AU2001242191A1 - Two way cable system with noise-free return path - Google Patents

Description

TWO WAY CABLE SYSTEM WITH NOISE-FREE RETURN PATH

FIELD OF THE INVENTION This invention relates to cable systems and more particularly to such systems with

a sufficiently noise free return path to support two-way broadband, multimedia content

delivery to and from the home.

BACKGROUND OF THE INVENTION

It is well known that the return path in a cable system is noisy and is frequently

referred to as a "noise funnel". There are three primary sources of such noise: Thermal,

fiber optic link and ingress. Thermal noise is generated in each of the active components

(amplifiers and receivers). The fiber optic link noise is generated in the return laser, fiber

and headend receiver. Ingress noise arises through home wiring and connections and

constitutes the major source of noise. A complete discussion of the return path and the

noise characteristics is provided in "Return Systems for Hybrid Fiber/Coax Cable TV

Networks" by Donald Raskin and Dean Stoneback, 1998 Prentice Hall, Inc.

Every cable system has a major trunk along which signals, are transmitted from a

headend in a forward direction to set-top boxes located in homes or business facilities

connected to the feeder lines. Connection of set-top boxes to a feeder line is provided by

connecting each set-top box to the feeder line via a tap. In the usual organization of a

cable system there are many set-top boxes connected to each feeder line. Moreover, each

feeder and/or trunk line includes bi-directional amplifiers which pass signals in a high

frequency band in the forward (downstream) direction and in a low frequency band in the

return (upstream) directions, which is well understood in the art. Signals in the low

frequency band originate at set-top boxes and are used to communicate in the upstream

direction to the headend. The problems with present return paths in cable systems arise from the fact that the

path from the set-top to the tap in the feeder line (the inside wiring and the drop) is

characterized by an unacceptable level of noise (ingress) which is picked up in the home

wiring and in drop cable in the low frequency band where the set-top box transmits.

Further, no other band (relatively free of such ingress noise) in a low-split cable system is

available for transmission from the home to the headend. Present low-split cable systems

are wedded to transmission from the cable headend in a high frequency band and

transmissions from set-top boxes in a low frequency band.

Yet the financial expectations of two way, broadband channels via a cable system

are so compelling that significant resources are being dedicated towards solving the

ingress noise problems in the return paths. The present remedial solutions are expensive,

cause system shut down, cause system instability, require repeated service calls to

subscribers facilities, and frequent home and drop rewiring or installation of special traps.

Moreover, with corrosion and deterioration of lines and connectors, there is a high likely

hood that continued attention by cable operators will be necessary.

In the last ten years the cable industry has been retrofitting its cable infrastructure

to allow for two-way communications on the cable plants. This is referred to in the

industry as activating the return path, the return path being in the 5-40 MHz frequency

band. The design of the return path started with rebuilds in the late 70's. In the late 80's

the bigger cable companies began to segment their service area into smaller groups called

"nodes", and changed their trunk system in many cases from using just co-axial cable and

trunk amplifiers to a hybrid fiber/co-axial cable system (HFC). At the same time active

and passive devices were replaced to increase the frequency spectrum in the downstream

direction from 50-350 MHz plants to 50-750 MHz, in some cases up to 850 MHz. The increased downstream frequency band allows cable companies to offer more channels of

video services. The increased bandwidth also can be used for digital services in the

forward direction. Also, by now activating the return path, two-way services such as

impulse pay-per view, interactive TV, cable modems, telephone service, and additional

services can be offered.

In the activation of the return path, it has been found by most of the cable

companies, that the 5-40 MHz frequency band, especially the 5-15 MHz spectrum is

extremely noisy. Because of the presence of the noise, most of the services presently

available in the lower frequency band are digital services that can work with low carrier to

noise signal levels. But since the noise is not consistent, services are seriously impaired at

times. Thus, a large number of cable companies are currently looking for ways to reduce

the noise in the 5-40 MHz frequency band. Most of the approaches have been to reduce

the number of homes connected to each node thereby reducing the total accumulated noise

collected in each segment of the node. There have also been approaches involving the

installation of 5-50 MHz blocking filters to reduce the noise from inactive subscriber's

homes in the 5-50 MHz frequency band from entering the main cable distribution network.

The current best approach is to divide the cable system into many nodes which service as

few as fifteen homes which is in effect providing a system of small clusters of homes, each

connected directly to the node.

