U.S. patent number 3,671,885 [Application Number 05/094,230] was granted by the patent office on 1972-06-20 for high frequency signal routing devices for use in catv systems.
This patent grant is currently assigned to Lindsay Specialty Products Limited. Invention is credited to Frank C. Pennypacker, Lindsay.
United States Patent |
3,671,885 |
|
June 20, 1972 |
HIGH FREQUENCY SIGNAL ROUTING DEVICES FOR USE IN CATV SYSTEMS
Abstract
Passive devices for signal routing such as directional couplers,
hybrid splitters and power inserters, for use in CATV or similar
signal distribution systems having improved operating
characteristics are obtained by the incorporation of pi-section
high-pass filters into such devices. Conventional splitters and
directional couplers are modified by the addition of inductances
and capacitances so that the required pi-section high-pass filters
are formed, with one inductive element of such a filter being
constituted by an inductive deviation, for example, a leakage
inductance of an existing component of such a device. Improved
radiofrequency signal return losses and inter-tap isolation are
provided over a much greater frequency range than was heretofore
possible.
Inventors: |
Frank C. Pennypacker, Lindsay
(Ontario, CA) |
Assignee: |
Lindsay Specialty Products
Limited (West Lindsay, Ontario)
|
Family
ID: |
27425418 |
Appl.
No.: |
05/094,230 |
Filed: |
December 2, 1970 |
Foreign Application Priority Data
Current U.S.
Class: |
333/131;
348/E7.053; 333/112; 333/126; 725/79; 333/124; 348/150;
348/149 |
Current CPC
Class: |
H03H
7/482 (20130101); H04N 7/104 (20130101); H03H
7/48 (20130101) |
Current International
Class: |
H03H
7/48 (20060101); H03H 7/00 (20060101); H04N
7/10 (20060101); H03h 007/48 () |
Field of
Search: |
;333/6,8-11 ;179/2C,2R
;340/310 ;325/308 ;307/3,73 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Paul L. Gensler
Attorney, Agent or Firm: Arne I. Fors Frank I. Piper
Claims
1. A signal routing device for use as a directional coupler having
at least three two-pole terminals with first poles of all said
terminals being electrically inter-connected by a base conductor
and with second poles of all said terminals being coupled together
in said device for the passage of electrical signals therebetween
and for the passage of radiofrequency signals between first,
second, and third terminals and, which includes a pi-section
high-pass filter connected between said first and second ones of
said terminals and said first and third ones of said terminals to
provide a radiofrequency signal return loss of at least about 20
decibels at said first, second, and third ones of said terminals
over an extended radiofrequency range, in which said first one of
said terminals is serially connected through a first coupling
capacitor to a first inductor effectively connected in turn to said
second one of said terminals, in which said first one of said
terminals is effectively grounded through a second inductor to said
base conductor, in which said first inductor is effectively
grounded intermediate its ends through a third inductor to said
base conductor whereby said first, second and third inductors and
said coupling capacitor together constitutes said pi-section
high-pass filter for the passage of radiofrequency signals from
said first one of said terminals to said second one of said
terminals at a first radiofrequency signal attenuation value, and
in which said third one of said terminals is inductively coupled to
said first inductor for the passage of radiofrequency signals from
said first one of said terminals to said third one of said
terminals at a second radio frequency signal attenuation value
greater than said first radiofrequency signal
2. A signal routing device as claimed in claim 1 in which said
second one of said terminals is connected to said first inductor
through a second coupling capacitor and in which fourth inductor is
connected to said second one of said terminals effectively to
ground said second one of said terminals to said base conductor to
provide a five-element pi-section
3. A signal routing device as claimed in claim 2 in which said
second and fourth inductors are connected to said base conductor
through a grounding capacitor to permit the passage of alternating
electric current up to about 400 Hz between said first and second
ones of said terminals serially
4. A signal routing device as claimed in claim 2 in which said
first inductor comprises a primary winding of a current-dividing
transformer, said primary winding being serially connected between
said first and second coupling capacitors, said primary winding of
said current-dividing transformer being serially grounded to said
base conductor through a primary winding of a voltage-dividing
transformer and said current-dividing transformer including a
secondary winding having a first end grounded to said base
conductor and a second end connected to a secondary winding of said
voltage-dividing transformer, and in which said secondary winding
of said voltage-dividing transformer is connected to said third one
of said terminals and serially grounded through a resistor
5. A signal routing device as claimed in claim 4 in which each of
said first and second coupling capacitors has a capacitance of from
about 500 to about 1,500 picofarads and in which each of said
second and fourth inductors has an inductance of from about 7 to
about 12 microhenries to provide a radiofrequency signal
attenuation value of from about 0.3 to about 1.5 decibels with a
radiofrequency signal return loss of at least about 5 MHz to about
300 MHz from said first one to said second one of said terminals
and a radiofrequency signal attenuation value of from about 8 to
about 16 decibels with a radiofrequency signal return loss of at
least about 25 decibels over said radiofrequency range of from
about 5 MHz to about 300 MHz from said first one to said third one
of said terminals.
