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Патент USA US2408120

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Sept. 24, 1946.
2,4083. 19
Filed May 16, 1939
2 Sheets-Sheet 1
y Wolf/Oft, E552 wia/âge@
Sept. 24, 1946.
' ¿408,1 I9
Filed May 16, 1939
2 Sheets-Sheet 2
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Patented Sept. 24, 1946
Walter H. Wirkler, Cedar Rapids, Iowa, assignor
to Collins Radio Company, Cedar Rapids,
Iowa, a corporation of Iowa
Application May 16, 1939, Serial N0. 274,039
8 Claims. (Cl. vZ50-_11)
My invention is directed broadly to radio di
rection finding systems and more particularly to
-ployed in energizing the locally energized anten
na circuit.
a method and circuit arrangement for determin
Other and further objects of my invention re
side in the system and the representative em
bodiment thereof hereinafter more fully de
scribed with reference to the accompanying
One of the objects of my invention is to pro
drawings, in which:
Figure l is a diagram illustrating the general
vide a method of interpreting the phase relation
of radio frequency energy received at spacially
arrangement of the elements of my invention;
related points by converting the radio frequency l0 Fig. 2 is a schematic diagram of the circuit ar
rangement represented in diagrammatic block
energy to audio frequency energy while preserv
ing the significant phase relation of the currents.
form in Fig. 1; Fig. 3 is an equivalent circuit
Another object of my invention is to provide
schematic diagram of the tuned loop circuits em
means for altering the frequency of radio signal
ployed in the system of my invention; and Fig. 4
energy in a direction finding system without 15 is a detailed -schematic diagram of the high fre
changing the relative phase thereof with respect
quency coupling circuit embodied in the circuit
arrangement of Fig. ‘2.
to a diiferent component of the'energy similarly
v'Considerable information is available regard
Still another object of my invention is to pro
ing the effects of time, frequency, and distance,
vide a rotatable antenna arrangement in a di 20 on such propagation phenomena as variation in
rection ñnding system employing separate re
apparent bearing, scattering eüects caused by
ceiving circuits connected with certain antennas
simultaneous arrival of signals from more than
and local oscillator means connected to energize
one direction, and change in polarization, in di
another of the antennas, with means for tuning
rection finding systems. 'These factors are, for
the various antenna circuits.
25 `the most part, beyond the control of the receiv
A further object of my invention is to provide
ing operator. 'My invention concerns a direction
a receiving system in cooperation with the rotat
ñnding system which will give an accurate indi
able antenna arrangement including the sepa
cation of apparent bearin-g, and while it is recog
rate receiving circuits and a differential circuit
nized that this result cannot be achieved in the
in common thereto for deriving the required di
_presence of scattering effects, it will be shown
rectional signal.
that «operation is not affected by polarization or
vertical angle -of arrival.
A still further object of my invention is to pro
Any direction finder may be said to depend for
vide an automatic gain control circuit >effective
in operation upon one of the signal receiving .cir
`i-ts indication on -a comparison of the radio fre
cuits to maintain a balance of amplification in > quency time-phase of voltages induced in differ
ing the relative direction of propagation of sig
nal energy received by a comparison of the phase
relations of audio frequency currents.
the separate circuits.
Another object of my invention is to provide
ent ‘parts of the antenna system, horizontally
spaced :from each other. This is accomplished
-quite simply inthe loop antenna in which the
high frequency coupling means in the ,separate
two vertical lsides of a square loop, constitute the
receiving circuits effective to transfer the high
frequency energy selectively with/a >minimum of 40 horizontally spaced elements. When a loop an
tenna is electrostatically balanced or shielded to
phase displacement of low frequency modula
tion energy.
