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Патент USA US2406406

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- Aug. 27, 1946.4
P. c1. sANDRET'ro ET AL
2,406,406
RADIO DIRECTION FINDER
Filed July 24, 1941 »
4 Sheets‘Sheet 1_
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Aug. 27, . A1946.
P. c.~ sANDRETTo ET_AL
2,466,406
RADIO DIRECTION` FINDER
Filed JùIy 24, 1941
4 Sheets-Sheet 2
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Allg- 27, 1945-
P. c. sANDRET-ro E-rAL
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2,405,406
RADIO DIRECTION FINDER
Filed July 24. 1941
4f Sheets-Sheet 4
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Patented Aug. 27, 194s
UNE'E'E
2,465,406
STATES PATENT @ENCE
2,406,406
RADIO DIRECTIÜN FINDER
Peter C. Sandretto, Chicago, and Elmer P. Buck
'thai, Brookiield, Ill., assignors to United Air
Lines, Inc., Chicago, Ill., a corporation of Dela
War@
l
Application July 24, 1941, Serial No. 403,5502
17 Claims. (Cl. Z50-11)
This invention relates to radio direction ñnd
ers, more particularly to ground station radio
direction finder systems for use at medium high
frequencies, and the invention has for an object
the provision of improved systems and apparatus
i this character.
Radio direction finders utilizing antennas hav
ing directional sensitivity are of course known
in the art, the usual practice being to employ
2
antenna arrangement, and selective means for
connecting the two loop antennas in opposed
parallel relation to suitable receiving means, or
for connecting one of the loop antennas and the
vertical antenna in parallel relation through a
suitable coupling means or phase shifter to the
receiving means.
The output of the receiving means, which pref
erably includes one or more fixed frequency oscil
two or more ground station direction ñnders 10 lators adapted to beat together with the carrier
supplied to the receiving means from the an
tennas, is connected by way of a rectifier to sen
determined, whereby bearings may be obtained
sitive instrument means having a movable ele
simultaneously at each station, and the position
ment adapted to trace a permanent record on a
tuned to the carrier frequency of the transmitter
on an airplane or ship whose position is to be
of the plane or ship located by triangulation.
The medium high frequencies presently available
for aircraft transmitters, however, are propa
gated by the ionosphere, and difficulties in ob
taining accurate bearings at such frequencies
have been encountered due to the various distor
tions and errors which are interjected by this
propagating medium.
constantly moving recording surface. In order
properly to orient the continuous record of signal
intensity thus produced with respect to the com
pass position ci the antenna arrangement, a
switching device is provided associated with a
20 rotating part of the antenna arrangement and
connected in circuit with a second movable record
tracing means, so that the recording surface will
Examples of some of the errors recognized by
receive periodic indications of the relative posi
the art as occurring in radio direction finders
tion of the antenna arrangement from which the
operating at such frequencies, and as to which 25 continuous record of the signal intensity may be
various corrective attempts have been made, are
properly oriented.
observational errors due to fading and to the
The present invention also includes within its
difîiculty oí" distinguishing between a “crisp” null
scope the provision of means for rendering the
and a “hollow” null, deviation errors caused by
output frequency cf the receiving means inde
minute-by-minute and second-by-second varia 30 pendent of the carrier frequency supplied to the
tions in the ionosphere, polarization errors due
receiving means by the antenna arrangement, as
largely to horizontally polarized sky waves, and
well as automatic means for controlling the re
the various errors due to the presence of static.
spective connections of the loop antennas and
In spite of all corrective attempts which have
the vertical antenna to each other and to the
heretofore been
it is a well recognized factk 35 receiving means, whereby accurate records may
that the bearing errors which occur even with
be obtained free from the usual bearing am
best equipment heretofore known, may be of
biguity and substantially uniniiuenced by static
magnitude as to render substantially useless
conditions. In addition, means may be provided
bearings taken even by skilled operators.
for insuring a constant phase displacement be
It is accordingly a further object of this inven 40 tween the energy input from the vertical antenna
tion to provide a radio direction finder system
and loop antennas, regardless of the carrier fre
for medium high frequency work capable of elim
quency, and if desired automatic volume control
inating, correcting or minimizing substantially
means may be employed so as to render the con
all ci the known and recognized errors, and of
tinuous records obtained from the improved sys
substantially automatically providing permanent 45 tem independent of variations in the intensity
records of individual bearings of such character
of the carrier.
that unskilled operators may readily determine,
For a more complete understanding of this
by mere inspection of any group of records, the
invention, reference should now be had to the
true bearing of the transmitting station.
accompanying drawings in which:
In carrying out the invention in one form, a 50
Fig. 1 is a somewhat diagrammatic representa
rotatable antenna arrangement is provided com
tion of the circuit connections and the various
prising a pair of spaced loops arranged in coaxial
operating parts of a radio direction finder em
relation and a vertical non-directional antenna
bodying the present invention;
coincidentl with the axis of rotation, together
Fig. 2 is an illustrative circuit diagram of a
with means for constantly rotating the entire 55 portion of the system shown in Fig. 1, which is
2,406, 406
3
4
be further described hereafter and which is rep
adapted to eliminate or minimize the eiïects of
resented in Fig. 1 diagrammatically and indicated
by the reference numeral 31. The oscillator
static on the continuous bearing records ob
tained;
means 3l beats with the carrier of the received
signal, and produces at the output of the radio
Fig. 3 is a circuit diagram of an automatic
means for controlling the antenna connections
selectively to produce a cardioid pattern in order
to remove the bearing ambiguity;
Fig. 4 is a circuit diagram of a somewhat modi
fied arrangement including means for insuring
receiver 29 a beat note of predetermined fre
quency, the output being connected by suitable
conductors 38 to a band-pass filter 39 capable
of passing the beat note frequency. The iîlter
Y39 is connected, as shown, to a rectiñer 4Q which
10
constant phase Shift between the respective in-Y Vis illustrated as comprising a suitable transformer
puts of the loop antenna and the vertical an
4I and a full wave rectifier tube of the duo-diode
tenna, regardless of the frequency of the com
mon carrier to which the respective antennas are
The output of the rectifier 4t is connected by
tuned;
.
the conductors/13 With the Winding 44 of sensi
Fig. 5 is a circuit diagram of a still further
tive instrument means comprising a milliam
modification, including automatic volume control
meter which is illustrated as including, in addi
means which will prevent overloading ’of the
Y tion to the coil 44, a permanent magnet 45 hav
receiving means and correct for fading Y_signals _ ,
ing an air gap Within Ywhich the moving coil is
without being detrimental to the accuracy of the>
mounted for rotation. Carried by the moving
20
direction iinder system; and
coil 44 is a suitable tracing element 41 which
Figs. 6, “7, and 8 are illustrative bearing records
may include a suitable ink supply, not shown,
which may be obtained under certain conditions
and which is arranged to record the rectiñed out
in the operation of radio direction finder systems
put of the receiver on a chart or recording sur
embodying this invention.
