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Патент USA US2404541

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July 23, 1946.
2,404,541
D. H. SLOAN' '
METHOD OF GENERATING HIGH FREQUENCY OSCILLA‘I‘IONSv
Original Filed Nov. 4, 1940
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Original Filed Nov. 4, 1940
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Patented July 23, 1946
2,404,541
UNITED STATES PATENT OFFICE
2,404,541
METHOD OF GENERATING HIGH
FREQUENCY OSCILLATIONS
David H. Sloan, Berkeley, Calif., assignor to Re
search Corporation, New York, N. Y., a corpo
ration of New York
Original application November 4, 1940, Serial No.
364,284. Divided and this application June 9,
1941, Serial No. 397,233
10 Claims. (01. 250—36)
1
2
This invention relates to electronic tubes, and
particularly to tubes adapted for the production
and modulation of ultra-high frequency oscilla
relative radio-frequency resistance‘ of highlim- ~
tions, i. e., oscillations of frequencies of the order
of 1,000 megacycles. This application is a di
of control voltages; fourth, ?xed relationship be
tween the various elements, irrespective of ‘tem
perature or ordinary shock, so that the frequency‘
vision of my prior application Serial No. 364,284,
?led November 4, 1940.
The progress of electronic and radio develop
ment since the inception of the art has been
marked by two steady advances. One of these ad
vances has been toward higher power, the other
toward higher frequencies. The latter line of ad
vancement has been, to a certain extent at least,
pedance, so that excessive energy will not be re
quired to swing them through the necessary range >
to which the device as a whole is tuned will not be ~
affected by relative changes of position; ?fth, '
minimum undesired or “incidental” radiation >
from the various elements of the tube and its aux
iliaries; sixth, a minimum of insulating material ‘ '
subjected to high-frequency ?elds. To these may
be added the secondary requirements of demount_ '
incompatible with the ?rst, since with increasing
ability for replacement of ?laments; facility in
frequency the effect of interelectrode capacity has 15 water cooling and avoidance of hot spots, and case 7
become greater and more troublesome. Neverth
less, up to the last few years, the diihculties have
been met by a steady evolutionary process consist
ing in large degree of re?nement in detail, which
of tuning.
From the conventional approach these require-
7
ments are incompatible to a large degree. A high‘
degree of control requires close spacing of cath
has enabled the vacuum tube art to keep pace 20 ode and grid, which leads to high inter-electrode '
with the increasingly rigid demands of the manu
capacity. Rigid structure ordinarily means mas; _
facturers and operators of transmitting and re
sive structure, which again leads to high inter
ceiving apparatus.
electrode capacity. Water cooling systems tend to
The attempt within recent years to carry the
form effective antennae, leading to large "stray
useful spectrum into the range of wavelengths in 25 power radiation. The broad'purpose of my inven
the range of a meter and less has involved di?‘i
tion is therefore to reconcile these and other ap
culties of a new order of magnitude.
parent incompatibles.
For one
thing, the frequencies involved are so high that
the transit time of an electron stream across the
interelectrode spaces of the tubes becomes an ap
preciable fraction of a cycle. For another, even
with connecting leads reduced to minimum
lengths, their inductance has been su?icient so
/
Pursuant to this general purpose, among the
objects of this invention are: To provide a' tube‘
30 which is capable of producing many kilowatts of'
power at extremely high frequencies; to produce '
a high frequency generator of great frequency
stability; to produce a high frequency ampli?er‘
and oscillator tube of relatively high e?iciency,
and particularly to produce such a tube wherein‘
that the capacities required in tuning them to the
desired frequencies are small in comparison with
the interelectrode capacities in conventional tum
the losses due to undesired radiation from the ~
tube itself are reduced to negligible proportions; ,
structures and these capacities have therefore be
come not merely a nuisance, limiting the efficiency
to produce a high frequency oscillator and am
of operation, but frequently an absolute bar to
pli?er which may be tuned to operate at any de
such operation; so much so, in fact, that it has 40 sired frequency throughout a reasonably‘ wide"
range; to provide a high frequency oscillator and
been only with tubes of very small size and conse
quent small power output that operation has been
ampli?er which may be constructed with thehigh'
obtainable at all.
degree of accuracy required to meet the close tol- '
erances demanded by the frequency of operation
There therefore exists at the present time a
need for a tube which will meet the severe re
and to maintain those tolerances under the
quirements of producing large power outputs by
changes of temperature produced by such‘ opera- '
generation or ampli?cation at extremely high fre
tion; to provide an electronic tube of the charac
quencies. These requirements are ?rst, a cath
ter described which may be fully ?uid cooled and
ode-grid structure which will effectively modulate
wherein the cooling system does. not introduce
material parasitic radiation of radio-frequency
an electron stream without the application of ex- '
cessive control voltages; second, a cathode-grid
power; to provide a high power oscillator and am
pli?er tube which is readily demountable: for re
structure whose capacity and inductance rela
tionships are so proportioned that they may be
placement of ?laments; to provide means ofv den
sity-modulating an electron stream at ultra-high
tuned to the high operating frequencies desired;
frequencies, in order to produce extremely short
third, a structure lending itself to circuits of low
2,404,541
3
4
bursts of electron emission occurring at the peaks
mounting the cathode in the region of sharpest
of the oscillation and of substantially uniform
velocity, whereby the conversion of energy into
high frequency power occurs at high efficiency;
to provide a-type of structure for high frequency
electronic. tubes which. is of great ?exibility, and
such a structure is to form the grid of pairs of
cylindrical surfaces whose axes are parallel to
the plane of the anode, and to make the cathode
as. a ?lament or strip having a flat or slightly
curvature.
One of the best ways of obtaining
concave face lying between the cylindrical sur
faces of the grid. This results in the lines of
force from accelerator or anode normally termi
nating in the grid structure, none of them reach
and effective method of tuning apparatus of‘the
ing' the cathode, from which emission is there
character described; and to provide a type of elec
fore normally suppressed. A few volts relative
trode support for high frequency electronic de
change. in. potential. of the cathode, as referred
vices which is massive and rugged; andwhich, at
to either accelerator‘ or control grid, results in
the same time, does not introduce interelectrode
capacities which either severely limit. the fre 15 some of the lines of force from the accelerator
terminating in the cathode surface, which is
quencies upon which the deviceis operative or the
accordingly subjected to an extremely powerful
power which may be developed at such frequen
field causing very large emission to the anode.
cies.
The result is what may be termed an “explosive”
My invention possesses numerous other'obje'cts
type of emission, giving electron bursts of high
and features of advantage, some of which, to
density for very short. periods. at the peaks of
gether- with theforegoing, will be set forth in the
the cycles. It will be evident that this structure
following‘ description. of. speci?c apparatus em.
results ina relatively high capacity as between
bodying‘ and utilizing my novel. method. It is
cathode and. grid, but the tuned transmission:
therefore to be understood that‘my method is ap
plicable to other apparatus, and that 1. do not 25 line support enables this capacity to be effectively
resonated with an inductance as smallas may be
limit myself, in any way, to the apparatus of the
desired and still form a sharply tuned, high‘ Q
present application, as I may adopt various other
circuit whose high resonant input impedance may
apparatus embodiments, utilizing the method,
appear as resistive, capacitive or inductive as the
within the scope of the appended claims.
conditions of operation may require.