Still another object of my invention is to .pro
vide a radio direction finding system employing
a locally energized antenna -circuit and super
heterodyne receiving circuits .coupled With sepa
rate antenna components, with a common oscil
lator supplying the conversion energy to the su
eliminate the ordinary antenna effect, it serves
as a very simple and reliable direction ñnder for
such signals as induce no lvoltage in its horizon
tal member. The Areason for the simplicity of the
loop direction iinder is that the two vertical coil
sides, whose induced voltages are under compar
ison, are included in the same tuned circuit; and,
at least when the wavelength is long as com
perheterodyne receiving lcircuits and being em 50 pared to the dimensions of the loop, the circuit
to prevent voltages along the horizontal connect
treats these two voltages exactly alike and a
Since, at high frequencies, conditions of polar
ing arm from getting into the antenna circuit.
This balance is not quite independent of fre
ization and vertical angle of arrival of the re
ceiving wave are seldom such that no voltage
is induced in the horizontal members, it is seen
that, as soon as the horizontal members are taken
at a considerable height above ground. Uniform
earth and, preferably, a ground screen immedi
ately :beneath the antenna are also desirable for
sharp null reading is possible.
into consideration, the 'loop cannot be split into
two parts which pick up the same voltage under
all conditions of polarization. Instead, it is neces
sary to use two or more antennas which are iden
tical in their horizontal as well as their vertical
portions, or to eliminate the horizontal portions
One scheme sometimes proposed is to compare
the'voltage of two identical horizontally spaced
loop antennas. While this would, in theory, pro
duce the required results, it must be remembered
that the effective height of Va loop antenna is but
a small fraction of the height of one of its sides
quency and makes it necessary to erect the device
an electrostatic balance.
The antennas have an
electrostatic field of considerable extent, and
10 movement of personnel in the immediate vicinity
of the antenna must be properly guarded against.
In addition, of course, the rotatable Adcock an
tenna must fulfill all of the requirements of the
stationary type as regards shielding and balanced
construction to eliminate antenna effects, spur
ious pick-up, and inequality of the two vertical
antennas and interconnecting leads. In particu»
lar, if it is desirable to tune the system above the
static screen, that is, on the primary side of the
20 coupling `.transformer in order to increase the
sensitivity, it is important that the tuning equip
and that considerable spacing is required between
the two loops if reasonable sensitivity is to’be
attained. It then becomes electrically impracti
ment |be very. symmetrical to avoid any unbal
tuned separately and the two currents compared
directly in an intermediate circuit, would require
greatly simplifies the construction and balance
requirements in the antenna system and radio
frequency circuits. A heterodyning voltage, dif
ancing effect.
My invention relates to a substantially dif
cal to 'include the two loops in the same tuned
circuit. Any arrangement in which the loops are 25 ferent system of direction finding, one which
so high a degree of identity between the two cir
fering by a low audio frequency from the ren
cuits as to be quite hopeless.
Practical direction finders have generally been 30 ceived signal frequency, is generated by a local
oscillator and induced from a centrally located
of the Adcock type in which the antennas are en
“injector” antenna into each of the other an
tirely vertical and untunedAup to the point at
tennas of the receiving system. Each receiving
which they are connected together for comparison
antenna is connected to a separate receiver. The
or cancellation of voltages. The relatively ineffi
cient tuning and coupling means necessary are 35 output of each receiver then contains an audio
compensated for by increasing the height and
frequency heterodyne tone. If the injection volt
spacing of the vertical elements as compared to
age induced into each antenna is of the same
radio frequency time-phase-as it will be when
those of the loop antenna.
the injector antenna is centrally located-it can
Effective Adcock direction finders have been
.built with either stationary or rotatable antenna 40 be shown that the phase relations of the audio
tones at the outputs of the receivers are the
systems. In the stationary type, some form of
same as those between the voltages induced by
goniometer is used to compare the phase of radio
the signal wave into the different antennas.
frequency currents received from several vertical
- Let
antennas. The ineiîicient power transfer of the
goniometer is compensated for by the use of rela 4:5
w=21r times the signal frequency,
tively high, widely spaced antennas. This re
p=27r times the heterodyne frequency, and
9=phase angle of received signal.
