fig. 4 is a diagrammatic view, showing a modi
iication of the system in Fig. 1.
With reference to Fig. 1, the numeral III desig
nates scanning apparatus for developing an im
age of the transmitted subject. This apparatus
is shown as being in the form òf a cathode ray
tube I2 provided with a gun I4 for developing a
ray I6 o! electrons and directing the same at a
iluorescent screen I8 on which the transmitted
picture is reproduced. Assuming that there are
to be 24 frames a second, each frame to have 180
lines horizontally, a plurality of electromagnetic
coils 20 are provided, that operate to deilect the
ray 43,20 times a second horizontally, and a plu 20
rality of electromagnetic coils 22 that operate to
deflect the ray simultaneously 24 times a second
vertically. For this purpose, a suitable generator
24 operates to develop a saw-tooth current wave
25 such manner that the amplitude or level of the
at 4320 cycles and to cause this wave to pass
picture and synchronizing signals supplied to the
scanning apparatus is maintained substantially
through the coils 20, while a suitable generator
constant.
Other objects and advantagesv will hereinafter
30
appear.
..
In accordance with my invention, the inter
26 operates to develop a saw-tooth current wave
at 24 cycles and to cause this wave to pass
through the coils 22.
Operating action of the scanning apparatus is 30
maintained in synchronism with that at f the
mitted together on a carrier wave as modulations
transmitter by synchronizing or control signals
eñective to drive the generators 24 and 26, as will
thereof, are passed through an electrical channel
hereinafter more fully appear.
cepted picture and synchronizing signals, trans
35 which supplies the scanning apparatus. The syn
chronizing signals are taken from this channel.
at a point therein where they are of suillcient
amplitude and of the right polarity, and are
rectiñed to develop an electrical potential the
40 amplitude of which varies proportionally with
occurring variations in the effective amplitude of
the synchronizing signals. The electrical poten
tial so developed is applied to one or more control
circuits in the electrical receiving channel, and
45 is effective to decrease the sensitivity of the lat
ter when the signal level tends to rise and to in
crease such sensitivity when the signal level tends
to drop.
My invention resides in the improved system
50 and method of operation of the character here
'inafter described and claimed.
For the purpose ol' illustrating my invention,
an embodiment thereof is shown in the drawing,
wherein
Figure 1 is a diagrammatic view of a tele
,
._
With regard to the various details of construc
tion in Fig. 1, these are assumed to be comparable
to those disclosed in the copending application
by Arthur W. Vance, filed June 17, 1931 and
bearing Serial No. 544,959.
For the purpose of reproducing the transmitted
picture on the screen I8, the picture signals are
applied to a control grid 28 forming part of the
gun I4, whereby the intensity of the ray I6 is
made tovary directly proportionally with occur
ring variations in the picture signals. A source 45
29 of anode potential is provided, and adjustment
of potentiometer 30 determines the positive po
tential applied to the ñrst anode 32.
For the purpose of illustration, it shall be as
sumed that at the transmitter the object or pic 50
ture is scanned to cause variation of current in `
the output circuit of some form of photosensitive
apparatus, whereby picture signals in the form of
a current wave are developed, as indicated at 34
in Fig. 2. Scanning action at the transmitter is
~ 2
2,109,618
the same as that at the receiverí- That is, the
object is scanned 24 times a second, and each
during return deflection thereof in the horizontal
and vertical directions.
scanning is made along 180 horizontal lines.
For the purpose of providing for the automatic
During about ninety per cent of each line control referred to above, the signal wave, as
period, the picture signals are developed, the am
represented in Fig. 2, is supplied by the connec
plitude at any instant of the picture current from tion 56 to the grid circuit of a plate circuit de
the axis 36 being directly proportional to theI tector 60. 'I'he peak amplitude :t of the syn
light intensity at that instant at the correspond
chronizing signals is a measure of, or is propor
ing elemental area of the object being scanned. tional to the strength of the incoming signals.
During the remaining period t of each line This condition is utilized to vary the plate cur
period, a synchronizing signal or impulse, indi
rent of the tube 60 automatically and substan
cated at 38 in Fig. 2, is developed by suitable ap
tially proportional to variations in the signal
I paratus operating independently of the appara
tus for developing the picture signals but syn
15
chronous with it.
