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Патент USA US2114036

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April 12, 1938.
J. w. SMITH Er A1.
2,114,036
FREQUENCY STABILIZATION SYSTEM
Filed oct. 17, '- 193e
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4 Sheets-Sheet> 1
HAIL/2ER
A TTORNEY
2,114,036
April 12, 1938.
FRÉQUENCY
' J. W.STABILIZATION
SMITH El' SYSTEM
Filed. oct. 17. 1956
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FREQUENCY STABILIZATIOÀÈ ‘.SYSTEM
'
4 Sheets-Sheet 5
Filed oct, ‘17,’ 1956
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J W SMITH
M THAYER
BY
ATTORNEK
April 12, 1938.
2,114,036
.1.w. SMITH ET AL
FREQUENCY STABILIZATION SYSTEM
Filed Oct. 17, 1936
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YER
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ATTORNEY .
«2,114,036v i
Patented ìApr. >12, 1938
‘UNITED s‘rii'iffi‘isy -' `PAT’rau-r;
orricsî '
sume '
MQUENGY _ BTAB'ILIZAÍIQN SYSTEM
Jenn w. animera-raton.'
'cnam
u.A
to Bell
Theron Glen aus». N. I.,
Ineerporatedr
'Newv
Telephon Laboratories.
York, N. Y., ‘corporation of New York
snpuesann'omm 1v. im. anni s». nous 'L_ _
~
s casina».v (Cl. lll-13» ’
This invention relates to high frequency com»
munication systems and more particularly to fre
quency stabilization means therefor.
„
The principal obiect of the invention is to ef
g fect the stabilization of the carrier frequency -in
very high .frequency communication systems. an
other object is to stabilize the mean frequency
of the carrier wave in frequency modulation sys
moves the unwanted frequency modulation 'without affecting the amplitude modulation.
I
These results are accomplished in accordance v '
with the invention by a feedback system which
picks up part of the radiated wave, analyses the 5
frequency variation thereof, converts the ,fre
.quency variations into corresponding amplitude
variations of a control current, and applies the
control current variations to the oscillator in
tems, and a third lobject isto eliminate or reduce which
radiated wave is generated in such 1o
10` >unwanted frequency modulations in amplitude mannerthe
andinsuchphase asto oppose the fre
modulation- systems. A further object is the
change.v
'_
`
~
elimination of distortion producing frequency quency
In the application of the invention to a fre»
.variations in frequency modulated systems.
In signaling systems designed to -operate at ‘quency modulation system. the varying control j
1l very high frequencies, for example, at frequencies current is fed back to thefrequency modulating- le.
device ci'.7 in eifect. to the moduiatingsignsl in-.
_ corresponding to‘iradio waves of the order of one
meter or less in length. modulation of the carrier
‘ wave may be-eifected by varying either its ampli-
put circuit. The control current preferably re-
.
produces all of the signal variations together- with A,
other frequency deviations that may occur.
tude or its frequency in proportion to the strength ' _any
for
example,
slow changes due to instability and w
' m of the modulating signal. In the case of ampli
other
causes.
The feedback is then of a stabiliz
tude modulation it is desirable Athat tho-carrier ing character and
system is analogous to the
frequency be‘stabilized at a constant preassigned stabilized feemckthe
ampliñcr mcribed by H. B.
frequency and in the case of frequency modula
in an article entitled “Stabiiiued Feedback
tion it is desirable that the mean frequency of the Black
Amplifiers”, ml! System Technical Journal, Jan»- 25
2s .carrier be held constant.
_
4 When frequency modulation is used', the carrier
wave lgenerator is »preferably an oscillator of a
type such that the frequency generated vcan be
uary 1934. ,By the use of a strong feedback or
control applied in reverse phase to the signal in
put, undesired frequency deviations are substan
"im, DEM.
varied readily through a wide range under the tißuy
’As stated above. preferably >the whole of the gg
w influence of an applied signal voltage. Fixed fre- - detected signal and the accompanying undesired
quency oscillators, such as piezoelectric crystal variations are fed back to exercise the stabilizing
controlled oscillatorsî are not suited for this pur
control. However, it is possible and may, in some
_ pose and other available types are subject to'
' slow variations which. at very high frequencies,
35 may amount to avery large number ~of cycles.