BRIEF DESCRIPTION OF THE INVENTION

The present invention is based on the realization that a portion of the downstream

frequency band (i.e. 50-750 MHz) can be used, in part to carry the return path signal from

a set-top box. That portion of the frequency band is presently used to provide TV signals and digital signals from the headend to the home. But that portion of the band cannot

presently be used to carry return path signals.

In accordance with the principles of this invention, the noise picked up in home

appliances, drops, connectors, etc and transported to the corresponding node in the feeder

line is avoided by reconfiguring the set-top box to transmit in the high frequency band

rather than in the low frequency band where most of the noise occurs. The signals from

the set-top box proceed in the downstream direction to the feeder line end, which in

addition is equipped with a high-to-low frequency converter and an amplifier to send the

signal in the return direction through the return path to the headend. The result is that set-

top box transmissions travel in the forward direction to the feeder line end where they are

received and retransmitted in a frequency band passed by the "reverse" amplifiers in the

feeder line. The noise (home to feeder line tap) is averted and the "reconstructed" return

signals are virtually free of ingress noise in the trunk and feeder lines. In this context,

each feeder line end has a terminator and the receiver and high-to-low converter may be

placed anywhere after the last amplifier in the feeder line and the terminator. The portion

of the feeder line between the last amplifier and the terminator is referred to herein as the

feeder line end.

Specifically, applicant herein adds to the cable system relatively inexpensive

equipment which permits the set-top box to feeder line end portion of the return path to

function as a forward path. This is accomplished, in one embodiment, by providing at

each feeder line end a receiver and a high to low frequency converter. The receiver

receives the signals in the high portion of the band and the converter converts the signals

to the 5 to 40 MHz band for transmission back to the node. The nature of the system is that it virtually eliminates ingress noise from house wiring and the drop, which is shown

schematically on page 57 of the above-noted publication.

A high pass filter is added between each tap to the feeder line and the set-top box

or any other device (s) in the home This is to ensure that signals in the low frequency

portion of the frequency band are blocked from entering the feeder line and only the high

frequency signal used by a set-top box are allowed to enter the feeder line.

In another embodiment, each feeder line end includes a receiver and a demodulator

to decode the received data. The decoded data is then used to modulate a signal in the

lower frequency band. The regenerated signal does not contain the noise that was

contained in the received signal. It is in effect a noise free signal.

Thus, in accordance with the principles of this invention, a technique is provided

for eliminating the ingress noise in the low frequency band from house wiring, device (s) in

the home, and the drop from entering the cable system, thus making the low frequency

band much more usable for the return path. Due to the noise reduction, the low frequency

band can be used for much higher modulation schemes such as QAM- 16, QAM-32, QAM-

64 etc. Current modulation schemes also become much more reliable and have much

lower bit error rates. Overall it makes the return path in a cable system much more usable.

With the resulting higher reliability there is likely to be fewer customer calls for service

and higher customer satisfaction. With the lower noise level, the low frequency band can

be utilized to carry even video channels.

This invention, illustratively, utilizes a portion of the 50-750 MHz frequency band

to carry the return signal from the subscriber locations, rather than the 5-40 MHz

frequency spectrum. But the return signal is transmitted first forward to the feeder line

end and then back to the cable headend. At the end of each of the feeder lines is a receiver that operates, illustratively in the 50-750 MHz band to receive the "return" signal. For

example, the 300-335 MHz band could be used to carry the return signal "forward" to the

feeder line end. The signals in this band are received by the receiver at the end of the

feeder line. The signals are down converted to the 5-40 MHz frequency band and sent

back along the feeder line (bypassing the drops) to the cable headend

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic representation of a prior art cable system including cable

headend, trunk, nodes and illustrative set-top box locations;

Fig. 2 are graphic representations of portions of the frequency band presently used

for cable headend, set-top box, and bi-directional amplifier operation in prior art cable

systems;

Fig. 3 is a graphic representation of ingress noise for transmissions in the low

frequency band of fig. 2;

Fig. 4 is a schematic representation of a cable system with a feeder lines

configured in accordance with the principles of this invention;

Fig's. 5 and 6 are graphic representations of portions of the frequency band used

for cable headend, set-top box, and bi-directional amplifier operation in cable systems in

accordance with the principles of this invention and the ingress noise with respect to

transmissions in those portions;

