March 2, 1948.
F. J. BINGLEY
‘2,437,067
ADJUSTING MEANS FOR TRANSMISSION LINES
Filed NOV. 17, 1943
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March 2,
1948.
2,437,067
F. J. BINGLEY
ADJUSTING MEANS FOR TRANSMISSION LINES
Filed NOV. 17, 1945
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Patented Mar. 2, 1948
2,437,067
UNITED STATES PATENT OFFICE
2,437,067
ADJUSTING MEANS FOR TRANSMISSION
LINES
Frank J. Bingley, Philadelphia, Pa., assignor, by
mesne assignments, to Philco Corporation,
Philadelphia, Pa., a corporation of Pennsyl
vania
Application November 17, 1943, Serial No. 510,671
6 Claims. (Cl. 178-44)
1
2
This invention relates to co-axial transmission
lines and has to do with the problem of main
taining matched impedances while providing for
impedances of the trombone and the connected
line sections.
Another important aspect of this invention is a
novel telescopic joint which serves to avoid the
line-length adjustments.
In ultra high frequency transmitting installa
creation of a superfluous and detrimental inter
tions—particularly television-it is common prac
tice to employ a co-axial transmission line for in
terconnecting the transmitter per se with the
radiating antenna; and for certain electrical rea
sons, which need not be explained here, it is ex
pedient to insert in such a line means by which
its electrical length can be adjusted. One such
means which is highly convenient comprises a
U-shaped portion of co-axial cable known as a
mediate characteristic impedance between the
trombone, or other adjusting section, and the ad
jeining quarter-wave sections-which latter im
pedance would function to destroy or impair the
impedance match which is intended to be
1,0
achieved.
While a trombone is generally the most desir
able form of line-length adjusting means for car_
rying out this invention, it will be pointed out
“trombone,” because of its similarity, in appear; 15 that, where circumstances permit, there can be
ance, to the slidable tube in the musical instru
employed, instead, a straight section capable of
ment of that name.
performing the same function as the trombone.
Interconnecting two sections of co-axial line
In the drawings which accompany this speci
through the medium of a trombone affords the
?cation
essential lengthwise adjustability; but, as prac 20 Fig. 1 is a schematic diagram of a television
ticed heretofore has resulted in objectionable im
transmitting system, showing a co-axial transmis
pedance mismatches-—which it is the primary ob
sion line with an adjusting “trombone” in accord
ject of this invention to avoid. That is to say, it
ance with this invention;
is the primary object to provide convenient and
Fig. 2 is a schematic diagram of an alternative
effective means whereby the length of a co-axial 25 arrangement showing a straight telescopic adjust
line can be adjusted without introducing an im
ing section which can be employed in place of the
pedance mismatch.
trombone;
It is a subordinate object to devise a trombone
Fig, 3 shows details of construction of the trom
type line-length adjustment which introduces no
impedance mismatch.
It is well known that two transmission line sec
bone;
30
Fig. 4 shows, for comparison, a trombone con
struction not in conformity with the invention;
and
tions having di?erent characteristic impedances
can be coupled without mismatching by interpos
Fig. 5 is a detail of the straight telescopic sec—
ing between the adjoining ends a quarter-wave
tion of Fig. 2.
length coupling section whose characteristic im 35 In Fig. 1, the rectangle I may be taken to rep
pedance is equal to the geometric mean of the
characteristic impedances of the line sections to
be coupled. That is to say, the coupled line sec
tions will be matched if
resent a television transmitter the output of
which is connected through a co-aXial transmis
sion line 2 to a dipole antenna 3. To provide for
adjustments of the length of the transmission
40 line there is inserted therein a trombone section
Z1=V Z222
(1)
4 which is slidably movable, as indicated by the
where Z1 is the characteristic impedance of the
double-headed arrow 5. It is old practice to make
quarter-wave-length coupling section and Z2 and
use of a trombone section for varying line length;
Z: are, respectively, the characteristic impedances
but in the past this practice has resulted in the
of the two line sections to be coupled.
