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Aug; 20, 1946.
E. LABIN
2,406,019
PULSE MODULATION SYSTEM
Filed April l. 1941
4 Sheets-Sheet 1
.n
. .
Wì| k
ATTORNEY
Aug. 20, 1946.
E. LABIN
PULSE uonULATIo? SYSTEM
Filed April 1, 1941
2,406,019
.
4 Sheets-Sheet 2
LV
.NÓEY
INVENTOR
ATTORNEY l
Allg. 20, 1946.
_
E, LABlN
2,406,019
-PULSE IODÚLATION SYSTEM -
Filed April 1, 1941
'
4 Sheets-Sheet 3
FIGA;
lNVENTOR
BY
ATTCRN l
Aug. 20, 1,946.
2,406,01 9
E. LABIN
PULSE MODÚLATION SYSTEM
vFiled April 1, 1941
4 Sheets-Sheet 4
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20» 1946
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2,409,019
PULSE MODULATÍON SYSTEM
Emile Labin, New York, N. Y., assignor to Inter
' national Standard Electric Corporation, New
Y York; N. Y., a corporation of Delaware
application April i, i941, serial »10,386,282
i2 claims.
(ci. 25o-»6)
l
,
This invention relates to improvements in
pulse modulation systems.
It is a primary objective of the invention to
provide an improved pulse modulating system.
Another object is to provide more interference
free system of radio communication.
'
A further object is to provide an improved sys
tem of radio transmission which may function
despite deliberate attempts to jam the transmis
sion frequency.
~
io
It is also an object to provide an improved and
2
(i. e., from the beginning to the end of the modu
lated pulse) to be intelligible as in the former
case. It might also be observed that neither of
the above-indicated systems is free of phase mod
ulation, as will later be clear.
In accordance with features of my improved
form of pulse modulation system only one ex
tremely short pulse is needed to identify a. signal,
no matter what the degree of modulation. This
improved method contemplates the time-dis
placement of a single pulse one side or the other
about a given norm in accordance with the de
simplified pulse modulation reception system.
Still another object is to provide an improved
system of secret radio transmission.
A further object is to provide an improved form
of pulse modulation system in which a. single,
gree of modulation; hereinafter alternately re
ferred to as time-modulation. Since the maxi
mum time-displacement of the impulses is pref
erably small in comparison with the time-inter
constant-width impulse may suiilce for indication
val between pulses. a large part of the time is not
of intelligence.
used for transmission; and suitable receiving ap
paratus may include a sharply selective circuit
It is also an object to provide a pulse modula
tion system adaptable to relatively simple receiver 20 tuned to the pulse frequency and blocking means
energized by said selective circuit for excluding
means.
substantially all noise but the displaced impulses.
Another object resides in provision of a pulse
Appropriate displacement responsive means may
modulation system in which there is no phase
modulation of, the impulses.
then detect out the audio` signal in a known man
Other objects and various further features of
novelty and invention will hereinafter be pointed’
I consider it preferable to a more ready under
out or will occur to those skilled in the art from
standing of my invention ñrst to indicate gen
a reading of the following specification in con-,
erally how I treat signals in accordance with fea
junction with the drawings included herewith.
tures of this invention, and then to describe pos
30 sible means for giving such treatment. Accord
In said drawings
Fig. l is a graphical showing of the effect of
ingly, vreference will first be made to Fig. 1 which
represents graphically the general treatment of
signal treatment in accordance with features of
my invention;
pulses in accordance with features of my modu
Fig. 2 is a block diagram of a pulse transmitter
according to my invention;
Fig. 3 is a block diagram of a pulse receiver
incorporating features o-f my invention;
Fig. 4 is a schematic circuit diagram of a por
35
lating system.
.
The pulses modulated as indicated correspond
to a spectrum of frequencies with bands located
near the harmonics of the pulse repetition fre
quency.
Each harmonic may be modulated in
tion of the transmitter of Fig. 2; and
40 amplitude by time modulation of the pulses. If
Fig. 5 is a graphical showing of successive
any particular harmonic of the transmitted en
changes in wave shape in portions of the circuit
ergy be selected for detection or demodulation,
of Fig. 4.
the original signal may be restored by 'relatively
simple means forming a, feature of this invention. .
