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Патент USA US2403549

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July 9, 1946.
‘
2,403,549
W. J. POCH
MODULATION SYSTEM FOR TELEVISION
Filed April 20, 1942. _
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Patented July 9, v1946
2,403,549 _ .
UNITED. STATES PATENT OFFICE
4 2,403,549
MODULATION SYSTEM ron TELEVISION
Waldemar J. Pooh, Moorestown, N. .I., assignor
to Radio Corporation of America, a corporation ‘
of Delaware
Application April 20, 1942, Serial No. 439,643
.5 Claims. (01. 178-'7.2)_
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1
2
My invention relates‘ to modulation systems
and particularly to modulation systems for tele
cated at 15 which isv supplied through a resistor
vision transmitters.
In portable television‘ equipment one of the
problems is to obtain satisfactory synchronizing
plate modulated by horizontal'and vertical syn
pulse generator l8 over a conductor I9 to an am
' signal output from a transmitter with the min- v
pli?er tube 2| which preferably is D.-C. coupled
imum weight of equipment. An object of the
present- invention is to provide an improved
means for modulating a radio transmitter by pic
Hi from a pickup tube and ampli?er I1, and itls
chronizing pulses supplied from a synchronizing
to an ampli?er tube 22.
Horizontal synchroniz
ing pulses are indicated at 20. As will be ex
plained below, the synchronizing pulses appear
ture signals and synchronizing pulses. Another i0 across a. cathode resistor 23 of the ampli?er tube
object of the invention is to provide an improved
‘system for modulating a carrier wave by a mix
ture of large amplitude pulses and smaller am
plitude signals.
22 and are applied with positive polarity to the
screen grids and plates of tubes l3 and It to in
crease their power output during the occurrence
of each synchronizing pulse. In the speci?c ex;
In one of the preferred embodiments of the 15 ample illustrated, the synchronizing pulses are
invention, as applied to a portable television
applied to the control grids of tubes l3 and I‘
transmitter in which a high'frequency carrier
along with the picture signal but this is not nec- '
wave is amplitude modulated both by picture‘ sig
essary as all synchronizing signals may be trans
nals and by horizontal and vertical synchronizing
mitted by the plate modulation.
.
‘
pulses, the picture signal modulation is obtained 20 The feature of amplitude modulating the grid
‘by grid modulation while' the synchronizing
pulse modulation is obtained by plate and/or
with picture signals and amplitude modulating
the plate with synchronizing pulses has two im
screen grid modulation. A modulation system of . portant advantages. First, the peaks of the syn
this character is described and claimed ina co
chronizing pulses cannot be clipped as a result of
pending application, Ser. No. 436,406, ?led March 25 the picture signal increasing in amplitudev enough
'27,.1942, in the name of Henry N. Kozanowski,
to move the “black” side of the signal into and
and entitled Modulation system of television. In
possiblybeyond the upper knee of the curve ob
accordance with my invention, I include a uni
tained by plotting power ampli?er grid voltage
lateral conducting device such as a diode in the
against radio frequency output current. It may
plate modulating circuit. The diode provides the 30 be noted that since the system shown in Fig. 1v
necessary impedance in the plate circuit for plate
employs A.-C. transmission (there being no D.-C.
modulation during the occurrence of a pulse but
it presents a low impedance for grid modulation
, during the occurrence of theinterspersed picture
signals.
.
_
insertion) the "black” side‘ of the picture signals ’
may sometimes-by moved beyond the upper knee
of the curve also by an increase in the picture
35 background component, that is, by ‘the overall
The invention will be better understood from
picture becoming lighter in tone. Secondly,
the following description in connection with the
more synchronizing power can be obtained from
accompanying drawing, in which Fig. 1 is a cir
given power ampli?er tubes since the synchron-'
cuit diagram of a‘ television transmitter embody
izing pulses may drive the plate voltages momen
ing my invention, and Fig. 2 is a circuit diagram 40 tarily beyond any plate voltage that can be ap
of another embodiment of the invention. In the
plied to the tubes continuously without damaging .
several ?gures, corresponding parts are indicated
them,
by the same reference characters.
'
The use of plate or screen grid modulation in
In Fig. 1 the invention is shown applied to ,a
a system such as the one described in the above
television transmitter comprising a power ampli 45 mentioned Kozanowski application will degener
her It having a tuned grid circuit II and a tuned
ate the'grld modulation to a certain extent be
anode or plate circuit 12. The ampli?er ill in
cause of the resistance required in the plate cir
eludes vacuum' tubes l3 and I‘, each having a _
cult of the power ampli?er. According to my
cathode, a control grid, a screen grid, and an
invention, I avoid this undesirable e?'ect by uti
anode or plate. 'A carrier wave is applied to the 50 lizing a unilateral conductingdevice such as a
tuned grid circuit H as indicated. The ampli?er
'diode 26 so connected that there-is the neces
output may be suppliedirom the tuned anode
sary resistance in the plate circuit during plate ,
circuit l2 to an antenna (not shown).