quires a considerable area of uniform ground or
ground screen and, in addition, the antennas and
connecting radio frequency transmission lines and
coupling systems must be maintained identical 5,0 The locally injected voltage may be written
in operation over the frequency range and under
conditions of temperature and mechanical strain
E0=COS (co-p) i
encountered in service. The goniometer must, of
course, function properly over the required fre
-and the voltage induced by the signal
quency range. In addition, the typical stationary 55
Adcock direction finder with four elements spaced
Es=cos (wt-H9)
at the corners of a square with a fifth in the cen
ter for sense direction has an inherent octant
Combining these two waves in a square law de
error dependent on the frequency, the spacing,
and the direction of arrival of the wave front.
The two element rotatable Adcock direction
finder, because it dispenses with the goniometer,
can be made with a more effective tuning and
coupling system so that it need not -be as large
physically as the stationary type. It can be
erected fairly rapidly and does not require eX
cessive space. Also, the octant error is eliminated.
where the term cos (pH-0) is the audio frequency
The rotatable type has the disadvantages of be
term, showing that the phase angle 0 has been
ing rather slow and cumbersome to handle. Fur
thermore, as the horizontal interconnecting leads 70 preserved. The indication of the direction finder
is then based on a comparison of audio frequency
must be above the earth, the antennas must be
phase relations, rather than on radio frequency
of the balanced type so as to balance out the
phase relations. As a result, the necessity of pre
khorizontally induced voltages. This requires a
cise equality of the high frequency and antenna
rather high degree of balance in >capacity to
ground of the two vertical halves of each antenna 75 circuits is greatly reduced.
In my copending application, Seri-al No.
256,339, ñled February 14, 1939, for Azimuth radio
direction finding system, I have disclosed a sta
tionary antenna 'system land -receiving circuits
adapted to operate calibrated instrument means
for providing visual :azimuth directional indica
tions. My invention described herein relates to a
rotatable antenna system with receiving circuits
operative to indicate ‘a -null yposition in the re
ception of signal energy by which the direction
loops ìare cach in ra position for 'maximumssignal
detection, andthe voltage induced >in loop I iis
in phase with that in loop 2._ The audio beat
note in .the `output of receiver "I, 8, 9, is also in
phase with that from receiver H, I2, È9, and a
sharp null will be obtained in the output of audio
amplifier I4 because the beat frequency energy
from the separate receivers is diiîerentially re
lated in the detectors. The differential auto
10 matic volume control vI5 functions under proper
conditions, as willrbe described, «to assure equal
gain in the separate -receivers to obtain accurate
differential results in the output of detector 9.
of incidence of the Wave front can be determined
from the position of the antenna.
Referring to Fig. .1., two similar -loop antennas
This direction ñnder has vthe same property as
I and 2 are mounted at the ends of a horizontal
support-ing .arm of Isuitable length pivot-ed on a 15 the Adcock in that the two receiving antennas
are identical, and 'that when they are on a line
vertical axis at its center, as .indicated on Fig. l.
Each loop
of the unbalanced type, tuned by
a variable condenser Ia, 12a, respectively, and
»connected Vdirectly to .the grid of a tuned radio
perpendicular to the plane of arrival of the sig-'
nals, a null indication is obtained independent.
,frequency `amplifier Ib, 2b, respectively.
voltage be induced in the horizontal members of
of wave polarization.
