Variable frequency CATV jamming method and apparatus

A frequency generating means, generates an initial frequency of greater amplitude than the amplitude of a television signal carrier wave. The generated frequency is compared to a reference frequency which would be suitable for jamming one of the channels to be jammed. If the generated frequency is too high or too low, the frequency generating means generates a new frequency which is, respectively, either lower or higher than the initial frequency it generated. If the new generated frequency is still higher or lower than the reference frequency, the frequency generating means generates another new frequency, which is respectively, either lower or higher than the previously generated frequency, but by a lesser amount than the amount by which the previously generated frequency differed from the frequency generated before it. The generation of new frequencies continues until one of them is within a desired range of the reference frequency, at which time the generated frequency is stored in memory. The same procedure is used to obtain memorized frequencies to be generated by the frequency generating means for jamming each channel to be controlled. On a time divisional basis the frequency generating means generates the jamming frequencies which are transmitted to each of the subscribers who are not entitled to receive the channel they are jamming. Periodically the jamming of channels is briefly stopped and the jamming frequencies are re-calculated and re-memorized, then the calculation process stops and the jamming resumes.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
The invention relates to CATV systems, and more particularly to a method 
and apparatus for selectively jamming selected channels to selected 
subscribers in a CATV system. 
2. Description of Related Art: 
CATV systems commonly provide a multiple of channels to their subscribers; 
such systems are well known in the art and have been for many years. Many 
CATV systems, however, do not require each of their subscribers to 
subscribe to every one of the channels they offer. The result is that an 
effective method, and apparatus to carry out that method, is needed to 
allow a CATV system to provide different numbers of channels to different 
subscribers, and at the same time retain the ability to provide up to all 
of their channels to up to all of their subscribers. It is even more 
desirable for a CATV system to be able to easily change the number of 
channels it is providing to any, of its subscribers, at any time, and from 
time to time. That is generally desirable because most CATV systems charge 
different amounts to their various subscribers, depending on how many of 
the supplied channels the particular subscriber wants to receive, and 
those features allow a subscriber to easily change the number of channels 
he receives. The result is that with those features a CATV system can 
easily sell additional channels to its subscribers, or stop sending 
channels to subscribers who do not want them or are not paying for them. 
Scrambling and de-scrambling systems have been developed and are used by 
some CATV systems to control which channels a particular subscriber 
receives. Certain channels are scrambled prior to transmission from the 
supplier's head end, and subsequently de-scrambled at the home ends of 
those subscribers who have paid for those scrambled channels. A device 
commonly referred to as a de-scrambler is installed in the paying 
subscribers homes, which restores the scrambled television signal. Those 
systems require access to the subscriber's home, and man power to do the 
installation, or to remove the de-scrambler in the event the subscriber no 
longer wants it, or has stopped paying the fee. Those systems also run the 
risk of channels being pirated by subscribers who have built, or 
purchased, their own illegal de-scrambler. 
Another known means of controlling subscriber access to the total channels 
in a CATV system is to selectively jam the channels to be denied to the 
subscribers who have not paid for them. The jamming of channels is usually 
accomplished by sending a separate jamming signal for each of the channels 
to be jammed, together with the television signals, to the subscriber(s) 
for whom those channels are to be jammed. Each jamming signal can be a 
signal having a repetition rate close to the repetition rate of the 
vertical synchronization signal of the channel to be jammed, and of a 
greater amplitude. The television will pick up the jamming signal as the 
synchronization signal and will therefore produce a vertically unstable 
picture. Similarily, the jamming signal can be a signal having a 
repetition rate close to the repetition rate of the horizontal 
synchronization signal of the channel to be jammed, and of a greater 
amplitude. The television will then pick up the jamming signal as the 
horizontal synchronization signal and will therefore produce a 
horizontally unstable picture. 
A device is required that will not only produce the required jamming 
signals, but also, will only combine the jamming signals with the 
television channel signals going to the subscriber(s) who have not paid 
for those channel. 
Some of the earlier prior art has used one separate line per subscriber, 
and one RF switch per subscriber, per channel that might be jammed. The 
separate subscriber lines are each coupled to a different RF switch for 
each channel that might be jammed, thereby creating a switch and 
subscriber line matrix in which each subscriber line has a unique RF 
switch for each channel that might be jammed, controlling that 
subscriber's access to said channel, and in which all RF switches 
controlling subscriber access to a particular channel are connected to 
each other. For example only, if the situation is that channel "C" is to 
be jammed to subscribers "101", "222", and "223", each of the channel "C" 
RF switches that couple the jamming signal to those subscriber lines must 
be closed. Accordingly, if there are 2500 subscribers and 4 channels to be 
jammed, 2500 separate subscriber lines are needed, and 
(4.times.2500)=10,000 RF switches are required. Accordingly, a large 
number of RF switches are required. In such a system it would be difficult 
to add further subscriber lines and switches to the switch and subscriber 
line matrix. 
Some of the more recent prior art use apparatuses that are capable of 
generating up to a fixed number of different jamming signals, (for example 
the maximum might be 6) sometimes continuously, and sometimes on a time 
divisional basis. In some of the more sophisticated present art systems 
the jamming signals are added on a time shared bases to the subscribers 
lines who are not permitted to view the particular channel being jammed. 
In many of the more sophisticated prior art systems that add jamming 
signals to subscriber lines on a time divisional basis the maximum number 
of jamming signals that can be generated is eight or less. Therefore, the 
maximum number of channels that can be jammed is eight or less. That is 
obviously a problem for a CATV system that wants to offer nine or more 
alternative channels. 
