Note: Descriptions are shown in the official language in which they were submitted.
1 2~Z
This invention relates to wired signal transmission systems and
more particularly it relates to an arrangement for encoding power flow for
the remote control of a subscriber's TV signals from a control center.
Background of the Invention:
Present cable TV systems generally transmit off-the-air television
broadcasts or other programs to subscribers who pay for the privilege of
receiving the programs. Within this field, there has long been a need for
a cost-effective method of controlling access to the cable system. At the
present time, particularly in a dedicated system where taps for connecting
subscribers to the system are installed during initial construction, a
technician is sent to a subscriber location and utilizes a lift-truck while
either connecting a subscriber's lead-in cable to a tap port, or disconnect-
ing the subscriber's cable from the port. It is obvious that a method for
providing such an action from a central office or control center would save
considerable time and money, and also improve the flexibility of the system
generally. A suitable remote control system would permit not only control
of a subscriber's access to the system as a whole, but might also allow for
partial access to the system on a time basis, an individual channel basis,
or both. Thus, a subscriber might be permitted to view none, one, several
or all of the available channels of programming. Furthermore, the sub-
scriber might be permitted to view one or more specific channels only at
specific times depending upon the terms of his subscription.
In addition to the advantages such a system can provide for the
control of basic services, it would be of even greater advantage in the
control of pay-TV services. For example, in some pay television systems
contemplated by the present art, it is proposed that coin boxes or other
receptacles suitable for receiving payment from a subscriber for viewing a
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particular television program be installed on the subscriber's television
receiver. Upon deposit by the subscriber of required payment into the pay-
ment receptacle, a switch located adjacent the receptacle or television
receiver would be actuated whereby viewing of the desired program would be
permitted. In order for the sponsor of the pay TV service to collect its
revenues it, too, would be required to dispatch an individual to the sub-
scriber's location to empty the payment receptacle. Enterprising subscribers
may, through the use of jumper wires, be able to bypass the payment recep-
tacle in order to view the desired program without making the required pay-
ment. Bypass is also possible where purchased tickets or other buying meansare needed to actuate the subscription channels.
It would be desirable to avoid these difficulties by permitting
the system management to provide or deny pay-TV or special channel services
on a remote control basis. Remote control of the provision of pay-TV service
on one or more channels would also be desirable to permit a multilevel
operation of these channels. As an example, it would be useful to provide
that a channel dedicated to pay-TV could be sold at one level of programming
(i.e., fee) in the morning, at a second level at midday, and a third level
in the evening, and to allow the system operator at the program center to
turn on or turn off subscribers who are buying or not buying that particular
level of service. In addition access to individual programs could be control-
led.
Still another remote control operation that is desirable, among
others, is the remote energizing of a transponder device which may very well
take signals from a store which serves as a memory for actions in the sub-
scrihar location, in a section of the cable system, in a nearby amplifier
or in a host of other potential locations where remote status indication is
of importance.
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One approach to remote control of a subscriber location has been in
essence to provide a duplicate of an RF paging system, requiring transmission
of special control signals below 300 khz transmitted in addition to programs
and power, but with some switches in place of the conventional "beeper" or
tone oscillator plus speaker. This is a complex system and extremely
expensive to implement, particularly for use in an outdoor environment. The
provision, installation and operation of the many required RF receivers makes
this system fail to meet the need for a cost-effective remote control cable
TV network.
Summary of the Invention:
The present invention meets these objectives and overcomes short-
comings of the prior art in providing a cable or wired transmission system
in which subscriber access is controlled in response to coding of the power
being transmitted in the system for normal energization of portions of the
system, such as repeaters or amplifiers.
A coaxial cable, as used in cable TV systems generally has two
separate bands of transmissions. One permits power to be carried in the
system, to provide energy for trunk and distribution amplifiers along the
system. The other band permits the transmission of the RF program signals.
In conventional systems, separate portions of the system, such as individual
trunks or groups of subscriber stations, may be powered by respective power
supply units, each energizing a section of the system allocated to a par-
ticular set of stations.
To utilize to the fullest extent the already existing systems, the
present invention provides an arrangement by which special subscriber connec-
tion d~vices (taps) are provided, each for coupling a small number (e.g.,
four) of subscribers to the cable system. Each tap served from any one power
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supply unit is given an individual address code, and when properly addressed
will actuate any one or more functions for the particular subscriber, such as
connecting or disconnecting the subscriber from the cable or jamming his
signal, either on an individual channel basis or completely, or even for a
predetermined time interval. The same power supply unit will supply energy
for controlling the various modes of subscriber access to the system as well
as energy for other electrical devices serving the taps, such as repeater
or distribution amplifiers.
To accomplish this, the required power produced at the power supply
unit is specially coded as part of this invention in accordance with tap-
address and control signals.
In order to have the multiplicity of power supply units provide
this coded power flow, each power unit may also be allocated a power unit
address code, and the coding of its power for actuating the required taps may
be appropriately controlled from the central control point ("head end") as in
response to a modulated RF carrier upon which both the power unit address,
the tap or subscriber address, and subscriber status information is encoded.
As a further economy in the system, the RF carrier used may be a pilot-
frequency carrier already utilized in the system, as for amplifier gain or
level control purposes.
The RF carrier signal transmitted from the central station may be
serially modulated with data defining the desired control functions relevant
to a subscriber and the address of the subscriber's tap and of the power
supply unit serving the tap. The modulated RF carrier may be transmitted to
all of the power supply units in parallel. Each power supply unit generates
power at a quiescent frequency while decoding the data transmitted on the
received RF carrier. When the address contained in a particular data
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word matches that of the respective power supply unit, the power output of
the power supply unit is coded pursuant to the present invention in accordance
with the subscriber tap address and instruction data of that word encoded
on the RF carrier to further transmit or relay that data to all of the sub-
scriber taps served by that power unit. The power transmissions received at
all the subscriber taps are continuously decoded, also in accordance with
the present invention. When the tap address encoded on the power transmission
corresponds to that preset in a tap, the subscriber tap port control function
apparatus for that tap is actuated in accordance with the information relayed
through the power transmission. In effect, the system can be thought of as
being powered by data which is arranged to control remote components in the
system.
In accordance with the invention there is provided an addressable
tap device for use in a wired broadcast cable system for disseminating
program materials from a central station to subscribers at any of a plurality
of remote terminals included in said tap device and adapted to be coupled to
respective controlled devices to achieve any of a plurality of desired con-
trol functions at each controlled device, said system including power-con-
suming units at differing locations along said cable system and at least one
power-supply unit for supplying power to said power-consuming units, said
supplied power from each power-supply unit being adapted to be encoded in
accordance with data signals each representative of a particular controlled
device and of a particular set of desired control functions for the control-
led device, said tap device being adapted to be coupled to said cable system
at a desired location interposed between said central station and one or
more of said controlled devices and also being adapted to be energized by
said supplied power; said tap device comprising: a decoder adapted to respond
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to said coded supplied power for deriving power to energize said tap device
and for deriving signals representative of one or more desired control
functions to be provided at the respective tap device, and one or more
further devices adapted to respond to said derived control function signals
for determining the functions obtainable at one or more of said terminals
included in the tap device, said system further including means for transmit-
ting said program materials to said tap device independently of transmission
of said coded power, and said controlled devices including switching devices
for controlling access by said subscribers to said program materials.
In accordance with a further aspect of the invention there is a
cable system comprising: a power cable, a plurality of subscriber devices;
a source of a plurality of command signals; a plurality of addressable tap
devices coupled to said cable and each assigned an individual address, each
tap device being adapted to be coupled to a group of one or more subscriber
devices; a controlling device included in each tap device and adapted to
cause each coupled subscriber device to assume at least one functional
condition in response to a respective predetermined command signal; a power
supply unit coupled to said cable and adapted to supply power for energizing
said tap device and their controlling devices, said power supply unit being
adapted to provide alternating power with individual cycles of either of two
fixed durations, in predetermined sequences of said cycles, certain of said
sequences being representative of the addresses of individual tap devices
and also being representative of particular command signals for determining
the functional condition of said subscriber devices; a decoder included in
each said tap device and responsive to those of such sequences of power
cycles which are representative of the address of said tap device and also
representative of a command signal for a particular subscriber device coupled
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to said tap device, for causing said latter subscriber device to assume a
functional condition corresponding to said command signal.
In accordance with another aspect of the invention there is provided
in a cable system in which supplied power is encoded by causing each full
cycle of said encoded power to have one of several durations in accordance
with signals representing the addresses and desired commands for a plurality
of controlled devices, the invention comprising an addressable tap device
adapted to be coupled to at least one of said controlled devices, said tap
device including: a controlling device energized by said encoded power and
responsive to said desired command signals to place at least one of said
controlled devices in any of at least one functional condition corresponding
to said commands; and a decoder energized by said encoded power and responsive
only to encoded signals representing an address individual to said tap
devices, for supplying to said controlling devices signals representative
of said command.