That is, even though a
loop I, it will be induced in the hcrizontal'mem
bers of loop 2 in the same sense. The advantage
of this antenna system overîthe rotatable Ad
anced loops may be employed, with somewhat
superior results. A third loop antenna 3, tuned
Iby condenser 3a, is mounted midway between the
cock lies in the use of shielded loop antennas
antennas I and -2 and serves as the injector .an
tenna. The three .loop antennas .are in parallel 25 rather than electrostatically balanced vertical
antennas. Horizontal voltages induced in the
planes., as indicated, and vare at right angles to
supporting arm itself are prevented from entering
the horizontal line of support. The variable con
the antenna circuits by the «electrostatic shields
densers Ia, 2a and 3a, tuning >the loop antennas,
rather than by .any form -of balancing. As a re
and the condensers tuning the radio >frequency
sult, the rotating structure need be only a few
amplifiers Ib and 2b are ganged together and
feet above ground and is considerably less cum
rota-ted by a small motor ‘It over the frequency
bersome than the rotatable Adcock.
range of the system. Each loop antenna is en
Small inequalities between the two antennas
closed by electrostatic »shielding mean-s, Íand the
and radio frequency transmission lines have com
high frequency circuits described are likewise
paratively little effect on the accuracy of the
shielded, as Iindicated generally at 5.
system, that is, instrument errors are caused only
The output of .each radio frequency amplifier .is
by inequalities in the audio frequency phase shift
'fed to an individual receiving circuit through a
of the beat note between the antennas and the
shielded transmission line. Thus, the output of
second detectors of the receivers. When the
`an’lplilier Ib is fed through shielded line 6 ‘to .the
receiving `circuit including first detector means Y! 40 structure is rotated so that the signal induces
voltages of like phase in the two loops, vit is not
and intermediate frequency lamplifier 3 connected
essential that Athe >radio frequency .phase shifts
to 'a second detector 9 `of differential character.
‘between antenna and receiver be equal on 'the two
Similarly, amplifier 2b connects through line Ill
sides, but rather that the diñerence fin phase
to detector II, thence through .intermediate fre
quency amplifier I2 to the differential detector -9. 45 shift between the signal Voltage and ythe locally
introduced heterodyning voltage be equal on the
The output lof the detector 9 is supplied to audio
two sides of the system. 'Since the heterodyning
frequency amplifier I4, and part of the loutput is
voltage diiîers in frequency from the signal fre
:diverted through dinerential automatic gain con
quency by only a small fraction of one percent,
trol means I5 effective on the intermediate fre
quency amplifier 8. The `receivers are .of the 50 this requirement is not ,prohibitively severe,
especially in the antenna system. This canl be
superheterodyne type .and are supplied with en
by considering the equivalent circuit of
ergy Vfor frequency conversion from the one
the antenna system and determining the 'effect
oscillator I6.
,of a Áchange in frequency on the phase shift _pro
The injector loop 3 -is energized through
shielded transmission 'line 'Il from a mixer cir
duced in the system; Fig. 3 gives the equivalent
circuit of one of the tuned loop antenna sys
cuit 'I8 supplied with energy from both oscillator
tems I-Ia or 2-2a.
`,I6 and a separate oscillator i9 operating at a
In Fig. 3, Es represents the induced signal volt
frequency differing from ‘the intermediate Afre
age; Eg, the voltage at the grid of the radio fre
quency of amplification in amplifiers 8 >and I2 by
a few hundred cycles to provide ultimately an 60 quency amplifier; L, the inductance of the loop;
R, the resistance of the loop; and C, the capacity
audible note in the output of detector 9 and am
of the loop tuning condenser.
p‘liñer I4. Tuning means in the receivers T and
Let w=’2fr times the radio Afrequency
II are ganged together and `tracked with the
wo=21r times the frequency at which
tuning means of the conversion oscillator I6
which is common to the two receivers; the fre
quency of oscillator I9 is ñxed, which thus deter
mines the ‘frequency ‘of the injected voltage
Fi-l-f which is sufficiently close to the signal fre
quency to produce :an audible beat frequency.
>In operation, then, the heterodyning frequency 70
is supplied to the injector loop antenna t and
induced in the receiving loop antennas I and 2
together with the received signal. When the
antenna system is turned perpendicular to the
plane of incidence of the arriving wave, the 75
When w=wo, the current I will be in phase with
Es, and Eg will be 90 degrees out of phase with Es.
