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Патент USA US2124544

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July 26, 1938-
Original Filed Oct‘. 23, 1,935
‘ *
2 Sheets-Sheet l
F1 5 - l_v
omjvuz. 4mg,
Jqly 26, 1938.
' 2,124,544
Original Filed Oct. 23, 1935
2 Sheets-Sheet 2
Local OJc/l/a‘for
AT+ Lp
Patented July 2c, 1938
. ‘2,124,544v
VISUAL mmcarme namo nmsorrou '
Howard .N. Collier, United States
avy, s...
- Pedro,andGcrhardB.Fishe:-,_ll
JApplicationOctober 2:, 1935, Serial ‘m. (6.314
9 Claims.
(0!. 250-11)
(Granted under the act of Bach
amended April 30,1928; 370 0- G. 75'!) ' y
This invention relates to radio direction ?nd- ,
-:~=~: ‘toemploytheusuaimeans
ing systems, more particularly to such systems of balancing heretofore used in radio direction
whereinreceptionof intelligence is accomplished
simultaneously with the determination of the
,5 direction of the transmitting station.
A speci?c object of this invention is to provide
an essentially automatic system for use on navi
gable craft whereby the navigator is enabled to
the antenna,’ and not the loop, the loop Signal 5
merely providing a superimposed signal neces
sary ior determining direction. For this reason
greater distance ranges can be obtainedthan
with the ordinary direction ?nder.
An additional important feature is that due to 10
keep closely to a predetermined course. .It is
10 further possible to ascertain the exact position
of a vessel by taking bearings 01 one or- more 'its inherent modulating system,'either cw or
radio transmitting stations by either rotating a modulated continuous wave signals can be re
loop antenna or turning‘ ,the vessel or aircraft ceived at all times without any switching or ad
provided with a ?xed directional antenna.
When applied to aircraft,lthe system aids in
locating landing ?elds and is of special utility
when the navigator is ?ying over unfamiliar
territory. The invention‘ is manifestly of par
ticular utility under conditions 01' poor visi
20 bility.
A further object of this invention is to pro
vide a radio direction ?nder that requires little
or no manipulation by the operator. ,
A further object of this invention is to pro
25 vide a radiodirection ?nder with a visual indi
cator which permits the taking oi! bearings with
more positive accuracy and with more‘ speed,
. than by means of aural methods.
Avstiil further object of the invention is to
30 provide .a system having a directional loop an
tenna in which by locking the loop in a zero posi-'
\ - tion, the instrument can function as a visual
homing indicator.
Another object of the invention is to provide
35 a direction ?nder in which the equipment per
The,device can beutilined by aircraft for the 15
approximate determination of drift .due to wind
under conditions when the surface 01’ the earth
is totally obscured.
This equipment enables the operator to ascer
tainthepresenceot“night"orsimilare?'ectboth 20
intermittently during periods when such e?ect
is generally existent, brief periods when the
e?'ect is absent, under which conditions bear
ingscanbetakenwhichcanbede?nitelyknown 25
tobei’reeoi'the abnormalerrorcausedbysuch
This direction ?nder does not makeuse oia
um signal but utilizes the full strength
oithesignalreceivedfromanopenantennaat 30
all times. Operating on the maximum signal
strength obtained from an open antenna'con
it permits the full use
ofa?snalproperlytnnedtoitsmaximumand 35‘
mits continuous listening-in to the transmitting thus permits the taking»! radio'bearlngs even
station even when taking bearings. The ordi
through'heavy. interference n'om Ions
nary radiodirection ?nder operates on a mini
mum or null. signal which usually results in
40 blanking out reception'of telegraph or speech
~ during the actual taking of a hearing.
The equipment requires no sense indicator, nor
any procedureior determining the sense of _a
bearing, other than to note which direction of
' 45 rotation of the loop is required to move the ‘visual
indicator to the right or left.
} man-made interference and'static. -
'Ihis direction ?nder system permits the 81-.‘40
locations, oi’ radio direction ?nder
en by one direction ?nder, and likewise permits
the simultaneous on at one location or '
radiodh'ection?nderbearlngstaken bytwoor 45
more distantly located direction ?nders.