Pulse modulation systems are known in which
the amplitude of the pulse is always maintained 45
In order to avoid combined amplitude and
constant and the duration of the pulse vmade to
phase modulation of harmonics and increase the
vary in accordance with speech or other modu
percentage of amplitude modulation of harmon
lating signals. It is also known that the whole
ics, I propose to displace alternate impulses sym
pulse-so modulated need not be transmitted, but
metrically and in opposed senses about their nor
rather two pulses, each marking one determinant 50 mal unmodulated position. In other words, the
end of the modulated pulse. This latter method
impulses are displaced to new, modulated posi-_
has advantages over the former, in that still
tions which are in time successively before and
greater-signal-to-noise ratios may be obtained,
after` the normal instants at which unmodulated
but has the disadvantage that a signal so trans
impulses would occur. In such a modulation sys
mitted requires just as much of a time-interval 55 tem the impulses may be considered as made up
g
2,406,019
3
Y
lof two superimposed trains of impulses, each o!
normal, unmodulated period T-in one of which
time-modulation occurs generally in onev direc
tion along the time axis, and in the other of which
` as will be clear.
After substituting Equations 4
and 5 in expression (3), we obtain
` time-modulation occurs generally inthe oppOsi
tion sense'.
`
Referring to the diagram in Fig.- 1, odd impulses
Now, if we assume that the time-displacement
0v is always very small, such that 0=-_Ktu,
- I, 3, 5 kare shown schematically with respect to
time and as being time-modulated in a sense op
(O<K<1), then, calling
posed to that of the modulation of even impulses
2, 4, Ii.` It wil1 be clear that if to represents the
15
' maximum amplitude of time displacement for the
Y
impulses, one set of impulses I, 3, 5 etc. will be
' displaced :2te with respect tothe other (2, 4, 6
2”,_‘„"t"=mwt„<1
. a distortion factor e may be described as
etc.) for maximum modulation, depending upon
the magnitude of modulation.
`
As stated above, the series of pulses shown in 20
e=2mTm<<i
simplifications for- our purposes:
Fig, 1 may be considered as formed of two identi
cal series, each having a period T, which series
cos mw0==11
we shall designate as P1 (for pulses I, 3, 5 . . .)
and
’
`
25
and P2 (for pulses 2, 4, 6 . . .), respectively.
<8)
Such an assumption will permit the following
tall mw9=mw0
By appropriate choice of time origin the center
Wherefrom an appropriate expression for Ap be
of the ñrst pulse I of series P1 may occurat time _
comes
_ AP: Em(
01, and the amplitude A of pulse I may be de
scribed as-
*_
Ap being the sum of amplitudes at frequencies
’"/r each of which is amplitude modulated bythe
‘
AP1=ZMAW cos mou-61)
signal 0, as will be clear.
Now, assuming the simplified case of 0 sinus
oidally varying with a period a, We may write
(l)
in which ,
l
and m is any harmonic. It will be noted that
no sine terms appear in this expression because
the function is symmetrical.
v(10)
once be observed that the depth of' modulation
(2)
Where 62 represents the time at which the center
»
mao. tan mwb=K.e. tan mob
It will be recalled that K is always equal to or y
less than 1, and that e is much less than 1.
45 Therefore. in order to obtain large orders of
modulation Ke. `tan mwb should approximate
unity, or tan mwb should equal
of impulse 2 occurs with respect to the time ,
origin.
0=K.ío. Sin (at-Ho)
` 40 for the mth harmonic is---
In the same Way, the amplitude of a pulse in
the series P2 may be written as_
Ap2=2„,.Á,„.-cos mw(t--02)
`
Upon examination of expression (9), it will at
„
By combining expressions (1) and (2) it will
be clear that the combined eiîect of both trains 50
of impulses will be described by
If `the time origin has been appropriately se
lected, a simpliñed solution may result. Assum
l
Ke
In determining what phase relation one series
of impulses should have to the other, care must
Vbe taken that at no time, with or without modu
lation, do the pulses of one series pass beyond
55 precisely the mid-point in time between two im-.
pulses of the other series. Such occurrence, it
will be clear, would give rise to the undesirable 1
effect of doubling the impulse frequency.
ing, then, a time-displacement of both series P1
In
order, then, to avoid a doubling of the period-T,
and P2 in opposite. directions by a time 0, We may
60 characteristic of each seriesl of impulses, we may
arbitrarily describe 61 and 62 as
define b as
T
01 :î- b- 9
.
