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Sept. 24, 1946.
_ W, H_ WIRKLER
2,408,122
HETERODYNE DIRECTION FINDER WITH SINGLE RECEIVER
Filed Nov. l5, 1940
2 Sheets-Sheet l
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v sept. 24, 1946.
2,408,122
W. H. WIRKLER
HETERODYNE DIRECTION FINDER WITH SINGLE RECEIVER
Filed NOV. l5, 1940
2 Sheets-Sheet 2
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AMPLIFIER
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INVENTon
Waffe/‘p 3E- WM5/eww,
BY
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Patented Slept. 24, 1946
2,408,122
UNHTED STATES PATENT OFFICE
2,408,122
HETERODYNE DIRECTION FINDER WITH
SINGLE RECEIVER
Walter H. Wirkler, Cedar Rapids, Iowa, assigner
to Collins Radio Company, Cedar Rapids, Iowa,
a corporation of Iowa
Application November 15, 1940. Serial No.. 365.826
16 Claims.
(Cl. Z50-_11)
1
2
This invention relates broadly to radio direc
tion finders, and more specifically to direction
certain inherent advantages with respect tophase
finders of the heterodyne ty-pe in which the indi- ‘
shift in independently tuned antenna circuits
.which have been completely described in my 'co
cation is based on the phase relationship between
audio frequency modulation products of a. locally
pending application YSerial No. 294,522, filed Sep
tember l2, 1939, for Radio direction finding sys
generated wave radiated from an injection an
tenna, and a signal wave arriving from a dis
tance.
One object of this invention is to provide an
tem, and in a number of related applications. lt
is the object of this invention to -retain the ad
indication of the relative phase of the received
signal voltage in two spaced antennas by means
of a single receiver alternately connected to each
antenna at a switching frequency which is higher
than the -lo‘w lfrequency modulation product re
sulting from the heterodyning action between the
distant signal and the-local oscillator.
Another1 object of thisv invention is to provide
automatic differential gain control action between
vantages of the heterodyne method while using
only a single receiver channel Vinstead of a sepa
rate receiver channel for each antenna circuit
asin the cases mentioned above. Direction lind
ers not of the heterodyne type commonly use a
single receiver channel cooperatively energized by
two receiving antennas Whichare connected di
rectly to the receiver at all times, although some
use a single receiver alternately switched tothe
two receiving antenna circuits. Since the switch
ing frequency in this arrangement must, of nec
essity, be much lower than the signal frequency,
the two antenna circuits, based on the presence
`of switching frequency components. in the output 20 the indication of phase difference between cur
of a single receiver channel.
A further object ‘of my invention is to provide
a heterodyne radio direction >finding system em
ploying a single radio receiver, alternately con
nected with separate receiving antennas, and a
rents in the two antenna circuits -is effective dur
ing only a small fraction of the total number of
l signal frequency cycles, and the directional sen
sitivity of such a device is relatively Ípoor in terms
of signal-to-noise ratio.
_
The-signal vfrequency in the system of my in
vention is reduced on the heterodyne principle to
parable lpha-se for determining phase differences
a beat frequency 'with respect to which the
indicative of direction.
switching frequency is .made relatively high, for
Still another object ofmy invention is t0 pro
vide a heterodyne radio direction finding system 30. example, abeat frequency of 250 cycles may be
employed with a switching frequency of 3G00 cy
employing a single radio receiver, electronically
cles; the theoretical wave form diagrams of Figs. 3
coupled alternately withseparate receiving an
and 4 are drawn accordingly. The frequencies
tennas at a predetermined switching frequency,
must be always sufficiently different for separa
and an inte-rmodulatíon arrangement involving
tion in filters, the switching rfrequency lbeing in
components of the switching frequency and the
variably greater than the beat frequency.
heterodyne beat frequency for providing a cur
In Fig. l, I have indicated a local oscillator l
rent proportional to the phase dilîerence between
differing in frequency from vthe signal frequency
the instantaneous currents from the receiver, for
novel arrangement for providing currents of corn
indicating direction.
Other and further objects of my invention re
side in the system and circuit arrangements here
' inafter described with reference to the accom
panying drawings in which:
`
Figure 1 is a block diagram illustratingT the
basic arrangement of elements in the system of
my invention; Fig. 2 is a schematicdiagram of
one embodiment of my invention, following the
arrangement of Fig. 1 and incorporating addi
tional features, such as the automatic dineren
tial volume control, for improved operation; and
Fig. 3 comprises theoretical wave form diagrams
of voltages in different portions of one circuit
connected with the output of the receiver, for
directional indications.