The tube of my invention involves two basic
Referring to the drawings:
concepts. The first of these. comprises forming
Fig. 1 is a longitudinalsection through a high
electrode supports of‘ sturdy coaxial metallic cyl
frequency oscillator tube. embodying my inven
indersiwhich constitute a radio-frequency trans
tion, the particular tube. illustrated employing a
mission line of at least one and preferably a plu
which will, because of such ?exibility, permit the
construction of tubes exactly adapted to a large
variety of powers and services; to provide a novel
rality of quarter wave-length electrical links, with
impedance irregularities at or near certain of the
quarter wave points, the electrodes themselves
forming a portion of these transmission. lines as
considered‘ electrically. Means are preferably
provided‘ for varying the‘ position of the imped
.. radial arrangement of. ?laments and grids.
Fig. 2 is a transverse section of the tube of Fig.
1, showing the-multiple coaxialgrid-?lament sup
ports, and water connections for cooling the ?la
ment mounting, the plane of section being on the
40 line 2—-2 of Fig. 1.
Fig. 3 is a transverse sectionthroughthe anode
structure of the tube, the plane of section being
indicated by the line 3-3 of Fig. 1.
Fig. 4 is an enlarged. detailed view illustrating
teristic impedances of the quarter-wave sections
water-cooling
connections from the exterior of
and their terminating impedan‘ces, it is‘possible 45
thetube to the ?lament mounting.
to‘ make the: radio-frequency impedance of the
Fig. 5 is a schematic sectional view through
supports as viewed from the electrodes themselves
?laments, control grid, accelerating grid, bound
extremely high, so that they overall effect. is- al
ary grid, and anode of the tube.
most: as though‘ the electrode capacities together
Fig. 6 is a sectional view through the. grid
with the: inductances required to resonate them
ance irregularities to provide exact tuning; but
this is not essential since, as will hereafter be
shown, by a proper‘ combination of the charac
were supported freely in‘ the- space‘within' an un
broken metallic shield This latter feature is se
cured‘ by providing multiple coaxial line sections
support line, showing the radio-frequency by
pass between accelerating and boundary grids
and the tuning mechanismfor isolating. the con.
forming'branch‘ pathsof greatly different imped
trol grid and water cooling, the same.
the’ grid opposed to‘ an anode or other accelerat
ing' electrode in such manner as to produce an
anode.
Fig. 14 is a fragmentary section of'the- anode,
Fig. '7 is. anenlarged detail showing the method
an‘ce, certain of these paths acting as Icy-passes 55
of insulating certainof the. supporting. rings upon
0f negligible impedance at points where it is nec
which the coaxial electrodeelements are carried.
essary that some' circulating currents should flow,
Fig. 8 is a section taken atrightlangles. to the
although D.-C. insulation must be maintained,
view- of Fig. l, andshowing the‘anode-supporting,
whileat the same time maintaining the high‘ im
pedance desired in other paths which would oth 60 cooling, and tuning system.
Fig. 9- is a perspective View of the accelerator
erwise lead to radiation. By placing these by
grid.
pass sections at current nodes, the FR losses
Fig. 10 is an elevation of the control-grid-struc
therein'may be made too small to‘need considera
ture.
tion.
Fig. 11 is a sectional view, taken on the plane
The second fundamental concept comprises 65
between the ?lament and grid structures, and
mounting on the ends of such supports, prefer
showing in detail the ?lament support.
ably in biaxially symmetrical con?guration, one
Fig. 12 is a‘ fragmentary axial‘. section taken on
or a; plurality of cathode=grid combinations which
the line l2—l2' of Fig. 1.1.
act, as before stated, as thetermini of the trans
Fig. 13‘ is anv elevation. of the active face of the
mission lines formed by the supports; mounting 70
the plane of section being’ indicated by the‘line
|a'_r4 in the preceding ?gure.
in the immediate neighborhood of the grid‘; and 75 Fig‘. 15 is an. elevation of the boundary grid;
electrostatic field between grid and accelerator
which comprises‘ lines of force very sharply curved
2,404,541
5
6
Fig. 16 is a sectional view taken on the line
internal recess or counterbore in an annular grid
Iii-l6 of Fig. 15, and showing a portion of the
anode in elevation.
Fig. 17 is an elevation of one of the ?laments.
Fig. 18 shows a modi?ed form of coaxial line
structure for grid-?lament support in a tube gen
erally similar to Fig. 1, but adapted for use either
?ange 3, clamping a boundary grid 4 between the
as an ampli?er or an oscillator with inductive
feed-back.
Figs. 19, 20 and 21 are sectional views through
the tube of Fig. 18, taken on the lines numbered
in accordance with the ?gures.
Fig. 22 is a longitudinal section through a tube
built in accordance with this invention but where
in a cylindrical, rather than a radial ?lament
grid and anode arrangement is used.
Figs. 23, 24 and 25 are transverse sections
through the tube of Fig. 22, taken on the lines
housing tube 2 and the ?ange 3. A rabbet on the
outer periphery of the ?ange 3 receives one end
of a main support cylinder 5, whose other end
terminates in another annular ?ange ‘I. All of
the parts thus far mentioned are of metal, and
I have found it convenient to make the ?anges of
steel, and the tube 5 also of seamless steel tubing,
while the ‘cylinder 2 may be either chromium or
copper plated steel or solid copper, with copper
preferred since it forms a portion of a resonating
circuit. Carrying on from the ?ange l is a glass
or “Pyrex” cylinder 2 which abuts a terminal
?ange I0.
‘
.
As has been mentioned already, the device as
whole is fully demountable. The ends of the tubes ‘
contact the ?anges with smooth machine ?t's.
The. joints thus formed are sealed by applying
Figs. 26 and 2'7 are detailed views indicating‘ 20 thereto ordinary wide elastic .bands as indicated
the tuning mechanism for the tube of Fig. 22.
by the reference characters I I , these bands being
indicated by the respective numerals.
Fig. 28 is a longitudinal section on a larger
smeared before-application with a small amount
scale through the ?lament support of the tube
of Fig. 22.
of vacuum line stop-cock grease.
Fig. 29 is a transverse section through the sup
porting columns of the tube of Fig. 22, showing
the construction of the centering mechanism, the
plane of section being indicated by the line 29-—29
of Fig. 28.
the structure thus far described with the excep- ,
as, in fact, are all of those herein described al
type of structure here shown is that the ‘ability of '
' '
It may be pointed out at this time that all or
tion of the terminal ?ange It is at D.-C. ground
potential, and as will later be shown in detail that ' '
the'entire exterior structure is substantially at
radio-frequency ground. This means thatthe
Fig. 30 is a sectional view taken on the line 30 insulating section ‘formed by the cylinder 91'is not
30-30 of Fig. 22.
subjected to R.-F. ?elds. It also renders easy the
Fig. 31 is a fragmentary section taken on the
support of the device by any desired ‘external
line 3l—3l of the preceding ?gure, showing the
means, Part of such support may be the connec-'v
passage of the cooling pipe past the anode and
tion to the pump, which is by a pipe l2 of rela
between the two sections of the ?lament support. 35 tively large interior diameter, welded or other
Fig. 32 is an impedance diagram for an open
wise secured'into the, bottom'of the anode hous-.
ended, half-wave length section of transmission
ing 2. This pipe is not ‘shown in Fig. 1, butis
line.
clearly visible at the bottom of Fig. 8.
