U.S. patent number 3,754,187 [Application Number 05/204,150] was granted by the patent office on 1973-08-21 for transmitter-receiver system.
This patent grant is currently assigned to The Alliance Manufacturing Company, Inc.. Invention is credited to Andrew F. Deming.
United States Patent |
3,754,187 |
Deming |
August 21, 1973 |
TRANSMITTER-RECEIVER SYSTEM
Abstract
A transmitter-receiver system is disclosed which may be used for
remote control purposes. The transmitter has a radiated signal with
a first frequency carrier modulated with a second frequency. A
subcoder may be selectively plugged into the transmitter and has a
third frequency which influences or modulates the radiated signal
at a third frequency rate. The receiver of the system has means
responsive to the first and second frequencies and also has a
decoder selectively plugged into the receiver which has a disabling
bias means and a third frequency responsive means. The disabling
means normally prevents any signal from reaching the load of the
receiver and the third frequency responsive means has an output
when the third frequency is present which terminates the disabling
means so that the receiver is enabled and a signal is passed to the
receiver load. Without the decoder plugged into the receiver, the
receiver is completely operable on the first and second frequencies
to supply a signal to the load.
Inventors: |
Deming; Andrew F. (Alliance,
OH) |
Assignee: |
The Alliance Manufacturing Company,
Inc. (Alliance, OH)
|
Family
ID: |
22756830 |
Appl.
No.: |
05/204,150 |
Filed: |
December 2, 1971 |
Current U.S.
Class: |
340/13.26;
341/176 |
Current CPC
Class: |
G08C
19/14 (20130101) |
Current International
Class: |
G08C
19/12 (20060101); G08C 19/14 (20060101); H04b
007/00 () |
Field of
Search: |
;325/37,64.55,392,393
;343/225,228 ;340/171R,171A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Safourek; Benedict V.
Claims
What is claimed is:
1. A modulated carrier system, comprising in combination, a
transmitter and a receiver,
said transmitter comprising output circuit means,
means to develop a first frequency carrier in said output circuit
means,
means to develop a modulation frequency,
and means connecting said modulation frequency developing means to
said output circuit means to establish a carrier wave output from
the transmitter influenced at said modulation frequency rate for a
first time period and to terminate said modulation frequency
thereafter;
said receiver comprising
a main load,
first means responsive to said first frequency to pass a signal
toward said main load,
disabling means having an output connected to said main load,
means responsive to said modulation frequency,
a conductor common to said disabling means and to said modulation
frequency responsive means,
means establishing said modulation frequency on said conductor,
means establishing a disabling voltage from said disabling means on
said conductor and operative in the absence of a received signal
containing said modulation frequency to disable the signal from
actuating said main load,
and said means responsive to said modulation frequency having an
output connected to terminate said disabling means output for at
least a second time period to enable said receiver.
2. A modulated carrier system as set forth in claim 1, wherein said
modulation frequency responsive means establishes said second time
period overlapping said first time period.
3. A modulated carrier system as set forth in claim 1, wherein said
modulation frequency developing means develops second and third
frequencies,
and said connecting means includes separable connections for said
third frequency developing means.
4. A modulated carrier system as set forth in claim 3, wherein said
modulation frequency responsive means is responsive to said second
and third frequencies,
means permanently connecting said second frequency responsive means
into said receiver to supply a signal to said main load in response
to the proper first and second frequencies,
and means establishing said third frequency responsive means
selectively disconnectable and connectable to the said receiver to
establish said receiver operative to pass a signal to said main
load upon the presence of a received signal containing said first,
second and third frequencies and subsequently said first and second
frequencies.
5. A modulated carrier system as set forth in claim 3, wherein said
modulation frequency responsive means is responsive to said second
and third frequencies.
6. A modulated carrier system as set forth in claim 1, including
means establishing at least part of said modulation frequency
developing means selectively connectable with said transmitter.