' By the'present invention these slow drifts of a
frequency modulated oscillator are substantially
prevented while at the same time the desired
frequency variations in accordance withthe modi-4
40 ulatingsignal‘are retained. '
cases, be desirable to feed hack only the slow
variations for the purpose of preventing` slow 35 ,
drifts of vthe mean frequency. This may he ac
complished by a slight modification of the inven- . Y
tion.
»
when the invention is applied to amplitude
modulation systems, the feedback or control is 40
not impressed on the signal input circuit, but on
In amplitude modulation systemsoperating at .an
auxiliary frequency control means through
the very high frequencies indicated above, rela
tively iarge power outputs are obtained most con
veniently -by means of an oscillamon generator
` 45 couples to the radiating antenna and oscillating
which it exerts a quick acting compensating con»
trol of the' frequency.
-
l
,
Since the stabiiizins ¿system of the invention 45
also acts as a detector for frequency modulated
directly at the carrier frequency. Crystal con
waves. it may be operated as a receiver vin con
trolled osclllatorsare not well- adaptedÀ to auch junction with the transmitter. therebyproviding
high `frequencies becausev of the minute dii-irgen-` s two-way transmitting and receiving equipment
u sions of» the crystals required. Furthermore, in vwhich frequency stabilization of the trans- 50
oscillation generators of the available types for mitt'er is accomplished with a minimum of ap
operation at these frequencies are generally sub
Other features of the invention relate to limit
ject to large simultaneous frequency modulations
when amplitude modulation is attempted.. The' ing the range of operation of the frequency sta
55 -controlsystem of the invention substantially re bilisation equipment and indicating the operative 66
A
2,114,086
' condition; ‘toV switching arrangements whereby
either frequency modulation or amplitude modu
lation may be'used as desired; and to means for
removing amplitude modulations in a received
frequency modulated wave.
_
»
The nature of the invention will be more fully
understood from the following detailed descrip
tion and by reference to the accompanying draw
ings, of which
Fig. 1 is a functional schematic of a complete
station for two-way radio communication em
bodying the invention;
`
proportional to the current intensity, thereby
changing ‘the natural Iperiod of the oscillator
tuned circuit and effecting a variation of the
carrier frequency substantially proportional to‘
the signal. Whenl the microphone is connected
to transformer I3, by operating switch I2 to the
left, the amplified speech voltage is superimposed '
on the steady plate‘ voltage of the oscillator
thereby producing amplitude modulation of the
carrier wave.
_
'
4
The feedback circuit includes an antenna con
sisting of a receiving doublet I8, i9’ so placed as
lo..
Figs. 2, 3, and 4 when ñtted together as shown to receive waves radiated from antenna 8, 8'.
in Fig. y6 constitute a more detailed schematic A transmission line 20 couples doublet i9, i9' tov
15 representation of such a station; and
a. demodulator 2i for transferring the intercepted 15
Fig. 5 shows the response curves of filters used
in the system.
.
The system shown schematically in Fig. 1 com
prises, essentially, a high frequency transmitter
20 arranged for operation either with frequency
wavesl to a lower frequency range by heterodyne
demodulation.
The frequency reduction ac
centuates the frequency variations and. at the
same time facilitates‘ampliilcation. The neces
sary beating oscillations for heterodyning are de 20
rived from an oscillator 22 -controlled by `a. piezo
electric crystal resonator !I, the frequency of the
modulation or with amplitude modulation and
provided with feedback circuits for the stabiliza
tion of the mean radiated frequency. In addi > generated oscillations being multiplied to a sult
tion to this, the system includes switching and able high value by means of a harmonic genera
25 circuit arrangements whereby part of the feed
tor 24.