6. A signal routing device as claimed in claim 5 in which said
second and fourth inductors are connected to said base conductor
through a grounding capacitor having a capacitance of at least
about 0.005 microfarads to permit the passage of alternating
electrical current having a frequency of up to about 60 Hz between
said first and second ones of said terminals.
7. A signal routing device as claimed in claim 5 in which said
second and fourth inductors are connected to said base conductor to
permit the passage of alternating electrical current having a
frequency of up to
8. A signal routing device having at least three two-pole terminals
with first poles of all said terminals being electrically
inter-connected by a base conductor and with second poles of all
said terminals being coupled together in said device for the
passage of electrical signals therebetween and for the passage of
radiofrequency signals between first, second, and third terminals
and, which includes a pi-section high-pass filter connected between
said first and second ones of said terminals and said first and
third ones of said terminals to provide a radiofrequency signal
return loss of at least about 20 decibels at said first, second,
and third ones of said terminals over an extended radiofrequency
range, in which said pi-section high-pass filter includes a first
coupling capacitor connected between said first one of said
terminals and an autotransformer inductor which is effectively
serially connected between said first coupling capacitor and said
base conductor, and a first inductor effectively connected between
said first one of said terminals and said base conductor, and in
which said second and third ones of said terminals are inductively
coupled to said autotransformer inductor for the passage of radio
frequency signals between said first one of said terminals and said
second and third ones of said terminals over said extended
radio
9. A signal routing device as claimed in claim 8 in which said
autotransformer inductor is connected intermediate its ends to a
center tap of a power-splitting inductor serially connected between
said second and third ones of said terminals with a shunt resistor
connected across
10. A signal routing device as claimed in claim 9 in which said
second and third ones of said terminals are connected to said
power-splitting inductor through second and third coupling
capacitors respectively and in which said second and third ones of
said terminals are effectively connected to said base conductor
through second and third inductors respectively effectively to
provide second and third pi-section high-pass filters connected to
said second and third ones respectively of said
11. A signal routing device as claimed in claim 10 in which said
center tap of said power-splitting inductor is connected to said
base conductor through a first grounding capacitor to provide a
T-section low-pass filter between said second and third ones of
said terminals and said first one of
12. A signal routing device as claimed in claim 11 in which each of
said first, second and third inductors has an inductance of from
about 6 to about 10 microhenries and in which each of said first,
second and third coupling capacitors has a capacitance of from
about 500 to about 1,500 picofarads to provide a radiofrequency
signal return loss of at least about 25 decibels over said
radiofrequency range of from about 5 MHz to
13. A signal routing device as claimed in claim 11 in which each of
said, first, second, and third inductors has an inductance of from
about 6 to about 10 microhenries, in which each of said first,
second and third coupling capacitors has a capacitance of from
about 500 to about 1,500 picofarads, and in which said first
grounding capacitor has a capacitance of about 5 to 12 picofarads
to provide a radiofrequency signal return loss of at least about 20
decibels at each of said first, second and third ones of said
terminals over a radiofrequency range of from about 5 MHz to about
300 MHz with an isolation between said second and third ones of
said terminals of at least about 25 decibels over said radio
frequency range of
14. A signal routing device as claimed in claim 13 in which each of
said first, second and third inductors has and inductance of from
about 6 to about 10 microhenries, in which each of said first,
second and third coupling capacitors has a capacitance of from
about 500 to about 1,500 picofarads, in which said first grounding
capacitor has a capacitance of about 5 to 12 picofarads and in
which said second grounding capacitor has a capacitance of at least
about 0.005 microfarads to provide a radiofrequency signal return
loss of at least about 20 decibels at each of said first, second
and third ones of said terminals over a radiofrequency range of
from about 5 MHz to about 300 MHz with an isolation between said
second and third ones of said terminals of at least about 25
decibels over said radiofrequency range of from about 5 MHz to
about 300 MHz and to permit the passage of alternating electrical
current having a frequency of up to about 400 Hz between said
first, second and third ones of said
15. A signal routing device as claimed in claim 11 in which each of
said first, second and third inductors are interconnected as well
as being connected to said base conductor through a second
grounding capacitor to permit the passage of alternating electrical
current between said first,
16. A signal routing device as claimed in claim 15 in which each of
said first, second and third inductors has an inductance of from
about 6 to about 10 microhenries and in which each of said first,
second and third coupling capacitors has a capacitance of from
about 500 to about 1,500 picofarads to provide a radiofrequency
signal return loss of at least about 25 decibels over said
radiofrequency range of from about 5 MHz to about 300 MHz.
Description
The present invention relates to passive signal routing devices for
use in community antenna television (CATV) systems in which
radiofrequency signals are distributed to individual households or
subscribers over a cable system from a community antenna.
With the ever-increasing acceptance of CATV systems and with the
ever-increasing number of television channels and FM radio stations
available to the public, the need for CATV system components
capable of effectively handling corresponding wider frequency bands
continues to grow. Furthermore, it is desired to provide said
passive devices for use in such systems which can not only be used
over such wider frequency bands but which will also provide
improved operating performance over such band widths.
