Note: Descriptions are shown in the official language in which they were submitted.
~066778
Background of the Invention
This invention relates generally to radio receiver devices, and
more particularly to radio receivers used as remote switching devices in
communication systems such as cable television, and the like. Specifically,
the present invention is directed to a code operated receiver which receives
signal information in the form of a serial code and applies this information
to a logic circuit which produces an output signal when the proper pre-
determined code for the logic circuit is received. The output signal from
the logic circuit then actuates switching means to allow passage through the
switching device of data information from a plurality of remotely located
data transmitters back to a control station.
~` In communication systems, such as cable television, or the like,
~ .
~ where data signal information is sent from a plurality of terminal points
;~ to a central data retriever it is often necessary to provide some means for
~ identifying the particular terminal point so that the exact source of the
- ~ data being received is known. To accomplish this the data transmission
equipment at each terminal point may be costly, particularly if the number
of terminal points is large. m erefore, it is desirable in large communica-
tion systems to reduce, as much as possible, the unit cost of each data
transmitting device at each terminal point.
CATV systems constitute one type of communications system that can
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be used for transmitting data over coaxial cables. mese cable television
systems often have a large number of subscribers constituting terminal points
within the system where television receivers are located and are to be
monitored. In a known system a plurality of television receivers make up a
data transmitting group which may be identified by a particular code. A
plurality of groups are provided in the system and each group has a different
code. To allow access of the data transmitting devices at the television
sets within each group a code operated switching device is utilized to be
actuated in response to the code associated with that group to allow direct
data transmission from the data transmitters located at the television sets
back to the central station or head end. However, the system utilizes a
plurality of code operated switches operated in response to RF frequency
` signals applied thereto. Each of the code operated switches includes an RF
frequency receiver which functions in a superheterodyne fashion and therefore,
require an oscillator to provide a frequency which is mixed with the in- -
coming RF frequency to develop an intermediate frequency therefrom. me
code signal information is then detected, as for example, by FM detector
` means, to produce code signal pulses. These code operated switching devices
- operate at relative high frequencies, in the order of 100 to 200 MHz.
~ 20 Therefore, the relative frequency stability of local oscillators is critical
t for proper operation. ~ue to environmental changes such as changes in am-
bient temperature the local oscillator must be of extremely high quality
v
desi8n and must use high quality components to insure stability of operation
throughout the temperature ranges
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that it is subjected to. This substantially increases the
cost of each of the coded switching devices within a coaxial
cable television system, and thereby increases the cost of the
overall system.
Summary of the Invention
Briefly, the present invention is directed to an apparatus
which eliminates the need for having a local oscillator in an
RF receiver device, This is done by transmitting two RF signals,
one or both of which can be modulated with control signal in-
formation. In the embodiment disclosed herein both signals aremodulated with FSK modulation. Ideally the spacing of the two
carriers in the illustrated embodiments is equal to the inter- ``-
mediate frequency of the receiver, e.g. in thè order of about
50KHz. However, other frequencies such as 455 KHz or 10.5 MHz
~ .
may be used.
In the FSK modulation arrangement used herein carriers
are shifted in opposite directions to produce a maximum dif-
. .
iference between the two carriers. There are two advantages of
this circuit arrangement. One is tha~ it eliminates the need
of an expensive oscillator circuit within the receiver when
, ~
using FSK type modulation, which is important when using such
~`receivers over a wide temperature range. The second advantage
is that it saves cost in building the receivers in that the
local oscillator is no longer needed.
~In summary, the present invention comprises code operated :`~
`,switching apparatus having input means for receiving first and -~
. ~ .
second RF frequencies from a central station and having a pre~
determined frequency difference, at least one of said first
. . . .
and second RF frequencies being modulated with a predetermined
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control signal at the central station, a single filter circuit coupled to
said input means for passing said first and second RF frequencies and said
control signal, detector means coupled to said input means for detecting an
intermediate frequency which includes said control signal, and switch means
coupled to said detector means to be operated in response to said control
signal.
