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Патент USA US2104916

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Jan._l1, 1938.
J. EVANS
2,104,916 7
CONSTANT RADIO FREQUENCY GENERATOR
Filed Oct. 51, 1955
2 Sheets-Sheet l
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Jan. 11, 1938.
J, EVANS
2 l 0 4. 9, l 6
CONSTANT RADIO FREQUENCY GENERATOR
Filed Oct. 51, 1935
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$2.5.
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2 Sheets-Sheet 2
Patented Jan. 11, 1938
UNETED STATES
2,104,916
CONSTANT RADIO FREQUENCY GENERATOR
John. Evans, @ollingswcod, N. J., assigncr to Ita
dre Corporation of America, a corporation of
Delaware
Application October 31, 1935, C‘serial No. 47,563
20 Claims.
My invention relates broadly to radio trans
mitters. More particularly my invention deals
with a generator of constant radio frequency.
An increasing number of radio transm ters
5 has brought the requirement that each trans"
mitter maintain, within very close limits, its as~
signed frequency. Deviation from assigned fre
quencies causes interference and lessens the effi
ciency of communication. Transmitters oper~
31' ating on frequencies of the present day broad
cast range employ piezo~eleotric crystals for
stabilizing their frequency. Such piece-electric
control is not entirely satisfactory at frequencies
of the order of 25 megacycles and upward.
5*
I am aware of the use of resonant lines for con~
trolling the frequency of oscillators.
Resonant
lines of the order of one quarter wave length have
been used with and without temperature control
for stabilizing the frequency of vacuum tube
oscillators. The arrangement generally em“
ployed is to connect a resonant line to the input
of a thermionic tube. The output of the tube is
loaded with an inductive reactance.
In a circuit
of this type the effective input impedance de
,\ pends upon the ampli?cation .factor of the tube,
’ the output load, and other factors which may
vary and affect the constancy of the oscillatory
frequency. My invention embodies means for
minimizing these e?ects.
1].)
One of the objects of my invention is to gen
erate constant frequency oscillations.
Another object of my invention is to embody
in
circuit means for generating oscillations
whose frequency will be constant throughout a
wide range of operating temperatures.
A further object is to improve the efficiency of
a constant high frequency transmitter.
A still further object is in the embodiment of
my invention in circuits which employ novel
L) temperature compensating means.
‘
Additional objects will be apparent from the
accompanying specification, drawings and claims.
My invention may be best understood by refer
;,
ence to the accompanying drawings, in which
Figure I is a schematic diagram of a trans_
mitter circuit embodying my invention,
Fig. II is a view, partly in section, of a trans
mi
embodying my invention,
III is a schematic diagram of the cathode
.1; heater circuit used in Fig. II, and
IV H) a more detailed illustration. of the
thermionic tube shown in Fig. II.
In Fig. I, a thermionic tube 5 having cathode
3. grid 5, and anode l electrodes is connected as
5.; follows: The cathode is heated by any suitable
(Cl. Zoe-36)
source which is shown as a battery 9 but may be
a source of alternating current. The cathode is
by-passed by a capacitor ii. The grid electrode
connected to a suitable point on the inner
electrode it of a concentric quarter wave line
it.
This quarter wavelength is measured from
the open end. of electrode is to the cross piece
it. The inner electrode is connected to the outer
electrode i 'i of the concentric line by a conductive
member iii. The cathode 3 is connected to the
outer member by a grid leak resistor 2i which
preferably bypassed by a capacity 23.
The anode circuit consists of a battery 25, or
other suitable source of power, whose negative
terminal is connected to the cathode. The posi
tive terminal of the power source is connected
through a radio frequency choke coil 21 to the
anode electrode l. The anode battery may be
bypassed by a capacitor 29. An extension 3! of
the outer member of the concentric line houses 20
the anode load circuit. The extension end of the
outer member of the concentric line is closed by
a conductor 33. In this extension a pair of con
ductor elements til-32 are ?xed to the centers
of the conducting members Ill-33, which close .
the line. A pair of condenser armatures 38-41
are ?xed to the free ends of the pair conductor
elements. The outer member ll‘ and the pair of
inner conductor elements 35-31 form, in effect,
a toroidal inductor. This toroidal inductor and
condenser form the anode load circuit. The
tuned anode load circuit is connected to the
anode by a capacitor 53 between the anode elec
trode ‘I and one of the armatures 39. The outer
member is connected to the anode battery by a
capacitor 45.
While the theory of operation is substantially
that of a triode oscillator in which the frequency
is primarily determined by the constants of the
circuits, I shall describe certain differences which 40
contribute to the results I have obtained.
