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Sept. 17, 1946.
Filed NOV. 18, 1943
mi .LA
Patented Sept. 17, 1946
Clyde E. Hallmark, Fort Wayne, Ind., assigner to
Farnsworth Television andRadio Corporation,
a corporation of Delaware
Application November 18, 1943, Serial No. 510,759
4 Claims.
(Cl. 178-7.2)
This invention relates :to frequency generators
and particularly to scanning frequency gener
ators for television systems.
Where it is desired `to control the frequency of
an oscillator automatically, it is customary to
use a so-called LC type of oscillator for 4the rea
son that a reactance tube may be employed as
In television systems it is common practice to
generate the scanning frequency voltages in such
the frequency varying means. Howeverll it fre
quently is desirable to use a Slo-called RC type of
a manner that the frequencies of these voltages
are maintained in a predetermined relationship
oscillator but, a device of this character is not
with a standardizing frequency. It generally is
susceptible of automatic frequency control by
convenient to utilize as the standardizing fre
means of a conventional reactance tube.
quency a 60 cycle alternating current derived 10
Another object of th'e invention is to provide a
from a commercial power source. According to
novel‘automatic frequency control for an RC type
the present RMA standards video signals are
of oscillation generator.
transmitted at the rate of 30 frames per second.
In accordance with the `present invention there
Each frame comprises an odd number of scan
is provideda means for producing oscillations of
ning lines and, where a 2 to 1 interlaced Scanning
a’distortedwave form at a submultiple frequency
pattern is used, th'e field scanning frequency is
of the standardizing source. The distorted wave
60 cycles per second.
form contains a number of harmonics of the sub
The scanning frequencies usually are derived
multiple frequency, one of which is nominally
from an oscillator which is operated either at a
equal to Vthe frequency of the standardizing
high or a low frequency. In the case of a low 20 source. This harmonic and the standardizing
frequency oscillator its frequency ordinarily is
frequency are compared'to develop an automatic
60 cycles per second and its output voltage is
frequency control `voltage for employment in
multiplied in frequency rto twice the line scan
connection with the oscillator.
ning frequency. Such an expedient is necessary
The form :of oscillation generator utilized com
for the reason that the line scanning frequency 25 prises a vacuum tube having the output and in
for an odd number of scanning lines is not an
put circuits thereof coupled by a phase shifting
even harmonic of the 60 cycle oscillator fre
network for the feedback of output circuit energy
quency When a 2 to 1 interlaced scanning pattern
to the input circuit. The network comprises a
is used. 'I'he line scanning frequency is derived
plurality of meshes, each including resistance
from the voltage having twice the line scanning 30 and reactance of one type only. The resistance
frequency by th'e use of a frequency divider.
element of one of the phase shifting meshes con
The 60 cycle frequency for the oscillator gener
sists of the space discharge path of a vacuum
ally is chosen for the reason that it conforms to
tube. The `magnitude of this resistance element
the ñeld scanning frequency and also to the fre
is varied by the automatic frequency control Volt
quency of the standardizing source. Numerous 35 age to vary the total phase shift of the feedback
arrangements have been utilized for comparing
energy and, thus, vary the frequency of oscilla
the 60 cycle oscillator frequency with the 60 cycle
alternating current derived from a commercial
For a better understanding of the invention,
power source and for utilizing the output of the
together »with other and Yfurther objects thereof,
frequency comparator to control the oscillator 40 reference is had to the following description
frequency so that it will be in agreement at all
taken in connection with the accompanying
times with the source of a standardizing fre
drawing, and its scope will be pointed `out in
the appended claims.
In an arrangement Wh'ere the oscillator is op
In th'e drawing, the single figure isa schematic
erated at a high frequency it also is necessary, 45 circuit diagram of a scanning frequency gener
in order to derive the low frequency scanning
ator and automatic frequency control apparatus
voltages and a voltage suitable for Vcomparison
embodying the invention.
withthe standardizing source, to employ a num
Having reference `now to the drawing, it is as
ber of frequency dividers.
sumed that `it is desired to generate scanning
It is an object of the instant invention, there 50 voltages for a -televisionsystem employing an odd
fore, to provide a novel means `for generatingtel
number `of scanning lines per frame and 30
evision scanning voltages definitely` related `in
frequency to a standardizing frequency and in
>framespersecond with a 2 to 1 interlaced scan
ning pattern. In such a case the frequency of
which theuse Qf'frequency» dividing apparatus
is obviated.
the field scanning 4voltage will be 60 cycles `per
second. Also, in this case thesource of stand~
ardizing frequency is assumed to be a conven
tional 69 cycle source of commercial alternating
current. In accordance with the invention
then, the oscillation generator is arranged to de
velop sinusoidal voltage at a sub-harmonic fre
quency of the frame scanning Vfrequency of 60
cycles. For illustrative purposes the i'lrst sub
harmonic of 30 cycles per second will be utilized.