In accordance with another aspect of the invention there is provided
in a subscriber cable television system for selectively addressing and
controlling from a central station any of a plurality of subscriber devices
to achieve any of a plurality of desired control functions at each subscriber
device, said cable system including power-consuming units at different
locations along said cable system and a power-supply unit for supplying power
to said power-consuming unit, said supply power from said power-supply unit
being encoded in accordance with data signals each representative of a
particular group containing at least one of said subscriber devices and of
a particular set of desired control functions for one of said group of sub-
scriber devices, by causing each full cycle of said encoded power to have
one of a plurality of durations in accordance with said data signals, the
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invention comprising a tap device adapted to be coupled to said cable
system at a desired location between said central station and said group of
subscriber devices, said tap device being also adapted to be energized by
said supplied power, said tap device comprising: a decoder responsive to
said encoded supplied power for deriving therefrom power to energize said
tap device and also for deriving signals from said encoded power represent-
ative of at least one desired control function to be provided for said group
of subscriber devices coupled to said tap device, and at least one controlling
device responsive to said derived control-function signals for determining
the control functions to be performed on a selected one of said group of
subscriber devices.
The present invention thus provides a wired program disseminating
system comprising a plurality of active elements, at least one power supply
unit for supplying AC power transmission to the active elements, means for
coding the powering, particularly as to frequency, and means for controlling
the operation of component parts of the system in dependence upon the coding
of the power.
It is therefore an object of this invention to provide apparatus
and a method of producing a coded power flow useful for an improved wired
broadcasting system in which the subscriber stations may be remotely control-
led from a central program exchange.
An additional object of the invention is to provide a system and
method for producing and utilizing a coded power flow useful in connection
or disconnection of a remote subscriber by instructions transmitted from a
program control center.
Another object of the invention is to provide a cable TV system
wherein control of subscriber access is economically achieved by coding the
power transmitted to energize operation of the subscriber taps.
Still another object of the invention is to transmit subscriber
access data to the power supply unit associated with each respective sub-
scriber tap by means of a readily available RF pilot carrier signal.
An added object of the invention is to provide apparatus and a
method for encoding power flow useful with remote control switching equipment
at or adjacent subscriber's stations addressable to each specific subscriber
station from a central program control facility.
Another object of the invention is to provide apparatus and a
method of encoding and decoding power flow useful in a system using conven-
tional program distribution facilities for carrying coded messages to
address the subscriber control stations.
A further object of the invention is to provide a cable TV system
wherein subscriber access to some, as well as all, of the available TV
transmission channels may be remotely controlled from a central station.
Still a further object of the invention is to provide a cable TV
system wherein all or part of an individual subscriber's access may be remote-
ly controlled in accordance with a time schedule.
Other and further objects of the invention will be apparent from
the following drawings and description of a preferred embodiment in which
like reference numerals are used to indicate like parts in the various views.
Description of the Drawings-
.
Figure 1 is a basic block diagram showing the general flow ofsignals from the head end to the subscriber function control switches in a
cable TV system incorporating the invention.
Figure lA is a system schematic block diagram of a preferred embodi-
ment of a system incorporating the invention illustrating the components of
the blocks of Figure 1 and their interconnection in a multi-subscriber
situation.
Figure 2 is a block diagram showing examples of the various types
of apparatus which can be used to transmit subscriber control information
from the head end of a cable television system incorporating the invention.
Figure 2A is a schematic diagram partly in block form of the head
end encoder of a preferred embodiment of the invention.
Figure 3 is a schematic diagram of a power inserter and RF tap
for the power supply of the preferred embodiment of the invention.
Figure 3A is a block diagram of a carrier receiver/detector useful
with the preferred embodiment of the invention.
Figure 4 is a block diagram of program circuits for encoding the
- power supply frequency with binary code data words.
Figure 4A is a schematic diagram of the d.c. power supply section
of a power supply unit useful with a preferred embodiment of the invention
with the power circuits shown in block form.
Figure 4B is a schematic diagram partly in block form of a power
switching circuit for the preferred embodiment of the invention providing
AC power, encoded with binary coded signals.
Figure 5 is a schematic diagram of the power supply section of a
tap useful with the preferred embodiment of the invention.
Figure 5A is a schematic diagram of a tap which may be used with
the apparatus of the present invention.
Figure 6 is a block circuit diagram of tap logic control circuits
for receiving and decoding program control data.
Figure 7 is a schematic diagram of a switch used to control access
of a subscriber to basic service and pay service useful with the preferred
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embodiment of the invention.
Figure 8 is a schematic diagram of a jamming oscillator.
Description of the Preferred~Embodiment:
Referring now to Figure 1, the control system is shown in general
block diagram form to illustrate the manner of communicating control signals
between a control center or head end 1 and a plurality of subscriber function
control switches 40a-c through a wired network of cables 4 which will pass
both low frequency power signals (in a range from 50 Hz to 50 khz for example)
and high frequency program signals (such as radio and television programs in
a range above 100 khz for example). The control signals in passing from
control center 1 over cable 4 to one or more remote power supply units 2 may
be carried as modulation on RF carrier frequencies. Each power supply unit
is preferably a pre-existing unit for supplying necessary power, such as to
repeater amplifiers, in the cable system, and adapted according to this
invention to provide control signals for determining the functioning of the
control switches 40a-c. This invention relates primarily to control signals,
the path of program signals being conventional and within the province of
those skilled in the art, as exemplified for example in United States Patents
3,423,521 and 3,922,482.
Simplified equipment is afforded by this invention over known type
of addressable paging receivers and decoders operating with radio frequency
and tone signals to select one of a plurality of stations for a transmission,
where both transmitting and receiving circuits are of necessity complex.
This simplification is accomplished by coding the power transmission from
power supply units 2 with control codes to transmit commands to addressable
tap units 3 over cable 42. A number of taps 3 may be serially connected
along a single line if desired. Thus each control center can program a
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plurality of power supply units 2 and each power supply unit can in turn
transmit commands to a plurality of addressable tap units 3, each tap unit
serving one or more subscribers. Each tap 3 includes a decoder unit 35,
the output of which determines the operation of switches 40a-c which control
the functioning of a local program display apparatus 46 such as a television
receiver.
Each power supply unit is controlled to provide under command of
the control center 1 power of either 60 Hz or 120 Hz on output cables 42.
The code for example can comprise a sequence of single cycle "0" or "1" bits.
In each addressable tap 3, a 120 Hz cycle is decoded as a logical "0" and a
60 Hz cycle as a logical "1" to thereby provide a digital control signal at
decoder 35. While it is preferable that the full cycles of encoded power
representing the data bits have a frequency relation of 2 to 1, this may be
modified to provide cycles of different frequencies, such as 3 to 1 or even
non-integrally related, but with substantially different durations. Thus
each subscriber may be addressed separately from a control center for control-
ling a plurality of selected functions at the subscriber station by operating
those control switches 40a-c. Accordingly, complex RF and tone receivers and
detectors are not required at the subscriber locations.
Figure lA illustrates a preferred embodiment of the invention, in
the form of a cable TV system such as a CATV system, showing the principal
components. The system comprises a central station or head end 1 from which
TV signals originate and by which access to the TV system by all subscribers
is controlled, and a plurality of controlled subscriber directional taps 3a
to which the television receivers 46 of the system subscribers are connected,
usually via tunable requency converters 45. Each of a plurality of power
supply units 2 provides power to RF signal amplifiers (e.g., 110) and to a
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number ~typically up to 1024) of subscriber taps 3 for energization of the
electrical and electronic components associated therewith, e.g., switches
40a-c, and control logic 135 forming part of decoder 35. Each subscriber
tap 3 has associated with it one or more switching devices 40a-c, which
permit appropriate TV signals transmitted by the cable TV broadcaster over
the system to be received by the television receiver 48 of the subscriber.
Certain switching devices may be used to isolate the receiver set 46 from
the cable TV system completely, while others may be used to enable or disable
specific TV programming channels where several programs are simultaneously
transmitted on respective channels.
The same RF signal transmission from the head end is received by
all of the system power supply units 2. Similarly, the coded power trans-
missions of a particular addressed power supply unit 2 are received
simultaneously by all of the taps 3 which are served by that supply unit 2.
As seen below, this permits the several power units to be addressed serially
at a high rate (e.g., 20 kilobits per second) so as to be almost simultaneous-
ly addressed, while the various sets of taps 3 actuated from the respective
power units may then be addressed simultaneously, in parallel, at a slow
rate (e.g., about 60 to 120 bits per second). In the operation of the system,
it will be understood that a signal need be sent out as to a particular
subscriber station only when a change is desired in the access of that
station to the cable system.