T
i
Hand
,
_
,
b=E--to
(11)
65 in which case, for m odd,
92
b -|- Ú
tan mwb= tan e =-1e
in which 2b arbitrarily represents the distance
between the axes of modulation of the ilrst two
and
cos mwb=sin e=e
pulses after the time origin, and from which
70 and, for m even,
and
'
-Y
cos mob-:cos e=1
75 The general term of series (3) may now be writ
2,406,019
5
.
ten in two forms, depending on whether m is odd
a
or even; thus, for m odd
2Am.e[1-K sin (at-l-qnl cos met
desired and interfering signals may be expressed
(12)
and, for m even -
assuming an interfering signal substantially _uni
2Amll-Ke2 sin (at-l-qù] cos mot
(13)
form with respect to time. Of courseffor best
From expressions (12) and (13) it will be noted
reception, free as possible from interference.
that the presence of e in the amplitude term will
make for odd harmonics of relatively small ampli 10
tude, while even harmonics, not being associated
.should be made small as possible; and in the case
with the factor e, will he relatively large. On the
of
`
other hand, odd harmonics are highly modulated,
whereas there is hardly any modulation of even
harmonics.
`
It will further be noted from these same ex
It will be seen that, for any given value YofV e, p
pressions that, inasmuch as ai and 02 vary in
is inversely proportional to m, and that, there
opposite directions, there are no phase modula
fore the higher the harmonic chosen for detec
tion terms, and that, therefore, all modulation
>is in amplitude. That such relative variation of 20 tion, the greater will be freedom from inter
ference. Since e may be selected as desired, it
6i and 02 is responsible for'elimination of phase
will also be appreciated that _to should be as small
modulation may be seen if we consider one series
as possible, both in order to obtain less prob
of impulses as unmodulated while modulating
ability of interference and to see that modula- the other. In such an assumed case, for m odd,
tion (see expression (7)) follows a substantially
we would obtain, instead, of expression (12)
25
linear4 rather than a tangential law. In review
ZAWeIÍII-â-ç sin (at-Hä] cos mw(t----g-) (14)
then, as high a harmonic as possible should so
be chosen that, when considered in view of the
smallest possible to and d, the term e is not so
lation is necessarily only one half that of the pre 30 large that linear modulation is impaired. In
ferred case of expression (l2), and that phase
any case, the final value chosen will be a com
promise between the frequency band available
modulation is present. It may be observed, how
and freedom from interference.
ever, in this connection, that the phase modula
In the drawings I show a preferred possible
tion present in the case of expression (14) is
not very harmful to speech transmission; but, of 35 circuit for obtaining the above-indicated de
sired results in accordance withfeatures of the
course, for utmost fidelity purposes, it would be
invention. In Fig. 2, which shows a transmitter
considered undesirable.
Y In this case it will be noted that depth of modu
Returning again to the preferred system in
_in block diagram form, impulse energy may be
derived from a pulse generator 20 and then sup
which both series of impulses are modulated in
opposite directions, let us consider reception and 40 plied to a converter circuit 2|, which preferably
includes a multivibrator, as will later be clear.
detection of signal impulses. Since each odd
Converter circuit 2| may simultaneously be fed
harmonic, as will be clear from expression (12), ~
by speech or other modulating energy by known
is purely amplitude-modulated, a circuit tuned .
means 2‘2. The appropriately modulated im
to some such odd harmonic of l/T would per
pulse energy output from converter 2| may
mit the amplitude modulated term to be removed
thereafter be treated in accordance with known
and thus result in detection of the signal. Fur
means, which are suitably labeled on the rest of
ther utilizing received energy in accordance with
-the transmitter diagram.
features of the invention, any Veven harmonic
Fig. 4 shows a possible circuit for converter
term, which as we have seen from expression '
(13) may be very large, may be employed, after 50 2| schematically and in some detail. In a pre
ferred form the circuit is designed to set up the
suitable shaping. to obtain a generally square
shaped blocking signal for blocking out recep
tion of energy for substantially the interval .be
tween pulses. By making the even harmonic cir
two series of pulses l, 3, 5 . . . and 2, d, 6 . . . so
that, when speech or other signals are applied,
time-modulation of one set of pulses will be op
cuit as selective as possible, it will be clear that 55 posed to time-modulation of the other. The cir
cuit of Fig. 4 may more readily be understood
parasitic disturbances may be reduced to a min
when viewed jointly with the wave forms of Fig.
imum, and that substantially only the signals
5. First, we shall consider the case of no modu
themselves will be admitted to the detection
lation, tracing wave treatment throughout the
circuits.