I
Direction ñnders of the heterodyne type have
by a low audio beat frequency, an injection an
tenna 2 for inducing equally into. receiving an
tenna circuits 3 and v4 vvoltages at the local oscil
lator frequency, and switching-means at '5, (6’),
which alternately supply the- input of a receiver
8 with energy from antenna circuits 3 and '13;
The antennas are switched alternately by means
of switching frequency voltage from switching
oscillator l. The audio output voltage from re
ceiver 8 is supplied through -frequency selective
network 9 to a demodulator or rectifier lil. Net
work 9 selects modulation components in a fre
quency band centered on the switching frequency
of 3,000 cycles per seco-nd. Rectifier lll is sup
plied also with switching‘frequency voltage di
rectly from oscillator l. The output of rectifier
“ IU, as it appears at phase shifting network f4,
2,408,122!
3
4
ulation at I0 with the aid of current from the
will contain voltage of beat frequency when a
switching oscillator, the wave of beat frequency
phase difference exists between the signal fre
je is established as at IV, Fig. 3, the phase of
quency voltages at antenna circuits 3 and 4 as
which is of particular interest.
explained below. The audio output voltage from
From Fig. 3, it will be noted that the peak y
receiver 8 is also supplied to frequency selective 5
of the fe wave coincides in phase with the inter
network II which selects currents of beat fre
mediate nodal point z between the phase dis
quency for application with the output of the
placed waves of beat frequency fb and fb', which
rectifier IíI, in 'proper phase, to the balanced rec
corresponds to the actual node z' of the average
tifier I6 for deriving an indicating voltage.
wave fA, wherefore the fB Wave is 90° out of phase
In Fig. 3, at I, curve fb represents the audio
with the average Wave ÍA of beat frequency.
output of receiver 8 when the receiver is continu
Through phase shifting means I4, the resultant
ously connected to antenna 3 for example. Curve
Wave of beat frequency ,?B is shifted substantially
fb' represents the output of receiver 8 when its
90° in phase, whereupon this component of beat
input is continuously connected to antenna 4.
Curves fb and fb’ have been drawn with a slight 15 frequency je and the component f». delivered
from filter I I are applied to the balanced rectifier
phase displacement such as would exist when the
I6 lessentially in phase, and a direct current volt
signal is arriving from the direction different
age is obtained proportional to the amplitude ‘of
from a perpendicular to a line joining the two an
the fe component and of polarity corresponding
tennas. Under the action of switching voltage
from oscillator 'I, the input of receiver Il will be 20 to the sense of je as referred to fA, the average or
composite wave of beat frequency.
connected alternately to the two antennas so that '
The significant component fB is zero when the
the audio output voltage from receiver Il may be
directional components fb and fb' are in like
expected to look something like the curve X, the
phase, and there is then no voltage output from
solid line in the group at I, Fig. 3. Network I I in
rectifier I6. The component J’B appears upon the
selecting currents of beat frequency delivers an
occurrence of any out of phase relation of com
output wave ÍA which is substantially the aver
ponents fb and fb’. and the output of rectifier I6
age of the curve X; the curve fA is shown in full
assumes a value proportional to the out of phase
line at II, Fig. 3.
relation. It might be again noted that low pass
Network 9 in selecting sideband components
around the switching frequency can be thought 30 filter II, operating at the low beat frequency, re
ceives portions of the beat-frequency waves fb
of as passing an alternating current of wave form
and fb’ alternately at the switching frequency,
somewhat similar to the curve X' at III, Fig. 3.
and effectively alleviates the pulsating character
Rectifier IB can be thought of as a reversing
switch operating synchronously with switching
voltage alternations from 1. Hence, the wave at
III, Fig. 3, when rectified ín III, might be expected
of the waves so that a substantially continuous,
composite wave of beat frequency is delivered
for coaction in the rectifier I6 with the continu
ous wave fe derived from both the fb and fb’ com
ponents through the rectifier I0.