Passive signal routing devices are used in conventional CATV
systems for many purposes such as, by way of illustration,
directional couplers for proportioning the signals carried by a
main trunk line of such a system to branch lines thereof.
Furthermore, signal routing devices conventionally known as
splitters are used for dividing such signals from branch lines
between the individual lines or cables provided for individual
subscribers. In many circumstances, it is also desired to provide
such devices by means of which low frequency alternating electrical
power, for example, 60 Hz power, can be inserted into the cables of
the CATV system for the purpose of energizing amplifiers
incorporated in the system to maintain signal strength throughout
the system or removed from the cables to power amplifiers and the
like.
For effective use in CATV distribution systems, it is generally
desirable for a device of the aforementioned type to provide the
best possible matching between the various input and output
signal-carrying cables connected thereto as indicated by the
highest possible return loss value, as well as providing maximum
isolation between the individual output cables so in turn
preventing the transfer of interference signals from one output
line to another. Such conventional passive devices generally can be
used for the distribution of signals over a frequency range from
about 30 to about 300 MHz and provide inter-cable isolation values
of about 23 decibels with radiofrequency signal return losses of
about 20 decibels.
It is a principal object of the present invention to provide
passive signal routing devices for use in CATV distribution systems
which can be used effectively over wider frequency ranges than
those previously known.
Another important object of this invention is the provision of
devices of the aforementioned type which provide improved
inter-cable isolation when such isolation is required and which
provide improved inter-cable matching, when such matching is
required, as indicated in the latter case by higher values for
radiofrequency signal return losses.
And another object of this invention is to provide passive devices
for use in CATV systems which can be constructed, if so desired,
for the passage therethrough of alternating electrical current such
as 60 Hz power for the purpose of energizing amplifiers or other
equipment incorporated in the system.
Other objects of the invention, and the manner in which they can be
attained, will become apparent as the description herein
proceeds.
The invention is based on the finding that the aforementioned
improvements in the operating characteristics of passive devices,
such as directional couplers, hybrid splitters and power-inserters,
for use in CATV distribution systems can be obtained to a
surprising extent by the provision in such devices of pi-section
high-pass filters conforming to certain requirements.
More broadly, the invention provides a device having at least three
two-pole terminals with first poles of all said terminals being
electrically interconnected by a base conductor and with second
poles of all said terminals being inductively coupled together in
said device for the passage of electrical signals therebetween and
for the passage of radiofrequency signals between at least first
and second ones of said terminals and, which device includes a
pi-section or multiple pi-section high-pass filter connected
between said first and second ones of said terminals to provide a
radiofrequency signal return loss of at least about 20 decibels
between said first and second ones of said terminals over an
extended radiofrequency range, a third one of said terminals being
inductively or otherwise coupled within said device to said first
one of said terminals to provide an isolation between said second
and third terminals of at least about 25 decibels over said
extended radiofrequency range.
The passive devices of this invention can be constructed in many
different ways. In the case of the application of the present
invention to the construction of power inserters, a novel device as
hereinbefore broadly defined is constructed so that the said third
one of its terminals is coupled through inductors within the device
to both the first and second ones of said terminals so as to
provide an isolation between said third one of said terminals and
each of said first and second ones of said terminals of at least
about 25 decibels over the extended radiofrequency range. With this
construction, alternating electrical current can be supplied
through said device from said third one of said terminals thereof
to both said first and second ones of said terminals while
maintaining the desired level of radiofrequency signal return
loss.
When the invention is applied to the construction of directional
couplers and splitters, the second and third ones of the terminals
of such a device are inductively and otherwise coupled within the
device to the first one of the terminals thereof through the
pi-section high-pass filter so as to provide a radiofrequency
signal return loss of at least about 20 decibels at each of the
second and third ones of said terminals and the first one of said
terminals over the extended radiofrequency range.
For use as a directional coupler, the first one of the terminals is
serially connected through a first coupling capacitor to a first
inductor effectively connected in turn to said second one of said
terminals, the first one of the terminals also being effectively
grounded through a second inductor to the base conductor. The first
inductor of such a coupler is also effectively grounded
intermediate its ends through a third inductor to the base
conductor so that the first, second and third inductors and the
coupling capacitor together constitute the pi-section high-pass
filter for the passage of radiofrequency signals from the first one
of the terminals to the second one of the terminals at a first
radiofrequency signal attenuation value, second and third inductors
acting effectively as one inductance. Furthermore, the third one of
the terminals of such a coupler is inductively coupled to the
aforementioned first inductor for the passage of radiofrequency
signals from the first one of the terminals to the third one of
such terminals at a second radiofrequency signal attenuation value
greater than the first radiofrequency signal attenuation value.
In the application of this invention to the construction of
splitters, a device in accordance with this invention and as
hereinbefore broadly defined is usefully constructed so that the
pi-section high-pass filter includes a first coupling capacitor
connected between the first one of the terminals and an
autotransformer inductor which is effectively serially connected
between that first coupling capacitor and the base conductor. A
first inductor is effectively connected between the first one of
the terminals and the base conductor, and second and third ones of
the terminals are coupled to such an autotransformer inductor for
the passage of radiofrequency signals between the first one of the
terminals and each of the second and third ones of those terminals
over the extended radiofrequency range.
