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Патент USA US2406803

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Sept. 3; 1946.
Filed nec. 1o. 1942
A A.
. Attorney
Patented Sept. 3, 1946
Praf‘ulla- Kumar Chatterjea and Leslie Wilfred
Houghton', London W. C. 2, England, assignors
to Standard Telephones and Cables Limited,
London, England, a. British company
Y Appiication December 10, 1era seriali No.r4sïs,572
~ ‘
¿In Great` Britain December 16, 1941
' 13 claims.
(Cl. 25o-'17)
A signalof this character is audible with quite
In nearly all time modulated pulse systems
used for transmitting intelligence of any kind,
good quality in a broadcast receiver designed for
the' amplitude of the*A signal` obtained at the re
ceiver is some-.function of the total time occurring
between the lead-ing and trailing edges of av pulse
in a trai-n of time Vmodulated pulses and it`V is
necessary to determine in general the duration
of each individual» pulse to reconstructY the in
the reception of arniîßlitude>> modulatedV Waves.
Another method and arr’a'ngernentsP have been'
proposed for achieving more or less the same ends
' by modifying the slope of one of tlieÀ edges of- the>
pulses-Lpreferably the edge which normally oc-v
curs at equal intervals of time, and preferably
the A.trailing edge.- Here thenV the' slopesf of the
A method of and arrangements for utilising- 10 trailing edge are characteristic of' the' amplitudes'
of a sound or like vvave.-- Inpractice,- itis foun’dY
pulseswhich are’ time modulated as a function
of the amplitude of a sound or like Wave have
that actually both edges are' modified’.
can be obtained from` one edge only of the sai
time modulated pulse'.`
The special advantages obtained from' these
been proposed in which the desired intelligence
' method-sy and-arrangementsare various, andpar-j
r15 ticular usefulness lies -inf the »dissemination of
The operation of this latter systemv is depend
ent upon transmitting atrai-n- of pulses so time`
modulated that said pulses-have a function char
propaganda, stoppage of» unwanted transmissiom
or transmission ofintelli'gfence over a large band
of frequencies. For example', one sig-nal can
transmit intelligence within' i6 dbs: level` over a
Wave (hereinafter also called “intelligence 20 band Width of 300 kc./s.»,- the signals being» re
ceived at frequency intervals throughout this
Wave”), said time modulation7 bei-ng character
acteristic of the Aanfipl-itude of a~ sound: or like
ise'd in that the ,time> interval betweenî the limits
of modulation is equal to the time> taken for a
fraction (preferably less than lyg) of a Wave
band and' the intervals being’. solely governed by
`the invention is> to render frequency modulation
intelligible in an amplitudeV modulation receiver.
the frequency of repetition of theV pulses. r- '
‘ The present invention has for its object to pro
length period of a radio frequency (this frequency 25 vide another .rr'iethodI of . and other arrangements
for achieving similar results. v Another .objectof`
itself is- large compared with the pulse repetition
At a- receiver said pulses .are used
to- interrupt a train' o'f oscillations (thesefbeing v
An electrical signal transmission system accord
at the carrier, i. e. at the said radio frequency)
and thel amplitude ci" the intelligence vwave r'e 30 ingï t'o the invention is characterised in that-once
a pulse train-has been initiatedi. e. a pulse dura
ceived is a function of the amplitude ofv the
tion of a certain repetition- freq'ue'ncy has been
damped oscillations at the interruptions' of the
pulse' train, which in turn is dependent at any' y rdecidedV upon,v the frequency or phase of the
m'oment on tlie time duration of the pulses-¿tinsV
carrier> alone is varied either _directly or indi
duration being modulated byY the intelligence 35 rectly according to the instantaneous >amplitude
Wave‘iny the manner described hereinbefore'. »
» of` the intelligence Wave.`
If fc be the carrier frequency at which the
The main requirement of such a system- is1 to
transmitter output is tuned, a change> ofv this j@
have at the transmitter a constant carrier (or
equal to -l_--Afc is-made characteristic of the ampli
r‘adioñ frequency generator which'. is set into os
cillation b'y one` edge of a sharp‘sh'ort pulse (say 40 tude ofthe intelligence Wave,` whilst the pulse
the loading edge). This oscillation buildsrup to
duration, the pulse repetition frequency, and the
a steady value in ati-ineI depending on- the sharp'
pulse slope arel maintained constant.
nessv of the initial rise' of the' pulse, among other '
factors, and the duration of the- pulse. The'trail
According to a feature of the invention the
trains of’r oscillations have initial amplitudes
ing edge of the same pulse in Ythis case initiates 45 which are characteristic ofthe modulating in
another forced oscillation intol the circuit', the^v
telligence Wave.
initial amplitui‘le‘l of this' second sety of oscilla
systems the transmission assumes the character
îsticsl of a’number of satellite side band- trans
As in all pulse transmission
tions being determi-ned mainly by the'v duration
of the pulse, other factors being' constant.
