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Патент USA US2404270

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July 16g-1946,
w. É. @äADLEY
l
.
`4 2,404,270
BAND PAssfwAvE FILTERy
Filed .my 24, 1942 '
„Jus-me45
ZÉ
/MPEo/mc:
OUTPUT
Patented July 1_6, 1946
v2,404,270 "
UNITED STATESA PATENT 'oFFics
BAND PAss WAVE FILTER
William E. Bradley„ Northampton, Pa.,4 assignor to
Philco Radio and Television Corporation, Phila-. _
delphia, Pa.„ a corporation of Delaware
.Application July 24,1942-, serial No. 452,229
6> Claims.
(o1. 17a-44)
1
networks’ or wave filters, and more particularly to
a band pass coupling network having a plurality
of substantially non-interacting coupling adjust
ments.
'
2
and Without any sacrifice in the gain of the stage.
It is a further object of the invention to‘pro
vide a Wide-band coupling network capable of
giving substantially the maximum gain obtain
This invention relates to` band pass coupling
able in a coupling network between tWo vacuum
’
An important class of band pass wave ñlters
frequently employed in the field of communica
tions isthat which utilizes transformers of the
y a wide-band coupling network having a novel
double-tuned, over-coupled type. Transformers
combination of impedance and admittance cou
of this character are commonly employed in the 10
pling.
intermediate frequency stages of conventional
superheterodyne receivers adapted for use in the
reception of amplitude modulated broadcast sig
nals. While these transformer coupled systems
tubes.
_
`
It is another object of the invention to provide
-
The invention itself, as well as other objects
thereof` will -be understood from the following
description and accompanying drawing, in which:
Fig. 1 is a generalized schematic diagram of the
have been generally satisfactory in certain limited 15 coupling system which comprises the present in
and conventional applications, including that just
referred to, there are other applications in which
the transformer coupled system leaves much to
vention;
'
1
Fig. 2 is a schematic diagram of a specific ern
lbodi'ment of the invention; and
Figs. 3 and 4 are explanatory diagrams which
be desired. Included in these applications are
cascaded wide-band systems wherein it is de 20 illustrate the operation and performance ofthe
coupling circuit ofthe invention.
sired to obtain a particular one of a wide variety
Reference is now made to the generalized sche
of response characteristics simply and reliably.
matic of Fig. 1 in which a double-tuned com
In systems such as these it is difficult, and some
pound-coupled filternetwork is illustrated hav
times impossible, for the: designer to obtain de
sired response and phase characteristics with 25 ing an impedance coupling element Zr and an
conventional over-coupled transformers, and this
admittance coupling element Yh.
The primary
circuit of the network Lcomprises an inductance
L1 tuned by a tuning condenser C1 and damped
acteristic is asymmetrical. All of these difficulties
by a damping resistor R1. The secondary circuit
are aggravated in production where it is impor
tant that all tuning operations be capable of 30 comprises the inductance L2 tuned by a tuning
condenser Cz and »damped by a damping resistor
quick, simple, and effective adjustment.
Rz. The primary and secondary circuits are pref
By the present invention a compound coupling
erably isochronous, i. e., tuned to thesame fre
system is provided which permits of substan
is especially so where the desired response char
tially individual control and adjustment of both
the high frequency and low frequency halves of
the response characteristic. In over-coupled cir
cuits exhibiting two resonant peaks, the inven
quency.
tion permits of individual» peak adjustments
R1 and R2 are
the tuning con
densers C1 and C2 respectively, it is to be under
stood that, alternatively, they may be connected t
which are- substantially independent of each
in shunt with the inductances L1 and Lz, or if ,
other, and which can be made as readily as the
adjustments of single-tuned circuits. Circuits of
this character are especially adapted for use in
wide-band systems, such. as the intermediate fre'
quency stages of television and frequency ymodu
lati-on receivers, and in special. applications which
may require response characteristics of an asym
metrical character.
It is a principalobject of this invention to pro
vide a band pass interstage coupling circuit with
which a wide variety of response characteristicsä
may be obtained simply and reliably.