'
25
' Amplification of the reduced frequency currents '
back circuit may be utilized for the detection and
reception of incdming signals and a guard cir
to a suitable degree is obtained in a- wide band
cuit for limiting the operation of the feedback 'amplifier 25 which provides substantially uni
control. The transmitter portion of the system form gain over a frequency range wide enough
so and its stabilizing circuits will be described ñrst. vto accommodate all of the frequency variations
The carrier wave generator comprises a triod'e likely to be encountered. The intermediate fre
quency amplifier preferably consists of a large'y
tube' i to the grid-> and- plate of Vwhich are con
nected Lecher wires 2 and 2’ forming an oscilla
number of stages, as shown in greater detail in
tion circuit. Preferably the oscillation generator ' Fig. 3, to‘produce a strong feedback effect.
at extremely .high frequencies, the frequency of
The portion of the feedback »path following the- 35
intermediate frequency ampliile'rincludes la de- .
'the oscillations is determined mainly by the re
tector-converter circuit wherein is developed a
actances' of the oscillation circuit. Plate current
control voltage corresponding in' magnitude and
sign to the variations of the frequency ofthe
carrier oscillations from a preassigned fixedv. value.
85 is of the negative grid type, in which case, even
,
is supplied to the oscillator tube from battery l
v40 and a suitable negative bias is applied to the grid
f by battery 4.- Alternatively the negative grid
bias may be furnished by the fall of potential due
to the plate current in choke coils 5 and l' in
serted in the ñiament leads. Condenser O con
45 nected across the ends `of _the Lecher wires forms
a short circuit for the high frequency currents
and high frequency 'chokes 'i4 and 1’ serve further`
to isolate the oscillation circuit `frolnthe cur
40
' The feedback circuit divides into two vpaths at -
.
_the outputl terminals of amplifier _!I, one path
including buffer amplifier 2l.' frequency selective
filter 21, rectifier 28, and output resistance 20,'
and the `other path including respectively corre
sponding elements 33, Il, 3l, and 3l. The ele
ments in the two paths are similar with the ex
‘ception of lthe illters 21 and. Il. v These are de
¿rent supply circuits. An antenna consisting of - signed to produce attenuations 'which are equal
50 a radiatingv doublet l, l' is coupled through a‘
transmission line „I to appropriate points on the
Lecher wires to effect the maximum energy trans
fer.
"
Adjustment or control of the carrier frequency
at vthe lassigned value of the mean ¿carrier fre 50
quency, but which vary in opposite senses with
variations of .tha frequency therefrom. The
. filters may be high-pass and low-pass types re
spectively so proportioned that their attenuation
is effected by a variable condenser comprising v characteristics cross in theranges 'of increasing
ilxed plates i5 and Il connected respectively to , attenuation adjacent the cut-ot frequencies.-
- -the plate and grid of the oscillator tube and mov
However, for operation at high frequencies, it
able plate Il symmetricallydisposed with respect will generally be more convenient to use simple
to the fixed plates. Plate Il is mounted on the resonant circuits tuned respectively to frequen
moving element of a polarized electromagnetic ' cies above and below the desired reference fre
:ging device I4.' the details oi’- the condenser quency. The transmission characteristics of a
'
its driving means v.being shown more fully pair of such- tuned~circuits arel represented by
in‘ Fig. Á2. The-motion of the' plate I1 isre
curves ll'and Blof Fig. 5. The point at which
the> curves cross represents lthe frequency at
strained by a spring Il which-_makes the dis
65 placement substantially proportional to the our
which the intermediate carrier, or its mean value,
- rent delivered to the‘devlce.
Microphone I0 -'is connected through a signal
amplifier Il and a two-way switch. l! 'eitherfto
the~terminals of device I4 or to a transformer.
i3, the secondary of which is included in the
oscillator plate circuit. When switch i2 is -moved
to the right the microphone is connected to the
actuating winding of device Il. Amplified speech
` currents from Vlmicrophone l0 `will then produce
is stabilizedthe actual carrier frequency being
equal to this value plus> the frequency of the fixed
heterodyne wave.
Ass
_
.
.
j
'
that >_the oscillation amplitudes vre
main constant at thel output terminals of ampli 70A
'fiers 2l and“, the outputl voltages of filters 21
and “_ will vary in amplitude in opposite ,senses
as the oscillation frequency varies and will be
equal at the frequency‘edetermined by the inter
synchronous displacements of condenser plate I1' section offthefllter characteristics. Rectification
3
_
_
.