Fig. 7 is a graphical representation of the function of a high-to-low frequency

converter in the system of fig. 4;

Fig. 8 is a graphical representation of the function of a band stop (notch) filter in

the system of fig. 4; Fig. 9 is a schematic representation of a prior art set-top box for the system of fig.

l;

Fig. 10 is a schematic representation of a set-top box for a cable system in

accordance with the principles of this invention; and

Fig. 11 is a schematic representation of a set-top box for a cable system in

accordance with the principles of this invention where the return path is moved all the way

up to the high end of the frequency spectrum.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THIS

INVENTION

A glossary of symbols and definitions is provided hereinafter as an aid to an

understanding of the drawings. The glossary is taken from Modern Cable Television

Technology by Walter Ciciora, James Farmer and David Large, Morgan Kaufmann

Publishers, Inc., San Francisco, CA 1999.

Fig. 1 shows a schematic block diagram of a prior art cable system to establish a

point of reference and terminology for the description of illustrative embodiments of this

invention: Specifically, fig. 1 shows a cable system 10 with a cable headend 11 and a

major trunk 12. Trunk 12 typically comprises a coaxial cable and is connected to node or

hubl3. Node 13 is connected to the cable headend via optical fiber (or a coaxial cable) 14

and (for the former) includes a laser for providing return signals from a subscriber set-top

box to the cable headend.

The major trunk includes a plurality of bi-directional amplifiers represented,

illustratively, at 17 and 18. The trunk also includes bridger amplifiers 20 and 21 to which

feeder lines 22,23 and 24 are connected as indicated. Also shown is a auxiliary feeder line 26 which also includes bi-directional amplifiers (represented at 27) and tap 28 to which a

drop cable 29 to the set-top box is connected.

A cable end is present at the end of trunk 12 as indicated at 30. The end of a feeder

line as indicated at 31.

5 Fig. 2 shows a set of related graphs of signal level versus frequency for the

headend, the set-top box, and the bi-directional amplifiers respectively, for a prior art cable

system. In the prior art system, the cable headend illustratively, receives signals in the 5-

40 MHz band and transmits over the entire, illustratively, 50-750 MHz band. The set-top

box operates in just the opposite manner. Specifically, the set-top box transmits in the 5-

10 40 MHz band and receives signals in the 50-750 MHz band.

The bi-directional amplifiers pass signals (forward, away from the headend) in the

50-750 MHz band and pass (return, toward the headend) signals in the 5-40 MHz band.

Thus, signals from a set-top box in the 5-40 MHz band occur exactly where most of the

ingress noise occurs. Fig. 3 shows a curve 33 representing the accumulated ingress noise

15 with maximum ingress in the 5-40 MHz band. It is clear that the usefulness of the present

return path can be severely limited by ingress noise.

Fig. 4 is a block diagram of a cable system in accordance with the principles of this

invention. The system 40 comprises a headend 41 connected to a node (or hub) 42 by

fiber optic (or coaxial) cable 43. The node contains a return laser (for fiber optic

0 systems). The system also includes a major trunk 45 with bi-directional amplifiers 47 and

48 (there usually are more amplifiers and they are located usually 500-1500 feet apart)

with bridger amplifiers 50, and 52. A feeder line 56 is shown connected to bridger

amplifiers 50 and terminating at end 58 at which a receiver 59 and a high-to-low converter

60 is located. Similarly, a feeder line 61 has a feeder line end at 62 which includes a receiver 63 and a high-to-low converter 64. High-to-low converters typically include an

amplifier to boost signals if necessary.

Receivers 59, 63, 70, and 116 are operative to receive signals illustratively

in the 50 to 750 MHz band. The set-top boxes in the system of fig. 4 are also operative to

5 transmit in the 50 to 750 MHz band. Thus, transmissions from a set-top box (the return

transmissions) are received first by receivers at the feeder line ends before they are

received at the cable headend. Transmissions in the 50-750 MHz band are blocked by the

reverse amplifiers in the trunk and in feeder lines and will pass signals in the return path

only in the 5-50 MHz band. It is to be understood that in accordance with the principles

10 of this invention, signals from a set-top box are in a frequency band which travels to a

receiver at the feeder line end rather than in a return path to the cable headend.