It is another object of the invention to provide
an over-coupled interstage coupling circuit in
which it is possible to adjust either peak of the
While the damping resistors
se shown
connected in shunt with
desired the damping resistors may >be eliminated
entirely, the required dissipation of energy asso
ciatecl with the condensers being achieved, for
example, by winding the inductancesv L1 and L2
>of a suitable resistance Wire.
,
Coupling between the primary and secondary
circuits is provided, firstly, by means of an imped
ance Zr connected between the common junction
ofi-.11 and Leon the one hand'andthe low poten,
tial ends of the condensers C1 and C2 on the other
hand, and secondly'by `means of an admittance
Ye connected between the high potential ter
minals of the primary and secondary circuits.
Although it is within the general purview of the
invention tol make all of ’the elements of. Fig. 1
two-peak response characteristic independently, 'I‘ 65 adjustable, it is within the special province of the
2,404,270
,
3
Y
.
invention that at least one, and preferably both,
ofthe coupling devices Yn and Zk be adjustable.
If the admittance coupling element Yu and the
impedance coupling element Zk are properly Aad
justed, a symmetrical frequency response char-l
' acteristic can be obtained which is similar to that
provided by a conventional double-tuned over
coupled transformer-system, for. example, sim
the frequency of the high-frequency peak as il
lustrated in Fig. 3. MoreoverV the height of the
high frequency peak may be varied byV adjust
ment of the shunt damping resistor Rh to pro
duce various response characteristics such as thoseV
illustrated in Fig. 4. Adjustments of the induct
'ance Lk and resistor Rk produce similar changes
in the position and height ofthe low frequency
ilar to thatf'illustrated‘by the curve (v_-a ‘of Fig._'3.
peak. Throughthe adjustmentgofthe >elements
.The novelty of the'present invention resides in 10 which Ycomprise the impedance coupling and ad
the fact that the compound coupling provided by _ lmittance coupling members, an extremely wide>
the two coupling elements Yh and Zk permits the. ».»S-.variety of response characteristics may be seindividual peaks of the double-humped response <
'
acured, anda desired response characteristic may
characteristic to be individually shifted in fre
_readily bev duplicated in production by means of
quency and varied in height or relative response,V4 1s. tuning adjustments which are individually as sim
Yeach rof the adjustments being substantially in-v y pleas those` normally made in single-tuned cir
dependent of the other, and having substantially
cuits of the simplest character.
no eiïectupon the shape of the other peak. If,
In coupling systems designed to have a sym
metrical response characteristic, i. e., in which
justable inductive admittance, then adjustment 20 the heights of the two resonant peaks are equal,
of the imaginary part ofthe admittance, i. e., the
the real components of Yh andZk, the elements
susceptance, will shift the frequency of the` high
Rh and Rk respectively, may be omitted.v In such
for example, the element Y1;` comprises an ad- -
' frequency peak as shownffor example, by the ì
curves-a-b and a-d in Fig. 3.
applications only the input damping resistor VR1
On the other
and the output dampingy resistor R2 need be em
hand if the rea1 part (the conductance) of the 25 ployed. In this case the circuit should be designed
admittance Yh is varied, the response or height of
the high frequency peak will be affected as is il
so that the ratio of R1 to R2 is equal to the ratio
lustrated in Fig. 4 by the‘curves e-f, e--y, .and
of C2 to C1. Thisarrangement will keep the peak
heights substantially equal,»even when C1 and C2
c-h. Adjustment of the imaginary and the real
are unequal, for all settings of `L11 and Lk.l
parts, the reactance and resistance respectively,r
of the impedance coupling element Zk will have
In the schematic diagram of Fig; 2 adjustable
.damping resistors have been associated vwith both
similar effects upon the shape of the low-fre
quencyresponse peak.
generality,»and suchan arrangement may be used
The invention also contemplates the use of ca
pacitive-coupling elements, and if this change is ~
in practice where it is necessary frequently to vary
the relative heights of the'two response peaks. In
made the coupling element Yh will control the
position- and height of the low frequency peak,
whilethe coupling,y element Zk will control the
position and’height of the high frequency re
most practical applications,- however, it is pre- '
Lh and Lk.