Inadvertent taking of a bearing 180 degrees ' Another-object of this invention is to provide
but will cause no delay nor- error, as reverse ',a direction ?nding system of the character de
bearings are always exactly 180 degrees in error.
Whereas ordinary direction ?nder receivers
- require manipulation 01’ a balancing condenser
scribed in which the number of pieces of appa
'ratusrequiredand theirweightmaybesmallm
so as to reduce the weight required to be car.
during the taking of bearings, this equipment ' ried byanairplane.
requires no balancing condenser. This device
possesses visual and aural means for indicating ablee?ects oitimingordetuningthe open an‘
55 perfect balance in the loop circuit at any time,
tennainrelaiiontotheloop antennaareen?re- 55
1y eliminated with the result that diet
of the
radio frequency circuits will not a?ect the radio
‘ By using a, modulated carrier and a special
?ltered receiver and loop circuit, the direction
?nder can be kept immune from interference
" except when such transmission uses exactly they
same carrier radio frequency and audio ire-V
Other objects of the invention will be apparent
from the following‘ speci?cations when read in
with - the accompanying
15 preferred embodiment of the device.
Fig. 2 shows the magnitudes of the various
circuit voltages at di?erent cycles of operation.
Fig. 3 shows variations in the wiring of the
direction ?nder.
2 in such a way that the radio frequency currents .
of Li and L2 neutralize each other. The cathode
voltage of tubes Ti and T2 is varied, by a local
A. 0. generator in such a way that while one tube
operates on the straight portion of its grid volt
age-plate current characteristic curve,vthe other
tube operates on the curved portion, with the
result that the ampli?ed R. F. current in Ll will
add to the currents received by A at one instant, 10
and subtract therefrom at the next instant. This
local generator also has a tendency to modulate
any CW signal received by the loop. If the loop
Figure l is a schematic wiring diagram of a
the loop is ampli?ed and coupled to the receiver .
. _
Fig. 4 shows a variation in the‘ wiring‘ whereby
the voltage necessary for modulating the loop
is in such a position that no‘radio frequency cur
rent will be received by it, the tubes Ti and T2, 15
and coils Li and L2 will not transfer any radio
frequency energy to L3 or to Lil. Incorporated
in the cathode circuit of tubes Ti and T2 is a
transformer AT. .This transformer is connected
in such a way that the output voltage is combined 20
with the voltage produced by oscillator T3 and
then impressed upon the cathodes of Ti and T2.
The bias of the potential E on the cathodes
of Ti and T2 should be selected so that these
tubes operate on a curved portion of their grid 25
25 antenna, A represents an open non-directive an
voltage-plate current characteristic curve, so that
tenna. A radio signal from a distant station is
- received by antenna A and ampli?ed by means _ during V2 cycle, at frequency V produced by the
local oscillator, increased plate current will flow
of tube Tél. The plate circuit of tube T55 is cou
in Ti and very little plate current will flow in
pled to the input of radio receiver 2, which con
. tube T2. During the next 1/2 cycle these condi 30
730 ?cation, a detector and audio ampli?er. The tions will be reversed. RE is balanced in such a
resulting signal is received in the headphones 5. way that these changesin plate current will cause
The signal from this open non-directive antenna ‘ no ?uctuation in the indicator 3, and it will re- '
main at zero reading.
- .
will never change in strength due to any varia
Now, when radio frequency energy is received
35 tion of the directional position of the vessel rela
circuit is derived from a distant transmitter along
with the R. F. signal.
‘ Referring to Fig. 1, 14» represents the loop
by antenna A, (but not by the loop), after being
detected and amplified‘ in receiver 2 and the
output voltage thereof impressed with the oscil
lator voltage upon Ti and'T2, no ?uctuation of
40 antenna Lp is provided which may be either tuned , the indicator‘ i results. If, however, the loop 40
or untuned, the center of this directional system antenna is receiving R. F. energy at the same‘
being grounded at d’, and the leads Lot and time ‘as A does, due to the fact that only Ti or T2
can work at one time, the loop R. F. voltage is
L122, respectively, being connected to the grid cir
tive to the transmitter, and regardless of what
position the receiver is oriented.