A
'
face 48. The chart 48 is preferably carried, as
Referring now to Fig. 1, the invention is illus 25 shown, on a rotatable drum 49 which is driven
trated as embodied in a radio direction ñnder
at a constant speed by a suitable motor 50, the
having rotatable antenna means comprising a
motor 50 being so synchronized with the driving
pair of spaced apart shielded loop antennas IEI
motor of the antenna arrangement contained in
and II, which are mounted in coaxial relation
the base I5 as to insure that the chart 48, which
30
on opposite ends of a horizontally extending beam
is graduated in the usual fashion to indicate dee
I2 secured for rotation on the upper end Vof a
grees of movement, will move through a distance
rotatable post I3, the beam I2 and the post I3
corresponding to 360° during each complete revo
being shown in broken lines since the mechanical
lution of the antenna arrangement. Thus it will
structure of these elements constitutes no part
be seen that an ink trace, such as indicated by
of the present invention. Intermediate the loop 35 the reference numeral 5I in Fig, ‘1, will be pro
antennas’lú «and II and mounted coincident' with
duced on the chart 48 so as to provide a per
the aXis of the post I3, is a vertical antenna I4.
manent record of the signal intensities supplied
and the entire antenna arrangement is mounted
to the receiver 29 during rotation of the antenna
on a suitable base I5 containing a drivingl motor
arrangement.
'
40
and suitable gearing (not shown) for rotating the
‘In order properly to orient the ink traces on
post I3v and the parts mounted thereon at a pre
determined constant speed.
As' shown, the loop antenna I0 is connected
by suitable transmission vlines I6 and YI'I to a
pair of slip rings I8 and I9, respectively carried
the chart 48 with the compass position of the
antenna means, the rotatable post I3 of the an
tenna arrangement is provided with switching
45 means including a rotating Contact 52 which is
by the rotatable post I3 and adapted to be en
gaged by suitable brushes 20 and 2l. Similarly,
the loop antenna I I is connected by transmission
lines 22 and 23 to the slip rings 23a and 24, re
spectively'carried by -the post I3 and adapted
to be engaged by brushes 25 and 26 respectively.
The brushes 2U and 2|, which are associated as
above described with the loop antenna I (l, are
permanently connected by means of suitable _con
ductors 21 and 28 to the input of a radioreceiver '
29 which may be of the conventional type hav
ing the usual detectors, radio frequency ampli
ñers, intermediate frequency amplifiers, audio
output, andV necessary interconnections. YThe
adapted to engage a co-operating stationary con
tact 53 once during each revolution of the an-tenna arrangement. This switching means is
connected, as shown, in circuit with a battery
54' and the energizing winding 55 of a relay, so
that each time the contacts 52 and 53 close, the
armature 555 of the relay will be attracted and
a suitable tracing element 51, which is 'carried by
the armature 5B, will be operated to trace on
the chart 48 a reference mark, such for example
as the mark 58, which may be used to orient the
ink trace 5I with the compass position of the
antenna arrangement. For example, if the ref
erence mark 58 corresponds to a true north-south
position of the antenna loops IB and I I, the rela
brushes 25 and 26, which are associated as above 60 tive compass positions of the various maximum
described-with the loop antenna I I, are per
and minimum intensity points indicated by the
manently connected to the stationary contacts
trace 5I may readily be determined.
30 and 3l of a multiple pole double throw switch
While various other antenna arrangements
ing or coupling means 32, and it will be observed
known to the art, such for example as the Adcock
that when the switch is thrown to a left-'hand
antenna system connected to the receiver by
position, as viewed in Fig. 1, the loop -antenna II
will be connected through the contacts 3Q -and 3I ,
means of a goniometer, may be utilized within
the broad principles of this invention, the particu
lar antenna arrangement illustrated in Fig. l has
circuit of the loop antenna I0, the connections 70 been found highly advantageous in eliminating
polarization errors which may arise due to‘the
being such that the two loop antennas _are con
presence of horizontally polarized sky waves. '
nected to the input of the receiver 29 in opposed
When the antenna arrangement shown in Fig.
parallel relation. `
l
occupies a position such that the beam I2 is
Associated with the receiver 29 is a suitable
oscillator means of fixed frequency, which will 75 pointing directly at the transmitter station, a
the switch blades 33 and 34, and the conductors
35 and »3s to the 'conductors 21 and 2a in the
2,406,406
5
vertically polarized ground wave will of `course
induce equal' and‘opposite voltages in the two
sides of each of the loop antennas, and no signal
will be supplied to the receiver 2t from the an
tenna arrangement. Likewise, when the beam i2
is at right angles to the direction of the trans
mitter, a vertically polarized ground wave will
induce maximum voltage in each of the coaxially
mounted antenna loops, hut since these antenna
6
antenna 64a. is connected in parallel with the
loop antenna â il through the switch blades 33 and
34 in order to prevent unbalance of the system,
in addition the vertical antenna is connected
through the knife blade ÈB, the switch Contact
34, a conductor
a phase shifter or coupling
means E6, which is shown diagrammatically in
Fig.Y 1, and by way of conductor El to the receiver
Ztl. The coupling means or phase shifter 66 in~
loops are connected
opposed parallel relation, 10 sures that the energy received from the vertical
zero signal intensity will again be supplied to the
antenna I4 will be displaced 90° from the energy
receiver. Accordingly. with a substantially en
received from the loop antenna it so that the well
tirely vertically pclariz. . wave. four nulls will
known cardioid pattern will be produced.
occur during'each revolution of the antenna ar
ri‘hus, in order to obtain a continuous record
rangement and the permanent record produced
which
with
the
record
direction
will befinder
free illustrated
of any bearing
in Fig.
on the chart »it will
show a null of zero or
minimum signal inten 'ty in each quadrant of
hiffuity, it is necessary only to throw the switch
each 350° record. Substantially entirely vertin
32 to its right-hand position for one or more
cally polarized waves will be supplied to the an
revolutions of the antenna arrangement, whereby
tenna arrangement. however, only when a plane
a cardicid pattern, having only
zero or m
is leaving the airport where the antenna arrange
mum intensity position, will he produced on the
i‘cd. At distance of approximately
to
chart
.its lett-hand
¿8, and thereafter
position soto asthrow
to produce,
the switch
during
60 miles. utilizing medium high frequencies of the
character heretofore indicated which may vary
succeeding revolutions of the antenna arrroigen
from 1.5 to 30 megacycles. it will be found that in 25 ment, a continuous trace of the signal intensity
addition to the vertically polarized ground Wave
of the character hereinbefore i- dicated.