‘This represents a condition of normal phase
shift. We are interested in how o, the angle of
departure from this normal phase shift, varies
Ywith frequency, so that we may determine 'the
2,408.1 1 9
difference in phase shift between'the signal volt
age Es and the heterodyning voltage Eo. We have
the arm is turned one degree from the null posi
tion is
5 meters
The error in bearing produced is therefore j
for a circuit with a Q of 50, one-half of one per
cent detuning, and an audio frequency of 300
c. p. s., and at a wave-length of 100vmeters, with
' loops spaced 5 meters.
Letting tan> ¢=y
This error increases with Q and with the audio
frequency, and decreases with the radio frequency
and with the spacing of the antennas. It is evi
dent that the error in this respect arising in the
intermediate frequency amplifier tuned circuits
20 of the receiver is greater because of higher Q and
lower carrier frequency. The problem is made
considerably simpler, however, by the use of the
common superheterodyne oscillator I6 for the
two receivers, whereby the intermediate fre
quency is exactly the same in each receiver.
intermediate frequency circuits are aligned quite
closely with each other, and comparatively few
stages are used in cascade while coils of extremely
high Q are avoided.
The complete circuit arrangement included in
the block diagram of Fig. 1 is shown schematically
in Fig. 2, wherein theV blocks are shown in broken
line outline and designated by like reference
characters. The ñrst detector circuits 1 and Il
are of conventional design employing multigrid
electron tubes 2l and 22, respectively. Each of
and, since A is small, neglecting A as a single term,
the intermediate frequency amplifiers 8 and I2
we have
includes two stages of electron tube amplification
2Q _. s approximately
with novel coupling means shown in detail in Fig.
dn- 1 -l- 4Q2A2
40 Lland hereinafter more fully described. ‘Ampli
fier 8 includes electron tubesV 23 and 24; and am
Supposing, now, the carrier frequency is 3000 kc.,
pliñer I 2, tubes 25 and 26. The second detector
the heterodyne frequency 300 c. p. s., and the Q
9 comprises a dual diode electron tube 21 serving
of the loop is 50. If the loop is resonant, A=0,
as two independent second detectors with the di
and the slope of the phase shift characteristic is
45 ode portion 21a connected with the output means
8a of ampliñer 8 and diode portion 21b connected
with output means l 2a of amplifier l2. The rec
tified voltages from the different diode portions
are applied in series opposition across resistors
50 28 and 29 in the output of the detector, and by
pass resistor-condenser combinations 56 and 51
d¢>=100><0~00011=0~01V radians=0.5‘73 degrees
are provided; by-pass combination 5B completing
phase shift for a 300 cycle tone.
the circuit from rectifier portion 21a. to ground,
and by-pass lcombination 51 completing the cir
Now supposing the other loop, instead of being
cuit from rectifier 21h to resistor 28. The differ
tuned to resonance is.' by reason of circuit in
ential voltage across resistor 28 is impressed on
equalities, tuned one-half of one percent from
input of amplifier I4 which, as shown, is a
conventional two stage resistance coupled audio
frequency circuit employing electron tubes 30
60 and 3|; the output at 20 includes a jack for con
nection to audio signal indicating means.
The portion of the differential voltage due to
the direct current in resistor 29 is applied di
d4): 801171.?
(0.0001) =0.008 l'adÍáLIlS>
rectly to the grid of electron tube 32. A com
:0.458 degrees
65 pensating tube 33 has the grid thereof grounded
The difference in audio frequency phase shift
with the end of the resistor 29 opposite from
the connection to the grid of tube 32, so that
is then
changes in power supply voltage do not affect the
difference in the grid potentials applied to am
plifier tubes 34 and 35 which are energized from
l=0.115 electrical degrees
the output of tubes 32 and 33 in opposite relation.