_
,
Y
ananas
l of these voltagesby rectifiers -28 and I! will there
variations representing signal distortion are elim->
fore produce variable low frequency voltages in
y resistances 29 and II corresponding to the -_fre
frequency. The elimination of the undesired fre
inated and which is stabilized about a fixed mean _
quency drifts is eßected in a manner analogous
to the elimination of non-linear distortion in the
quency variations of .the carrier. By connect
» ing the resistances diiferentially'to a common cut
stabilized feedback amplifiers described in the lar-v
put> circuit. a differential voltage kis obtained
ticle by H. S. Black previously mentioned.
therein which is directly proportional to the
In the system illustrated frequency- modulation
' frequency vdeviation from the assigned carrier
is producedby electromechanical control of the
frequency and which is of sign corresponding to
the direction of the deviation.
l
In order that the input voltagesof ñlters 2_1
and I4V may' be maintained free from amplitude
variations. a quick acting automatic volume cori
trol, which will be described later, is provided for
oscillator tuned circuit; Since _the stabilizing con
trol currents are fed back to the-signal input
circuit, it is manifest that the stabilizing action,
in the case of frequency» modulation, is independ
ent of the particularmeans used to effect the
amplifiers 26 and-Il. Volume limitera of known ‘
modulatiomwhether electrical orv mechanical, and
.The differential control voltage derived from
transformer il. The feedback circuit in this case
typesmay also be used. for example, the tubes of the _type of oscillator. l
When the system' is operated with amplitude
of amplifiers fl and Il_may be operated at a
'modulatiom
_the signal voltage is impressed on
point above plate current saturation so that'the the plate of the
oscillator vacuum tube through
outputs are held substantially constant. '
the detector-converter F_circuit is applied to a
push-pull direct current amplifier“, l2, through
an equalizer or filter network Il. vThe output
, terminals of the direct current ampliñer are con
. nected to the actuating winding of control device
I4, 4the connection being so poledy as to bring
Ä about the proper frequency compensating action.
The purpose> of'equalizer network ll. is to insure
that the control currents are maintained in the
30
proper phase relation at all frequencies in the
operating range. Usually this networkl may be
omitted since the phase >variation in the feed
back loop is generally negligibly small.
does not reproduce the amplitude' variations of
the carrier, because of the amplitude control of
amplifiers 28 and 3ft, but does produce control
currents corresponding to frequency variations of
thecarrier. These will, in general, include varia
tions due to oscillator instability and also vun
wanted frequency modulations produced by and
corresponding to the modulating signal voltage.'
The control currents are fed back to control de
vice i4, as in the case of frequency modulation,
and act thereon to produce a compensatingad
justinent of the oscillator frequency. Since there
is no' degenerative feedback to\tl1e signal input
'The stabilizing action of the .feedback control ~ circuit a less powerful signal input maybe used.
may now be described.
' -
_
_'
_
. For both of the methods of operation described
n
above, it is desirable that the whole of the feed
Consider, first, the case -of _frequency modula
tion,- vfor which the input signal or
cur
rents -areimpressed directly upon the frequency
control or modulating device Il. Variations of
the radiated frequency corresponding to the >signal currents are produced bythe action of de
vice i4. These variable frequency oscillations are
.picked up by antenna I9, i0', together with any
other variations that may arise' in the
e
Aitself due to instability or other causes.
feedback circuit the detector-con'_verterl repro
duces the signal currents in'.I amplified form to
' `gether with other current components corre
back loop be capable of transmitting freely all of
the signal'I frequencies, for example the voice' '
range. and frequencies down to zero. It ls possi
ble by a simple modification to confine the trans
mission in the feedback loop lto very low frequen-'
cies, thereby stabilizing the oscillator‘against slow
variations only. This may beaccomplished by
substituting for the phase equalizer 30 a Aresist
ance~capacity filter designed to transmit only
direct current and very _low frequencies. With
this arrangement, however, the stability obtained
is mu'ch less complete than with the broad-band
l
sponding to the unwanted frequencylvariations. . feedback and the several advantageous operating
All of these currents are fed back into the signal characteristics mentioned above are not obtained.
input circuit from the output of ampliiier 3|, lf, ' In order that the operation of the stabilizing
in such phase as to oppose the original signal feedback control may be confined tothe frequen- '
. cy range between the resonances of thefilters 21
currents
therein.