there will be received at the antenna arrange
The cardioid pattern itself cannot he used for
ment horizontally polarized s’sy waves propagated
determining the true bearing of the transmitter
by the ione-sphere, and t. at a distano.. of approxi
station, due to the polarization errors and the
mately 206 miles the ground wave will substan 30 like which may cause a variation in the null of
tially disappear.
the cardioid of such great magnitude as to render
The horizontally polarized sky waves will of
the cardioid pattern useless from the bearing
course induce in each or" the loop antennas a
voltage which cannot be eliminated merely by
standpoint. The cardioid pattern will, however,
indicate in'what quadrant a plane or transmi Ling
rotating one of the antennas, but, as in the case 35 station is located, and the quadrant having thus
of a vertically polarized ground wave, the voltages
been determined, the true bearing may readily be
induced in the two loop antennas, when the beam
ascertained from the continuous records produced
i 2 occupies a position substantially at right angles
with
two loop antennas connected in parallel
to the direction of the transmitting station, will
opposed rela-tion as described above.
cancel out, due to the fact that the two loops are 40
In Fig. 6 there is shown a typical trace 68 on a
connected in opposed parallel relation and that
linear chart constituting a portion of the chart
in this position there will
no diversity error.
lit, which trace $8 represents a true bearing havm
In all other positions of the antenna arrange-v
ing a readily discernible null or minimum Ei*
ment a diversity error'occurs due t0 the differ
which represents the true bearing of the plane
ence in time phase of the incoming waves with 45 or transmitter. By referring the point 69 to one
respect to the two spaced loops.
ofthe reference marks 5S
by the tracing
From the above it will be clear that as the
element 5‘! on the chart 48, the correct bearing
antenna arrangement is rotated at a constant
of the transmitting station may readily be noted.
speed, there will be prodi'> .d on the chart 48 a
In Figs. 7 and 8, representative ink traces are
continuous record wh' h t. .l show either two or 50 shown which indicate false bearings, the ink trace
four positions of m .icio l or zero signal in
tensity during each revo
‘on of the antenna
’lo in Fig, 7 having a series of points li, l2, and
'i3 whichl might easily have been mistaken for a
arrangement, depending noon the character of
true bearing if headphones had been used in the
the incoming wave, and accordingly there will be
customary manner connected to the output of the
an ambiguity in the record since obviously only 55 receiver 29.
,.
one of these positions of minimum signal in
unskilled
It is a relatively
operator simple
that amatter
trace having
to teachthe
even
gen
tensity indicates the true bearing of the plane or
transmitter station.
eral conñguration shown in Fig. 6 and only that
It is for the purpose of overcoming this bear
trace represents an accurate bearing. According
ing ambiguity that the vertical antenna te and 60 ly, by mere inspection the operator can discard
its associated connections are provided, the verti
traces such as are shown in Fig. 7 from any single
cal antenna being connected as shown by a trans~
group, and thus eliminate all of those bearings
mission line 59 to a slip ring @t carried by the
which are obviously false.
erroneous trace
rotating post i3, and a brush El, which is ar
illustrated in Fig. '7 may of course be due to fading
ranged to contact the slip ring Sii, connects the 65 and to deviation errors caused by minute-by
vertical antenna through
conductor 62 to the
minute variations in the ionosphere. Prefer
movable blade @3 of the switch 32. When the
ably, the antenna arrangement is rotated at the
switch 32 is in its left»l'iand position, as pre
rate of approximately i5 revolutions per minute.
viously described so as to connect the loop an~
and by thus taking a relatively large number of
tennas l0 and l! in opposed parallel relation, the 70 traces during a short period it is possible to ob
vertical antenna I4 is open circuited and the
continuous record or trace heretofore described is
obtained. When, however. the switch 32 is
thrown to a right-hand position, the loop antenna
Il is cut out of circuit and a suitable artificial 75
tain one or more true bearings when fading is
nonexistent, even though over the general period
severe fading conditions may exist.
In Fig, 8 there is shown a chart having an inl;
trace 'I4 thereon which is identical with the ink
2,406,406
7
trace 10.0f Fig. '7, and superimposed on the trace
14 there is indicated in broken lines a trace 15
which would have been formed if no fading had
~ which the band-pass ñlter 39 is designed to pass.
For example, if the band-pass ñlter ís designed
t0 pass a frequency of 1020 cycles plus or minus 30,
the frequencies of the crystal oscillators will be so
selected as to have a frequency difference equal to
been present. While movements or changes in
the ionosphere during the time that a bearing is
being recorded are indicated by irregularity in the
trace 5|, a true bearing may be located by compar- '
ing the portion of the false trace adjacent to the
apparent minimum with a standard trace of a true
bearing. Thus, if a trace corresponding to a true
bearing is printed or otherwise made on a trans
parent card, formed for example of Plexiglas or
other similar material, such a standard bearing
may be superimposed on a bearing trace such as
the bearing trace in Fig, 8, and it will immediately 15
become apparent that the trace 14 represents a
false bearing and may be discarded. Thus it is
possible by comparison with a standard trace to
eliminate the element of judgment, and even un
skilled operators may readily discard all improper 20
bearings and determine immediately those traces
which represent true bearing readings.
In order to assure the accuracy of the bearings
obtained, the loops Il! and I l, and hence the drum
»11.9, may be allowed to rotate a number of times 25
(at least l5) for each bearing desired. In this
manner a number of bearings are superimposed
one over the other and can be readily averaged to
secure a resultant bearing more accurate than
any individual bearing.