The manner in which the concept of the invention is applied in
practice to the construction of such particular types of devices
will be more readily understood as the description herein proceeds
with reference to the specific embodiments shown in the
accompanying drawings.
The invention will now be described merely by way of illustration
with reference to the accompanying drawings in which:
FIG. 1 is a fragmentrary and schematic diagram of a CATV
distribution system showing the manner in which several different
embodiments of passive signal routing devices in accordance with
this invention can be utilized therein;
FIG. 2 is an enlarged schematic diagram of one of the directional
couplers utilized in the system shown in FIG. 1 showing
schematically the manner in which that coupler operates;
FIG. 3 is an enlarged schematic diagram of one of the splitters
utilized in the system shown in FIG. 1 showing schematically the
manner in which that splitter operates;
FIG. 4 is an enlarged schematic diagram of the power inserter shown
in FIG. 1 showing schematically the manner in which that power
inserter operates;
FIG. 5 is a circuit diagram of one previously known power inserter
showing that inserter connected in a CATV trunk distribution line
as in FIG. 1;
FIG. 6 is a circuit diagram of a power inserter in accordance with
the present invention;
FIG. 7 is a circuit diagram of one previously known two-way hybrid
splitter shown as being utilized, for example, in the CATV
distribution system of FIG. 1, and additionally constructed for the
passage of 60 Hz electrical power between its terminals;
FIG. 8 is a circuit diagram of an embodiment of two-way hybrid
splitter constructed in accordance with this invention;
FIG. 9 is an equivalent circuit of the splitter shown in FIG. 8 and
included herein for the purposes of explanation;
FIG. 10 is a graphical representation illustrating the improved
transmission characteristics of the splitter shown in FIG. 7;
FIG. 11 is a circuit diagram of another two-way hybrid splitter
constructed in accordance with the present invention which will
allow the passage of 60 Hz electrical power between its
terminals;
FIG. 12 is a circuit diagram of one previously known directional
coupler for use in a CATV distribution system; and
FIG. 13 is a circuit diagram of a directional coupler in accordance
with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIG. 1, there is shown therein generally at 10 a
CATV distribution system of a conventional type and intended for
the distribution of radiofrequency television and high frequency
radio signals from a community antenna (not shown) to a plurality
of households or subscribers indicated schematically at 11 through
18.
The CATV system 10 of FIG. 1 includes a trunk distribution line
fragmentarily shown at 20, extending from the community antenna
station (not shown) and to which the individual subscribers or
households 11 to 18 are connected by means of directional couplers
generally indicated at 21 and by hybrid splitters generally
indicated at 22.
For the purpose of maintaining adequate signal strength at all
positions along the trunk distribution line 20, it is conventional
to incorporate amplifiers 24 in that line 20. Such amplifiers 24
are conventionally powered by 60 Hz electrical current supplied to
the amplifiers through the main trunk line 20. Such power can be
inserted into the trunk line 20 at the community antenna station
but it is also conventional to insert additional power into the
trunk line 20 at one or more positions remote from the antenna
station. The system 20 is shown in FIG. 1 merely by illustration as
being supplied with such power from a step-down transformer 25
connected to the line 20 through a power inserter indicated at 26,
the transformer 25 being in turn supplied, for example, with
110-volt current from a power line 28.
It will be understood that, although the trunk line 20 and the
distribution cables between that line and the various sub-units of
the system 10 are shown in FIG. 1 by single lines, such cables will
customarily be in the form of coaxial cables having outer
conductive sheath electrodes which are interconnected through the
metallic casings of the various sub-units. Such second lines will
be referred to herein as ground or base lines but it should be
understood that such references are not intended to restrict the
invention to systems in which such lines are actually at ground
potential.
It must further be understood that the overall system 10 as shown
in FIG. 1 is included herein merely for the purpose of explanation
and that such system can be modified in many ways without departing
from the scope of the invention. Before proceeding further to set
down the novel features provided by this invention for use in the
signal routing devices which can themselves be utilized in the
system 10 shown in FIG. 1 or in other such systems, some further
observations concerning the various sub-units of that system will
now be considered.
In the first place, it will be understood that, in order to obtain
the lowest possible extent of radiofrequency signal reflection at
any of the components of the system 10, for example, at the
directional couplers 21 and at the hybrid splitters 22, it is
essential to have optimum impedance matching between the several
lines connected to such sub-units. It is also frequently desirable
to reduce the signal strength losses which occur on passage of
signals through such sub-units to the maximum possible extent.
Furthermore, maximum signal isolation between the individual
outputs of each of the hybrid splitters 22 is desirable as is well
known to those conversant with conventional CATV distribution
technology.