This has been done for the sake of
ferred to employ only one of the adjustable damp
ing resistors, and then only in conjunction- with
a predetermined one of the vtwo coupling> ele
sponse peak.h It has been found however that the 40 ments to produce the required asymmetry. V
use of inductivef‘coupling elements provides a
- Although the _invention is not limited toany
higher gain than can be obtained with the use of
particular method of tuning the inductances Ln
capacitive coupling elements, and for this reason
and Lk, it is preferred that this be accomplished ¿
inductive `coupling elements are preferred.
‘
by means of adjustable copper or powdered iron
Reference is now made `to Fig. 2 in whichthere Y, 45 cores in a mannerwhich is well understood in
is illustrated a specific embodiment of the in
vention employed as a coupling network between
‘two amplifier tubes V1 and V2. In this partic
the art.
'
,
-
The damping resistors Rh and Rk »may be as
sociated with their respective inductances in any
desired manner to produce the required damping
ular instance the inductive `rform of coupling has
been chosen for illustration. In Fig. 2 the ad 50 effect, but it is preferred that the damping re
justable inductance L11 and the vadjustable re
sistor R11 be connected in parallel with the cou
sistor-R11 comprise the imaginary and real parts,
pling inductance L11, and that the damping re
respectively, of the coupling element Yh of Fi'g..1.
sistor Rk be connected in series with its induct
Similarly'the adjustable inductance Lk andthe
ance Lk. Likewise, if desired, the coupling in
adjustable resistor Rk comprise the imaginary and 55 ductances Lk and'Lk may be replaced `by adjust- .
real parts, respectively, of the coupling element
able condensers of suitable size.
i
f
Zk. In the circuit'chosen for illustration, the
It has' been found that the frequency range of
primary and second tuning capacities, C1 and C2,
the resonant peak controlled bythe- inductance
may be provided in whole, or in part, by the out
Lk is larger, ordinarily,qthan that controlledby
put capacity of the amplifier V1 and the input 00 the inductance Lk, becauseV the inductance of L11
capacity of the ampliñer V2, respectively.. Plate
in practice is usually larger than the inductance
voltage for the ampliñer V1 may be supplied from
Lk. In consequence the inductance L11 tends to
'a highpotential source B+, through a ñlter com
resonate with its >distributed capacity, making the
prising a series resistor R3 and a shunt condenser
apparent inductance of this l coupling element
C3, and thence through the damping resistor R1, 65 larger than the actual inductance of the coil. '
to the anode of V1. In order to isolate the'input
Because of Vthis self ¿resonantl action of Ln it is
grid of the tube V2 from the high voltage applied
possible to control the high frequency Vpeakfover
to the plate of V1 a direct current blocking con
a considerable frequency range. "It is not so easy
denser C4` may be provided as shown. VA suitablev
t0 obtain wide control of the' :low frequency peak,
bias, or automatic volume control voltage, 70 because the value of Lk is not` lonly much smaller
maybe supplied to the grid circuit of V2 through
than rthe other inductances involved, -but its leak
. -a filter comprising the series resistor R5 and the
age inductance is `relatively large. This situa
`shunt condenser C5 as illustrated.
’
tion can be relieved by the Vprovision of some'
With the form of circuit shown in Fig. 2„ ad
mutualy inductancezbetween4 L1 and L2 so phased
justment of the inductance L11 effects changes in 76 :as to produce the opposite signof inductive cou
/
2,404,270
5
6
,
cumstances Lk can be increased to a larger value,
with the result that its tuning range is greatly
extended.
Y
ary circuits, the degree of over-coupling being
such that a double-peaked frequency-response
characteristic is achieved; one of said coupling
elements including a real component, the magni
tude of which determines the height of one of
said peaks vwithout substantial effect upon the
pling to that produced by Lk. Under these cir
'
The coupling network of the present invention
is especially well suited for use in multi-stage
amplifier systems, in which a plurality of indi
height of the other of said, peaks.
K
.