A number of difficulties have to be overcome when jamming signals are not 
continuously added to the appropriate subscriber lines. However, the 
benefits of adding jamming signals to the appropriate subscriber lines on 
a time divisional basis are great. Therefore it is worth the effort of 
trying to overcome the difficulties involved in time divisional jamming. A 
major benefit to time divisional jamming is that only one line can be used 
to carry all of the different jamming signals to one subscriber. Only one 
line has to be used, because when the jamming signal being transmitted is 
to jam a channel the subscriber is not entitled to receive, then the RF 
switch to that subscriber's single jamming signal line is closed, hence 
the subscriber receives the jamming signal, and that channel is jammed on 
the subscriber's television set. However, when the jamming signal being 
transmitted is to jam a channel the subscriber is entitled to receive, 
then the RF switch to that subscriber's single jamming signal line is left 
open, hence the subscriber does not receives the jamming signal, and that 
channel is not jammed on the subscriber's television set. The result is 
that the channel is jammed during the time its jamming signal is being 
transmitted, but not during the time it's jamming signal is not being 
transmitted. Therefore, if the time between transmissions of the same 
jamming signal is too great, the channel will only be jammed sometimes, 
hence it would be partly viewable. It should therefore be a goal of time 
divisional jamming systems to reduce the time between transmissions of the 
same jamming signal so that the channel is humanly unviewable. 
It is more desirable to produce a horizontally unstable picture than a 
vertically unstable picture, as the former is more difficult to watch. To 
produce a horizontally unstable picture the jamming signal must be sent to 
each subscriber who is to be jammed by it many thousands of times per 
second, thereby effectively always jamming the television signal. To 
accomplish transmitting different jamming signals on the same line many 
thousands of times per second, rapid switching is required; rapid or 
continuous generation of the jamming signals is also required, and 
finally, the rapid switching and the jamming signals must be combined 
correctly to the appropriate subscribers. Those skilled in the art will 
perceive many problems in rapidly switching between frequencies and 
maintaining accuracy of frequency within a small range. 
Some of the more sophisticated prior art systems have used fixed inductive 
circuits which are alternately coupled with an oscillator to generate 
different frequencies through that oscillator. Some of the other more 
sophisticated prior art systems have used a voltage controlled oscillator 
to generate the different jamming frequencies on a time divisional basis. 
The goals in the prior art have generally been to effectively jam the 
largest number of channels with the least amount of expensive components, 
while at the same time allowing for control of what channels are jammed to 
which subscribers, from the head end, with a minimum of equipment 
malfunction. The goals of the present invention are the same as the stated 
generally accepted goals in the prior art. The present invention 
accomplishes those goals in a new and effective way not contemplated by 
the prior art, and for a greater number of channels than the prior art 
inventions of which the Inventors of the present invention are aware. 
SUMMARY OF THE INVENTION 
The invention teaches a method for controlling the reception quality of 
individual subscribers to CATV, and is comprised of the following steps. 
First, selecting and generating a Reference Frequency ("RFz") for each of 
the channel "z" to be jammed, wherein each RFz is a suitable frequency for 
jamming channel z. Second, sending an initial Frequency Generation Signal 
("FGSa") to a generating means, which causes the generating means to 
generate a Jamming Frequency ("JFa") that is similar to the carrier wave 
frequency of a typical television channel's signal, and of a slightly 
greater amplitude. Third, comparing JFa to RFz, and if JFa is higher or 
lower than RFz, sending a different FGSa, which is either lower in voltage 
or higher in voltage, respectively, than the previous FGSa, by an initial 
amount, to the generating means, causing it to generate a new JFa. Then 
again comparing the generated JFa with RFz, and if JFa is higher or lower 
than RFz, sending a new FGSa, which is either lower in voltage or higher 
in voltage, respectively, than the previous FGSa, by less than the 
previous amount, to the generating means, causing it to generate a new 
JFa, which is again compared to RFz, until the last increase or decrease 
in the voltage of FGSa resulted in a frequency change in JFa of &lt;I, {where 
"I" is a frequency value such that RFz+I would jam the television signal 
for which RFz is a reference frequency, if the amplitude of RFz+I was 
within the correct parameters}. Fourth, storing the last FGSa, as FGSz, 
where FGSz is the FGSa that causes the generating means to generate a JFa 
that will jam channel z. The JFa that will jam channel z is called JFz. 
Fifth, continuing the second, third and fourth steps until there is a 
stored FGSz for each channel z, and then suspending the second, third and 
fourth steps. Sixth, in continuous rotation, each for durations suitable 
for jamming the horizontal synchronization signal, combining JFz with the 
television channels signals being transmitted to subscribers who are not 
entitled to receive the television signal which JFz is jamming. Seventh, 
suspending the sixth step for a period long enough for the second, third, 
fourth and fifth steps to be repeated, and then resuming the sixth step. 
A preferred method of determining the correct FGSz values is to reduce or 
increase the JFa by half of the previous amount it was reduced or 
increased by, (i.e. using a binary convergence method) until the change in 
JFa is less than I. It is also preferred to store a FGSa, as the FGSz, 
that resulted in JFa&gt;RFz. Therefore it is preferred to continue the 
comparision of JFa to RFz until: (a) the last increase or decrease in JFa 
was &lt;I, and (b) the second last increase or decrease in the JFa was &lt;I, 
and (c) the second last increase or decrease in the JFa was the opposite 
of the last increase or decrease in JFa, and then to store as FGSz, 
whichever of the last and second last FGSa's resulted in JFa&gt;RFz. 