The oscillation generator comprises _a vacuum
tube I which, in the present instance, is illus 10
trated as a pentode. However, it is contemplated Y
that other types of tubes may be employed with 'Y
equal facility without departing from the spirit
or scope of the invention. The cathode ofthe
tube I is connected to ground and-the anode is
connected through a load inductor 2 to the posi
tive terminal of a source of direct current such
lector tube network includes series condensers 38,
39 and 4I, the latter of which preferably isV ad
justable so as to provide for an adjustment in the
natural oscillation period of the selector circuit.
The shunt elements of the phase shifting net
work are resistors 42, 43 and 44, the latter of
which preferably is in the form of a potentiome
ter„having an adjustable contact 45. The con
tact` 45 is connected through a resistor 46 to the
control grid 47! of the selector tube 32. The con-.
>trol grid of this tube also is by-passed to ground
by a condenser 43. Although the phase shifting
networks associated with tubes I and 32 are
similar, the output energy feedback to the input
circuit, in the case of tube I, is suflicient to sus
tain oscillation at a frequency of Y3!! cycles per
second, whereas, in the case of tube 32, the feed
as a battery 3, of which thelnegativeterminal ,is . back energy is insufñcient to sustain oscillation.
connected to ground. The suppressor grid 4 of
It is merely sufficient to enable the tube 32 to act
the tube I is connected directly to ground and the 20 as a lfrequency selective amplifier responsive only
screen grid 5 is connected through a resistor 6
to a frequency of 60 cycles per second.
to the positive terminal-of the battery 3 and also
In order to furnish a control voltage for driving
through a by-pass condenser 'I to ground.
the selector tube 32 at the desired frequency of
The anode-cf the tube I’is connected to a triple
60 cycles per second, the anode of theY distortion
mesh phase shifting network of capacitance and 25 tube 22 is coupled by an arrangement including
resistance elements.` As illustrated, the network
a condenser 43 and va resistor 5l to the control
is formed of series condensers and shunt re
grid 4l of the selector tube. Preferably, the
sistors. It is contemplated that a network of
resistor 5I is in the form of a potentiometer hav-series resistors and shunt condensers are within
ing'an adjustable contact 52 >which is connected
the scope of this invention. Condensers B, 9 and 30 bya resistor 53 to the potentiometer` contact 45
II comprise, respectively, the capacitance ele
in the feedback circuit of the selector-tube 32 and
ments of the first, secondïand third network
also through a resistor 46 to the grid 4l of the
meshes. The resistance elements of the succes
sive network meshes comprise, respectively, the
The anode Vof the selector tube 32 is coupled
space discharge path of a triode Vacuum tube I2, 35 by means of a condenser 54 and a potentiometer
and‘resistors I3 and i4. The network is termi
55, having an adjustable contact 56, to the phase
nated in a resistor I5, one terminal of which is
comparator. This apparatus includes a diode 51
grounded and the other terminal is connected
having an anode which is connected lto ground
throughV a resistor I6 to the control grid Il of
through a resistor 58 and also to the potentiome
the oscillator tube I. The control grid also is 40 ter contact 55 through a condenser 59. YThe
by-passed to ground by a condenser I8.
cathode of the diode 5l is connected to an adjust- '
» 4The anodel of the oscillator tube I is coupled
able contact 6I of a potentiometer 62, of which
by a condenser I8 to the control `grid 2| of a
the terminals are connected to a grounded source
pentode vacuum tube 22 serving as the wave form
of a standard 60 cycle alternating current sourc
distorter, A resistor 23, connected between the 45
connected to the terminals 63.
control grid of the tube 22 and ground,’serves as
The automatic frequency control Voltage de
the grid leak resistance for this coupling circuit.
veloped by the phase comparator is impressed
The screen grid 24 of the tube 22 is connected
upon the frequency determining circuit of the
through a resistor 25 to the positive terminal of
oscillator tube I by means of a connection from
the battery 3 and the suppressor grid 2B is con 50 the anode of the diode 5l through a resistor
nected directly to ground. The anode of the
64 to the control grid of the triode I2. The con
tube 22 is connected through an inductor 2l,
trol grid of this tube is connected to an adjust
which is by-p-assed by a condenser 28, and
able contact 65 of a potentiometer 66 and also
through the resistor 25 to the positive terminal
of the battery 3. The cathode of the tube is con
through a filter condenser 6l to ground.
