Note: Descriptions are shown in the official language in which they were submitted.
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PIDI REC'rlC~N~L UNlCAI3LE S~,'l'C~IING S~ST~3~
This invention relates to a two-~ay coaxial .scnding and
re,ceiving system wherein a single coaxial cable is used to send and
receive television signals Wit]l each subscriber drop being assigned
its own specific allocated band o frequencies.
It is well known in the art that cable televisibn systems
today have the capabilities of delivering up to 35 different television
channels of programming plus the full spectrum of ~M services
to all subscribers. Existing systems are "party line" type
systems whereby the same programming is delivered to all sub-
scribers. These cable systems also have the capability of returning
television signals to the headend.
There have been other types of systems proposed in the
past whereby each subscriber has separate downstream and up- -
stream cab]es thereby permitting him to remotely select any avail-
able program. The subscriber could dial the desired program and
at a local switching center, the subscriber's cable would be inter-
cormected to that channel. This type of switching system presents
the possibility of a subscriber being able to request television
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prograrns from libraries of video tapes providing educational pro-
grarns, foreign language lessonsJ cultural or sporting events.
This system had one inherent weakness: the requirement for a
separate feeder cable to every subscriber. This requires the use,
in either aerial or underground construction, of large bundles of
cables. This type of system - in spite of its promise - has not
succeeded in this country, because of excessive costs.
It is the general object of this invention to provide the
above noted services by using a system wherein a single coaxial
cable is used to deliver television programs to many subscribers,
where each subscriber has a specifically allocated television channel
or band of frequencies for reception of desired programs, where
each subscriber independently selects the program to be sent on
the subscriber's assigned channel, where all subscribers can receive
FM signalsJ and ~here a descending order of television frequencies
is delivered to subscribers on the feeder cable. The same feeder
coaxial cable that is used for reception of the signal is used to transmit
back to the amplifier or control station a signal irom the subscriber
to select the desired program.
A still further general object of this invention is the use of
this sarne feeder coaxial cable to send back to the control station
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a televisic)n signai on the assigned channel. This program can be
used for two-way television of broadcast quality between any two
subscribers or for a conference of subscribers.
This in~ention is similar in concept to the prior art "Wired
Broadcasting Systems" shown by Eric J. Gargine, patent ~'3, 665, 311
and Ralph Porton Gabriel, patent ~13, 801,, 735. A major difference
in this system, frorn the above systems is that rather than providing
two separate feeder cables to each subscriber (one downstream, the
other upstream), up to 35 subscribers can utilize the same feeder
cable for receiving signals downstream and sending them upstream.
Each subscriber on a given leeder coaxial cable is allocated a separate
channel for reception and transmission of programs plus the trans- -
mission of control signals. These channels are allocated to individu-
al subscribers on the basis of distance along the feeder from the
control station with the closer subscribers being assigned a higher
frequency spectrum.
The primary advantage of this system along with the other
switching type wired broadcasting systems is that each subscriber
has the capability of remotely selecting one of possibly hundreds of
available television or other programs at any time. The immediate
applications using existing single trunk cable systems is primarily
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one-way, downstream where the subscribers choice is limited to
35 televislon channels and full spectrum of FM as this is the total
delivered to each control station and therefore the total available
for connection to the subscribers who requested them. Later there
can be additional or;gination of programming at the control station
(which could be located in a public school or library). To further
increase the subscriber's program cho;ces the cable operator can
duplicate the trunlc part of the system. Other possible applications,
where the trunl; part of the system is two-way, are for the sub-
scriber's return signals to be sent to other parts of the system upon
being received at the control station.
It is still a further object of this invention to apply it to
multi or single dwellings. Since both the downstream and upstream
services use the same bandwidth for each subscriber and since
this bandwidth is wide enough for a television channel, it is possible
for one or any number of subscribers to simultaneously originate
television programming. This programming can be automatically
routed back to the control station onto an upstream trunk line to the
headend, and then do~stream to another preselected subscriber.
It is a still further object of the instant invention that it is
distinjguished from present CATV systems in the following manner:
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CATV systems generally have up to two line extender ampliriers
cascaded in the feeders from each output of the bridger amplifier;
the proposed system eliminates these line extenders. The limiting
factor for distance of subscriber service from a feeder, in a CATV
system, is the attenuation of the coaxial cable at the top frequency
for which the system is designed. The instant invention extends
feeders more than twice as far without amplification as its limiting
factor is the attenuation of the coaxial cable at channel 2. This
feature provides reduced system cost and elimination of system
distortions as introduced in the line extenders. The feeder is a
coaxial cable whose size (and ther efore attenuation) is determined
by the distance to the furthest subscriber. Several feeder cables
can be paralleled for areas of high density of homes.
