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Патент USA US2406800

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Sept. 3, 1946.
H. a. BUSIGNIES
2,406,800
DIRECTION FINDER WITH FTLTER
Fiied March 13, 1941
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INVENTOR.
BY
Patented Sept. 3, 1946
2, 6,80
UNITED STATES PATENT OFFICE
2,406,800
DIRECTION FINDER “71TH FILTER
Henri G. Busignies, Forest Hills, N. Y., assignor to
International Standard Electric Corporation,
New York, N. Y., a corporation of Delaware
Application March 13, 1941, Serial No. 383,111
11 Claims.
(Cl. 250—11)
I
2
The present‘ invention relates to radio direc
tion ?nders and more particularly to direction
?nders having a pick-up member physically or
effectively rotating at a constant angular velocity.
a band pass or tuned ?lter rather than merely
a brute force or smoothing ?lter of the untuned
type.
A local generator 1 is arranged to be driven
by the same motor 3 which drives the goniometer
2. The outputs of this local generator 1 and of
It is an object of the invention to provide an
improved radio direction ?nder which shall be
capable of being used over a wide range of fre
the ?lter 6 are then combined in a suitable com
quencies without critical readjustment of a num
bining circuit 3 and used to produce an indica
ber of separate antenna means while yet en
tion in a suitable indicator 9. The combining
abling a unidirectional indication to be obtained. 10 circuit 8 and indicator 9 may be of any suitable
It is a further object to provide such a wide
type. If the output of ?lter 6 is to be sinusoidal,
range direction ?nder which shall give a direct
which would be the case with all ordinary types
reading unidirectional indication.
.
of ?lters and also with the ?lters shown in Figs.
3, 4 and 5, and if the output of the local gen
erator ‘l is to be a series of Very brief contact
It is a further object of the invention to pro
vide an improved direction ?nder capable of
giving a precise and unvarying indication of the
closures (or openings), then the combining cir
direction of arrival of radio waves, even though
such radio Waves be keyed, modulated or even
cuit 8 and indicator 9 may have the form shown
in Fig. 6. As shown in this ?gure the sinusoidal
interrupted for substantial intervals of time.
output from ?lter 6 is separated into two sine
The exact nature of my invention may best be 20 waves in phase quadrature by a phase splitter
understood from the following detailed descrip
tion taken in conjunction with the annexed
drawings in which:
Fig. 1 diagrammatically illustrates a radio di
rection ?nder system embodying my invention.
5| and is thereupon applied to the de?ecting
plates 64, 65 of the cathode ray tube 9' so as to
produce a rotating ?eld. The brief circuit clo
sures from generator 1, on the other hand, mo
25 mentarily drive the vacuum tube 52 beyond cut
Fig. 2 is a series of related curves useful in
o? thus producing momentarily high positive
explaining the principles of my invention.
Figs. 3, 4 and 5 illustrate di?erent forms of
potential on accelerating electrode 63 of cathode
ray tube 9'.
As explained in my copending application,
?lters which may be used in the embodiment
shown in Fig. l in accordance with a special fea 30 Serial No. 380,982 ?led Feb. 28, 1941, the effect
ture of my invention.
of this potential on electrode 63 is to produce a
Fig. 6 illustrates one form of combining cir
radial de?ection of the spot on the cathode ray
cuit and indicator schematically represented in
screen. Thus the indication given on the oath
Fig. l, which form is suitable for use with ?lters
ode ray screen has the form of a circle with a
of the types illustrated in Figs. 3, 4 and 5.
radial line extending inward from one point of
Fig. '7 illustrates an alternative form of ?lter
the circumference thereof toward the center.
which may be used in accordance with a further
Such radial line will not quite attain the center
feature of my invention.
but may be caused to approach thereto by the
Fig. 8 illustrates a modi?ed system embodying
application of suiiicient potential to electrode 63.
my invention.
‘
Referring more particularly to Fig. 1 crossed
loops la and lb are connected to a collector which
is shown as a crossed-stator variocoupler of the
type generally referred to as a goniometer driven
by a motor 3 although it may alternatively be an
electronic collector for performing an equivalent
40
Other forms of combining and indicating cir
cuits may be substituted for the forms shown
in Fig. 6. Thus, for example, if generator 1 be
arranged to give a sine wave, the output from
this generator may be connected to another
phase splitter similar to phase splitter 6| of Fig.