45 introduction of impedance mismatches between
One of the major aspects of the present in
the interconnected line sections-the mismatch
vention resides in the concept that a trombone
in each case being due to the fact that the char
section can be made to match, as to characteristic
acteristic impedance of the trombone was not
impedances, each of two line sections, and can
identical with that of the interconnected line
be made to maintain the impedance match 50 sections, and the further fact that the trombone
throughout all adjustments, by interposing be
tween each leg of the trombone and its respec
could not be made to operate as a matching sec
tion because it could not be a quarter-wave
tively associated line section a quarter-wave sec
length long, or odd multiple thereof, in more than
tion having a characteristic impedance which is
one position of adjustment.
equal to the geometric mean of the characteristic 55 My invention consists, in part, in the provision
2,487,067
3
A
of two quarter-wave sections 6 and ‘l intercon
necting the two ends of the trombone with the
two line sections 8 and 9-each quarter-wave
side of Equation 2, there is obtained an equation
expressing the dimensional properties which must
obtain between each quarter-wave section and
section having a characteristic impedance equal
to the geometric mean of the characteristic im
the line sections which it intercouples in order
to realize an impedance match.
pedances of the sections which it interconnects.
Thus, the characteristic impedance of quarter
Thus:
wave section 6 must be equal to the geometric
mean or" the characteristic impedances of trom
logm
logm
logm
bone ti and line section 8. This is expressed 10 'The'dimensional ‘quantities A1, A2, A3, B1, B2 and
B3 are indicated in Fig. 3. The left side of Equa
mathematically by the previously stated For
tion 3 de?nes the characteristic impedance of
each quarter-wave section while the two factors
under the radical on the right side de?ne, re
the transmitter I or antenna 3, and is generally 15 spectively, the characteristic impedances of sec
tions 8 and it, or sections 9 and 4—as the case
preferred for that reason. But where it is not
mula 1.
The arrangement of Fig. 1 makes it possible
to adjust line length Without disturbing either
inconvenient to move the transmitter or antenna
maybe;
It W-lllc'bé seen that the only variables entering
there may be employed, instead of the trombone,
into determination of the characteristic imped
a straight adjusting section ID, as shown in Fig. 2.
The arrangement of Fig. 2 is in all other respects 20 ance of a co-axial cable are the diameters B and
A and the ratio
identical with that of Fig. 1.
In Fig. 3 there is illustrated in detail the con
B
struction of that portion of the line which in
A
cludes trombone 4 and quarter-wave sections 6
and that the length of the line is irrelevant. '- The
and ‘I, together with fragments of line sections
8 and 9.
'
'actual dimensions‘ A and B are immaterial, ex
Each section of the line, including the trom
bone section and the quarter-wavesections, as
cept insofar as they affect the
cross-section. Line section 9 is composed of
similar conductors 9a and 9b; and quarter-wave
section '5 of corresponding conductors 1a, ‘lb.
the quarter-wave ‘sections ‘would'be destroyed;
and, of course, the impedance match between the
main line sections would also'be destroyed in
B
well as main sections 8 and 9, is a co-axial cable
A
comprising an outer tubular conductorand an 30
ratio. '
axial conductor which is centralized with the
It follows ‘from the above that‘ if the ‘telescopic
outer tubular conductor by means of suitable in
joints‘ea'ch presented a‘ short intervening portion
sulators. Line section 8 is composed of an .outer
'of line. having a characteristicimpedance of its
tubular conductor 8a and an axial conductor 81),
own-differing from that of' the quarter-‘wave
both of circular cross-section. Quarter-wavesec 35 sections and di?ering'from that ‘of the trom
tion 6 is composed of an outer tubular conductor
bone-the impedance match between the trom
Ga and an axial conductor 61), likewise of circular
bone and main line sections ‘brought ‘about by
Trombone 1% comprises an outer tubular conduc
tor do and an axial conductor lib, each of circular
cidentally. In the structure of Fig. 3 the tele
scopic joints! do not possess any characteristic
cross-section.
impedance which differs from the characteristic
The axial conductors are centralized and sup
impedance of the ‘respective ‘quarter-‘wave sec
ported by means of insulating discs Ill.
45 tions. This is true because, irrespective of the
The length of each quarter-wave section can
position of adjustment of the trombone, the
be either one quarter-wave length (at the trans
mitted frequency) or any odd multiple thereof.