'I'he synchronizing signals,
therefore, occur at the rate of 4320 a second,
and during the periods t, when there are no plc
ture signals. 'There are also developed, with the
synchronizing signals, other control signals, in
20 dicated at 40 in Fig. 2, where are termed framing
ring“ variations in the amplitude :c of the syn
chronizing signals.
'I’hat is, the anode end of
the resistor becomes more negative with an in-l
crease in .'c, and when :c decreases it becomes 20
correspondingly less negative. The electrical
potential so developed is applied to the grid cir
tially greater duration than the latter. At the
transmitter, also, the connections and operating
action are such that the polarity of the picture
signals, representative of conditions of light at
the transmitted subject, is opposite to the po
diate frequency ampliñer 48, as indicated by the
larity of the synchronizing and framing signals,
The picture signals and the synchronizing and
framing signals, transmitted together on a car
rier Wave as modulations thereof, are intercepted
by an electrical channel A, having at'its input
end aradio-frequency, alternating current am
plifier 42.
'I'he incoming lcarrier wave is demodulated to
a lower, intermediate frequency by a detector 44
and an associated local oscillator 46. The beat
40 wave, at the intermediate frequency, is amplified
by an intermediate frequency amplifier 48. 'I'he
beat wave is then rectified by a second detector
50 at the output end of the channel A, to obtain
the signal wave which is amplified by a low fre
45 quency amplifier 52 supplied from the second
detector.
y
In the output connection 54 from the amplifier
52, the signal wave and the polarities are as rep
resented in Fig. 2, with the synchronizing signals
in the
The
ate to
tively.
“black” direction and of positive polarity.
synchronizing and framing signals oper
drive the generators 24 and 26, respec
The generator 24-begins a new cycle of
its operation with the occurrence of each syn
chronizing signal. The generator 26, in like man
ner, begins a new cycle of its operation upon the
occurrence of each framing signal, and this gen
erator is so constructed and adjusted that it will
not respond to the synchronizing signals which
60 are of substantially shorter duration than the
framing signals.
The construction and adjustment of the gen
erators 24 and 26 is such that they are not af
65
electrical potential is developed whose amplitude 15
varies substantially proportionally with occur
signals and occur at the rate of 24 a second.
« The framing signals have the same amplitude
as the synchronizing signals, but are of substan
30 as indicated in Fig. 2.
50
strength. The result is that across a resistor 59
in the output or plate circuit of the tube 60, an
fected by the peak picture signals, but only by
the control signals of greater amplitude.
'I'he signal wave, as represented in Fig»- 2, is
applied by the connection 56 to the input of the
picture signal circuit 58. From the output of this
circuit, the- picture signals representative of con
70 ditions of light on the transmitted subject are
of positive polarity, and the synchronizing and
framing signals are of negative polarity. 'I'hese
signals are applied as indicated to the grid 28 of
the tube I2. 'I'he amplitude of these signals is
75 sufficiently high to completely cut 01T the ray I6
cuit of one or more of the stages of the interme
connections 64 and as shown in Fig. 3. As the
electrical potential becomes more negative, the
sensitivity of the electrical channel is decreased
correspondingly, and as the potential becomes
less negative, the sensitivity of the channel is
increased correspondingly. In this manner, the 30
level of the signals applied to the scanning appa
ratus I 0 is maintained substantially constant.
For the same purpose, the negative control po
tential developed in the plate circuit of the tube
60 may be applied to the grid circuit of one or 35
more stages of the radio frequency amplifier 42,
as indicated by the broken lines 66.
'
For the purpose of normally biasing the grids
of the controlled tubes to the best operating po
tential, a potential source 61 is provided, the 40
positive terminal of which is connected to ground
and the negative terminal of which is connected
to the cathode end of the output resistor 56.
By adjusting the bias applied to the grid of
the tube 60 from a source 68 the signal amplitude 45
at which the control becomes effective may be
determined.