Brief Description of the Drawings
Figure 1 is a simplified block diagram of a cable television system
wherein the code operated receiver switch devices of this invention are
10 utilized;
Figure 2 is a simplified block diagram of a code operated receiver
switch constructed in accordance with the principles of this invention; and
Figures 3 and 4, when placed side by side, illustrate the detailed
schematic arrangement of the code operated receiver switch of this invention.
` Detailed Description of the Illustrated Embodiment
Referring now to Figure 1 there is seen a communications system
constructed in accordance with the principles of this invention and designated
- generally by reference numeral 10. me communications system 10 preferably
is of a coaxial cable type, it being understood that other types of trans-
mission systems or means may be used, for example, telephone lines or micro-
wave transmission between line-of-sight powers, and the like. Also it will
` be understood that multi-cable coaxial systems can incorporate the novel
aspects of this invention.
The communications system 10 includes a plurality of transmitting -~
groups 12, 14, 16, and 18, etc., each transmitting group
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including a plurality of separate data transmitting devices associated with
each of the subscribers in that group. These data transmitting devices are
primarily of the type which convert the data of decimal number information
into binary coded information to be transmitted serially over coaxial cables
of the type used in CATV systems. In the contemplated use of the system 10,
each discrete data transmitting means may represent a single user or sub-
scribers home, which may be referred to as a terminal point, and the data
which is transmitted is derived from a television converter device or other
input means such as a burglar alarm, fire alarm, or the like, it being
understood that such data transmitting devices can be used to transmit data
corresponding to a multitude of homes if desired.
To maximize the number of individual homes from which data can be
received, the system can be divided into discrete zones or areas corres-
ponding to the groups 12, 14, 16, and 18 and each home in the area is des-
ignated with a particular code, it being assigned a known frequency in the
i~ illustrated embodiment, so that all data received on that frequency will be
known to have come from that particular data transmitting device. For
example, group 12 may consist of a plurality of homes 20, 21, 22 etc., while
group 14 consists of a plurality of homes 23, 24, 25, etc. In similar
fashion, group 16 includes a plurality of homes 26, 27, 28, etc., while
` group 18 consists of a plurality of homes 29, 30, and 31, etc. Since the
groups of homes are distinct from one another there can be similar
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frequencies assigned to homes of different groups. For
example, homes 20, 23, 26, and 29 may be assigned a given
frequency and thus designated by reference letter A. The
other corresponding homes having the same frequencies are
thus designated by reference letters B, and C. Each of the
data transmitting units associated with the respective homes
are designed for continuous operation and need not receive
interrogation signals to be turned on to transmit data. While
a plurality of homes are illustrated with each group it will
be understood that a single home or transmitting unit may
correspond to a group as disclosed herein.
To receive the data from each of the groups, there is pro-
vided a coder and retrieval unit designated generally by refer-
ence numeral 32 and which includes circuit means to generate
a predetermined code corresponding to a predetermined code of
one of a plurality of-code operated switching devices associated
with each of the plurality of groups of transmitting devices.
For example, a code operated switch device 38 is placed in
communicative connection between the coder and retrieval circuit -
~32 and the group 12, while a second code operated switch device
39 is placed in communicative connection between the coder and
retrieval unit 32 and the group 14. Similarly, a code operated
switch device 40 is placed in communicative connection between
the group 16 and the coder and retrieval unit 32 while a fourth
code operated switch device 41 is placed in communicati~e
connection between the group 18 and the coder and retrieval
unit 32. The code information will activate the selected one
of the plurality of code operated switch devices 38, 39, 40,
or 41 and simultaneously deactivate any other previously
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activated code operated switching device so that only signal
information from a single group is received at a given time.