7. A modulated carrier system as set forth in claim 1, including
means establishing at least part of said modulation frequency
responsive means selectively connectable with said receiver.
8. A modulated carrier system as set forth in claim 1, wherein said
modulation frequency developing means develops second and third
modulation frequencies,
means permanently wiring said second frequency developing means
into said transmitter to establish a modulated frequency output
from said output circuit means,
and means establishing plug-in connection of said third frequency
developing means to permit operation of said transmitter with only
two frequencies or selectively with three frequencies.
9. A modulated carrier system, comprising in combination, a
transmitter and a receiver;
said transmitter comprising output circuit means,
means to develop a first frequency carrier in said output circuit
means,
and modulation frequency developing means selectively connectable
to said output circuit means to establish a modulated carrier wave
output from the transmitter for a first time period and to
terminate said modulation frequency thereafter;
said receiver comprising a main load,
first means responsive to said first frequency to pass a signal
toward said main load,
modulation frequency responsive means and disabling means
selectively connectable to said main load with said disabling means
operative in the absence of a received signal containing said
modulation frequency to disable the signal from actuating said main
load,
a first connector as a part of said selectively connectable
means,
means establishing said modulation frequency on said first
connector,
means establishing a disabling voltage from said disabling means on
said first connector to disable the signal from actuating said main
load,
and said modulation frequency responsive means having an output
connected to terminate said disabling means output for at least a
second time period to enable said receiver to thus pass current to
said main load upon the presence of a received signal containing
said carrier and modulation frequencies.
10. A modulated carrier system as set forth in claim 9, including
means supplying an operating voltage from said receiver to said
selectively connectable modulation frequency responsive means and
disabling means.
11. A modulated carrier system as set forth in claim 9, including
means supplying operating voltages from said transmitter to said
selectively connectable modulation frequency developing means.
12. A modulated carrier system as set forth in claim 9, wherein
said modulation frequency responsive means terminates said
disabling voltage on said first connector to enable said receiver
during said second time period.
13. A modulated carrier system, comprising in combination, a
transmitter and a receiver;
said transmitter comprising output circuit means,
means to develop a first frequency carrier in said output circuit
means,
means to develop in said output circuit means a second frequency
modulating said carrier frequency,
and third frequency developing means selectively connectable to
said output circuit means to establish a second frequency modulated
carrier wave output from the transmitter influenced at said third
frequency rate for a first time period and to terminate said third
frequency thereafter;
said receiver comprising a main load,
first means responsive to said first frequency to pass a signal
toward said main load,
second means responsive to said second frequency to pass a signal
toward said main load,
third frequency responsive means and disabling means having an
output and selectively connectable to said main load with said
disabling means operative to disable said main load in the absence
of a received signal containing said third frequency,
and said third frequency responsive means having an output
connected to terminate said disabling means output for at least a
second time period to enable said receiver to thus pass current to
said main load upon the presence of a received signal containing
said first, second and third frequencies and subsequently said
first and second frequencies.
14. A modulated carrier system as set forth in claim 13, wherein
said third frequency developing means includes a bridge T filter
tuned to said third frequency.
15. A modulated carrier system as set forth in claim 13, wherein
said third frequency developing means includes a mechanically
vibratable tuning fork.
16. A modulated carrier system as set forth in claim 13, wherein
said third frequency responsive means includes a parallel resonant
circuit resonant to said third frequency.
17. A modulated carrier system as set forth in claim 13, wherein
said third frequency responsive means includes a mechanically
vibratable tuning fork.
Description
BACKGROUND OF THE INVENTION
The disclosed transmitter-receiver system may be used in remote
control systems, for example, a remotely controled garage door
opener. In such use the transmitter may be a hand-sized battery
powered low output power transmitter complying with Federal
Communication Commission regulations as to radiated power. The
carrier may be in the VHF range, for example, with modulation in
the audio or super-audio frequencies.