As can be seen in Figure lA, the head end or central station 1
comprises an RF television program signal source 102 having an output at
which there are provided RF signals modulated with audio and video television
inQrmation for perception by a subscriber's standard TV receiver. Also
included in the head end 1 is an RF signal generator 8 which can be a con-
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ventional pilot signal generator.
The generator 8 provides at its output a constant frequency RF
carrier signal. In a preferred embodiment of the invention the nominal
frequency of the RF carrier signal is 220 megahertz. However, the invention
is not limited to use with carrier signals of this frequency and other
frequencies may be used in the practice of the invention. The RF signal
generator 8 may be the same signal generator used to provide a reference or
pilot signal for controlling gain or level of amplifiers in the CATV cable
provided that the system is one which is operable with an unmodulated pilot
signal. If an unmodulated pilot signal generator is not available one can
be added to the system in the manner known to those skilled in the art.
The output Qf the RF pilot signal generator ~that is, illustrative-
ly the 220 megahertz signal) is applied to the input of an encoder 104
located at the head end 1. The encoder 104 modulates the RF signal from the
generator 8 with subscriber control function information in a manner to be
described and provides a modulated RF signal at its output. The RF signal
modulated with such subscriber control function information and the RF
television program signal from the source 102 can both be combined in a
conventional summing circuit 105 and transmitted from the head end 1 on a
common coaxial cable 4 to the power supply units 2.
Each of the system power supply units 2 comprises a power inserter
24 (shown in more detail in Figure 3) which has an input 140 to receive the
RF carrier signal modulated with subscriber control function data from
encoder 104 and an output 146 for applying that modulated signal from encoder
104 to a carrier receiver/detector 25 (shown in more detail in Figure 3A)
which demadulates that carrier signal. In addition, the power inserter 24
has a second input 150 for receiving power from the output of a power switch
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22 (shown in Figure 4B) and a second output 141 for transmitting the received
power from the power switch 22 and the RF TV signals along the cable portion
42 connecting the power supply 2 with a plurality of addressable subscriber
taps 3.
The transmitted power from the power switch 22 is AC having a
square wave form derived by switching the input to the power switch 22
between respective positive and negative output terminals of a DC power
supply 106. The DC power supply 106 may be a standard source of alternating
current such as of 50 or 60 Hz which is converted to DC at appropriate vol-
tage levels, or can comprise one or more batteries to provide the necessarydirect voltages. In a preferred embodiment of the invention the positive and
negative DC outputs of the power supply 106 between which the power switch
22 alternates are illustratively of the value of + 62 volts respectively. The
DC power supply 106 also has outputs through which the plus or minus direct
voltages are applied to a power supply logic circuit 108.
The power supply logic circuit 108 (shown in Figure 4) includes
digital circuitry for decoding the modulation indicative of subscriber
address and control function information which is provided at the output of
the detector 25 and for applying a control signal to the power switch 22 for
correspondingly alternating the input of the power switch 22 between the
positive and negative outputs of the DC power supply 106. At the output of
the power switch 22 there are produced AC square waves which are encoded
with digital data according to the subscriber control function information
originally modulated on the RF carrier from the generator 8 at the head end 1.
The encoded AC square waves have a variable cycle and carry data at one bit
per cycle, that is, at a variable bit rate.
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The encoded AC square waves are applied to the input 150 of
the power inserter 24 and are inserted through the output 141 of the power
inserter 24 onto the cable portion 42 for transmission to the addressable
subscriber taps 3. The power output of the power supply units 2 may be
applied back along the cable portion 4 toward the head end 1 as well as
forward toward the taps 3 along the cable portion 42. This may energize
amplifiers and other equipment either between the head end 1 and power supply
units 2 or between the power supply units 2 and their associated subscriber
taps 3 with appropriate power. The power transmitted along the cable portions
4 and 42 may for example be utilized to drive repeater amplifiers 110 for
amplifying the program signals being transmitted to the subscriber taps 3.
Each addressable subscriber tap 3 has a basic service module 112
having an input at which the RF program signals and power are received and
an output through which the RF program signals and power are transmitted to
the remaining addressable taps. The output of the basic service module 112
is also applied through switches 40a (one for each subscriber served by the
tap 3, shown illustratively as four in number) to frequency converters 45,
each connected to one subscriber's television receiver 46 of the set which is
served by that particular addressab,le tap 3. The output of the basic service
module 112 may contain all of the transmitted RF program signals, such as
basic TV programs, pay-TV channel programs, and other special services.
In order to prevent unauthorized subscriber access to particular
channels (e.g. a pay-TV channel for which no subscription has been taken~
jamming oscillators 116a and b may b,e connected through switches 40b and c
respectively to the inputs of the frequency converters 45 associated with
the respective television receivers 46 to be barred. Each of the jamming
oscillators 116a, b provides at its output a signal the frequency of which is
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varied about a nominal center frequency nearly equal to the carricr frequency
for one of the channels to be barred.
The frequency of the jamming oscillators is varied by means of a
wobbulator circuit, such as an oscillator with a frequency tuning element
such as varactor diode to which a varying voltage is applied. As the
voltage applied to the varactor diode changes so does tllc frequency of the
wobbulator output. A variable-frequency jamming oscillator is preferable
to a fixed frequency oscillator in that a fixed frequency jamming signal has
been found to be only partially effective in denying non-subscribers access
to the information on the pay channels which are to be provided only upon
special subscription.
Complete service to a subscriber is enabled by closing the switch
40a linking the output of the basic service module to the tap output port
49 serving the subscriber's converter and by opening the switches 40b, c
on the jamming oscillators which connect the outputs of the jamming oscil~-
ators 116a, b to that output tap port 49. Directional couplers ~not shown)
may be provided between the output of the basic service module and the output
port 49 to prevent signals from re-entering the output of the basic service
module, which might cause one subscriber to interfere with the reception of
another subscriber due to the limited isolation available in the basic service
module.
In a preferred embodiment of the invention a single addressable tap
3 serves four subscribers. In each subscriber tap there are three switches
40a, b, c associated with each of the respective four subscribers or a total
of 12 switclles connecting the four subscribers' television frequency converters
45 to the basic service module 112 and jamming oscillator modules 116a and b.
The first (40a) of the three switches connects the subscriber's output port
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49 with the basic service module 112. The remaining two switches 40b, c
connect the subscriber's output port 49 with the jamming oscillators 116a
and 116b respectively.
In addition to the 12 control function codes associated with the
twelve switches 40a, b, c there are two further control codes each of which
controls program reception for all four subscribers. These two control codes
and reset devices control all the switches 40a-c of the basic service module
and jamming oscillators. Specifically, one of these two codes sets all of
the output latches in the tap logic circuitry (to be later described in con-
junction with Figure 6) to a logical value of "1" and the other code resets
the latches to "0".
A DC power supply 120 for the tap 3 receives at its input from the
power supply unit 2 the AC square wave power encoded with subscriher control
function information. The tap power supply 120 provides at its outputs 120a
and 120b DC power for energi7ing the jamming oscillators 116a, b and a tap
logic circuit 35. The incoming power flow and program signals are routed via
lead llOa through the basic service module 112 and is interrupted if the
basic service module 112 is removed.
The encoded square wave signals from the power supply unit 2
received in the tap power supply 120 are also supplied by lead 120c to a
data output of the power supply 120. This data output of the power supply
120 is connected to an RC filter the output of which is applied to the data
input 35a of the tap logic circuit 35. The data encoded on the AC square
wave power is decoded in the tap logic circuit 35, and the decoded data is
converted into signals which are applied from outputs 35b of the tap logic
35 to the control inputs of function switches 40a-c to regulate subscriber
access to the programs of the system.
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At the head end 1, a bit stream comprising a data word is formulated
for each individual system subscriber. The data word includes information
identifying the subscriber's unique tap address, his system access control
functions and a power supply address which uniquely corresponds to the power
supply unit that energizes the subscriber tap which is to be controlled.
All the complete data words are sent out in sequence, and simultaneously
to all the power supply units 2. Only those data words received at a given
power supply unit 2 which contain address information corresponding to the
address of that power supply are used to modulate the power output from
that power supply unit 2. Data words which are not intended for that power
supply unit and its associated taps are ignored, and have no effect upon
the output of that power supply unit. Each subscriber tap thus responds
only to data words contained in the power supplied to it from its own power
supply unit. This reduces the amount of address decoding necessary in each
tap and the time to communicate with all the taps in the system. When one
power supply unit is communicating with a tap, a second power supply unit
can be addressed so that it will concurrently communicate with a tap in its
section.
As shown schematically in Figure 2, the head end of the system
generally includes an RF pilot generator 8 the output of which is of constant
frequency and amplitude. The RF pilot generator may be conventional in
design, and any suitable carrier frequency may be used, a frequency of 220
MHz being employed in a preferred embodiment of the invention. This signal
may now perform two functions, namely, the usual pilot-frequency function
(e.g., for gain level control of repeater amplifiers) and as a carrier for
the subscriber control flmction information.