Therefore, since all of the data transmitting units 20-31
are continuously transmitting data, only the units which are
associated with a particular group which will transmit signal
information into the retrieval unit 32. Once the desired code
operated switch is activated, all of the data transmitting
units simultaneously supply data to the cable 36 and into à
plurality o~ tuned circuits associated with the retrieval unit
32. The frequency of the data information received is pre-
selected to identify the particular home from which the slgnals
originated,
In accordance with the novel aspects of this
invention a pair of RF frequency oscillators 42 and 43 are
associated with the coder and retrieval unit 32 and provide
the carrier waves which are modulated in response to the
coded signal information necessary to actuate the switching
devices 38, 39, 40 and 41 The RF oscillators 42 and 43
preferably are FSK modulated, and these osclllators are
modulated substantially simultaneously in opposite directions
from one another, i.e. one oscillator increasing in
' frequency while the other oscillator is decreasing in
frequency. For example, oscillator A may operate at a
frequency of 113.4 mc while the oscillator B may be operated
` at 113.45 mc. The difference frequency between these two -
oscillators provides an intermediate frequency of 50 kc
; which corresponds substantially to the IF frequency of the
radio receiver portion of the code operated switching devices
38, 39, 40 and 41. It will be understood however, that
other intermediate frequencies may be utilized, particularly
frequencies corresponding to the sum of the oscillators A
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1066778and B as well as fre~uencies corresponding to the difference
of these oscillators. By so providing a pair of master RF
oscillators at the head end or central station the need of
local oscillators at each of the radio receiver portions of
the code operated switches is thereby completely eliminated.
Referring now to Fig. 2 there is seen a block
diagram of the code operated switch 38. This switching device
is a remote control radio receiver which will operate in
response to coded signal information delivered thereto along
RF frequency transmission lines 36. While only the code operated
switch 38 is shown herein in detail, it will be understood that
the code operated switches 39, 40, and 41 are substantially of
similar construction and operation, it being understood that
the only primary difference is in the logic board associated
with the code assigned to the switches. The logic board arrange-
ment therefore identifies the switch with a particular code to
` gain access to each of the associated ones of transmitting groups.
The code operated switch 38 includes an input terminal
50 coupled to a highpass filter circuit 51 and a lowpass filter
circuit 55. The output of the highpass filter circuit 51 is
directed to a directional tap element 52 to apply this signal
` to an output terminal 53 through a second highpass filter
circuit 54. During normal operation return signals from each
of the data transmitting devices within a particular group
will not pass from output terminal 53 to input terminal 50 as
a result of the blocking characteristics of the high pass filters
51 and 54. Therefore, signal information only passes in one
direction through the tap element 5~. The RF frequencies from
oscillators A and B are then delivered to the input of an RF
amplifier 56 which boosts the signal strength thereof and
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applies these signals to a detector or mixer stage 57. The mixer stage is
provided with a tuned circuit at the output thereof for extracting the dif-
ference frequency of the frequencies produced by oscillators A and B. mis
difference frequency is an IF frequency delivered to an IF amplifier, detector
and AF amplifier stage 58. mis stage preferably being formed of an in-
tegrated circuit component having a multiplicity of active electronic elements
; associated therewith.
e output of the stage 58 is an audio signal in the order of about
4 kc, which is applied to one of the input terminals of a comparator circuit
1~ 59. The comparator circuit can take any suitable form and will function as
a threshold or level setting device. For example, the second input of the
comparator circuit includes a variable voltage element or potentiometer 60
so that a threshold level can be set on the comparator circuit, which is
here illustrated as an operational amplifier, to allow passage of only those -
control signals which exceed a predetermined minimum value. This therefore, -~
`Y eliminates the possibility of extraneous pulse signals or other signals from
effecting the code sensitive circuitry of the receiver.
e output of the comparator 59 is applied to a logic driver stage
61 which, in turn, is coupled to a logic board 62. m e logic board 62 can
be formed of any suitable logic coding circuit, which may be, for example, a
series to parallel converter type so that a given code signal in serial form
will energize a switching device 63.
In the illustrated embodiment the switching device 63 takes the
for~ of a relay having a relay coil 64 and a pair
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of movable contacts 64a and 64b. Relay 63 is shown in the
energized condition in Fig. 2. The holding coil 64 of the
relay is energized by a relay driving stage 66. When the
contacts 64a and 64b are positioned, as shown in Fig. 2, the
relay is deenergized and signal information from the plurality
of data transmitters of the group 12 will be delivered through
the code operated switch 38.