Referring now to FIG. 2, it will be seen that the directional
coupler 21 shown schematically therein is designed and constructed
to receive radiofrequency signals from the trunk line 20 and to
distribute a fraction of such a signal to the branch line indicated
at 31 while permitting the balance of the signal to pass to the
continuing main trunk line as indicated at 20'. To provide such
desired proportioning of the signal intensity, directional
couplers, such as directional coupler 21, are usually constructed
to give a signal attenuation between the lines 20 and 20' of about
0.2 to 1.5 decibels as indicated by the arrow 32 and a signal
attenuation range of about 8 to 16 decibels between the lines 20
and 31 as indicated by the arrow 33. The isolation between the
lines 20' and 31 is generally of the order of about 20 to 50
decibels. Although the directional coupler 21 is shown in FIG. 2 as
being designed for signal passage from the line 20 to the lines 20'
and 31, radiofrequency signal flow through that directional coupler
in the opposite direction generally is possible with conventional
directional couplers and is, in fact and as will be explained in
greater detail hereinafter, frequently a desirable feature in CATV
distribution systems incorporating devices constructed in
accordance with the present invention.
In the event that it is required to pass 60 Hz electrical power
through the directional coupler 21, that sub-unit is provided
internally with a connection between the lines 20 and 20' as
indicated schematically by the broken line 34 to permit such
current flow. As will be more fully understood as the description
herein proceeds, the present invention embraces directional
couplers with or without such power passing means.
The hybrid splitter shown at 22 in FIG. 3 differs from the
directional coupler 21 of FIG. 2 in that it is designed and
constructed to divide the input signal from the branch line 31
equally between its output lines 36 and 37. As was the case for the
directional coupler 21 of FIG. 2, maximum signal return loss in the
hybrid splitter 22 is desirable as is maximum isolation between its
output lines 36 and 37. If it is desired to pass 60 Hz power
between the input line 31 and the output lines 36 and 37, power
passing connections 38 and 39 are provided within the splitter 22
as will be explained in greater detail hereinafter.
It should be understood that, although each of the hybrid splitters
22 is shown in FIGS. 1 and 2 as being provided with two output
lines 36 and 37, it is equally possible to construct such a
splitter with three or more such output lines.
Referring now to FIG. 4 of the accompanying drawings, the power
inserter shown schematically at 26 therein is designed and
constructed to permit the passage of radiofrequency signals between
its terminals to which the main trunk lines 20 and 20' are
connected, such radiofrequency signal passage being indicated by
the broken line 41 and being effected with minimum signal
attenuation. The passage of radio frequency signals from either of
the lines 20 and 20' to the power supply line 40 from the
transformer 25 is essentially prevented. The power inserter 26 is
also constructed to allow 60 Hz power supplied from a supply line
40 to pass to either of the lines 20 and 20' as indicated by the
broken lines 42 and 43.
The manner in which signal routing devices, as exemplified by
hybrid splitters, directional couplers and power inserters are
constructed to provide the functions hereinbefore described will be
more readily understood when specific embodiments of such devices
are described in greater detail hereinafter with reference to the
remaining figures of the accompanying drawings.
Before proceeding further with such a detailed description, it
should, however, be noted that the system 10 is shown in FIG. 1 as
additionally being coupled to a radiofrequency signal source 50
intended for feeding radio frequency signals to the trunk line 20
for the passage of such signals to the aforementioned antenna
station. Such a signal source can, for example, be provided at a
location from which a "programm" may be "transmitted" to the
antenna station for subsequent "re-transmission" over the system 10
to the individual subscribers connected to that system.
In conventional CATV distribution systems, it is frequently
necessary to distribute radio frequency signals over a frequency
range of from about 54 to about 216 MHZ, corresponding to the
frequencies of existing television channels 2 to 13. Conventional
devices, as exemplified by hybrid splitters, fall short, however,
of optimum performance over such a frequency range. In general, it
has been customary to obtain about 20 decibels return loss in a
hybrid splitter and about 23 decibels isolation between the
individual output lines of such a splitter over the same frequency
range.
As already stated, it is an important object of this invention to
provide a signal routing device, such as a hybrid splitter, by the
use of which higher return losses as well as improved isolation
between the output lines of the splitter can be obtained. A further
important object of this invention is, as already explained, to
provide such improved performance over a wider frequency range than
was heretofore possible, thereby allowing a system incorporating
such devices additionally to be used for the transmission of
radiofrequency signals to the antenna station from a location
connected either directly or indirectly to the main trunk cable
without interference with the television program signals being
distributed over the system as well as to carry more than the
regular 12 channels. In such a circumstance, the devices of this
invention usefully are designed to operate effectively over an
extended frequency range of from about 5 to about 300 MHz.
Referring now to FIG. 5 of the accompanying drawings, there is
shown therein generally at 26 a conventional power inserter of the
type already described with reference to FIGS. 1 and 4 of the
accompanying drawings. The power inserter 26 has first and second
terminals 50 and 51 which are directly interconnected within the
inserter 26 by a conductor 53. In use, the terminals 50 and 51 of
the inserter 26 are connected, for example, in the trunk
distribution line as indicated at 20 and 20' to allow the unimpeded
passage of radiofrequency signals through that power inserter as
indicated by the double-headed arrow A.
