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Патент USA US2134175

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Oct. 25, 1938.
L. F. CURTIS
2,134,175
WAVE `FILTER
Filed June 27, 1956
2 Sheets-Sheet l
ll/l
INVENTOR.
ATTORNEY.
oct. 25, 193s.
L_ F. CURUS
'
2,134,175
WAVE FILTER
Filed June 27, 1956
2 -Sheè’cs-Shee’c 2
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WQ@ ,4 @MAZ
ATTORNEY.
Patented Oct. 25, 1938
g
A2,134,175
UNITED STATES
2,134,175
' WAVE FILTER
VLeslie
Curtis, S‘pring?ìeld„M_ass., assignorrto
yUnited American Bosch Corporation, 'Spring
field, Mass., a corporation Vof New ,York‘
.
Application June 27, 1936, .SerialNo-. _87,711
4 claims. (c1. 17a-'44)
This invention relates to radio apparatus and
more particularly to a tuned filter circuit for elim
inating an undesired frequency from a band of
transmitted frequencies.
In the past, filters of various kinds have been
employed in the antenna circuit- of radio receiv-.
ers to minimize the effect of interfering stations
and were commonly known as “wave traps”. `In
the smaller types of superheterodyne receivers
static 'shield'l may be used if necessaryto elimi
nate undesired electrostatic' coupling betweenthe
inductance 2 or condenser :Sand the outputster-`
minals of> the device.~ The inductances. 2 and ,4 _
are magnetically .coupledland'on'e ofthe induct- _ Ol
ances is movablysupportedto provide a variable.
coupling between.the»-inductances; aslwill ,later
`be shown and explained in detail.
In Fig.2 there is showna top plan view of the>`
the antenna isr connected to the first detector
stage and no intervening stage of tuned radio
frequency is employed. In such receivers an
insulating base. ï The .reference numeralsA indi
interfering signal at or near the frequency ¿to
Fig. 1 Awill be' applied tolike parts in Fig. Zand
Whichüthe intermediate frequency amplifier is
tuned will be transmitted directly through the
first detecto-r to the intermediate frequency am
plifier. Since 465 kilocycles has become almost a
standard tuning frequency for the intermediate
amplifier, the interference is usually code trans
20 mission from stations- handling ship to shore '
trañìc and operating on frequencies near 465
kilocycles. While filters according to the prior
art practice reduced the interference from a
particular station, the interfering signal was not
eliminated and the reproduction of a desired pro
gram suffered accordingly.
It is therefore one of the objects of this inven
tion to provide a ñlter circuit which shall be
more effective in blocking a given transmitted
frequency.
Another object is to provide a filter circuit
which may be included in the> receiver construc
component filter elements- as, arranged .onfan y
cating the diagrammatic showing of. the parts'in>>
the followingiigures.
Í
’
.«
-
~
The assembly'ismounted:upon a base .8 whichv
16'
may be a disk of any suitable insulatingmaterial ,_
such as one of the synthetic resins. lAttached`
to the base 8 by> means of.` mounting bolts 9 and
nuts l 0 is double alignment condenserofithetype
commonly used in intermediate frequency.k trans
former's. `The double ¿alignment condenserÍcomf ’
prises a vceramic base" I Iv upon V»which is mounted
compression-'type variable lcond'ens'ers - 3 `and`l5
which may beadjusted by the compression screws
I4 and I5 respectively. The condenserr 5 has
terminals I6 and I 'I which project upwardly
through slots in the ceramic base II, and the
condenser 3 has similarly arranged terminals
I8 and I9. A bow. spring 20 kof non-magnetic
material is secured to the ceramic base II byv
means of the mounting bolts 9 and extends trans
versely over the base II asbest seen in Fig. 3.
tion ormay bein the form of a separate unit.
Still another object is to provide a filter unit
A longitudinal slot is provided in the bow spring ' ' »y
which is more stable in construction and requires
form supporting the inductance 4. Secured by
less frequent adjustment.
_
A further object is to provide a filter unit which
is more compact in structure and economical in
assembly.
Other objects and advantages will in part be
40
specifically stated and in part be obvious when
the following specification is read in connection
with the drawings, in which:
Fig. 1 is a schematic diagram of the filter;
Fig. 2 is a top view'of the íilter assembly; Fig.,3
is a section taken on line 3-3'of Fig` 2; and Fig.
4 is a botom View of the filter assembly.