,
30
1020 cycles. When the frequencies of the two
crystal oscillators and the carrier are impressed
on the control electrodes of the converter tube 16,
two beat frequencies will be generated equal re
spectively to the difference between the carrier
frequency and the frequency of oscillator 80, and
to the >difference between the carrier frequency
and the frequency of oscillator 8l, and these two
beat frequencies pass from the converter tube 16
to the I. F. amplifier indicated diagrammatically
by the reference numeral 82. From the I. F, am
pliñer these frequencies pass to the detector and
audio stage indicated diagrammatically and iden
tified by the reference character 83, and beat to
gether at the detector to form a beat note equal to
the difference between the two intermediate fre
quencies. It will be found, upon analysis, that
the frequency transmitted to the band-pass filter
will always be equal to 1020 cycles, i. e., the differ
ence between the frequencies of the two crystal
oscillators, regardless of the carrier frequency of
the transmitter, and accordingly the entire band
will be successfully passed by the band-pass filter
39. By thus insuring that the entire useful fre
quency band transmitted to the band-pass filter
39 will be within the range of the filter, and by
As heretofore mentioned, various errors may be
very sharply tuning the band-pass filter, the
introduced into the continuous records or traces
effects of static may be very substantially min
obtained with the direction finder system illus
imized or entire eliminated, and accordingly more
trated in Fig. l, due to the presence of static con
ditions, and in order to eliminate or minimize the 35 accurate bearing traces will be obtained on the
chart 48 ofFig.l.
‘
1
‘ '
effects of static the band-pass filter 39 is inter
In the direction finder system illustrated in
posed in the output circuit of the radio receiver,
Fig. 1, a manual switch 32 is shown for control
as shown in Fig. 1, which band-pass filter is very
ling the antenna connections so
to 'produce
sharply tuned so as to pass only a very narrow
band of frequencies. As is the usual practice in 40 a cardioid pattern when desired, in order to re
move the ambiguity from the true bearing rec
radio direction finders used today for determining
the position of airplanes on commercial airline
ords obtained on the chart 48, but it has been
found desirable to provide automatic means for
systems, the receiver 29 of the direction finder
controlling the antenna connections in order to `
system shownl in Fig. 1 is capable of receiving only
stations transmitting-a carrier frequency having a 45 produce the cardioid, and in Fig. 3 there is shown
means for automatically exercising a proper con
fixed relation to the fixed frequency of oscillator
trol of the antenna connections.
Y
31, and the band-pass ñlter is tuned to pass only
« In Fig. 3 the coupling means for the antennas
the beat note frequency resulting from the re
is illustrated as an electromagnetic relay or
ceived carrier and the frequency of the oscil
lator 31;
'
It has been found, however, that the frequency
of the transmitting station, although intended to
be a fixed value, will vary over such a wide range
that the beat note frequency supplied to the band
pass filter may vary as much as '750 cycles. Varia
switch having an operating winding 85 and a
movable magnetizable core or armature 85 ar
ranged to operate a plurality of contacts 33, 34,
and 63, which respectively correspond to the sim
ilarly numbered knife blades of the manual
switch 32 in Fig. 1. This electromagnetic relay,
which may be termed the cardioid relay, is like
Wise provided with the stationary contacts 39
and 3l which correspond to the similarly num
beredcontacts of the switch 32, and which are
culty the arrangement illustrated in Fig. 2 is pro
60 normally engaged by the movable contacts 33 and
vided.
34 for connecting the loop antenna H in paral
In Fig_ 2 the receiver 29, which receives the car
lel relation with the loop antenna lil through
rier frequency from the antenna arrangement
K the conductors 35, 26, 21, and 2B, as described
through the conductors 21 and 28, is shown some
what diagrammatically as including a converter
in connection with Fig. 1.
When the winding B5 of the cardioid relay is
tube 16 having a plurality of control electrodes 11,
energized, the circuit of the loop antenna Il is
18, and 19, the control electrode 19 being supplied
with the carrier frequency through the radio fre
interrupted at the contacts 33 and 34 and the
quency stage (not shown) of the receiver 29, and '
artificial antenna 54a is connected in parallel
the control electrodes 11 and 18 being respectively
with the loop antenna iii through an upper pair
connected, as shown, to separate crystal oscil 70 of contacts engaged by the movable contacts 33
and 34. At the same time, the movable contact
lators 80 and 3| which correspond to the oscil
63 of the cardioid relay closes a circuit similar
lator means 31‘of Fig. 1. The two crystal oscil
to that hereinbefore described in connection with
lators 8i! and 8| are arranged to produce fixed
Fig.. 1, whereby the vertical antenna ill isvcon
frequencies, there being a frequency difference loe
tween the'two oscillators equal to the frequency 75 nected through the conductor 62, the contact 63,
tions of this magnitude would of course mean
that certain of these frequencies would not pass
the filter S9, and in order to overcome this diffi
2,406,406
9
10
the stationary contact 64 and a conductor @aand
condenser II8 to the ground connection |22.
by way of the phase shifter Së- to the receiver 23.
It will thus be apparent that the cardioid relay,
when alternately energized and deenergized, ef
The energizing circuit for the relay iël2 estab
lished by closure of the contacts Ill' may be
traced 4from one side of the condenser IES,
through the conductor |22, the contacts Ill, the
fects the Same circuit connections as are effect
ed by throwing the manual 'switch 32 from one
of its positions to the other.
In order properly to control the operation of
conductor |23, the winding |2I of the relay |82,
conductor |25, the contacts QQ 'on relay 88, which
as previously described has been operated by clo
the cardioid relay, a rotatable lSwitch 3l is pre-_
vided, which is preferably associated with the 10
rotating post i3 of the antenna arrangement,
and arranged to complete a circuit once during
each revolution ci
post i3. Closure of the
switch El completes an energizing circuit for a
control relay 83 having an energizing winding 15
89, two pairs of normally open contacts ëü and
löta, respectively, and a pair cf ,'oorrrially` closed
contacts 9i.
circuit may be traced from
sure of the switch means 8l, and by way of the
conductor 29 and the ground _connections ‘|253
and I 2d tothe other side ‘of the condenser I I8.
Following> initial energization thereof, the 1' -
lay m2 is held in its operated position by a hold
ing circuit which maybe traced from the posi
tive termina1 92, through the conductors 93, Sá,
95, and |36, contacts ISSUL, conductor Kila, con
tacts |38a, conductor |3911, the winding |2IY of
the relay Iû2, conductor í2fì, contacts 39, and by
the positive side of a »suitable source of energy
way of the conductor Sil to the ground connec
indicated by the reference numeral Si?, through
the conductors
Q5, Q6, and e?, the switch
8l, the conductor
the relay winding £9, and
tion Iilt‘.