A third terminal 52 of the inserter 26 is connected therewithin to
the conductor 53 through a high impedance inductor 54 so that 60 Hz
power, for example, at 30 volts, supplied to the terminal 52 from
the secondary winding of the power supply transformer 25 can pass
through the inductor 54 to the main trunk line 20, 20' as indicated
by the arrow B while essentially preventing the passage of
radiofrequency signals in the opposite direction.
The terminal 52 of the power inserter 26 is isolated from the trunk
line 20, 20' by capacitor 55 and inductor 54 to prevent
transmission of radiofrequency signals to terminal 52.
A power inserter constructed in accordance with the present
invention is shown generally at 58 in FIG. 6 of the accompanying
drawings. The power inserter 58 corresponds to the power inserter
26 already described herein in that it has first, second, and third
terminals 50, 51, and 52 respectively, terminals 50 and 51 being
intended for connection in the main trunk line 20, 20' and terminal
52 being intended for connection to the power supply line from the
transformer 25.
Internally, the power inserter 58 differs from the conventional
inserter 26 already described in that the first and second
terminals 50 and 51 thereof are interconnected by a pi-section
high-pass filter including first and second inductors 59 and 60
respectively and a coupling capacitor 61 connected between the
terminals 50 and 51. The third or power insertion terminal 52 is
connected to the opposite ends of the inductors 59 and 60 as will
readily be understood from FIG. 6 and the third terminal 52 is
internally grounded through the capacitor 55 as was the case in the
power inserter 26.
Typical component values and typical performance characteristics
for the conventional power inserter 26 (FIG. 5) and for the novel
power inserter 58 in accordance with the invention (FIG. 6) are
compared in Table I.
TABLE I Prior art Inserter 58 of inserter 26 the invention
_________________________________________________________________________
_ Inductor 54 6 microhenries -- Inductor 59 -- 6 microhenries
Inductor 60 -- 6 microhenries Capacitor 61 -- 820 picofarads
Capacitor 55 7.5 microfarads 7.5 microfarads Operating frequency
range (1) 30-300 MHz 5-300 MHz Minimum signal return loss (1) 20
decibels 23 decibels
_________________________________________________________________________
_ Notes: (1) Measured at terminals 50 and 51. (2) Measured over
specified f requency range.
The considerable gain in operating performance obtained by
constructing a power inserter in accordance with the teachings of
this invention will readily be apparent from the figures of Table
I.
In general, it can be noted that the coupling capacitor 61 normally
will have a capacitance of from about 500 to about 1,500
picofarads, more preferably of from about 500 to about 800
picofarads, while each of the inductors 59 and 60 generally will
have an inductance of from about 6 to about 10 microhenries, more
preferably of from about 6 to about 8 microhenries. The grounding
capacitor 55 usually will have a capacitance of at least about
0.005 microfarads.
Before describing the construction of a typical hybrid splitter in
accordance with this invention, the construction of a conventional
splitter which is also adapted to pass 60 Hz power will first be
described with reference to FIG. 7 of the accompanying
drawings.
The conventional two-way hybrid splitter generally indicated at 22
in FIG. 7 includes an autotransformer inductor 68 connected between
the first or input terminal 65 of that splitter and a base or
ground line or conductor as represented by a conductive casing 69
of the splitter. The autotransformer inductor 68 of such a splitter
is generally tapped as indicated at 70 at a position which will
give an output voltage equal to about 0.7 times the input voltage
and the tap-line 71 is connected to a center-tap position 72 of a
power-splitting inductor 73, the tap-line 71 being connected
through a grounding capacitor 74 to the base conductor 69. A shunt
resistor 75 of appropriate value is connected between the ends of
the inductor 73 while second and third output terminals 66 and 67
respectively are also effectively connected to opposite ends of the
inductor 73. Together with the flux leakage inductances of the
inductors 68 and 73, the capacitor 74 forms a T-section low-pass
filter.
If the conventional hybrid splitter 22 of FIG. 7 is to be used for
passing 60 Hz power between its input terminal 65 and its output
terminals 66 and 67, as actually shown in FIG. 7, blocking
capacitors 78, 79, and 80 are provided between the terminals 65,
66, and 67 respectively and the inductors 68 and 73 in the manner
shown in FIG. 7. Power-shunting inductors 81 and 82 connected
between the input terminal 65 and output terminals 66 and 67
respectively to allow the passage of such 60 Hz power across the
splitter.
As is the case with conventional splitters, hybrid splitters can be
constructed in accordance with this invention with or without such
power-passing circuitry. For the sake of simplicity, the
construction and operating features of a hybrid splitter in
accordance with the invention will first be described herein with
reference to FIGS. 8 to 10 of the accompanying drawings in which
such power-passing circuitry is omitted. The modification of the
splitter of FIG. 8 for its additional use in power-passing will
then be briefly described with reference to FIG. 11 of the
accompanying drawings.
