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Патент USA US2406881

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Sept. 3, 1946.
` Filed Sept. 19, 1942
ëÍ D %
Patented Sept. 3, 1946
Norman H. Young, Jr., Jackson Heights, N. Y., as
signor to Federal Telephone and Radio Corpo
ration, a corporation of Delaware
Application September 19, 1942, Serial No. 458,934
8 Claims. (Cl. 179-1.5)
This invention relates to a new method and;
system for communicating intelligence, and is
tion I0. The output of the receiver 38 is con
nected, on theone hand, to a pilot filter 40 which
particularly adapted for use as a secret radio
is sharply tuned t0 the frequency 0f the pilot
l Accordingly, an object of this invention is to
oscillator I2 a1; the transmitting station and to
a harmonic filter 44 tuned and employed to ex
provide a novel and simple method and means
tract the phase modulated harmonic component.
for communicating intelligence secretly.
`Another' object of this invention lies in provid
The pilot filter 40 is used at the receiver 35 as
a local pilot frequency generator, and the output
therefrom passes through a frequency multiplier
ing a novel method and means for transmitting ,
intelligence which can be intelligibly received 10 ¿i2 comparable to the frequency multiplier IG at
only upon a properly correlated receiver.
the transmitting station. By means of a bal
Other objects and advantages of the invention
anced detector 46 the phase-modulated harmonic
will become apparent from the following descrip
tion of a preferred form of system, illustrated
in the accompanying drawing, in which:
Fig. 1 is a block circuit diagram of a complete
transmission system in accordance with the pres
ent invention; and
Fig. 2 is a diagram illustrating the operation
of the system by means of correlated curves.
Referring specifically to Fig. 1, and more par
ticularly to the transmitting station I0, the latter
will be provided with a constant frequency source
derived from the filter 44 and the unmodulated
harmonic derived from the frequency multiplier
42 are compared and the diiîerence in phase is
translated into suitable audio frequency signals
which, through an amplifier 4I are impressed
upon the loud speaker 50. The balanced detector
4:6 used for demodulation may be of the type
20 known in the television art as a “discriminator”
such as described, for example, in the book “Prin
ciples of Television Engineering" by Donald G.
Fink, page 405, Fig. 250, published by McGraw
Hill Book Company, Inc. 1940.
is passed through a frequency multiplier I6 to ,25 It is believed that the operation of the afore
produce oscillations at a harmonic frequency.
described system will be clear to those skilled in
The frequency multiplier I6 is preferably a fre
this art. It involves the principle of modulating
a carrier wave as for example, by amplitude mod
` quency tripler of some suitable well-known con
struction. The outputl from the frequency multi
ulation or frequency modulation, by means of a
plier I6 passes through a suitable phase modu 30 wave which is a-combination of a fundamental
such as a pilot oscillator I2, the output of which
lator 22.
’ At ,I8 I have provided a microphone as an eX
ample of a suitable intelligence translating de
vice, the output of the microphone I8 being pref
erably amplified by audio amplifier 20 and ap
plied to the phase modulator 22 to phase modu
late the harmonic oscillations received from the
frequency multiplier IE.
wave such, for example, as a 10 kc. wave and
the phase-modulated harmonic thereof, such as
a phase-modulated 30 kc. wave. The resultant
signal or intelligence which is transmitted will be
35 diflicult of detection and can only be reconverted
into an intelligible signal provided the receiver
is equipped with means for providing a source
_of frequency exactly the same as that provided
at the transmitter and with the proper accurately
In a suitable mixer 26 the phase modulated
harmonics from the phase modulator 22 are 40 designed harmonic filter. If the frequency multi
plier I ‘à at the transmitter also reverses the phase
added to the fundamental wave derived from the
of the harmonic by 180° the modulation of the
pilot oscillator I2 to produce, by simple addition,
a resulting wave which will vary slightly in ac
carrier wave in accordance with the transmitted
intelligence will be most difficult to detect by un
cordance with the amount of phase deviation of
the harmonic component. This resulting wave is 45 authorized receivers, as the resultant voltage
change in the modulating wave will be extremely
impressed upon a modulator 28 connected be
slight. This may be graphically illustrated by
tween a suitable carrier wave source 32 and the
transmitter 30. The resultant modulated carrier
way of example in Fig. 2, in which the wave A
wave will then be radiated by antenna means 34.
may represent the fundamental frequency pro
The receiving station generally indicated at 35 50 duced by the pilotI oscillator I2 while B repre
sents the third harmonic with a 180° phase shift.
will include an antenna 36 connected to a re
ceiver 38, which will include suitable demodu
The resultant wave produced by the addition of
lating means for demodulating the basic carrier
waves A and B when the wave B is exactly 180°
in accordance with the type of modulation em- '
out of phase with the wave A, is represented by
ployed at modulator 28 of the transmitting sta
the curve C. The phase modulation of the har
monic B which, in most cases, will not exceed
30° of the harmonic or 10° of the fundamental
ceiver, a frequency multiplier connected to said
pilot frequency filter, a balanced detector fed
will produce a wave C’ which, it will be noted,
will differ only slightly in amplitude from the
wave C. The Wave C’ is the resultant of the ad
from said harmonic filter and said frequency
dition of the fundamental A to the harmonic
B' shifted 30° relatively to the wave B. It will
be noted that by shifting the harmonic 180"V with
respect to the fundamental A the peak of the
harmonic substantially coincides with the peak’
of the fundamental thus producing sharply de-1
fined peaks in the resultant wave. As previously
2. The combination according to claim 1, in
which said frequency multipliers include means
for shifting the phase of the derived harmonic
multiplier, and audio output means connected to
said balanced detector.
