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Патент USA US2410122

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Oct. 29, 1946.
w. R. MERCER Erm.
2,410,122
BALANGED DETECTOR FOR ALTIMETERS
Filed June 9, 1944
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WILLIAM INVENTORS
R. MERCER
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Patented 0st. 29, 1945
ZAiMZZ
UNÍTED S'E’À’EES PÀ'Ã'ENT GFFHQE
2,410,122
BALANCE!) DETECTOR FOR ALTIMETERS
William R. Mercer, Hightstown, and Ben R.. Cole,
Princeton, N. J., assignors to Radio Corporation
of America, a corporation of Delaware
application .rune 9, i944., serial No. 539,528
8 Claims. (ci. 250-27 )
l
2
Our invention relates to balanced detectors for
altimeters or other distance measuring systems
of the frequency modulated or FM type.
in application Serial No. 445,720, ñled June 4,
1942, in the name of Royden C. Sanders, Jr., en
titled Frequency modulated altimeter or distance
indicator, there is described a balanced beat fre
quency detector comprising diodes and a tuned
line in which undesired amplitude modulation in
the following description taken in connection
FM distance measuring systems such as altim
split-line loop, and
eters.
Figure 7 is a sectional view illustrating a modi
ñed structure for the detector shown in Fig. 1. ,
with the accompanying drawing in which
Figure 1 is a sectional view of a balanced de
tector embodying the invention,
Figure 2 is a view, partly in section, taken on
the line II-II 0f Fig. l,
f
Figure 3 is a sectional view taken on the line
III-III of Fig. 1,
Figure 4 is a schematic diagram showing the
an FM altimeter or radar system is balanced out. 10 electrical circuit of the detector illustrated in
The present invention is an improvement on bal
Figs. 1, 2 and 3,
anced detectors of this type.
Figure 5 is a simplified circuit diagram show
An object of the present invention is to pro
ing the audio frequency portion of the circuit i1
vide an improved detector of the balancedY type.
lustrated in Fig. 4,
A further object of the invention is to pro 15
Figure 6 is a View taken on the line VI-~VI of
vide an improved balanced detector for use in
Fig. 2 showing a double loop for coupling to the
_
A further object of the invention is to provide
a detector of the balanced type that can be ad
J'usted to an exact balance with a minimum of
difñculty.
In the several figures, similar parts are indi
cated by similar reference characters.
Referring to Figs. 1, 2 and 3, the parallel feed
A still further object of the invention is to pro
vide an improved balanced detector for centimeter
portion of the detector comprises a tuned coaxial
line consisting of an outer tubular conductor I0
25 and an inner conductor I I. The inner conductor
Wave signals.
According to one preferred embodiment of the
II is a solid rod that has two longitudinal holes
invention the detector comprises a tuned coaxial
I2 and I3 therein through which pass a pair of
line and a pair of diodes connected in parallel
conductors I4 and I6, respectively.
relation across one end thereof by means of 30
An annular spacing and supporting member
capacitors. The signal from the receiving an
Il is provided at the lower end of the coaxial line
tenna (which is the signal from a reflecting sur
at which point it short circuits the line. The
face or object) may be applied to the coaxial line
coaxial line is tuned by a slidable short-circuiting
whereby this signal is fed to the diodes in parallel
ring I8 that carries flexible contact fingers I9.
relation. The signal direct from the transmitter, 35 The ring I8 may be adjusted by means of a pair
which functions as a heterodyning signal, is fed
of rods 2I and 22 that are slidable in the spacer
to the diodes in push-pull relation as a result
of the following arrangement:
The inner conductor of the coaxial line is split
ring Il.
Signal from the receiving antenna may be ap
plied to the coaxial line l0. II through a pair of
or bifurcated at the end adjacent to the diodes 40 coaxial conductors 23, 24 as indicated in Fig. 2.
to form a loop or two-wire line which is capacity
The upper end of the outer conductor l0 is
terminated to function as a resonant line. The
joined to a transverse tubular section 26 into
heterodyning signal is applied to this split-line
which the upper end of the inner conductor II
loop through a coupling loop positioned adjacent
extends. A pair of diodes 2l' and 28 of the “light
thereto. Since the two diodes are connected to 45 house” type are supported in opposite ends of
thevinner coaxial line conductor at opposite sides
the section 26 with their anodes I5 and 20 oppo
of the split-line portion, the result is that the
site the inner conductor II. The anodes I5 and
heterodyning signal is applied to them in push
2c are conductively connected by means of clips
pull relation. The resulting beat frequency sig
3| and 32 to the conductors Ill and I6, respec
nal, which may be either audio or intermediate 50 tively, these conductors being brought outside the
frequency, is taken from the diodes through a
inner conductor II through holes in the sides of
pair of conductors that pass axially through the
the conductor I I which join the longitudinal holes
inner conductor whereby they are properly shield
I2 and I3.