A further desirable feature of my invention 60 circuit of Fig. 4, as depicted, in an exaggerated
`manner for purposes of clarity, by waves a
may be seen in its use as an- improved secrecy
through g of Fig. 5. A source (not shown) of
system. Since the steady component existing
continuous variations preferably supplies input
in the signal is modulated but very slightly, ordi
terminals 23, 24 with sinusoidal variations (see
nary detection methods will only be able to de
tect a small unintelligible disturbance, and com 65 Fig. 5a) in synchronism with impulses later to
be superimposed thereon, that is, such impulses
mon circuit and other noise will probably be large
preferably occur whenever these 'sinusoidal
enough compared with such very slight modula
variations pass through zero. For purposes that
tion that the signal may be completely unintel-y
will later become apparent I next prefer to shift
ligible, as will be clear.
This brings us to a consideration of the signal 70 the phase of this input voltage so that it is sub
stantially in quadrature with the impulses, that
to-noise ratio and related factors. If we assume
is. so that the impulses later to be superimposed
that the receiver is blocked continuously except
occur at instants of time corresponding to posi
during the pulse and modulation interval
tive and negative maxima of the input voltage.
2me-d, d rheling the length of the pulse, the prob
ability of interference for equal amplitudes of 75 A circuit for eiïecting the desired phase displace
2,406,01 9
8
,
ment may. for example, include series capacitance
to tube V4 momentarily drives thatidischarge de->
means Ca and shunt resistance means Re, as
shown.` 'I'he input sinusoidal voltage, so shifted
in phase may then be substantially squared on
by well-known limiter means including an over
vice below cut-oiï, thus permittingv a sharp in
crease in plate voltage. This relatively positive
potential on the plateìis transmitted through
excited amplifier tube V1 and appropriate cir
cuit elements. Output energy from tube V1 may
Thereupon, because' of the conducting state ‘of
condenser C, to render tube V5 conducting.
tube Vt, a resultant drop in cathode resistor R
shifts cathodes of both multi-vibrator tubes posi
preferably divided for application to tubes V2
tively. This shift has the effect of making the
and V3 in push-pull. The outputs of tubes V2 10 control grid of tube V4 so negative with respect
and Va may be connected in parallel as shown so
to the cathode that the cut-off condition set up
that a unidirectional output signal may be ob
by the momentary impulse is maintained a little
longer.
v
tained. For purposes hereinafter to be indi
cated the t'ap of potentiometer 25 is so adjusted
The cut-oiï state of tube V4 will in every in
that the push-pull control potentials applied to 15 stance be maintained for a period of time de
tubes V2 and V3 are unbalanced; that is, one is
pending upon the magnitude of negative impulse
substantially- greater than the other. As a re
applied. For example, pulse 21 being more nega
sult of the limiting eii’ect, adjustment of `poten
tive than pulse 30 will retain tube V4 in the cut
tiometer 25, and the parallel output connection
oiî state longer than pulse 30 will. This will be
of‘the tubes V2 and V3, an output wave form 20 clearly seen from the fact that condenser C1 is
somewhat conforming to Fig'. `5b is obtained.
variously charged depending upon the magni
At this Ystage òf the sinusoidal input signal
tude of the positive pulse output of tube V4 when
treatment impulse energy (shown in Fig. 5c to
the latter’s conductivity is first cut off. This
be substantially in quadrature with the sinus
positive potential in the form of a charge -on
oi'clal voltage, that is, characterized by impulses` 25 condenser Ci will continue to be _applied to the
occurring as the sinusoidal input passes through
control grid of tube V5 (thus keeping tube Va
zero) may be superimposed upon the wave form
conducting) until the leakage effect of resistance
of Fig. 5b by appropriate grid control means 26,
Riso reduces the magnitude of the charge that
21 shown associated with tubes^V2 and Va', re
the output current of tube V5 is insuiiicient to
spectively. The resultant wave so obtained will 30 maintain the drop in cathode resistor R necessary
be of the general form shown in Fig. 5d as will
to keep tube V4 below cut-oil. When the drop
be clear.
in resistor R gets that low, then, tube V4 will
In accordance with features of my invention, I
again conduct and tube _Vs will be non-conduct
next apply the Wave of Fig. 5d to a multivibrator
ing. This is the point at which the operation of
circuit of known form including tubes V4 and V5. 35 the multi-vibrator was assumed to commence,
These multivibrator tubes are preferably so ex
and so a complete cycle of multi-vibrator action
cited that an impulse, say 21 (Fig. 5d) of a cer
has been described.