But each feeder line end, also in accordance with the principles of the

invention, includes means for receiving those signals and means for converting those

signals into signals which are passed and amplified by the amplifiers in the trunk and in

15 feeder lines. In the embodiment of fig. 4, the means for receiving signals in the 50-750

MHz band are receivers 59, 63, 70 and 116. The means for converting those signals into

"return path" signals in the 5-40 MHz band comprises high-to-low converters 60 and 64

and additional transmitters if required. Similarly, the modulators 72 and 118 regenerate

the data received from demodulators 71 and 117 respectively into return signals in the 5-

20 40 MHz band. The modulators may include amplifiers to boost the signals if required.

Fig. 5 shows a set of related graphs of signal level versus frequency for a cable

headend, a set-top box and for a bi-directional amplifier respectively for a cable system in

accordance with the principles of this invention. As shown in Fig. 5, the headend receives

in the 5-40 MHz band as in the prior art, but does not transmit over the entire 50-750 MHz band. The 300-335 MHz portion is notched out. The set-top box transmits in the

300-335 MHz portion and receives in the 50-300 MHz and in the 335-750 MHz bands.

The bi-directional amplifiers, of course, operate as they do in prior art systems to pass

"forward" signals transmitted by the headend in the 50-750 MHz band and to pass

"return" signals only in the 5-40 MHz band.

It is clear from fig. 5 that signals transmitted by set-top boxes in the system of fig.

4 are not passed by the reverse amplifiers to the headend. Instead, those set-top box

transmissions are passed in a "forward" direction to the corresponding feeder line end

where they are received, converted to 5-40 MHz signals and retransmitted. The signals

now are passed by the reverse amplifiers to bridger amplifier 50 and back to the cable

headend.

Fig. 6 shows a graph of ingress noise 100, corresponding to that of fig. 3, along

with the portion of the frequency spectrum 300-335 MHz in which set-top boxes transmit

in accordance with the principles of this invention. It is clear that ingress noise is

insignificant over the portion of the spectrum now used by set-top boxes in the system of

fig. 4.

High frequency to low frequency converters (60 and 64) are operative to convert

signals in the 300-335 MHz band to signals in the 5-40 MHz band as indicated in fig. 7.

Modulators (72 and 118) generate signals in the 5-40 MHz band. The resulting signals (in

the 5-40 MHz band) are send along the feeder line and trunk to the headend, providing

return path signals virtually free of ingress noise.

A system, in accordance with the principles of this invention, also includes

band stop (notch) filters at the start of auxiliary feeder lines (i.e. 110) in the system to

ensure that transmissions from a set-top box in the 50-750 MHz band are only received by one feeder end in the system. Such filters are located at the start of auxiliary feeder line

(i.e. 112) to ensure that the signal for each set-top box is received only at one feeder end

(i.e. the signal from set-top box 55 is received by receiver 70 only, since band stop filter

112 blocks the signals from being received by receiver 116. High pass or "window" filters

are shown at 80, 81, 82, 83, 84 in fig. 4. High-pass filters block out all signals below

50 MHz from entering the feeder line (i.e. blocking out the major ingress noise from

entering the feeder line). The window filters block out all of the return band except a

window 2-3 MHz wide for analog set-top returns. This allows the old addressable set-top

communications to pass while attenuating any other ingress. Fig. 8 shows a graphical

representation of a band stop filter which passes signals in the 50-750 MHz band except

for signals in the 300-335 MHz (notch) portion of the band. The presence of such filters

prevents signals from a set-top box (in the 300-335 MHz band) from being received by

more than one feeder end.

Fig's. 9 and 10 show schematic representations of a prior art set-top box and a set-

top box in accordance with the principles of this invention, respectively. In the prior art

set-top box of fig. 9, a high pass filter 104 excludes signals in the 5-40 MHz band and

passes signals in the 50-750 MHz band. The set-top box also includes a low pass filter

101 which excludes signals in the 50-750 MHz band and passes signals in the 5^ 0 MHz

band.

The set-top box of fig. 10 is considerably different. Specifically, the set-top box of

fig. 10 includes a band stop filter 102 which passes 50-750 MHz but notches out signals in

the 300-335 MHz band. The set-top box also includes a band pass filter 103 which passes

signals in the 300-335 MHz band. Thus, the set-top box of fig. 10 receives and transmits

in the same (high) band (i.e. 50-750 MHz) whereas the set-top boxes of the prior art receive and transmit in high and low (considerably different) bands respectively. The set-

top box also transmits signals in a frequency band which cannot be received by the cable

headend.