Upoll receiving two RF frequencies which are FSK modulated
to produce a control signal in accordance with a predetermined
code set into the circuitry of the logic board, the logic
board 62 will then provide an output signal to energize the
relay 64 through the relay driver 66. This transfers contact
64a and 64b to engage the upper set of terminals 64c and 64d
thereby connecting these terminals together. The signal in-
formation from the data transmitters 20, 21, and 22 are then
delivered through the input terminal 53, a lowpass filter
67, a series connected capacitor 68, contacts 64d and 64c,
capacitor 71, low pass filter 55 back to the input terminal 50.
` Therefore, the signal information from the data transmitters
travels in a direction opposite that of the direction from
which the code signal information is received.
The logic board 62 of code operated switching circuit
38 has a logic circuit arra~gement which identifies that
particular switching device, and correspondingly identifies the
` particular group of data transmitters to which it allows access
to. Other switching devices 39, 40, and 41 have logic boards -
which have different logic circuit arrangements so that access
to these switches is obtained only when their particular code
signal information is received. Also, it will be understood
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that àccess to any one of the code operated switches causes
automatic deactuation of any other previously actuated code
operated switch.
A rectifier and transformer stage 72 are provided to
supply power to the logic board 62 through a regulator stage
73. To eliminate alternating current signals from the data
signal transmission, a~pair of choke networks 74 and 76 are
provided as filters.
In operation, the head end or central station has code
signal information FSK modulated upon the carrier waves pro-
` duced by the oscillators 42 and 43. This is serial signal
information delivered along the transmission line 36. This
serial code signal information is delivered to all of the
code operated switches 38, 39, 40, and 41 simultaneously.
The FSK modulation is received and amplified by the RF amplifier
and the IF signal is extracted after passing through the mixer
57. The IF signal provides high selectivity of a particular
frequency within the frequency spectrum being used. When the
code operated switch 38 is an off conditon, i.e. contacts 64a
and 64b engaging the lower terminals, a relatively high
impedance or return signal path from output terminal 53 to
` input terminal 50 exists by means of impedances 69 and 70.
; This then substantially completely blocks all signals developed
at the data transmitting devices at homes 20, 21, and 22.
Upon receiving the proper interrogation code at the logic
board 62 the relay 63 is then actuated so that contacts 64a
and 64b move to their positions as shown in Fig. 2 to engage -
contact 64c and 64d. While resistance elements 69 and 70 are
shown any suitable impedance device can be used. This then
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substantially reduces the return impedance path from output
terminal 53 to input terminal 50 and allows the signal in-
formation at the data transmitters to flow through the now
closed circuit path of the code operated switching device
back to the central station.
For a better understanding of the particular details of
the code operated switch 38 reference is now made to Figs. 3
and 4, placed side by side to one another (Fig. 4. to the right
o Fig. 3.), which illustrates one particular component
arrangement to provide the novel switching receiver arrangement
in accordance with the principles of this invention. The
particular circuit arrangement illustrated in Figs. 3 and 4
represents a code operated switch 38 and is here intended to
be a device which receives a digital command signal at 113.4 mc,
detects that signal, decodes it, and controls a relay which
disables a 5 to 30 mc portion of a CATV spectrum in a cable
television system. The digital command signal consists of
two RF carriers, one at 113.4 mc and the other at 113.45 mc.
These carriers are frequency key shifted (FSK modulated)
so that the difference between them is in the order of about
50 kc for a logic zero statè and 54 kc for a logic one state.
In a cable television system of the type contemplated
herein a VHF carrier wave, having a frequency of between 50 -
and 270 mc, is applied to the input terminal 50. This carrier
wave is generated and controlled at the head end or central ~
station of the system where the oscillators 42 and 43 and -
.
coder and retrieval units are located. The term carrier wave
in the present invention is intended to include two frequencies.