In an
ordinary tuned grids-tuned plate oscillator, the
coupling between the grid circuit and the plate
circuit is the capacity between grid and plate.
The feedback effects, through the grid to plate
capacity, required to sustain oscillations, are only
obtained in the proper phase when the plate cir
cuit load.
inductive. In this arrangement, the
effective input capacity is dependent upon. the
ampli?cation factor of the tube and the plate ciru
cuit load. Any change in either of these elements
affects the frequency of oscillation. Oscillators
of this type have notoriously poor frequency
regulation for the reasons set forth.
Feedback in the circuit of Fig. I is not entirely
2
2,104,916
dependent on the grid-anode capacity. The con
ductive member 29 is common to the grid and
anode circuits. This common conductive con
nection acts as a feedback coupling. With this
common coupling, the grid circuit may be tuned
to a. quarter wave length by a suitably propon
tioned line 55. The anode circuit is made res
onant to the fundamental frequency although
connected to a circuit equivalent to a half wave
length, and will feed back energy in the proper
phase to sustain oscillations. The grid and anode
circuits are therefore in the proper phasal rela
tion to insure maximum coupling. Since the
system will not generate oscillations when the
16 tuned anode load circuit offers a capacitive re
actance, I prefer to adjust the anode load cir
cuit slightly on the inductive side of resonance.
I prefer to avoid the use of mica insulation
in capacitors carrying the oscillatory energy as
mica has a deleterious effect on frequency sta
bility and power factor.
In the oscillatory cir
metallic bellows ‘H which permits the copper
tube 75 to expand with respect to the invar rod
T3. The variations in configuration of the bel
lows, and corona discharge from the end of the
inner electrode are neutralized by a corona shield
79, which surrounds the bellows. Since the outer
electrode 5? and its invar rods ‘H and the inner
electrode 75 and its invar rod '13 both expand the
relative spacing between the end plate of the con
centric quarter wave line 15 and the corona shield
will remain substantially constant thereby mini
mizing capacity changes.
The upper section 65 of the concentric line 5‘!
has within it a variable capacitor 8i which may
be arranged as follows: An invar rod 83 is se
i5
curely fastened to the dividing conductor H. A
copper armature plate 85 is fastened to the free
end of the invar rod. A copper tube 8'! surrounds
the invar rod 83. The copper tube is fastened
to the dividing conductor and is connected to the "o
armature by a metallic bellows 89. A similar
cuits of Fig. I extremely high efficiency is ob
invar rod 9!, copper tube 93, bellows 95, and ar
tained by the use of substantial copper conduc
tors and the avoidance of dielectric losses. The
mature 9‘.’ are arranged on the metal head mem
grid lead is connected to the optimum feedback
position in the grid circuit. I have further in
creased the efficiency of the oscillator by an effec
tive arrangement of short leads. The preferred
embodiment of my invention will be described
the head so as to provide adjustable means for ‘
more in detail in connection with Fig. II.
as the inner invar rods expand. The expansion
of the outer invar rods increases the spacing of
In Fig. II, a metallic end plate 5! is suitably
insulated from a grounded metallic base 53. The
end plate and the base form the armatures of a
bypass capacitor 55. An outer electrode 51 of
a concentric line is fastened to the end plate by
bolting, brazing, or the like. The opposite end
of the outer electrode is closed by a metal head
member 59. This head member may be secured
to the outer electrode 5‘! by bolting or any means
insuring a good mechanical and low resistance
electrical connection. Intermediate the ends of
the outer electrode is fastened a conductor 6|
which divides the outer electrode into two sec
tions 68,
Each of these sections preferably
includes an expansion joint El, 69. These ex
pansion joints may be formed by spinning one or
more concentric corrugations in each section of
the outer electrode. All of the parts thus far
described are preferably made of copper, al
though other metals may be used.
By way of example, for a transmitter operat
ing at a frequency of the order of 40 to 50 mega
cycles, the outer electrode consists of a copper
cylinder having a length of 75 inches, an inside
diameter of 12 inches, and a thickness of 14 inch.
A copper cylinder of this size will expand and
contract with temperature changes. Such
changes will alter the electric length of the cir
cuits and cause serious variations in frequency.
lib The effects of temperature changes may be min
imized by connecting the head and lower end
plates by several rods ‘ii of invar steel. Invar
steel has a very low coefficient of expansion.
The invar rods will limit the expansion of the
copper to the expansion joints and thereby sub
stantially maintain the electric length. At high
frequencies it is desirable to compensate for vari
ations in the length of the invar rods as will be
described below.