,
'
ed from the radio frequency signals.
For radio frequency signals, the anodes I5 and
The invention will be better understood from 55 20 of the diodes are connected capacitively
2,410,122
U
through mica spacers 33 and 34 to opposite sides
considerable loss whereby proper termination of
of the inner conductor I l.
Referring now to the push-pull portion of the
circuit, the upper end of the inner conductor Il
is split to form a two-wire line or loop 31 that is
the line is less critical.
capacitively terminated, the di-electric for the
capacity termination being a piece of. mica 36 in
the example illustrated. Also, a loading resistor
35 is connected across the split end of conductor
H to reduce the Q of the push-pull circuit considerably below the Q of the parallel feed circuit.
The loop circuit 31 is the portion of the inner
conductor l I that surrounds the rectangular open
ing or split 31’.
The heterodyning signal (the signal direct from
the transmitter) is fed to the loop 31 through
a loop 4I (Figs. 2 and 4) coupled thereto. In the
example shown, the loop lll is a double loop for
improving balance which is described and claimed
in application Serial No. 538,052, ñled May 30,
1944, in the name of Daniel Blitz, and entitled
Balanced detector for altimeters. If preferred,
a single loop may be used to couple to the split
The transmitter end of the line ‘E1 is grounded
at a point e9 for insuring balanced excitation of
the line 61 from the transmitter and hence bal
anced excitation of the detector. However,
grounding the transmitter end of the line B1
does not always eliminate all signal due to unbal
ance excitation for the reason that the grounded
point t9 is not always exact as to location. It is
because of this that the double loop ¿il is em
ployed. It will be apparent that the coupling
to >the detector loop 31 from any part of the
double loop lll will include both sides of the line
61 and any current diñerence will be averaged .
out.
Figs. 4 and 5 are schematic diagrams which
show more clearly the electrical circuit of the
balanced detector, Fig. 5 being a diagram of the
. audio frequency portion‘of the circuit only. The
radio frequency portion of the circuit, with its
push-pull and parallel modes of operation, has
been fully described. The audio or beat fre
quency portion of the circuit may include two
conductor loop 31. The flow of heterodyning
current around the loop 31 is indicated in Fig. 4 ~ transformer primary windings 1l and 12 which
by the arrows.
receive signal from the diodes 21 and 28, re
The upper end of the split-conductor loop 31
spectively, and which are connected in opposing
is balanced with respect to the transverse tu
relation. A secondary coil 13 supplies the audio
bular member '26 (which, preferably, is grounded)
signal to a frequency counter or other utiliza
by means of a capacity plate 42 which is ec 30 tion circuit (not shown).
centrically attached to a rotatable supporting
One end of the primary 11 is connected to the
rod 43. Thus, the anodes I5 and 2l) at a given
anode l5 through a resistor 1li which together
instant are above and below ground potential,
with the capacity indicated at 1S acts as a radio
respectively, by a like amount. It will be ap
frequency filter. The other end of the primary
parent that this is the desired push-pull appli
1i is connected through a conductor 15 to the
cation of the heterodyning signal to the diodes
cathode 59 which is held at ground potential by
21 and 23.
a large electrolytic capacitor 1Q. Also, one end
The diodes 21 and 28 are supported in tubular
of the primary 12 is connected to the anode 2€!
members ¿l5 and L31, respectively, by means of
through a resistor 11 which together with the
supporting rings 48v and 49. The tubular mem
capacity indicated at 13 acts as a radio frequency
bers f2.6 and ¿l1 are fastened to the tubular mem
ñlter. The other end of the primary 12 is con
ber 26 in coaxial relation therewith by means of
nected through a conductor .Eli and a loading
threaded clamping rings 5| and 52, respectively.
and self-biasing resistor 82 to the cathode 58
The supporting rings 48 and 49 have flexible
which is grounded through a cathode pin and
i-lnger contact rings 53 and 54, respectively, .=~ a socket (not shown). The resistor 82 is by
mounted thereon. The contact rings 53 and 54
passed for` the beat frequency by a ñlter capaci
are insulated from their supporting rings 48
tor 83.
and ¿59 by means of mica washers 5E and 51 as
It will be noted that the diodes 21 and 28 are
illustrated.
in series for direct current but are in parallel
The fingers of the contact rings 53 and 54 L 0 for the beat frequency signal. The D.-C. voltage
are in contact with the diode metal wall sec
drop across the resistor 82 opposes current ñow
tions which are connected to the diode cathodes
due to contact potential at the diodes.