Referring, therefore, to the embodiment of the hybrid splitter 85
of FIG. 8, that splitter is generally similar to the splitter 22 in
that its input terminal 65 is connected to one end of an
autotransformer inductor 68 which is itself tapped at 70 and the
tap-line 71 is connected to a center tap 72 of a power-splitting
inductor 73 which is, in turn, connected between the output
terminals 66 and 67 and in parallel with a shunt resistor 75. A
capacitor 74 grounds with aforementioned tap-line 71 to form an
internal T-section low-pass filter as already described with
reference to FIG. 7.
The hybrid splitter 85 differs from the splitter 22, however, in
that a third inductor 86 is connected between the input terminal 65
and the base conductor 69 while the input terminal 65 is also
connected to the autotransformer inductor 68 through a first
coupling capacitor 87. The inductor 86, the coupling capacitor 87
and the autotransformer inductor 68 effectively form a pi-section
high-pass input filter as will be explained in more detail
hereinafter with reference to FIG. 9 of the accompanying
drawings.
In accordance with a preferred feature of this invention, the
output terminals 66 and 67 of the hybrid splitter 85 are connected
to opposite ends of the resistor 75 through second and third
coupling capacitors 88 and 89 respectively and such output
terminals 66 and 67 are also individually connected to the base
conductor 69 through first and second inductors 90 and 91
respectively. In this way, pi-section high-pass output filters are
effectively provided in the splitter 85. The various components
constituting such output filters will be more readily understood
when the equivalent circuit of FIG. 9 is hereinafter
considered.
Referring, therefore, to FIG. 9 of the accompanying drawings, there
is shown an equivalent circuit of the hybrid splitter 85 of FIG. 8.
In FIG. 9, the autotransformer inductor 68 is shown as being
shunted by an inductor 92 which represents the magnetic coercive
force necessary to establish a magnetic field in the core of the
autotransformer coil 68. Furthermore, inductances 93 and 94 are
shown as being serially connected in the tap-line 71 between the
inductors 68 and 73. The inductances 93 and 94 represent
inductances due to flux leakages in the inductors 68 and 73
respectively. An inductor 99 shunts inductor 73 and, additionally,
a resistor 95 is shown as being connected in parallel with the
resistor 75, the resistance 95 representing resistive losses which
occur in the inductor 73. The deviations specifically hereinbefore
mentioned are those which have proved to be particularly
significant in determining the operating characteristics of hybrid
splitters of the type in question.
In order to obtain the desired improvements in accordance with this
invention in splitter operation, the inductance values of the
inductors 86, 90, and 91 and the capacitance values of the
capacitors 87, 88, and 89 are selected so as to provide the
required pi-section high-pass filters. In particular, the
pi-section high-pass input filter already mentioned is formed by
the inductance of the inductor 86, the capacitance of the capacitor
87 and by what might be described as the effective self-inductance
of the autotransformer inductor 68 as represented by the inductance
92 shown in the equivalent circuit of FIG. 9. Similarly, the
pi-section high-pass output filters are effectively constituted by
appropriate ones of the inductors 90 and 91 and of the capacitors
88 and 89 as well as by the effective self-inductance of inductor
73 represented by inductance 99.
Typical component values and operating characteristics for a
conventional two-way hybrid splitter as shown in FIG. 7 without the
power-passing function described and for a two-way hybrid splitter
in accordance with this invention as already described with
reference to FIGS. 8 and 9 of the accompanying drawings are set
down in Table II. Unless otherwise stated, identical components
were utilized in the two
splitters.----------------------------------------------------------------
-----------TABLE II Prior art Splitter 85 of splitter 22 the
invention
_________________________________________________________________________
_ Inductor 99 6 to 50 microhenries 70 microhenries Resistor 75 200
ohms 200 ohms Inductors 86, 90, 91 6 microhenries 6 microhenries
Capacitors 87, 88 and 89 1000 picofarads 820 picofarads Effective
frequency range (1) 30-300 MHz 5-300 MHz Minimum return Loss (1) 20
decibels 26 decibels Isolation (2) (3) 23 decibels 29 decibels
_________________________________________________________________________
_
FOOTNOTE: (1) Measured at each output terminals 66 and 67 and input
terminal 65.
FOOTNOTE: (2) Measured over specified frequency range.
FOOTNOTE: (3) Measured between output terminals 66 and 67.
In general, the inductors 86, 90, and 91 will each have an
inductance of from about 5 to about 8 microhenries, more preferably
from about 6 to about 7 microhenries, while the capacitors 87, 88,
and 89 will each have a capacitance of from about 600 to about
1,000 picofarads, more preferably from about 750 to about 850
picofarads.
The typical operating characteristics of the two hybrid splitters
reported in Table II are shown graphically in FIG. 10 of the
accompanying drawings which shows in broken lines the signal
transmission efficiency and signal return losses as represented by
voltage standing wave ratios (VSWR) for the conventional splitter
22 and, in solid lines, the same characteristics for the splitter
85 constructed in accordance with this invention. The considerable
improvement in operating characteristics obtained by the
application of this invention will readily be apparent from FIG.
10.