In the lower section 63 of the concentric line,
an invar steel rod '33 is fastened to the center of
the dividing conductor 6|. The invar rod is sur
rounded by a copper conductor tube 15 which is
also fastened to the dividing conductor 6|. The
free terminal of tie copper tube terminates in a
ber 59 but the rod and tube are threaded into
raising and lowering the upper armature with
respect to the lower armature for tuning the cir
cuit. In this section 65, as in the lower section
53, the outer electrode and its invar rods expand
the armature plates, but expansion of the inner
rods decreases the spacing. Thus the armature
spacing and resulting capacitance tends to re
main substantially constant.
The upper section 65 of the concentric line
forms, in effect, a toroidal inductor, the arma
ture plates 85-81 forms a capacitor 8| , the com
bination is a timed anode load circuit. It is
adjusted to be substantially equivalent elec- *
trically to a half wave length, or slightly less
than twice the wave length of the grid circuit,
as I prefer to keep slightly on the inductive side
of resonance. The tuned anode load circuit may
be coupled to an external circuit, such as a push
pull ampli?er. The coupling is preferably ar
ranged through two small capacitors 99--l0l.
Each armature of the tunable anode circuit may
also form an armature of the coupling capaci
tors. The other armatures l03—l05 of each of
these coupling capacitors 89—I0l. are circular
copper plates supported by suitable insulators
£81, 109 fastened to the dividing conductor El
and the head plate 59. The edges of the several
armature plates are rounded to avoid the effects
of corona discharge.
The circuit connections have been briefly de
scribed in connection with Fig. I. I shall here
point out certain features. The thermionic tube
H! is supported by brackets not shown. These 60
brackets may be fastened to the outer electrode
of the concentric line. The tube may be ofv the
water cooled type. The water jacket is supplied
by cooling water fed through an insulated hose
H5. The anode electrode III, which is also the
water jacket, is connected to the anode supply
through a radio frequency choke I IS. A by-pass
condenser IN is connected between the choke
and the outer electrode. The exposed anode I I1
is coupled to the tuned anode load circuit by a
coupling capacitor [23. This coupling capacitor
is comprised of the anode itself and a copper
band I25 which surrounds the anode H7, but is
insulated therefrom. The copper band I25 is
connected directly to the circumference of the
2,104,916
lower armature plate by a conductor IZ'I. This
connection is made through a suitable ori?ce I29
in the outer electrode.
The grid electrode of the thermionic tube is
connected by a conductor I3I directly to an ap
propriate point on the inner electrode of the con
centric quarter wave line. The ?lament or
cathode of. the tube is energized by a special
means I33 which will be described in connection
10 with Fig. III. The grid leak resistor I35 is con
nected from the lower end plate 5I to the
grounded base 53. The grid leak path may in
clude an ammeter I31 for adjusting purposes.
The grid resistor I35 is by-passed by the capaci
tor 55 formed by the end plate and‘ the grounded
base.
In certain cases I have found that the electric
length of the grid-cathode path may be such as
. to include reactances which prevent the genera
tion of high frequency oscillations. This effect
may be eliminated by virtually grounding the
cathode. The method and means for virtually
grounding an electrode is disclosed in copending
application Serial No. 41,540, ?led by John Evans
on September 21, 1935 entitled Ultra high fre
quency oscillator and assigned to the same as
signee as the present application. In Fig. III, a
transformer primary 20I is connected to a source
of alternating current 203. The secondary 205
of the transformer is connected to an adjustable
inductor 201 which is hollow. Within the in
ductor is an insulated wire 209. The heating
currents for the ?lament 2“ are carried by the
hollow inductor 201 and inner connecting wire
239 which are connected to the ?lament 2“.
The ?lament is by-passed by a capacitor 2l3.
The outer inductor is connected to ground by a
capacitor 2I5. The inductor is adjusted so that
its effective length or inductance will resonate
with the grid cathode capacitance and form a
circuit of very low impedance at the lower or
parasitic frequencies. At frequencies other than
the resonant frequency the shunt impedance of
the grid cathode circuit will be relatively low.
This arrangement virtually grounds the cathode.
Similar results may be obtained by tuning the
inductor with a capacitor.
The thermionic tube proper is shown in Fig.
IV. This tube may be an RCA Type 846, or the
like. Tubes of this type are water cooled. The
connections 2I1 to the water source are through
electrically insulated hose connections II5 to
avoid grounding the exposed anode. The grid
'
tion of different materials, copper or silver plat
ing and the like, .and physical arrangements,
within the scope of my invention will occur to
those skilled in the art. I do not limit my in
vention to the precise devices shown and de
scribed, but intend to only limit same as required
by the prior art and appended claims.