5B and 59 (Figs. 4 and 5). Thus the cathodes
It will be understood that any signal due to
58 and 59 are connected at radio frequencies to
amplitude modulation at the detector will be
the tubular section 26 through capacitors 5l and
in phase at the anodes l5 and 2in and therefore
E52 (Fig. 4) which have the washers 5B and 51
will be balanced out in the transformer 1l, 12,
(Fig. l) as the dielectric.
13. The beat frequency signal, on the other
Before discussing in more detail the electrical
hand, will be 180 degrees out of phase at the
circuit of the balanced detector, the double cou
anodes H3 and 2l) whereby the beat frequency
pling loop 4l will be described with particular
outputs of the two diodes will add and appear
reference to Figs. 2 and 6. The two loops 4I
in the secondary 13.
are supported by a block 63 of insulating ma
Fig. '7 illustrates a different method of coupling
from the transmitter to the two-wire line or loop
terial and, as shown in Fig. 2, are positioned
31. In this case the coupling is made by a pair
above the split conductor section 31. The loops
IH> are covered by a rectangular shielding can S5 65 of conductors 86 and £1 that extend through
two additional longitudinal holes E33 and 82 in
that is attached to the tubular section 26.
the inner conductor Il. The conductors §55 and
As shown in Figs. 4 and 6, one of the loops
81 have resistors 9| and 92, respectively, in se
4| is connected through a resistor 66 to one side
of the input line 61; the other end of this loop 70 ries therewith for terminating the line 61.
The conductors 86 and 81 are cross-connected
is connected to the shielding can 65. Likewise,
to opposite sides of the loop 31 at the junction
the other loop lll is connected through a resistor
of the comparatively wide upper portion 31a and
68 to the other side of the line 61; and the other
a comparatively narrow lower portion 31h. Thus
end of this loop is connected to the shielding can
the output of the line 61 is connected across the
65. The line 61 preferably is of a type having 75 portion 3112 of the complete loop 31, the impe
5
2,410,122
6
dance of this portion being a comparatively small
3.
The
invention
according
to claim 2 wherein
percentage of the total loop impedance because
said last means includes a transformer having
of the narrowness of the slot forming the portion
two primary windings and a secondary winding
31h.
andl wherein said pair of conductors are con..
It Will be evident that the coupling into the $1 nected to supply diode current to said’two pri
loop 31a, 3lb is due to the current ilow from the
mary windings, respectively.
conductor 86 down one side of the loop portion
31h, up the other side of loop portion 3112 and
into the conductor 8l as indicated by the arrows.
4. A balanced detector comprising a tuned co
axial line having an outer conductor and an in
ner conductor, said inner conductor having an
The loop 3l is in quarter wave length reso 10
end section that is bifurcated and capacity ter
nance. If properly excited and loaded, the po
minated to form a tuned two-Wire line sectionl a
tential on the capacitive end of the loop 31 will
pair of rectiñers each having an anode and a
be symmetrical to ground. The slot forming 31h
cathode, one rectifier having its cathode connect
is made narrow so that the potential distribution
ed through capacity to said outer conductor and
on the loop 3l will remain practically symmetri 15 having its anode connected through capacity to
cal regardless of unbalance of the energy in the
one side of said bifurcated section, the other rec
direct coupling lines 6l.
tiñer having its cathode connected through ca
The termination of each of the coaxial lines
pacity to said outer conductor and having its
formed by the center conductors 86 and 81 and
anode connected through capacity to the other
by the associated outer conductors consisting of
side of said bifurcated section, means for apply..
the walls of the holes 88 and 89, respectively, is
ing signal to said coaxial line, said signal lying
inthe loop 31h. The electrical center of each
within the frequency range to which said coax
coaxial line termination is not in the center of
ial line is tuned, means simultaneously for ap
the lower end of the slot I¿lb but is displaced by
plying signal?to said two-wire line section, said
an amount approximately equal to the amount 25 last signal lying within the frequency range to
that the center conductor extends beyond the
which said two-wire line section is tuned, ‘and
upper end of its outer conductor. Therefore, for
means for supplying from said diodes to a uti
maximum inherent symmetry the slot 31h should
lization circuit any beat frequency signal result
be made as narrow as mechanical limitations
ing from an instantaneous frequency diiïerence
permit.