The transmitter sends a signal to a corresponding receiver and if
the proper carrier and modulation frequencies for that set of
transmitter and receiver is received by the receiver, then an
output signal is given. This output signal may be used to remotely
control some particular device, for example, a garage door. In many
cases the garage door being controlled is in a garage attached to
the home and if unauthorized persons were able to easily operate
the garage door operator receiver, then unauthorized access to the
garage and to the home could be achieved. Thus a security problem
occurs and it becomes increasingly important to increase the number
of codes and the complexity of the codes in order to prevent
unauthorized access to the garage and home. If there are only six
different carrier frequencies and six different modulation
frequencies, then this gives a total of six times six or 36
different possible codes. If there are 10 carrier frequencies and
ten modulation frequencies, for example, then this would give a
total possibility of 100 codes. However because of FCC regulations,
the number of carrier frequencies which may be used without
interference with each other is limited, thus limiting the total
possible number of codes. Also, with only six or ten carrier
frequencies plus a similar range of modulation frequencies, it is
relatively easy for a law-breaker to gain access to the garage. For
example, if such a person had six or ten different transmitters
each on one of the assigned code of carrier frequencies, then each
in turn could be turned on and gradually adjusted through the range
of audio frequencies. Thus, all 36 or 100 possible codes could be
swept through in a matter of 1 or 2 minutes and the lawbreaker
could easily gain access to the garage or home.
In many areas of high saturation of garage door operators, there is
an increasing problem of the transmitter of a neighbor operating
the wrong garage door operator receiver. Thus the operator of an
automobile driving along a street and depressing the transmitter
push-button switch, could trigger receivers to open garage doors,
which are the wrong garage doors, unless the carrier frequencies
and modulation frequencies of the coding scheme have sufficient
separation therebetween, and do not have a tendency to heterodyne
to produce one of the carrier or modulation frequencies of the
coding scheme.
In order to make the garage and home more secure, more codes have
been suggested but this method of increasing the number of possible
codes by increasing the number of carrier or modulation
frequencies, runs into difficulty with the FCC regulations and runs
into further difficulty with trying to select frequencies which do
not interact with each other by heterodyning so as to produce one
of the frequencies of the codes.
One prior art attempt at increasing the security was to produce a
transmitter and receiver system wherein the transmitter had one
carrier frequency out of a number of possible frequencies, for
example, 6 or 10. Next, two separate modulation frequencies were
provided in the transmitter with the transmitter first emitting a
radiated signal of the carrier modulated by the first modulation
frequency and then immediately afterward the first modulation
frequency ceased and the second modulation frequency commenced for
an additional time period. The receiver of that particular set
would be tuned to that particular carrier frequency and would have
a detector means to detect the first and second modulation
frequencies with a time delay on drop out of detection of the first
modulation frequency. This meant that the first modulation
frequency had to be detected first, with a time delay hold-over of
the relay contacts being held closed during the time that the
second modulation frequency was detected, in order for an output
signal to be developed by the receiver. This increased the security
but required a considerably more complex receiver system and
required a more complex transmitter system such that only the first
and second modulation frequencies were transmitted and were
transmitted in sequence but not simultaneously.
A serviceman has an extremely difficult time to locate the cause of
spurious responses because the receiver is usually on 24 hours a
day on a standby basis, awaiting the reception of a proper signal.
The peculiar circumstances which cause a spurious signal to trigger
the receiver will normally not occur when a serviceman is present
and thus he seldom can find the cause. This is different from a
complete breakdown of the equipment where he can use a signal
generator or other serviceman's equipment to locate the break or
short in the circuit and have it repaired.
Another disadvantage with this prior art system is the increased
number of transmitters and receivers which must be manufactured and
which must be stocked by a distributor. If there are ten different
first carrier frequencies and ten different second modulation
frequencies plus ten different third modulation frequencies, this
is 10 times 10 times 10 or 1,000 different transmitters and
receivers which must be manufactured and also 1,000 different
transmitters and receivers which must be stocked by the
manufacturer and the distributor. This is sufficiently burdensome
that it becomes increasingly difficult to find a distributor who is
willing to stock all of these units.