To accomplish the more desirable determination of the FGSz values, and the 
more desirable FGSz values the following third and fourth steps would 
replace the previously stated third and fourth steps. New Third Step, 
comparing JFa to RFz, and if JFa is higher or lower than RFz, sending a 
different FGSa, which is either lower in voltage or higher in voltage, 
respectively, than the previous FGSa, by an initial amount, to the 
generating means, causing it to generate a new JFa. Then again comparing 
the generated JFa with RFz, and if JFa is higher or lower than RFz, 
sending a new FGSa, which is either lower in voltage or higher in voltage, 
respectively, than the previous FGSa, by half of the previous amount, to 
the generating means, causing it to generate a new JFa, which is again 
compared to RFz, until: (a) the last increase or decrease in the voltage 
of FGSa resulted in a frequency change in JFa of &lt;I, {where "I" is a 
frequency value such that RFz+I would jam the television signal for which 
RFz is a reference frequency, if the amplitude of RFz+I was within the 
correct parameters} and (b) the second last increase or decrease in the 
voltage of FGSa resulted in a frequency change in JFz of &lt;I, and (c) the 
second last increase or decrease in the voltage of FGSa was the opposite 
of the last increase or decrease in FGSa. New Fourth step, storing 
whichever of the last and second last FGSa's resulted in JFa&gt;RFz, as FGSz, 
where FGSz is the FGSa that causes the generating means to generate a JFa 
that will jam channel z. The JFa that will jam channel z is called JFz. 
The method taught by the invention also allows the same jamming signal to 
be used to jam both the horizontal and the vertical synchronization 
signals of the channels to be jammed. To accomplish jamming both the 
horizontal and the vertical synchronization signals, of the channels to be 
jammed, the Sixth Step is divided into two steps, Six (a) and Six (b). 
Step Six (a) is identical to the old sixth step. In step Six (b), in 
continuous rotation, each for durations suitable for jamming the vertical 
synchronization signal, each of the JFz's is combined with the television 
channels signals being transmitted to subscribers who are not entitled to 
receive the television signal which JFz is jamming. Steps Six (a) and Six 
(b) are carried out, on a time shared basis, as determined by the method 
operator, in the period of time during which the old Sixth Step would have 
been carried out. The other steps of the method are performed exactly the 
same whether there is only a Sixth Step, or whether there is a Step Six 
(a) and a Step Six (b). 
The invention, in addition to the stated method, also teaches an apparatus 
for controlling the reception quality of individual subscribers to CATV, 
which apparatus is comprised of the following components. A Voltage 
Controlled Oscillator ("VCO") for generating a frequency ("JFa") that is 
similar to the frequency of a typical television signal's carrier wave 
frequency, and having a duration similar to a typical horizontal 
synchronization signal's duration, and of a slightly greater amplitude. A 
set of Subscriber Jamming Signal Switches, each of which receives the JFa, 
and each of which will transmit the JFa to the line of the television set 
of the subscriber to which it is connected. A Reference Frequency 
Generating Means that generates a reference frequency ("RJFz") which is 
suitable for jamming channel z. A Comparision Means that receives the JFa 
and that receives the RJFz, and can divide the JFa by a factor of "D", 
where D is a factor such that if JFa is the correct frequency to jam 
channel z, then JFa/D=RJFz, and which comparison means can compare the 
RJFz to JFa/D and determine if RJFz is greater than or less than JFa/D. A 
service control center ("SCC") that receives information from the head end 
on which subscribers are entitled to receive which television signals. 
Additionally, the SCC outputs a Frequency Generating Signal ("FGSa") to 
the VCO, that determines the frequency of JFa. Additionally, the SCC, 
based on the information it receives from the head end as to the 
frequencies of the channels to be jammed, determines the value of D that 
the Comparison Means must divide JFa by. Additionally, the SCC sends the 
information of what value D should be to the Comparison Means, at the 
appropriate time. Additionally, to start the system the SCC begins step 
"Test" by sending a FGSa to the VCO, causing the VCO to generate JFa; then 
the SCC sends the appropriate information on the value of D, so that 
RJFz.times.D would be the appropriate frequency for jamming channel z, to 
the Comparison Means. The Comparison Means sends a first signal to the SCC 
if the comparison resulted in JFa/D&gt;RJFz, and a second signal to the SCC 
if the comparison resulted in JFa/D&lt;RJFz; if JFa is higher or lower than 
RJFz.times.D, then the SCC sends a different FGSa, which is either lower 
in voltage or higher in voltage, respectively, than the previous FGSa, by 
an initial amount, to the VCO, causing it to generate a different JFa. 
Then, when the SCC receives the result of the new comparison from the 
Comparison Means, if JFa is higher or lower than RJFz, the SCC sends a 
different FGSa, which is either lower in voltage or higher in voltage, 
respectively, than the previous FGSa, by less than the previous increase 
or decrease, to the VCO. The SCC again receives the results of the 
comparison of JFa/D to RJFz, and the SCC continues to receive the results 
of the comparison and to send out different FGSa's which are either 
increased or reduced by less than the increase or decrease of the previous 
FGSa was, until the last increase or decrease in the frequency of JFa was 
&lt;I, {where "I" is a pre-determined, fixed, frequency value such that 
(RJFz.times.D)+I is close enough to RJFz.times.D, to jam the television 
signal of channel z if it's amplitude were high enough}, the SCC then 
stores the last FGSa, as FGSz, where FGSz is the FGSa that causes the 
generating means to generate a JFa that will jam channel z. The JFa that 
will jam channel z is called JFz. Additionally, the SCC continues to 
operate as stated until there is a stored FGSz for each of the channels to 
be jammed. Once all of the FGSz's have been stored step Test is ended. 