Id'eallyfo'f courseY the edges oi’ the pulse> have 50 , Using only the1 frequency modulation system
to' be absolutely straight to’make‘ possible the
faccording'to the" present invention, intelligible re
proper control of the initial' stage" of the" damped'
ce'ptionï` cannot-nodi be obtained in' receivers de'
oscillation, this is inv generall rather di-iiîcult1 t0
signe'df‘ only" for4 amplitude modulated' Waves'v be=
achieve without _extra precautioninî thev circuit
cause- a detectcr'for' amplitude modulated Waves
by itself is immune to Variations of frequency of
the applied oscillation amplitude results.
the applied wave. It will be convenient at this
point to indicate something of the relation be
tween phase modulation and frequency modula
It will be appreciated that frequency modula
tion and phase modulation are so related that
taking the simplest conception, a frequency modu
is shown in chain-line in Fig. 3. This would
also be the case if three or other odd number of
half-cycles of the applied oscillation occurred
during the pulse duration. It will be observed
that the amplitude of the damped trains set up
in the circuit is dependent upon the frequency
of the applied oscillations, providing the applied
lated wave is one with unvarying amplitude whose
" oscillations
frequency is varied cyclically above and below a
mean unmodulated value, and phase modulation 10 with the trailing edge of the pulse, and that the
applied oscillation Vswings through Zero during
in its simplest form can be shown to result in fre- .
the leading edge of the pulse. There thus oc
quency modulation.
curs the interaction of the Adamped waves due to
In Fig. 1 of the accompanying drawing is shown
the continued damped oscillation of the circuit
a vector OP representing an unmodulated carrier
on account of the applied oscillation (now ter
frequency w/21r where w=21rf, f being the fre->
fminated) and the damped oscillation set up by
thechange of voltage due to the trailing edge of
quency. Let its phase be advanced and retarded
sinusoidally (say) between -I-oi and -<p2 with
the pulse. The result is a damped train of waves
respect to the unmodulated state (e020). the Y „
whose frequency is that of the applied oscillations
20 and whose amplitude depends upon the Yrelation
This results in a peak-to-peak modulation
between the pulse duration and the periodic time
of the applied oscillations.
but it is important to note that only at the ex
Thus if the frequency of the applied oscilla~
treme excursion positions is the frequency of the
tions is made to depend upon the instantaneous
amplitude of an intelligence or other wave, both
rwave identical to the unmodulated state, the fre
vector remaining constant during the operation.
quency having alternately increased and de
creased With frequency maxima and minima oc
curring at P, the unmodulated state. In ’other
words, the instants of maximum phase. displace
ment and maximum frequency change are dis
placed from each other by 90° at the modulating
frequency. Thus if phase modulation is assumed
the frequency of the damped waves and the am
to be a certain function if, the frequency modu
plitude Vthereof carry the intelligence and the
amplitude modulation can be received by receiv
ers designed for amplitude modulated waves,
whilst frequency modulation can only be received
by receivers designed for reception of frequency
modulated waves. It will be understood by those
versed in the art that the amplitude of the
lation is inherently the rate of change of phase,
4 damped waves generated could be amplified and
i. e., the frequency modulation is a function, \I'
where \lf is the first differential Vwith respect to
ing the amplitude modulation. When the ampli
time of «In A very simple case is shown here to
express the similarity Ybetween frequency modu
lation and phase modulation. It is known that
constant phase modulation at all modulating fre
quencies results actually in more frequency modu
lation when higher modulation frequencies are
used than for lower modulating frequencies.
passed through a limiting device, hence eliminat
tude modulation is used, forced reception in re
ceivers for amplitude modulated waves is obtained
over a wide range of carrier frequencies and these
, carrier frequencies are determined by the pulse
repetition frequency of the constant duration
pulses applied to the circuit which produces the
damped trains.