I claim as my invention:—
1. An oscillation generator comprising an ain
pli?er having input and output terminals, 2. con
centric line whose effective length is substan
tially equal to one-quarter of the fundamental
wave connected to said input terminals, a tunable
circuit connected to said output terminals includ
ing a concentric line whose electrical length is
substantially half the length of the fundamental
wave, means for compensating for the effects of
temperature changes in said quarter wave line.
and means for compensating for the effects of
temperature changes in said tunable circuit,
whereby there is obtained in said tunable circuit
oscillations of a constant frequency correspond
ing to the frequency of the fundamental wave.
2. A generator of high frequency oscillations
comprising a thermionic tube having input and “
output terminals, a concentric line whose effec
tive length is substantially one~quarter of the
fundamental wave connected to said input ter
minals, a tuned circuit whose electrical length
is substantially hall the length of the funda 30
mental wave connected to said output terminals
and including a hollow inductor and a capacitor
located within said inductor, means for compen
sating temperature changes in said quarter wave
line, and means for compensating temperature
changes in said tuned circuit, whereby there is
obtained in said tunable circuit oscillations of
a constant frequency corresponding to the fre~
quency of the fundamental wave.
3. An oscillation generator comprising a therm
ionic tube having an input and an output cir
cuit; a concentric line having two sections, one
of said sections including a line whose length is
substantially one-quarter of the fundamental
wave connected to said input circuit, the other
of said sections including a circuit whose elec
trical length. is substantially one-half of the
length of the fundamental wave and connected
to said output circuit; and means for compen
sating for the e?ects of temperature changes in i
the two sections of said line, whereby there is
obtained in said tunable circuit oscillations of
a constant frequency corresponding to the fre
quency of the fundamental. wave.
4. An oscillation generator comprising a therm- '
terminal 2!!! is shown as projecting toward the
right.
The ?lament connections 22I extend be
low the tube. The lower section 223 of. the tube
is class. The glass is welded to the copper anode
which also acts as the water jacket. The anode
ionic tube having grid, cathode, and anode elec
coupling capacitor I23 is formed by the anode
length is substantially one-quarter of the funda
II‘.’ and the spaced copper band I25. The band
supported by a suitable insulator which is not
shown.
I have described a high frequency generator.
The tuned circuits of this generator are arranged
mental wave connected to said grid. and cathode
electrodes, the other of said sections including a
tunable circuit whose electrical length is sub~
‘ within concentric lines.
Temperature compen
sation means are included whereby the electrical
length remains substantially constant. The fre—
quency of oscillation is very constant. In actual
experiments. I have found a constancy of fre
quency exceeding a piezo-electric element and
the required frequency multipliers. In the em
bodiment shown the leads are very short.
Several kilowatts of power may be handled in a
single generator embodying my invention.
Various modi?cations, such as, the substitu
‘
trodes: a hollow member having two sections, one
of said sections including a concentric line whose
stantially half the fundamental wave and cou
pled to said cathode and anode electrodes; and
means for compensating for changes in the elec
trical length of said sections, whereby there is
obtained in said tunable circuit oscillations of a
constant frequency corresponding to the fre
quency of the fundamental wave.
5. In a device of the character of claim 4, means To
for making the grid-cathode circuit a path of
low impedance for parasitic frequencies.
6. In a device of the character described a pair
of circuits included within a concentric line, one
of said circuits comprising a quarter wave line
,....
Ir)
4
2,104,916
having means for compensating for the e?ects
caused by variations in temperature, and the
other of said circuits comprising a tunable cir
cuit whose electrical length corresponds to sub
stantially one-half the fundamental wavelength
and having means for compensating for the ef
fects caused by variations in temperature, where
by there is obtained in said tunable circuit oscil
lations of a constant frequency corresponding to
the frequency of the fundamental wave.
'7. In a device of the character described, a pair
of circuits included within a. concentric line. one
of said circuits comprising a line whose effec
tive length is substantially one-ouarter of the
fundamental wave having means for compensat
ing for the e?ects caused by variations in tem
perature. the other of said circuits having an
electrical length corresponding to substantially
half the fundamental wave length. and having
means for compensating for the effects caused
by variations in temperature, a thermionic tube,
and means coupling said thermionic tube to said
circuits so that oscillations of high and constant
frequency corresponding to the frequency of the
k. Cl fundamental wave are generated.