Additionally, the SCC then suspends the operations of step Test and begins 
step Jam by, where N is the number of television signals being jammed, 
sending, in continuous rotation, each for durations suitable for jamming 
the horizontal synchronization signal, each of the FGSz's to the VCO, and 
closing each of the Subscriber Jamming Signal Switches to the subscribers 
who are not entitled to receive the television signal of channel z, when 
FGSz is being sent to the VCO, and opening the Jamming Signal Switches of 
those subscribers who are entitled to receive channel z, when FGSz is 
being sent to the VCO. Additionally, after a pre-determined period of time 
the SCC suspends step Jam for a period of time long enough for step Test 
to be performed, and again performs step Test, and then again suspends 
step Test and again resumes step Jam, and continues to do so at the 
pre-determined periods of time. 
The apparatus taught by the invention also allows the same jamming signal 
to be used to jam both the horizontal and the vertical synchronization 
signals of the channels to be jammed. To accomplish jamming both the 
horizontal and the vertical synchronization signals, of the channels to be 
jammed, the SCC performs step Jam as follows: the SCC sends, in continuous 
rotation, each for durations suitable for jamming the horizontal 
synchronization signal, each of the FGSz's to the VCO the SCC also, in 
continuous rotation, on a time shared basis, as determined by the system 
operator, also sends, each for durations suitable for jamming the vertical 
synchronization signal, each of the FGSz's to the VCO, and the SCC causes 
the closing of each of the Subscriber Jamming Signal Switches to the 
subscribers who are not entitled to receive the television signal of 
channel z, when FGSz is being sent to the VCO, and causes the opening of 
the Jamming Signal Switches of the subscribers who are entitled to receive 
channel z, when FGSz is being sent to the VCO. 
A preferred method of determining the correct FGSz values, in an apparatus 
of the invention, is to reduce or increase the JFa by half of the previous 
amount it was reduced or increased by, (i.e. using a binary convergence 
method) until the change in JFa is less than I. It is also preferred to 
store a FGSa, as the FGSz, that resulted in JFa&gt;RFz. Therefore in a more 
preferred apparatus, the SCC would perform the following Step Test; the 
SCC begins step "Test" by sending a FGSa to the VCO, causing the VCO to 
generate JFa; then the SCC sends the appropriate information on the value 
of D, so that RJFz.times.D would be the appropriate frequency for jamming 
channel z, to the Comparison Means. The Comparison Means sends a first 
signal to the SCC if the comparison resulted in JFa/D&gt;RJFz, and a second 
signal to the SCC if the comparison resulted in JFa/D&lt;RJFz; if JFa is 
higher or lower than RJFz.times.D, then the SCC sends a different FGSa, 
which is either lower in voltage or higher in voltage, respectively, than 
the previous FGSa, by an initial amount, to the VCO, causing it to 
generate a different JFa. Then, when the SCC receives the result of the 
new comparison from the Comparison Means, if JFa is higher or lower than 
RJFz, the SCC sends a different FGSa, which is either lower in voltage or 
higher in voltage, respectively, than the previous FGSa, by half of the 
previous increase or decrease, to the VCO. The SCC again receives the 
results of the comparison of JFa/D to RJFz, and the SCC continues to 
receive the results of the comparison and to send out different FGSa's 
which are either increased or reduced by half of what the increase or 
decrease of the previous FGSa was, until: (a) the last increase or 
decrease in the frequency of JFa was &lt;I, {where "I" is a pre-determined, 
fixed, frequency value such that (RJFz.times.D)+I is close enough to 
RJFz.times.D, to jam the television signal of channel z if it's amplitude 
were high enough}, and (b) the second last increase or decrease in the 
frequency of JFa was &lt;I, and (c) the second last increase or decrease in 
the frequency of JFa was the opposite of the last increase or decrease in 
JFa. Additionally, the SCC then stores whichever of the last and second 
last FGSz's resulted in JFa/D&gt;RJFz, as FGSz, where FGSz is the FGSa that 
causes the generating means to generate a JFa that will jam channel z. The 
JFa that will jam channel z is called JFz. Additionally, the SCC continues 
to operate as stated until there is a stored FGSz for each of the channels 
to be jammed. Once all of the FGSz's have been stored step Test is ended. 
Step Test has two functions. Firstly, it allows the SCC to determine all of 
the FGSz values, and store them, so that the SCC is able to cause the 
appropriate jamming frequencies to be generated at the appropriate times. 
The second purpose of step Test, is that it allows the SCC to periodically 
re-determine all of the correct FGSz values. Temperature, humidity, and 
other variables can result in different frequencies being generated from 
the same FGSz values, after a period of time. Therefore, it is necessary 
to periodically re-calculate the FGSz values, as after a period of time 
those values may have to be changed, because what was at one time causing 
a correct jamming frequency to be generated, at another time could be 
causing an incorrect jamming frequency to be generated. By periodically 
performing step Test, the SCC periodically correctly calculates and stores 
FGSz values, which are correct at the time they are calculated, and should 
remain correct approximately until step Test is again performed, if the 
correct time periods have been chosen by the system operator. 