.
In the ensuing speci?cation the invention will
The various elements which contribute to the
?rst be described in its various aspects as applied 4:0 electronic action of the tube are mounted‘ within
to an oscillator tube of moderate power (i. e.,
the envelope thus formed on columnar supports‘
approximately 10 kw. peak output at 20 to 40
each of which has transmission ‘line character- '
centimeters Wavelength). Following this there
istics designed to meet its particular‘ function.‘
will be described two modi?cations illustrating
These elements are shown in schematic arrange~'
respectively the application of the principles of 45 ment in Fig. 5, and comprise an anode 13, a
my invention to a similar tube adapted for am
boundary grid 4, an accelerating grid £5, a con
pli?cation or for generation of oscillations by
trol grid l6,'and a ?lamentary cathode l1.
_
inductive feed-back, and to a somewhat higher
s Fig. 5 is drawn to a greatly enlarged scale and
output device showing the principles as applied to
shows a fragmentary section of the'elements 00
a tube constructed with cylindrical rather than 50 operating with a single ?lamentary cathode. ‘ In
radial arrangement of electrodes.
the tube here shown'six such cathodes are used
The tube shown in longitudinal section in Fig.
and the portions shown of the other elements are”
1 is of the demountable, constantly pumped type,
repeated for each cathode. One advantage of the ‘
though the principles involved are not limited for 55 the tube to supply power output varies almost' "
use in such tubes. From the structural point of
directly as the number of ?laments used, and that
view the tube comprises a series of ?anges con
the changes required to add additional filaments
nected by sections of tubing and held together in
are relatively minor. ‘Tubes have been designed
compression. From a practical point of view it
conforming substantially to the structure here
is advantageous to have the ?anges pierced for 60 shown with as high as twenty-four ?laments,
and held by circumferential bolts to hold the
each with its attendant grid-anode structure, but
parts ?rmly in position when the tube is not un
since each of these assemblies is merely the dupli
der vacuum, but when in use the external air
cate of the others as far as performance'is con,~
pressure tends to hold the entire device together,
cerned it'is 'su?icient for the present to consider .
and the tube has actually been operated without
one only.
Considering, therefore, the 'portio-n'of the ele-.'
the retaining bolts, these have therefore been
omitted in the drawings since they add a further
ments shown in Fig. 5, the anode i3, preferably 1
complexity of detail to an already complex struc
ture.
operated at the maximum potential'of the system,‘
made of high conductivity oxygen-free copper, is:
Considering for the moment, therefore, only 70 say 10 to 50 thousand volts positive. It is pro
the external structure which forms the housing
and which supports the remainder of the equip
ment, the tube comprises an anode housing ?ange
I which is grooved to receive tightly the end of a
tubular anode housing 2.
This housing ?ts an -
vided with a V-shaped- groove 20 with'its axis‘
parallel to the axis of the ?lament.‘ Next; pro‘
' ceeding toward the ?lament, is the boundary grid
4, which is also preferably made of oxygen-free ‘
copper. This is provided withan aperturelsur
2,404,541
?
8
rounded by a collar 2| in accurate alinement with
the groove 23 in the anode. Next in line is the
accelerator grid It, with an aperture 22 which
grid is so adjusted that emission can occur only
for an instant at the cycle peaks, and cut-off
may occur even before the ?rst electrons emitted
have traversed the space charge region. Fur
thermore, While in this region there is a maxi
mum difference of velocity as between electrons,
is somewhat narrower than the opening in the
boundary grid, and which is operated at a poten
tial above the cathode of from 5 to 20 thousand
volts. All potentials mentioned are illustrative
and relative only, since the actual values used
will depend upon the size, power output and op
both by reason of differing initial velocities of
emission and, more important, by reason of dif
fering acceleration due both to phase of emission
erating frequency of the device. Furthermore, 10 and ?eld strength at various parts of the cathode
modi?cations in design are possible whereby the
surface.
The important point is that because the region
functions of certain of the grids are combined,
other electrodes are operated at ground potential,
is so shallow all of the electrons emitted do get
through it before the cycle has advanced too far,
etc. Such modi?cations will be considered later;
the purpose here is to show the application of the 15 and, having traversed it, fall into the region of
high potential gradient where acceleration to~
principles of my invention to the present tube.
ward the anode is very great; space charge ef
The most important portion of the combina
tion is the arrangement of the cathode-grid
feet is of no further moment, and they receive
so large a portion of their ?nal velocity that their
structure. The important features here are ?rst,
differences of velocity in the initial region are
that the control-grid elements comprise parallel
immaterial.
cylindrical surfaces, curved as they are present—
It should be realized that while space-charge
ed to the ?lament. In the present case they are
effect prevents some emission and decreases the
acceleration of electrons emitted, it will not drive
plate without affecting their performance. Be 25 those which have been emitted back to the cath
ode nor prevent their reaching the anode. It
tween these surfaces, and slightly back of the
follows that the space-charge region may be con
plane of their centers of curvature, lies the ?la
rods or wires, but they could be cylindrical sur
faces formed as the edges of a slot in a ?at
ment, which has a ?at or preferably a slightly
sidered as a reservoir for emitted electrons. With
hollow ground face presented to the anode. It
conventional grid-cathode structures it is rel
is convenient to operate the ?lament at ground
atively deep, so that, at the frequencies and
potential (disregarding for the moment the slight
powers at which this tube is intended to oper
ate, transit therethrough occupies a major por
voltage drop along the ?lament) and, for the
powers here considered, to operate the grid [6
tion of the cycle, and with the varying velocities
at 200 to 500 volts negative.
obtaining while in this region the electrons
It will be seen that at the orders of voltages 35 straggle through to reach the anode in such
given the major ?elds are from the accelerator
varying phases that the density modulation of
grid 15 to the control grid. As is well known.
the stream is almost if not entirely lost.
the lines of force constituting such a ?eld termi
With the arrangement of my invention, how
nate at right angles to the surfaces of the ?eld
ever, the space-charge region is so shallow that
de?ning electrodes. It follows that in the region 40 even the stragglers among the emitted electrons
adjacent the cathode the lines of force emerge
traverse it in less than a quarter cycle and in
from the grid wires in the general direction of
stead of the density modulation of the electrons
the cathode and then curve very sharply to
being lost they reach the anode in bursts of such
ward the anode in a direction nearly at right
power and suddenness and with such close ve
angles to their direction of emergence. There is
locity grouping that I have termed cathode-grid
also a fairly strong ?eld between the control
combinations of this type “explosive.” The ob
grid and the cathode itself, which is superim
ject of the design is to make the electron reser
posed locally upon the ?eld between the control
voir constituted by the space-charge region as
grid and accelerator grid, and is directed toward,
shallow as possible, and in practice the ideal can
instead of away from the cathode. As a result 60 be so far realized as to permit density modula
of the interaction of these two ?elds none of the
tion of electron streams at frequencies in the
lines of force from the accelerator-grid normally
terminate upon the surface of the cathode.
Emission has therefore no tendency to leave the
latter, since the space adjacent it is nearly neu
tral, with such weak ?eld as exists therein di
rected toward the cathode.
As is the case with any grid-controlled tube
range of 1,500 megacycles, where in the past it
has been necessary to use velocity modulation,
involving larger and more complicated struc
tures, to get reasonably effective results, even in
smaller sizes and at much lower powers than
those here contemplated.