B
A
makes it easy to maintain the essential im 50 ratio within each telescoped portion remains con
pedance match between the trombone andthe
stant, andlalways equal to that of one ‘of the two
two main line sections 8 and 9 residesin the ar
connected fsections-iinrthis case the quarter
An important feature of this invention, which
rangement of the telescopic joints H and 12,
wave section.
which afford slidable interconnection between
In order to achieve that condition certain re
the trombone and the quarter-wave sections; and 55 quirements must be rmet. These requirements
in order to make clear the signi?cance, from an
electrical standpoint, of the particular arrange
ment of joint shown, it will be eXpedient'to dis
cuss briefly the mathematics involved in the de
termination of characteristic impedance of co
axial conductors, and to restate in dimensional
terms the previously given equation for matching
impedances.
The formula for computing the characteristic
' are (1) theiconductors ‘of each of the twointer
telescope'd sections must be external and internal,
respectively, in relation to the ‘corresponding con
ductors of the other section, and (2) the external
60 axial conductor must-beco-terminous with the
internal tubular conducton. Applying this rule,
it will be seen that section 6..(Fig_ 3) is composed
of a tubular member 6a constituting the internal
tubular member of joint vl-l, while the companion
impedance of a co-axial cable comprising a cir 65 member 61) constitutes the external axialmem
cular outer tube and a circular axial conductor is
berof the joint. The other half of joint H is
composed vof an external tubular member lia and
an internal axial member. llb. This satisfies the
?rst requirement of the rule. The second re
wherein Z is the characteristic impedance to be 70 quirement of the rule- is satis?ed by the fact that
the lower end of conductor '51) is co-terminous
determined; 13 is the inside diameter of the tube;
with the lower end of conductor ‘6a. That is to
and A is the outside diameter of the axial con
sayrt-hey terminate in thesame lateral plane.
ductor.
If they did not so terminate there would be 'in~
Substituting in the general Formula 1 expres
sions according to the form of the right hand 75 vtroduc'ed a section of intermediate character
1. §'
(2)
5
2,487,067
6
lstlc impedance which would impair the imped
and concentric with said external axial conduc
ance match.
tive member, said tubular conductive members
of each joint being slidably telescoped together,
With the view to further clari?cation of this
important point, there is shown in Fig. 4 a trom
said axial conductive members of each joint being
bone structure which is the full equivalent, me
slidably telescoped together, said external axial
chanically, of Fig. 3, but quite different electri
cally in that it does not satisfy the requirements
of the above-stated rule and, therefore, will not
conductive member being co-terminous with said
internal tubular conductive member.
2. In a co-axial transmission line, two co-axial
maintain an impedance match when the trom
impedance-matching sections each having an
bone is moved in either direction from the one 10 electrical length equal to an odd number of quar
precise setting in which it is shown in full lines.
ter-wave lengths, and a U-shaped co-axial trom
The only constructional difference between
bone section interconnecting said matching sec
Fig. 3 and Fig. 4 is that in Fig. 4 the relation
tions and adjustably movable with respect there
ship of the axial conductors ‘lb’ and 6b’ is re
to, there being a telescopic sliding joint formed .
versed as compared to the corresponding con 15 between one end of said trombone section and
ductors of Fig. 3. Axial conductors 8b’ and 9b’
one end of one of said matching sections, and a
are shown smaller than corresponding conductors
second telescopic sliding joint formed between
8b and 9b in order to conform to the essentialities
the other end of said trombone section and one
for obtainment of an impedance match with the
end of the other matching section, one half of
trombone in the position of adjustment wherein 20 each said joint comprising an internal axial con
it is shown in full lines. In that position and
ductive member and an external tubular conduc
no other the characteristic impedance of the
tive member surrounding and concentric with
trombone of Fig. 4 is matched to those of the
said axial conductive member, the other half of
main line sections 8' and 9'; and that is true
each said joint comprising an external axial con
because when the trombone is moved to any other 25 ductive member and an internal tubular conduc
position such, for example, as that indicated by
the dot-dash lines, there is introduced at each
tive member surrounding and concentric with
said external axial conductive member, said
tubular conductive members of each joint being
joint 2. new intermediate characteristic imped
ance which arises from the presence of a new
slidably telescoped together, said axial conduc
80 tive members of each joint being slidably tele
B
. scoped together, said external axial conductive
A
member being co-terminous with said internal
ratio. This ratio, with the trombone moved up
tubular conductive member,
wardly, would be
3. A co-axial transmission line comprising two
35 main sections, an adjustable movable section for
a
A3
and with the trombone moved downwardly it
would be
2
A1
varying the length of the line, and two coupling
sections, all of said sections being connected in
series, said coupling sections each having an elec
trical length equal to an odd number of quarter
40 wave lengths, and each interposed lengthwise
in Fig. 3 embodying the novel telescopic joints
therein shown represents the preferred practice.