8. A high frequency generator comprising a
Water cooled thermionic tube havin‘T a grid, cath
ode, and exposed anode. a concentric quarter
wave line connected to said grid and. cathode.
a tunable circuit whose electrical length is sub—
stantially half the fundamental wave length cou~
pled to said anode by a capacitance formed by
said anode and an armature insulated therefrom,
and means for transferring high frequency en~
ergy from said tunable circuit to an external cir
cult.
9. In a device of the character of claim 8,
means for compensating for the effects of tem
perature changes which tend to vary the elec
40 trical lengths of said circuits.
15. A concentric line resonator comprising an
outer hollow conductor and an inner hollow c0n~
ductor, means for mechanically connecting to
gether said conductors at one of their adjacent
ends, a rod having a low temperature coe?icient
of expansion within and extending substantially
the entire length of said inner conductor and
mechanically connected to said means at said
one end of said conductors, a metallic shield sur
rounding a portion of and extending beyond the 10
other end of said inner conductor and connected
to said rod, and an expansible metal bellows
located within said shield and connected at one
end to said shield and at its other end to said
inner conductor.
16. A tuned resonator comprising a pair of
inner and outer conductors coupled together
more closely at one of th lr adjacent ends than
at their other ends, an expansible metallic bel
lows attached to and extending beyond said other ‘
end of said inner conductor, and a metallic shield
surrounding said bellows and a portion of said
inner conductor, said shield being also connected
to said bellows.
17. A concentric line resonator having an inner
and an outer conductor, said outer conductor
having an expansion joint intermediate its ends,
and a plurality of rods of low temperatin‘e coe?i
cient of expansion extending parallel to the length
of said outer conductor
securely fastened to
both ends of said outer conductor for maintain
ing the length of said outer conductor substan
tially constant.
18. A concentric line resonator having an inner
and an outer conductor, said outer conductor '
having an expansion joint in the length thereof,
electrodes, a hollow tube closed at both ends
and formed into two sections by a transverse
and two rods of low temperature coe?icient of
expansion extending parallel to the length of
said outer conductor, located on substantially op
posite sides of said outer conductor and securely
fastened to both ends of said outer conductor
for maintaining the length of said outer conduc
tor substantially constant.
19. An ultra high frequency oscillatory circuit
conductor intermediate sai _ ends, an expansion
comprising a substantially enc
joint in each of said sections, rods having a low
coefficient of expansion linking Sold ends to limit
the expansion of said tube, a rod having the
same coef?cient of expansion as the aforemen
tioned rods secured within one of said sections
and forming therein a quarter wave length line,
face of revolution,
capacitor comprising two
separated plates wihin said enclosed surface of
revolution, a metallic supporting rod devoid of
10. A high frequency transmitter comprising
a thermionic tube having grid, cathode an ' anode
a pair of rods of the same coefficient of expan
sion as the aforementioned rods for supporting
armatures within the other of said sections and
forming with said armatures a circuit electri
cally equivalent to a half wave length line, means
coupling said quarter Wave length line to said
grid and cathode, and means coupling said elec
trically equivalent half wave length line to said
anode and cathode.
11. A device or" the character of claim 10 fur
ther characterized by a conductive coupling e?ec
tively located between said lines.
12. In a device of the ‘character of claim 10,
65 means located at the end of said quarter wave
line for minimizing corona discharge from said
quarter wave line.
13. In a device of the character of claim 10,
copper rods surrounding the tubes positioned
within said line and connected
expansion bel~
lows to free ends of said rods.
14. In a device of the character of claim 10,
means for virtually grounding said cathode elec
trode.
Lil)
ed metallic sur
concentrated reaotanoe directly connect i
vf said plates to said surface, said rods forming ,
an inductance which, taken toeether with said
capacitor, comprise the oscillatory circuit, the
adjacent ends of said rods being separated sub
stantially by the distance between said plates,
and leads capacitively coupled to said plates and
extending externally of said surface of revolu
tion.
20. An ultra high frequency oscillatory circuit
comprising a substantially e
losed metallic sur~
face of revolution, a capacitor omprlsing two (50
separated plates within sai'i enclosed surface of
revolution, a hollow metallic supporting rod de~
void of concentrated reactance connecting each
of said plates to said surface,
expansible metal
bellows between each plate and its supporting iii
rod, and a rod of low temperature coeflicient
of expansion located within each sup_ ting~ rod
and mechanically
said surface of
linked
revolution,
to its associated
....d supporting
rods forming an inductance which, taken to
gether with said capacitor, comprise the oscilla
tory circuit.
JOHN EVANS.
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