tain magnitude will energize one of the tubes V4
It has just been pointed out that a longer time
and V5, and a drop below a certain exciting po
will elapse before decay to a predetermined trip
tential, say 28 (Fig. 5e), will cause operationof 40 level 28 for larger applied pulse magnitudes than
the other multivibrator tube. The circuit of
for lesser applied pulse magnitudes. An at
these tubes (V4 and V5) preferably includes ap
tempt has been made Ato show this phenomenon
propriate time-constant decay circuit means for
in the curve of Fig. 5e._ It will be obserbed that
deriving an output from the multivibrator of the
pulse 21 and pulse 38 of Fig. .5d represent re
general form shown in Fig. 5e. The multivi 45 spectively pulses _one of greater magnitude than
bratorcîrcuit including tubes V4 and V5 is one
the other. Pulse 21, being relatively larger, causes
capable of controlling the instant of transition
a relatively large output voltage 29, with the
from one condition to another, and operates
. result that decay from this voltage to the level
spontaneously without external control to return
28 takes a relatively long time t'. Pulse 30, being
to the ñrst condition. The multi-vibrator ac 50 xsomewhat smaller in magnitude than 21, conse
tion is attained by virtue of a conventional for
quently causes a lesser output voltage 3l, with
ward coupling from tube V4 to tube V5 over a
the result that decay from yvoltage 3| to level
resistance capacitance arrangement R7, C1, R1,
28 takes a correspondingly smaller time interval
together with a back coupling from the output of
t” than t’ in the case of pulse 21.
tube V5 to the input of the tube V4 by virtue of a 55
It will now be clear that the respective widths
common cathode resistor R. The forward cou
t’ and t" each recur regularly with a periodicity
pling through R7, C1, R1 is like an ordinary inter
T. In_accordance with features of my inven-stage coupling except that the values of> con
tion I employ the relative position of the instant
denser C1 and resistance R1'are such that con
at which the decaying voltages reach level 28,
denser Ci may be charged to a substantial value 60 that is, when the drop across cathode resistor R
in a few microseconds.
due to conduction of tube V5 decreases to such a
In considering operation of the multi-vibrator
magnitude that the control grid of tube V4 is
circuit, assume as an initial condition an instant `
no longer effectively biased beyond cut-oil?, to de
be taken from across a potentiometer 25 and is
or so before occurrence of impulse 2‘1 (Fig. 5d),
termine the two series of impulses I, 3, 5 . . . and
when tube V4 is carrying relatively high plate 65 2, 4, 6 . . . of period T.
current; thusmaking its plate far less positive
To obtain the two series of pulses from the
than the potential of plate supply. This reduc
curve of Fig. 5e I prefer to employ a Well-known
tion in the plate potential of tube V4 has the
resistance-capacitance derivative circuit, which
effect of applying a'negative potential on the
may‘include capacitance C2, resistance R2 and
control grid of tube V5 after a delay, instituted 70 an over-biased tube Vs, in the output of the
by condenser C1 and resistor R1, suflicient to
multi-vibrator. Output from the derivative cir
allow the negative potential to be substantially
cuit, as obtained across R3 may be of the form of
attenuated and permit tube V5 to draw grid cur
rent. Thisy is the condition of tubes V4> and Vs
Fig. 5f, as will be clear. It will further be clear
that peaks 32, 33, 34, etc. so obtained represent
when pulse 21 appears. Application of pulse 21 75 the desired. appropriately displaced two series
2,406,0_1 9
of impulses. Since the other peaks 35, 36, 31, etc.
increaslngthe retardation or decay time. Con
versely; a decrease in R, or decrease in bias, will
result in an opposite displacement eñect. Rela
tive displacement of the two series> of pulses, one
with respect to the other, may be varied by ad
obtained from the derivative circuit are all regu
larly spaced with period T/2 andare independent
of the magnitudes of pulses 2l, 3d, they are of no
use to a transmitter in accordance with my in
vention, and may therefore be suppressed by
justment of the ground tap on potentiometer 25,
well-known means (not shown), as I have indi
which, as we have seen, controls the »relative
cated schematically in Fig. 5g. The unmodu
iated signal of Fig. 5g is now fully prepared for
Fie. 5b.
amplitudes of adjacent lobes of the curve of
v
modulating potential, shown in Fïg. 5h. It will
be clear that the voltage of Fig. 5h may represent
speech or other intelligence to be transmitted..
While a form of converter circuit 'shown has
been described in particular detail, it is to be
understood, of course, that such description is
merely by way of example to illustrate how the
desired form of impulse treatment may be ef
fected.