The output of the RF pilot generator 8 is applied to an RF switch 9
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which when closed permits transmission of the RF carrier to a cable 19 and
which when opened cuts off RF carrier transmission to cable 19. Thus by open-
ing and closing the RF switch, pulses of RF carrier transmission may be pro-
duced with the width of the pulses depending upon the duration of the closing
of the RF switch. The switch thus serves as a modulator for the pilot
frequency signal. By assigning two possible widths to each pulse produced by
RF modulator switch 9, each pulse may contain one bit of information. For
example a wide pulse may signify a binary 1 while a narrow pulse signifies a
binary 0.
The 25-bit data words are serially encoded on the RF carrier by the
use of pulse duration amplitude modulation (PDM), as described. While other
modulation schemes may be used, and this invention is not limited to the
particular modulation scheme employed in the preferred embodiment, PDM has
been found desirable in that the data is self-clocking, obviating any require-
ment for complicated bit synchronization, and because standard pilot carrier
transmitters and receivers may be easily adapted to the application herein
described. In view of the number of bits that must be received by a tap to
select and control the subscriber access, as will subsequently be described,
a data rate from the head end of 20 kilobits per second has been found useful.
The opening and closing of the RF switch is accomplished in response
to the output of an output module 41 which may receive data representing the
identities of each of the subscribers and the latest control function status
assignable to each of the subscribers. As discussed more in detail below,
this data may be derived from a mini-computer 11, a keyboard and display 12,
or a recorder such as a paper or cassette tape unit 13. Subscriber control
data may be manually inserted into the system by an operator by means of a
manual control box 10 operatively connected to the RF switch for opening and
-20-
z
closing the RF switch according to the entered subscriber data.
A 25-bit word has been found suitable for trans~itting access
information for each subscriber of a moderately large size cable TV system.
Two of the 25 bits are used to signify the start and stop of each data
word, respectively. Seven bits are used to identify the address of the
power supply unit serving the subscriber tap which is to be controlled by
the data word. This permits communication with up to 128 (27) power units.
Ten bits are used to identify the subscriber tap address to be controlled.
The use of a ten-bit tap address permits communication with up to 1,024
four-subscriber taps for each of the power units in the system or up to
4,096 subscribers per power unit. Five bits of information are designated
for defining the desired control function for the individual subscriber
whose access to the system is being determined. The five-bit control seg-
ment of the data word can control, for example, up to 16 two-state control
functions, e.g., two-position switches. This will provide 4 functions for
each of the four subscribers. One bit is provided for a parity check of
the transmission links. Using one RF pilot frequency, therefore, up to
524,288 subscribers can be controlled. By adding more frequencies, this
number can be increased.
In the manual control mode shown in Figure 2, utilizing control
box 10, the control signals serially applied to the input of the RF switch 9
can come from a plurality of encoded switches. Electronic logic decoders
provide the 25 bits of information to be transmitted. In such a manual
system, a customer "address" book is referenced by an operator who sets the
switches to indicate the bits of information which are to be transmitted.
A "transmit" button (not shown) may then be pressed, at which time the control
box 10 will automatically serially transfer the entered data to the amplitude
-21-
2:
modulator 9 to encode the RF carrier signal with the desired subscriber
address and control data.
In a more sophisticated system, less prone to operational errors,
a mini-computer 11 and keyboard with a small display 12 are provided. The
subscriber "addresses" ~for power unit and tap) can now be easily entered in
decimal notation. With a teletype machine, or other printer (not shown), a
printed record of all entries may be maintained, as well as a permanent
paper or magnetic tape, if desired, for future automatic updating or control
of the network. Another system option incorporates a dual magnetic cassette
or cartridge storage and thermal printing machine 13. One cassette or
cartridge can contain the customer addresses (in any order desired), and
another a record of entries for the day (week or month). For a reasonably
sized system, several cassettes or cartridges will be required to hold all
of the customer addresses. Updated address tapes can be made, by the same
mini-computer (from the entry record tape and the keyboard) during off hours.
A large tape unit, e.g., a reel-to-reel recorder employing magnetic tape
may be used to hold all customer data on a single tape.
A further optional refinement to the system includes a large disc
memory 14, a real time clock 15, and a high speed line or form printer 16.
All of the customer's data may now be in the disc memory, such as name,
address, financial record, tap and power unit addressesl and program(s)
desired, etc. This system can automatically maintain billing status;
generate invoices and internal program usage printouts; automatically turn
on and off the desired programs for customers; and automatically update the
entire system (at night) to catch up with low priority updates and correct
any noise-induced errors. If a two-way trunk is in use, the return data may
include status information from the power units on signal levels, quality,
etc., as well as customer data, all of which may be monitored by the
computer.
In a preferred embodiment of the invention, keyboard and display
12 is used to enter the data for subscriber addressing and function control
in decimal form. Referring now to Figure 2A, the data is manually entered
in decimal form by means of a conventional keyboard 122 operatively connected
to a conventional storage register 124. A commonly available electronic
desk calculator may be used to provide the keyboard storage register and
display operatively interfaced to the output module 41. Digits punched on
the keyboard 122 are individually stored in the register 124 for display on
an indicator ~not shown) of the type commonly found on electronic calculators
(e.g., light-emitting diodes or gas discharge numeric indicators). The output
of the storage register 124 is connected to an interface module 126 which
includes a conventional 7-segment to binary-coded-decimal (BCD) converter 128.
The output of the converter 128 is connected to eight individual conventional
parallel/serial registers 130a-h, the first 130a of which holds 5 bits of
information and the remaining ones 136b-h each capable of storing up to four
bits of information, that is, each having four bit positions. The individual
parallel/serial registers 130a-h are connected to form a single par./ser.
register capable of storing 25 bits of information, that is, having 25-bit
positions, in a conventional manner known to those skilled in the art, and
may be replaced by a single 25-bit register. The data output of the par./ser.
register 130a-h is then applied to the RF amplitude modulator 9 which
correspondingly amplitude modulates the RF carrier signal from the RF signal
generator 8, as described.
A 25-bit data word for coding on the RF carrier signal is stored
in the parallel/serial registers 130a-h as follows. A stop bit is automatic-
-23-
~1~2~
ally entered into the first bit position of the par./ser. register 130a.
The second bit position of the register 130a holds a parity bit the pro-
vision and purpose of which will later be described. The remaining three
bit positions of the first par./ser. register 130a hold the first three bits
of the power unit address of the binary-coded data word. The second register
130b holds the remaining four bits of the power unit address. The 10-bit
tap address is stored in par./ser. registers 130c-e. Register 130f holds a
2-bit control function identifier word segment and register 130g holds two
bits for individual subscriber selection. Register 130h holds one bit
indicating the desired state (on or off) of the selected control function
switch and an automatically entered start bit.
The power unit address, tap address, subscriber address, and 3-bit
control function information are thus entered in decimal notation via the
keyboard 122 into the storage register 124. The data is then transferred
from the register 124 through a 7-segment to BCD converter 128, where each
digit is converted to binary form, and then placed into the parallel/serial
registers 130a-h. As is conventional in the desk calculator 11, the data
stored in the storage register 124 is sequentially strobed, that is, de-
multiplexed, since only one digit may be read out of the register 124 at a
given time. To distribute the data among the registers 130a-h the digit
- select strobe signals are used to demultiplex the stored digits from the
register 124 for loading the eight registers 130a-h. Eight wires are pro-
vided leading from the strobe output of the calculator 11 to the eight
respectively parallel/serial register load control inputs. A strobe signal
appears on each of the 8 wires in sequence permitting the selected register
to which the wire is connected to accept the data output of the converter
128 which is a binary representation of the decimal digit stored in the
-24-
&2
selected position of the storage register 124. A BCD representation of
the 22 bits of information representing the power unit address, the tap
address and the control function data is thus stored in the registers 130a-h.
The stop and start bits of 1-0-- logical value generated in the
interface module 126 are added as part of the data transfer sequence. Also
included in the interface module 126 is a conventional parity tree which may
be in the form of two modulo-two adders. Each functional output of the
registers 130a-h is connected to an input of the parity tree 134 to count
the number of "ones" in the data word. If the total number of "ones" is an
odd number, a "0" is stored in the parity bit position in the register 130a.
If the total number of "ones" is even, a "1" is stored in the parity bit
position of the register 130a. In this manner the parity of the complete
25-bit data word stored in the parallel/serial registers 130a-h is always
odd. Maintenance of odd parity is used to permit a check on the validity
of the data received at the cable TV system power units 2. Any interference
with the RP signal which changes any data bit will change the parity of
the transmitted word from odd to even thereby indicating invalidity of the
data received at the power units 2.