When the tube here shown is used as an OS
cillator in the manner now to be described, the
positive some of the lines of force from the ac (50 various potentials are so arranged and propor
celerator-grid which formerly terminated on the
tioned that the transit time of the burst of elec
control grid now terminate on the cathode, and
trons is substantially one-half cycle. The anode
as the cycle progresses the cathode-control grid
I3 is in a tuned circuit, as is also the grid IS.
?eld weakens or even reverses, permitting emis
The condition of oscillation then is that the po
sion toward the anode, and a space charge builds
tentials of the anode and the grid swing in the
up in the region immediately in front of the
same sense, so that the grid reaches its peak of
cathode face which has the usual effect of lim
positive potential at the same instant as does
iting emission. The distinguishing feature here
the anode.
is that the region where the ?eld is weak enough
One of the results of the conformation of the
to permit such space charge effect is very shal~
electrostatic ?elds is a strong focusing action
low, so that even with the low velocities impart
upon the electron bursts, and these bursts accord
ed to them by such relatively weak ?eld the elec
ingly fall upon an extremely limited portion of
trons can and do traverse it in a reasonably small
the anode surface, substantially none reaching
fraction of a cycle.
either of the intermediate grids. The anode area
operated through cut-off, when the grid swings
The biasing potential between cathode and 76 upon which the electron bursts impinge is that
2,404,541
9
10
included in the V-shaped slot 20. The reason for
this arrangement is to spread the area of impact
At its upper end it is threaded to receive a grid- support ring 21, whichis clamped between locking nuts 29 and 30, and an additional locking screw
and so increase the size and decrease the in
tensity of maximum local heating, while increas
ing the cross-sectional area of thermal conduc
tivity by which cooling occurs, and also to insure
that secondary electrons are not projected into
regions of high ?eld intensity which would ac
celerate them so that they, in turn, would cause
serious heating effects.
It has already been stated that the transit time
of the electron burst is one-half cycle of oscilla
tion, and it follows that immediately after the
electron burst has occurred the anode has started
3| (Fig. 10) is also provided for further security.
The pairs of parallel grid wires I6 project from
the ring 21 parallel to its radii, six pairs of grid
wires being provided in the present‘design, the
pairs being equidistantly spaced around the
periphery of the ring.
10
,
,
Two sliders are mounted on the column 25.
The upper slider 28 comprises'a short section of
tubing 32 surfaced to a sliding ?t on the column
25 and shouldered at each end to receive discs‘33
and‘ 34 between which a short section of tubing
The electrons accordingly 15 35 is clamped. The column 25 is provided in this
to swing negative.
reach their maximumgvelocity at or about the
region with a longitudinal slot for the passage
plane of the accelerator grid-ideally, just as they
pass the effective plane of the boundary grid 4.
As the anode continues to swing negative they
of a-screw 31’ which engages a piece of tubing
In passing through this decelerating ?eld the
by sliding the rod 4|.
39 sliding within the column. The tubing 35 ter
minates in an annular block 40, and an adjusting
encounter a decelerating ?eld, either in an abso 20 rod 4| is threaded into one side of the block and
lute sense or, if still being accelerated by the
passes to the exterior of the tube through a gland
D.-C. ?eld, from the anode, at least in compari
box ‘42 and a “Wilson seal” 43. It is apparent
'son to the acceleration of the D.-C. ?eld alone.
that the position of the slider may be adjusted
, ~~
electrons are delivering energy to the anode cir 25
A word. as to the Wilson seal may here be in
cuit, and they are traveling at minimum relative
order, and in this connection attention is drawn
velocity when they enter the slot 20. This slot
to the showing at thelower right of Fig. 8. The
acts in some degree as a Faraday space, and the
seal proper consists of a normally ?at washer 45
electrons su?er little change in velocity or energy
of synthetic or natural rubber, which is forcedv
as they pass through it. Therefore their Work 30 against a conical seat 41 by the internally conical
is done and their transit time effectively over as
edges of a gland 49. When the washer is un
soon as they have entered it.
stressed the aperture therethrough is slightly too
Since the acceleration of the entire burst of
small for the rod 5|! which it is desired to seal.
electrons takes place with substantial uniformity
The seal is lubricated with a small quantity of
they retain their close grouping at the time of 35 vacuum stop-cock grease. Such a seal is vacuum
impact, and since the impact occurs when the
tight under conditions where other known types
electrons constituting the burst have suffered
maximum deceleration there is a minimum of
energy wasted as heat and the oscillator conse
quently operates at relatively high e?ciency.
of packing would leak badly, since the di?eren
tial pressure on the washer serves to make it hug
the central rod more tightly and it remains tight
40 whether the rod be subjected to rotary or sliding
For operation in the manner described the
motion in either direction.
desiderata are that the control grid l6 and ?la
Returning to the general tube structure, the
ment ll should be e?ectively isolated from each
second and lower slider 5| is essentially similar
other both as regards D.-C‘. and radio-frequency
in construction to that just described, except that
45
potentials, and should have an effective capacity
its actuating rod 52 is mounted externally of the
sufficiently low so that it may be tuned to the
column 25 through’the gland box 42 and Wilson
desired operating frequency, or, in other terms,
seal 53.
it must be capable of being connected in circuit
The slider 5| makes a close sliding fit within
with an inductance su?iciently small to tune to
a
cylindrical
conductor 54 mounted in the ?ange
that frequency. The accelerator grid I5 must be 50 I0 accurately concentric with the column 25 and
insulated from the other elements to maintain
maintained in this concentric relation both by
its D.—C. voltage, but should be effectively ground
the slider 5| itself and by an'auxiliary diaphragm
ed as regards radio-frequency potentials. The
or spacer 55. The tubing 54 does not extend the
boundary grid 4 should also be grounded to radio
full length of the central column, but terminates
frequency and for convenience in operation and 55 a distance above the flange 1 which is somewhere
safety’s sake should preferably also be grounded
in the neighborhood of one-eighth of a wave
as regards D.-C. potential, as it is electrically con
length at the mean frequency for which the tube
tinuous with the envelope. The anode should be
is designed.
_
‘
'
free as regards both A.-C. and D.-C. potentials.
Accurately coaxial with the column 25 and its
60
The various mounting and auxiliary means next
surrounding conductor 5| is a third conducting .
to be described are designed to meet the desid
cylinder 51, mounted on the flange 1 and extend
erata as fully as possible. In this description
ing below it for approximately one-eighth wave-v
terms such as “above” or “below” are used to
length, so that the two conductors 54 and 51 over
indicate position as shown in Fig. 1. They have
lap by a distance approximately equal to one
no other signi?cance, as the device may be op 65 quarter wavelength of the average operating fre
erated in any position.
quency of the device, wavelengths in this sense
Starting at the bottom of Fig. l, with the flange
being used to mean the wavelength of the fre
I9, a high conductivity column or pipe 25 extends
quency transmitted along the two tubes as a
a major portion of the length of the entire device 70 coaxial transmission line. There is no metallic
to the plane of the ?ange 3 and the boundary
contact between the two conductors 54 and 51,
grid ll, This column is brazed or otherwise per
and they are separated by vacuum so that dielec
manently secured into the ?ange in so as to be
tric loss-does not occur in the space between
accurately concentric with the remainder of the
tube structure and, of course, to be vacuum tight. 76
Column 51 is brazed or otherwise secured in
them.