The converters, demodulators, modulators, receivers, transmitters and other

components herein are all commercially available or easily reconfigured from available

components by a change in, for example, capacitor values in such components. Any such

components operative as required herein may be used in accordance with the principles of

this invention.

Fig. 4 also shows an auxiliary feeder line 110 extending from feeder line 66. It is

important that a transmission from a set-top box of the system of fig. 4 be received only by

the receiver at the end of one feeder line to which the transmitting set-top box is

connected. In order to prevent signals from, for example, a set-top box connected to

feeder line 66 being received by a receiver 116 connected to an auxiliary feeder line (110),

the auxiliary feeder line includes a band stop filter 112 to exclude such transmissions as

discussed herein before.

Alternatively, the cable headend may be configured to poll (i.e. enable) a set-top

box and the corresponding feeder line end receiver simultaneously so that only signals

from that receiver are received at the headend. The cable headend will of course, require

additional software in this case. This would allow the cable operator to choose the size

and location of the return frequency band. Frequency agile band stop filters and

frequency agile band pass filters can also be used in the system to utilize any portion of

frequency band desired by the system operator. The frequency bands selected herein are

only illustrative and other bands and/or notches may be suitable as is clear to one skilled in the art. For example, the operator could use the 700 MHz and up band for the return path.

In this case the configuration of the set-top box would change to that shown in fig. 11.

It is anticipated that the novel set-top boxes shown herein will have wireless

capability added to them to allow them to communicated wireless to other devices in the

home and business facilities such as personal computers, videophones, telephone etc.

It is to be understood that although the invention has been described illustratively in terms of a set-top box, any two-way communication device, such as a cable modem, can be used.

GLOSSARY

Subscriber taps. Used to couple power from main line to two to eight subscriber ports. In two-way systems, subscriber ports are used as insertion points where upstream signals are combined into the composite upstream spectrum.

Amplifier (generic). May represent either a gain block or a complete coaxial amplifier station, dependening on context. If used to represent an amplifier station, the symbol may represent either a one or two-way unit. Also may represent an optical amplifier.

Multiple output coaxial amplifier station. May be either a trunk/ bridger or system amplifier. Where there is a center output, it will be the trunk, and may operate at a lower level to reduce composite distortions.

Two-way coaxial amplifier station. The larger triangle represents

Input the downstream direction, and the smaller triangle indicates the upstream direction. Note that, by convention, "input" and "output" port designation are used that are correct only for downstream transmission.

Headend. The point where most of the signal processing is done in a cable system.

_Down_str_eam Diplex filter. Used to sepβratβ an incoming spectrum into two combined outputs, with frequencies exceeding some value exiting one port, while frequencies below that frequency exit the other port. The most common use is to seperate upstream from downstream frequencies u^pstream j_n amplifier stations. Can be used as a combiner in reverse.

Attenuator. Used to attenuate an RF spectrum by a value that is nominally independent of frequency.

Claims (52)

WHAT IS CLAIMED IS

1. A cable system comprising a major trunk and a plurality of feeder lines, each of

said feeder lines being connected between a node in said trunk and a feeder line end, each

of said feeder lines including a plurality of taps and a two-way communication device

connected to each of said taps, each of said feeder lines including bi-directional amplifiers

for passing signals in a high frequency band forward from said headend to said two-way

communication devices and for passing "return" signals in a low frequency band to said

headend, said two way communication devices being configured to both receive and

transmit in said high frequency band, each of said feeder line ends including a receiver for

receiving transmissions in said high frequency band and a means for converting signals in

said high frequency band to signals in said low frequency band.

2. A cable system as in claim 1 wherein said feeder line end also includes a means for

amplifying signals in said low frequency band.

3. A cable system as in claim 1 wherein both of said two-way communication devices

and said headend transmit in said relatively high frequency band.

4. A cable system as in claim 1 wherein the connection between said two-way

communications device and said feeder line also includes a high pass filter.

5. A cable system as in claim 1 wherein at least one of said feeder lines includes an

auxiliary feeder line, said auxiliary feeder line including a band stop filter.

6. A cable system as in claim 4 wherein at least one of said feeder lines includes an

auxiliary feeder line, said auxiliary feeder line including a band stop filter.