Referring now to Fig. 2, the same general cir
beat frequency displaced approximately 90 de
grees in time phase from the beat frequency com 40 cuit arrangement shown in Fig. 1 is evident in
the provision of antennas 2, 3 and 4 coupled re
ponent fA directly obtained from the output of
spectively to a source of injection energy Ia-Ic
the receiver. This beat frequency component ÍB
and switching means 5 and 6; switching oscillator
from rectifier IU is therefore passed through
l, which may be of any suitable form; receiver 8,
phase shifting network I4, in order that the com
shown as of the superheterodyne type; filters 9
ponent J‘B may be applied to rectifier I6, Fig. 1,
to look something like the curve fia at IV, Fig. 3.
Curve ÍB at IV is seen to contain a component of
in phase with the beat frequency component fA
received from the output of receiver 8 through
low pass filter II. The output of the rectifier I6
is applied to indicating means Vat I'I. Rectifier
I6 will produce D.-C. output voltage proportional
to the phase differences between the signal volt
and II; rectiñers I0 and I6; phase shifting
means at I4, which is supplemented by phase
shifting means I2 in the connection from ñlter
II; and the indicating means I‘I. The switching
means are disclosed as multi-grid electron tubes
biased to cut-off by a source of potential 23 but
alternately operable under the action of the con
trol voltage from switching oscillator 'I to ener
beat frequency component fe, and of polarity in
gize the receiver. The rectifier I0 is of the doubly
dicating the sense of this phase difference as evi
vdenced by the polarity of the fe component with 55 balanced or “ring” type, and is supplied with
ages in antennas 3 and 4 as evidenced by the
components of switching frequency from oscilla
tor ‘I in phase with the components of like fre
quency delivered from the band pass ñlter 9.
signal and heterodyne waves as Fs and Fh, re
sideband components of the beat frequency (IV
spectively, with Fh components being supplied to
receiver 8 with Fs components from antenna 3 60 in Fig. 3), are thus detected and supplied, through
phase shifting means I4 and such amplification
and Fs’ components from antenna 4, alternately.
means at I5 as may be required, to the rectifier
In the receiver 3, the primary function> is the
I6 which is also of the doubly balanced or “ring”
mixing of the signal and heterodyne components
type.
to produce beat frequencies fb and fb', corre
sponding in phase to the signal components FB 65 The low pass filter II is connected with recti
fier I6 through phase shifting means I2 and such
and Fs', respectively. A_t the same time, receiver
amplification means at I3 as may be required.
8 operates to produce beat frequency components
The phase shifting means I2 and I4 are corn
as sidebands of the switching frequency. In the
plementary in character, and together effect the
output of receiver 8, filter II averages the pri
mary beat frequency waves fb and fb’ and passes 70 substantially 90° phase adjustment of the beat
frequency component ,fB with respect to the com
the resultant wave fA to the balanced rectifier I6.
posite average wave fA. Rectifier I6 operates at
Filter 9, _also connected with the output ofthe
the beat frequency and delivers direct current for
receiver, passes the sideband components cen
operation of the meter means shown at I1 as a
tered on the switching frequency f, the output
being as represented at III, Fig. 3. After demod 75 result of an out of phase relationship in the beat
respect to that of the fA component.
In Fig. 1, I have indicated the high frequency
S
Gî
frequency components fb and fb', evidenced
.
2. By this arrangement, the local injected ‘fre’
through J‘B and corresponding to a like relation
quency fas it :appears in the intermediate ‘fre
ship in the signal components Fs and Fs', as here
quency channel of the receiver will lbeconstant
inbefore explained, for indicating distance.
and independent of the .receiver tuning, andhence
Rectifier I6 depends for operation `upon beat 5 its phase delay-and the envelope phase delay for
frequency current of Vpropery phase character from
sidebands around this locally introduced fre
rectifier I8 through network `Ill. This current
quency--will be constant Aas far as the -interme
(fe) is present only when there is -a phase in
diatefrequencies are concerned, and the adjust
ment of the phase shifting network 20 will vbe
equality between the lcurrents fb and fb'. Hence
the zero-center D.-C. -meter indicator Il shows ' more nearly independent of receiver tuning.
a deflection only when the antenna system is
This is effected, as shown in Fig. 2, by employ
rotated olf bearing, the sense of said indication
ing-‘a mixer circuit Ic to feed the injection an
-showing the directionof 'this off-bearing rotation.
tenna ~2, and supplying the mixer lc with energy
The ’meter shown at VI-'I‘represents one type of
from oscillator la of ‘fixed frequency and‘oscilla
indicating means adaptable to the system of my
tor lb which is also the conversion oscillator for
the superheterodyne receiver 8. Oscillator la
invention, but it will be understood that oscillo
operates at a frequency differing from the inter
scopio `or other Vequivalent vmeans may be em
ployed, -as desired.
mediate frequency of the receiver by the beat
frequency fb. The frequency of the energy sup
In the direction finder here described, the two
bea't‘frequency components applied‘to I6 are-ob- ~ plied to'tlie linjector loop has a frequency Fh dif
fering from the signal frequency Fs bythe de
tained effectively vthrough» different channels.