Some of the advantages of the method and apparatus taught by the invention 
are that a very effective jamming of each of the channels to be jammed is 
achieved, and that only one jamming signal switch may be required per 
subscriber. Another advantage is that access to the subscriber's home is 
not needed to allow the subscriber to receive channels that are jammed, 
and access to the subscriber's home is not needed to deny the subscriber 
access to channels that are being jammed. Another advantage is that 
additional subscribers can easily be added to the system as each 
subscriber need only be connected to the system by one subscriber 
connection and one jamming signal switch, accordingly, to add on an 
additional subscriber all that may be needed is to add on to the end of a 
linear series of subscriber connections and jamming signal switches, one 
additional subscriber connection and one additional jamming signal switch. 
Another advantage to the invention is that which channels any subscriber 
receives can be programmed into the system from the headend, with no need 
to touch the subscriber's receiver end. Another advantage is that the 
method of the invention, and an apparatus built according to the method of 
the invention can jam up to twelve channels. Another advantage is that 
which of the channels are jammed can be determined at the head-end. The 
operator merely has to decide which channels are to be jammed, within a 
certain range, and the SCC determines what the values of D should be. 
Therefore, if at one time the system is jamming channels 7, 8, 9, 10, 12, 
15, 16, 18, 19, 20, 21, and 22, and then at a later time it is desired 
that the system should not jam channels 12 and 21, that can be programmed 
into the system from the headend, with no need to touch the receiver ends. 
If at another time it is desired to no longer jam channels 10, 16, and 20, 
but to begin jamming channels 13, 14, and 17, that can be programmed into 
the system from the head-end with no need to touch the receiver ends, and 
so on. Another advantage to the invention is that it allows the same 
jamming signal to be used to alternately jam the horizontal and vertical 
synchronization signals, thereby allowing for a very effective jamming, as 
not just one but both synchronization signals are being jammed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred embodiment of the method for controlling the reception 
quality of individual subscribers to CATV, where each of the channels, 
generally referred to as channel "z", are to be selectively jammed to 
selected subscribers, is comprised of the following steps. First, 
selecting and generating a Reference Frequency ("RJFz"), such that where D 
is a number, RJFz.times.D would be a jamming signal for channel z. Second, 
sending an initial Frequency Generation Signal ("FGSa") to a generating 
means, which causes the generating means to generate a jamming frequency 
("JFa") that is similar in frequency to the carrier wave frequency of a 
typical television channel's signal, and of a duration similar to that of 
a typical horizontal synchronization signal's duration, and of a slightly 
greater amplitude. Third, dividing JFa by D and then comparing JFa/D to 
RJFz, and if JFa/D is higher or lower than RJFz, sending a different FGSa, 
which is either lower in voltage or higher in voltage, respectively, than 
the previous FGSa, by an initial amount, to the generating means, causing 
it to generate a new JFa. Then again comparing the generated JFa/D with 
RJFz, and if JFa/D is higher or lower than RJFz, sending a new FGSa, which 
is either lower in voltage or higher in voltage, respectively, than the 
previous FGSa, by half of the previous amount, to the generating means, 
causing it to generate a new JFa, which is again divided by D and compared 
to RJFz, until: (a) the last increase or decrease JFa was &lt;I, {where "I" 
is a frequency value such that (RJFz.times.D)+I would jam the television 
signal for which RJFz is a reference jamming frequency, if the amplitude 
of (RJFz.times.D)+I was within the correct parameters}, and (b) the second 
last increase or decrease in the JFa was &lt;I, and (c) the second last 
increase or decrease in the JFa was the opposite of the last increase or 
decrease in JFa. Fourth, storing whichever of the last and second last 
FGSa's resulted in JFa/D&gt;RJFz, as FGSz. FGSz is the FGSa that causes the 
generating means to generate a JFa that will jam channel z. The JFa that 
will jam channel z is called JFz. Fifth, continuing the second, third and 
fourth steps until there is a stored FGSz for each channel z, and then 
suspending the second, third and fourth steps. Sixth, where N is the 
number of television signals being jammed, in continuous rotation, each 
for durations of approximately 6 to 10 .mu.S, combining JFz with the the 
television channels signals being transmitted to subscribers who are not 
entitled to receive the television signal which JFz is jamming. Seventh, 
where N is the number of channels being jammed, in continuous rotation, 
once approximately every 15 to 20 mS/N, each for durations of 
approximately 150 to 300 .mu.S, combining JFz with the television channels 
signals being transmitted to subscribers who are not entitled to receive 
the television signal which JFz is jamming. Eighth, during steps six and 
seven, varying the amplitude of JFz approximately ten times per second by 
up to 6 db. Ninth, suspending the sixth and seventh steps for a period 
long enough for the second, third, fourth and fifth steps to be repeated, 
and then resuming the sixth and seventh step. 
The jamming signal being transmitted for duration of between approximately 
6 and 10 .mu.S will jam the horizontal synchronization signals of channel 
z. That same jamming signal, being transmitted for durations of 
approximately 150 to 300 .mu.S will jam the vertical synchronization 
signal of channel z. It therefore can be seen that the preferred 
embodiment of the invention uses the same jamming signal frequency to, at 
one point, jam the horizontal synchronization signal, by transmitting it 
in bursts lasting only 6 to 10 .mu.S; and at another point, jam the 
vertical synchronization signal, by transmitting the JFz in bursts lasting 
150 to 300 .mu.S. 