Accordingly, an object of the invention is to provide a
transmitter-receiver system obviating the above-mentioned
disadvantages.
Another object of the invention is to provide a transmitter
subcoder such that the transmitter simultaneously transmits three
different frequencies.
Another object of the invention is to provide a transmitter system
wherein the security of a load actuated by a remotely controled
receiver is materially increased.
Another object of the invention is to provide a transmitter
subcoder wherein the subcoder does not detune the transmitter
circuit transmitting the modulation frequency.
Another object of the invention is to provide a receiver-decoder
wherein the decoder does not detune the receiver circuit to its
sensitivity to a second modulating frequency.
Another object of the invention is to provide a transmitter
subcoder wherein a third frequency is provided for only a short
length of time and then ceases to thus increase the security by
requiring that the receiver be responsive to this third frequency
and then responsive to the termination of the third frequency with
only a modulated carrier wave.
Another object of the invention is to provide a transmitter system
of increased security against spurious operation by requiring that
the power supply switch be closed, and the carrier frequency,
modulation frequency and subcoding frequency all be correct in
order to transmit a proper signal which will operate a receiver
system.
Another object of the invention is to provide a receiverdecoder
wherein the presence of a third frequency is detected on a
conductor and the receiver is disabled by a voltage condition on
that same conductor.
Another object of the invention is to provide a receiver-decoder
which may be plugged into an existing test point jack on an
existing receiver which normally is used with only a first carrier
and a second modulation frequency.
Another object of the invention is to provide a
transmitter-receiver set which permits a customer to purchase a
simplified transmitter-receiver operative on only first and second
frequencies and later to add a subcoder and decoder with a third
frequency response, if more security is desired or if spurious
operating signals are encountered.
Summary of the Invention
The invention may be incorporated in a modulated carrier system,
comprising in combination, a transmitter and a receiver; said
transmitter comprising output circuit means, means to develop a
first frequency carrier in said output circuit means, means to
develop a modulation frequency, and means connecting said
modulation frequency developing means to said output circuit means
to establish a carrier wave output from the transmitter influenced
at said modulation frequency rate for a first time period and to
terminate said modulation frequency thereafter; said receiver
comprising first means responsive to said first frequency, a main
load, disabling means connected to disable said main load and
operative in the absence of a received signal containing said
modulation frequency, and means responsive to said modulation
frequency and having an output connected to terminate said
disabling means output for at least a second time period to enable
said receiver to thus pass current to said main load upon the
presence of a received signal containing said modulation frequency
and subsequently said first frequency.
Other objects and a fuller understanding of the invention may be
had by referring to the following description and claims, taken in
conjunction with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic diagram of a transmitter circuit;
FIG. 2 is a schematic diagram of a subcoder connectable to the
transmitter of FIG. 1;
FIG. 3 is a schematic diagram of a modified form of subcoder;
FIG. 4 is a schematic diagram of a main receiver responsive to
first and second frequencies;
FIG. 5 is a schematic diagram of a receiver decoder which may be
connected to the receiver of FIG. 4 and which adds a third
frequency capability;
FIG. 6 is a schematic diagram of an alternative receiver decoder
which may be electrically connected to the main receiver of FIG. 4;
and,
FIG. 7 is a graph of voltages obtainable in the circuit.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a schematic diagram of a transmitter 11 which
incorporates the invention. This transmitter has a means 12 to
develop a carrier frequency and this is shown as a carrier
frequency oscillator. The transmitter 11 also has a means 13 to
develop a modulation frequency and this means 13 is shown as a
modulation frequency oscillator. A power supply 14 is provided in
the transmitter and this may be a primary battery, especially where
the transmitter is of low power for example, a hand-sized VHF
transmitter usable with remote control of garage door operator
receivers. A switch such as a push-button switch 15 is provided as
is output circuit means 16. Means is provided including the switch
15 to connect the power supply 14 to the frequency developing means
12 and 13 to establish an output from the output circuit means 16
which contains both the carrier and modulation frequencies. To this
end, the carrier frequency oscillator 12 includes a transistor 20
having an emitter 21 connected through a jumper 22 and an output
load impedance shown as an output load resistor 23. The resistor 23
is connected in the output circuit 16 and this output circuit means
may include a parallel resonant circuit of a capacitor 25 and
inductance 26. The inductance may have a movable permeable core 27
for tuning purposes. Capacitors 29 and 30 connect the lower end of
the parallel resonant circuit 25-26 to the base 31 of transistor
20. These capacitors provide a feedback from the tank circuit 25-26
in order to sustain oscillations. The upper end of this tank
circuit is connected to the collector 32 of the transistor 20 in
order to complete the output circuit means 16.