`With a spacing of the two loops> of five meters
The plates of tubes 34 and 35 receive alternat
and the wave-length -of the received signal 100
ing current in balanced relation, from secondary
36a on power transformer SIL-through a center
meters, the electrical phase diiîerence between
lthe signal voltages induced in the two loops when
Vtap on the output transformer 31. Unbalance in
and 55, have identical L, C‘, and Q, and a like
the grid, voltages of tubes k34 and 35 results in
coupling coefficient
somealternating current voltage being delivered
through transformer 3-1: to the grid of an» ampli
Iier 38. This alternating current;
applied to
transformer 39 and therethrough, in opposition,
the arrangement will have very little effect on
to the plates of a balanced. rectifier 4153. Simul
the audio frequency modulation. Adjustment of
taneously, alternating current from secondary
the coupling., therefore, furnishes a convenient
36h on power transformer 36 is applied to; the
method for controlling the audio phase shift for
balanced' rectifier liû. in parallel. Resistors 4Ia
the purpose of equalizing the operation of the
and Mb- connected in branch circuits from the 10 separate receiving circuits in this respect.
secondary 36?) to the». cathodes of the balanced
A convenient check on possible errors in the
rectifier'. will carry current separately according
system is furnished by changingA the audio beat
to which bank of the balanced rectifier is con.
frequency slightly. After a sharp null has been
ductive,` which depends; uponl the relative polar
obtained by turning the antenna system and
ity of the alternating currentA in transformer 3,9,
adjusting the gain of one of the receivers, the
as determined by which tube, 34 or- 35; is more
frequency of oscillator, I9, Figs. 1 and, 2, is
conductive._ Accordingly,- resistor 42 will have a
changed slightly. As the audio. phase shift is
voltage of polarity dependent upon which receiv
proportional to the audio frequency, a phase dif
ing circuit introduces the more gain and of mag
ferencev in the two beat notes will appear if there
nitude dependent uponthe difference in grain,
is any inequality in the system, and a new direc
tional setting will be necessary to reestablish the
null. If the null> remains when the beat fre
quency is changed, however, the setting is correct.
and this voltage i-s- applied as' an automaticgain
control to the grids off tubes Z3 and 24 inthe
amplifier 8 for the purpose; of equalizing the
gain. In operation, the automatic gain control
Oscillator I9 may be frequency modulated over a
tends to equalize the gain asv the antenna system 25 range of about 200 cycles by means of a small
is' rotated so that a> sharp null may> be noticed
motor-driven condenser so that the beat note
in the output 20 when substantially in phase
changesy continuously from approximately 200v to
signal voltages are induced in. theÍ loop antennas
LlOIl cycles. An adjustment of. the phase shift
I and 2.,. In this conditi'on- voltages of equal mag
characteristic of one. of the. receivers. may then
nitude> are opposed in resistors 28; and' 29 so 3.0 be made. manually while turning the. direction
that no signal isÉ evident at. the output` 20; and',
finder, until no beat note is audible. This phase
in the differential gain control,h no unbalance
adjustment can be accomplished by adjusting the
exists on the grids of tubes 34 and 35.. The grids
couplingv of one of the intermediate frequency
of tubes 34 and 35 are supplied
stages,Y as. above described in relation to Fig. ‘1.
tial from the voltage across, a resistor'I 4:3 in cir
cuit with the usual rectified power supply; Ad
justment for balance isV provided by potentiome
Under these conditions, no instrument error due
to maladjustment will exist, and the bearing
obtained will be correct.
ter 44, for the adjustment of which switches 45
The. advantage of the heterodyne direction
and 4B are providedt to isolate the control I5
of my invention over the known Adcock
and to connect the audio indicating means. at out 40 system is, morev pronounced for ultra-high fre
put 2B with ampliñer'38, respectively. When the
quencies. At a wavelengthA of five meters, for
circuit is so arranged, potentiometer M is ad
example, a rotatable structure with antennas
justed until. no alternating current is present in
four meters apart would be feasible. The phase
the output.