'
r
'
2,404,541
1i
the flange 1, is made of highly conducting mate
rial (preferably oxygen-free copper) and is pref
erably provided with a cooling system comprising
a water pipe (59 coiled around and soldered to
the external surface of the column. The ends
of this pipe are brought out through the ?ange
‘l at the right of Fig. 1.
The upper end of the column 51 carries an
intermediate ring 6! which supports indirectly
one end of each of the ?laments IT. The other
ends of these ?laments are carried by a group
(here six) of pipes 62 mounted in the annular
inter-space between the column 51 and the outer
shell 5. The lower ends of the pipes 62 are
mounted in a ring 63 which is bolted to and insu
lated from the ?ange l as is shown in Figs. 2
and '7. The ring 63 is counterbored at three
equidistant points to receive insulating beads 64
of porcelain, lava, or other refractory insulating
material which beads space the rings slightly
from the ?ange ‘I. A cap screw 65 passes in turn
through a clamping cap 61, a second bead 69, the
12
is 50 mils. The grinding is preferably performed
in a jig which deforms the wire slightly in the
longitudinal direction, so that the ends‘of the
?lament are ground a few thousandths of an inch
thinner than is the central portion. This grind
ing forms the flat emitting surface of the‘ ?la
ment, and if done with a relatively small wheel
whose axis is maintained parallel to the length
of the ?lament, it gives the slight hollow grinding
which has already been stated to be advantageous.
The effect of thinning the two ends, adjacent the
point where the ?lament is clamped, is to give
a greater current density at these points, with a
consequent greater liberation of heat which com
pensates for the heat conduction to the clamping
means and results in substantially constant tem
perature and substantially constant emission over
the entire effective length of the ?lament. Being
of pure tungsten, the ?lament retains a degree of
resiliency even at its emitting temperature, and
this, together with its resilient support, prevents
buckling or change of plane of the emitting sur
face when in operation and keeps the electrical
rings 63 and the bead 54 to clamp the ring ?rmly
constants of the device ?xed under such minor
to the ?ange. It should be noted that the poten
tials which this arrangement must withstand are 25 variations in operating temperature and expan
sion, and inequality in these factors as between
of low frequency and are only those across the
the several ?laments, as inevitably occur in
?lament, i. e., the insulation need only be of suffi
practice.
cient value to withstand a few volts (three at 60
Cooling for the support of the inner ends of
cycles in the instant structure) and the insulating
material is not subject to dielectric heating from 30 the ?laments is accomplished by conduction
through the support rings ‘M and BI to the col
radio-frequency ?elds.
umn 5'! and thence through the cooling coil 60.
The actual ?lament mounting can best be seen
Cooling for the outer supports is by circulatory
in Figs. 11 and 12. Each of the tubes 62 carries
system within the support pipes 62 themselves.
an inwardly projecting L-shaped lug l0, and the
inner ends of the lugs are provided with slots ‘H 35 A small water pipe 99 enters the side of each of
the support pipes 62, and extends axially within
for receiving the downturned ends of the staple
it to a point adjacent the lug ‘HQ, 50 that water
shaped ?laments ii, the ends being clamped into
entering this pipe will be squirted against the
place by set-screws '12. The inner ends of the
inner end of the lug. From there it returns
?laments are clamped in an annular groove 13,
through the pipe 62 externally of the pipe 90 to
formed in an inner mounting ring 'i'li which is the bottom of pipe 62, where the end 90' of the
supported on column 51 by the intermediate ring
next pipe is connected to carry the water to the
6! before mentioned. The actual clamping of
next ?lament support, circulation thereby occur
the ?lament ends is accomplished by pairs of set
ring through each of the support pipes 62 in
screws 75 hearing on small blocks ‘H.
45
The pipes 62 are surrounded by open-ended
The supply for this circulatory system is
cylindrical conductors 79, which terminate at the
through a ?tting designated by the general ref
level of the upper end of the lug and extend down
erence character 9!, comprising coaxial pipes 92
over the pipe 62 for approximately one-quarter
and as which connect respectively to the two ends
wavelength and are supported by the ring 6!.
of
the system. The outer of these pipes is perma
Within the conductors 19 are inner tubular con
nently secured to the support ring 63 (see Fig. 4) .
ductors 6B of substantially the same length, open
The ?tting 9! passes through the flange 1 and is
at their upper ends and mounted by their lower
insulated therefrom by insulating bushings 94 of
ends on the pipes 62 by means of conductive
steatite or other refractory between which is a
blocks 8|. The concentric tubes 19 and 8B are
both open at the ?lament end, being notched to 55 compressed rubber washer 95 forming a vacuum~
tight seal. A connecting lug 91 for connecting
clear the lugs ‘is and also being provided with
one ?lament supply lead is mounted upon the
alined holes to permit tightening of the set-screws
?tting SI, and the ring 63, and the circulatory
72. It will thus be seen that the only connection
system comprising pipes 90 and 62 all constitute
between the inner column El with its supporting
rings El and ‘M and the group of ?lament sup 60 the conducting systemfor supplying the ?lament
current. The return circuit is through the col
port tubes 82 is the ?laments themselves.
succession.
These are shown in Fig. 1'7, and as will be seen
,
_
umn 57 and the ?ange 1, to which a second con
necting lug (not shown) is attached.
are relatively short and rigid. They are prefer
There are two other features comprised within
ably of pure tungsten and have a considerable
degree of strength. It will further be seen that 65 the ?lament-grid structure and their supporting
systems. The ?rst of these is a sliding plug 99
the support afforded their outer ends by the tubes
mounted in the end of the inner support column
52 and lugs ‘it is light and of small inertia and
25, and adjustable as to position by means of an
that the tubes 62 have relatively large resiliency.
operating rod H33, and an offset extension rod l?l
The ?laments therefore are very unlikely to be
passing through a Wilson seal I02 in the gland
ruptured by shock on the device as a whole, and
box 42. The second is a. cooling pipe H23 which
there is ample ?exibility to take up their ex
extends substantially the full length of the inner
pansion.
column 25 and is soldered thereto adjacent its
Each ?lament is preferably formed of round
upper end for better heat transfer.
tungsten wire, one surface of which is ground
We are now in a position to consider the elec
?at or slightly concave. The diameter here used
2,404,541
13
~
trical characteristics of the ?lament-grid struc
ture in view of the desiderata above set forth,
and it is believed appropriate to do this at this
point, since the same principles are involved in
the supports for the remaining elements of the
device and the explanation of all will be simpli?ed
if these principles are in mind. The necessary
14
a‘ number of aspectsall depending on the general
relationships above set forth, "but in the treat
ment, here adopted they are generally considered
as divided into sections of quarter-wave length,
or thereabout, as'thisis believed to lead to the
simplest explanations.
I ‘
separation of the elements as regards D.-C. or low
Weare interested in the impedance of the grid
?lament support line as viewed from the grid
frequency potentials have already been accounted
end, but ‘this, impedance is dependent upon the
for. There is no metallic connection between the 10 terminating or output impedances of the various
grid-support column 25 and the ?lament-support
sections and, therefore, in order , to determine
what the grid-end impedance will be, we must
system comprising the column 51, and the sup
port pipes 62. Remaining to be accounted for is
consider the various elements, section by section,
the impedance relationship between the grid and
starting from the outermost or lower end of the
?lament members, and this is dependent upon 15 tube as shown in Fig. 1. c 7 7
From this aspect the ?rst section of the struc
the impedance of the coaxial transmission line
ture is. the section including the adjusting rods
formed by the inner and outer columns 25 and 51
and the coaxial conductors associated therewith.