55 terminals of the potentiometer are connectedY to
nected through a self-biasing resistor 29 to
ground and a condenser 3l is connected to by
pass the resistor 23. The self-bias voltage devel
oped by this arrangement is to cause the tube to`
operate in the anode current saturation'region.
the terminals of a source of biasing voltagesuch
as a battery 68.
The anode of the. distortion tube 22 also is
coupled to a high frequency selecting cir-cuit 69
by means of a condenser 1B. The selector 69
may be substantially similar to the selector in
The apparatus for selecting the low frequency
scanning Voltage of 60 cycles per second and the
cluding the pentode tube 32, except that the phase
voltage for comparison with the source of stand
shifting network therefor is designed to operate
ardizing frequency includes a pentode vacuum
the high frequency selector at the line scanning
tube 32. The cathode and the suppressor grid 65 frequency.33 of this tube are connected directly to ground. >
'I'he output circuit of the field scanning fre
The anode of the tube 32 is connected through a
quency selector including .the tube 32, is connect
load resistor 34 to the positive terminal of the
ed toa Vertical scanning generator 1l. Similarly,
battery 3. The screen grid 35 is connected
the output circuit of the line scanning frequency
through a resistor 36 to the positive terminal of 70 selector 69 is connected to a horizontal scanning
the battery 3 and also is by-passed to ground by '
a condenser 3l. As in the case of the oscillator
tube I, the low frequency selector tube 32 is pro
vided with a phase shifting network similar to
that connected to the oscillator tube; The se
generator 12. The scanning generators `-II «and
12 lmay be conventional and are not shown in
detail herein for the reason that they form no
part of the present invention.
Referring now to the operation of the illustra
tive embodiment of the invention, .assume that
the oscillator tube l, together with Vits frequency
determining circuit including the series con
the condenser ‘50. .So long as the cathode and
anode voltages arein phase the anode-to-‘cathotde
potential of the diode remains constantxand vthe
vdensers B, 9 and Il and the shunt triode I2 and
current conduction .through .the .diodeand‘th'e 1re
sistor 58 is'maintainedata .constant value‘w'hich
is dependent upon the relative magnitudes :of
the anode and cathode voltages. `A phase devia
tion of .these `voltages effects a corresponding
resistors I3, ld and l5, effects the generation of
a voltage of sinusoidal wave form having a fre
quency cf 30 cycles per second. This frequency
is determined by the parameters of .the vphase
shifting meshes connected between the output
and input circuits of the tube. Each mesh, in
change in the diode potential
cluding a series condenser, such as 9, and a shunt
resistor, such vas I3, effects a Vphase shift, in `the
instant embodiment of the invention, of approx
imately 60° in the voltage of that portion of vthe
energy delivered by the `output circuit ‘of the tube .
to the `frequency Vdetermining circuit. Thus,
and, consequently„in .the value of .the current
conduction through `the diode and the resistor 58.
Thus, a unidirectional Voltageis developed in the
resistor of a magnitude Vcorresponding `to the'rde
gree of the phase deviation.
This unidirectional voltage is combined with
the biasing voltage derived from the potentiom
eter 66 to form an `automatic frequency `control
voltage. The magnitude and polarity of this con
with the .three disclosed meshes of this charac
ter, the voltage of Athis energy is shifted 180° in
trol voltage represents the instantaneousphase
This phase-shifted energy is impressed
upon the input circuit of the tube I in suiìicien-t 20 deviations of the oscillator derived 60 cycle volt-V
age from the voltage derived from -the standard
magnitude .to produce `sustained oscillations in
izing source. The control voltage is` impressed
the output circuit. The oscillator frequency may
upon the grid of the triode l2 in the manner de
be varied by adjusting one or more of the fre
scribed. Any alternating current component
qency determining circuit parameters, for ex
ample, the value of one of the shunt resistors. 25 which may be present in the voltage derived from
_ the output circuit of the diode 5l’ is substantially
A modification of the shunt resistance consist
eliminated from the frequency control voltage `by
ing of the triode l2 will effect a change in the
the ñlter condenser 6l. The control voltage im
amount of phase shift produced by the first mesh.
pressed upon the grid of the triode l2 effectively
Consequently, a similar change will be effected in
the total phase shift, thereby .to change the os 30 varies the impedance of the space discharge `path
cillation frequency.
of this tube. A variation in this impedance “ef
fects a corresponding variation in the »degree >of
The `.sine Wave voltage derived from the oscil
phase shift produced in the first mesh' of the
lator tube l is converted by the distortion tube
22 into a substantially rectangular wave form
phase shifting network connected between the
voltage having a frequency of 30 cycles per sec 35 output and input circuits of the oscillator tube i.