'
~
,
_
When the gain in the feedback circuit is large
so :that a strong feedback is obtained, `the net
result is a large reduction of the effective signal
input voltage as compared with the voltage deà
livered by the signal ampliner Il. The gain in
this ampliner must therefore be made large
enough so that the net resultant inputv is- lsuffi
cient to produce the desired range of frequency
‘ modulation. We have found that with a strong
' reversed phase feedback, those .frequency varia
and Il a guard circuit is provided winch inter
rupts the plate current supply to ampllner Si,
32, when the frequency approaches these limits.
’I‘he guard circuit branches from the output of '
intermediate frequency amplifier 25 and includes
amplifier Il, band-pass filter 41, detector _“,
load resistance B0, direct current ampliner ii and
relay Il, the back contact of which controls the
plate current supply to tubes 8l and 3_2. The
pass-band of filter _41 lies between the resonance
frequencies of filters 21, and 34. as indicated by
tions which havetheir origin in the voscillator
' itself, and which therefore do` not correspond »to curve u of Fig. 5. When’ the oscillations lie.
‘the signal input, are reduced in magnitude in sub v‘within this range, relatively large currents areA
~ stantially the same proportion as the effective passed to rectifier 4l and a correspondingly large
voltage is developed across resistance
signal input voltage is reduced -by the feedback. negative
Il.
This
negative voltage is impressed on the
`By making the 'feedback very large. the unde
gridof
amplifier
Il, reducing the plate current 70
sired frequency 'variations may be therefore sub
and
causing
relay
B0 to release and close the ain-l
»stantiallyeeiiminatedr Both slow drifts of the
pliiier plate circuit. When the oscillation fre
- oscillator frequency .due to. temperatureor v_olt- _
age changes and rapid shifts due-to other types. _ quency lies outside the pass-band of niter 41 sub
stantially no current is passed. with the result
of instability are eliminated. A frequency-modu ‘that
relay Il .is operated and the ampiißer is
lated wave is thus obtained from which frequency
9,114,086
disabled. A meter JI or other indicating device,
such as a lamp, in the plate current supply lead
shows the condition of the circuit.
'I'he need for the guard circuit occurs when
the oscillation generator is started up or ' is
momentarily interrupted in the normal routines
to amplitude modulation is effected by the oper
ation of switches I2, l2, and". ' i t
,
In atypical example, the carrier oscillator was
designed to operate at a frequency of 300 mega
cycles per second. The heterodyne frequency
furnished by harmonic generator 24 ' was ,295
of operation.l During the "intervals «when ’ the megacycles, the intermediate-frequency of the
cathode temperature and the plate voltage of the ' feedbackcurrents being ñve million cycles per
oscillator tube are being established, the oscilla
10 tion frequency varies through a very wide fre
quency range'. If the-stabilizing control were per--
mitted to operate before the frequency has
reached a value within the operating range of the
converter ñlters, its action would be reversed and
15 the operation would tend to drive the oscillation
second. Filters 21 and Il 'were designed to have
-their characteristics cross at this frequency and 10
to have their resonances separated by about
400,000 cycles. The degreeof stability obtained
was thus substantially that of the crystal oscil
lator 22, since any variations of the control point
of filters 21 and 34 could affect only the relatively 15
frequency towards either a zero or an inñnitely low intermediate frequency and could affect that
large value.- If the filters could be. made to have ' only to a very small extent.
,l
, continuously rising characteristics, this could not
Details of the circuits of the complete-system
happen.y Such filters, however. are difficult and
20 costly to construct for operation at radio fre'
quencies. Wide frequency variations may also
occur when the oscillator plate voltage is applied
after the cathode has‘been fully heated. In this
case the frequency reaches approximately its
25 normal value very rapidly.