6. Then the rotating ?elds from the two phase
splitters (fed respectively from the output of
function.
The output of goniometer 2‘ is combined, if
?lter 6 and the output of generator 1) may be
desired, with the pick-up from a non-directional
applied to two sets of de?ecting plates so as to
antenna lc, such combined wave is then ampli 50 produce ?elds rotating in opposite directions.
?ed and preferably also heterodyned and tuned
The result will be an oscillatory non-rotating
in receiver 4 and thereafter detected in detector‘
?eld whose angle indicates the phase relation‘_
5. The output of detector 5 is then passed
through a ?lter 6 which in accordance with an
ship between the wave from generator ‘I and
the wave from ?lter 6. Thus, under the in
important feature of my invention is designed as 55 ?uence of such oscillatory ?eld the cathode ray
2,406,800
3
spot will trace a line indicative of the direction
of the received radio wave.
Such an arrangement is described and shown
in more detail in the copending application of
F. Bac and me, Serial No. 23,966, ?led October
8, 1938, for “Systems for indicating the direc
tion of propagation of electro-magnetic waves.” 1
See especially Figs. 3 and 4.
In general, many
4
during which the incoming signal vanishes. For
the present it will be most convenient to consider
only that portion of the curves of Fig. 2 falling
within the time interval WX.
By virtue of the addition of energy from the
non-directional antenna lo a curve which is
shown in II should ideally be produced. A wave
such as shown in curve II, corresponds to the
well-known cardioid which is generally assumed
cators may be used, in accordance with the 10 to exist when the output of a non-directional an
tenna is combined with that from the goniometer
present invention. Although the particular
or other means having a rotating reception pat
forms shown in Fig. 6 require sinusoidal output
tern. As a matter of practical fact, however,
from ?lter G and a sharp momentary pulse from
' different kinds of combining circuits and indi
generator 1, whereas certain other forms require
sine wave outputs from both the '?lter
the '
it is difficult to adjust the relative strengths of
the signal from'the non-directional and the sig
nal ‘from the rotary ‘means so as to givefor all
generator and still other forms require sharp
wave lengths .a combined wave resembling that
pulses for both outputs, all of such systems may
shown in curve II.
be used with the general system of Fig. 1 merely
It may be thatthe ideal adjustment repre»
by changing the local generator ‘I to fit the re
quirements and by selecting either a ?lter giving 20' sented in curve II is attained for two or'threc
a sinusoidal output or one of the special forms of
?lters shown in Figs.’ '7 and 8 which give sharp
pulselike outputs.
In direction ?nders wherein a rotation-mod
ulated signal is detected before being used for
giving an indication, it ‘has previously been sug
gested to pass such detected faves through an
ordinary smoothing ?lter, consisting of con
Wave lengths within ‘the range but it will gener
ally occur that at some wave lengths an ‘excess of
non-directional energy will be .fed to the receiver
giving a total input like thatof curve III. Like
wise, at certain other wave lengths it will gen
erally occur that the energy from the non-direm
tional antenna lc will be smaller than the-energy
from the effectively rotating pick-up means and
will thus give a resultant wave such as shown in
densers and resistors for eliminating the radio
frequency component while retaining the low 30 curve IV. In order to avoid the occurrence of a
wave such as shown in curve IV, it ‘would be
frequency wave form substantially unaltered.
necessary to provide elaborate adjustments for
the antennae 105, lb and is or else ‘to normally
?lter
In accordance'with
5 is provided which
theis present
of the general
invention
class
of ?lters sometimes known as “tuned” ?lters in
contract to the ?lters of the so-called “brute
force” type. Such “tuned” ?lters are propor
adjust the system so that at most wave lengths
the energy receivedefrom antenna to was Very
greatly insexcess of that required. Such excessive
non-directional energy, however, is undesirable
tioned with respect to a predetermined cut-off
since the percentage of modulation produced by >
frequency so'as to provide a very great discrim
the effectively rotating. pick-up system is thereby
ination between those frequencies lying above
said cut-off and those lying below. Such ?lters .40 reduced thus reducing the accuracy of the direc
tional indication.
