Apparatus for tapping CATV signals from a cable and for controlling the distribution

In order to facilitate the installation of off-premises equipment which distributes CATV signals from a distribution cable to subscribers and to allow different subscribers to receive different classes of service (basic service alone or with one or more premium or pay-per-view channels), a pair of housings are used, one containing circuits for tapping the signals from the cable and the other for electronics hardware which processes the signals and distributes them to subscribers in accordance with the class of service which is ordered by the subscribers. The housing containing the tapping circuits is permanently connected to the cable and need not be removed or replaced when connecting additional subscribers or changing the class of service. The housing containing the electronics hardware for processing the signals may be attached to or along side of the first housing. The first housing may be suspended from the strand which supports the cable in an aerial mount configuration. The second housing may be attached to and suspended from the first housing. The first housing is smaller than the second housing so that the assembled housings constitute a body having a conning tower provided by the first housing.

The present invention relates to CATV signal distribution apparatus, and 
particularly to off-premises equipment which tap and process signals from 
the cable before delivery of the signals to television sets in the 
subscribers' premises. 
The invention is especially suitable for use in off-premises systems which 
deliver different classes of service (basic service or basic service plus 
premium and pay-per-view channels) by interdiction of channels which are 
not ordered by subscribers. In such systems, the interdiction electronics 
hardware constitutes the majority of the off-premises equipment and is far 
more expensive than tapping devices which are located along the cable in 
the vicinity of subscribers' premises. It is therefore desirable to 
install off-premises signal processing equipment, only and particularly 
interdiction equipment, as and where required and to facilitate the 
installation or removal of such equipment. More particularly, it is 
desirable to install the equipment without the need for reworking the main 
distribution cable by cutting it, changing its length, installing 
connectors and rerouting the cable. Such reworking is particularly 
difficult because the cable is large in diameter and is very stiff. It is 
also desirable to facilitate changes in the off-premises equipment, for 
example going back to conventional distribution devices as may use 
on-premises convertors. In other words, it is desirable to provide 
off-premises equipment which can function as a conventional tapping device 
as well as with processing equipment capable of providing different 
classes of service, such as use interdiction technology. 
Further information as to off-premises equipment capable of distributing 
and processing signals for providing selected classes of service and to 
signal processing equipment operative by interdiction through the use of 
jamming signals may be had from U.S. patent application Ser. No. 
07/445,316 filed Dec. 4, 1989 now U.S. Pat. No. 4,963,966 in the names of 
Michael Harney et al., and assigned to the same assignee as this 
application. The system is also described in an application note, 
published by Scientific Atlanta Inc., August 1989 by John Cochran and 
entitled "Off-Premises Addressable System - Interdiction Through Jamming". 
Reference may also be had to U.S. Pat. No. 4,578,702 issued Mar. 25, 1986 
for further information respecting tapping devices used in CATV 
distribution systems. 
Accordingly, it is the principal object of the present invention to provide 
improved off-premises equipment useful in CATV (cable antenna television) 
signal distribution networks. 
It is a further object of the invention to provide improved CATV signal 
distribution apparatus which facilitates the installation or removal of 
off-premises signal processing equipment such as off-premises subscriber 
control units which enable different classes of CATV service to be 
provided to subscribers and also facilitate removal of such control units, 
whenever it is desired to use other equipment for providing service to 
subscribers such as conventional set-top converters. 
Briefly described, the invention as embodied in a CATV signal distribution 
system using a cable to distribute the signals to subscribers, the signals 
being generated at the head end of the distribution network by the cable 
operator, utilizes apparatus for tapping the signals from the cable and 
for processing the signals to selectively control the distribution thereof 
to different subscribers, thereby enabling the subscribers to order 
different classes of service. The inventive apparatus makes use of a first 
housing and a second housing, both of which are adapted to be located off 
the subscribers' premises and adjacent to the cable and supported with the 
cable by a strand in aerial mount configuration. In such configuration, 
the strand is carried on poles and the cable is suspended from the strand. 
The first housing contains circuitry connected to the cable for tapping 
signals from the cable. The second housing contains circuitry for 
selectively controlling the distribution of the signals to the 
subscribers. The second housing has connectors for feed cables extending 
to the premises of the subscribers. The first housings are permanently 
mounted at locations along the cable. The cable has ends which are 
connected to terminals extending from the first housing so that the TV 
signals pass through the housing, while being tapped from the cable in the 
housing by the tapping circuitry therein. The second housing is mounted 
adjacent to the first housing. In one configuration, the first housing is 
much smaller than the second housing and is attached to the strand on the 
top side thereof. The first housing is also attached to the second housing 
and suspends the second housing from the bottom thereof. The circuitry in 
the first and second housings are interconnected so that the signals 
tapped from the cable are applied to the circuitry in the second housing 
for processing. In another configuration, the second housing is suspended 
from the strand. A plate closes the bottom of the first housing. The 
terminals in the plate and in the second housing are interconnected by a 
second cable which carries the signals tapped from the main cable by the 
tapping circuitry in the first housing to the second housing for 
processing therein.