The advantage of varying the amplitude of the jamming signal, continuously, 
a number of times per second, is that it improves the effectiveness of 
jamming on all television sets. Some television sets have noise filters 
that could potentially filter out a jamming signal of a fixed amplitude, 
however, they would, in most cases, not be able to filter out a jamming 
signal of a varying amplitude. 
The preferred embodiment of an apparatus according to the invention is 
illustrated in FIG. 1. The TV signal 10, which is received by the 
preferred embodiment carries all of the possible television channels the 
preferred embodiment is built to jam, and may also carry additional 
television channels. The preferred embodiment is comprised of: a set of 
television signal splitter circuits 21; a set of jamming signal switches 
23; a set of subscriber signal combiner modules 22; a voltage controlled 
oscillator ("VCO") 24; a Digital to Analog Converter ("DAC") 25 18; a 
Shift Register ("SR") 26; a Service Control Center ("SCC") 27; a Quartz 
crystal reference frequency generating means ("REF") 28; a Frequency 
Comparator Circuit ("FCC") 29; an Integrator 30; a Buffer 31; a master 
switch 32; a variable attenuator 33; and a low pass filter 34. 
In the preferred embodiment each of the television signal splitter circuits 
21 receives the TV signal. The set of jamming signal switches 23 in the 
preferred embodiment is made up of M (where M is an integer) PIN Diodes RF 
switches. Each of the jamming signal switches receives the jamming signal. 
The set of subscriber connections in the preferred embodiment is made up 
of M signal combiner modules. In the preferred embodiment the signal 
combiner modules are constructed using splitter circuits. Each subscriber 
connection connects the signal being put out from that subscriber's 
television signal splitter circuit and the signal being put out by that 
subscriber's jamming signal switch. Accordingly, when the subscriber's 
jamming signal switch is closed whichever channel is being jammed by the 
jamming signal will be jammed on that subscriber's television set. 
The FCC is a circuit that receives two inputted frequencies, one that is 
constant, and one that varies, it divides the variable inputted frequency 
by a determined factor, and then compares the divided inputted frequency 
to the constant inputted frequency and determines which is greater. In the 
Preferred embodiment the FCC also divides the constant inputted frequency 
by a factor before making the comparison, however, that is not essential. 
It is only necessary that the FCC be able to divide the inputted frequency 
that will vary, by different factors. 
In the preferred embodiment the REF puts out a frequency of 4 MHz, within 1 
KHz, which is divided in the FCC by 32 to provide a constant reference 
frequency of 125 KHz. The constant reference frequency used does not have 
to be 125 KHz. Any suitable constant reference frequency could be used. 
The suitable reference frequency which the FCC uses will be called "REF". 
It is not essential that the REF is a frequency that resulted from an 
initial frequency being divided by a factor before being used by the FCC 
for comparison. The REF could be a frequency that is used directly by the 
FCC, in which case it would not be necessary to have the FCC divide the 
REF by a factor before using it. 
The output of the FCC is pulsatory, and could be depicted as a square wave 
whose duty cycle varies. The Integrator is needed to average the pulsatory 
output of the FCC and send one of two continuous signals to the SCC; which 
of the two signals it sends depends on the result of averaging the output 
of the FCC. 
FIG. 5A is a schematic diagram of the master switch 32 of the preferred 
embodiment, which illustrates its construction. The master switch is a PIN 
diodes RF interruptor that has a controlled rise and fall time to minimize 
the generation of spurious products during switching. The master switch is 
made up of the following components: a grounded capacitor connected with 
an inductor (which is called an "RF Choke"); six additional capacitors; 
five diodes; and four additional inductors. A first capacitor, which is 
the input, is followed by a shunt RF Choke, followed by a series first 
diode, followed by a shunt second capacitor, followed by a series second 
diode, followed by a series first inductor, followed by a shunt third 
capacitor, followed by a series third diode, followed by a series second 
inductor, followed by a shunt fourth capacitor, followed by a series 
fourth diode, followed by a series third inductor, followed by a shunt 
fifth capacitor, followed by a series fifth diode, followed by a shunt 
fourth inductor, followed by a series sixth capacitor, which is the 
output. When the master switch is on, direct current flows through the 
diodes and they become conductive; the master switch is then the 
equivalent of a low pass filter having a cut-off frequency higher than the 
highest frequency of interest, the schematic diagram of that equivalent 
circuit is illustrated in FIG. 5B. When the master switch is off the 
current stops flowing through the PIN diodes and then each diode becomes 
like a small capacitor; the master switch is then the equivalent of a 
capacitive ladder attenuator, which equivalent circuit is illustrated in 
FIG. 5C. 
The Variable Attenuator of the preferred embodiment is illustrated in FIG. 
6. It has two purposes, firstly it is used, when necessary, to adjust the 
amplitude of JFz to a level slightly higher than the amplitude of the 
signal it is jamming, secondly, it is used to, on instruction from the 
SCC, continuously make small changes to the amplitude of JFz at the rate 
of approximately 10 Hz. The Variable Attenuator is made up of the 
following components: a grounded capacitor, followed by three resistors, 
six additional capacitors, three additional resistors, and three 
attenuator type pin diodes. It can be seen from FIG. 6 that the Variable 
Attenuator circuit used in the preferred embodiment is made up of a first 
capacitor, followed by a shunt resistor and a resistor and capacitor in 
parallel, but in series with the signal, followed by a shunt diode, 
followed by a coupling capacitor, followed by a shunt resistor and a 
resistor and capacitor in parallel, but in series with the signal, 
followed by a shunt diode, followed by a coupling capacitor, followed by a 
series resistor, followed by a shunt diode that is in series with a 
coupling capacitor. The SCC of the preferred embodiment sends a voltage 
that will dynamically modify the resistance of the pin diode of the 
Variable Attenuator, thus giving it continuous range. 