tolerance requirements in the antenna system
The gain of the amplifiers 8' and I2 may be
are greatly reduced, because the audio beat fre
manually controlled> by a ganged resistance- ar
quency is a very small vfraction of the carrier
rangement as shown aty 41 controlling the cathode
frequency. 'I‘he comparatively large tolerance
potential in tubes'l 23'--2Iï. lilqualityr of gain is
of this system in the matter of equality of an
manually adjusted' by potentiometer` 48' in con' 50 tennas and transmission lines is of real value at
junction with the gangedv control' 41S.
these high frequencies, and the difficulty of using
The oscillatorv circuits I6 and t9 may be of
comparatively large antennas spaced almost one
any suitable construction, preferably ofthe elec
wavelength apart is eliminated. Spacings of
tron tube type shown. Triod'esI 49 and 5u are
greater than one wavelength would, of course,
shown in oscillators' IS and i9', respectively, with
result in ambiguity.
the tuned circuit of oscillator lliv ganged with
While I have disclosed my invention in certain
the tuning controls of detectors 'I' and I‘I as here
preferred embodiments, I desire it understood
inbefore noted. ‘The mixer circuit I8 is» of con
that modifications may be made therein without
ventional design employing multi-grid tube 5I"
departing from the principles of my invention as
and including control means at 52 for regulating
disclosed, and that no limitations upon my inven
the power supplied to loop 3. The output of 60 tion are intended except as are imposed by the
mixer I8 is unmodulated.
scope of the appended claims.
Referring now to Fig. 4, tubes 23 and 24 in am
What I claim as new and desire to secure by
plifier 8, for example, are coupled by a connec
Letters Patent of the United States is as follows:
tion from the anode of tube 23 through a con 65
1. In a> radio direction finding system,l the
method of determining the radio frequency time
denser 53 to the control grid of tube 2.4, thus pro.
phase of signal voltagesv induced in different parts
viding a high frequency path subject. to. minimum
of a, directional antenna system which comprises
phase complications. in respect to. the heterodyne
supplying radio frequency energy locally in equal
tone modulation. selectivity is provided by tuned
circuit 54 connected the. anode-cathode circuit 70 relation Ito the different parts of- the antenna
system for inducing therein second voltages> of
of tube 23. A parasitic circuit 55., variably cou
like. phase characteristics, the frequency of said
pled with tuned circuit 54, permits adjustment
locally supplied` energy being different from that
of the audio'modulationgphase by variation of
of the. signal energy in a- relatively small degree,
the coupling between the circuits 54 and 55,
where necessary. If the two tuned circuits, 54 75 separately mixing the voltages induced in each
part of the antenna. systemrto obtain separate
10W frequency components the phase relation of
which is the same as that of the signal voltages
induced in the different parts of the antenna sys
tem, said low frequency being equal to the dif
ference in frequency of the signal energy and the
locally supplied energy, combining said low fre
quency components, and indicating the phase re
phase relation of said low frequency currents and
accordingly the phase relation of the signal ‘volt
.tages induced in said receiving loop antennas as
a function of the resultant current in the last said
5. A radio direction finding system as set forth
in claim 4 and including intermediate frequency
amplifiers in said separate receiving circuits, a
lation of said loW frequency components as a
conversion oscillator connected in common to
function of the resultant derived from the com 10 said detector means, the outputs of said detectors
bination of said components.