by lway of a conductor to to the `negative side
of the source of energy or a ground connection,
indicated by the reference numeral lili),
Associated with the control relay $3, and the
rotating switch means Eil are a plurality of ad
ditionalcontrol relays 252i, to2, and
the en
ergizing winding Iilél of the relay ¿53 being c 'i
nected in the output circuit of a full
re
-
`
Closure of the contacts |25 of the‘relay |02
establishes an energizing, circuitV for the winding
l|29 of the relay lill; which circuit may be traced
from the positive terminal 92 through conductors
93, 94, and |26, contactsjlZö, conductors |21 ‘and
|28, and by way of the winding I 29 tothe ground
connection |30. The relay IUI is thus operated
and the energizing circuits thus far traced con
tinue to exist until the circuit is broken at the
contacts of the switch means 8'l,'at which time
the relay 8S is deenergized, allowing contacts ISSa
pair
ñer £25
of cathodes
having a ill?,
pair and
of plates
a pairorofanodes
controlloll,
ele
and Sû to open and contacts 9| to close.A Opening
0f the contacts |36a‘ interrupts, the previously
traced holding circuit for the relay |52, and the
ments or grids H98. As shown, the grids or ccn
trol elements lûâ are adapted to be energized
from a secondary winding log of a suitable cou
‘ consequent opening of 'the contacts |25 on the
pling transformer, the primary winding ¿Iii of
relay |ü2 in‘ turn interrupts the energizing circuit
for the relay ItìI. Simultaneously, however, clo
which is connected to a suitable antenna for eu
ergization by the carrier of the transmitting sta
tion to which the radio direction under systea-„i
preferably
of Fig. lisconnected
tuned. YThe
to _the
primary
systemwinding
of
lliï;
at a
sure of the contacts 9| on'the relay 88 provides a
self-holding circuit for the relay lill, which may
be traced from the positive terminal 92 through
the conductors 93," 94, S5, and |36,A contacts 9|,
conductor |37, contacts I S2, ’conductors |38 and
or`
point
it may,
between
if desired,
the filter
be connected
E@ and theto rectifier
an entirely
separate antenna and receiver. En order to pro
|28, and by way of the winding 'I 29 tothe ground
connection |36. This transfer of the holding cir
cuit for the relay EOI is accomplished without
vide a constantnegative bias on the control ele
ments iílß or the rectifier tube itâ, the midpoint
aîîecting the operated condition'of the relay, be
`of
ground
the secondary
as shown and
winding
the cathodes
lol?, is connected
iol are con
nected to a suitable potentiometer represented as
cause this relay is of the slow-to-release type as
indicated 'diagrammatically in'Fig. 3 by the usual
copper'slug`
COmIJYîSing the resistanceelements l il connect 50
|39.`
,
'
'
'
’
Operationuof the` relay IDI of course causes
ed across the direct current source of energy rep
closure of the relay contacts I 3|, thereby coin
resented bythe positive terminal 92 and the
pleting an energizing circuit for the cardioid re
ground connection I l2.
lay which may be traced from the positive source
Whenever carrier energy is being supplied to
of energy`92 through the conductors 93, 9&3, 95, 96,
the rectifier tube throughthetransformer, cur 55 and I33,_the`contacts I3‘I, the conductor |34, and
rent will flow through the winding `lofi of the
by way of the operating winding 650i the cardioid
control relay Illâ through a circuit which er;
relay to the ground connectionf'lää. Upon eher
tends from the 'positive `source of energy 22
gization of this operating winding 85, the arma
through theconductors 93 and IIS, the Winding
ture 8E `V>of the cardioid'relay is operated to its
|04, the conductor ll-fl, the anodes lot, the cath 60 uppermost ‘posi'tion‘so' 'asfto >connect the'vertical
odes IIl'I, and by way of the conductor H5 to the
antenna kin circuit th'rou'gh‘the contacts B3 and
movable contact H3 on the potentiometer iii.
64, as heretofore described, During the’ensuing
In describing the operation of the automatic
revolution- of the' antenna; means a cardioid pat
control means it ywill be assumed that power has
tern is produced on ~the chart 48 of Fig. l. j
been applied to the operating mote-rs of the an
65
tenna arrangement, thereby operating ‘the Iswitcl'l
means 8l, and that a carrier is being supplied to
the 'winding H8 of the transformer ‘so as to ef
This connection exists until the contacts :of the
switch means 8T, are againfclosed after one com
plete revolution rof the‘rotatable’post` I3, where
upon the relay` 8B will again be `energized through
fect operation of the relay lili. Upon closure of
the previously traced energizingcircuit causing
the contacts H'i' of the relay I?ë, a condenser 70 the contactsol to open and interrupt the pre
||8 will effect energization of the relay 532, the
viously traced self-holding` circuit‘for `the relay
condenser having previously been charged
|0|. The capacity of the condenser H8 and the
through a` circuit which may be traced from the
ohmic resistance of the resistor I I9 areso chosen
positive terminal 82, through the conductors 93
and H3, theV resistor H9, conductor |22, and the
that during successive closures Aof the contacts
1,5
of the switch 'means 8_1“ there will elapse an in
afìoefioe
.
11
suiiîcient time to permit the accumulation on the
condenser I I8 of a charge of suiiicient magnitude
to eiiect operation of the relay |02." Therefore,
even though the initial energizing circuit for the
relay |02 is completed through the contacts 90
of the relay 98 when this relay is again operated,
12
_
mined relation to the carrier frequency received
from the two antennas, and accordingly beats
therewith to generate identical intermediate fre
quencies. The coupling transformer |46 to which
the intermediate frequency from the vertical an
tenna is supplied, is connected as shown through
the conductors |59, the phase shifting device 66
the relay |92 will not operate, and accordingly the
and the conductors |5| to the conductors |52
relay |9I opens, thereby interrupting at contacts
which lead from the coupling transformer |42 of
|3| the energizing circuit for the cardioid relay.
the vertical antenna to the intermediate fre
Thus the cardioid relay returns to the position 10 quency
amplifier and detector |49.
'
shown in the drawings, and the antenna circuits
Thus, the adjustment of the phase shifter 66,
are connected with the parallel opposed loops in
for effecting the desired phase shift in the energy
circuitV as heretofore described. Due to the fact
received from the vertical antenne, I4 with re
that> theecapacity and >resistance values of the
spect to the energy received through the loop
15
condenser H9 and the resistor ||9, respectively,
antenna IIì, is a function of the intermediate fre
are‘chosen as indicated above, the operating cycle
quency only and will accomplish the proper phase
cannot be nrepeated unti1 sufficient time has
shifting regardless of the frequency to which the
elapsed-to permit the condenser IIB to attain a
two antennas are tuned. From the I. F. ampli
new charge of sufficient magnitudeV to operate the
ñer and detector |43 the combined energy from
20
relay |92.
’
` "
the two antennas is supplied through suitable
However, after the desired record has been
conductors to the rectifier and the recording
made from which a true bearing may be located
and the system has been allowed to rest for a
relatively short time, operating voltage will build
means of Fig. 1 so as to trace on the chart 48
an accurate cardioid pattern of the combined
energy received.