52, 4|’, etc., the ?ange I0, and the section of the
The impedance characteristics of transmission
tubular conductor 54 illustrated as below the end
lines whose lengths are of the same order of mag 20 of the column 57. Electrically this portion of the
nitude as the wavelengths of electrical oscillations
structure is asingle conductor, and viewed from
its upper end constitutes an end-fed antenna.
transmitted thereby are now well known, but they
It is preferable that its length be of the order
are restated here for convenience in the explana
of one-half wavelength at the operating frequency
tions that follow. Most of them can be derived
from the impedance diagram of a half-wave line
of the device, in which case its effective imped
ance Z2 will be in the neighborhood of 1,000 ohms.
open at the output end, as shown in Fig.32, which
If<its length be reduced to one-quarter-wave
indicates such a line diagrammatically, and shows
length its effective input impedance will likewise
the approximate curve of relative impedance
be reduced to the neighborhood of from 50 to 100 .
looking into any portion of the line from the
right, resistance of the conductors themselves 30 ohms, the quarter wavelength conditionbeing the
least desirable in practice. This antenna is con
being assumed to approach zero. Extremely
sidered as being fed'by the coaxial transmission
short sections show a high capacitive reactance,
line comprising the tubular conductor 54 as the
which falls to the characteristic impedance of
inner element and the column 51 as the outer
of the line at the 1/8 wavelength point, and to
zero at the quarter-wave point, i. e., a quarter
wave open-ended line acts as a dead short.
From
this point on the apparent reactance is inductive,
rising again to the value
element. With the spacing shown such a trans
mission line will havea characteristic or surge
impedance Zn of about 10 ohms, and as has already
been stated the length of this section of trans
mission line is approximately
k
4
where A is the wavelength at the frequency of
operation. If we consider the quarter-wave con
at the % A point and approaching in?nity at 45 dition to be ful?lled exactly'the impedance look
ing into the coaxial line’ from the grid end will be
1/2 A.
‘
The same diagram may be taken as represent
ing the impedance of a shorted-end line if the
origin be taken at the nodal or quarter-wave
_Z_o2
'
point, which appears as a short when looking 50 If .the antenna section of the system have ‘an im-_
pedance of the order of 1,000 ohms, the character
istic impedance of the line being 10 ohms, the '
into the line. For short sections the reactance
is small and inductive, it rises to
at the 1A; x point and approaches in?nity at
A
4
Since this appears as an open circuit, increasing
the length of the line repeats the portion of the‘
diagram shown at the left of the nodal point.
Stated in another manner, a quarter-wave open
line or a half-wave shorted line appears much
like a series resonant circuit, while a quarter
wave shorted line or a half-way open line appears
like an anti-resonant or parallel resonant circuit.
input impedance of the line will therefore be 11¢;
of an ohm. This low impedance therefore be
comes the closing impedance of the sectionmof
line immediately preceding it. From one .point
of vi'ew‘it acts as a radio-frequency by-pass be
tween the inner conductor 54 and the outer con
ductor 51, so that viewed from the input end,
at radio-frequencies the cylinder 54 and outer
column 51 appear as a single conductor, and
form, in connection with inner column 25, a single
radio-frequency transmission line considered as
fed from the grid-?lament end through a slight
impedanceiirregularity where the inner cylinder
54 terminates. Its effect from another point of
view will be considered later.
'
‘
'
‘
Even if the conditions as to impedance of an
The only other relationship necessary to the
understanding of the present invention is that
tenna and length of the coaxial line constituting
the column 51 and cylinder 54 are not exactly '
the characteristic impedance of a quarter-wave
line is the geometric mean between its input and 70 met the result will be substantially the same. The
antenna impedance can easily be kept above 100
closing impedances. The short-circuit and open
ohms, making the impedance looking into the
circuit conditions are, of course, merely special
quarter wavelength line 1 ohm. If the "length:
cases of this general relation.
of the line section is not'exactly one-quarter
The lines comprising the element supports of
the tube of my invention may be considered from 76 wave,v butv is'still materially greater than ‘one
2,404,541
15
16
eighth wavelength, ‘the input impedance will still
impedance to a ?nite value and introduce large
losses through radiation and dielectric phenom
be low in comparison with the characteristic im
pedance of the line, and although more power
ena.
will escape than if optimum conditions are met
The design problem to be met, therefore, is the
the amount of power wasted by such undesired UL design of a structure which, when terminated by
an impedance approaching in?nity, will have the
radiation will be very small.
properties of an anti-resonant circuit as viewed
The section of the inner line comprising the
from cathode and grid. This structure is pro
cylinder 54 and column 25 terminates in the
vided by two additional quarter-wave sections of
slider 51, which, as it is of large area and makes
good contact with both conductors, may be con 10 the same line,
The ?rst of these sections extends to include
sidered as of zero impedance. This section may
the upper slider 28, and its design is such that
be tuned to exactly one-quarter wave by moving
its electrical length may be changed in opposite
the slider. Due to the spacing between the two
sense to its physical length; i. e., such that it
conductors the characteristic impedance of this
may be “?tted in” beneath the section above it
section of transmission line is high, and if the
even when the length of the upper section in
resistance of the line were zero the input im
creases with decreased frequency of operation or
pedance would be in?nite. Actually it may always
vice Versa.
be made to exceed 100,000 ohms and under opti
This effect is obtained by means of the ir
mum conditions may reach ten times this value.
This section therefore forms a tuned radio-fre 20 regularity introduced by the low-impedance line
section constituted by the slider 28. From the
quency choke of extremely high impedance inter
posed betWeen the ?lament-grid structure and
the outside world, and the impedance involved is
so high that practically all energy reaching it is
top of the high impedance section already de
scribed to the slider is a length of relatively high
impedance line of less than 1/4 wavelength which
re?ected back to its source.
25 therefore appears as a capacity variable from
zero to some small value as the slider is moved
What actually happens can be expressed more
nearly in the terms of low frequency power line
transmission if we think of the antenna as a load
to change its length from zero toward
A
which is fed by a line terminating immediately
4
above the top of the column 511, Current fed to 30
this line from the central column 25 must pro
To this is connected the relatively great capacity
ceed down the column, across the slider‘, and back
of the slider portion of the line about 1/8 A in
to the top of the conductor 54, since owing to
length, but presenting an eifective capacity many
skin effect none will now transversely through
times as great as and apparently in parallel with
the wall of the conductor, In so ?owing the cur
that of the lower section, so that moving the
rent meets an enormous impedance—say 100,000
slider to change the length of the section below it
changes the apparent capacity as viewed from
ohms. From there the line continues down the
outside of conductor 54 to the antenna and back
above relatively little. Therefore a very short
length of the high impedance line above the
within the column -51 to the terminus above the
top of conductor 54. This latter length of line, 40 slider is all that is necessary to tune this e?ec
tive capacity to resonance, thus completing the
including the load imposed by the antenna, has
quarter-wave section of line and bringing the
an impedance of, say, 1 ohm, and since the volt
node or quarter-wave point of the composite sec—
age available at the termini of the line will divide
itself across this low impedance and the high
tion a small distance above the upper slider face.
