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Патент USA US2403616

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July 9, i945»
Filed July 25,' 1944
Patented July 9, 1946
2,403,616 l
Mrap STATES PATENT y `orlé‘lcia‘,
Royden C. Sanders, Jr., Hightstown, N. J., as
signor to Radio Corporation of America, a cor
poration of Delaware
Application `Fully 25, 1944, Serial No. 546,537
6 Claims. (Cl. 172-239)
This invention relates to wave shaping circuits,
The product Bfm is the rate of change of trans#
and more particularly to improvements in the
mittedV frequency. in megacycles per second per
invention described and claimed broadly in U. S.
The distance sensitivity, in beat fre
application Ser. No. 512,153, iiledNovember 29,
quency cycles per foot of distance is-thus directly
1943, by Irving Wolff, and entitled Vibratory 5 proportional
to the rate of change of transmitter
mechanical systems. The present invention is , frequency Bfm.
disclosed but not claimed specifically in said
Practical experience has shown it to be desir
Wolff application.
able to employ a vibrating type modulating unit,
The principal object of the instant invention
preferablya capacitor device» in which the ca
is to provide an improved method of and means
pacity could be varied cyclically to vary corre
for producing wave shapes of the type required
spondingly the transmitter frequency.- A coll
in the practice of the invention disclosed in said
driven diaphragm unit of this type is described
Wolfi’ application.
in copending U. S. application, Ser. No. 471,003,
Another object is to provide an improved
filed January 1, 1943, by S. V. Perry, and entitled
method of and means'for cyclically frequency
Capacity modulator unit. Generally the varia
modulating a radio transmitter in such manner
tion of capacity with respect to time need not be
that the product of bandwidth swept times the
linear, or in accordance with any other` particular
modulation frequency is independent of the
law, as long as it is cyclical. However, certain
modulating frequency.
FM distance and speed measuring systems do re
'I'he invention will be described with reference
to the accompanying drawing, of which Figure 20 quire accurately linear triangular wave frequency
modulation in order to perform properly ti. e
1 is a schematic circuit diagram of the invention
for which they are intended.> While
as applied to a frequency modulator system; Fig
such modulation is obtainable with reactance tube
ure 2 is a graph of a square wave voltage em
ployed in the operation of the system of Figure 25 modulators and the like, it is highly desirable,
particularly in aircraft and other mobile appli
1; Figures 3 and 4 are graphs of voltages derived cations,
to retain the advantages of light weight,
from said square wave voltage in the operatión
compactness, and simple construction character
of the system of Figure 1 ; and Figure 5 is a graph
istic of the vibrating diaphragm type unit. This
of the wave applied to the actuating coil of the
vibrating capacitor unit of the system of Figure 1. 30 choice, however, presents the problem of driving
the diaphragm, with its physical properties of
One important application of the invention is
mass, resilience, and friction, so as to provide
in modulation in radio distance measuring de
truly linear variation of capacitance with time.
vices, such as FM altimeters and the like. FM
Referto Figurel. A variable capacitor unit I
altimeters are well known, such altimeters being
of the type described in the aforementioned
described in Bentley Patent 2,011,302 land in
Perry application is provided ‘with a stationary
Espenschied Patent 2,045,071. In these systems
plate 3V coupled to the tuned circuit of an oscil
a radio Wave that is radiated to a reflecting sur
lator, not shown. 'A diaphragm 5 constitutes the '
face or object is cyclically frequency modulated.
capacitor electrode, which may be driven
In a receiver which is located close to the point
of radiation, the reflected signal is picked up and 40 by suitable means, _such as an electrodynamic
drive. The drive is lrepresented as a Winding 7.
mixed or heterodyned with some of the frequency
Energy for the driving-winding 1 is provided by
modulated signal received' directly from the
a modulator amplifier 9, through a coupling
transmitter. The resulting difference frequency
transformer II designed to match the output im»
is a measure of the distance from the transmitter
of the amplifier to the impedance of the
to the reflecting surface or object, since this fre 45 pedance
winding 1. l
quency is determined by the time required for
the radiated signal to reach the reflecting object
wave shape modification network I3, described
and return to the receiver.
more fully hereinafter and is connected~ to yan
The beat, or difference frequency, is
intermediate tap on a voltage divider I4. One
50 end ofthe voltage dividers is connected to the
positive terminal B+ of the- anode, potential
where B is the band width-swept, in megacycles
per second, fm is the modulating frequency, in,
supply (not shown) and the other end is con
nected through a switch I5 to ground._ A battery.
I1 is connected through 'a switch I9 toa motor
cycles per second, and d is the distance in feet. 55 2i, preferably the motor section of a. conventional
.„ „
dynamotor used to supply anode potential for
the ampliñer 9 and other equipment. The shaft
of the motor 2| carries, or is mechanically cou
pled to a cam 23 for periodically operating the
switch I 5 to produce square wave impulses which
are modiñed by the network I3, amplified by the
amplifier 9` and applied to the actuating winding
1 of the variable capacitor device II.