The low pass filter 34 of the preferred embodiment is made up of capacitors 
and inductors. The purpose of the filter is to eliminate the harmonics 
from the oscillator and master switch circuit. 
The buffer 31 prevents feedback from getting to the output end of the VCO 
when the master switch switches on or off. 
The service control center 27 is an electronic control unit. The service 
control center of the preferred embodiment is made up of a microcontroller 
with a ROM program, RAM circuits, logic I.C.'s, operational amplifiers and 
the necessary assorted inputs, outputs and standard circuitry necessary 
for operation. The service control center, when it first starts operating 
initializes the system by closing the master switch and opening all 
switches in the set of jamming signal switches 23. The SCC then begins 
step "Test" by outputting a digital code that represents a signal ("DCSa") 
to the SR 26, which the SR outputs to the DAC 25, which converts it into 
an analog voltage which we will call the frequency generating signal 
("FGSa") which it sends to the VCO. The FGSa determines the frequency 
which is outputted by the VCO, which frequency is referred to as "JFa". 
The SCC also, based on the information it receives from the head end as to 
the frequencies of the channels to be jammed, determines, for each channel 
"z" to be jammed, the value of D that the FCC must divide JFa by, so that 
if JFa/D=REF, then JFa will jam channel z. The SCC sends the information 
of what value D should be to the FCC, at the appropriate time. The FCC 
also receives the JFa from the Buffer 31. The FCC compares JFa/D to REF 
and sends the result to the Integrator, which sends a first signal to the 
SCC if the comparison resulted in JFa/D&gt;REF, and a second signal to the 
SCC if the comparison resulted in JFa/D&lt;REF; if JFa/D is higher or lower 
than REF, then the SCC sends a different DCSa, which will result in a JFa 
that is either lower in frequency or higher in frequency, respectively, 
than the previous JFa, by an initial amount. Then, when the SCC receives 
the result of the new comparison from the Integrator, if JFa/D is higher 
or lower than REF, the SCC sends a different DCSa, which will result in a 
JFa that is either lower in frequency or higher in frequency, 
respectively, than the previous JFa, by half of the previous increase or 
decrease. The SCC again receives the results of the comparison of JFa/D to 
REF, and the SCC continues to receive the results of the comparison and to 
send out different DCSa's, which will result in JFa's that are either 
increased or reduced by half of what the increase or decrease of the 
previous JFa was, until: (a) the last increase or decrease in the 
frequency of JFa was&lt;I, {where "I" is a frequency value such that JFa+I 
would jam the same television signal that JFa would jam}, and (b) the 
second last increase or decrease in the frequency of JFa was&lt;I, and (c) 
the second last increase or decrease in the frequency of JFa was the 
opposite of the last increase or decrease in JFa. Additionally, the SCC 
then stores whichever of the last and second last DCSa's resulted in 
JFa/D&gt;REF, as DCSz. DCSz is, of course, the DCSz that results in the VCO 
generating a JFa that will jam channel z. The JFa that will jam channel z 
is called JFz. The SCC continues to operate as stated until there is a 
stored DCSz for each of the channels to be jammed. Once all of the DCSz's 
have been stored step Test is ended. The SCC then suspends the operations 
of step Test and begins step Jam by, sending, in continuous rotation, each 
for durations of approximately 6 to 10 .mu.S, each of the DCSz's to the 
VCO, and closing each of the Subscriber Jamming Signal Switches to the 
subscribers who are not entitled to receive the television signal of 
channel z, when DCSz is being sent to the VCO, and opening the Jamming 
Signal Switches of those subscribers who are entitled to receive channel 
z, when DCSz is being sent to the VCO. The SCC also, during step Jam, 
sends, approximately once every 1.2 to 1.7 mS, in continuous rotation, 
0.15 to 0.30 mS long pulses of each of the DCSz's to the VCO, and closes 
each of the Subscriber Jamming Signal Switches to the subscribers who are 
not entitled to receive the television signal of channel z, when DCSz is 
being sent to the VCO, and opens the Jamming Signal Switches of those 
subscribers who are entitled to receive channel z, when DCSz is being sent 
to the VCO. The SCC, also during step Jam, instructs the Variable 
Attenuator to vary the amplitude of JFz approximately ten times per 
second, by up to approximately 6 db. The SCC also, during step Jam, varies 
the digital code it sends out as DCSz, so that the frequency of JFz varies 
slightly (preferably within a range of 0 to 800 KHz). The SCC also, after 
a pre-determined period of time T1 suspends step Jam for a period of time 
T2, which is long enough for step Test to be performed, and the SCC again 
performs step Test, and then the SCC again suspends step Test for a period 
of time T1, and again resumes step Jam for period T2, and continues to 
alternate between steps Test and Jam, during periods T2 and T1, 
respectively. 