`
upV across the condenser ||8 and the above de
In Fig. 5 there is shown a still further modified
scribed cycle of ' operations may be repeated.
circuit arrangement which may be employed
Such an operating voltage will not build up across
when it is desirable to prevent overloading the
the condenser |I8 until the system is allowed to
radio direction finder system shown in Fig. 1
reist because of the'fact that the’ condenser is dis
without interfering with .the accuracy of the var
charged each time the contacts 99 of the relay 88 30 iations of signal intensity received as a function
close, the discharge howevef being insuñicient to
of the position of the loop antennas.> It will, of
effect operation of the relay |92. In the pre
course, be clear that, if the usual automatic vol
ferred arrangement, control of the automatic
ume control is employed on the receiver 2'9Iof
cardioid control means illustrated in Fig. 3 may
be accomplished by providing a manually oper 35 Fig. 1, this control will tend to maintain con
ated control button or switch which serves simul'-~
taneously to connect the source of energy to the
circuit of Fig. 3 and to the operating motors I5
stant the output of the receiver and thus will
destroy the sharpness of the nulls used to deterL
mi-ne the true bearing ofV the transmitter. In
Fig. 5, however, an automatic volume control ar
and 50 of the radio >direction finder system shown
in Fig. 1, and it will be observed that when the 40 rangement is shown which is not detrimental to
the accuracy of the direction finder: AS illus
energy source is thus connected, the above cycle
trated in Fig. 5, the loop antenna I9 is connected Y
of operations will automatically be carried out
to a radio receiver which correspondsto the re
whenever a suitable carrier is‘applied to the pri
ceiver 29 of Fig. 1 and is shown as including
mary winding' | l0.’
'
anV R. F. stage, a first detector, and two I. F.
In Fig. 4 a somewhat modiiied arrangement of
amplifiers having the control elements of each
the circuits is shown which may be employed in
tube connected together in the conventional man
the radio direction finder system of Fig. l in order
ner through suitable resistors |53, |54, |55, and
to insure that the radio frequency energy received
|56. The output from the receiver 29 may vbe
in the loop antenna I0 and the vertical antenna
connected through a suitable rectifier correspond
I4, when these two antennas are connected to
ing to the rectifier 49 of Fig. 1 to recording means
gether for the production vof a cardioid pattern,
for producing a trace of the signal intensity re
be' shifted to the proper phase relation for pro
ceived by the antenna I9.
,
duction of a cardioid pattern at al1 times, even
The
vertical
antenna
I4
in
this
arrangement,
though the tuning of the antennas be variable so
however, is connected to a separate receiver in- Y
as to receive the carrier frequencies of transmit
dicated diagrammatically and identified by the
ters operating on different radio frequencies. In
reference numeral |51, which may be entirely
the circuit shown in Fig. 4, the radio receiver 29
conventional and which includes a detector |58
is represented diagrammatically as including a
having a suitable resistance |59 connected in its
radio frequency stage having a tuning trans
former |40 and a converter tube I4| connected 60 output circuit. The rectified output of thevde
tector |58 is, of course, a function of the signal
by a converter transformer |42 to the interme
intensity received on the vertical antenna and
diate amplifier and detector indicated diagramf
this rectiñed output is impressed by meansof
matically by the reference numeral |43. The ver
the conductor |69 on the gain control or grid
tical antenna I4, instead of being connected di~
rectly to the phase shifter 56 of Fig. 1, is con 65 circuits of the various elements of the directional
nected to a receiving means comprising a radio
frequency stage identical with the radio fre
quency stage of the receiver 29 and comprising
a tuning transformer |44, a'converter tube |45,
anda coupling transformer |46. .
receiver 29.
.
While the output of the receiver 29 supplied
to the rectifier and recording means is a function
of the position of the loop antenna I9 and the
70 direction of the transmitter, this output will be
substantially independent of variations in the
carrier intensity due to the» automatic volume
control exercised by the> connection to-thede'
tector output of the vertical antenna receiver
frequency oscillator |49. The radio frequency
supplied by the oscillator |49 bears a predeter-l 75 |51, and accordingly‘overloading and errors .'due
The converter tubes |4I and |45 are provided
Y with control grids |41 and |48, respectively, which
control grids are' connected to a suitable radio
13
:2,406,406
to fading are minimized or prevented. It will
of course, be understood that use of the separate
receiver l5? is in addition to, rather than in place
of, the circuit connections for the vertical an
tenne, shown in Figs. 1 and 4, the receiver |51
being separately coupled to the vertical antenna
le or being energized from an entirely separate
vertical antenna if desired.
As previously described and as shown in Fig. 1,
the preferred directional antenna means oom
prises the loops I@ and H mounted on opposite
ends of the horizontally extending beam l2 which
is supported at its midpoint on the rotatable post
i3. While the detailed mechanical structure of
thebeam nI2 .forms no part of this invention, it
is important that the beam be suil‘lciently strong
and rigid to withstand any tendency of the loops
to twist relative to each other, as any such twist
ing would introduce diversity errors into the bear
ing readings.
Although the loops may be secured to the beam
i2 in any desired relation thereto, they are pref
erably supported thereon at their lower edges,
selectively operable to one of two positions to
couple one of said loop antennas and said non
directional antenna to said receiver in parallel
relation and to the other of said two positions to
couple said pair of loop antennas to said receiver
in opposed parallel relation, relay means respon
sive to rotation of said antenna means for auto
matically operating said coupling means between
said two positions, and recording means energiz
10 able in accordance with the output energy of said
receiver for producing a lasting visual record of
the signal intensities supplied to said receiver
during rotation of said antenna means with said
coupling means in either of said two positions.