The network I3 includes an integrating section
25, a differentiating section 25, and a combining
section comprising series connected resistors 29.
3|, 33 and 35. The resistors 29, 3|. 33 and 35
also function as a load or termination for the
differentiating section 21. 'I'he integrating sec
tion 25 comprises a resistor 31 and a capacitor 39
connected in series between the switch I 5 and
by the amplitude of the square wave voltage and
the constants of the integrating circuit (values
of capacitor 39 and resistor 3l) , and is substan
tially independent, throughout the operating
range, of the square wave frequency.
Thus, if
the speed oi the motor 2|V decreases, decreasing
the frequency of operation of the switch I5, the
amplitude of the triangular wave output of the
integrating circuit will increase correspondingly,
since the capacitor 39 has correspondingly longer
periods of charge and discharge. The slope. l0r
rate of change of voltage, of the triangular wave
thus remains constant.
The graph of Figure 3 is also representative of
the form of the desired motion of the diaphragm
5 of the modulator unit I as a function of time.
However, if the voltage across the .capacitor 39
ground. .The values of .the resistor 31 and the
were applied to the actuating coil 1 without mod
capacitor 39 are selected so that their RC prod
iñcation of wave shape, the motion of the dia
uct, or time constant, is long with respect to the
phragm would not be a linear function of time,
period of one cycle of operation of the switch 20 owing to inertia.
I5. A suitable modulation frequency is approxi
At each extreme oi its excursion, the dia
mately 110 cycles per second. A coupling capac
phragm tends to continue moving in the same
itor 4I is connected from the junction between
direction after the driving force reverses, lagging
the resistor 31 and the capacitor 39 to a point on
the actuating current both during deceleration
the combining section between the resistors 3|
and acceleration and thereby producing a dis
torted wave of capacitance variation. In the
and 33.
The differentiating network 21 includes a series
practice of the instant invention. this effort is
capacitor 43 having a value with respect to that
counteracted by predistorting the driving force
of the total resistance of the resistors 29, 3|, 33 30 by the addition of a sharp impulse at each re
and 35 such that the RC product is small as com
versal to overcome the momentum tending to
pared to the period of operation of the switch I5.
cause continued motion in one direction and
Also included in the network 21 is a series re
,supply an opposite momentum to start motion
sistor 45 and a shunt capacitor 41, connected like
in the reverse direction.
A preferred method of producing said impulses
the resistor 31 and the capacitor 39 of the inte
grating network. The function of these elements
is by time differentiation of the square wave volt
age of Figure 2, by the action of the capacitor 43
is described below.
A resistor 49 is connected between the point
and the series resistors 23, 3|, 33 and 35. Neglect
B+ and the junction between the resistors 33
and 35.
ing momentarily the eilect of the resistor 45 and
The resistors 49 and 35 function as a 40 the capacitor 41, the capacitor 43, being relatively
voltage divider from which a positive bias voltage
small, charges fully to the peak value of the ap
plied square wave almost instantaneously upon
opening of the switch l5. The short pulse of
charging current, flowing through the resistors
of the tube 5 I.
45 29, 3|, 33 and 35, causes a similar pulse of voltage
at- the input circuit of the amplifier 9. Upon
In the operation of the above-described system,
closure of the switch I5, the capacitor 43 dis
the switch l5, whenclosed, connects the voltage
charged through the same circuit, providing a
divider I4 between the point B+ and ground.
voltage pulse of opposite polarity to the charging
The .voltage at the tap of the voltage divider I4
pulse. The pulse shape depends primarily upon
is, therefore, somewhere between zero and the
the slopes of the leading and trailing edges of
B+ potential, having a value dependent upon the
is applied to the control grid circuit of the elec
tron discharge tube 5| of the amplifier 9. A self
bias resistor 53 is provided in the cathode circuit
adjustment of the tap. When the switch I5 is
open, the full B+ potential is applied to the tap
through the lower portion of the voltage divider
I4. Thus as the switch I5 is opened and closed,
the voltage applied to the network I3 is cyclically
and discontinuously alternated between two defi
the square wave input to the capacitor 43. It is
found in practice that the leading edge of the
pulse may be too sharp to provide the desired
.operation of the system. The resistor 45 and the
capacitor 41 are included to decrease the slopes
of the edges of the square wave voltage before
nite values, providing a square wave form as
illustrated in Figure 2.
application to the capacitor 43, in order to reduce
the slope of the leading edges of the derived
As the switch I5 opens, the capacitor 39 starts
pulses. The resistor 45 and capacitor 41 operate
to charge through the resistor 31. The increase
in the same manner as the resistor 31 and thel
of voltage across the capacitor 39 is substantially
capacitor 39 of the integrating section 25, but to
linear with respect to time during the period the
a much smaller extent.