The above mentioned and other features and objects of this
invention and the manner of attaining them will become more apparent
and the invention itself will best be understood by reference to the
foliowing description of embodiments of the invention taken in con-
junction with the accompanying drawing the description of which follows:
Figure 1 is a diagrammatic representation of the Trunk,
Bridger and Control Station and feeder cable of the instant invention
which is similar to a conventional CATV system such as th2t shown
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in "Two-way Applications for Cable Television Systems in the 70's. "
(Ronald K Jurgen, Spectrum of IEEE, November 1971, Figure 4,
page 45. ) A significant difference however is the elimination of
line extender and the modifications to the Trunk and Bridger Station
to include a Control Station.
Figure 2 is a diagrammatic representation of a typical feeder
cable showing ~he Control Station terminal and the coaxial cable
disclosing subscriber drops along its effective length~
Figure 3 is a diagrammatic representation from the Control
Station showing the downstream paths of the television signals to
the individual subscribers.
Figure 4 is a diagrammatic representation of the Control
Station showing the downstream, upstream and control signal paths.
Figure 5 is a diagrammatic representation of a section of
the Control Station that processes the subscriber's control signal.
Figure 6 is a diagrammatic representation of a two-way sub-
scriber drop from the feeder cable to the receiver and back.
In present CATV systems, at some trunk locations, some
of the broadband TV and FM signal is split off with a directional
coupler, amplified in a bridger amplifier and distributed down feeder
lines which pass the various subscriber locations. For those wishing
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to subscribe, a tap is made into the feeder cable and to a cable drop
to the subscriber's residence, which drop is connected to the sub-
scriber's TV set. All channels are on the cable and are received
by al~ subscribers.
This system incorporates separating into individual channels
the combined signals at the control Station, converting them to
common I.F, frequencies and switching each one to the desired
outgoing R. ~. channel and feeder cable to satisfy the request of
a subscriber. The switching circuitry can be of any type capable
of being controlled by a remote voltage. Therefore) by the applica-
tion of a frequency selective voltage, any subscriber can have any
channel connected to his/her feeder cable.
As by way of example the frequency allocation to each feeder
can be as follours
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SUBSCRIBER FREQUENCY A LLOCA TlONS
.
Subscriber No. MHz
_ , ;
294- 300
2 288 - 294
3 282 - 288
4 276 - 282
270- 276
6 26~1 - 270
7 258 - 26d
8 252 - 258
9 246 - 252
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SuDscriber No. MHz
240- 246
11 ; 234 - 240
1.2 228 - 234
13 222 - 228
14 21~ - 222
210 - 216
16 . 204 - 210
17 ~198 - 204
1 8 . 192 - 19 8
1 9 1 86 - 1 92
2 0 1 80 - 1 86
2 1 . 1 74 - 1 80
~2 168-.174
23 . 162 -.'168
24 ~ 1~6-- 162 :
1 50 - 1 56
26 144 - 150
27 . 138 - 144
28 132 - 138
29 126 - 132
._120 - 126
31 82 - 88 -
32 76 -. 82
33 70- 76
3~ ~ - 70
58 - 64
~ote: . 88 - 108 l~IHz is used for F. M, signals to all subscribers.
108 - 3~0 MHz is not used as it includes aircraft na~7igation
band - even though there should be no radiation problem.
In the follo-~ing detailed descriptioll and the drawing, lilie
reierence characters indicate lil;e parts.
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In ~igure 1 is shown a Trunk and Bridger ~nplificr and
Control Station where the Control Station 1 receives signals irom
the bridger arnplifier.2 and sends them to the subscribers. It
also receives signals from subscribers and sends them upstream to
the cable s~stem headend by wa~ of the ~eturn Trunk Amplifier 3.
In Figure 2 is shown a Control Station 1 and a feeder cable
10, descending from said (:~ontrol Station. The closest subscriber
4 is allocated the TV channel spectrum of 294-300 MHz plus the
FM spectrum 88-108 MHz and the most distant subscriber 5 is
allocated the TV channel spectrum 54-60 MHz plus the FM spec-
trum of 88-108 MHz. The other subscribers on the feeder cable
are assigned TV channel spectrums in a descending order plus the
FM spectrum 88-108 MHz.