A possible and preferred form of receiver for
detecting impulses, transmitted as outlined above,
is shown schematically in Fig. 3. Impulse
In a preferred form this speech may be applied
energy received by antenna t5 may ñrst be
its transmission by any desired means.
The case of unmodulated pulses has first been
taken for discussion because it is obviously
simpler than when the impulses are modulated.
Figs. 5h through 5l illustrate this latter more
complicated case for an assumed sinusoidal
10
to modulate the pulse signals at the push-pull 20 treated in a customary manner in radio and in
termediate frequency ampliñer stages,f shown
rectider stage V2, V3 of the converter of Fig. 4.
generally as a block B6. Thereupon it may be
According to this embodiment, balanced, that is
equal, speech signals are applied by means of
detectedl and some disturbing effects removed
an input transformer 33 to appropriate control
by suitable limiter and detector means dl. At
grids of rectiñers Ve and Va.
25 this point, in accordance with a feature of my
The edect of such application of speech sig
invention I provide means, responsive to the out
put of detector t?, for blocking out reception of
nais may be to vary the curve of Fig. 5d as shown
any signals substantially for the period between
in Fig. 5i, that is, to make pulses corresponding
successive impulses. Such blocking means pref
to 2l and 3d of either greater-or lesser relative
magnitude in accordance with the modulation. 30 erably includes a sharp selective circuit 68, tuned
Thus. pulse 39, being at an unmodulated point,
twice to the pulse frequency (i. e., of period T)
is unmodulated, and hence of the same magni
and a square-wave generator t9 controlled there
by. By suitable adjustment means (not shown)
tude as pulse 217. However, pulse 40, being dis
placed by the rising portion of the modulating
the square-wave output of generatorßil may be
potential, is of lesser magnitude than pulse 3i). 35 made to produce a blocking signal occurring only
Recalling the discussion in connection with Fig.
when no impulses are due for reception. 'I‘his
blocking signal when applied to the earlier stages
5e, it will be seen that pulse 39 will cause a multi
vibrator output signal of duration t'; Whereas
46 or ßl of the receiver may effectively cut out
pulse dd, being of lesser magnitude than pulse
substantially any and all parasitic disturbances
3d, will cause a multivibrator output signal of 40 which would otherwise interfere with reception
of the impulses.
still shorter duration (tm) than t", as will be
clear.
A relatively simple blocking signal of uniformly
The next succeeding impulse ¿il of series 39,
recurring duration may be derived by well-known
el, d2, which may correspond to series i, 3, 5 . . .
of Fig. l, _has been so modulated that its peak
is of considerably greater magnitude than those
of 2t or 39. Consequently, voltage decay from
means utilizing, say, the second harmonic of the
impulse period T. Such a signal could, for ex
ample, be obtained by half-wave rectification of
the second harmonic and adjusting generator 49
the multivibrator output voltage corresponding
to give as large a constant-width blocking sig
to pulse di may be of proportionally greater
nal as possible without interfering with impulse
duration tm' than t', for pulses 2l and 39. Con 50 reception. Suitable oparatus for obtaining a
sidering this phenomenon as to its effect on the
signal of the indicated nature having a desired l
displaced peaks of Fig. 5k, it will be apparent
that, as the modulating signal is, say, increas
`width has been disclosed in the copending ap
plication of H. G. Busignies, Ser. No. 380,186,
` ing, the pulses (3W di) of one series (39, di, d2)
filed February 24, 1941, and entitled "Radio
are time-modulated or displaced in one direc 55 electric impulse systems." Such a blocking sig
tion (i. e.. retarded in time) from their 'unmodu
nal is shown schematically by the dash-dot-dot
lated relative positions, and the pulses (say tii’)
line 50 in Fig. l, and is designated as a simple
of the other series (fili, 43, M) are time-modu
blocking signal. It will be observed, however,
lated or displaced in the opposite sense (i. e.,
that such a blocking signal is not effective com
advanced in time) from their unmodulated rela 60 pletely to block out reception between pulses in
tive positions. When prepared for transmission
treatment, the modulated pulses, corresponding
to a modulating signal of Fig. 5h, may then re
semble the curve of Fig. 5e, as will be clear.
that one series of pulses, as we have seen, is other
than exactly in phase opposition to the other
series of impulses, and, furthermore, modula
tion of one series is opposite in sense to that of
In the circuit of Fig. 4 it will be appreciated 65 the other. What is needed, therefore. for much
that many adjustments may be made to vary
greater blocking efñciency, is some sort of com
the relative displacement of the two series of
plex signal which will block reception for both
pulses, width of pulses, modulation depth, etc.