Thus, the phase of the feedback energy impressed
ond. The rectangular Wave form voltage is pro
upon the input circuit of the oscillator tube is
duced by driving the tube to saturation through
the use of the self-biasing resistor 29. A rectan
altered in one sense or the other, thereby to effect
a corresponding change in the frequency of the
gular Waveform `is referred .to merely for illus
trative purposes, Substantially any distorted 40 generated voltage.
The frequency of the voltage developed in `the
wave form containing the desired harmonics will
serve with equal facility.
output circuit of the low frequency selector tube
.A portion of the energy of the rectangular wave
32, ‘being 60 cycles per second, is suitable :for con
trolling the generation of the field scanning volt
form -voltage is employed to drive the low fre
quency selector, including .the tube 32, in e, man 45 age since it is desired that this voltage @be `gener
ated _at this frequency. The `harmonic of the
ner to develop in the output circuit of this tube
generated 30 cycle voltage, which the high- fre
a substantially sinusoidal voltage having a fre
quency selector G9 derives from the rectangular
quency of 60 cycles per second which is the sec
30 cycle wave developed in the output circuit of
ond harmonic of the generated frequency. The
natural period of the network including the se 50 the distortion tube 22, produces a Voltage in the
output circuit of the high frequency selector hav
ries condensers 38, 39 and 4l and ythe shun-t re
ing the desired line scanning frequency.
sistors 42, 43 and 44 is substantially 60 cycles
While it will be understood that the circuit
per second. By means of the adjustment of the
specifications of a scanning frequency generator
potentiometer contact 45 the magnitude ofthe
phase-shifted energy developed in the network is 55 embodying this invention may vary according to
the frequency requirements of any particular
maintained below the value necessary to sustain
television system, the following circuit speci
oscillations in the output circuit of the tube 32.
fications for a generator employed to develop volt
This energy is combined with enough 60 cycle en
ages at 60 cycles per second and 15,750 cycles per
ergy derived from the rectangular wave form
voltage, as determined by the adjustment of .the 60 second are included, by Way of example only:
potentiometer contact 52, to produce feedback
Vacuum tubes 1 and 32 ______________ __
Inductor 2 _________________ __henries"
Battery 3 _____________________ __vo1ts__
Resistors 6 and 36 ____________ __ohms__
65 Condenser 7 ___________ __microfarads__
Condensers 8, 9 and 28 _________ __do____
energy at 60 cycles per second of suiiìcient mag
nitude to drive the tube 32 at this frequency.
The phase comparator, including the diode 51,
functions to detect deviations of the 60 cycle de
rived frequency from .the standard 60 cycle fre
quency. These frequency deviations are mani
Condenser 11 _________________ __do___„
fested as phase displacements of .the derived volt
Vacuum tube 12 _____________________ _l
age wave with respect to the standardizing volt
Resistors 13 ,14, 15, 34, 42, 43, 44 and
age wave. iThe voltage of the diode cathode 70
53 ________________________ __ohnis_varies sinusoidally under the control of the stand
Resistors 16 and 46 ____________ __do____
ardizing frequency voltage derived from the po
Condensers 18 and 48____-micro-n1icro
tentiometer 62. The voltage of the diode anode
also varies sinusoidally under the control of the
oscillator derived voltage impressed upon it by 75
___________________________ __
Condenser 19 __________ __microfarads--
Vacuum tube 22 _____________________ __
Resistors 23, 58 and 66.A____ __megohm-Resistor 25 ________________ _\___ohms__
Inductor 27 ________________ __henries--
, 1
Resistor 29
Condenser 31 __________ __microfarads“,
Condenser 37 _________________ _»_do____
Condensers 38 and 39 _________ __do____
Condenser 41 _________________ __do____
tions of a distorted wave for-m at a submultiple
»frequency of a low frequency ñeld scanning volt~
age and containing a plurality of harmonics of
said submultiple frequency, means including a
low frequency selector coupled to said oscillation
producing means to produce a deilecting voltage
for said television system at field scanning fre
quency, and means including a high frequency
Condensersl49~ and 70 _________ __do____
Resistors 51 and 55 ________ __'___ol1ms__ 100,000
selector coupled to said oscillation producing
Condenser 54 __________ __microfarads--
television systemat line scanning frequency.