A 20 kHz clock 136 has its output connected through a gate to the
clock input of the parallel/serial registers 130a-h. During transmission,
the clock serially shifts the parallel-stored data out of the registers
130a-h to the modulator 9 for varying the amplitude of the RF carrier from
the generator 8 at a 20 kilobits per second rate.
In modulating the amplitude of the RF carrier to create pulses of
the carrier signal at the output of the amplitude modulator 9, wide pulses
(preerably greater than 25 microseconds where a 25 microsecond clock pulse
is used at the decoder) are employed to indicate a logical "1" and narrow
~2~2
pulses (less than 25 microseconds) are employed to indicate a logical "0".
Pulse widths of 31 microseconds and 19 microseconds have been found satis-
factory for the wide and narrow pulses respectively when a 25 microsecond
clock pulse is used at the decoder. Other pulse durations may, however,
be used within the scope of the invention.
In addition to serially encoding the 25 bits of address and control
information onto the carrier signal from the generator 8, the modulator 9
is caused to encode an additional 25 bits of information all with logical
value "1" on the carrier following each 25-bit coded data word. Thus for
each data word 50 bits are transmitted over the cable 4 to the power inserter
24 of each of the power units 2 in the cable system. Since the start and
stop bits are of logical "O" value the possibility of transmitting 25 con-
secutive bits other than the intended binary-coded control word with first
and last bits having zero value is effectively precluded. All data words
intended to be transmitted have 23 consecutive bits bounded at both ends
by "0" bits, and the power units are made to respond only to such data words
as will later be explained, thereby effectively precluding false responses.
The pulse-duration amplitude-modulated carrier signal containing
the subscriber access control information from modulator 9 is combined in
a summing circuit 105 with the program signals from the RF program signal
source 102 and the composite signal is transmitted to all of the system
power units 2. The input 140 of the power inserter 24, shown in schematic
form in Figure 3, receives all coded RF carrier signals transmitted from the
head end 1 on the cable 4. These signals are coupled by the resistor 142
and capacitor 144 to the first (data) output 146 of the power inserter 24
to the RF carrier receiver/detector 25 (Figure lA). The program signals
received at the input 140 of the power inserter 24 are also permitted to
~2~&~
pass through the power inserter, to output 147 with low frequency components
removed by a blocking capacitor 148, to the subscriber taps 3 served by
the power unit. The program signals are thus permitted to pass directly
through the power inserter 24 to the subscriber taps.
The direction of the power is controlled by conducting links 152
and 154. As shown in Figure 3, power supplied at input 150 from power
switch 22 (Figure lA) may travel in both directions from the power inserter
24, that is, both toward the head end 1 and away from the head end 1, e.g.,
toward the subscriber taps 3. Removal of link 152 prevents power flow from
the power inserter toward the head end 1. Similarly, removal of link 154
prevents the flow of power away from the head end 1 or toward the taps 3.
Grounded capacitors 156 and 158 equalize the frequency response of the
signals transmitted through the power inserter. Respective LR chokes 166
and 168 remove undesired high frequency components from the power received
at the input 150 and transmitted back toward the head end 1 or forward
toward the taps 3. Capacitors 160, 162 and 164 also remove high frequencies
from the power.
Referring additionally to Figure 3A, the RF signals flow from
the output 146 of the power inserter to the input of a conventional
impedance-matching circuit 170 in the RF carrier receiver/detector 25. The
output of the impedance matching circuit 170 is connected to the input of a
first RF amplifier 172. The signal is amplified in the RF amplifier 172a
and then filtered in the filter 174a. There is further amplification and
filtering in the amplifier 176 and filter 178a. The signal is again amplified
in the RF amplifier 180a and then applied to a detector circuit 182a, where
the envelope of the RF carrier signal containing the address and control
information is detected.
~ z~
The detected A~ signal is amplified in a DC amplifier 184 and
then applied to an RC filter 186a to remove any remaining RF carrier signal.
The output of the RC filter 186a is connected to the input of a level shifting
buffer 188a whose output signal control data is applied to a decoder 6 in
the power supply logic circuit 108 (see Figure 4) for decoding and data
conversion and to a clock pulse generating monostable multivibrator (one-shot)
172 for operating the decoder 6 and a 25-bit shift register 174.
The data is serially received by the shift register 174 in the order
it appeared in the parallel/serial registers 130a-h at the head end. That is,
the bit in the first position of register 174 is the stop bit, and the next
bit is the parity bit, the next 7 bits represent the power unit address, the
following 10 bits indicate the tap address, the next 4 bits identify the
individual subscriber's function control switch to be operated, the following
~it determines the state of the function control switch to be operated, and
the last bit is the start bit. As will be recalled, the stop and start bits
are "0".
The positive-going edge of each input data bit signal at the output
of the buffer 188a triggers a monostable multivibrator 172 to provide a 25
microsecond pulse, that is, 1/2 of the clock period of the input data for a
20 kbps bit rate. Each clock pulse loads the data and shifts the contents
of shift register 174. The decoder 6 is responsive to a long pulse data bit
("1") and short pulse data bit ("0"). The start bit and stop bit are used
to identify that a word has been entered into the register 174, as detected
from the outputs of the respective inverter buffers 180 and 182 being "l"s.
A conventional parity tree 178 (which can be a modulo-two adder)
determines the parity of the received data word. The output of the parity
tree 178 is high when parity is odd and low when parity is even. The first
~2~}~2
and last bit outputs of the shift register 174 are connected to respective
inverter amplifiers 180 and 182. If the stop and start bits are "0" (or
low) the outputs of the inverters 180 and 182 will be "1" ~or high). A 7-bit
comparator 176 is enabled by the clock pulse at lead 441 and receives the
first 7 bits from register 174. The other comparator inputs are connected
to a 7 polel double throw switch, preset during installation of the power unit
2. The outputs of the 7-bit comparator 176, parity tree 178, and inverters
180 and 182 are applied to four respective inputs of an AND gate 184. It
will be recalled that each 25-bit data word is separated from an adjoining
word by 26 "l"s and that the start and stop bits will only have "O" value
when the complete received data word occupies its proper position in the
25-bit shift register.
Only when all of the inputs to the AND gate 184 are high is the
output of the AND gate 184 high. A high output signal from the AND gate 184
enables an 18-bit parallel/serial register 186 to receive 15 bits of data
from the 25-bit shift register 174. Specifically, the data stored in the
10th through 24th bit positions of the 25 bit shift register 174 is trans-
ferred to the 3rd through 17th bit positions of the 18 bit parallel/serial
register 186 in conventional manner. The number of "l"s in the transferred
15 bits is counted in a parity generator 188 by which a "1" or "0" is placed
in the second bit position in the 18 bit shift register 186 as required to
make the parity of the word stored in the 18-bit shift register 186 even.
Start and stop bits of logical value "0" are automatically inserted in the
last and first bit positions in the 18-bit shift register 186.
The continuous data readout from parallel/serial register 186 is
caused to operate power switch 22 by way of lead 451. As each bit is read
out it enables formation of the next clock pulse transmitted through lead
-29-
3 ~ 2
452. The readout is synchronized by 120 Hz clock oscillator 192, which
free runs unless synchronized from the power line input lead 454. Clock
pulses at 120 Hz are on line 455, inverted pulses on line 458.
The parallel/serial register 186 output bits respectively provide
one full cycle of either 120 Hz (where the shorter pulse is binary "0")
or 60 Hz (where the longer pulse is binary "1") at the output of NAND gate
459, and each positive clock edge on line 452 shifts parallel/serial register
186 to the next stored bit. Thereafter "1" bits are continuously generated
by shift register 186 to thereby produce an output normal 60 Hz transmission
at data line 451 in the absence of presentation of further data words. That
is, a single coded word is read through whenever the power unit is addressed
and otherwise the power supply is uniformly 60 Hz. The constant condition
is simply met by holding voltages on lines 460 and 470 constant without
transition. Thus the nature of the signal output of parallel/serial
register 186 is a DC level changing when data goes from "0" to "1" and vice
versa, generally known in the art as a non-return-to-zero type signal.
The parallel/serial register data is taken bit by bitfrom line 460
and the presence of a "1" polarity signal will gate AND circuit 461 for 60
Hz oscillations from counter 456 and lead 457, which then pass through enable
gate 461 and then to the OR circuit 462 and the polarity inverter 501 to
output NAND gate 459. The opposite polarity "O" signal by way of inversion
at the input buffer 502 will gate AND circuit 463 to thereby gate the 120
Hz oscillations on line 455 to the output NAND gate 459.