the short interval of time between, say, pulses i ~
etc. For instance, by changing the value of re
and 2, 3 and ß, 5 and 6, etc. and for the longer
sistor R,- or varying the bias on tube V4, the width 70 interval between pulses 2 and 3, d and 5, etc., as
of pulse in Figs. 5e or 5i may be controlled,»in
will be clear.
that ampliñcation, thus controlled, willoccasion
A possible arrangement for this odd propor-`
diiferent pulse widths t’ or t", etc. Thus, an
tioning of blocking signals could include appa
increase of resistance R, or increase in the nega
ratus similar to that outlined above in connec
tive bias of tube V4, will displace all pulses by 75 tion with the simple blocking signal (for the
2,406,019
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.
,
y
11
_
-
shorter intervals) and an additional superim
posed blocking signal suitably phased with re
understood that many additions, omissions, sub
stitutions, and modifications may be made within
spect to the first-mentioned blocking signal in
the scope of the invention.
What I claim is:
accordance with teachings in the above men
- tioned H. G. Busignies application and recurring
with a period T for substantially> blocking out the
longer intervals. It will be clear that known
wave-shaping methods may bel employed for uti
lizing preferably the second harmonic to obtain
1. An impulse communication system, impulse
generator means for supplying a plurality of
relatively short impulses, means for time-modu
lating said impulses substantially without phase
modulation of odd harmonics of the impulse fre
the additional superimposed, as well as the first
quency, and a receiver including means sharply
indicated blocking'signal. The complex blocking
selecting frequencies in the neighborhood of an .
signal 5| so obtained has been designated as such
in Fig. 1 and is shown as a dotted line.
«by it is possible to demodulate by ordinary ampli-,
After the above-indicated treatment o_f re
ceived signals, it will be seen that output tothe
rest of the receiver vial line 52 will include only
frequency.
date the modulating frequencies either side of
the harmonic selected. Thereafter, simple
detector 54, audio ampliñer 55, and speaker
3. _A receiver for an impulse-modulation com
munication system, said receiver'including ñlter
with theoretically perfect ildelty. as will be ap
impulses, amplitude-detecting means, 'and block
preciated.
ing means responsive to an even harmonic of
odd harmonic of the' impulse frequency, where
tude detection of an odd harmonic of the impulse
2. A radio communication system including a
transmitter and receiver, said transmitter in
the pulses themselves with a very slight amount
cluding impulse generator means for generating
of adjacent parasitic noise, which may com
two series of impulses of the same impulse fre
pletely have been eliminated in the limiter cir
cuit 41. It will be recalled from the above dis 20 quency, and means for time-modulating one of
said series of impulses with respect to th'e other
cussion of theory involved that any odd harmonic
in line 52 will include amplitudeé-modulated
of said series, said receiver including filter means
passing substantially only a band of frequencies
pulses; see expression (12). Thusfall that now
is needed is an appropriate band-pass filter 53 for
immediately about an odd harmonic of the im
selecting the desired odd harmonic, the pass 25 pulse frequency of one of said series, and ampli
band being, of course, wide enough to accommo
tude-detection means.
'
means passing a band of frequencies including an
, means 56 may restore the original input signals 30 oddv harmonic of the frequency of the received
said frequency of the received impulses, said
-It might here be observed that theoretically
any amplitude-modulation receiving set ought
blocking means including a generator responsive
to be able to listen-in on pulse-modulated sig-. 35 to said even harmonic for supplying energy to cut
out reception of signals during substantially the
nals` in accordance with features of this inven
period between received impulses.
tion. Practically, however, it seems unlikely
that such will be possible. for it would be neces
4. In a receiver for receiving and detecting
time-modulated impulsev energy, blocking means
sary to have a set including an extremely stable
and critical local oscillator for receiving only 40 for suppressing reception during the-interval be
ordinary set would not be provided with my novel
tween impulses of the received impulse energy,
said blocking means including a sharp selective
blocking means, so that the average signal-to
circuit attuned to an even harmonic of the fre
. one particular odd harmonic.