maybe of the low-pass type or of the band-pass
In ‘accordance with the present invention the
type and in some vcases may be merely tuned
circuits, thus being capable of passing only a
“tuned” type ?lter 6 is provided so as to enable
single frequency. In all cases, ‘however, itis pro~
posed in accordance with my invention to design
the-?lter 6 with reference to a particular fre
quency determined by the rate of rotation of
goniometer 2 or of the pick-up loop, if a rotat
ing loop is used ‘instead of crossed loops and a
goniometer. In general, it may be stated ‘that
the ?lter is to be proportioned with respect to
the frequency of effective rotation of the recep—
waves such as those shown in curve IV to be em~
collector, or Whether it comprises a single loop
If the output of the detector 5 is passed
through a sharp “tuned” type ?lter 6, however,
ployed even with inertialess indicating devices
such as cathode ray oscillographs. The action of
?lter 6 is best shown in the two curves "J of Fig. ‘2.
The
sulting
solid
from
line ‘curve
detection
V indicates
of curve
theIVwave
withform
simple
smoothing to remove the radio frequencies. It
will be clear that the form of this solid. line curve.
is far from sinusoidal and is therefore wholly un
suitable for passing through a phase splitter such
tion pattern of the pick-up arrangement em
as phase splitter .61 of Fig. 6. Likewise, such
ployed whether this pick-up arrangement com
form is also unsuitable for many other sorts
prises Adcock antennae or crossed loop antennae 55 wave
of combining and-indicating circuits.
with some sort of rotating or e?ectively rotating
which itself rotates.
' '
the wave form shown in the solid line curve V is
It is preferred, moreover, that the ?lter '6
should have a su?iciently steep change in atten 60 changed to the ‘form’ shown in the dotted curve V.
For the purpose of removingthe irregularities of
uation with frequency so that a frequency one
the wave form shown in the. portion WX of curves
octave above the desired frequency will be sub~
V, it'is satisfactory to employ a ?lter capable of
stantially suppressed. Preferably, too, the ?lter
strongly discriminating against the second har
should be designed so as to substantially suppress
even those frequencies lying ten per cent. above 65 monic of the desired frequency. For some pur~
poses, however, it is preferable to make the ?lter
and below the desired frequency.
have a still sharper characteristic.
>
The advantage of using such a tuned ?lter
In the case of keyed waves or waves which are
having a comparatively sharp cut-oil can be ‘best
interrupted for short periods by
other means,
explained by reference to the curves of Fig. 2.
Curve I represents the output from goniometer 2. 70 it is highly desirable to arrange that the indi~
cations shall be constant in spite of the tem
As is Well-known such output will be modulated
porary cutting off of the Wave being measured.
to such an extent as to involve phase reversal
(schematically represented by alternate vertical
and horizontal hatching). The time interval XY
is assumed to correspond to a keying interval
Thus, vreferring to Fig. 2 it is desirable that the
dotted
sinusoidal curve V should continue
through interval XY even though the solid line
2,406,800
5
curve is shut off during this interval. In order
to so continue the output of ?lter 6 it is merely
necessary to proportion this ?lter so as to cut
off the side bands which would correspond to
'pacity an output voltage may be obtained in the
manner of a condenser microphone.
Since the
input is electromagnetic whereas the output is
electrostatic direct coupling independent of the
a modulation of the desired sine wave at the
fork is minimized. f is a test winding which may
be incorporated in a Hartley oscillator circuit to
drive the fork for test purposes.
Fig. 5 shows an arrangement similar to
it
but using a vibrating reed in place of a tuning
it is merely necessary to proportion ?lter 6 so 10 fork. The damping factor of such reed can read
as to strongly discriminate against the fre
ily be adjusted thus varying the e?ective Q of the
quencies of 20:5 (i. e., against the frequencies
?lter.
15 and 25) while still passing the desired fre
Fig. 7 illustrates a ?lter arrangement adapted
quency (20 cycles per second).
to give pulselike peaks in place of sinusoidal
If the ?lter is so proportioned, it will perform
waves for the ?lter output. Such ?lter may be
two separate functions: Not only will it remove
used with combining circuits'and indicators of
the harmonics of the desired wave and thus pre~
the form shown in Fig. 6 provided that local
vent distortion as a result of the phenomena
generator 1 is arranged to give a sinusoidal out
shown in curves IV and V but also it will prevent
put. In such case the connections from gener
interruption of the ?lter output as a result of a 20 ator ‘! and ?lter 5 are merely interchanged so
brief interruption of the incoming signal such as
that the sine wave output of generator ‘5 is
frequency corresponding to the time interval
XY. If, for example, the time interval KY is
1/5 of a second whereas the desired frequency
of the output of ?lter 6 is 20 cycles per second,
represented by the interval XY.
applied to phase splitter at of Fig. 6, whereas
A third bene?cial result obtainable by the use
of a “tuned” type ?lter 6 is that in the case of
the peaked output of ?lter 6 is applied to tube 52.