In addition to the above described receiving
system, a loop antenna or spaced directional
cuits of tubes T8 and T2. The plate circuits of
Ti and T2 are connected to coils Li and L2 which
in turn are coupled inductively to L3 which rep-
resents the plate circuit ‘of T43 and tothe input
circuit LG of the receiver 2. L9 and L2 are
wound in such a way that they oppose each other.
50 In the plate circuit of tubes Ti and T2 is further
incorporated a balancing resistance RG and a
visual indicator l having a scale marked "Left
Zero-Right”. A local audio frequency oscillator
is provided consisting of tube T3, and an oscillat
55 ing transformer M consisting of primary and
secondary windings p and 'pi , the secondary being
center tapped. The outside terminals of pi are
connected to the cathodes of tubes Ti and T2,
respectively, and the center tap of pi is con
60 nected to the secondary of transformer AT and
thence to ground. The primary of AT is con
nected to the output of receiver 2. Current is
received by A, ampli?ed by Til, ampli?ed further,
detected and ampli?ed at audio fremiency in the
receiver 2. The signal'may be observed in the
telephone head set 5, on a shadow timing device
7 ll, in ,a ?ltered output meter 3. or by means of a
tuned reed indicator 5. Energy is also received
by means of the loop or directional antenna Lp
having a ?gure i3 characteristic. This loop an
tenna may be‘ tuned for
Perfect symmetry is obtained by grounding atlil
the loop 140 in its exact center. The outside ter
minals‘of the loop are connected to the grids of
tubes Ti and T2, so that the radio frequency in
at one instant subtracting therefrom, which in
turn -will result in causing ?uctuation of the
voltages in AT; or in other words, during 1/2 cycle
the voltage will be large, and during the next 1/2
cycle, small. This dissymmetry in turn is again
transferred back to Ti and T2, resulting in a
variation in plate current which will in turn
cause the visual indicator i to move. By turning
the loop antenna the phasing between loop and ‘
antenna currents can be materially changed, so
that with the loop antenna receiving no voltage
from the distant transmitter the visual indicator 55
will read zero, and with the loop turned to‘ the
right the indicator will move right, and with the
loop turned to the left the indicator will move
In some installations it is necessary to
connect a resistor R2 in series with the antenna 68
A to produce ‘the proper phasing. In general,
bad distortion effects are ordinarily incurred as
a result of combining tuned antennas with loops.
By using a buffer stage as shown any undesir
able e?'ects are eliminated.
As above set forth, a voltage component de
rived-from the output of receiver 2 is, through
transformer AT, impressed upon the center'tap of
secondary pi and thence upon the cathodes of
tubes Ti and T2. It is obvious that the com
ponent thus impressed upon said cathodes will
be at the frequency of the output of receiver 2
and also of oscillator T3, ‘from which it is de
rived, andv that it will have'the same phase on
both cathodes. However, the‘ polarity of this
‘component does not have a constant relation to
that ofthe voltage in pl but varies in accordance
with the direction of deviation‘of the plane of
onlysllghtly due to its inherent balancing charac
It is possible to connect as many visual indi
loop Lp from perpendicular to the path of the cators in parallel as necessary to make simul
5 8181181 and hence destroys the balance existing be
taneous observations at di?erent locations, of 6
tween the .outputs of tubes Ti and T2 when the ‘ bearings being taken.
,_ plane of the loop is at right angles to the signal
By, means of reslstorhRl it e possible to move
'. path, causing the indicator l- to be actuated. It the pointer of indicator i ‘from its center posi
will be noted that tubes Ti and T2 feed into re , tion and in such a way apply any corrections
ceiver 2 through‘radio frequency coupling and which might be desired.
. 10
hence the audio frequency from oscillator'l‘i is
Fig. 3 shows variations in the wiring of the di
inemciently transferred and is inconsequential rection ?nder in which it is not necessary to
in the output of reclnver 2 when the loop voltages return the output of receiver 2 to Tl, or T2. This
are balanced and no radio frequency is being put is accomplished by using an electrodynamometer.
[5 into-receiver 2.
'This simpli?es the circuit as no transfer of the
In Fig. 2 are shown juxtaposed for purpose
of comparison. the magnitudes of the various
voltages at different points in the circuit during
the different cycles of operation. When loop La:
50 is at right angles to the line from the loop to
receiver output energy to\ the loop circuit is‘ re
_ quired.