The power supply 14 has first and second terminals 34 and 35,
respectively, of different voltages. The first terminal 34 is the
positive terminal of the power supply 14 and is connected to a
conductor 36 and through a current limiting resistor 37 to the base
31 of transistor 20. The second power supply terminal 35 is
connected through the push-button switch 15 to a conductor 38 and
this may be considered the ground side of the power supply 14. This
conductor 38 is connected through a bias resistor 39 to the base 31
of transistor 20. Conductor 38 is also connected to the
interconnection of capacitors 29-30 and resistor 23. The transistor
20 with the connections as shown will oscillate at a frequency
determined by the parallel resonant circuit 25-26 which may be in
the VHF range, for example, 250-300 MHz.
The modulation frequency oscillator has a circuit quite similar to
that of the carrier frequency oscillator except with different
values of components to have the modulation frequency lower than
the carrier frequency, for example, in an audio or super-audio
range of 500-20,000 Hz. The modulation frequency oscillator 13
includes a transistor 40 with an emitter 41 connected through a
resistor 43 to the conductor 38. A parallel resonant tank circuit
is provided in this modulation frequency oscillator 13 including a
capacitor 45 and inductance 46. The inductance 46 may have a
movable permeable core 47 for tuning to the desired modulation
frequency. A feedback capacitor 50 connects the lower end of the
tank circuit 45-46 to the base 51 of transistor 40. The upper end
of the tank circuit 45-46 is connected to the collector 52 by a
conductor 53 which also connects together the tank circuits of the
two oscillators 12 and 13. A current limiting resistor 57 connects
the conductor 36 to the base 51 and a resistor 59 connects the base
51 to the conductor 38. The transistor 40 will oscillate at the
modulation frequency determined by the values of the parallel
resonant circuit 45-46. A power supply capacitor 58 may be directed
across the power supply 14.
First, second and third junctions 61, 62 and 63, respectively, are
provided in the transmitter 11. Junction 61 is connected to the
interconnection of emitter 21 and jumper 22. The second junction 62
is connected to the ground conductor 38 and the third junction 63
is connected to the positive power supply terminal 34 via conductor
36. These junctions 61-63 provide a ready means for connection to a
subcoder 66 shown in FIG. 2. This subcoder 66, together with the
transmitter 11, has a means 68 to develop a third frequency. This
third frequency may be a subcode and preferably is a frequency
lower than either the carrier or the modulation frequency. The
third frequency developing means 68 is at least partly in the
subcoder 66 and in this preferred embodiment is shown as being
incorporated in circuitry of the subcoder 66. The subcoder 66 has
first, second and third terminals or connectors 71, 72 and 73.