‘
modulation but substantially no resistance
therein during grid modulation. Diode 2s 1s
In accordance with my invention the‘ carrier
wave is grid modulated by picture signal indi 55 connected between the anodeol' ampli?er tube 22
2,403,540
3
4
.
.
n will be evident that we diode a a non
conducting during the application of a synchro-v
nizing pulse since its cathode is driven beyond
and the midpoint of the inductor in the tuned
plate circuit l2, the diode plate being connected
through a resistor 21 to the anode 0! tube 22,
and the diode cathode being connected to said
midpoint through a resistor 28. Resistors 21 and
the positive potential of the diode plate. There- I
tore, the diode 26 provides the necessary'imped
ance in the power ampli?er plate circuit for plate
modulation. Between synchronizing pulses. and
28 have small resistance and are included in the
circuit merely to suppress parasitic oscillations.
Condensers.“ and“ are radio frequency and.
during grid modulation by the picture signal,
however, the diode 28 is conducting whereby the
A voltagesource such as a battery 3| supplies 10 impedance of the power ampli?er plate circuit
anode voltage to the tube 22 through a con- . is very low. It follows that any undesirable de-'
generative e?'ect during the picture modulation
ductor 22 and anode, voltage to the tube -2|
intervals is avoided. In the particular example
through a coupling resistor 34. -It also Supplies
illustrated, the power ampli?er tubes H and H
screen grid voltageto the power ampli?er tubes
l3 and I4 through resistors 28 and II. The ca 1.5 are screen grid tubes but it should be understood
that they may be triodes if properly neutralized.
paci-tor 28 across battery 3| may be provided for
Fig. 2 illustrates an embodiment of the inven
bypassing the video and synchronizing pulse fre—
vvideo frequency bypass condensers, respectively.
' tion in which a triode ‘I is substituted for the
quencies.
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_
,
cathode resistor 23 of Fig. 1.
Synchronizing
A capacitor 4| connected between the cathode
of tube 22 and the cathode of the diode 26 is an 20 pulses are applied with negative polarity'to the
grid‘of tube 5| irom a cathode resistor 52 of'the
important element of.‘ my improved circuit be
ampli?er tube 2|. It will be evident that the op
cause its voltage is added in series to the voltage
eration of this embodiment is the same as pre
of source 3| in response to the occurrence of a
viously described, the di?erence being that'in
Fig. l the cathode resistor 23 is eilectively in
shunt to the battery 3| during the application of
synchronizing pulse, and this increased voltage
is applied to the screen grids and anodes oi the
power ampli?er tubes l3 and II. This action will
be understood by following through the circuit
operation as follows: The synchronizing pulses
._ a synchronizing pulse and will draw some current
whereas in Fig. 2 the'tube 5| has high?anode- '
are applied 'with, negative polarity to-the grid of > 1
cathode impedance during,this time and draws
the tube 2|. Between pulses, therefore, this grid ' 30 little, if any, battery current.
is at about cathode potential and the potential
at the anode of the tube 2| is at about its mini
mum value. This minimum voltage applied to
the control grid of tube 22 biases the tube close
to plate current cut-‘oil’ since its cathode is above
ground potential and positive with respect to the
control grid due to ‘plate current ._ ?ow (even
" though a small amount) through the cathode
resistor 23.
Because of this,
the circuit of Fig. v2 may be preferred when the
voltage supply source ll is a‘ battery and it is im
portant to keep the current drain to a minimum.
It should be understood that the invention is
I not limited to the particular circuits illustrated.
For example, the D.-O. connection between the
tubes 2| and 22 in Fig. 1 may be replaced by
‘A.-C. coupling. On the drawing the values of.
.certain circuit elements have been indicated.
Thus, between synchronizing pulses the anode 40 merely by way of example,v in ohms, microfarads,
cathode impedance of tube 22 is high and the . and micro-microfarads.
I claim as my invention:
' capacitor ll is charged substantially to the volt
1. In a television transmitter, means for pro
age of the plate supply 3|. This charge is ac
ducing a carrier wave, an ampli?er connected to
quired through a path that may be traced from
the positive ‘terminal of battery 3| through re 45 amplify said carrier wave, said ampli?er having
a cathode, a control grid and a third electrode,
sister 21, diodell‘ and a conductor 02 to one side
a source of picture signals and synchronizing sig
of capacitor-l | , and from the other side of capac
nals, means for appwing said picture signals to
itor 4| through cathode resistor 23 to ground and
said grid to amplitude modulate said carrier
to the negative terminal of source 2|.