2. In a radio direction finding system, the
method of determining the phase relation of radio
frequency signal voltages induced in different
parts of a directional antenna system which com
prises supplying radio frequency energy locally
in equal relation to the different parts of the an
tenna system for inducing therein second volt
being supplied to said intermediate frequency am
plifiers, said low frequency currents being car
ried as modulations in said intermediate fre
quency amplifierswith the relative phase thereof
substantially unchanged in the intermediate fre
quency amplifiers, and' second detector` means
connected with said intermediate frequency am
plifiers for delivering said low frequency cur
ages of like phase characteristics, the frequency
of said locally supplied energy being different '20 e 6. A radio direction 'finding' system as set forth
from that of the signal energy in a relatively small
in claim 4 with said receiving circuits also in
degree, separately mixing the voltages induced in
cluding a conversion oscillator connected in com
each part of the antenna system and a locally
mon to said detector means, 'separate 'interme
generated voltage to produce modulated inter
diate frequency amplifiers connected with the
mediate frequency components the modulations 25 outputs of said detector means, and separate sec
of which are of a lowfrequency equal to the
ond detector'mean's connected with said ampli
difference in frequency of the signal energy and
fiers; and with said means for exciting said ln
the locallysupplied energy `and have the same
phase relation as the signal voltages induced in
the different parts of the antenna system, am
plifying said intermediate frequency components
with substantially no' alteration in phase of the
jector antenna including said conversion oscil
lator, an oscillator of a fixed frequency differing
from the intermediate frequency by the low fre
quency of said individual currents,l and a mixer
circuit for deriving energy of the required fre
modulations, rectifying said intermediate fre
quency from both saidloscillators for exciting
quency components, combining the low frequency
said injector antenna.
modulations in the rectified components, and in 35 7. A radio direction finding system as set forth
dicating the phase relation of said lowfrequency
in claim 4 with individual variable tuning means
modulations as a functionrof thevresultant de
connected with said receiving loop antennas and
rived from the combination of said modulations.
said injector lo'op antenna, and means for simul
3. `In a radio direction finding system, Vthe
taneously operating each of said tuning me‘ans
method as set forth in claim 2 and including 40 for synchronously tuning 'all said antennas over
combination of said locally generated Voltage and
a predetermined frequency range.
a second locally generated voltage of a frequency
8. A radio direction finding system comprising
a'pair of receiving antennas mounted for rota
differing from the intermediate frequency by the
low frequency of said modulations to provide the
radio frequency energy supplied locally to the
different parts of the antenna system.
4. A radio direction ñnding system comprising
a pair of tuned loop receiving antennas mounted
for rotation in diametrically opposite positions
about a middle vertical axis and arranged in
parallel planes, a tuned loop injectorV antenna
mounted at said axis in fixed parallel relation
With respect to said receiving loop antennas and
spaced coupled invariably in like relation to both
said receiving loop antennas, electrostatic shield
ing means for said loop antennas, means for elec
trically exciting said injector antenna With en
ergy of frequency differing from that of received
signal energy in a relatively small degree, sepa
rate receiving circuits connected with said tuned
loop receiving antennas each including detector
means for mixing the voltages induced in each
of said receiving loop antennas by -the signal
energy and energy from said injector antenna for
producing individual currents of low frequency
tion in diametrically opposite positions about a
45 middle vertical axis, an injector antenna mounted
at said axis and space coupled in like relation to
both said receiving antennas, means for electri
cally exciting said injector antenna With ‘energy
of a frequency differing from that ofY received
50 signal energy in a relatively small degree, sepa
rate receiving circuits connected with said re
ceiving antennas each including detector means
for mixing the voltages induced in each of said
receiving antennas by the signal energy and en
55 ergy from said injector antenna for producing in
dividual currents of low frequency equal to the
difference in frequency in said voltages, means
connected in common with said receiving circuits
for combining said low frequency currents in dif
60 ferential relation, gain control means energized
by the resulting differential of the individual low
_frequency currents in said combining means and
operatively related to one of said receiving cir»
cuits for substantially equalizing the amplitudes
of said individual currents, and means connected
with said combining means and energized by the
resultant current for indicating the phase rela
tion of said low frequency currents of substan
equal to the diñerenc'e in frequency in vsaid volt
ages, the difference between the signal energy
phase shift and the injection energy phase shift
being substantially the same between each
tially equal amplitude, and accordingly the phase
shielded receiving loop antenna and the respec 70 relation of the signal voltages induced in said
tive receiving circuit, means connected in com
receiving loop antennas, as a function of said re
mon with said receiving circuits for combining
sultant current.
said low frequency currents, and means con
nected with the last said means for indicating the
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