Referring more particularly to
'7, an input
speech modulated Waves or waves which are
coil ab excites a vibrating reed V on the end of
modulated by natural or man-made interfer~
ence, the directional indications given will be
which is insulatedly mounted a conducting plate
G. A pair of capacitative plates Pi and P2 are
substantially as clear as if the modulations were
mounted on either side of the rest position of con
not present. Thus, for example, if the rotation
ducting plate G. A high frequency from a suit
rate of the rotary pick~up means is 20 per second
and the ?lter 6 is arranged to discriminate
able source S is applied to P! whereas a detector
DI is connected to P2. When G occupies its rest
strongly against the second harmonic and all
position there is a substantial coupling between
higher harmonics thereof, it is at once clear that
P2 and Pi by way of element G and therefore
voice frequency modulations, whose lower limit
the output of such detector DI after ampli?ca
is ordinarily not lower than 40 per second, will
tion if necessary in the ampli?er H may then be
be completely removed.
delivered to output circuit CD for application to
If the goniometer 2 is of the mechanically ro~
the combining circuit.
tating type shown in Fig. 1, such goniometer will
In operation the reed V is set in vibration by
ordinarily be rotated at some rate of the order
waves of the desired frequency across input ter
of 10 to 50 rotations per second. in such case the 40 minals AB. As the reed passes through its rest
frequency to be handled by ?lter 6 will be 10 to
position, a momentary surge of high frequency
50 cycles per second if a non-directional antenna
from oscillator S is coupled through member G
such as to is used, or will be 20 to 100 cycles
from plate PI to P2 and after recti?cation in de
per second if such non~directional antenna is
tector D! and ampli?cation in H produces a brief
omitted and a bilateral indication is to be given.
pulse at output terminals CD. Such brief pulse
In either case, however, it is clear that the fre
occurs twice per complete cycle of reed V at the
quencies in question are so low
to make it ex
moments of passage of this red through its cen
pensive to provide ?lter elements of reasonably
tral position. A bilateral indication will there
high Q and therefore in accordance with. a parfore be given even though the input to AB be
so
ticular feature of the present invention it is pro
derived from a system employing a sensing an
posed to employ electromechanical filter means
tenna such as 10 of Fig. 1.
for use in connection with direction ?nders em~
In order to avoid sensing ambiguities addi
ploying actual rotation of some mechanical mem
tional plates P3 and P4 may be provided, plate P4
ber for producing the required effective rotation.
being connected in parallel with plate Pl while
of the reception pattern.
t should be noted,
plate P3 may be placed in parallel with plate P2
however, that in cases where the eifective rota
by means of a switch. When plate P3 is con
tion of the reception pattern is produced electron
nected, an extra pulse in addition to the two brief
ically ordinary conventional electrical ?lters may
pulses per cycle which have been above described
conveniently be employed.
will be given during the time when the reed is at
Figs. 3, 4 and 5 illustrate preferred forms or‘ 80 the right-hand extremity of its swing. Such ex
electromechanical ?lters to be used with ‘ dio
tra pulse will be easily distinguishable from the
direction ?nders having mechanical rotation.
two pulses previously mentioned by virtue of its
In Fig. 3 there is shown a tuning fork used for
greater duration. This extra pulse being dis
coupling together two coils cd and ab. Prefer~
posed at 90° with respect to the two short pulses
ably, the fork is permanently magnetized. and is
above mentioned will serve to indicate which one
driven by ?eld from input coil oh, the opposite
of these short pulses represents the true direction
tine of the form then serving to deliver energy
of the incoming waves.
to output coil cd of the ?lter arrangement.
