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Патент USA US2409475

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- Oct. 15, 1946.
R. e._ CLAPP
HIGH FREQUENCY ATTENUATOR AN’D DIVIDER CIRCUITS
. Filed May 13, 1943
2’,409,474_
~ Oct. '15, i946.
'
v
R. G. CLAPP
7
I
2,409,474
HIGH FREQUENCY ATTENUATOR AND liIYIDER CIRCUITS
F'ilégl May 13, 1943
2 Sheets-Sheet 2 h -
2,409,474
Patented Oct. 15, 1946
UNITED STATES PATENT OFFICE‘
2,409,474
HIGH-FREQUENCY ATTENUATOR AND
DIVIDER CIRCUITS
Richard G. Clapp, Haverford, Pa., assignor, by
mesne assignments, to Philco Corporation,
Philadelphia, Pa, a corporation of Pennsyl
vania
Application May 13, 1943, Serial No. 486,877
10 Claims.
(01. 178—44)
1
2
This invention relates to- high frequency con
trol circuits, and more particularly to high fre
quency attenuator andhigh frequency divider cir
cuits and structures.
Attenuator and divider structures and circuits
L2 is preferably a one-turn loop (see Fig. 3) of
which only the middle portion is magnetically
coupled to L1 through an opening 2 in the shield
structure 3. Because of the presence of the shield
there is no appreciable electrostatic coupling be
tween the primary winding L1 and the secondary
adapted for use at audio frequencies and at low
radio frequencies are well known in the art, and
there are numerous conventional and satisfactory
winding L2. The grounded contact member I
may be arranged, by any suitable mechanical
means, to slide on the secondary inductance L2,
devices available for such applications. At very
high frequencies, however, say in the tens or 10 so that it can be positioned to ground any de
sired point thereon.
hundreds of megacycles, these conventional de
By means of the arrangement described, the
vices are of no utility.
Accordingly, it is a principal object of this
middle portion of L2 serves somewhat as a var
iable auto-transformer, while the two ends there
cuit capable of performing satisfactorily at very 15 of function as variable series inductance elements
in the attenuator. The shunt resistor R1, which
high frequencies.
is connected across the secondary inductance L2,
It is another object of this invention to pro
may have a relatively low resistance, for example
vide a simple attenuator or divider structure for
200 ohms. The resistors R3 are terminating re
use at very high frequencies.
It is a further object of this invention to pro 20 sistors for the coaxial transmission lines T1 and
T2 and may have conventional resistance values.
vide a variable voltage divider device capable of
The resistance of the line coupling resistors R2
dividing a high frequency signal between two load
should be high in comparison with the resistance
circuits in any desired ratio.
of R1 and R3,. and may be, for example, of the
It is another object of the invention to provide
an attenuator for dividing a high frequency sig 25 order of a thousand ohms. The resistors R2
serve to isolate the transmission lines from the
nal between two load circuits in any desired pro~
attenuator, and help to keep the load on the in~
portion with ‘minimum reaction on the signal
invention to provide an attenuator or divider cir
source.
ductance L2 constant, regardless of the position
'
of the contact member 5. The switch S of Fig.
be apparent from the following description of the 30 l constitutes a re?nement, and for the moment
it will be assumed to be absent.
accompanying drawings, in which:
A satisfactory mechanical structure for the
Fig. 1 is a schematic circuit diagram of a high
device illustrated schematically in Fig. 1 is illus
frequency attenuator adapted to divide an input
trated in Figs. 2 and 3, wherein like reference
signal between two load circuits;
These and. other objects of the invention will
Fig. 2 is a sectional view of an attenuator and 35 characters designate corresponding elements in
divider device constructed in accordance with
the teachings of the present invention;
Fig. 3 is a sectional View taken alongr line 3-—3
of Fig‘. 2; and
Figs. 4, 5, and 6 are explanatory illustrations
the circuit diagram of Fig. 1. In the embodiment
illustrated, the single-turn inductance L2 is in
sulatingly supported from the base portion of the
showing, in polar coordinates, typical attenuation
The shield structure 3, in addition to prevent
ing electrostatic coupling between the inductances
L1 and L2, also shields the two lines T1 and T2
curves which may ‘be provided by the apparatus
of Figs. 1 to 3.
'
Reference may now be had to Fig. 1, wherein
shield 3 by means of the stand-cit insulators 4
and 5.
from both of the inductances.
Preferably, as is
‘E is a source of high frequency signals, and T1 45 indicated in Figs. 1, 2, and 3, the line coupling re
sistors R2 pass through small. holes in the shield
and T2 are a pair of load circuits, in this case
structure 3. By this procedure the opposite ends
transmission lines, between which the signal from
of the resistors are shielded from each other. It
is also desirable to provide an additi0na1 shield
50 structure 6 to prevent electrostatic coupling be
contact member I on the inductance coil L2.
tween the input circuits and terminals of the
Considering the circuit in detail, the primary
two transmission lines.
inductance coil L1,, which is connected to the
In order that a high maximum. voltage ratio
signal source E, may be, for example, the tank
may be secured between the two lines T1 and T2
coil of an oscillator, or the anode load induct
ance of an ampli?er. The secondary inductance 55 it is important that the contact member I actu
the said source may be divided in any desired
proportion byaadjustment of the position of the
2,409,474
3
ally be capable of reaching the ends of the in
ductance L2, so that the minimum inductance in
either of the extreme positions of the slider may
be negligible.