In the modification shown in Fig. 4, the pic
ture and synchronizing signals are fed directly
to the picture signal circuit 58 from the low fre 50
quency amplifier 52, as in Fig. 1. For the pur
pose of the automatic control action, however,
the signals, as represented in Fig. 2, are first
taken from the low frequency amplifier 52 and
passed through an auxiliary amplifier 1l of a 55
conventional design to pass only the synchroniz
ing and framing signals in Fig. 2, rejecting the
picture signals of opposite polarity. The ampli
iler 10 supplies a suitable form of separating cir
cuit 12 which operates to separate the synchro
60
nizing and framing signals, so that in the out
put connection 14 from this circuit there will
appear only the synchronizing signals, and in
the output connection 16 there will appear only
the framing signals. The generator 24 is, there
fore, supplied only with synchronizing signals by
the connection 14, andthe generator 26 is sup
plied only with framing signals by the connec
tion 16.
The control signals for the input circuit of the 70
tube 60 can be supplied from the connection 18,
or from the connection 80, or from either of the
connections 14 and 16. In doing this, it will be
understood that the conditions of polarity must 75
2,109,618
be correct so that the desired control of sensitivity
of the channel A is obtained.
In lieu of the tube 80, it will be understood that
other known devices, such as a diode or a grid
leak rectiñer, can be used for the same purpose,
in which case consideration will be given for the
correct conditions of polarity of the signals sup
plied to the rectiñer device, as will be well under
stood.
10
'
From the foregoing, it will be seen that I have
provided an improved'television system wherein
the receiving apparatus is controlled automatical
ly to maintain the level of the picture and con
trol signals substantially constant irrespective of
15 occurringr atmospheric disturbances, tuning from
one station to another, and the occurrence of any
electrical effects which might tend to cause this
level to vary, and that for this purpose the syn
chronizing signals are used.
While but one embodiment of my invention has
been disclosed, it will be understood that various
modiñcations are possible without departing from
3
said channel comprising an amplifier at the input
end thereof, a detector supplied from said am
plifler, a second amplifier supplied from said de
tector, and a second detector supplied from said
second amplifier; a third amplifier supplied from
said second detector and operating to supply pic
ture and synchronizing signals directly to said ap
paratus under conditions such that the picture
signals representative of conditions of light at the
transmitted subject are of opposite polarity both 10
to the synchronizing signals and to the picture
signals representative of conditions of shade at
the transmitted subject, means supplied from said
third amplifier and operating to develop an elec
trical potential of negative polarity which be
comes more negative upon an increase in‘ the ef
fective amplitude of the synchronizing signals
and which becomes less negative upon a decrease
in such amplitude, and connecting means for ap
plying such electrical potential to at least one 20
control circuit in said channel effective to vary
the sensitivity of the latten»
the spirit of my invention or the scope of the
4. In a television receiving system, a cathode
~ ray tube for developing an image of the trans
claims.
mitted subject and provided with a screen and 25
I claim as my invention: '
25
1. In a television receiving system, apparatus with means for developing a ray of electrons
for developing an image of the transmitted sub
and directing the ray at said screen, means for
ject, an electrical channel for intercepting pic
causing the ray to scan a given area of said screen
ture signals and synchronizing signals trans
30 mitted together on a carrier wave as modulations
thereof, a rectifier at the output end of said chan
nel, an amplifier supplied from said rectifier and
operating to supply said apparatus directly with
picture signals and synchronizing signals, the
35 picture signals representative of conditions of
light at the transmitted subject being of opposite
polarity both to the synchronizing signals and to
the picture signals representative of conditions of
shade at the transmitted subject, means supplied
40 from said amplifier for developing an electrical
potential whose amplitude variesin response to
and in accordance with occurring variations in the
effective amplitude of the synchronizing signals,
and connecting means for applying such elec
45 trical potential to an operating circuit in said
channel effective to control the sensitivity of said
channel in accordance with occurring variations
in amplitude of the applied potential.
I
2. In the art of television, the method of op
50
eration Which comprises transmitting picture sig
nals and synchronizing signals together on a
carrier wave as modulations thereof and under
conditions such that the picture signals repre
sentative of conditions of light at the transmitted
subject are of opposite polarity both to the syn
55
chronizing signals and to the picture signals rep
resentative of conditions of shade at the trans
mitted subject, utilizing the received synchroniz
ing signals to develop an electrical potential
whose amplitude varies in response to and in ac
cordance with occurring variations in the effec
tive amplitude of the synchronizing signals, and
applying the developed electrical potential to the
receiving apparatus to vary the sensitivity thereof
in the sense that an increase in the amplitude
of the received synchronizing signals causes a
decrease in the sensitivity of said apparatus and
a decrease in the amplitude of the received syn
chronizing signals causes an increase in the sen
70 sitivity of said apparatus.