Fig. 8 shows a modi?ed system wherein the pas
Fig. 4 shows an improved form wherein electro
sage of a light beam through aligned openings is
static output coupling is employed to void pose 70 made use of to replace the electrostatic coupling
sible direct action between the input and output
of Fig. '7, Whereas the simple rotating pointer 9"
independent of the fork. In this figure a capaci'
illuminated by such light beam replaces the cath
tor plate adjacent to the output tine of the fork
ode ray tube 9' of Fig. 6, as well as generator ‘1.
varies the capacity output terminals CD. By
Referring more particularly to Fig. 8 pick-up
applying a suitable polarization across such ca 75 means la, lb, I c, 2 and motor 3 are substantially
2,406,800
7
.
'8
as in Fig. 1 whereas receiver and detector 4 and
inating strongly against frequencies ten per cent.
5 have been combined under a single apparatus 45.
above and below said predetermined frequency.
For ?lter '6 there is provided reed V excited by a
coil connected across AB substantially as in Fig. '7
but instead of bearing a conductive coupling mem
ber such as G this reed V bears a shutter T pierced
by a small opening. A light source LS projects
a light through the small opening of T and
through an aligned opening in another shutter
3. A radio direction ?nder comprising pick-up
means effectively rotating at a predetermined
frequency for picking up signals modulated at
said frequency by virtue of such rotation, further
T2 to illuminate the rotating pointer 9” which
means for non-directionally picking up signals
and adding them to said signals modulated at said
frequency to yield resultant signals whose en
velope curve contains a component of said pre
determined frequency, means for detecting said
resultant signals, an indicator controllable by
sinusoidal waves, a mechanically vibratory, mem~
ber having a natural frequency substantially
is rotated by motor 3. Since the light beam can
only pass through the openings T and T2 when
V is in its central or rest position the pointer will
be illuminated only for two brief instants during
each cycle of the vibration of the reed V.
15 equal to said predetermined frequency, means for
setting said member into vibration under con
Due to .the persistence of vision therefore a
trol of said detected signals, and means for de
pointer will be seen as standing stationary in two
livering sinusoidal waves to said indicator in re
positions 188° apart. A suitable graduated scale
sponse to vibrations of said member.
GS placed in proximity to the pointer 9" serves
4. A radio direction ?nder comprising pick-up
to facilitate direct reading of the direction to .20
means effectively rotating at a predetermined
be indicated. In order to avoid sense ambi—
frequency for picking up signals modulated at
guities an auxiliary shutter Tl may be pivotally
said frequency by virtue of such rotation, fur
mounted so as to cut 05 the beam’s light except
ther means for non-directionally picking up sig~
when de?ected by a sensitive meter movement
M. A photocell F is then arranged to actuate 25 nals and adding them to said signals modulated
at said frequency to yield resultant signals whose
the meter movement Min response to illumina
envelope curve contains a component of said
tionand this photocell so positioned as to be
predetermined frequency, means for detecting
come illuminated momentarily each time that the
said'resultant signals, an indicator controllable
shutter T is withdrawn to its right-hand position
by the vibration of reed V.
30 bysharp electrical pulses, a mechanically vibra
tory member having anatural frequency substan
If the meter movement M and associated shut
tially equal to said predetermined frequency,
ter Tl are arranged to have a suitable operating
means for setting said ‘member into vibration
time it will then result that when the reed V
under control of said detected signals, and means
reaches its extreme right-hand position the meter
for delivering sharp electrical pulses to said indi
movement will commence to be energized and the
cator in response to vibration of said member.
resulting withdrawal of shutter T! will be com
5. A radio direction ?nder comp-rising pick-up
pleted at about the time when the openings in
means effectively rotating at a predetermined fre
shutters TI and T2 become aligned during the
quency for picking up signals modulated at said
succeeding half cycle. Thus when reed V passes
through its central position while moving from 40 frequency by virtue of such rotation, further
means for non-directionally picking up signals
right to left the beam of light will be momen
and adding them to said signals modulated at said
tarily permitted to fall upon pointer 9". Therm
frequency to yield resultant signals whose en
after during the time’ when the reed V travels
velope curve contains a‘component of said pre
from its central position to its left-hand position
and back the shutter Tl wlil return to normal and 45 determined frequency, means for detecting said
resultant signals, an indicator controllable by
block the passage of the light so that no illumi
brief flashes of light, a mechanically vibratory
nation will be provided at the instant when the
member having a natural frequency substantially
reed, V passes through its central position from
equal to said predetermined frequency, means for
left to right.