Vacuum tube 57 ____________________ __
means to produce a deflecting voltage for said
3. In a scanning frequency generator for a tele
Condenser 59 __________ __microfarads-0.1
vision system, an electronic oscillation generator
Resistor 62 __________________ __ohms__
for producingsinusoidal oscillations at a submul
Resistor 64 ___________________ __do____ 230,000 15 tiple frequency of a low frequency scanning volt
Condenser 67 __________ _„microfarads__'
age, means for converting said sinusoidal oscilla
Battery 68 _______________ __'_____volts__
It is evident that a scanning frequency gen
erator in accordance With the instant invention
possesses a number of advantageous features not
previously realizable in prior art systems. Since
the line scanning frequency and the field scan
ning frequency are not related harmonically in
a system, where an odd number of scanning lines
per frame and an even number of interlaced fields
per frame are necessary, the generation of a
sub-harmonic of the field scanning frequency
makes it possible to dispense With the multiplicity
of frequency dividers and/or frequency multi
pliers required in prior art systems.
-Also, when
using an oscillator of the type described, the ap
plication of an automatic frequency control volt
tions into oscillations of a substantially rectangu
lar Wave form, said rectangular oscillations being
produced at said submultiple frequency and con-~
taining substantially all harmonics of said sub
multiple frequency, a low frequency selector
coupled to said Wave form converting. means to
produce a control Voltage at the low scanning >fre
quency, a generator coupled to said lowfrequency
selector for control thereby to produce a deflect
ing Voltage for said television system at ñeld
scanning frequency, a high frequency selector
coupled to said wave form Vconverting means to
producea control voltage at the high scanning
frequency, and another voltage generator cou
pled to said high frequency selector Vfor control
thereby to produce a deflecting volta-ge for said
television system at line scanning frequency.
age thereto in the novel manner disclosed makes
4. In a scanning frequency generator for a tele
it possible to positively lock the frequency of the
oscillator in a predetermined relationship to a 35 vision system, an electronic oscillation generator
for _producing sinusoidal oscillations at a sub
source of standardizing frequency.
multiple frequency of a low frequency scanning
K While there has been described what, at pres
voltage, a distorting vacuum tube for converting
ent, is considered the preferred embodiment of
said sinusoidal oscillations into oscillationsof a
the invention, itvwill be obvious to those skilled in
the art that various changes and modifications 40 substantially rectangular wave form, said rectan
gular oscillations beingproduced at said submulj
may be made therein Without departing from the
tiple frequency and containing .substantially all
invention, and therefore, it is aimed in the ap
harmonicsof said submultiple frequency, a loW
pended claims to cover all such changes and mod- ‘
frequency selector including a driven oscillator
iñcations as'fall within the true spirit and scope
coupled tothe output circuit of said Ydistorting
of the invention.
tube to produce a control voltage at the low scan
What is claimed is:
ning frequency, the natural period of oscillation
1. In a scanning lfrequency generator for a tele
of said low frequency selector oscillatorbeing
Vision system, means for producing oscillations of
equal to the low frequency scanning voltage, a
a distorted Wave for-m at a submultiple frequency
of a low frequency ñeld scanning voltage and ~
containing a plurality of harmonics of said sub
multiple frequency, means coupled to said oscil
lation producing means and controlled by a harmonicof said distorted Wave form oscillations to
produce a deñecting voltage for said Vtelevision <
system at field scanning frequency, and means
coupled to said oscillation producing means and
controlled by another harmonic of said distorted
Wave form oscillations to produce a deflecting
voltage for said television system at line scanning
2. In a scanning frequency generator for a
television system, Ymeans for `producing oscilla
vertical scanning voltage generator coupled to
said 10W frequency selector for control by said
low frequency control Voltage to produce a de
ñecting voltage for said television system at field
scanning frequency, a high frequency selector
coupled to the output circuit of said distorting
tube to produce a control voltage at the high
scanning frequency, and a horizontal scanning
voltage generator coupled to said high frequency
selector for control Iby said high frequency control
voltage to produce a deflecting voltage for said
television system at line scanning frequency.
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