15
3. A radior direction finder comprising a re
ceiver, directional antenna means including a pair
ci" loop antennas ?ixedly mounted with respect to
each other in spaced substantially coaxial rela
tion, means for rotating said antenna means at
20 a substantially constant speed about an axis sub
stantially parallel to the planes of said loops, a
non-directional antenna, coupling means selec
tively operable to one of two positions to couple
as shown, and the beam l2 may act as a horizon
one of said loop antennas and said non-direc
tal antenna. Consequently it may be desirable, 25 tional antenna to said receiver in parallel relation
in order to minimize any coupling between the
and to the other of said two positions to couple
beam and the loops, to support the loops with a
pair of loop antennas to said receiv r in
slight inclination from a true right angular ver
opposed parallel relation, and relay means con
tical relation to ythe beam, although maintain
trolled by rotation of said antenna means for
ing, of course, the substantially coaxial relation 30 initially operating said coupling means to said
of the loops. The respective dimensions of the
one position and for thereafter operating said
loops l@ and Il and the spacing therebetween of
coupling means to said other position upon com
course depends to a large extent upon the fre
pletion of a predetermined rotation of said an
quencies employed, the spacing of the loops being
tenna means.
less than one-half wave length, and the entire 35
e. A radio direction ñnder comprising a re
antenna structure, as heretofore stated, is ro
pair
c
’
er,
of directional
loop antennas
antenna
fixedlymeans
mounted
including
with re
tated at a constant speed which may preferably
be on the order of 15 R. P. M.
spect to each other in spaced substantially co
While particular embodiments of the invention
axial relation, means for rotating said antenna
have been shown, it will, of course, be under 40 means at e, substantially constant speed about an
stood that the invention is not limited thereto,
axis substantially parallel to the planes of said
since modiñcations may be made, and it is there
loops, a non-directional antenna, coupling means
fore contemplated by the appended claims to
selectively operable to one of two positions to
cover any such modifications as fall within the
couple one of said loop antennas and said non
45 directional antenna to said receiver in parallel
true spirit and scope of the invention.
Having thus described our invention, what we
relation and to the other of said two positions to
claim and desire -to secure by Letters Patent is:
couple said pair oi’ loop antennas to said receiver
1. A radio direction ñnder comprising a re
in opposed parallel relation, recording means en
'crgizable in accordance with the output energy
ceiver, directional antenna means including a
pair of loop antennas iixedly mounted with re 50 of said receiver for producing a lasting visual
spect to each other in spaced substantially oo
record of the signal intensities supplied to said
receiver during rotation of said antenna means
axial relation, means for rotating said antenna
means at a substantially constant speed about
with said coupling means in either of ,said two
an axis substantially parallel to the planes of said
positions, and relay means controlled by rotation
of said antenna means for initially operating said
loops, a non-directional antenna, coupling means
coupling means to said one position to produce
selectively operable to one of two positions to
a cardioid pattern on said recording meansy and
couple one of said loop antennas and said non
for operating said coupling means to said other
directional antenna to said receiver in parallel
position after completion of said oardioid pattern
relation and to the other of said two positions
to couple said pair of loop antennas to said re 60 to record the signal intensity supplied to said
receiver during subsequent rotations of said op
ceiver in opposed parallel relation, and recording
posed loops.
means energizable in accordance with the output
5. In a radio direction ñnder having directional
energy of said receiver for producing a lasting
antenna means including a plurality of antennas
visual record of the signal intensities supplied to
said receiver during rotation of said antenna 65 adapted to be selectively coupled together in pre
means with said coupling means in either of said
determined dil'lîerent circuit relations, and a ro
tating part the compass position of which is re
rlected in the signal intensity output of said an
2. A radio direction finder comprising a re
tenrla means, the combination of coupling means
ceiver, directional antenna means including a
pair of loop antennas ñxedly mounted with re 70 operable between two positions to vary the said
circuit relations of said antennas, a source of
spect to each other in spaced substantially co
energ‘ , means connected to said source for stor
axial relation7 means for rotating said antenna
ing a charge of energy during idle periods of said
means at a substantially constant speed about an
`axis substantially parallel to the planes of said
direction ñnder, means jointly responsive to rota
loops, a non-directional antenna, coupling means 75 tion of said antenna part and to a carrier received
two positions.
2,406,406
'l5
by said antenna means for discharging said stored
16
ceiver, directional antenna means coupled to said`
receiver and having a rotatable part the com
energy to operate said coupling means to one of
pass position of which is reflected in the signal
said positions, means effective upon completion
intensity received from said antenna means, re
of a predetermined rotation of said part for op
erating said coupling means to the other of said U1 cording means including a pair of relatively
movable parts respectively comprising a record~
positions, and means for preventing recharging
ing surface and a co-operating tracing element,
ci’ said energy storing means during further rota
means for rotating said rotatable-part of said an
tion of said antenna part.
6. A radio direction finder comprising a re
tenna means at a constant speed, means for mov
of loop antennas fixedly mounted with respect to
each other in spaced apart relation, means for
rotating said antenna meansat a substantially
constant speed abo-utV a substantially vertical
medial axis, a non-directional antenna, coupling
means selectively operable to one of two positions
to couple one of said loop antennas and said non
directional antenna to said receiver in parallel
relation and to the other of said two positions to
couple said pair of loop antennas to said receiver
in opposed parallel relation, and recording means
energizable in accordance with the output energy
synchronism with said antenna part, means for
moving the other of said parts of said recording
means in accordance with the output of said
ceiver, directional antenna means including a pair 10 ing one of said parts of said recording means in
of said receiver for producing a lasting visual
receiver to form on said recording surface a con
tinuous record of the signal intensity received
from said antenna means, means controlled by
the rotation of said rotatable antenna part for
automatically orienting said continuous record
with respect to the compass position of said an
tenna part, and means for comparing said con
tinuous record with a standard record to produce
an evaluation of the compass >bearing quality.
10. A radio ldirection ñnder comprising a re
ceiver, directional antenna means coupled to said
receiver during rotation of said antenna means 25 receiver and- having a rotatable part the com
pass position of which is reflected in the signal
with said coupling means in either of said two
intensity of ’said antenna means, recording means
positions.
.
including a pair of relatively movable parts re
’7. A radio direction finder comprising a re
spectively comprising a recording surface and a
ceiver, directional antenna means including a
pair 0I" loop antennas iixedly mounted with re 30 co-operating tracing element, means for rotating
said rotatable part of said antenna means at a
spect to each other in spaced apart relation,
record of the signal intensities supplied to said
means for rotating said antenna means at a sub
constant speed, means for rotating one of s-aid
parts of said recording means in synchronism
stantially constant speed about a substantially
with said antenna part, means controlled by the
vertical medial axis, a non-directional antenna,
coupling means selectively operable to one of two 35 rotation ofV said rotatable antenna part for auto
m-atically recording on said surface a reference
positions to couple one of said loop antennas and
position or“ said antenna part, means for moving
said non-directional antenna to said .receiver in
the other of said parts of ~s_aid recording means
parallel relation and to the other of said two posi
in accordance with the output of said receiver
tions to couple said pair of loop antennas to said
receiver in opposed parallel relation, recording 40 to form~ on said recording surface during each
revolution of said one part and said antenna part
means energizable in accordance with the output
a continuous record of the signal intensity re
energy of said receiver for producing a lasting
ceived from said antenna means, the continuous
visual record of the signal intensities supplied to
records formed during succes-sive revolutions be
said receiver during rotation of said antenna
means with said coupling means in either of said 45 ing superimposed on said'recording surface to
provide a resultant average of said signal inten
two positions, and means for comparing with a
sity, and comparative means comprising a trans
standard bearing record the continuous visual
parent element having a standard bearing trace
record produced during said opposed parallel
thereon for determining by comparison with
connection of said loops to evaluate by inspection
the co-rnpass bearing quality of said continuous 50. each of said records the quality of the compass
bearing indicated thereby.
record.