7. A cable system as in claim 1 wherein said two-way communication devices include

set-top boxes.

8. A cable system as in claim 4 wherein said two-way communication devices include

set-top boxes.

9. A system comprising a major trunk and a plurality of feeder lines connected

between said trunk and respective feeder line ends, each of said ends including a receiver

for signals in a high frequency band, said system including a headend connected to said

trunk and two-way communication devices connected to said feeder lines, both said

headend and said two-way communication devices being configured to transmit signals in

said high frequency band, said feeder lines including bi-directional amplifiers which pass

signals forward to said two-way communication devices only in said high frequency band

and pass return signals to said headend only in said low frequency band, said feeder ends

including first means for receiving signals in said high frequency band and a second means

for transmitting said signals in said low frequency band.

10. A system as in claim 9 wherein said devices comprise set-top boxes.

11. A system as in claim 9 wherein said first means comprises a receiver of signals in

said high frequency band and second means for generating signals for transmitting in said

low frequency band.

12. A system as in claim 9 wherein said second means comprises a high to low

frequency converter and a transmitter for transmitting signals in said low frequency band.

13. A cable system including a cable headend and a major trunk, said trunk having

taps there along, said system having at least one feeder line connected between one of said

taps and a feeder line end, said feeder line including at least one set-top box, said set-top-

box and said cable headend being configured to transmit signals indifferent portions of a

high frequency band.

14. A cable system as in claim 13 wherein said headend is configured to receive

signals only in a low frequency band and transmit signals in said high frequency band.

15. A cable system as in claim 14 wherein said system includes means for including a

notch in said high frequency band in which said headend does not transmit, said set-top

box being configured for transmitting in said notch.

16. A cable system as in claim 15 comprising a plurality of feeder lines each having a

feeder line end wherein each of said feeder line ends includes a receiver for signals

transmitted in said notch and means responsive to said signals for re-transmitting said

signals in said low frequency band.

17. A cable system as in claim 16 wherein said means comprises a high-to-low

frequency converter and a receiver of signals in said notch.

18. A cable system including a headend and a plurality of two way communication

devices in which signals only in a first frequency band are transmitted in a forward

direction from such headend and signals only in a second frequency band are transmitted

in a return direction to said headend, said system being characterized by unacceptable

noisy portions at said devices for signals in said second frequency band, said system

including devices configured to transmit in said first frequency band, said system

including means responsive to signals in said first frequency band from said devices for re¬

transmitting said signals in said second frequency band.

19. A cable system including forward amplifiers which pass signals in a first

frequency band, said system including two-way communication device comprising first

means for receiving transmissions in said first frequency band, said device also including

second means for transmitting in said first frequency band.

20. A cable system wherein two-way communication devices as in claim 19

comprising set-top boxes.

21. A cable system comprising a cable headend, a return node and a plurality of

feeder lines, each of said feeder lines being connected between said return node and a

feeder line end, each of said feeder lines including a plurality of taps, a plurality of two-

way communication devices connected to said taps, said cable headend and said two-way

communication devices being configured to transmit in a high frequency band, each of

said feeder line ends including first means for receiving transmissions in said high

frequency band and second means for re-transmitting the received transmissions in a low

frequency band.

22. A cable system as in claim 21 wherein said headend is configured to receive

transmissions only in said low frequency band and said feeder lines include means for

amplifying transmissions in said high frequency band only in a first direction towards said

feeder line ends and for amplifying transmissions in said low frequency band only in a

second direction towards said headend.

23. A cable system as in claim 22 also including a major trunk, said feeder lines

being connected to said major trunk, said major trunk also including first and second

amplifiers for amplifying transmissions in said high and low frequency bands in said first

and second directions respectively.

24. A cable system as in claim 23 wherein said major trunk extends from a return

node to a trunk end and said return node includes a return laser and is connected to said

headend via a fiber optic cable.

25. A cable system as in claim 21 wherein said first and second means include a

receiver and a high-to-low frequency converter respectively.

26. A cable system as in claim 21 wherein each of said feeder lines is connected

to said major trunk via a band stop filter.

27. A cable system as in claim 26 including an auxiliary feeder line extending

from a tap in one of said feeder lines to a (auxiliary) feeder line end, said auxiliary feeder

line including a band stop filter and said tap, said auxiliary feeder line also including a

receiver and a high-to-low frequency converter at the auxiliary feeder line end.