- The carrier wave is routed from the input terminal 50 through
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the highpass filter network 51 into the 10db directional tap
52. In the illustrated embodiment the highpass filter 51
comprises a pair of series connected capacitors 80 and 81,
which are in the order of about 30 and 39 picofarads, respec-
tively. The high pass filter network 51 further includes an
inductance element 82 having one end thereof connected to a
circuit point intermediate of the capacitors 80 and 81 the
other end thereof connectèd to chassis ground or to earth
ground potential. One of the output terminals of the 10db
directional tap 52 is coupled to an inductance element 83
which, in turn is connected in series with a capacitor 84 to
ground potential and this series inductance capcitance net-
work forms part of the highpass filter network 51.
The input terminal 50 is coupled to the output terminal
53 through the highpass filter network 51 and the series con-
nected highpass filter network 54 which comprises a pair of
series connected capacitors 86 and 87. Capacitor 86 is in
the order of about 39 picofarads while capacitor 87 is in the
order of about 30 picofarads. An inductance element 88 has
one end thereof connected to a circuit point intermediate the
capacitors 86 and 87 and the other end thereof connected to
ground potential. The highpass filter network 54 also includes
whatever inductance and capacitance components are measurably -
significant in a coaxial or shielded cable 89 connected
between the output of the 10db directional trap 52 and the
input of the highpass filter 54. The two highpass filter
networks 51 and 54 have a cutoff frequency of approximately
50 mc to eliminate signal interference from frequency spectrums
outside of the cable television system. The insertion loss
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of VHF frequencies over the VHF pass band is approximately
1.5 db. Connected to both the input terminal 50 and the out-
put terminal 53 are gas discharge devices to provide surge
protection to the entire circuit. These gas discharge devices
are conventional.
Also connected to both the input and output terminals
are test points 90 and 91, respectively, which are arranged
to provide a 20 db reduction in signal so as to enable a tech-
` nician to observe circuit operation with test equipment such
10 as oscilloscopes and the like. The test terminal 90 includes
a series connected resistor 92 and capacitor 93 connected to
the terminal 50 at a circuit point 94. A filter capacitor 96
is connected between the terminal 94 and ground potential.
Test terminal 91 includes a series connected resistor 97 and
capacitor 98 connected to a circuit point 99 which is associated
with the output terminal 53. A capacitor 100 is connected to
the circuit point 99 to provide filtering in the same manner
as capàcitor 96.
The portion of the spectrum below the band pass, i.e.
20 that portion between S and 30 mc, is picked up at output
~ terminal 53 and routed through a lowpass filter network 67
s comprising an inductance element 99 and a capacitor 102 through ;;
a line 103 and through a bypass capacitor 104. The value of
the bypass capacitor 104 is in the order of .01 micorfarads
while the value of capacitor 102 is in the order of 120
picofarads. The lowpass filter path continues through to
ground potential through the left hand movable con~act 64b ~;~
and a series inductance element 106, capacitor 107 and resistor
108. At input terminal 50 there is also provided the lowpass
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filter network 5-5 which comprises a series connected induct-
ance element 109, capacitor 110, bypass capacitor 111, through
the second movable contact 64a through a series connected in-
ductance element 112 and capacitor 113 parallel by a resistor
114. This then effectively connects the lowpass filter net-
works to ground potential when the relay holding coil 64 is
in a deenergized state, with the contacts 64a and 64b sub-
stantially as shown in the drawings. When relay 64 is ener-
gized, or in the on position, an additonal inductance element
116 is connected in series with the lowpass filter path so
that a lowpass coupling connection is made between input
terminal 50 and output terminal 53. This may be used to allow
return of signal information from the plurality of data trans-
mitting units at each of the houses within a particular group
to pass through the radio controlled and code operated switch-
ing device 38 back to the head end or central station.
` The lowpass filter arrangement as described above provides --
approximately a 1 db insertion loss over the sub-band, i.e.