That applied to amplifier-I3, for example, is di
sired beat frequency over the tuning range, and
rectly the output voltage from the receiver; while
its intermediate frequency remains constant, due
that obtained from vl5 is passed‘through there
to the interrelation of the conversion frequency
ceiver as sidebands around the switching fre
quency before being converted to‘current of beat
`of-'oscillator-'lb, ‘as-disclosed.
frequency. The result'is that the relative phase
delay of these two currents is ‘rather indeter
minate and it is essential that a'rather ~high order
general and preferred embodiments, various mod
While I have disclosed my invention in certain
ifications may be made therein and I desire it
understood thatno limitations upon my inven
tion are intended thereby `but only by the scope
of amplitude equality 'exist' between signal cur- -
rents from the two antenna circuits. For this
reason automatic differential gain control `means
VVare provided. The output of‘re'ceiver 8 will con
of the appended claims. '
What I claim as new and desire to secure by
Letters Patent of the United States is as follows:
tain components of `switching‘frequency depend
i.. In a heterodyne radio direction finding sys
ing 'on the amplitude'difference between carrier Si; tem, in‘combination: a direction'a-l‘antenna sys
or Fh currents ‘from 3 and ’4, Yas `'distinguished
tem,»inc'luding a'pair of signal receiving antennae
and a locally energized injector antenna coupled
from the sideband components around the
switching frequency which ‘indicate phase differ
-in like relation to both said receiving‘antennae; a
ence ‘between V`the two signal currents. The
receiving circuit including detector means;
switching frequency components resulting from
`switching'means for connecting said receiving
amplitude difference are passed through a nar
row band pass ñlter I8 to 'rectifier I9; 'Rectifier
Vcircuit alternately with each of said receiving an
I9 also receives switching frequency components
quency components, derived in said detector
termae for producing heterodyne output beat fre
directly from oscillator 1, through phase shifting imeans from receivedsignal energy and energy
'network '20. The result vis that a `direct voltage 40 fronrsaid injector antenna, and varying in phase
of suitable polarity is obtained from the output
‘relation as the signals received at the respective
of i9 and applied as gain 'control voltage to tube
receiving antennae; said beat frequency com
'6 through lead 2l, the arrangement including
ponents being interrupted at the frequency of
blocking condenser '22., Ajl'iigh order of differ _ ‘said switching means and constituting amplitude
ential gain control can b'e'obtaîned ‘by‘inserting 00 modulation ‘sidebands'of the switching frequency
an audio frequency amplifier 'between VI8 'and I9.
‘proportional in amplitude to the phase relation
of lsaid beat frequency components; means for de
tif-ler lfd as in the rectifier l0, even when the sig
tecting said modulation sidebands for producing
nalfcomponents are out of phase, because the
a beat frequency-current proportional in ampli
band width of filter I8 is limited so vtha‘t'only 55 tude to the phase relation of said received sig
components of switching frequency may pass, and
nals; said beat frequency components, pulsating
accordingly the output of Vrectifier 'I9 is a direct
at said switching frequency, comprising» together
current resulting from rectification of carrier
a continuous wave constituting an average beat
energy, as distinguished from the ‘alternating'cur
frequency `current of effectively'iixed phase; bal
rent of beat frequency present as a sideband and 60 anced rectifier means cooperatively energized by
detected in rectifier I0. 'That is,'whe`n an ampli
both said beat frequency currents in substantially
tude difference exists between the carrier volt
like phase for producing a direct voltage propor
ages received from the two antenna‘circuits, the
tional-to the'phase relation of said received sig
D.-C. output from-the receiver iiuctu'a‘tes in syn
_ nals, and direct-ion indicating means energized
VNo modulation sidebandsia're found in the rec
chronism with the switching operation. 'Rectifier
i9, considered as a synchronously Voperating 're
D by'said direct voltage.