In the preferred embodiment period T1 varies for 5 minutes up to 15 Minutes 
when the system is warming up, and T1=approximately 60 Minutes after the 
system has reached its operating temperature. In the preferred embodiment 
period T2=approximately 1 second. The lengths of time of periods T1 and T2 
can, of course, be varied without altering the teachings of the invention. 
FIG. 2 illustrates a typical television signal frequency spectrum, and 
where the jamming signal of the invention would appear. The jamming signal 
of the invention has an amplitude greater than that of the synchronization 
signal. 
The television sets of the subscribers who have had a jamming signal added 
to their television signals, if tuned to the jammed channel, will 
therefore lock onto the jamming signal (since it is of a greater 
amplitude) instead of the proper horizontal synchronization signal, during 
the 6 to 10 .mu.S pulses, and will have a horizontally unstable picture. 
During the 0.15 to 0.30 mS pulses the television sets tuned to the jammed 
channel will lock onto the jamming signal instead of the proper vertical 
synchronization signal, and will have a vertically unstable picture. The 
preferred embodiment jams both the horizontal synchronization signal and 
the vertical synchronization signal of every channel to be jammed, to the 
appropriate subscribers, many times every second. The preferred embodiment 
therefore achieves a much more effective jamming than any of the prior art 
embodiments which only jammed either the vertical synchronization signal 
or the horizontal synchronization signal, but not both. 
In the preferred embodiment a very effective jamming of each of the 
channels to be jammed is achieved, and only one jamming signal switch is 
required per subscriber. Additional advantages to the preferred embodiment 
are also apparent. Access to the subscriber's home is not needed to allow 
the subscriber to receive channels that are jammed, and access to the 
subscriber's home is not needed to deny the subscriber access to channels 
that are being jammed. Subscribers can easily be added to the system as 
each subscriber need only be connected to the system by one subscriber 
connection and one jamming signal switch, accordingly, to add on an 
additional subscriber all that is be needed is to add on to the end of the 
linear series of subscriber connections and jamming signal switches, one 
additional subscriber connection and one additional jamming signal switch. 
It is anticipated that generally the invention and especially the preferred 
embodiment of an apparatus of the invention will be used in conjunction 
with a control means and with TV signal switches instead of television 
signal splitter circuits. FIG. 1A illustrates the invention working in 
conjunction with a control means 35 and with TV signal switches 36. In 
operation the TV signal, has sent along with it, coded information that 
tells the control means which TV signal switches 36 should be turned on, 
and which subscribers should have which of their channels jammed. The 
construction of a control means able to receive coded information telling 
it which TV signal switches to turn on, and which subscribers should have 
which of their channels jammed, and able to turn on the appropriate TV 
signal switches and able to inform the SCC which subscribers should have 
which of their channels jammed, is well known in the art. TV signal 
switches is also well known in the art. For example only, they could be 
PIN Diodes RF switches or RF relay switches. 
When the preferred embodiment of an apparatus of the invention is used in 
conjunction with a control means and with TV signal switches it is very 
simple for a CATV operator to deny certain channels to certain subscribers 
from the head end. The CATV operator merely enters the appropriate 
information into the system at the head end. The information is then 
transmitted along with the TV signal to the control means, which decodes 
that information and provides it to the SCC. The SCC then causes the 
appropriate subscribers' jamming signal switches to close at the 
appropriate times and the appropriate jamming signals are combined to 
those subscribers received television signals, thus denying them the 
appropriate channels. 
Variations to the preferred embodiment can easily be made. The signal 
combiner modules could be constructed using directional couplers instead 
of splitter circuits as is used in the preferred embodiment. The switches 
of the set of jamming signal switches, could for example only, be RF Ga As 
Fet switches instead of PIN Diodes RF switches as are used in the 
preferred embodiment. The master switch, for example only, instead of 
being constructed as described for the preferred embodiment, could be 
constructed using a Ga As Fet RF switch assembly. 
Additional variations to the preferred embodiment are also possible, the 
following are only a few additional examples. The Quartz crystal reference 
frequency generating means of the preferred embodiment is preferred 
because Quartz is very stable, and when a circuit passes the correct 
current through it, it will give out a resonances frequency that is very 
stable and reliable under temperature and other changes. However, for 
example only, a coil and capacitor circuit could be used to replace it, as 
could any type of device or circuit that will generate a reliable 
frequency. 
The Integrator of the preferred embodiment is not essential to the 
invention. It is only essential that the result obtained by the comparison 
performed by the FCC be communicated to the SCC, any means of 
communicating that result to the SCC will allow the invention to function. 
Similarily, an SCC could output a voltage directly to the VCO, eliminating 
a need for a Shift Register and a DAC. The preferred embodiment employs a 
Shift Register and a DAC to allow serial transmission of the information 
from the SCC, instead of parallel transmission, which would require more 
output connections from the SCC. 
The Variable Attenuator is also not essential to the functioning of the 
invention, as the invention could function without varying the amplitude 
of JFz within a range of workable amplitudes. However, the invention would 
not be as effective, on all television sets, if the amplitude of JFz was 
not varied, however, it would still be effective enough to perform its 
function. 
Finally, many alternative ways to construct the service control center and 
some of its components will be clear to those skilled in the art. 
Accordingly, many alternatives to the construction of the preferred 
embodiment, some of which are obvious to those skilled in the art but not 
specifically stated herein, will be apparent to those skilled in the art. 
This disclosure is therefore to be understood as illustrative of the 
invention and not as a limitation of the invention. All such modifications 
and alternatives which do not depart from the teachings of this invention 
are intended to be included within the claims.