3. The method of transmitting and receiving
intelligence'which includes the steps of phase
modulating a harmonic of a predetermined pilot
frequency >in accordance with audio signals, add
ving 'the phase-modulated harmonic and the
mentioned,'however, the peaks of the resultant
wave will differ only slightly in amplitude for
relatively large phase shifts in the harmonic. 15 >'fundamental pilot frequency together, transmit
ting the wave resulting fromrthis addition, re
Preferably, the amplitude of the harmonic Will
ceiving Vsaid wave, separating the pilot frequency
be approximately no greater than 30% Of the
and harmonic, changing the filtered pilot fre
amplitude of the fundamental. It is to be noted
quency to the same’frequency as the harmonic,
that if the frequency multiplier I6 at the trans
mitting station includes means to shift the phase 20 comparing the phase deviation between the fil
tered harmonic and the- derived harmonicLand
of .the harmonic 180°, similar means must be in
r'ern‘o'dlicing> the `audio signals in laccordance with
clude'd in the frequency multiplier 42 at the re
ceiving station.
said phase deviation.
scribed 'system Without departing from the prin
cîples of thev present invention. As has been
previously mentioned, the manner in which the
carrier-'wave is 'modulated by the ’resultant phase
’ modulated wave is unimportant.
_4. A transmitting station including, in com
vlÍt will be clear to those skilled in this -art 'that
various changes may be 'made in ‘the afcrede
bination, a transmitter, -a source of carrier Waves,
a modulator connected between said transmitter
and carrier wave source, a iirst constant fre
quency source, a
second constant frequency
, source producing a frequency which is a harmonic
The manner in 30
of said first constant'frequency source, means
which the pilot >frequency Vand harmonic are gen
for modulating the phase of said harmonic in
erated `is likewise of no particular importance.
instead of phase ’modulating the harmonic by
translated audible signals, the source of intelli
gence can be of any type which will suitably
operate the phase modulator v22. Changes in the
'details of the transmitter l0 will also result in
comparable Achanges in details of the' vapparatus
accordance with signals to be transmitted, means
for adding saidV phase-modulated harmonicV to
used at 'the receiver 35. It is also obvious that
said ñrst constant frequency source, and means
for impressingY the 4resultant _of such addition
upon said carrier wave modulator.
l’5. The combination according to claim 4, in
combination with a receiver adapted to be tuned
to ’said transmitter, means connected to said re
as far 'as the basic principles of this invention
ceiver for 4obtaining the `phase-modulated har
are concerned, it is possible to phase modulate
the ‘lower frequency wave instead of the higher
'frequency wave provided, of course, the yfrequen
monic, >a 'constant frequency source at said re
cies are harmonically related.
While the system ‘according to my invention
is particularly adapted for use in radio Ycommu
nication, it will also be clear that a direct line
y ceiver producing the unmodulated harmonic,
means forV comparing ksaid phase-modulated har->
monic with; said locally generated harmonic, and
means'ifor reproducing the transmitted signal in
accordance with the differences in phase between
said harmonics.'
‘connection between the transmitting stationk and
y675A ‘transmitting station including, in combi
the receiving stationcan be used, if desired.
Accordingly, while for the purposes of ldescrib
ing the invention, reference hasbeen made to
nation, a transmitter, a lsource ofl carrier waves,`
a modulator connected between said transmitter
certain speciñc ‘devices and'relationships, it is to
‘be understood that the invention is not limited
thereto except as maybe required 'by the claims
which follow.
~What I claim is:
A transmission >system comprising, in com
source, 'a frequency Vmultiplier Iconnected Vto said
and carrier wave source, a constant frequency
constant frequency source, a phase modulator
Aconnect/ed 'to said frequency multiplier, a mixer
connected to said carrier wave modulator, means
for feeding the> output 4of vsaid constant frequencyY
source and of said phase modulatorjto said mixer,
loination a’transrnitting station 'including a trans- `
and a variable frequency signal source opera
tively connected -to said phase modulator.
mitter, a source of carrier waves, a modulator
'connected between said transmitter and carrier 60 Y"7. The combination vaccording, to claim lo, in
wave source, ‘a 'pilot oscillator, a frequency mul
which lsaid frequency multiplier includes means
tiplier connected to said pilot oscillator, a phase
for shifting 'the phase of 'the harmonic 180".
modulator fed by said frequency multiplier, a
8. The method of signaltransmission, which
mixer connected to saidvcarr'ier modulator, means
includes the steps :of lphase modulating a waveV of
‘for Iïf'ee'ding'the output of sai-'d` pilot oscillator and 65 frequency -harinonically related to 'a ‘predeter-~
said phase modulator to said mixer, and an audio
mined 'pilot frequency in Yaccordance with the
frequency source connected to said phasemodu
signals to betlîansmitted, adding the phase modu
later, and a receiving station including a receiver
lated >frequen cy to the ‘pilot frequency, and ‘moduf
adapted to‘receive signals from said transmitter,
lating a carrier 'wave‘by the wave resulting from
aïpilot frequency filter and a harmonic frequency 70
filterboth connected to the »outputof said re
this addition.
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