3. In a television receiving system, apparatus
for developing an image of the transmitted sub
ject, an electrical channel for intercepting picture
signals and synchronizing signals transmitted to
gether on a carrier wave as modulations thereof;
and comprising means for deflecting the ray in a
given direction at a given frequency, an elec
30
trical channel for intercepting picture signals and
control signals transmitted together on a carrier
Wave as modulations thereof, means supplied with
picture signals from said channel and operating
to vary the intensity of said ray in accordance 35
with occurring variations in such signals, said
ray-deflecting means being supplied with the
_control signals from said channel and being
maintained thereby in operation at said fre
quency, means supplied from said channel with 40
an electrical wave comprising the picture and
control signals for developing an electrical effect
which becomes more negative in response to an
increase in the effective amplitude of the control
signals and which becomes less negative in re 45
sponse to a decrease in such amplitude, and con
necting means for applying such electrical effect
to at least one control circuit in said channel ef
fective to vary the sensitivity of the latter.
5. In a television receiving system, a cathode 50
ray tube for developing an image of the trans
mitted subject and provided with a screen and
with means for developing a ray of electrons and
directing the ray at said screen, means for caus
ing the ray to scan a given area of said screen 55
and comprising means for deñecting the ray in
a given direction at a given frequency, an elec
trode for Varying the intensity of the ray, an
electrical channel for intercepting picture sig
nals and control signals transmitted together on 60
a carrier wave as modulations thereof; said chan
nel comprising an amplifier at the input end
thereof, a detector supplied from said amplifier.
a second amplifier supplied from said detector,
and a second detector supplied from said second 65
amplifier; a third amplifier supplied from said
second detector and operating to supply the pic
ture and control signals to said electrode under
conditions such that the picture signals repre
sentative of conditions of light at the transmitted 70
subject are of opposite polarity both to the con
trol signals and to the picture signals represen
tative of conditions of shade at the transmitted
subject, means supplied from said third ampli
ñer and operating to develop an electrical eiîect 75
4
2,109,618 -
which becomes more negative upon an increase
in the effective amplitude of the control signals
and which becomes less negative upon a decrease
in such amplitude, and connecting means for
applying such electrical eiîect to at least one
control circuit in said channel eiïective to vary
the sensitivity of the latter.
for maintaining the scanning at the receiver' in
synchronism with the scanning at the transmit
ter.
7. In a. television system of the type in which
picture signals and synchronizing signals are 5.
transmitted as a composite signal and in which
_
the picture signal voltage representative of con
ditions of light is of opposite polarity to the
a view is scanned at the transmitter and a screen synchronizing signal voltage with respect to the
is scanned at the receiver and in which picture `alternating current axis of said composite sig 10
signals and synchronizing signals are transmitted nal, a receiver comprising a signal channel in
6. In` a television system ofthe type wherein
as a composite signal and in which the picture
signal voltage representative of conditions of
light is of opposite polarity to the synchronizing
l 5 signal voltage with respect to the alternating cur
rent axis of said composite signal, a receiver
comprising an electrical discharge device having
a control electrode, means for deriving a uni
directional control voltage from` said composite
2 0 signal which voltage varies substantially in ac
cordance with the amplitude of said synchro
nizing signals as measured from said axis, means
for applying said control voltage to said control
electrode whereby the operation of said electric
discharge device iscontrolled in accordance with
rthe amplitude of said synchronizing signals, and
means for utilizing said synchronizing signals
cluding an ampliñer for amplifying a carrier
modulated by said composite signal and a detec
tor located at a later point in said channel for
reproducing said composite signal, said ampli 15
iler including a gain control means, means for
deriving a uni-directional control voltage from>
said reproduced composite signal which voltage
varies substantially in accordance with the am
plitude of said synchronizing signals as measured 20
from said axis, and means for appplying said
control voltage to said gain control means in
such direction that the gain of said ampliñer
is decreased in response to van increase in the
amplitude of said synchronizing signals as meas 25
ured from said axis.
~
'
`
RALPH S. HOLMES.
Документ
Категория
Без категории
Просмотров
0
Размер файла
608 Кб
Теги
1/--страниц
Пожаловаться на содержимое документа