wave by picture signals, and meansfor applying
Upon the occurrence of a synchronizing pulse,
said synchronizing-signals to said third electrode
the anode-cathode impedance of tube 22 is re
to amplitude modulate said carrier wave by syn
duced to a comparatively low value whereby the
chronizing
signals, said last means including a
time 22 functions as a switch to connect the lower
unilateral conducting device and means for so
or negative side of capacitor 4| to the positive’
connecting it as'to provide'external impedance
terminal of the battery 2|.. Since the capacitor 4|
for said third electrode in ‘response to and for
is or large capacity, any charge lost during the
the duration of each synchronizing signal and to
application of a synchronizing pulse does not
provide a comparatively small external imped
lower the voltage thereacross very much. The
result of the above switching action is that there
is applied to the cathode of diode 28 and to the.
anodes and screen grids of power ampli?er tubes
l2 and I‘ a voltage that is, in an ideal circuit.
double the voltage of source 3|. This increased
voltage at the positive'side of capacitor ll is
impressed upon the power ampli?er anodes
ance therefor during the occurrence of picture
signals.
cuit l2. ‘It is impressed upon the power ampli;
?er screen grids through a coupling capacitor 48
and the resistor 21. Consequently, the power out
put of'tubes I3 and I4 is increased upon the oc 70
wave is amplitude modulated by these pulses.
This momentary additional power is actually ob
tained from the large capacitor 4| which is star
in: energy between pulses.-
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ducing a carrier wave, an ampli?er connected to
' amplify said carrier wave, said ampli?er having
a cathode. a control grid and alplate, a source of
through resistor 28 and the inductor of tuned cir- '
' currence of synchronizing .pulses,_i. e. the carrier
'
. 2. In a television transmitter, means for pro
picture signals and synchronizing signals, means
for applying said picture signals to said grid ‘to
amplitude modulate said carrier wave by picture
signals, and means for applying saidsynchroniz
'ing signals to said plate to amplitude modulatev
said carrier wave by synchronizing signals, said
last means including a unilateral conducting de
vice and means for so‘ connecting it as to pro
vide external plate impedance for said ampli?er
in response to and for the duration of each syn
chronizing signal and to provide a comparative
2,403,549 .
5
ly small external plate’ impedance therefor dur
a direction to conduct current to said electrode, a
capacitor and switching means connected in se
ries with each other, said series combination be- ‘
ing connected across said device.
ing the occurrence of picture signals.
3._ In a television transmitter,- means for pro
ducing a carrier wave, an ampli?er connected to
amplify said carrier wave, said ampli?er having
5. In a television transmitter, means for pro- _'
a cathode, a control grid and a ‘third electrode,
a source of picture signals and synchronizing sig
ducing a carrier wave, an‘ ampli?er connected to
nals', means for applying said picture signals to
a a cathode, a control grid and a third electrode,
' a source of picture signals and synchronizing sig
said fgrid to amplitude modulate said carrier wave
amplify said carrier wave, said ampli?er having
by picture signals, and means for applying said 3% ‘rials, means for applying said picture signals to
syndhronizing signals to said third electrode to
amplitude modulate said carrier wave .by syn
chronizing signals, said last means including a
' diode and means for so connecting it as to pro
vide external impedance for said third electrode
in response to and for the duration of each syn
chronizing signal and to provide a comparative
ly small external impedance therefor during the '
occurrence of picture signals.
4. Ina television transmitter, means for pro
ducing a carrier wave, an ampli?er connected to
amplify said carrier wave, siaid ampli?er having
-a cathode,,a control grid a'nd'a third electrode,
a source of picture signals and synchronizing sig
nals, means for applying ‘said picture signals to
said grid to amplitude‘ modulate said carrier wave
by. picture signals, and means for applying said
synchronizing signals to said third electrode to
amplitude modulate said carrier wave by syn
vchronizing signals, .said last means including a so
source of positive potential for said third elec
trode, a unilateral-conducting device connectedv
‘between said source and said third electrode in
said grid to amplitude modulate said carrier Wave
by picture signals, and means for applying said
Synchronizing ‘signals to said third electrode to
amplitude modulate said carrier wave by syn~_
chronizing signals, said last means including a
source '01’ positive potential forsaid ‘third elec
trode, a unilateral conducting device connected
betweensaid source and said third electrode in
a direction to conduct current to said electrode,
a capacitor and an electric discharge tube con
nected in series with each other, said electric dis
charge tube having a control electrode, said se~
ries combination being connected across said vde
vice whereby said electric discharge tube con
nects the voltage appearing across said capacitor
in series-aiding relation with said source of po~
tential in response to the application of said syn
chronizing pulses to said, control electrode with
positive polarity to increase the positive p0ten~
tial on said third electrode of the ampli?er tube
during the occurrence of a synchronizing pulse.
WALDEMAR J. POCH,
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