These connectors are connectable to the junctions 61-63,
respectively, and for ease of this interconnection the subcoder 66
may simply be plugged into the transmitter 11 by having male
connectors 71-73 on a terminal strip 74 receivable in female
connections of the junctions 61-63. The transmitter 11 may be
mounted on a printed circuit board as an example, and the subcoder
may be mounted on another smaller printed circuit board with the
terminal strip 74 an integral part thereof. This subcoder 66 in the
preferred embodiment of FIG. 2 includes a Darlington transistor
pair 75 connected to null resonant circuit means 76 to act as an
oscillator which oscillator may be the principal component of the
third frequency developing means 68. The circuit means may take one
of several forms and in FIG. 2 is shown as including a bridge T
filter network. Resistors 77, 78 and capacitor 79 form one T and
capacitors 80, 81 and variable resistor 82 form another T which
together form the bridge T 76. This bridge T network 76 has
terminals 83 and 84. A feedback capacitor 85 establishes the
transistor 75 oscillating at the null frequency of the bridge T
circuit 76. A bias resistor 86 biases the transistor 75 into a
proper operating condition.
The second connector 72 is connected to a ground conductor 88 and
third connector 73 is connected to the positive power supply
voltage in transmitter 11 and is connected to a conductor 89 in the
subcoder 66. This conductor 89 is connected through a resistor 90
to the terminal 83 of the null resonant circuit means 76. This null
resonant circuit means 76 is one which has a null at the desired
frequency, hence a minimum output across terminals 84 and conductor
88. The output at terminal 83 is passed by a coupling capacitor 91
and resistor 92 to an output circuit which includes a transistor
94. The resistor 92 is connected to the base 95 of this transistor
94. The emitter of transistor 95 is connected to the connector 72
and the collector of this transistor is connected through a current
limiting resistor 96 to the connector 71. Accordingly, the
conduction or non-conduction of transistor 94 gives an output
signal on connectors 71 and 72.
A timing circuit 99 is provided in the subcoder 66 to provide a
time delay period. This may be considered a second time delay
period with the first time delay period that established by the
resonant circuit means 76. Many such resonant circuit means take a
certain finite time to "ring" or come up to full resonance. Such
first time delay period may be quite short, for example, 0.01
seconds up to 0.1 seconds. The timing circuit 99 includes primarily
a capacitor 100 and a transistor 104 to amplify the effect of
capacitor 100. Resistors 102, 103 cooperate with capacitor 100 for
an RC charging time delay network. This time delay may be any
suitable value for example, 1/10 second to three seconds and after
the capacitor 100 is charged, then the transistor 104 is turned on
continuously. This turns on transistor 94 continuously for a
minimum potential difference across terminals 71 and 72. This is
after the second time delay period of perhaps 1/2 second and during
that second time delay period, while capacitor 100 is charging, the
transistor 20 is influenced at the third frequency rate by the
output from Darlington transistor pair 75 appearing at terminal 83.
This means that during this second time delay period the transistor
94 is turned on and off at the third freguency rate. When
transistor 94 is not conducting, this means there is a high
impedance condition between terminal 71 and 72. This turn on and
off of transistor 94 interrupts the radiated modulated carrier at
the third frequency rate. This is like 100% modulation with a
square wave.
OPERATION
Now referring to FIG. 1, it may be observed how the subcoder 66
affects the transmitter 11. When the connectors 71-73 are plugged
into the junctions 61-63, then the interconnection of connector 72
and junction 62 establishes a reference potential in the subcoder
66. This is the 0 volts or ground reference potential. The
interconnection of junction 63 and connector 73 establishes another
potential in the subcoder 66 at a potential different from that on
terminal 72. Accordingly, an operating voltage is supplied to this
subcoder 66. In the example shown this is plus nine volts applied
to the subcoder 66. The interconnection of junction 61 and
connector 71 establishes that the output of the subcoder 66 is
applied to the transmitter 11. More particularly, the output of the
subcoder 66 appears on connectors 71 and 72 and it will be seen in
FIG. 1 that this output is applied to junctions 61 and 62 which is
in parallel with the output load resistor 23. The jumper 22 may
easily be formed from a U-shaped bend in the lead of this resistor
as it is mounted on the printed circuit board. This jumper may
easily be cut by a person plugging the subcoder 66 into the
transmitter 11. With this jumper 22 cut, then the output of the
subcoder is no longer in parallel with the resistor 23, instead it
takes the place of this resistor 23. Preferably the effective
impedance of the transistor 94 plus resistor 96 when this
transistor 94 is conducting is the same as the resistance of
resistor 23. In one practical embodiment of a circuit made in
accordance with this invention, resistor 23 was 560 ohms, resistor
96 was 470 ohms and transistor 94 when conducting had the
difference of about 90 ohms impedance. Accordingly, it will be seen
that the transmitter 11 operation is virtually unaffected in its
operation during the time transistor 94 is conducting, because
there are no changes in impedance or circuit parameters. Thus, as
the transistor 94 intermittently conducts at the third frequency or
subcoding rate, this establishes the influence on the transmitter
11 at this third frequency rate. More specifically, the output
circuit means 16 of this transmitter 11 will radiate a modulated
carrier wave interrupted at the third frequency rate. In one actual
embodiment of transmitter made in accordance with this invention,
this third frequency was on the order of 300 to 15,000 Hz. The
radiation is from the inductance 26 which acts as a radiating
antenna.