In addition to, the indicators provided in the
output circuit of receiver 2 it is possible to include
a neon tube in the same circuit to’determine the 20
the source In of the received energy, as'in the _ silent sector above a radio transmitting station.
uppermost portion of the ?gure, all voltages in
To permit aircraft to “home" despite interferi
the loop are equal and opposite‘ and there is no I once, a variation of the direction ?nder circuit
resultant e?'ect on indicator ‘i. Next below are is shown in Fig. 4. In this system, the local oscil
:5 shown the conditions when Lp is rotated to the ‘ lator necessary for modulating the loop circuit is 25
right; the voltages from the loop are still equal
eliminated, and the voltage necessary‘ for this
_ ‘and opposite, as are those from transformer AT,
modulation is derived from reception of a modu
lated continuous wave signal, in which the audio
1 but the phase relations are such that the result
ant of the two gives a small current from T2 and
i) a large current from TI, causing indicator l ‘to
' give an indication “righ ”. The lowermost part
of the ?gure depicts L2 turning to the left, with
frequency modulation is predetermined, and this
received audio frequency energy is passed through 30
‘a ?lter circuit in the direction ?nder. The audio
frequency voltage so derived is in turn applied
a resultant greater voltage on T2 than on Ti
and a greater plate current from T2, producing
out of phase to the grids of\_Tl and ‘132. Thus‘
5- the indication “left”;
As antenna A always receives a maximum sig
_ 'nal ,on'account oflits non-directional character
by means of a center-tapped transformer 180°
even if there should be set up radio interference 35
on exactly the same carrier frequency, the air
craft would still be able to "home” unless the
istics, reception of messages is possible even when
carrier frequency was continuously modulated
taking bearings.
withexactly the same audio frequency modula
Due to the perfect symmetry employed in the
circuit, no balancing condenser is required.
The direction ?nder can be checked at any time
for proper operation by observing that when vis
ual indicator l reads “zero”, the modulation ire
5 quency of the local oscillator should not be heard
in the'phones nor be observed in any of the vis
ual indicators shown in Fig. 1. If these two con
ditions do not check, there. exist two possibilities:
(1) a breakdown of electrical circuits in the di—
0 rection ?nder, or>(2) the existence of “night”
‘orsimllare?'ect. Duringactualtestsitwas
observed that during the presence of night effect _
the indicator could be ‘kept‘at aero whereas the
modulating frequency would actuate any of the
indicators shown in the output of receiver 2; or
‘the e?ect of the modulating frequency could be
While this invention is especially adaptable
‘to aircraft it is evident that it also can be used
forpther purposes.’
It is obvious from the preceding description
that this invention is not con?ned speci?cally 45
to the circuits asshown, but that different means
'_ may be employed for combining the signal ener
gies intercepted by the directive and non-direc
tive absorbing means, or that other changes may
be“ made which do not aifect the underlying 50
‘principles of this invention.
The invention disclosed herein may be manu
factured and used by or for the Government of
the United States without the payment of any
royalty thereon.
, -~
We claim:
,1. In ‘a direction ?nding system, a pair of
amplifying-thermionic tubes, a directional loop
kept out oi the same indicators, but the visual
.indicator Ii would continuously swing to the right
and left, indicating the presenceof night etiect. ‘ antenna grounded at its midpoint, connections
’ After some time alllindicators would again act extending from the terminals of said loop to the 60
normally simultaneously‘and so_ show that the ‘grid electrodes of said tubes forming input cir
As antenna 4 represents an essential part for
vreceiving the signal, .it is ‘this antenna which de
cuits for said tubes, output circuits including a
coil for. each of said tubes, said coils being wound
in such a way that they oppose each other, means
for causing said tubes to alternately operate, one
| serving any change in the visual indicator-on
the calibrated loop'scale, it is- possible to ap
detecting radio frequency waves,>means for im-.
disturbing in?uences had subsided, thus enabling
_ the taking'of normal bearings.
as an eihcient ampli?er operating‘on the rela
termines the range of the direction ?nder.