Referring in more detail to Fig. 1, the numeral
I indicates any suitable antenna. A series reso
50 nant circuit comprising an inductance 2 and a
variable condenser 3 is connected between the
antenna and ground. A parallel resonant circuit
comprising inductance 4 and variable condenser
5 is connected in series with the antenna I and to
55 the antenna post of a receiver 6. An electro
20 through which projects a tongue 2I on the coil'
a mounting bolt 9 and extending angularly from " .
the ceramic base II is a coil bracket 22 of sheet -
`metal which supports -the coil form 23 and in
ductance 2. The inductances 2 and 4 are each
universal wound and in two sections as illustrated 40
by the inductance 2 of Fig. 2.
`
In Fig. 3 is shown a cross section of the device
taken on line 3--3 of Fig. 2. The movable in
ductance >4 is adjusted bythe screw r2li which is
carried by a threaded opening inA the mounting
strip 25. A metal shell 26 having a mounting
bracket 2l is spun over and secured to the insu'
lating base disk 8.
-
Fig. 4 is a bottom View of the device showing
the condenser adjusting screws I4and I5 acces- Í
sible through >an opening in the base disk 8. The
mounting strip 25 is secured by the screws 9 and
extends transversely across the opening in the
disk 8, carrying the centrally located coil adjust
ing screw 24.
.
‘
`
'
55
'2,134,175
In the operation of the device, the series cir
cuit comprising inductance 2 and capacity 3
and the parallel circuit comprising inductance
4 and capacity 5 are both tuned approximately
to the interfering frequency which is to be elim
inated.~ Even though the circuits are tuned ex
actly to the undesired frequency, there will be a
residual voltage at this frequency due tothe radio
lfrequency resistance of the inductances 2 and 4.
By suitable regulation of the mutual coupling
between the inductances, the< residual voltage in
of said frequency differing in phase from the
residual voltage of said shunt impedance arm,
and means for establishing a mutual coupling
relation between said impedance arms, whereby
said residual voltages may be substantially elimi
nated.
2. In a filter circuit for the attenuation of a
predetermined frequency, a shunt impedance
arm comprising a series resonant circuit tuned to
said frequency'and having a residual Voltage of 10
said frequency across the terminals thereof, a
the respective circuits may be made to cancel out ’ series impedance arm comprising a parallel reso
nantcircuit tuned to said frequency and having
and the terminal voltage at the interferingfre
quency will be reduced to substantially Zero.l a residual ,voltage of said frequency differing
When the circuits are slightly off tune with the ’ in phase from the residual voltage of said shunt 15
’ interference, the voltage thereof. may still be re
duced to zero by the adjustment of coupling.
Inductances having a relatively ‘poor Ypower fac-'
tor may be employed in this present device and.
20 so reduce the expense of parts, whereas in the’
prior art devices their eifectiveness depended
upon the >reduction of the power factor to the
lowest possible values. In tests it has been
found that an interfering signal can be reduced
on' the order of 30:1 or slightly better by‘ the
proper> adjustment of coupling, over Ythe reduc
tion possible with the same circuitsv without the
. mutual coupling vbetween inductances.
It will be obvious that many uses and special
30 applications of the invention exist, other than
the particular one illustrated and described.
Likewise, many changes and` modifications may
be made in the invention by any one skilled in
the art without departing from ‘the spirit- and
" scope of the invention as set forth in the follow
ing claims:y '
V
I claim:
Y,
l. In a filter circuit for the attenuation of a
predetermined frequency, a shunt impedance
40
arm tuned to said frequency and having a re
sidual voltage; of saidfrequency across the terf
minals thereof,> a series impedance arm tuned
to said frequency and having a residual voltage
impedance arm, and means for establishing a
mutual coupling relation between said imped
ance arms, whereby said residual voltages may
be substantially eliminated.
3. In a ñlter circuit for the attenuation of a
predetermined frequency, a shunt impedance
arm tuned to said frequency and having a re
sidual voltage of said frequency across the ter
minals thereof, a series impedance _arm tuned
to said frequency and having a residual voltage 25
of said frequency differing in phase from the re
sidual Voltage of said shunt impedance arm, and
means for combining said residual voltages in
one of said impedance arms, whereby they may
be substantially eliminated.
30
4. In a filter circuit for the attenuation of a
predetermined frequency, a shunt impedance
arm tuned to said frequency and havinga re
sidual voltage of said frequency across the ter
minals thereof, a seriesimpedance arm tuned to 35
said frequency and having a residual voltage of
said frequency differing in phase from there
sidual Voltage of said shunt impedance arm, and
means for impressing upon theshunt impedance
arm the residual voltage existing across said 40
series impedance arm, whereby the residual volt
age may be substantially eliminated.
‘
_
LESLIE F. CURTIS.
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