I
2. A band pass coupling network, as claimed
vidual stages (e. g. five or six), each constructed
in claim l, characterized further in that, in addi
in accordance with the invention, may be con
nected in cascade. In such a system it is often 10 tion to the coupling provided between said pri
mary and secondary circuits, said primary and
desirable to “stagger” the tuning of the various
secondary windings are coupled by means includ
stages, i. e., to peak the individual circuits at pre
ing mutual inductance, said mutual inductance
being of such sign as to oppose the coupling ef
a large number of stages, each having charac
teristics similar to that of the curve a-a of Fig. 15 fect of said impedance coupling element.
3. A -band pass coupling network comprising:
3, but each with its characteristic displaced in
a primary circuit including a primary Winding
frequency a predetermined amount, may be con
and a primary tuning capacitance; a secondary
nected in cascade to provide a wide-band, sub
circuit including a secondary winding and a sec
stantially iiat-top, characteristic having greater
determined different frequencies. For example,
overall gain and a more‘desirable overall phase 20
characteristic than could be obtained’by means
of an equal number of identically-tuned ñat
topped circuits connected in casca/de. In other
instances it may be desirable to combine ampli
iiers having characteristics similar 'to the one 25
designated e-g in Fig. 4 with amplifiers having
characteristics of the type designated e-h. In
all of these multistage applications, the feature
ondary tuning capacitance; a first variable-in
ductance coupling coil; means for connecting
said primary winding, said primary tuning ca
pacitance and- said coupling coil in a closed series
circuit; means for connecting said secondary
winding, said secondary tuning condenser and
saidcoupling coil in a second closed series cir
cuit; and ra second variable-inductance coupling
coil connected between predetermined high p0
tential points on said primary and secondary
of the network which makes it possible to adjust
independently either peak of the two-peak re 30 windings; the inductance of said coupling coils Y
« being of a magnitude such that an over-coupled
sponse is of great importance.> This makes pos
condition is effected Abetween said primary and
sible simplified production adjustment of the
secondary circuits, the degree of over-coupling
stages, the various trimmers being “peaked” at
being such that a double-peaked frequency-re
definite frequencies with a signal generator and
sponse characteristic is achieved, the position of
output indicator, the correct response character
said peaks along the frequency axis being sub
istic then following automatically.
,
stantially independent functions of the adjust
While the invention has been described with
ment of said coupling coils,
`
particular reference to a speciñc embodiment and
4. A band pass coupling network as claimed in '
‘to a particular mode of operation, it will be un
derstood that ythe kinvention is capable of general 40 claim 3, characterized in the provision of resistive
means in damping relation to at least one of said
application and is adapted to other forms of phys
coupling coils, the resistance of which determines
ical expression and is, therefore, not to be limited
the relative height of said peaks.
`
5. A band pass coupling network as claimed in
to the speciiic disclosure, but only rto the scope of
the appended claims
I claim:
45 claim 3, characterized in that, in addition to the
1. A band- pass coupling network comprising:
coupling provided between said primary and sec
ondary circuits, said primary and secondary
windings are coupled by means including mutual
inductance, said mutual inductance being of such
ondary tuning capacitance; and an impedance 50 sign as to oppose the coupling effect of said iirst
variable-inductance coupling coil, and thus to
coupling element connected in .a circuit which is
permit the use of a larger-than-normal ñrst cou
common to both said windings, said impedance
pling inductance, thereby to increase the fre
coupling element having an adjustable imaginary
quency range obtainable through adjustment of
component; an admittance coupling element con
a primary circuit including a primary winding
and a primary tuning capacitance; a secondary
circuit including a secondary winding and a sec
nected between a high potential point on said
primary winding and a high potential point on
said secondary winding, said admittance cou
pling element having an adjustable imaginary
component; said coupling elements being charac
terized in that they are non-resonant, and of 60
such magnitude that an over-coupled condition
is effected between said primary and second
' said coupling coil.
6. A band pass coupling network as claimed in
claim 3, characterized in the provision of resis
tive means for damping said primary circuit, and
independent resistive vmeans for damping said
secondary circuit.
-
WILLIAM E. BRADLEY.
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