Referring first to FIG. 1, there is shown a prior art tapping device 10 
which is mounted on a strand 12. The strand 12 may be strung between poles 
in a typical aerial mount configuration. The cable 14 which distributes 
the CATV signals may either be the main cable or a feeder cable connected 
to the head end. It is suspended from the strand 12 on hangers as shown at 
17 or with lashing. The tapping device 10 is connected across a gap in the 
cable. The cable is a coaxial cable which is connected to connectors 16 at 
opposing ends on opposite sides of the gap in the cable. These connectors 
extend from the housing of the tapping device 10. A clamp 25 on the top of 
the housing of the device attaches the device to the strand 12. The 
tapping device has a printed circuit board 18 contained therein to which 
the center conductors 20 and 21 of the cable 14 are connected via seizure 
posts 24 and 26 which extend from the board. The tapping circuitry 18 
distributes the CATV signals to subscribers in the location of the tapping 
device 10 by way of drop cables (subscriber cables) 28. Tapping devices as 
shown in FIG. 1 are adapted for use in conventional CATV distribution 
systems where set top converters are used on the subscribers' premises for 
processing the CATV signals to obtain the level of service which is 
ordered by the subscriber from the cable operator. 
FIG. 2 shows the off-premises equipment of the type containing a subscriber 
control unit as described in the above-referenced article by John Cochran 
and in the Michael Harney, et al. patent application, also referenced 
above. An aerial mount configuration on a strand 12 is shown. The cable is 
suspended from the strand by lashing or hangers 17. The subscriber control 
unit 30 has a housing with a cover 32 and a base section 34. The cover 32 
contains tapping circuitry on a board 36. A length of coaxial cable 38 
extends from the board 36 to a connector 38 to which one end of the cable 
14 is connected. The other end of the cable is separated from the end 
connected to the connector 38 by a much longer gap than used in the case 
of the tapping device 10 shown in FIG. 1. The opposite end of the cable is 
connected to a connector 40. The tapping circuitry 36 is connected to 
signal processing (interdiction) electronics schematically shown as a 
board 42 which is contained in the base section 34 of the unit 30. This 
board processes the signals in accordance with the level of service 
selected by subscribers in premises 44 via connectors 46 on the unit 30. 
The unit 30 is expensive and it is not desirable to install such a unit 
except in locations where subscribers are present and where the 
subscribers order various levels of service so that the interdiction 
electronics can provide the requisite level of service. Moreover, the use 
of the length of cable 38 provides at least one additional termination 
between the cable and the tapping electronics board 36. It is desirable to 
avoid such additional termination in order to improve the transmission 
performance of the CATV distribution system. It will also be apparent that 
removal of the unit 32 and replacing it with a conventional tap when the 
level of service at any location must be changed back to a lower level of 
service by installing a conventional tapping device, presents a difficult 
installation problem requiring removal of the original cable or replacing 
it with extra lengths of cable so as to accommodate the smaller tapping 
device. Moreover, any such installations require that service to 
subscribers down the cable be interrupted. 
The present invention enables off-premises equipment having an off-premises 
unit to be installed or removed without difficulty. Off-premises control 
units can then be installed only as and where required to meet 
subscribers' needs. Two configurations of the off-premises system are 
shown; one in FIGS. 5 and 6 and the other in FIG. 7. Each of these 
configurations utilizes a standard subscriber control unit in which the 
tapping electronics in the cover section is removed. The connector ports 
50 and 52 at the opposite ends of the units which normally receive the 
cable (see connectors 38 and 40 in FIG. 2) are plugged. 
The first configuration is illustrated in FIGS. 3 to 6. The equipment as 
assembled is a body having a conning tower configuration. The conning 
tower is provided by a first housing 54. A second housing 56 containing 
the subscriber control unit electronics, illustrated schematically as a 
printed circuit board 58, is also part of the off-premises equipment. The 
housing 54 contains circuitry shown mounted on a circuit board 62. This 
circuitry provides the tapping electronics and may be of the type 
illustrated in FIG. 8. The circuitry has an input side at a seizure 64 (J1 
in FIG. 8) and an output or through side to the downstream portion of the 
distribution network. This output side terminates at a seizure 66 (J2 in 
FIG. 8). The cable 14 has ends separated by a gap which are fastened in 
connectors 68 and 70 on the input and through ends on opposite side walls 
of the housing 54. The cable is suspended from a strand 12 and aerial 
mount configuration by hangers or lashing as shown at 17. 