28. A cable system as in claim 21 wherein said two-way communication devices

comprise set-top boxes.

29. A cable system as in claim 21 wherein said headend is configured to transmit

in said high frequency band except for a notch portion therein, and said two way

communication device is configured to transmit in said notch portion.

30. A cable system as in claim 28 wherein said headend is configured to transmit

in said high frequency band except for a notch portion therein, and said set-top box is

configured to transmit in said notch portion.

31. A cable system as in claim 29 wherein said two way communication device

includes a band stop filter with an associated receiver of signals from said headend, said

device also including a band pass filter and an associated transmitter.

32. A cable system as in claim 30 wherein said set-top box includes a band stop

filter with an associated receiver of signals from said headend, said set-top box also

including a band pass filter and an associated transmitter.

33. A set-top box including a band stop filter and a receiver, said band stop filter

being operative to exclude a first portions of a frequency band in which signals can be

applied to said receiver, said set-top box also including a band pass filter and a transmitter, said band pass filter being operative to pass from said transmitter only signals in the

excluded first portion of the frequency band.

34. A set-top box including a low pass filter and an associated receiver, said low

pass filter being operative to pass to said receiver only signals in a low portion of a high

frequency band, said set-top box also including a relatively high pass filter and a

transmitter, said relatively high pass filter being operative to pass from said transmitter

only signals in a high portion of said high frequency band.

35. A set-top box as in claim 33 wherein said frequency band is from 50 MHz to

about 1,000 MHz and said first portion is from about 300-335 MHz.

36. A set-top box as in claim 35 wherein said band pass filters is operative to pass

signals in the 300-335 MHz from said transmitter.

37. A set-top box as in claim 34 wherein said low pass filter is operative to pass

signals in about the 50-700 MHz band and said high pass filter is operative to pass signals

in the 700 MHz to about the 1,000 MHz band.

38. A cable system as in claim 19 in which said two way communication device is

connected to said cable system by a high pass filter.

39. A cable system as in claim 38 also including reverse amplifiers that pass

signals in the low frequency band blocked by said high pass filter.

40. A cable system as in claim 38 also including reverse amplifiers that pass

signals towards the headend in said second frequency band blocked by the said high pass

filter.

41. A cable system as in claim 38 also including means for receiving signals in

said first frequency band at the feeder line end and a means for converting signals received

in the said first frequency band into signals in the second frequency band.

42. A cable system including a high-to-low frequency converter at least first and

second feeder line ends.

43. A cable system as in claim 42 including forward amplifiers that carry signals

in the high frequency band and reverse amplifiers that carry signals in the low frequency

band.

44. A cable system as in claim 43 including set-top boxes that have means to

receive and transmit in said high frequency band.

45. A cable system as in claim 44 where the set-top boxes are connected to the

cable system via high pass filters.

46. A cable system including a feeder line and an auxiliary feeder line extending

therefrom via a bridger amplifier, said auxiliary feeder line including a band stop filter at

said bridger amplifier, said auxiliary feeder line also including a receiver to receive signals

in the high frequency band and a high-to-low frequency converter at the end thereof.

47. A cable system as in claim 46 which also includes bi-directional amplifiers in

the auxiliary feeder line.

48. A cable system as in claim 47 which also include two way communications

devices that are connected to auxiliary feeder line via taps and a high pass filters, said two-

way communications devices having means to receive signals from said auxiliary line in

the high frequency band and to transmit signals to auxiliary feeder line in the high

frequency band.

49. A cable system including an auxiliary feeder line extending from a bridger

amplifier in one of feeder lines to an auxiliary feeder line end, said auxiliary feeder line

including a band stop filter and also including a receiver for receiving signals in the

notched out frequency band, said auxiliary feeder line end also including a means to generate signals in the low frequency band, two way communications devices being

connected to said auxiliary feeder line via taps, said two way communication devices

transmitting in the notched out frequency band, said two way communications devices

also have a receiver.

50. A cable system as in claim 49 wherein said two way communication devices

are connected to said auxiliary feeder line via high pass filters.

51. A set-top box as in claim 33 is connected to a feeder line via a high pass filter.

52. A set-top box as in claim 34 is connected to a feeder line via a low high pass

filter that is lower in frequency than said low pass filter and said relatively high pass filter.