The distance between the slider and the node will
impedance line section in series therewith in the
vary with frequency, of course, but only slightly
proportions of the magnitudes of those imped
with the position of the slider.
ances, and since the current ?owing at the input
It has already been pointed out that the node
points of the respective sections is the same, it
is effectively equivalent to a short-circuit, and
follows that the energy delivered to the respective
impedances will also be in proportion to their 50 hence, since by moving the slider we may ‘move
the position of the node, by so doing we may tune
magnitudes, and only 1/ 100.000 of that delivered to
the line will be transmitted to the antenna to
be radiated thereby-still less if optimum con
the uppermost section of the line including the
?lament and grid. We have made that portion
ditions are met.
of the line below the slider and above the im
pedance loop relatively ineffective in tuning, so
From still a slightly different aspect, the small
and largely resistive impedance offered by the
that we have an "elastic” or extensible quarter
wave section of line.
The ?nal or grid-?lament section may thus be
resonated or otherwise tuned to give optimum
the value of PR, is vanishingly small, the R in
this case being the apparent input impedance of 60 operating conditions. In the case of Fig. 1, where
capacity feed~back between anode l3 and grid
the outer line and 12B (practically) the energy
cap 99 is used, the desired tuning of this section
radiated.
must provide a capacitive reactance. This is
From whatever aspect the matter be considered
obtained by making the grid-?lament section
the result is the same: The sections of the trans
slightly longer than one-half wavelength or, in
mission line above the current node terminate in
other terms, tuning it to a slightly lower fre-‘
what is equivalent to an open circuit, just as
quency than that of the desired oscillation, so
would a low frequency line connected across an
that as viewed at grid and ?lament it presents a
ordinarily good insulator. There is some con
small anti-resonant capacitive reactance. Under
sumption of power, which can be neglected in fur
ther consideration, (as in the case of the insu 70 these circumstances the ?lament-gridsystem ap
pears as a capacity in series with the capacity
lator) and the succeeding sections can be treated
between the grid structure and the anode, and
as if they terminated at this point in an in?nite
outer line is at a current node. We therefore
have a very small current ?owing, and therefore
this latter capacity is adjustable by varying the
position of the cap 99. When, therefore, the po
an insulator for the line sections would drop the 75 tential of the anode swings, the grid will assume
impedance. It should be noted, however, that at
the frequencies we are considering substitution of
2,464,541
17
18
boundary grid, and anode, which elements are
a potential with respect to the ?lament (and
ground) which is intermediate between cathode
and anode potential, and which bears the pro
portion to the total potential between anode and
?lament that the effective series capacity between
anode-grid and grid-?lament bears to the ap
shown in'elevation in. Figs. 9, 15 and 13 respec
tively; The accelerator grid is mounted from a
side tube I05, which. is welded to project through
the wall of the housing 5 immediately below the
?ange 3. This side tube carries at its outer end
a ?ange I01 which is surfaced to receive the
tubular ‘glass insulator we, and the latter, in
parent capacity between ?lament and grid. In
other words, the arrangement is essentially a
capacitive voltage divider which swings the grid
turn, carries a terminal flange H0. This struc
potential in the same sense that the anode poten 10 ture may best be seen in the?enlarged detail view
tial swings, and in ?xed and predetermined pro
of Fig. 6. As in the case of the main tube en
portion thereto. Since the criterion for oscilla
velope, the tie-bolts which'hold the structure to
tion of the device is that the grid and anode
gether are omitted, but it will be understood that
should swing in the same sense and in step, the
it is assembled in the same fashion as is the main
result is a highly effective capacity feed-back 15 envelope with ground surfaces reenforced by
which is under control either by varying the ac
greased rubber bands or gaskets I II ,which'form'
tual capacity coupling with the cap 952 or by vary
the seals. Two tubular conductors are ?xed to.
ing the effective resonant input capacity of the
and project inwardly from ?ange H 0. The inner
grid-?lament circuit by varying the position of
conductor I I2 is spaced from the outer conductor
the slider 28.
20 H3 and is held accurately concentric therewith
By the use of the two sliders the device is thus
by an annular spacer H4. The accelerator grid
given its very considerable tuning range. The
I5 is supported from the‘inner member by a tubu
lower slider El brings the current node to the
lar bracket H5, the end of which ?ts within the
point where the antenna is fed; the upper slider
conductor H2 and is rigidly secured thereto. 'A
28 moves the nodal point immediately above it
cooling pipe I", bent into‘ a ring to surround
and thus tunes the ?lament-grid section. The
the accelerator grid, has its ends brought ‘down
actual point of importance is that by adjusting
parallel to the support bracket H5 and enters
the position of the sliders the effective resonant
the inner‘ conductor on either side thereof, the
impedance of the ?lament-grid combination may
ends of the pipe passing into the ‘inter-conductor
be made to assume any value which may be de 30 space distally of the spacer H4 and emerging
sired, since the node above the slider 28 may be
through the ?ange H0. A tuning slider H9,
moved near enough to the rather large lumped
which nearly, ?lls the space between ‘the inner
cathode-grid capacity to embrace between the
and outer conductors and does not make vactual
node and that capacity the exact small line in
contact therebetween, is operated by means of a
ductance required for tuning it. In actual prac- ‘
hook I20 whose end projects through a longi
tice the effective impedance will be made capa
tudinal slot in the conductor H2. A controlrod
citive and small in comparison with the phys~
I2 I is threaded to the end of the hook and emerges
ical grid-cathode capacity, but it might, if de
through a Wilson seal I22.
‘
sired, equally well be made inductive or resistive.
The supporting bracket H5 and cooling tubes
Furthermore, since the effective resistances in 40 I H. are carried up to the interspace between the
the circuit are extremely low, the losses are also
control grid and the boundary grid through an
small even though the circulating currents may
angular ?tting or shield I25, which passes‘through
be large.
'
a notch I 21 cut in one side of the ?lamentsup
A system of transmission lines, chokes and by
port ring 6i. This constructionris shown in Figs.
passes similar to‘ that used in the ?lament-grid
1,6 and 11, each of these ?gures showing sections
circuit is employed across the ?lament to prevent
of the ‘shield. The shield is electrically con
transmission of energy to D.-C. insulation and
tinuous with a pan I29 overlying and contacting
to prevent ?lament damage by R.-F. currents.
the ?lament support ring; 14 and slotted im
The actual ground point on the ?lament circuit is
mediately above the ?laments, which forms an _
the ?ange ‘l on the outer casing 5 of the device. 50 additional shield or barrier to separate, com
This, however, is unimportant and the e?ect of
pletely the anode and control-grid sections of the
the transmission line arrangement may be con
tube except at the points where intercommuni- -'
sidered as though the ground point were at the
cation is necessary or desired. ‘The shield and
inner end of the ?lament. This may be con
pan therefore form one terminus, and the ac
sidered as terminus of a quarter wavelength co
55
celerator grid and cooling pipe] I'I form the other
axial transmission line comprising the tubular
terminus of the radio-frequency transmission line
conductors 19 and 80, which is open at its lower
comprising the side tube I05 and the tubularcon
end, terminating in a high impedance. The
ductors H2 and H3.