Fig. 4 shows in block diagram an arrangement
stant duration pulses are used, since the deviation 45 for carrying out ’the invention. Here 3 represents
a pulse generator, the output of which causes os«
of the carrier frequency is made characteristic of
cillator l!A to start and stop as described, The
the intelligence. This is achieved by frequency
frequency at which this oscillator oscillates at any
modulating a carrier wave in a certain predeter
time is characteristic of the signal (i. e. the out~
mined manner, and then modulating by a train4
of pulses of constant duration. The application ‘Í ï put of the modulation amplifier 5), thig frequency
Y being generated by any known method,
of phasemodulation to provide a similar result
The details 'of one circuit arrangement em
will be apparent to those skilled in the art from
bodying the invention is shown in Fig. 5. InV this
the description hereinbefore given on `the simi
arrangement the carrier is provided by an oscil
larity between phase and frequency modulation.
The term “angular modulation” is used herein to "' lator cut in and out of use under the control of
'In one way of carrying out the invention con- '
denote both frequency and phase modulation.
The invention will be further elucidated in the
following description. Referring to Fig. 2 of the
accompanyingdrawing, a pulse which is> applied
to a resonant circuit is shown as of such dura
tion that one cycle of a carrier wave applied to
the same circuit is allowed to occur. The pulse
is shown as occurring as the oscillation swings
the constant duration pulses and whose frequen
cy is under the control of the intelligence wave
to be transmitted. In Fig. 5, the reference 'è
indicates an voscillator. valve with associated
tuned circuit l comprising inductance L and ca
pacity C. This oscillator is normally negatively
biased so that it oscillates only during the period
`that a positive pulse is applied to the grid thereof
from a valve ¿i which is the output valve of a
in the positive direction and the forced oscillation
set up by the trailing edge of the pulse is in op 65 pulse generator. The frequency at which valve
6 oscillates is governed, not only by C, but by the
position t0 the applied oscillation. Assuming that
input capacitance of valve 9 which is in parallel
the amplitude of the forced oscillation is equal
with the tuned circuit l. By means of the cir
to the amplitude of the applied> oscillation, the
cuit associated with valve 9 the input capacitance
resultant amplitude of the circuit oscillation is
zero, so that if the applied oscillations are inter 70 of valve 9 can be'made to vary by varying its bias
voltage, which can be made to represent a given
rupted at the'moment of the trailing edge of the
modulationA signal,V obtained from valve if! and
pulse, the circuit ceases to oscillate. If the oscila
its associated circuit. rThe valve il! may, >for in
lation frequency is as shown in Fig. 3, the volt
stance be an amplifier for the intelligence wave
age induced by the trailing edge 2 will be in phase
with the applied oscillation, and a voltage of twice> " Ul ' to be transmitted, and whose output is passed
amplitude ,of .the respective trains also in ac
throughV a bias resistance in the grid-cathode cir
cuit of the valve 9,. A capacity Il çis connected
between the grid of 9 and the tuned circuit ‘LC
cordance with the instantaneous amplitude of
4-saidintelligence Wave.
6. An electrical signal transmission system as
of valve 6.
‘ ` ‘ `
The resulting varying dampedl train formed C31 claimed in claim 4 wherein the said resonant cir
cuit is comprised in the regenerative feedback
in circuit 'I may be obtained by any known method
of coupling shown in the drawing as' being in
circuit of an oscillator, andthe pulses are applied
ductively coupled to L, .and should .preferably be
vto set said'oscillator into oscillation and are ap
plied also to the said resonant circuit whilst the
transferred directto a transmitting aerial indi
intelligence wave to be transmitted as the angu
cated at A.
lar modulation of said trains of waves is applied
What is claimed is:
to control the frequency of said resonant circuit.
1. An electrical wave signal transmission sys
7. An electrical signal transmission system as
tem comprising means for generating short trains
of damped carrier waves, an intelligence wave
claimed in claim 4 wherein the said intelligence
wave is applied to control a capacity in said res
source, means for subjecting the carrier waves
comprising said wave trains to angular modula
onant circ-uit.
8. An electrical signal transmission system as
tion in accordance with the instantaneous ampli
tude of the intelligence Wave, and means for im
claimed in claim 4 wherein said resonant circuit
includes a capacity comprising the grid-cathode
pressing the resultant modulated wave trains up
20 capacity of a thermionic tube and means is pro
on a transmission medium.
2. An electrical Wave signal transmission sys
tem comprising an oscillator for generating car
rier waves, a source of constantly repetitive elec
trical pulses, an intelligence wave source, means
for applying said pulses to said oscillator to cause
it to generate short trains of carrier waves, the
duration of a train after the end of the initiating
pulse depending on the duration of said pulse,
means for angularly modulating the carrier
waves comprising said Ywave trains in accordance
with the instantaneous amplitude of the intelli
gence wave, and means for impressing the re
sultant modulated wave trains upon a transmis
sion medium.