20 between 5 and 30 mc. When the holding coil 64 is in the de-
energized position both the input and output lowpass filter
sections are terminated to ground potential through the com-
ponents illustrated above. During the off condition of the
relay, however, there is approximately a 40 db insertion loss
between the input and output terminals. The choke element 74
is paralled by a second choke device 120 and serves to divert
60 volt AC line power around relay 64. A pair of capacitors
121 and 122 are used for RF bypass filtering.
The RF amplifier stage 56 is designed to operate in the
VHF spectrum which is taken off of th~ tap port 124 of the
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10 db directional tap 52. This provides a signal 10 db below
the level of the signal which is delivered to the input term-
inal 50 of the code operated switching device. This signal
is then fed through a coupling capacitor 126, which is in the
order of about 150 picofarads, to the input tap 127 of a
resonant tank circuit 128. The tank circuit 128 includes a
tapped inductance element 129, a variable capacitance element
130, and a feedback, or return path capacitor 131.
The tuned circuit 128 is tuned to a frequency oE 113.4 mc
and has a band pass characteristic which allows passage of
both of the signals delivered from the oscillators 42 and 43,
Fig. 1: that is the tuned circuit allows passage of fre-
quencies of 113.4 and 113.45 MHz. These frequencies are
delivered to an operational amplifier circuit formed as an
integrated circuit 132 which has a gain factor of approximately
25 db. The amplified signal through the operational amplifier
132 is applied to a tuned circuit 133 comprising a tap induct-
: `
ance element 134, a variable capacitor 136, and a feedback `
capacitor 137. The tuned circuit 133 is tuned also to the
input frequency of 113.4 MHz, and also has a band pass char-
acteristic to allow passage of both the 113.4 MHz and
113.45 MHz signals. The output of the RF amplifier stage 56 is
delivered through a capacitor 138, which has a value of
approximately 100 picofarad to the base electrode of a trans-
istor 139 which forms the active element of the detector stage
57. A voltage divider network comprising series connected
resistors 140 and 141 provide bias potential to the base
, electrode of transistor 139 so that transistor operates as a
class A amplifier from power received over a power line 142.
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The power line 142 can be connected to any suitable regulated
source of voltage of for example, a ten volt source. The
detector stage 57 also includes an inductance element 143 and
parallel capacitor 144 which function as a tuned circuit which
is tuned to the intermedia~e frequency, here it being the
difference frequency of the two transmitting oscillators 42
and 43. This tuned circuit is therefore tuned to approximately
50 kc and has a coupling capacitor 146 connected thereto
for delivering this intermediate frequency to one input
~erminal 147 of the IF amplifier, detector, and audio frequency
amplifier circuit 58. This network 58 can be formed by any
suitable integrated^circuit package available. One of such
integrated circuits is available from RCA under part number
CA3075.
The two signals which are produced by the 50 kc difference
in the detector stage are the frequency key shifted signals
which are developed ~y changing the frequency of the carrier
., , :
wave in opposite directions. For example, the 113.4 mc
signal is frequency key shifted to a lower frequency of
apporoximately 2 kc to produce a logic one state control sig-
nal. On the other hand, the 113.45 mc signal is frequency key
~;` shifted upwardly s~proximately 2 kc to produce the logic one
state. Therefore, the frequency key shifted modulation ~;
signals that produce the control signal appear at the output
of the integrated circuit 58 are approximately 54 kc for a
logic one state and approximately 50 kc for a logic zero
state.
:~ - . ,
An inductance element 150 and variable capacitor 151 form
a resonant discriminator circuit tuned to approximately 52 k~.
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A resistor 152 may be used for deQing the circuit to a desired
band width while a capacitor 153 is used to set a minimum
range of adjustment for the capacitor lSl. The value of
inductance ele~ent 150 is in the order of 22 millihendres
while resistor is in the order of about 39 K ohms. The value
of capacitor 153 is in the order of about 100 picofarads
while the range of capacitance of adjustable capacitor 151 is
between approximately 90 to 450. A high frequency bypass
capacitor lS4 is connected to the audio discriminator circult
and ground potential for filtering purposes.