The tapping electronics is generally of the type described in the 
above-referenced Michael Harney, et al. patent application. It includes a 
plug-in directional coupler on the board 62 which is capacitively coupled 
by C1 and C2 to the input and through ends of the cable. A bridging 
inductor L1 for carrying power down the cable shunts C1, C2 and the 
directional coupler. A protective circuit L2, E1 and C3 is connected to 
one end of the cable. This protective circuit taps off power to supply 
electronics on circuit board 58. A similar protective circuit (not shown) 
is connected to the opposite or input end of the cable. In this protective 
circuit, E1 is a gas discharge tube. The coupler is connected to a 
low-pass filter in parallel with a high-pass filter. The low-pass filter 
L4-L8, C4-C6 enables signals from the subscriber to be fed back to the 
head end via the cable. The high-pass filter (C7-C11 and L9-L11) is 
connected to an adjusting pad and equalizer and carries the TV signals 
tapped from the cable to the subscribers. There are two lines from J3 and 
J5 illustrated in FIG. 6 at 74 and 76 which connect the tapping circuitry 
on the board 60 to the signal processing circuitry. The signal processing 
circuitry has in this embodiment four outputs at four connectors 46 (as 
was the case in FIG. 2) which are connected to the subscribers' premises 
via drop cables 28. 
Both the housing 54 and the subscriber control unit housing 56 are 
generally in the shape of rectangular parallepipeds. The design of the 
housing 54 is shown in FIGS. 3, 4, 4A and 4B. In these FIGS., the circuit 
board 60 is removed. The housing is generally of cup-shaped configuration 
and has a top 80 and side walls 82. Opposite ones of these walls contain 
threaded holes 68A and 70A which receive the connectors attached to the 
opposite ends of the cable. The printed circuit board 60 is mounted on 
posts 84. These posts have threaded holes for receiving screws (not shown) 
which attach the board 60 so it is spaced from the top 80 and so that the 
seizures thereon receive the center conductors of the cable 14 as shown in 
FIG. 5. The outside of the top has attached thereto clamps 88. These 
clamps attach the housing to the strand 12 as shown in FIGS. 5 and 6. The 
clamps are tightened by bolts 90 which extend to holes, which may be 
partially threaded in the jaws of the clamps 88. 
The housing has a bottom 92 with a bottom surface 94. This bottom surface 
is in the form of a flange with ears 96. The ears have threaded holes 98. 
The bottom surface also has a groove 100 therein which contains an O-ring 
seal. 
In the conning tower assembly shown in FIGS. 5 and 6, the cover of the 
housing has four holes 102 and a hole 104 which is in alignment with the 
open bottom 92 of the first housing 54. The leads 74 and 76 extend through 
these aligned holes to the signal processing electronics as shown in FIG. 
5. Bolts 106 extend through the holes 102 in the top of the cover of the 
second housing 56 past the bottom surface of the housing and attach the 
second, subscriber unit housing 56 to the bottom of the first housing 54. 
The first housing is supported on and suspended from the strand 12. 
The second housing 56 is attached via the connector elements provided by 
the bolts 106 and threaded holes 98 from the first housing thereby 
providing the conning tower assembly. It will be appreciated that if the 
subscriber control unit off-premises equipment is not necessary, all that 
needs to be done is to attach a plate 110 across the open bottom 92 of the 
first housing 54 to seal the unit. The O-ring seal provides a sealed 
enclosure whether the first housing is closed by the top of the cover of 
the second housing 56 or with the plate 110. 
Referring to FIG. 7, there is shown another aerial mount configuration of a 
subscriber control unit 120 and a tapping unit 122, both suspended from a 
strand 12 which also suspends a cable 14 on hangers or lashing as shown at 
17. The tapping unit 122 may either be a conventional tap wherein opposite 
ends of the cable across a gap therein are connected to connectors 126 on 
opposite sides of the enclosure or housing of the tapping device 122. The 
tapping device 122 may be a conventional tapping device or the device 
shown in FIGS. 3 to 6 (i.e., the first housing 54 with its tapping 
circuitry). A bottom plate 128 is provided with a connector 130 which 
receives an end of a second cable 132. This second cable is connected to 
lines from the circuitry in the tapping device 122. The subscriber control 
unit 120 has a connector 50 which receives the cable 132 and connects the 
lines therein to the electronics of the control unit 120. 
The subscriber control unit housing or second housing is connected by 
clamps 136 to the strand and is suspended therefrom adjacent to and along 
side of the tapping device 122. The cable 14 extends along side and 
outside of the housing of the subscriber control unit 120, bypassing that 
unit as it proceeds in a downstream direction. 
From the foregoing description it will be apparent that there has been 
provided improved off-premises equipment for use as CATV signal 
distribution apparatus. Variations and modifications in the 
herein-described equipment, within the scope of the invention, will 
undoubtedly suggest themselves to those skilled in the art. Accordingly, 
the foregoing description should be taken as illustrative and not in a 
limiting sense.