As already explained, a hybrid splitter in accordance with this
invention can also be constructed so as to have a power-passing
function and a splitter so constructed is shown generally at 95 in
FIG. 11 of the accompanying drawings. To avoid duplication of the
description herein, identical components of the splitters 85 and 95
are indicated by the same legends in both figures.
In the power-passing splitter 95, the inductors 86, 90, and 91 are
interconnected at 96 to provide 60 Hz current paths from the input
terminal 65 to each of the output terminals 66 and 67. Grounding of
the inductors 86, 90, and 91 and formation of the desired
pi-section high-pass filters is effectively obtained by the
provision of a grounding capacitor 97 connected between the common
connection point 96 and the base conductor 69.
Referring finally to the conventional directional coupler generally
indicated at 21 in FIG. 12 of the accompanying drawings, it will be
seen that the coupler 21 includes a current-dividing transformer
100 and a voltage-dividing transformer 101. The current-dividing
transformer 100 has a center-tapped primary winding 102 effectively
connected between the input terminal 103 and the output terminal
104 of the coupler which are connected to the main trunk line
sections 20 and 20' respectively. The secondary winding 105 of the
transformer 100 is connected between the base conductor as
indicated at 106 and a center tap 107 of a primary winding 108 of
the voltage-dividing transformer 101 while the secondary winding
109 of the transformer 101 is connected between the base conductor
106 and the center tap 111 of the primary winding 102 of the
transformer 100. One end of the primary winding 108 of the
transformer 101 is grounded at 110 through a resistor 112 while the
opposite end of that winding is connected to the third terminal 113
of the coupler 21. It will be understood that the center tap of
primary winding 102 and primary winding 108 can be omitted in
certain applications where a degraded return loss is acceptable or
where high attenuation between lines 20 and 31 is permissible.
The known directional coupler 21 is also shown in FIG. 12 as being
provided with a power-passing shunt inductor 120 interconnecting
the trunk line terminals 103 and 104 for the passage of 60 Hz power
therebetween, and with blocking capacitors 121 and 122. Since the
directional coupler 21 is conventional, it is considered
unnecessary to describe it in greater detail herein.
The directional coupler in accordance with the present invention as
indicated generally at 125 in FIG. 13 of the accompanying drawings
differs from the directional coupler 21 already described in that
separate first and second inductors 126 and 127 respectively are
connected between the terminals 103 and 104 respectively and an
internal connection point 130 which is effectively grounded through
a grounding capacitor 131.
The capacitors 121 and 122 and the inductors 126 and 127 together
with the effective inductances of the transformers 100 and 101
serve to form a five-element pi-section high-pass filter.
Improved operating characteristics were obtained with the
directional coupler 125 as compared to those obtained with the
conventional directional coupler 21 exactly as was the case for the
power inserters and hybrid splitters already described herein.
It will be understood that numerous variations can be made in the
construction of the directional coupler 125 without departing from
the scope of the invention. For example, if that coupler does not
need to have a power-passing function, the inductors 126 and 127
can be connected directly to the base conductor 106 and the
grounding capacitor 131 can be omitted. Similarly, in such a case,
one of the inductors 126 and 127 could be omitted so that the
coupler includes a three-element pi-section high-pass filter
instead of the five-element filter already described.
In the directional coupler 125 shown in FIG. 13, each of the
inductors 126 and 127 generally will have an inductance of from
about 7 to about 12 microhenries, more preferably from about 9 to
about 10 microhenries, while the coupling capacitors 121 and 122
will generally have a capacitance of from about 330 to about 650
picofarads, more preferably from about 400 to about 500 picofarads.
The grounding capacitor 131 will normally have a capacitance of at
least about 0.005 microfarads.
Such a directional coupler will usually provide a radio frequency
signal attenuation of from about 0.3 to about 1.5 decibels between
the input terminal 103 and the first output terminal 104 and a
radiofrequency signal attenuation of from about 8 to about 16
decibels between the input terminal 103 and the second output
terminal 113. For a typical directional coupler constructed as
shown in FIG. 13, a radiofrequency signal return loss of about 20
decibels between each of the output terminals 104 and 113 and the
input terminal 103 was obtained with an isolation between the two
output terminals 104 and 113 of at least about 20 decibels higher
than the said signal attenuation between terminals 103 and 104 over
a radiofrequency range of from about 5 MHz to about 300 MHz.
It will be understood that although the foregoing examples and
description relate to devices for the frequency range of from about
5 MHz to about 300 MHz, similar devices embodying the invention can
be used for higher or lower frequency ranges by decreasing or
increasing capacitors and inductors proportionally. For example, a
frequency range of from about 10 MHz to about 600 MHz can be
obtained by decreasing the capacitors and inductors to one-half
their values and a frequency range of from about 21/2 MHz to about
150 MHz can be obtained by raising the capacitors and inductors to
twice their values.
Also, although the foregoing description and examples relate to a
75 ohms impedance, it will be understood that the system can be
readily designed by the artisan for other impedances such as 50
ohms. For example, the impedance can be raised by increasing the
inductors and decreasing the capacitors and the impedance can be
lowered by decreasing the inductors and increasing the
capacitors.
* * * * *