The output at output terminal 156 is delivered through
a series connected inductance element 157 and capacitor 158
to the input portion of an audio amplifier at terminal 159,
this preferably being done through a current limiting resistor -
160. The junctures between resistor 160 and capacitor 158
is provid~ with a signal developing resistor 161 which has
one end thereof connected to ground potential. This audio
is then amplified within the integrated circuit 58 and applied
to an outputterminal 162 which produces approximately 1.6
volts peak-to-peak of audio signal information from an origin-
ally detected 0.1 volt signalat terminal 156. An RC network
comprising resistor 163 and capacitor 164 is provided to
remove extraneous high frequency components from the audio
control signal while a diode 166 receives signals through a
capacitor 167 to establish a reference æero logic state of
substantially zero volts at the input terminal of the ~ffl-
~h~r~o~
pan1txn-stage 59.
The o~m~u~Lla: stage 59 comprises an integrated circuit
arranged from an operational amplifier having two input term-
`` 1066778inals. An a~justable terminal 170 is coupled to the level set
potentiometer 60 which applies approximately 0.8 volts above
`~ a logic zero state which appears at the second input 171
Co~ ~ t of
of the ~u~par~tor~ The output of the comparitor is then fed
to a driver transistor 172 which functions as the active
component ûf the driver logic stage 61. The control signal
is delivered through a current limiting resistor 173, and
a portion of which is fed back through a feedback capacitor
174. Stabilizing capacitor 176 is provided or improved
operational characteristics while power supplied to the com-
paritor through a 5 vol~ terminal 177 through the resistance
element of the potentiometer 160 and a fixed resistor 178.
Operating bias to driver transistor 172 is provided through
a 10 volt terminal 179. The signal from transistor 172 is
coupled over a line 180 to an input terminal of the logic
board 62. The logic board comprises decoding circuitry to
establish that this particular code operated switch has been
actuated by the proper code address signal. An output line
from the logic board 62, labelled A, is delivered to an input
terminal, labelled A, on Fig. 3, which passes through a series
connected limiting device, here illustrated as a Zener diode
181 to the base electrode of a transistor 182 which forms
~, .
the relay driver circuit 66. The transistor 182 is biased
to a conductive state only when a signal exceeds the Zener
level of the diode 181, and this signal is then developed
across a signal developing resistor 183 and applied to the
base electrode of transistor 182 through a series connected
resistor 184. A 12 volt source is applied between terminal
186 thereby being available at one end of the relay holding
coil 64. The other end of the relay holding coil 64 is coupled
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to the collector of transisitor 182 and is held in a deener-
gized state as long as transistor 182 is non-conductive. A
shunt diode 187 is connected in parallel with holding coil
64 to prevent extraneous spike signals from being developed
and damaging components.
To operate the entire receiver code operated switch 38
a power supply 72 is provided and includes a step down trans-
former 1~0 having a primary winding 191 connectable to any
suitable source of alternating current voltage and a secondary
winding 192 to which is coupled a bridge rectifier network
193. This bridge-rectifier network develops approximately
12 volts~at its output terminal and delivers this 12 volts
through the regulator network 73 which comprises a transistor
194 which, in turn, has the base electrode thereof coupled
to ground potential through a Zener diode 196. To insure
proper stability of the logic board 62 a 5 volt source, which
can be developed by suitable voltage dropping resistor networks
is applied to an input thereof and is regulated as a result
of the parallel network comprising the Zener diode 197 and
capacitor 198 together ~ith a resistor 199.
To provide a telermetering indication that the receivèr
code operated switch 38 has been in fact, energized in response
to the code signal delivered thereto, test means 200 provides `
an RF carrier signal coupled to one side of the relay contacts,
here being illustrated as being connected to movable contact
side 64b and this radio frequency signal is then received at
the head end or central station when the test signal is coupled
through an inductance element 116 and the associated relay
switches. This is only one means of providing indication that
the relay is in fact actuated.
- 21 -
., ~