3. An electrical wave signal transmission sys
tem comprising an oscillator including an elec
tron tube having a cathode, an anode, a control
vided to apply said intelligence wave to Vary
the grid bias of said last-mentioned tube in ac
cordance with the amplitude of said intelligence
9. An electrical signal transmission system as.
claimed in claim 4 wherein said resonant circuit
is coupled to a radiant acting antenna.
10. The method of electrical carrier wave sig
nal transmission which comprises generating a«
30 first series of vshort trains of damped carrier
waves, superposing a second series of short trains
of damped carrier waves on said first series, dis
placed a predetermined constant time with respect
to said first series, and varying the frequency of
said carrier Waves of both said series in accord
ance with the instantaneous value of an intelli
grid, and regeneratively coupled anode and grid
circuits, means for negatively biasing said grid .to
inhibit oscillation, a source of positive electrical .
pulses, means for applying said pulses to said
grid so as to cause said oscillator to generate
shorttrains of carrier waves, means to cause the
time duration of said pulses to determine the
time duration of said trains in excess of said
pulses, an intelligence wave source, means for
gence wave to be transmitted.
11. An electrical wave signal transmission sys
tem comprising a resonant circuit, means to vary
the resonance of said circuit in accordance with
the instantaneous Values of an intelligence wave
to be transmitted, means t0 apply an oscillation
at the frequency of said resonant circuit to said
circuit for repeated short periods of time, Where
by trains of damped oscillations are set up in
said resonant circuit, means for repeatedly shock- ,
angularly modulating said trains of carrier waves
ing said resonant circuit at a constant time after
in accordance with the instantaneous amplitude
the setting up of said trains of oscillations, where
of the intelligence wave, and means for impress
by additional trains of oscillations of the same
ing the resultant modulated wave trains upon 50 frequency are set up in said circ-uit having a phase
a transmission medium.
relation to the oscillations of said first trains
4. An electrical wave signal transmission sys
which is dependent on said constant time, a
tem comprising means for generating short trains
transmission medium, and means for impressing
of carrier waves, a source of constantly repetitive
the resultant modulated oscillation trains in said
electrical pulses of constant time duration, an 55 resonant circuit upon said transmission medium.
intelligence wave source, means kfor angularly
12. An' electrical wave signal transmission sys
modulating said carrier waves comprising the re
tem, comprising a resonant circuit, means to vary
spective trains in accordance with the instanta
they resonance of said circuit in accordance with
neous amplitude of said intelligence wave, a res
an intelligence wave to be transmitted, means to
onant circuit, means for applying said carrier 60 generate short trains of damped. carrier waves in
' waves to said resonant circuit, means for apply
ing said pulses to said resonant circuit in such
time relation with respect to said carrier waves
said resonant circuit at the frequency of said cir
cuit, means to generate additional trains of car
rier waves in said circuit at a constant period of
that each pulse is applied substantially at the
time after the initiation of said ñrst wave trains,
instant when the carrier amplitude is passing 65 said period of time «being such as to give a maxi
through zero amplitude in the same direction as
the pulse, and means for coupling said resonant
mum output of said resonant circuit as a result
ant of both said trains of carrier Waves for one
extreme frequency adjustment of said resonant
circuit, whereby the resultant of said two trains
nal transmission which comprises generating 70 of carrier waves Will depend for its amplitude on
said period of time, a transmitting medium, and
short damped trains of carrier waves, angularly
modulating the carrier waves comprising the re
~ means for impressing said resultant modulated
spective trains in accordance with the rinstan
wave trains upon said transmission medium.
lf3. An electrical Wave signal transmission sys
taneous amplitude of an intelligence wave to be
transmitted, and amplitude modulating the initial 75 tem comprising means for generating constantly
circuit with a transmission medium.
5. The method of electrical carrier wave sig
repetitive electrical pulses of constant time dura
carrier waves by the trailing edges of said pulses,
tion, a resonant circuit, means to initiate in said
means to vary the resonance of said resonant cir
cuit in accordance with an intelligence wave to
resonant circuit trains of oscillations at’the ire
quency of said circuit, said means being operative
be' transmitted, a transmitting medium, and
for the time duration of said pulses, whereby'the Ul means to impress the resultant of said trains of
trains of carrier waves continue as damped os
carrier waves in said resonant circuit upon said
cillations after the cessation of said initiating
transmitting medium.
means, means to apply said pulses to said reso
nant circuit so as to create additional trains of
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