It is necessary however to remove all DC levels from the system
power and to have proper phase synchronization at the end of a "O" cycle
and the start of a "1" cycle or vice versa. Since the period of the 60 Hz
square wave is twice that of the 120 Hz square wave, the beginning of a
-30-
&~2
cycle of the first 60 Hz square wave will not always coincide with the end
of a 120 Hz cycle. l'herefore, there may be times when a "1" is to be trans-
mitted following the transmission of a "0" at which time the 60 Hz signal will
be in the middle of a cycle, that is, crossing from positive to negative.
At these times the inverse of the 60 Hz signal will be at the beginning of a
cycle and hence a cycle of the inverse signal is desirably selected for
application to the AND gate 461. In this fashion a complete 60 Hz cycle of
the proper polarity is always available for application at the output of the
NAND gate 459 whenever a "1" is detected and similarly a 120 hertz cycle is
always available whenever a "0" is detected. Thus, the 60 Hz and 120 Hz
cycles all have the same polarity.
The output of the 120 Hz clock oscillator 192 is applied to flip-
flops 465 and 468. The 120 Hz clock signal is also applied to inverter 505.
The 120 Hz output of inverter 505 is connected to the dock input of a divide-
by-2 counter 456 and also to the input of the AND gate 463. The appropriate
60 Hz signal from the counter 456 is applied to the gate 461 depending on the
output of an AND gate 507 which is applied to the reset input of the counter
456. The output of the AND gate 507 is high whenever a "0" from the register
186 is followed by a "1". A "0" from the register 186 is inverted in a NAND
gate 509. The output of the NAND gate 509 enables the flip-flop 465 to pro-
vide a "1" at its output to the AND gate 507. The output of the AND gate 507,
however, remains low due to the action of the inverter 511. If the next bit
out of the shift register 186 is a "1" the output of NAND gate 509 goes to a
"0" and is reinverted in the inverter 511 to a "1" or high signal applied
to the previously low input of the AND gate 507. The result is a high signal
at the output of the AND gate 507 which resets the counter 456 so that the
next 60 hz alternating squarewave is initiated in proper phase. The output
-31-
of flip-flop 468 is caused to go to a "0" when a capacitor 513 coupled
positive transition occurs at the output of the OR gate 462, causing the
output of the NAND gate 459 to remain at a "0" until the next positive edge
of the 120 Hz clock 455, thus removing any transients from the output of
NAND gate 459.
The circuit of Figure 4 thus constitutes the power unit logic 108,
which converts the data signals into coded power transmission, with inter-
mixed full cycles of 60 Hz and 120 Hz frequency, each 120 Hz cycle repre-
senting a binary "O" and each 60 Hz cycle representing either a binary "1"
or an uncoded period of power flow.
Referring now to Figure 4A the output of the power unit logic 108
(see Figure lA) is applied to a control input 194 of the power switch 22.
The power switch 22 has power inputs connected to plus and minus direct
voltage sources (of preferably +/-62 volts) respectively, provided by the
power supply 106. A power tranformer 196, preferably of the saturating
type to prevent over-voltage, is used in the power supply 106 with a center
tapped secondary for providing +/- DC power by way of full-wave rectifier 198
and capacitor filters 200 and 202. The power transformer 196 also provides
squared output wave forms for synchronization. To compensate for input
under-voltage, batteries 204 and 206 may be connected via diodes 208 and
210 to the DC lines 212 and 214. The batteries 204 and 206 are preferably
trickle-charged through resistors 216 and 218. Fuses and circuit breakers
(not shown) are preferably used in a conventional manner.
The power switch 22 switches either + 62 volts or - 62 volts to its
output by means of a transistor switching circuit. Preferably there is a
limit imposed on the slew rate dv/dt to prevent harmonics and amplifier power
supply problems. One such circuit configuration is shown in Figure 4B.
-32-
Referring to Figure 4B a conventional polarity detector 271 pro-
duces the positive drive to transistor switch 272 and the negative drive to
transistor switch 273 thereby providing an AC signal wave power output
from the power switch 22. Amplifiers 274a, b drive respective optical
isolators 275a, b or equivalent voltage level changers for operating respec-
tive driver amplifiers 276a, b for causing switching of the transistor
switches 272a, b. The optical isolators 275a, b each include a light
source responsive to the respective outputs of amplifiers 274a, b and a
light sensor having a voltage output which is a function of the intensity
of the light from the source. The optical isolators 275a, b electrically
isolate the signal input section of the power switch 22 (polarity detector
271 and amplifiers 274a, b) from the power switching output section. A
current-limit control device 220 is desirable for protecting the output
transistors 272 and 273. The outputs of the transistors 272 and 273 are
applied to respective snubber circuits each of which includes a diode
222a, b in parallel with a series combination of a capacitor 224a, b and
resistor 226a, b. The snubber circuits prevent the positive direct voltage
output from going over the positive DC supply voltage and the negative
direct voltage output from going under the negative DC supply voltage and
neutralize the inductive effects of the load, i.e., the system's cables.
In operation the power switch 22 senses at its input the polarity
of the low level signal output pulses from the power logic 108 which is a
series of squarewave pulses, each cycle of which has a frequency of 60 hert~
when it represents a "1" and 120 hert~ when it represents a "0" and in
response produces power pulses of frequency and polarity similar to those of
the low level input pulses (60 or 120 Hz).
The decoded power output signals of the power switch 22 are applied
-33-
-
to the input 150 of the power inserter 24 IFigure 3) as herebefore described
and are then transmitted along the cable portion 42 toward the taps 3 and/or
back to the head end 1 depending on the configuration of links 152 and 154.
At each addressable tap 3 (Figure lA) powered by the power unit 2, the coded
power output of the power unit 2 and the accompanying RF program signals
are received at the power supply 120 disposed in the tap 3.
Referring now to Figure 5 there is shown a schematic diagram of
the tap power supply 120. The signals received at the tap input 228 are
filtered in LC filters 230 and 232 to remove the high frequency program
transmissions, leaving only the coded power to be applied to the primary
winding of a power transformer 234. The secondary of the power transformer
234 has a grounded center tap. Pick-off points are provided on the secondary
winding of the transformer 234 for applying the AC secondary signals to a
full-wave bridge rectifier 236, to rectifier diodes 238 and 240 and to an
input of the jamming oscillators 116a, b. Input regulation to the full-wave
rectifier 236 is provided by oppositely polarized series connected zener
diodes 242 and by the saturating core design of the transformer.
The output of the full wave rectifier 236 is filtered in capacitor
244. Zener diode 246 provides a regulated -15 volt direct voltage output
of the rectifier diode 238. A capacitor filter network including capacitors
248, 249, 250, 251, 252 and 253 filters the positive and negative outputs of
the full-wave rectifier 236 to provide DC outputs of +/-4.2 volts respec-
tively. A negative 14 volts DC is provided at the output of the diode 240.
The direct voltages of +/- 4.2 volts, -15 volts and -14 volts are used to
power the tap circuitry including the tap logic 35 and jamming oscillators
116a, b.
The data-coded power flow is taken from the secondary winding of
-34-
28~Z
the transformer 234 and filtered in an RC network comprising a resistor 260
and capacitor 262. The filtered data signal is then applied to a data input
of the tap logic circuit 35 (Figure lA).
The previously described power supply of Figure 5 is only one of
several types that may be used. Figure 5A illustrates in schematic form a
tap circuit including another power supply configuration for powering one
type of tap logic circuit~ basic service module and a controlled-channel
module connected to a filter trap. In the circuit of Figure 5A the cable 42
is tapped at transformer 677 to obtain the television program signals and
at line 678 to obtain the coded AC power transmission from the power unit 2.
The coded power is applied to an LC filter to remove high frequency components
and then to the primary,winding of the tap power supply transformer. The
coded power is then applied to the tap logic circuit 35 which controls an RF
switch 690 for allowing or preventing the application of the television
signals to subscriber stations. A filter trap 692 filters out a specific
channel of television program signals for which no subscription has been
taken.
A diode switch 697 in parallel with the filter trap 692 can be
closed in response to a signal from the logic 35 to short circuit the filter
692 for permitting access by a subscriber to the television programs on the
channel.
A more detailed description of a different tap 3 which contains
variable frequency (wobbulated) oscillators to selectively jam one or more
channels of television programming which are to be denied to a subscriber
follows.
Referring to Figure 6 the tap logic circuit 35 of Figure lA decodes
the data-coded power received at its data input for operating the tap switches
40 in the basic service module 112 and jamming oscillator 116a, b to
control the access of the subscriber to the programs.
In Figure 6 the coded power pulses are continuously applied to
the input of the 18-bit shift register 264. Each positive going edge of
the received coded power signal triggers a monostable multivibrator 525, the
inverted output of which illustratively is a 6.2 millisecond pulse which is
applied to the positive edge triggered clock input of shift register 264
and serves to detect the data on the power and to shift the 18 bits stored
in the register one bit position to the right. At the end of a 6.2 ms. pulse
triggered by a 120 Hz cycle ~"0" bit), the coded power will be negative, and
entered into the shift register as a "0". At the end of a 6.2 ms. pulse
triggered by a 60 Hz cycle ("1" bit), the coded power will be positive, and
entered into the shift register as high or "1". In this way, shift register
stores an 18 bit segment of the coded power pulses, that segment changing as
each new coded power pulse occurs by dropping the last bit and inserting the
new bit.