'
2. In a heterodyne radio direction finding sys
versing switch, will then have in its output a
tem, the combination set forth in claim l where
D.-C. component, the polarity of 'which Vdepends
in the switching frequency is greater than said
on which of the two antenna circuits delivers the
beat frequency, and including filter means be
stronger carrier voltage. Such D.-C. Voltage will 70 tween said receiving circuit Yand the means for
be suitable for the differential “gain >correcting
detecting ‘said modulation sidebandssaid filter
-function operating >on the grid bias voltage of
means being tuned vto pass> sideband energy’cen
switching tube'G.
_tered on- said switching frequency, and additional
I prefer the arrangementfsliownrfor- obtaining y 'filter meansconnectedïwiththe output of. said re
" 'current to ‘be introduced into
ection l antenna
‘75'ieei’ving 'nlroei-tirer :selectively `passing and inte
2,408, lâßî
‘î’
grating the components of beat frequency com
prising said average beat frequency current of
effectively fixed phase.
3. In a heterodyne radio direction finding sys
tem, the combination set forth in claim 1 where
in the detected beat frequency current and the
average beat frequency current, as produced, are
in phase quadrature; and including phase shift
ing means for aligning .said currents in like phase
for cooperatively energizing said balanced recti 10
fier means.
ll. In a heterodyne radio direction finding sys
tem, the combination set forth in claim 1 where
in said switching means includes an electron tube
amplifier in circuit with each receiving antenna,
and a control oscillator connected with each elec
ent upon the phase relation of two independent
signal currents, means including a single receiv
ing circuit for providing components of said `cur
rents Vin alternate periods at` a rate substantially
higher than the frequency of said currents; means
for integrating said components, to produce an
average current of fixed phase; means for detect
ing the differential of successive components, to
produce a'separate current proportional in am
plitude to the phase relation of said two inde
pendent signal currents; and means cooperatively
energized |by said average current and said sepa
rate current, in like phase, for producing a direct
voltage proportional to the phase relation of said
independent signal currents,for directional indi
cations; the polarity of said direct voltage being
dependenton the sense of the differential of the
successive components, as detected relative to the
fixed phase of said average current.
5. In a heterodyneradio direction finding sys
9. In a heterodyne radio direction finding sys
tem, the combination set forth in claim l'where 20
tem wherein directional indications are depend
in said switching means includes an electron tube
ent upon the phase relation of two independent
amplifier in circuit with each receiving antenna,
signal currents, means for producing said cur
and a cont-rol oscillator connected with each elec
rents as impulses occurring in successive periods
tron tube amplifier for blocking the transfer of
energy alternately from the respective antennae; 25 at a frequency substantially greater than that of
said currents, means for integrating said impulses
said means for detecting the modulation side
to produce an average ycurrent of fixed phase,
bands of said switching frequency having a con
means for detecting the differential of successive
nection with said control oscillator for receiving
impulses to produce a separate current propor
current of switching frequency from said oscillator in proper phase for detecting said modulation 30 tionalin amplitude to 'thephase relation of said
two independent signal currents, and means co
tronf tube amplifier for blocking the transfer of
energy alternately from the respective antennae.
sidebands.
6. In a heterodyne radio direction finding sys
tem, the combination set forth in claim 1 where
in said switching means includes an electron tube
amplifier in circuit with each receiving antenna,
and a control oscillator connected with each elec
tron tube amplifier for blocking the transfer of
energy alternately from the respective antennae;
operatively energized by said average current and
said separate current in like phase for producing
a direct voltage proportional to the phase rela
tion of said independent signal currents and of
a polarity dependent upon the sense of the dif
ferential of the successive impulses as detected
with respect to the fixed phase of said average
current, for directional indications.