'
transmission line impedance is again low, being
From what has gone before it is believed that
of the order of, say, 5 ohms, and the line there 60 the operation of this arrangement will be readily
fore forms a negligible series impedance as before,
apparent. Again we have an antenna system
acting as a Icy-pass to the inner conductor. This,
comprising the control rods I2I and cooling tubes
again, is a quarter wavelength line with the pipe
I ll, plus the projecting end of the conductor‘ I I3,
62 as its inner conductor, terminating in a dead
which is fed by and oifers a relatively high im
short, and therefore o?ering very high imped 65 pedanceto a quarter wavelength transmission
ance. As the potential imposed across this im
line of low impedance formed by the side ‘tube
pedance is merely that which can build up across
I05 and the conductor H3, and there'is accord
the short ?lament, amounting to a few volts at
ingly a radio-frequency by-pass between the
most, the escape of power through the ?lament
grounded outer case 5 and tube I05 of the con
support may be neglected, and the high imped '10 ductor H3. Within this there is another series
ance effectively in series with the ?lament pre
section of transmission line comprising the con
vents circulation of R.-F. currents which might
ductors H2 and H3 and terminating in a short
otherwise cause hot spots and burn-outs.
'
formed by the spacer-H4. = This v-inner line is
We are now ready to consider the mounting of
. tuned to a quarter wavelength byrmeans of the
the remaining elements, i, e., the accelerator grid,
slider I20, which acts as a loading capacity and
2,404,541
19
increases greatly the electrical length of the line.
In practice this slider is moved back to a point
from which the line appears as a very large in
ductance at the operating wavelength. The
proper point is that at which the remaining in
ductance and capacitance of the line, considered
from the grid end, make it just a quarter wave
20
Owing to the necessity for providing cooling
the body itself must be water-tight, and accord
ingly it is constructed of a ?ared cylinder I41,
to the ?ared end of which the anode face I3 is
hard—soldered. The other end of the cylinder is
closed by a threaded disc I49.
The supporting pipe I44 enters the ?ared cyl
inder I41 through an aperture in the side thereof.
The end of the pipe is threaded into a boss I48
I I4, forming a very high impedance at the shield
where the grid I5 and cooling tube II‘! are sup 10 on an inner ba?ie cylinder I 50, which boss is
soldered to the inner wall of the cylinder I47.
ported, and preventing any appreciable power
The boss I48 extends internally to form a cylin
being transmitted past this point to be radiated.
drical chamber !5 I , which connects by a side pipe
The capacity of the grid I5 to the boundary grid
I52 through the end I53 of the baffle cylinder,
4 is large, and that to the control grid I6 is small;
so that water introduced through the pipe I44 is
there is little coupling tending to swing the ac
discharged directly against the active face I3 of
celerator grid I5, and it consequently tends to
the anode, and thence is forced around the ex
maintain very nearly zero R.-F. potential.
terior of the baifle cylinder to reenter its open
As has already been described and as shown in
end. It can then return within the cylinder to
detail in Fig. 16 the boundary grid ii is ?rmly
enter the open end of a return pipe I513, which
clamped between the ?ange 3 and the anode
length from the inner end to the shorting spacer
housing 2, and is therefore physically and de?
nitely at the ground potential of the housing.
is mounted concentrically within the pipe I44 by
means of a perforated cap I55 which ?ts over
the end of the pipe I44, its lower end passing out
The boundary grid and the anode face I3 again
through the discharge chamber I5I. The cap
form the termini of a resonant line, comprising
the housing 2 as its outer conductor and a cylin 25 compresses a rubber gasket I46, sealing the joint
between the pipe I44 and the anode body to make
drical anode body, designated by the general ref
it water and vacuum tight.
erence character I39, within the housing. This
The upper end of the pipe I54 is centered in
resonant line is one-half wavelength long, and
the pipe I44 by means of a metal bellows I57
may be considered as terminating between the
inner face of the ?ange I and the end I35 of the 30 which is sealed to both pipes and. permits differ
ential expansion between the two. Water is in
anode body. This will be recognized as an open
troduced
into the pipe I44 through a side pipe I59,
ended half wave line, and therefore of extremely
and its course can be traced by the arrows in
high impedance when viewed from either end.
the drawings through the outer pipe, the perfo
The construction and method of support of the
rations in the cap I55, the side pipe I52, and
anode body are best shown in Fig. 8. The sup
thence around the bali‘le cylinder I50 and back
port is from the mid- or quarter wavelength point
through the central pipe I54.
of the anode, i. e., at a potential node, so that
The action of the mounting follows the prin
there is little tendency for power to escape from
ciples already set forth, although the application
the support structure. Such tendency as there is
is somewhat different. A disc I00 is connected
for power to leak from the support point is sup
to the ?ange I4! both electrically and mechan
pressed by either or both of two methods. First,
ically, and carries a cylinder ISI. The pipe I44
and preferable in the cases where the tube may be
and the cylinders I 40 and IGI form a transmis
predesigned to operate at a ?xed wavelength, is
sion line one full wavelength long. Electrically
a movable plate I32 mounted on the sliding rod
this might equally well be a half wavelength line,
59 of the Wilson seal ?rst described, and making 45 but additional space is needed for the insulat
contact with the ?ange I by means of a spring
ing cylinder I42, which must withstand the full
skirt I33. This may be adjusted to bring the node
D.-C. anode potential of 20,000 volts or more.
of the resonant line accurately at the point of
The
length of this section is measured from the
support. This method of preventing direct radia
anode and its housing, and the impedance at its
tion from the anode was adopted in the ?rst
outer end is very high, so that looking into it
of these devices constructed. It was quickly
from the anode the impedance is also very high.
found, however, that the plate I32 was more use
This high impedance is connected in shunt
ful as a tuning device, and therefore the prin
across the line formed by the anode body I 30 and
ciple of transmission-linerchoke support was
again employed to prevent power escape. In the 55 anode housing 2 very near the nodal point, where
the impedance of the latter line- is low, and ac
construction then adopted and here shown a
cordingly a very small portion of the current
side tube I40 of relatively large diameter is welded
?owing
at this point will take the high imped
at substantially the midpoint of the anode hous
ance
path
to the outer world.
ing 2. The side tube carries a metallic ?ange
In other terms, the full wave line is connected
I4I, with a glass insulator tube I42 ?tted against 60
so near the node Of the main anode oscillator
it and in turn carrying a terminal ?ange I43.
circuit that only a few volts are eifective across
Through this terminal ?ange passes a pipe I44
its
termini, and therefore very small currents will
which projects through a pass hole I45 in the
tend to ?ow therein, representing a power loss of
side of the anode housing and on the end of which
V2
the anode body is attached. The action here will
‘5
be described following the mechanical description
of the anode, as the expedients adopted are pred
where V is the small input voltage and Z is the
icated upon the necessities of the mechanical
large input impedance. Moreover, since the line
structure.
is one wavelength long, only the small voltage
From the electrical point of view the anode 70 V will be effective to cause radiation from the
body is a simple cylinder with closed ends. Its
radiating system constituted by the end of the
complexity, as shown in Fig. 8, is due primarily
line. It should be noted, however, that by de
to the provision for circulating cooling water
liberately unbalancing the anode resonator by
within it, and to the provision of what may be
means of the plate I32 the support systemcan
75 be converted to a horn ‘antenna which can be
termed a “rough tuning” device.
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