50 setting said member into vibration under con
What I claim is:
trol of said detected signals, and means for me
1. A radio direction ?nder comprising pick-up
chanically controlling the passage of brief flashes
means effectively rotating at a predetermined fre
of light to said indicator in response to vibration
quency for picking up signals modulated in ac
of said member.
cordance with such rotation, means for detecting
said signals, means for non-directionally picking 55 - 6. A direction ?nder according to claim 4
wherein said means for delivering sharp elec
up signals and for adding them to said signals
trical pulses comprises means for deriving oscil~
modulated in accordance with said rotation
whereby the resultant signals after detection con
tain a component of said predetermined fre
lations of a frequency high in comparison with
said predetermined frequency, means for cou
quency, indicator means for giving a directional 60 pling said oscillations to an output circuit in a
indication under the control of such detected sig
nals, means for applying said detected signals to
said indicator means, and a tuned ?lter propor
tioned to pass said predetermined frequency while
sharply varying manner under control of the
vibrations of said member, and means for deliver-
ing to said indicator such coupled oscillations.
7. A direction ?nder according to claim 5
discriminating strongly against frequencies ten 65 wherein said means for delivering sharp elec~
trical pulses comprises means for deriving os~
per cent above and below said predetermined fre
oillations of a frequency high in comparison with
quency before application to said indicator means.
said predetermined frequency, means for cou
2. A direction ?nder according to claim 1 fur
pling said oscillations to an output circuit in a
ther comprising means for non-directionally
picking up signals and for adding them to said 70 sharply varying manner under control of the
signals modulated in accordance with said rota
tion whereby the resultant signals after detection
contain a component of said predetermined fre
quency, and wherein said ?lter is proportioned to
pass said predetermined frequency while discrim~ 75
vibrations of said member, means for detecting
the oscillations coupled to said output circuit
and means for delivering to said indicator such
detected oscillations.
8. A radio direction ?nder comprising pick-up
2,406,800
means e?’ectively rotating at a predetermined fre
quency for picking up signals modulated in ac
cordance with such rotation, means for detect
ing said signals, indicator means for giving a
directional indication under the control of such
detected signals, means for applying said de
tected signals to said indicator means, and a tuned
10
10. A radio direction ?nder comprising pick-up
means eifectively rotating at a predetermined fre
quency for picking up signals modulated in ac
cordance with such rotation, means for detect
ing said signals, indicator means for giving a
directional indication under the control of such
detected signals, means for applying said detected
signals to said indicator means, and a tuned ?lter
proportioned with respect to said predetermined
?lter proportioned with respect to said predeter
mined frequency for ?ltering said detected sig
nals before application to said indicator means, 10 frequency for ?ltering said detected signals, be
comprising a mechanically oscillatory member
fore application to said indicator means, com
having a natural period of vibration, input means
prising a mechanically oscillatory member hav
for setting said member into vibration under con~
ing a natural period of vibrations, input means
trol of said detected signals, and output means for
for setting said member into vibration under con
in?uencing said indicator means under control of 15 trol of said detected signals, and output means
the vibrations of said member.
for delivering brief ?ashes of illumination to said
9. A radio direction ?nder comprising pick-up
indicator means under control of the Vibrations of
means effectively rotating at a predetermined
said member.
frequency for picking up signals modulated in
11. A radio direction ?nder comprising pick-up
accordance with such rotation, means for de 20 means effectively rotating at a predetermined fre
tecting said signals, indicator means for giving
quency for picking up signals modulatively rotat
a directional indication under the control of such
ing at a predetermined frequency for picking up
detected signals, means for applying said de
signals modulated in accordance with such rota
tected signals to said indicator means, and a tuned
tion, means for detecting said signals, indicator
?lter proportioned with respect to said predeter 25 means for giving a directional indication under
mined frequency for ?ltering said detected sig
the control of such detected signals, means for
nals before application to said indicator means,
applying said detected signals to said indicator
comprising a mechanically oscillatory member
means, and a, tuned ?lter proportioned to pass
having a natural period of vibration, input means
said predetermined frequency while discriminat
for setting said member into vibration under con~ 30 ing strongly against frequencies ten percent above
trol of said detected signals, and‘ output means
and below said predetermined frequency.
for delivering brief electrical signals to said indi
cator means under control of the vibrations of
HENRI G. BUSIGNIES.
said member.
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