11. The method of determining the bearing
8. A radio direction finder comprising a re
quality characteristics of portions of a continu
ceiver, directional antenna means coupled to said
ously recorded trace of the signal intensity re
receiver and having a rotatable part the com
pass position of which is reiiected in the signal 55 ceivedY by a radio direction iinder receiver, which
comprises preparing on a transparent medium a
intensity received fro-m said antenna means, re
cording means including a pair or relatively
movable parts respectively comprising a record
standard bearing trace corresponding to a true
bearing trace for the said receiver, superimposing
said transparent medium on the continuous rec
ing surface and a coi-operating tracing element,
means for rotating said rotatable part of said 60 ord of said signal intensity, and causing portions
vof said standard bearing trace to coincide with
antenna means at a constant speed, means for
portions of said signal intensity trace visually toY
moving one of said parts of said recording means
establish the character of variations from said
in synchronism with said antenna part, means
standard’bearing trace in other por-tions of said
for periodically recording on said surface a ref
erence position of said antenna part, means for 65 signal intensity trace.
l2. In a radio direction finder having direc
moving the other of said parts of said recording
tional antenna means including a plurality of
means in accor-dance with `the output of said re
antennas adapted to be selectively coupled to
ceiver- to form on said recording surface a con
gether in predetermined diiïerent circuit rela
tinuous record of the signal intensity received
from said antenna means, and means for deter 70 tions and a rotating part the compass position
of which is renected in the signal intensity output
mining from said continuous record of signal in
of said antenna means, the combination of cou
tensity the behavior of the radio wave propagat
pling means operable between two positions to
ing medium during the time of operation of said
vary the said circuit relations of said antennas,
radio direction finder,
9. A radio direction ñnder comprising a re 75 means for operating 'said coupling means, relay
2,406,406
17
means for selectively energizing said operating
means to operate said coupling means between
said two positions, and interlock means for ren
dering said relay means effective to energize said
operating means only when a carrier is being
received by said antenna means.
13. In a radio direction ñnder having direc
tional antenna means including a plurality of
18
one 0f said parts in synchronism with the rota
tion of said antenna means, and means for mov
ing the other of said parts in accordance with
the output of said receiver means to form on said
recording surface a continuous record of the
signal intensity received from said spaced loops.
16. A radio direction finder responsive to fre
quencies in the range wherein bearing deter
minations are affected by the characteristics of
antennas adapted to be selectively coupled to
gether in predetermined different circuit rela
the ionosphere, comprising directional antenna
tions and a constant speed rotating part the com
means including a pair of loops ñxedly mounted
pass position of which is reiiected in the signal
with respect to each other in spaced substantially
intensity output of said antenna means, the com
coaxial relation, means for rotating said antenna
bination of coupling means operable between two
means at a substantially constant speed about
positions to Vary the said circuit relations of said 15 substantially the vertical axis of symmetry of
antennas, relay means controlled by rotation of
said spaced loops, receiver means adapted to pro
said antenna part for selectively operating said
duce in the output circuit thereof a signal inten
coupling means between said two positions, and
sity continuously proportional to the signal in
interlock means for rendering said relay means
tensity supplied to the input circuit thereof,
effective to operate said coupling means only 20 means coupling said receiver means to said an
when a carrier is being received by said antenna
tenna means whereby the compass position of
means.
said loops is reflected in the signal intensity sup
14. In a radio direction finder having direc
plied to said receiver means, recording means
tional antenna means including a plurality of
including a pair of relatively movable parts re
antennas adapted to be selectively coupled to
spectively comprising a recording surface and a
gether in predetermined different circuit rela
co-operating tracing element, means for moving
tions and a constant speed rotating part the
one of said parts in synchronism with the rota
compass position of which is reñected in the
tion of said antenna means, means for moving
signal intensity output of said antenna means,
the other of said parts in accordance with the
the combination of coupling means operable be 30 output of said receiver means to form on said
tween two positions to vary the said circuit rela
recording surface a continuous record of the
tions of said antennas, relay means controlled
signal intensity received from said spaced loops,
by rotation of said antenna part for selectively
and means for periodically recording on said
operating said coupling means between said two
surface a reference position of said loops relative
positions, said relay means including interlock 35 to said continuous record.
means responsive to a carrier received by said
17. A radio direction ñnder responsive to fre
antenna means for preventing operation of said
quencies in the range wherein bearing deter
coupling means when a carrier is not being re
minations are affected by the characteristics of
ceived by said antenna means.
the ionosphere, comprising directional antenna
l5. A radio direction finder responsive to fre 40 means including a pair of loops fiXedly mounted
quencies in the range wherein bearing deter
with respect to each other in spaced substantially
minations are affected by the characteristics of
coaxial relation, means for rotating said antenna
the ionosphere, comprising directional antenna
means at a substantially constant speed about
means including a pair of loops ñxedly mounted
substantially the vertical axis of symmetry of
with respect to each other in spaced substan
said spaced loops, receiver means adapted to pro
tially coaxial relation, means for rotating said
duce in the output circuit thereof a signal inten
antenna means at a substantially constant speed
sity continuously proportional to the signal in
about substantially the vertical axis of symmetry
tensity supplied to the input circuit thereof,
of said spaced loops, receiver means adapted to
means coupling said receiver means to said an
produce in the output circuit thereof a signal 50 tenna means whereby the instantaneous compass
intensity continuously proportional to the signal
positions of said loops during rotation are re
intensity supplied to the input circuit thereof,
flected in the instantaneous signal intensities
means coupling said receiver means to said an
supplied to said receiver, and recording means
tenna means whereby the compass position of
energizable in accordance with the output of said
said loops is reflected in the signal intensity sup 55 receiver means for producing a lasting record
plied to said receiver means, recording means
trace proportional at all points to the signal
including a pair of relatively movable parts re
intensities received from said spaced loops.
spectively comprising a recording surface and a
PETER C. SANDRETTO.
co-operating tracing element, means for moving
ELMER P. BUCKTHAL.
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