The third through twelfth bits of the data word stored in the shift
register 264 are continuously compared with the ten bit address assigned to
the subscriber tap in the comparator 266 by means of switches 268. The
output of the comparator 266 is applied to an AND gate 300. Also applied to
inputs of the AND gate 300 are the first and last bits of the word stored in
the 18 bit shift register ~that is the stop and start bits, respectively) and
a parity signal from a parity tree 302. The parity tree 302 adds the "l's"
in the shift register 264 and puts out a high signal (logical "1") only when
the sum is even. The parity of the coded power signal is made even in the
power supply logic 108. When the comparator 266 indicates that the subscriber
tap address received in the shift register 264 is identical to the tap
-36-
address assigned to the particular subscriber tap, that the start and stop
bits are equal to "1'' in the respective first and last positions in the
shift register and that parity is even, an enabling signal from the AND
circuit enables a one-of-14 decoder circuit 304.
The one-of-14 decoder 304 is supplied with the thirteenth through
sixteenth bits from shift register 264 and decodes the four bit control
function portion of the 18 bit data word to determine which control function
is desired. The one-of-14 decoder 304 enables one bit position of a 12 bit
latch circuit 306. The on-off control bit which is the 17th bit of the data
word in the shift register 264, is applied to each of the 12 latches in the
latch circuit but only the latch selected by the l-of-14 decoder 304 is
actuated in accordance with the on-off control bit. The l-of-14 decoder
also responds to two master codes that will produce logic signals to set
all 12 latches to a "1" or reset all 12 to a "0". The outputs of the latch-
ing circuit 306 in turn control 12 switch current drivers 308 which are
connected to and which control the RF switches 40 a-c.
Thus the 12 RF switches, controlled by the switch current drivers
in the latch circuit 306, may control specific channels of programming as
well as the respective subscriber's total service for each of four sub-
scribers. For example, one of the RF switches may be a double-pole double-
throw switch which in one position opens the circuit between the subscriber's
tap transformer 234 and the tap port 49 to which a television receiver
converter is connected while in the other position the tap transformer and
terminal output are suitably connected for television viewing by the subscriber.
Good performance has been achieved using inexpensive PIN diodes to accomplish
the switching.
A charged capacitor may be provided as a back-up power source to
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Z~i2
maintain the states of the switches 40a-c in the event of a brief power
failure. If the power failure is of sufficient duratioll to cause the
capacitor to discharge, provision is then desirably made to set all switches
40a-c to provide all services to all subscribers.
Tllere are several possible approaches to cleactivating specific
channels. In one approach, an LC type of trap witll a single-pole single-
throw switch across it is employed in a T design. Wllen the switch is closed,
the trap is short-circuited and the program for that channel passes. lYhen
the switch is open, the trap blocks the program. A more complex approach
is a pi type of filter which recluires a double-pole double-throw switch. A
furtller approach to single channel deactivation is the use of an oscillator
to jam the particular picture carrier. The oscillator may provide a signal
at a single frequency, which is for example the carrier frequency, or at a
variable frequency, or it may provide narrow band noise as the jamming
signal.
An RF switch arrangement 40a-c used in a preferred embodiment of
the invention is schematically illustrated in Figure 7. Each of the RF
switches 40a-c has a control input 310 and an RF input 312. To the RF input
312 for each switch 40a there is appliecl the basic program signal (e.g. all
television programs), and for each switch 40b and 40c to its RF input 312
is applied the jamming oscillator signals. When a low control signal ~nega-
tive voltage) is applied to the control input 310, i.e., when the control
function bit has a logical value of "0", diodes 314, 316 and 318 are forward
biased and hence conduct. Diodes 320 and 322 are then bac~ biasecl and there-
fore non-conducting. The switch is tllen "off". Inductors 324, 326, 328,
330 and 332 provide RF isolation. Capacitors 334, 336, and 338 provide DC
isolation.
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-~ ~z~
l~hen the control signal applicd to input 310 gocs higll, diodes
314, 316 and 818 arc back biased ancl non-conductive whilediodes ~20 and 322
become forward biascd and hence condllctive thcrcby providing elcctrical
continuity between the RF input 312 and thc output 340 of e;3ch switch 40a-c.
The switch is then "ON". The switching currcnt applied to tlle switches
40a-c by the switch current drivers 308 may be on the order of 1 to 3
milliamperes.
Referring now to Figurc 8 of the drawings, a jamming oscillator
116a, b used in a preferred embodiment of thc invention is shown scllematical-
ly. The jamming oscillator 116a, b has a powcr input 350 at which there is
applied 4.2 volts DC from the DC output of the powcr supply 120. Thc AC
signal from the sccondary winding of the transformer 234 in the power supply
120 is applied to a "wobble" input 352 of the jamming oscillator. Coil 354
and capacitor 35G filter the input power. Thc input direct voltage biases
the base of an oscillator transistor 358 at a nominal level through
resistor 374. The base voltage of the oscillator transistor 358 is varied
by applying thc AC signal to thc base of the transistor 358 via the wobble
input 352. The collector of transistor 358 is connected to DC power through
RF choke 372.
A tank circuit for determining the oscillator frequency includcs
capacitor 364 in series with the parallel combination of inductor 360 and
capacitor 362. In addition, a varactor diode 366 is colmected between ground
and the basc of thc trallsistor 358 forming a part of thc tank circuit. The
AC power signal from the sccondary of the transformer 234 applied to the
wobble input 352 is filtcred by an RC filter including resistor 368 and
capacitor 370. Thc circuit goes into oscillation at the tank resonant
frequency. Tlle output voltage from the collector of thc transistor 358 is
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c~.' ~,.
Z~
fed back to the base of the transistor through the intrinsic collector-to-
base capacitance. As the voltage across the varactor diode 366 changes so
does its capacitance and as this capacitance changes, the resonant frequency
of the tank circuit of the oscillator is varied. Hence, the signal at the
collector of the transistor 358 has a variable frequency oscillation suitable
for jamming the television program carrier signal the frequency of which is
within the frequency variation range of the jamming oscillator 116a, b. The
output of the jamming oscillator transistor 358 is applied to a band pass
filter including capacitors 376, 378, 380 and 382 and inductor 384 to confine
the jamming signals to the desired band and prevent interference with other
channels.
The following tables 1-3 illustrate some of the various respective
combinations of apparatus units which may be included at the head end, power
units, and addressable taps of a cable television system according to the
invention. The tables are exemplary only and are not intended to disclose
all possible combinations of apparatus employable at the head end, power units
or taps.
TABLE 1
HEAD-END CONTROL UNIT COMBINATIONS
Component Units 1 2 3 4 5 6 7 8 9 10 11 12
A. Interface Unit O O O O O O L~ L~ O O O L_~_
B. CPU ~ KeYboard O O O O O O O O O O
C. CRT O O O O O O O O O = =
D. Printer O O O O O O
E. S re ~ _ _ O _ O _ _ _ _ _ _
F. Large Tape Store _ _ _ O _ O O _ _
G. Real Time Clock _ _ _ _ _ _ O _ _ _
H. Large Main-Frame _ _ _ _ _ _ _ _
Interconnect O O
I. Manual Unit = = = _ = = = = = O
Table 1 illustrates 12 possible combinations of component units
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which may be used at the head end, in the general system of Figure 1.
The following is a brief description of the nature of one form of
the component units listed in the table.
Interface Unit - A device for converting the entered data to binary
form for storage in the parallel/serial register at the head end and for
adding stop, start and parity bits.
C P U ~ Keyboard - A keyboard for entering data into the memory
(e.g. register) of a central processor unit ~e.g., a modified desk calculator).
CRT - A cathode ray tube device for displaying the entered data.
Printer - A device for typing the entered data on a paper record
for subsequent reference.
Small Tape Store - A device for recording the data, as it is
entered, on a magnetic tape loaded in a small cassette.
Large Tape Store - A device for recording the entered data on
magnetic tape stored on large reels, e.g., as in a reel-to-reel recorder.
Real Time Clock - A timer for causing the data to be transmitted
at predetermined times for enabling and disabling specific services of
individual subscribers at those times.
Large Main-Frame Interconnect - A device for connecting the head
end data transmitting apparatus to a remote computer wherein data is process-
ed, transmitted to the head end and then encoded on the RF carrier signal
at the head end for transmission to the power units and subscriber taps.
Manual Unit - A device including manually actuated switches for
entering data into the shift register at the head end for encoding on the
transmitted RF carrier.