and including in said combination filter means
10. In a heterodyne radio direction finding sys
connected with the output of said receiving cir 40
tem
wherein directional indications are depend
cuit for selectively passing components of switch
ent upon the phase relation of two independent
ing frequency resulting from difference in am
Signal currents, in combination, meanscfor pro
plitude of carrier energy in the input of said re
ducing said currents as impulses occurring in
ceiving circuit, means for rectifying said com
successive -periods at a frequency substantially
ponents of switching frequency for producing a
greater than that of said currents', means for
direct voltage proportional to said amplitude dif
deriving from said impulses a first substantially
ference, and means for controlling the gain in
continuous current o_f fixed phase as the average
one said electron tube amplifier in accordance
of said current impulses and a second substan
with the magnitude of the last said direct voltagecontinuous current dependent upon the
7. In a heterodyne radio direction ñnding sys 50 tially
phase relation of said independent signal currents
tem, in combination: a directional antenna sys
in amplitude and polarity, and means for indi
tem, including a pair of signal receiving antennae
cating the amplitude of said second current, and
and a locally energized injector antenna coupled
its polarity in reference to the polarity of said
in like relation to both said receiving antennae;
first current of ñxed phase, for determining di
a receiving circuit including detector means;
switching means for connecting said receiving
circuit alternately with each of said receiving an
tennae, for producing heterodyne output beat
frequency components varying in phase relation
as the signals received at the respective receiv 60
ing antennae; means for deriving from said beat
frequency components, interrupted at the switch
ing frequency, a beat frequency current propor
rection.
'
.
ll. In a heterodyne radio direction finding sys
tem, the combination set forth in claim l0 and
including automatic differential gain vcontrol
means operative to maintain said independent
signal currents equal rin amplitude prior to the
operation of the first said means.
12. In a heterodyne radio direction ñnding sys
tern, in combination: a directional antenna sys
tional in amplitude to the phase relation of said
tem` including a pair of signal receiving antennae
received signals; means for integrating said beat
and a locally energized injector antenna coupled
frequency components, pulsating at the switch
"in
like~ relation to both said receiving antennae;
ing frequency, to produce an average beat fre
areceiving circuit including detector means;
quency current of fixed phase; balanced rectiñer
switching means for connecting said receiving
means cooperatively energized by both said beat
circuit alternately with eachvof said receiving
frequency currents in like phase for producing a
v antennae for producing independent heterodyne
direct voltage proportional to the phase relation
output-.beat frequency currents as impulses oc
of said received signals and direction indicating
curring in successive periods at said switching
means energized by said direct voltage.
.,frequency, »said currents being> derived in said
8. In a heterodyneradio direction ñnding sys
:detectormeans from received signal energy and
75
i tem wherein directional indications are depend
energy from said injector antenna and varying
in phase relation as the signals received at the
respective receiving antennae; means for inte
grating said impulses to produce an average cur
rent of ñxed phase; means for detecting the dif
ferential of successive impulses to produce a sepa
rate current proportional in amplitude to the
phase relation of said independent heterodyne
beat frequency currents; balanced rectiñer means
cooperatively energized by said average current
and said separate current in like phase for pro
ducing a direct voltage proportional to the phase
relation of said received signals; and direction
indicating means energized by said direct Voltage.
13. In a heterodyne radio direction ñnding sys
tem, the combination set forth in claim 12 where
in said switching means includes an electron tube
amplifier in circuit with each receiving antenna,
and a, control oscillator connected with each elec
tron tube ampliiier for blocking the transfer of
energy alternately from the respective antennae.
1G
receiving circuit for producing a direct voltage
proportional to said diiferential, and means for
controlling the gain in one said electron tube
ampliñer in accordance with the magnitude of the
last said direct voltage.
15. In a heterodyne radio direction finding sys
tem wherein directional indications are depend
ent upon the phase relation of two independent
signal currents, in combination, means for pro
ducing said currents as impulses occurring in
successive periods at a frequency substantially
greater than that of said currents, means for
deriving from said impulses a substantially `con
tinuous current dependent upon the phase rela
tion of said independent signal currents in ampli
tude and polarity, means for combining said suc
cessive impulses for producing a substantially
continuous wave of effectively ñxed phase, and
means for indicating the amplitude of said con
tinuous current, and its polarity in reference to
the polarity of said continuous Wave of eifectively
14. In a heterodyne radio direction ñnding sys
nxed phase, for determining direction.
tem, the combination set forth in claim 12 Where
16. In a heterodyne radio direction nnding sys
in said switching means includes an electron tube
tem, the combination set forth in claim 10 in
amplifier in circuit with each receiving antenna, 25 cluding means for producing phase quadrature
and a control oscillator connected with each elec
relation of the first and second currents, and
tron tube amplifier for blocking the transfer of
phase shifting means for aligning the currents in
energy alternately from the respective antennae;
like phase for cooperatively energizing the indi
and including in said combination separate means
eating means.
for detecting the diiîerential of rectified carrier 30
WALTER H. WIRKLER.
energy in successive periods at the output of said
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