-
The guard circuit- also serves to provide auto
I matic volume control for the ampliñers of the
feedback path. For this purpose a resistance 48
shunted by acondenser of low capacity is inserted
30. in series with rectifier Il and the output of filter
of Fig. l are shown in Figs. 2, 3, and 4, which nt
>together in the‘manner indicated by Fig. 6. Fig. 20
2 shows the circuits of the carrier wave oscillator
and constructional features of the tuning control
device I4. Fig. 3 shows the circuits of the hetero
dyne generator comprising oscillator 22 and har
monic producer 2l and of demodulator 2l and
intermediate frequency amplifier 2l. Fig. 4
shows the remaining portion of the feedback cir
cuit and the guard circuit.
41. . The rectified current develops a negative _ moving coil type.
voltage in this resistor which is transmitted by
>conductor 52 to the several amplifiers 25, 28, 33
and demodulator 2| and is-applied to the grids of
'
'
In its preferred form, as shown in Fig. 2, the
tuning control ldevice I4 ~is of the electromagnetic
i1 is attached rigidly to the supporting frame l5
of the moving coil, its plane coinciding with the
coil axis. Fixed plates- Il and Il are disposed
_the vacuum tubes thereof. The capacity in shunt
toresistance 49 should be large enough to act as
a by-pass for the carrier frequency currents, but
not large enough to reduce the signal frequency
variations of the rectified voltage. TheY rapidity
of the control may be adjusted by,suitable re
symmetrically with respect to plate I‘l and par
allel thereto with about 50 per cent .overlap for
'the -normal position of the coil. VMotion of the
coil along 'its axis thus varies the’capacity4 be
. sistance-capacity nlters which may be included
l within the amplifiers.V For demodulator 2| and
act as the coil restraint and also serve to hold it
amplifier 25v the volume control should 'be sum
cientlyslow in action to permit amplitude varia
tions of signal frequency to occur. In the case of
amplifiers 20 and n, .the control- should be very
rapid sol that all signal or speech frequency vari
ations ofthe amplitude are wiped out. By this
means the amplitudes> of the inputs to thecon
4verter filters 21 and I4 `are maintained substan
tially constant.
`
"
.
.
The feedback portion of the circuit _may also
be used for the reception of signals from a distant
` station operating on vthe same frequency as the
carrier oscillator. For this purpose a push-pull
signal amplifier 40, 4| is connected'y by switches
42 and Il to the output of'thedetector-converter,
the ampliñer output being coupled to a telephone
receiver M. While receiving, the transmitting
:sol
The movable condenser plate
tween plates l5 and I0 substantially proportion
ally to the displacement of thecoil. Springs I8 40
centrally in the magnet air-gap. Resonance of
the moving system may be prevented by applying
mechanical damping thereto, for- example, by
covering the surfaces of springs 'Il 'with dissi
pative material, such as felt, or with a thin coat
ing of lead. The damping should not be great
enough to prevent yresponse of the device at any
frequency in the signal range. Alternatively,
electrical damping may -be provided _by‘a suitable
,resistance 54 connected acrossy the moving coil
terminals. A ñeld winding Il .is provided for
polarizing the magnetic circuit.
The power for all of the vacuum tubes and 'for
magnet winding I8 is supplied by full-wave recti
‘ner s1, sa. Fig. s, and an associated smoathingm
ter, connected to' a 60 cycle alternating current l
source 59. A separate winding 6| is provided
on‘the power input'transformer for energizing the
oscillator may be disabled _by interrupting itsV vacuum tube cathodes.' An additional smoothing 60
plate Acurrent supply by means of transmit-re l filter 60 is included in the oscillator platel supply
Iceive switch j". _With this connection the sys _ circuit as'a further precaution against unwanted
' ’ tem is in condition for the reception of frequency
the vacuumïtubesfexcept the guard circuit input
tude modulated waves, switch l2 -is arranged to
connect amplifier Il iii-.parallel with the input of
amplifier lt-rare connected to ground at a point
intermediate the positive and v„negative potentials
guard circuit amplifier 5| and switch I3 is oper
'of thepower supply.
ated to disable amplifier 4l.
'w
`frequency modulations. ,The cathodes of all of ,
modulated waves.- For- the reception of ampli
- "
`
_,
.