This Table, 1, shows twelve possible combinations of such units,
a zero in a numbered column and opposite a vertically listed component unit
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.fB2~
indicating that that particular component unit is used in combination with
other units having "O" in the same column. For example, in combination 3 of
Table 1 a keyboard is used for~manually entering the power unit address, tap
address and control function data into the memory of a central processor
unit, whose data may be displayed on a cathode ray tube, typed on a printer,
and converted for coding on the RF carrier signal by means of an interface
unit.
Table 2 illustrates 8 possible combinations of component units for
use in a cable system power unit.
TABLE 2
POWER UNIT COMBINATIONS
Component Units 1 2 3 4 5 6 7 8
A. Standard_Power Unit_ _ _O O O O O O O O
B. 60Hz Keyer O ,~_ _ _ O _ _ O
C. Battery Pack _ _ O _ O O O _ _
D. _Data Keyer Unit _ O O _ O O _
E. Status Transmitter _ _ _ O O O O
These units are:
Standard Power Unit - A saturation transformer for use in cable
television systems for regulating the power from the mains.
_O Hertz ~eyer - A device having inputs at which positive and
negative direct voltages are applied and an output at which there is gener-
ated 60 hertz power signals for continuously energizing where the power is
uncoded.
Battery Pack - A device employing conventional batteries to pro-
vide a supplementary voltage source, usually for backing up the system power
supplies in the event of brownouts.
Data Keyer Unit - A device for controlling the system power switch
22 for encoding the power according to the data encoded on the RF carrier
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transmissions from the head end.
Status Transmitter - A device which can be remotely interrogated
from the head end to determine if the power unit or specific circuits
therein are functioning properly.
TABLE 3
SUBSCRIBER TAP COMBINATIONS
Component Units 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
A. Tap O O O O O O O O O O _O O O _O _ O O
B. Basic Service Module _ O O O O O O O O O O O O O O O
C. CH.A Trap = O = O O = O = O O ~ = O = _
D. CH.B Trap _ O O _ O O _ O O _ _ _
E. House Feed-Thru _ _ _ _ O O _ _ _ _ _ _ _
F. CH.A Oscilator _ _ _ _ _ _ _ _ O _ _ _ _ = _ _
G. CH.B Oscillator _ = = = = _ _ O = = = = = = = =
H. Single CH Converter _ O _ O _ O
I. Block Converter _ = = = = = = _ = = = _ O =
J. Transponder _ _ _ _ _ _ _ _ _ O _ _
K. Reverse Path Switch _
L. Reverse Path Atten. _ = _ = = = = _ = = = = = C = =
M. Section Bypass _ _ _ _ _ _ _ _ _
Component Units 17 18 19 20 21 22 23 24 25 26 27 28 29 30
A. Tap O O O O O O O O O O
B. Basic Service Module O O O O O O O O O O O O O O
C. CH.A Trap
D. CH.B Trap _ O _ _ _ _
E. House Feed-Thru O _ O O
F. CH.A Oscillator = = = O _ _ O O _O = _ _ _ _ _
G. CH.B Oscillator _ = = O O = = = O = = _ =
H. Single CH Converter _ O _ O _ _ _ _
I. Block Converter _ O _ _ _ _ _ _ _ _ _
J. Transponder O _ _ _ O _ _ _
K. Reverse Path Switch _ O
L. Reverse Path Atten. = _ = = = = = = = = = = O =
M. Section Bypass _ _ _ _ _ O
Table 3 illustrates 30 possible combinations of component units
which may be used in a tap of an addressable subscriber control system
according to the invention.
These units are:
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Tap - An input device to the addressable subscriber tap for deriv-
ing the RF transmissions from the cable.
Basic Service Module - A device for receiving the television
program information for all channels at the addressable tap and supplying it
through frequency converters to the television receivers of the subscribers.
Channel A Trap - A filtering device for removing from the RF
television program signal a band of frequencies associated with one specific
channel ("A") to prevent reception of that channel.
Channel B Trap - A device similar to the channel A trap but tuned
to filter out a different channel ("B") of television programming.
House Feed-Thru - An optional added device for relaying the coded
data received at the subscriber taps to a location within the homes of the
respective subscribers for controlling one or more devices within the sub-
scriber's home.
Channel A Oscillator - A device for providing a signal within the
frequency band of a particular channel ("A") for jamming that channel thereby
preventing its reception by a subscriber.
Channel B Oscillator - A device similar to the channel A oscillator
but tuned to a different frequency band for jamming another channel ("B").
Single Channel Converter - A device for receiving one channel of
television program information on one frequency or group of frequencies in-
compatible with a subscriber's television receiver and for converting the
television program information to another channel frequency or group of
frequencies compatible with the subscriber's television receiver for reception
of the channel.
Block Convert0r - A device for simultaneously receiving signals
containing several channels of program information and for providing at
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~t~,&~Z
reSpective outputs separate channel signals each of which corresponds to a
different channel tunable by a subscriber's television receiver.
Transponder - A device which can be remotely interrogated ~e.g.,
from the head end) for transmitting a signal from the tap to indicate the
condition of cable system components at the tap or along the return trans-
mission path.
Reverse Path Switch - A switch for use in a two-way system and
operable from a remote location (e.g., at the head end) for selectively
enabling or disabling the flow of signals from the tap along a return path
toward the head end, as for example in trouble shooting cable faults or by-
passing malfunctioning components disposed in the cable path.
Reverse Path Attenuator - A device for selectively attenuating, but
not completely blocking, a signal transmitted along the return path from the
tap for use in trouble-shooting the cable system.
Section By-Pass - A parallel cable branch providing an alternate
path for signals in the event of a malfunction in a portion of the primary
cable path.
RF Module - A device for receiving control data coded on an RF
signal (as opposed to the coded power transmissions) for controlling sub-
scriber access to the cable system.
The previously disclosed basic service module may be replaced byan RF receiver basic service module for special services and in cases where
the system requires a number of terminal points in excess of the 4,096 sub-
scriber control points which are provided for each power unit in the pre-
ferred embodiment. The oscillators, traps and converters may have selectable
requencies or requency bands.
In addition to controlling a subscriber's access to the cable
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~L~Zi~ 2
transmission system and for controlling individual selected channels,
there are other functions to which the present invention may be applied,
which do not relate to subscriber access.
Although the preferred embodiment of the invention has been
described for use in a cable television system it is to be understood that
the invention has utility in applications other than cable television broad-
casting and may be used, for example, in any situation wherein power and
signal intelligence are transmitted to a common apparatus. For example,
electrical utility companies can use the invention to control the power
consumption, using measuring apparatus located at each consumer's residence
or facility for billing one type of usage ~e.g. heating) at a rate different
from the rate for another type of usage ~e.g. lighting) by coding the trans-
mitted power and installing at the measuring apparatus a decoder and switches
responsive to the decoded data for switching between two types of consump-
tion.
Communication systems such as telephone systems provide another
example wherein the invention can be used to provide local control from a
central station.
Various control functions at a locality can be controlled from a
remote power generating point by coding on the transmitted power enabling
signals at the time when a function is to be enabled and disabling signals
at a later time when the function is to be disabled. The number of remote
functions which can be controlled from a central station is virtually un-
limited. Since the transmitted data is serially coded onto the transmitted
power the only limit on the number of bits of information which can be used
in a coded word is the time period to be allotted to the word.
Another example is in a two-way system where signals are sent from
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1~2~
the head end and return signals are received at the head end. Transponders
located at remote terminals, equivalent to subscriber taps, may be selec-
tively actuated to test the return path from the remote terminal to the
head end. Similarly, remote transponders may send back a signal containing
data representing a measure of received signal quality. A further possible
use of the present invention may be to actuate selected attenuators of
known value distributed along the reverse signal path (that is, the path
from the terminal to the head end) for use in trouble-shooting noise or
spurious signals on the reverse path. Remote control circuits may also
be actuated by similar means in order to provide alternate transmission
paths when a main path fails due to a malfunction therein.
While in the example described above, each tap address code may
serve up to four subscribers (the particular subscriber of the four being
determined by certain bits of the command portion of the data signal), it
will be understood that an individual address may be allocated to each sub-
scriber, and the tap device may then respond to any of, say, four subscriber
addresses to forward individual command signals for a particular subscriber.
It will also be understood that the present system for encoding
and decoding power transmission (which may be regarded as using data signals
for power) is not confined to use with the foregoing systems or even address-
able taps, but is suitable for use wherever both power and data transmission
may be desired, and may also be used for data transmission alone. In
addition, the particular encoding and decoding arrangement is not restricted
to use of 60Hz/120Hz, but other similarly related frequencies may be used.
Thus, while the invention has been described in terms of one
application for which it is particularly well suited, i.e. cable television
systems where data words are coded on transmitted power, it is not to be con-
fined to such systems but is defined by the following claims.
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