J By taking simultaneous readings on the radio tively straight portion of its grid voltage plate
direction ?nder‘ and magnetic compass and’ ob- ~ current characteristic cln've while the other operl
ates on the curved portion, a substantially non
proximately determine and make correction for
local electrical-interference, static and man
i made interference will a?ect this direction ?nder
directional antenna, means for amplifying and -
pressing on the input circuit of said last means ,
the radio frequency waves ampli?ed by said pair
,of tubes and the radio frequency waves derived
rrom said non-directional antenna, means for
applying a component of potential between the
cathode and the grid electrode of each tube of
said pair of tubes in
at the output fre
quency detected by said detector and means con
nected in the output circuit of said tubes and
said transiorm'er for amplifying the algebraic sum
or the waves impressed thereon and detecting the
same, means for varying the potential difference
between the grid electrode and the cathode of
each of the tubes of said pair in phase in accord
responsive to the di?erence between the value or
ance with the detected component of current de
the ~average anode current in said pair of tubes
for indicating the relative position of said loop
antenna with respect to a radio transmitting
rived from said detector, means including a de
vice having a substantially constant low fre
quency output for causing said tubes to alternate
1y operate, one as an emcient ampli?er operating 10
on the relatively straight portions of its grid
voltage plate current characteristic curve while
the other operates on the curved portion, and
means for indicating which of said pair of tubes
has the greater average output current ?owing 15
therein and for indicating the value of the diner
10 station transmitting waves received by said an
2. A direction ?nding system in accordance
with claim 1 in which a visual indicator is con
nected to be‘energized solely by the output cur
15 rents from said means for detecting radio fre
quency waves.
3. A" direction rm‘ .
system in accordance
with claim i in which an audible signal indica
tor is connected to said means for detecting radio
20 frequency waves whereby said system may be used
for the reception of intelligence simultaneousiy '
with its use-as a direction ?nder.
4. A system in'accordance with cl
1 in
which an indicator tor indicating the presence
25 of night effect is connected to be energized by
the output from saiddetector.
5. A system in accordance with claim ii in
which both visual and aural indicators are con-'
nected to be energized by the output from said
30 detector.
6. ‘In a direction ?nding system, a substan?aliy .
non-directional means for receiving a radio fre
ential current.
‘7. A system in‘ accordance with ‘claim 6 in
which an indicator for indicating the presence of
“night’{ e?ect is connectedto be energized bysaid
8. In a. direction ?nding system, a. pair of heater
type thermionic amplifying tubes having cathode,
anode and control electrodes, a; directional loop
antenna connected to the control electrodes of 25
said tubes so as to impress thereon received radio
frequency waves of the same frequency and am
plitude but of 180° phase di?erence in the two
tubes, 9. source of modulating frequency connected
to the cathodes of said tubes to vary the poten 30
tial of said cathodes with respect to ground at the
same frequency and amplitude but at 180° phase
quency wave irom a'transmitting station, a sec
ond means for receiving a radio frequency wave
erence in the two tubes, a substantially non
tector connected to the secondary winding of
W :1;
directional antenna, means for amplifying and
detecting radio frequency‘ waves,- means for si 35
Ca: C11 from the transmitting station, said second means
comprising a loop antenna having, a grounded multaneously impressing on the input circuit of
midpoint, a pair of thermionic amplifying tubes, said last means the radio frequency waves set up
means‘connecting one of the terminals of said in the output circuits of said pair of tubes and
loop to the control grid of one of said tubes, ‘ the radio frequency waves from said non-direc
40 means connecting the other of the terminals of tional antenna, means for varying in phase the 40
said loop to the control grid of the other of said potential of both of the cathodes of said pair of
tubes, a radio frequency output circuit for each tubes with respect to ground at the frequency
of said tubes, said output circuits each including derived from said detector and an indicating de
vice responsive' to the di?erence of current ?ow
the primary winding of a radio frequency trans
former, said primary windings being so wound as in the output circuits of said pair of tubes.
9. A system in accordance with claim 8 in
to oppose each other, a secondary winding coupled
to said primary windings and to an additional which an indicator for indicating the presence of
“night” e?ect is connected to be energized by
primary winding, means connecting said addi
tional primary winding to be energized under 7 the means for detecting radio frequency waves.
50 control of the radio frequency waves received by
u. coumnn.
said non-directional means, an ampli?er and de
s i
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