’- v 'Harmonic generator ‘M comprises three fre
With two systems of the above type operating`> quency multiplying-.stages each using screen-grid
on> the same frequency, a two-way communica
tion channel can be established. Switching from
the transmitting condition to the receiving con
dition is effected by the operation of the single
pentode tubes with -indirectly heated cathodes.
75 switch 45. " Changing from frequencymodulation
cation. Demodulator 2i also uses `a screen-grid
The output circuitof oscillator 22 is so arranged
that a harmonic of the generated frequency is
supplied to the input of the harmonic generator,
thereby securing additional frequency multipli
2,114,086
pentode tube with indirectly heated cathode, the
-
‘
'
'
.
_
5
posing said varying strength currents upon the
Iincoming oscillations being impressed on the con- oscillationsv from said signal source to counter
trol grid and the heterodyne oscillations on the actthe frequency modulation of the carrier wave.
suppressor grid between the screen and the anode. '
2. In a high frequency communication system,
l5 Intermediate frequency amplifier 25 comprises a carrier wave generator, means for modulating 5
live pentode stages coupled together and to the
demodulator by double tuned circuit broad-band
filters.
,
'
The output -of amplifier 25 is fed into buffer
10 amplifiers 26 and 33 in the plate circuits of which
are connected the converter filters 21 and 34.
These filters consist of simple anti-resonant circuits tuned to different frequencies and propor-
the frequency of said generator in _accordance
with signal currents, a source of signal currents, a
signal input- circuit coupling said source and said
modulating means, a feedback path coupling the
output lof said generator and said signal input 10
circuit, said, feedbackvpath including means for
reproducing from the carrier wave currents hav
ing -strength variations corresponding to the
tioned to provide response characteristics inter-i frequency modulations thereof, and means for
15 secting in the manner shown by curves 52 and
‘ 53. The rectiflers shown, at 28 and 35 inl Fig. 1
are constituted by the space paths between auxillary' anodes 62 and 63 and the cathodes of tubes
40 and 4I, which are of the diode-triode type.
20 The‘switches 42 and I3- of Fig. 1 are combined
impressing said varying strength currentsv upon 15
said input circuit, the transmission characteris- .
tic of said lfeedback path and its connection to
said input circuit being such that the fed back
currents are in substantially opposite phase re-_
lation to the signal currents from said source and 20Á ‘
» in a two-way double throw switch 61. The' out-
are approximately equal thereto in magnitude.
put of ampliflers 40 and 4l goes to transformer
' 66 and thence through an additional low frequency amplifier 69 to -telephone. receiver . 44.
25 Guard circuit ampliñer 46 has its control grid ex'-
3. A system in accordance with claim 2 in
which the said modulating device is responsive to
signal frequency currents and frequencies down '
'to zero, and in which the feedback path is-respon- 25 \
cited in parallel with amplifiers 26 and 33 by the- sive to frequency variations at corresponding
output of amplifier 26. Bandi-pass ñlter I1 com- rates.
prises a pair of tuned circuits suitably coupled to '
4. In a' high frequency communication system,
‘
provide the desired pass-band.
Rectifier I8 is
a carrier wave oscillator comprising a tuned cir
30 constituted by the space paths between auxiliary
cuit which determines the frequency of the gen- 30
anodes 65 and 66 of amplifier tube 5i which is a
eraíted waves, a variable tuning element in said
double diode-triode. Electrodes 66 and 66' are
connected together through a condenser., the output of filter 41 being'connected to anode 66. Re~
tuned clrcuit,'means determining a substantial
ly fixed frequency, means for automatically ad
justing said tuning element in response to de»
l 3154 sistance A50 from which theI grid of tube 5I is Vex-
partures of said oscillator from said fixed fre- 35 _
cited is connected »in shunt between diode 65 and
the tube cathode. A small high frequencyl choke
coil is included in series with this resistance to
quency, and means simultaneously controlling
said tuning element in accordance with signals.