In Figure 3 is shown the downstream functions of the Control
Station 1, to one of the feeder cables, which receives the multi-
channel output of the bridger amplifier 2 through directional couplers
6 and processes each TV channel separately, through the down
converters 7 that provides a common. 1. F. band of frequencies 41
to 47 MHz. The outputs of these converters are connected with
further directional couplers 6 to the input terminals of switching
network 8. The output of the switching network connects the requested
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channel's l.F. to TV channel up-converter 9. This switching can
be n~echanical, electronic or any automatic type where a desired
program ca~ be sent to the proper channel converter through additional
directional couplers 6 to feeder cablè 10. Local TV program origina-
tion whether live or by tape is handled the same way. This is shown
by videotape player 11 connected to modulator 12 for conversion of
video to 1. F. and is available to be switched to any subscriber.
By this system the Control Station connects any desired I . F. modu-
lation to any output channel on any feeder.
The FM signals are handled differently in that the broadband
spectrum 88-l 08 MHz is maintained throughout; further directional
couplers 6 connect the bridger amplifier's output to FM amplifier
13 and the various feeder coaxial cables 10. By this system the
Control Station connects FM to all feeder cables.
In Figure 4 is shown the downstream, upstream and control
functions of the Control Station 1. The downstream functions are
the same as shown in Figure 3.with signals from bridger amplifier
2 being connected via directional coupler 6, being converted to I.:F.
by down-converter 7, being switched by 8 to the desired channel
up converter 9 and connected to the feeder cable 10 through a
chamlel bandpass filter 14.
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l~e upstream television signals from feeder cable 10 are
fed through directional coupler ~ through the channel bandpass filter
14, through other directional couplers to an I. F. down-converter 7,
then through the automatic switch network 8 to the desired channel
up-converter 9 and through a directional coupler to the return trunk
amplifier 3, in the Trunk and Bridger Amplifier and Control Station.
These functions enable the TV or data return channels to be ultimately
fed to the Cable System headend, there to be redistrlbuted to any
other subscriber.
The upstrearn control signals are fed to the frequency selective
voltage control network 15 where they provide frequency selective
voltages to control the automatic switching of both upstream and
downstream signals. For a detailed description of this network see
~igure 5.
In Figure 5 is shown varlous functions that are employed in
controlling the switching networ~ that allocates the television channels
being sent and received by a subscriber. This is done by a network
that receives and responds to a ~control signal from a subscriber
subscriber can send this signal by modulating with a discrete
frequency the lower R.F. band edge of the subscriber's allocated
channel. All taps, cable, filters and accessories on the feeder cable
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10 are two-way so this control signal is split off the feeder at the
Control Station by a directional coupler 6, connected to channel
R.F. bandpass filter 14, to an R.F. detector 16, then a low
frequency bandpass filter 17 that accepts the desired frequency
selective signal and feeds it to amplifiers and that develops a
control voltage for the automatic switching. Items 16, 17 and
18 are components of the frequency selective control network 15
in Figure 4. Items 6, directional couplersJ which are in the control
path after 14 are not shown on this figure 6.
The conversion of any incoming television channel at the
Control Stations to an outgoing television channel is accomplished
by converting all incoming channels to a common I. F. frequency,
switching them by means of control signals and then reconverting
them to the desired outgoing frequency.
The switching~ which is not shown, can be typical of any
of those that are employed in two-uray cable television systems such
as that shown at the program exchange in patent #3, 801, 705 of
Gabriel, referred to above, for non-duplication or other services.
It can be electronic, mechanical or any automatic type wherein the
control signal from any subscriber will actuate the switching circuit
and cause the desired program to be sent to the subscriberO
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In. Figure 6 is shown a two-way subscriber drop which includes
the t~,ro-way feeder cable 10, directional coupler 28 and an FM band-
pass filter 19 to pass FM to the subscriber irrespecti~e of TV
channel allocation. The feedthru section of the FM filter connects
all TV signals to a TV channel bandpass filter 14, to the subscriber's
two-way interface -terminal 20 and to the TV receiver 21.
The upstream TV transmitting circuit can comprise of a
TV camera 22, microphone 23 and modulator 24. An upstream
control signal transmitting circuit could include a lower band edge
R.F.. oscillator 259 a discrete low frequency oscillator 26 and a
mixer or modulator 27. This control signal can be switched on by
the subscriber's interface terminal 20. .
VVhile the principles of the invention have been described in
connection with specific apparatus, it is to be clearly understood that
this description is made only by way of example and not as a
limitation to the scope of the invention.
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