between and interconnecting one of said main
sections and one end of said adjusting section,
each of said coupling sections having a charac
teristic impedance equal to the geometric mean
of the characteristic impedances of the said sec
tions to which it is immediately connected.
4. A co-axial transmission line comprising two
main sections, an adjustable movable section for
Details of construction of the adjusting ar
varying the length of the line, and two coupling
Any arrangement utilizing the trombone sec
tion, or its equivalent, in combination with the
two quarter-wave sections, to achieve a constant
impedance match is within the contemplation
of this invention; but the arrangement illustrated
rangement of Fig. 2 are shown in Fig. 5, and 50 sections, all of said sections being connected in
series, said coupling sections each having an elec
it will be observed that this is electrically
trical length equal to a quarter-wave length, and
identical with Fig. 3.
each interposed lengthwise between and inter
Obviously, the legs of the trombone can be
connecting one of said main sections and one end
made of any convenient length; and the length
of adjusting section“! can likewise, be anything 55 of said adjusting section, each of said coupling
sections having a characteristic impedance equal
desired.
to the geometric mean of the characteristic im
Iclaim:
pedances of the said sections to which it is im
1. In a co-axial transmission line, two quarter
wave-length co-axial matching sections, and a
mediately connected.
U-shaped co-axial trombone section intercon 60 5. A co-axial transmission line comprising two
necting said quarter-wave-length sections and
main sections, an adjustably movable U-shaped
adjustably movable with respect thereto, there
trombone section for varying the length of the
being a telescopic sliding joint formed between
line, and two coupling sections, all of said sec
one end of said trombone section and one end of
tions being connected in series, said coupling
one of said quarter-wave-length sections, and a 65 sections each having an electrical length equal to
second telescopic sliding joint formed between
an odd number of quarter-wave lengths, and
each interposed lengthwise between and inter
the other end of said trombone section and one end of the other quarter-wave-length section,
connecting one of said main sections and one end
one half of each said joint comprising an inter
of said trombone section, each of said coupling
nal axial conductive member and an external 70 sections having a characteristic impedance equal
tubular conductive member surrounding and
to the geometric mean of the characteristic im
concentric with said axial conductive member,
pedances of the said sections to which it is im
the other half of each said joint comprising an
mediately connected.
external axial conductive member and an in
6. A co-axial transmission line comprising two
ternal tubular conductive member surrounding 75 main sections, an adiustably movably U-shaped
2,487,067
7
'8
trombone section .for varying the length of the
REFERENCES CITED
line, and two coupling sections, all of said sec
tions being‘rconnected in series, said coupling
sections each having an electrical length equal
The following references are of record'in the
me Of this Patent;
to a quarterjwave length, and each ‘interposed 5
UNITED STATES PATENTS
lengthwiseibetween and interconnecting one of
said main sections and one end of said trombone
section, each of said coupling; sections having a
characteristic impedance equal to the geometric
'
Number
Name
1,841,473
1927393
mean of the characteristic impedances of the said =10
21233-165
sections to which it is immediately connected.
FRANK J. BINGLEY.
23661353
Date
Green ——————————— —— Jan- 191 1932
Darbord ———————— —— Sept- 19’ 1933
'
Hahn ———————————— —- Feb‘ 25- 1941
Jakel —————————— —- De°- 23- 1941