5. In a highfrequency communication system,
suppress the carrier frequency currents.l Resist-40 ance 49 in which the automatic volume control
potential is developed is included in series between the output of filter I1 _and the cathode of
a carrier wave oscillator comprising a tuned cir-l
cuit which determines the frequency ofthe gen- 40 '
erated waves, a variable tuning element in said
tuned circuit. means for determining a substan
the tube. Connections from taps in this resist-
tially ñxed frequency, means for varyingv said y
ance are led to the grids of the several controlled
tuning element in accordance‘with signals, means
` 45 amplifiers and provide volume control voltages - detecting departures of the oscillator from the 45
of suitable magnitudes therefor. Lead 10 sup- fixed frequency, said detecting means being op
plies the control voltage to the grids of amplifiers erative over a range of frequenciesincluding the
26 and 33 through filter 1l, the time constant of signals, and means 4for automatically-adjusting
which is made sufllciently small so thatV signal the tuning element in response to frequency de
50 frequency variations are transmitted. Control Partllres 0f Signal and’ l10n-Signal Origin.
y A 60
bias is supplied to the tubes of ampliñer 26 and
6. In a high frequency communication system,
demodulator 2| through lead 12 and filter 13, the a carrier wave oscillator comprising a tuned cir
time constant of which is large enough to per- cuit which determines the frequency of the gen
mit only slow variations to be transmitted. lli erated waves, a' variable tuning element in said
66 'steady initial grid bias for all of these tubes is tuned circuit. means determining e substantially 55
provided by the fall of potentialin resistance 16
which is connected in series with resistance 15
between the negative terminal of the power supply rectifier and the cathodes. The indicator
60 39, meter or lamp, is included inan auxiliary circuit connected to the front contact of .relay 60
liñei’ plate currather
than asdirectly
rent circuit
m Fig, in
1, the amp
65
What is claimed is:
_
Y
1. In a high frequency
communication
system,
fixed frequency, means foil varying said _tuning
element 'in accordance with signals, means for
detecting departures of the oscillator from the
ñxed frequency. scid detecting means beine re
sponsive to slow departures of frequency and to so
departures at signal rates. and means for auto
matlcally adjusting said tuning element in re
-
sponse to said departures of both kinds.
'1. In a high frequency communication system,
ing a tuned cir- 65 u.
,
l
a carrier wave oscillator compris
y
a carrier' wave generator, a, source of signal osr impressing oscillations from
cillations,
said
sourcemeans
upon fo
said generator
whereby the fre’
cuit which determines the frequency of the gen
erated waves, a variable reactance element in said
y
tuned circuiti means
determining
ai Substantially '
ting means for automati
of the carrier wave in the output of said genern
ator, means for deriving from said detected fre-
from said fixed frequency and separate means forv
controlling said variable element in. accordance
quency modulations currents having> correspond-
with signals;
transmitting and receivinß ‘l5
j 8. In a combined
quency of the generated carrier wave is modu70 lated in accordance with the signal oscillations,
means for detecting the frequency modulations
16 ing strength variations, and means for superim-
ñXed frequency. slow acl
cally adâusting said variable clement in response 7o
to slow departures of the said oscillator frequency
6
9,114,086
station for high frequency communication, a car
rier oscillator comprising a tuned circuit which
determines the frequency of the generated waves.
9. In afrequency stabilized oscillator system
comprising an oscillator generator, frequency
correcting means therefor, means determining a
a variable reactance element in said tuned cir
substantially fixed frequency, and means for
cuit, a transmitting antenna connected to said automatically adjusting said correcting means in
oscillator, a detector of frequency fiuctuations, a l response to departures of the generated frequency 5
receiving antenna connected to said detector and from said fixed frequency, an auxiliary transmis
exposed to the inñuence of said transmitting an
sion path coupled to the output of said generator
tenna, control means actuated by the detector to and responsive to impressed oscillations in a
automatically adjust said variable element to limited range of frequencies centered about saidmaintain the generated frequency substantially fixed frequency, and current responsive means 10'
constant, a telephone receiver also actuated by in the output of _said path for disabling said cor
the detector to reproduce signals in accordance _rective means when the frequency of the gen
with frequency ñuctuations, and means to dis
erated oscillations lies outside said limited range.
15 able the`carrier oscillator during reception of
waves from another station.
JOHN W. SMITH.
.
GORDON _ N. THAYER.
15
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