switch I5 is open. When the switch I5 closes,
The triangular wave voltage from the integrat
the capacitor 39 starts to discharge through the 65 ing section is applied through the capacitor 4| to
resistor 31, since the voltage across it is higher
the resistors 33 and 35. and the pulse train from
than the voltage at the tap of the voltage divider
the differentiating section appears across the re
I4. The decrease of voltage across the capacitor
sistors 29, 3l, 33 and 35 as explained above. The
is also substantially linear with respect to time
resultant voltage at the tap of the resistor 29
because the RC product of the resistor 31 and
contains components comprising both the tri
the capacitor 39 is large in relation to the period 70 angular wave and the pulse train. The propor
of operation of the switch I5. Accordingly the
tions of these components to each other is de
voltage across the capacitor 39 varies as shown
termined by the position of the tap. The input
by the graph of Figure 3, constituting a linear
to the control grid of the amplifier tube 5| is of
triangular wave. It should be noted that the
the form illustrated by the graph of Figure 5.
slope of the wave of Figure 3 is determined only 75
The ampliiier output .wave is of the same shape
but greater amplitude.
The relative amplitudes of the triangular wave
and pulse components are adjusted by means of
the voltage divider 29 so that the pulses just
reverse the momentum of the diaphragm 5 at
to one of said networks and at least one .other
resistor connected between said networks,~ an ad- justable tap on said second resistor, and ampli
fier means including an input circuit connected
each end of its excursion, as described above.
between said tap and a point on said ñrst men
The amplitude of vibration of the diaphragm 5
tioned resistor, and an output'circuit connected
may be adjusted by means of the voltage divider
id, which controls simultaneously the amplitudes
of .both components of the wave of Figure 5. As
'pointed out above, the amplitude of the triangular
wave voltage varies inversely with variation in
the modulating frequency.
The amplitude of
vibration of the diaphragm 5 varies likewise, so
that the range oi’ variationln oscillator tuning,
B, is inversely proportional to the modulating fre
quency fm. Thus the product Bim remains con
stant, and the distance sensitivity is independent
of the modulating frequency im.
square wave source, a voltage combining
circuit including at least one resistor connected
to said actuator.
3. In a modulator for radio reflection system
including a vibratory variable capacitor with an
electrical actuator, a system for energizing said
actuator, including a source of square wave
voltage, a voltage integrating network- compris
ing a resistor and 9, capacitor 'connected in low
pass ñlter configuration and a voltage dineren
tiating network comprising - a resistor and a
capacitor connected in high pass iilter conflgura- '
tion, both of said networks being connected to
20 said square wave source, a voltage combining
The invention is described as an improved
circuit including at least one resistor connected
method of and means for providing linear tri
across the output of one oi! said networks and
angular wave capacity variation for FM radio
at least one other resistor connected between one
distance measuring systems with a diaphragm
output terminal of said dinerentiating network
type vibrating capacitor modulator. A square 25A and one output terminal of said integrating net
wave voltage is produced by means of a periodic
work, an adjustable tap on said latter resistor,
switch and a source of D.-C.„modiñed by an in
and means i'or energizing said- actuator in re
tegrating network to triangular form, and ap
spouse to the voltage between said tap and an
plied ‘to the actuating magnet of the capacitor
other point 'in said~ combining circuit.
unit. To overcome the enect of the inertia ofv 30. ` 4. A wave shaping circuitl for radio reilection
the diaphragm upon linearity of operation oi the
modulator systems, comprising a pair of input
modulator, a pulse train is derived from the
terminals, a pair of output terminals, an output
square wave and added alsebraically to the tri
circuit comprising a plurality of resistors con
angular wave, to onset the momentum at the end
nected in series between said output terminalsra `
of each vibration of the diaphragm and supply 35 resistor and a storage capacitor connected lin
opposite momentum at the beginning oi each
series between the ñrst of said input terminals
and the second of said output terminals, >a
I claim as my invention:
couplingcapacitor connected from the junction
l. In a modulator system including a vibratory
of said .storage capacitor and said last men
variable capacitor with an electrical actuator, a 40 tioned resistor to an 'intermediate point in said
system for energizing said actuator, including a
output circuit, and a dinerentiating capacitor'
source of square wave voltage, means for integrat
ing said voltage to provide a voltage of triangular
wave form, means for dinerentiating said voltage
to provide a voltage pulse train of alternating
polarities, a network for combining said tri
connected from said first input terminal to the
ñrst of said outputterminals.
5. The invention as set forth in claim ’4, -’in
cluding a further resistor in series said dineren
tiating capacitor, and a lfurther storage capaëitor
angular wave voltage and said pulse voltage, said '
connected from the Junction of said >last men
network including common means for dineren
« tioned resistor with said dinerentiating capacitor '
tially adjusting the magnitudes of said combined
voltages, and means for energizing said actuator
in accordance with said combined voltages. \
2. In a modulator fior radio reilection systems
including a vibratory variable capacitor provided>
to said second output terminal.
_ ,
6. The invention as set forth in claim 4, where
in one of said series connected resistors oi' said
, output circuit includes an adjustable tap where
by the enects ot sai'ddinerentiating capacitor
with an electrical actuator, a system for energiz
and said storage capacitor may be regulated dii'- y
ing said actuator, including a source oi square 55 ferentially.
wave voltage, a voltage integrating network andy
a voltage differentiating network, both connected
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