Where a slider is employed as a
contact member, as in Figs. 2 and 3, the minimum
inductance may further be made low by bring
ing both ends of L2 as close to the grounded end
of the slider as possible. It is important that the
impedance from the sliding contact to ground be
4
has the effect of raising the voltage delivered to
each line at the middle position, relative to the
maximum delivered to the line. Thus, in Fig. 1,
when the slider is in the 90° position the voltage
delivered to each line is not a great deal less than
the maximum voltage delivered in the 0° and
180° positions. An attenuation curve resulting
from the use of a relatively low value of R1 is
illustrated in Fig. 5.
negligible, since this impedance is common to 10
If R1 is relatively high in impedance, compared
both sides of the attenuator. Preferably the
to the impedance of L2, the shunt resistor has no
slider l is of spring steel plated with some ma
substantial effect regardless of the slider position.
terial providing low contact resistance between
Fig. 6 is a typical attenuation characteristic which
it and the loop L2. 'The slider may be mounted
may be secured when R1 is high compared to the
on a rotatable shaft 1 having one end journaled 15 impedance of L2.
in a wall of shield 3 and having its other end
The device illustrated in Figs. 1 to 3 has been
supported by a bearing 8, and carrying a con
described particularly with reference to its use as
trol knob 9. Good contact between the slider
a combined voltage divider and attenuator. How—
and. the bearing ‘8 (which is grounded to the
ever, it will be evident that the device can also
shield 3) may be secured by means of a spring 20 be used solely as an attenuator operating between
washer or a ?exible connector (not shown).
If
these precautions are observed, and proper shield
ing provided, it is possible to secure voltage ra
ties between the two lines of the order of 20 to
a source E and a single load circuit, say the line
T1. In such use, the resistors R2 and R3, and,
of course, the line T2, could be dispensed with.
The resistor R1 might, or might not, be retained,
l or better.
25 depending upon the shape of the attenuation
It is an important feature of the invention that,
curve desired.
because the inductance elements L1 and L2 are
The invention is, of course, capable of various
loosely coupled magnetically, and because the
embodiments and modi?cations such as fall
coils are electrostatically shielded from each
, within the scope of the appended claims.
other, and moreover because the load on L2 is 30
I claim:
substantially constant, regardless of the adjust
1. The combination with a high frequency sig
ment of the contact member, there is no substan
nal source and a pair of load circuits to be sup
tial reaction on L1 regardless of load conditions,
plied therefrom, said load circuits having a com~
or of contact member adjustment.
morn terminal, of a signal divider and attenuator
The particular embodiment illustrated in Figs. 2 35 including a ?rst inductor connected to said source,
and 3 employed a single-turn secondary induct
a second inductor having only a portion thereof
ance L2 of approximately two inches in diameter.
disposed so as to be magnetically coupled to said
The circular opening 2 in the forward wall of the
?rst inductor, shielding means for substantially
shield structure was approximately one inch in
eliminating electrostatic coupling between said
diameter. The various resistors had the follow~
inductors, means including an impedance network
ing values: R1=200 ohms, R2=1,00O ohms,
connecting the respective ends of said second in
R3=100 ohms. The apparatus operated in the
ductor to the respective load circuits, an adjust
range 100 to 200 megacycles. The slider I was
able contact engaging said second inductor, and
adjustable over a 180° arc.
It has been found that the size of the opening
2 determines the magnitude of the maximum volt
age obtainable and to some extent the shape of
the attenuation curve. The shape of the attenu
ation curve can also be varied by changing the
shape of the loop which forms the inductance L2.
A typical attenuation curve is illustrated in Fig.
4. The curves are plotted in polar coordinates,
and consequently the radii drawn from the origin
correspond in position to the adjustment of the
means connecting said contact to said common
" terminal of said load circuits.
2. The combination with a high frequency sig
nal source and a pair of load circuits to be sup
plied therefrom, of a signal divider and attenuator
including a ?rst inductor connected to said source,
a second inductor in the form of a single-turn
loop connected to said load circuits and having
only an intermediate portion magnetically coupled
to said ?rst inductor, shielding means for sub
stantially eliminating electrostatic coupling be
slider l as viewed in Fig. 3. If the slider is rotated 55 tween said inductors, and means including an
from the right-hand horizontal position, through
the angle ¢' the voltages applied to the transmis
sion lines T1 and T2 are 61 and c2, respectively.
If the slider is rotated through the angle ¢", the
relative magnitudes of the voltages are reversed.
It has been found that the shape of the atten
uation curve can be varied considerably by
grounding the center point of the shunt resistor
R1, and by varying its resistance value. To ob‘
tain this effect the switch S of Fig. 1 is closed.
If a relatively low value of R1 is selected (i. e. low
with respect to the impedance of Le), the load on
the one-turn loop varies over a two-to-one range
adjustable contact engaging said second inductor
for varying the magnitudes of the voltages applied
to said load circuits.