Furthermore, an
quency of said received impulses, wave-shaping
noise ratio might, and would in all probability,
be so great'as not torpermit reception at all. 45 means for generating a generally square-shaped
signal to occur substantially during the'interval
Thus, it will be seen that transmission and ap
between said impulses, and means responsive
propriate reception in accordance with my in
to the output of said last-mentioned means for
vention may even take place without suspicion
suppressing effective operation of said receiver in
by anyone that any such communication is tak
50 accordance with said generally square-shaped
ing place.
N
signal.
In accordance with ,still another feature of the
5. An impulse time-modulation transmitter
invention, still better signal-to-noise ratios may
according to claim 11, in which the impulses gen
be obtained. I propose to utilize the interval be
erated by said impulse generator are relatively
tween blocking impulses (in the receiver), which
interval is relatively short compared to the time 55 short with respect to the interval between succes
sive impulses, and in which, for the same degree
between pulses, momentarily to increase the gain, ’
of modulation, time retardation of impulses of
say, of amplifier 55. Although the means for
one of said series is of substantially the same
so improving reception has not been shown, it
magnitude as the time advance of impulses of the
will be appreciated that it may include suitable
wave-shaping means for applying a momentary 60 other of said series.
' abnormally high voltage to the anode or, say, an
6. In an impulse time-modulating transmitter,
accelerating electrode in an amplifier tube of cir
cuit 55. While sustained application of such a
an impulse generator for supplying a series of
regularly spaced impulses, circuit means syn
chronously related to said impulses for supplying
voltage might ordinarily harm this tube, a
momentary application thereof conceivably will 65 a full-wave rectified alternating wave of a fre
quency one-half the recurrence frequency of said
not. At the same time, it will be clear that
impulses and having oddv maxima greater than
amplification and efliciency of the tube may be
even maxima, means for superposing said im
materially increased for this, the desired and
pulses and said rectified alternating wave, multi
useful instant of time.
It will be seen that I have provided a rela 70 vibrator means responsive to such superposed
energy and includingtime-constant decay means
tively simple radio transmission apparatus of
for delayingalternative operation of said multi
greatly improved efllciency and having many
vibrator means in accordance with the magnitude
other desirable features. While the invention
of said impulses so superposed, and derivative
has been described in particular detail and pre
ferred forms illustrated, it is, of course, to be 75 circuit means responsive to the output of said
2,406,019
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multivibrator means for deriving impulse peaks
corresponding to alternative action of said multi
11. In an impulse time-modulation transmit
ter, an impulse generator for generating a ñrst
vibrator means.
series of regularly spaced impulses and another
7. A transmitter according to claim 6, in which
additional circuit means responsive to modulat
ing energy is provided for modulating the magni
series of regularly spaced impulses of the same
frequency of recurrence _as said first mentioned
series, modulating means for time-modulating
impulses of said first mentioned series of im#
_ tude of successive maxima of said Wave.
pulses in one sense and for time-modulating im
8. A transmitter according to claim 6, in which
pulses of said other series in an opposed sense,
additional circuit; means responsive to modulat
ing energy is provided for modulating the 10 and means displacing impulses of said ñrst series
in time with respect to those of said other series,
greater maximaof said alternating wave in one
said displacing means being eiîective to displace
sense concurrently with modulation of the lesser
said iirst and said other series respectively to an
maxima of said alternating wave in a sense oppo
extent that an impulse of said first series always
site the said first-mentioned sense.
9. A receiver for an impulse-modulation com 15 precedes an impulse of said other series with an
interval of time greater than that by which an
munication system, said receiver including filter '
impulse of said ñrst series follows animpulse of
means passing a band of frequencies including
said other series, whereby succeeding impulses
a harmonic of the frequency of the received im
alternately determine an interval greater than
pulses, amplitude-detection means, and blocking
means responsive to a harmonic of said frequency 20 one-half the periodic recurrence of impulses of
one of said series and a succeeding interval lessof the received impulses, said blocking means in
' than said one-half.
cluding a generator responsive to said last-men
12. An impulse time-modulator transmitter
tioned harmonic for supplying» energy to cut out
according to claim 11, in which said displacing
reception of signals during substantially the pe
means is eiïective to displace said ñrst and said
riod between received impulses.
25
other series respectively to an extent that at
l0. A receiver for detecting time modulated
maximum modulation of impulses defining said
impulse energy, odd impulses of said energy re
succeeding interval, said succeeding interval will
curring with a given periodicity, said receiver
not exceed one-half the periodicity of recurrence
comprising filter1 means passing substantially
‘
only a band of frequencies immediately about 30 of impulses of one of said series.
an odd harmonic of said periodicity and ampli
EMILE LABIN.
tude detection means.
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