30 of said signals, said last means including a pair
We claim as our invention:
of conductors that pass through two longitudinal
1. A balanced detector comprising a tuned co
holes in said inner conductor and which are con
axial line havingr an outer conductor and an in
nected to an electrode of each of said diodes,
ner conductor, said inner conductor having an
respectively.
end section that is bifurcated and capacity ter 35
5. The invention according to claim 4 wherein>
_ minated to form a tuned two-wire line section, a
said last means includes a transformer having
pair of rectiñers, one rectifier being connected
two primary windings connected in opposing re
between said outer conductor and one side of said
lation and having a secondary Winding connected
bifurcated section, the other rectifier being con
to said utilization circuit and wherein said pair
nected between said outer conductor and the 40 of conductors are connected to supply diode cur
other side of said bifurcated section, means for
rent to said two primary windings, respectively.
applying signal to said coaxial line, said signal
6. A balanced detector comprising a tuned co
lying within the frequency range to which said
axial line having an outer conductor and an in
coaxial line is tuned, means for simultaneously
ner conductor, said inner conductor having an
applying signal to said two-wire line section, said " end section that is bifurcated and capacity ter
last signal lying within the frequency range to
minated to form a tuned two-wire line section, a
which said two-wire line section is tuned, and
pair of .rectiliers each having an anode electrode
means for supplying from said diodes to a uti
and a cathode electrode, one rectifier having one
lization circuit any beat frequency signal result
ing from an instantaneous frequency difference of
said signals.
CO
2. A balanced detector comprising a tuned co
axial line having an outer conductor and an in
ner conductor, .said inner conductor having an
end section that is bifurcated and capacity ter
minated to form a tuned two-wire line section, a
55
of its electrodes connected through capacity to
said outer conductor and having its other elec
trode connected through capacity to one side of
said bifurcated section, the other rectifier having
one of its electrodes connected through capacity
to said outer conductor and having its other elec
trode connected through capacity to the other
side of said bifurcated section, means for apply
ing signal to said coaxial line, said signal lying
pair of rectiñers, one rectifier being connected
between said outer conductor and one side of said
within the frequency range to which said coaxial
bifurcated section, the other rectifier being con
line is tuned, means comprising a loop adjacent
nected between said outer conductor and the 60 to said two-wire line section for applying signal
other side of said bifurcated section, means for
thereto, said last signal lying within the fre
applying signal to said coaxial line, said signal
quency range to which said two-wire line section
lying within the frequency range to which said
is tuned, and means for supplying from Said di
coaxial line is tuned, means for simultaneously
odes to a utilization circuit and beat frequency
applying signal to said two-wire line section, said 5 signal resulting from an instantaneous frequency
last signal lying within the frequency range to
difference of said signals, said last means in
which said two-wire line section is tuned, and
cluding a pair of conductors that pass through
means for supplying from said diodes to a utiliza
two longitudinal holes in said inner conductor
tion circuit any beat frequency signal resulting
and which are connected to an electrode of each
from an instantaneous frequency diiîerence of 70 of said diodes, respectively.
said signals, said last means including a pair of
7. A balanced detector comprising a tunable
conductors that pass through two longitudinal
coaxial line having an outer conductor and an
holes in said inner conductor and which are con
inner conductor, said inner conductor having an
nected to an electrode of each of said diodes, re
end section that is bifurcated and capacity ter
spectively.
75 minated' to forma tuned two-wire line section,
2,410,122
7
a pair of rectiñers, one rectiñer being connected
between saidl outer conductor and one side of
said bifurcated section, the other rectifier being
connected between said outer conductor and the
other side of said bifurcated section, means for
applying signal to said coaxial line, said signal
lying within the frequency range to which said
coaxial line is tuned, means for simultaneously
applying signal to said two-wire line section, said
last signal lying within the frequency range to
which said two-wire line section is tuned, said
last means comprising a pair of conductors that
pass through two longitudinal holes in said inner
conductor and which are cross-connected to op
posite sides of said bifurcated section, and means
for supplying from said diodes to a utilization
circuit any beat frequency signal resulting from
an instantaneous frequency difference of said
signals.
8. A balanced detector comprising a tuned co
axial line having an outer conductor and an in
ner conductor, said inner conductor having an
end section that is bifurcated and capacity ter
minated to form a tuned two-wire line section, a
pair of rectiñers each having an anode electrode
and a cathode electrode, one rectifier having one
of its electrodes connected through capacity to
S
said outer conductor and- having its other elec
trode connected through capacity to one side of
said bifurcated section, the other rectiiìer having
one of its electrodes connected through capacity
to said outer conductor and having its other elec
trode connected through capacity to the other
side of said bifurcated section, means for apply
ing signal to said coaxial line, said signal lying
within the frequency range to which said coaxial
line is tuned, means for simultaneously applying
signal to said two-wire line section, said last sig..
nal lying within the frequency range to which
said two-wire line section is tuned, said last
means comprising a pair of conductors that pass
through two longitudinal holes in said inner con
ductor and which are cross-connected to oppo
site sides of said bifurcated section, and means
for supplying from said diodes to a utilization cir
cuit any beat frequency signal resulting‘from an
instantaneous frequency difference of said sig
nals, said last means including a second pair of
conductors that pass through two longitudinal
holes in said inner conductor and which are con
nected to an electrode of each of said diodes,
respectively.
WILLIAM R. MERCER.
BEN R. COLE.
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