3. The combination with a high frequency sig
nal source and a pair of load circuits to be sup
plied therefrom, of a signal divider and attenu
ator including a ?rst inductor connected to said
source. a second inductor having only a portion
thereof magnetically coupled to said ?rst in
ductor, an impedance network including series
and shunt resistors connecting said second in
ductor to said load circuits, shielding means for
substantially eliminating electrostatic coupling
between the condition where the slider is in the
between said inductors, an adjustable contact en
middle of the loop and that where it is at one 70 gaging said seccnd inductor and movable over
end. When the slider is at one end, the load on
substantially the entire length thereof, and means
the loop L2 is R1/2, whereas when the slider is in
connecting said contact to a common terminal of
its center position the load is R1. Thus the volt—
said load circuits.
'
age across the whole of L2 is lower when the slider
4. The combination with a high frequency sig~
is at the ends than when it is at the middle. This 75 nal source and a pair of load circuits to be sup
2,409,474
5
6
plied therefrom, of a signal divider and attenu
ator including a ?rst inductor connected to said
said second inductor, a pair of series resistors
connecting the ends of said second inductor to
the respective load circuits, shielding means for
source, a second inductor having only a portion
thereof magnetically coupled to said ?rst induc
tor, a resistor connected in shunt relation With
said second inductor, a pair of series resistors
connecting the ends of said second inductor to the "
respective load circuits, shielding means for sub
stantially eliminating electrostatic coupling ‘be
substantially eliminating electrostatic coupling
between 'said inductors, an adjustable contact
engaging said second inductor and movable over
substantially the entire length thereof, means
connecting said contact to a common terminal of
said load circuits, and means operable at will to
tween said inductors, an adjustable contact en 10 connect the mid-point of said shunt resistor to
said common terminal.
gaging said second inductor and movable over
substantially the entire length thereof, and means
8. In a high frequency attenuator, an inductor
in the form of a single-turn loop, shielding means
connecting said contact to a common terminal
for said inductor having an opening adjacent an
of said load circuits.
5. The combination with a high frequency sign 15 intermediate portion of said inductor, a contact
slider engaging said‘inductor, and another in
ductor on the opposite side of said shielding
means and having a portion adjacent said open
ing, whereby only the said portion of the ?rst
turn loop having only an intermediate portion 20 named inductor is magnetically coupled to said
thereof magnetically coupled to said ?rst induc
last-named inductor.
tor, an impedance network including series and
9. In a high frequency attenuator, an inductor
in the form of a single-turn loop, a shielding en
shunt resistors connecting said second inductor
closure about said inductor, said enclosure having
to said load circuits, shielding means for substan
tially eliminating electrostatic coupling between 25 an opening adjacent an intermediate portion of
said induct/on a contact arm pivoted adjacent
said inductors, an adjustable contact engaging
the extremities of said inductor and engaging the
said second inductor and movable over substan
tially the entire length thereof, and means con
same, and another inductor outside said enclosure
‘and having a portion adjacent said opening,
necting said contact to a common terminal of said
load circuits.
‘
.
30 whereby only the said portion of the ?rst-named
inductor is magnetically coupled to said last
6. The combination with a high frequency sig
nal source and a pair of load circuits to be sup
plied therefrom, of a signal divider and attenu
ator including a ?rst inductor connected to said
source, a second inductor in the form of a single
named inductor.
. 10. The combination with a high frequency sig_
plied therefrom, of a signal divider and attenu
nal source and a pair of load circuits to be sup:
ator including a ?rst inductor connected to said
source, a second inductor in the form of a single 35 plied therefrom, of a signal divider and attenu
ator including an inductor in the form of a sin
turn loop having only an intermediate portion
gle-turn loop, a resistor connected between the
thereof magnetically coupled to said ?rst in
extremities of said inductor, a shielding enclosure
ductor, a resistor connected in shunt relation with
about said inductor and said resistor, said en~
said second inductor, a pair of series resistors
connecting the ends of said second inductor to 40 closure having an opening adjacent an interme
the respective load circuits, shielding means for
diate portion of said inductor, another inductor
outside said enclosure and having a portion adja~
substantially eliminating electrostatic coupling
cent said opening, whereby only the said portion
between said inductors, an adjustable contact en
of the ?rst-named inductor is magnetically cou
gaging said second inductor and movable over
pled to said last-named inductor, means con
substantially the entire length thereof, and means
necting the last-named inductor to said signal
connecting said contact to a common terminal of
source, a pair of series resistors connecting the
said load circuits.
extremities of g the ?rst-named inductor to said
7. The combination with a high frequency sig
load circuits, an adjustable contact engaging said
nal source and a pair of load circuits to be sup
plied therefrom, of a signal divider and attenu- . ?rst-named inductor, and means connecting said
contact to a common terminal of said load cir
ator including a ?rst inductor connected to said
cuits.
source, a second inductor having only a portion
RICHARD G. CLAPP.
thereof magnetically coupled to said ?rst induc
tor, a resistor connected in shunt relation with
nal source and a pair of load circuits to be sup
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