The timing circuit 99 establishes the charging of capacitor 100
from the power supply source 14. This is the second time delay
period and this might be 1/10 to 3 seconds, for example. After this
second time period, the capacitor 100 is charged, which means that
transistor 104 is turned fully on and this turns transistor 94
fully on. Accordingly, it is no longer influenced by the output
from the oscillator 68. Also this continuous conduction of
transistor 94 means that the transmitter 11 is no longer influenced
at the third frequency rate. More specifically, the continuous
conduction of transistor 94 means that the carrier wave is
transmitted as a modulated carrier wave modulated only at the
modulation frequency of oscillator 13 and is not influenced at any
third frequency rate. This has the advantage that it does not
detune the modulation frequency oscillator and hence the receiver
of the transmitter-receiver set will be receiving a modulation
frequency and a carrier frequency at the proper values.
SECOND EMBODIMENT
FIG. 3 shows an alternative subcoder 106 which may be used in place
of the subcoder 66 of FIG. 2 and will also plug into the junctions
61-63 in the transmitter of FIG. 1. To this end the subcoder 106
again has the connectors 71-73 to be connected to the junctions
61-63. This subcoder 106 has a means 108 to develop a third
frequency which includes a transistor 109 and resonant circuit
means 110 shown as a tuning fork. This may be any of the usual
forms of tuning fork oscillator circuits, with a capacitive plate
112 cooperating with the tuning fork 110 and supplying drive to the
base of transistor 109. Another capacitive plate 113 cooperating
with the tuning fork has a feedback from the output of a transistor
114 to sustain oscillation. The oscillation of transistor 109 is
supplied to an emitter follower resistor 115 and this output is
passed by a coupling capacitor 116 to the base input of transistor
114. The output of transistor 114 appears at the collector for the
aforementioned feedback and is coupled through another coupling
capacitor 117 to the base 95 of transistor 94. Again a timing
circuit 99A is provided which includes transistor 104, resistor 103
and capacitor 100.
OPERATION
When the subcoder 106 is plugged into the transmitter 11 it
operates in essentially the same manner as when subcoder 66 was
plugged into transmitter 11. A first time delay period is
established after push-button switch 15 is closed. This first time
delay period is caused by the tuning fork 110 or resonant circuit
means building up the amplitude of oscillations to the normal
value. This might be 1/100 to 1/4 of a second. The timing circuit
99A establishes a second time delay period during which the
modulated carrier wave being radiated is influenced at the third
frequency rate. During this second time delay period, the capacitor
100 is charging and also during this time the oscillator 108 is
oscillating and affecting the base 95 of transistor 94 at this
third frequency rate. Accordingly, transistor 94 is turned on and
off at this third frequency rate which turns on and off the
modulated carrier frequency radiated from the output circuit means
16 at this third frequency rate. At the completion of the second
time delay period, the capacitor 100 is virtually charged which
means that transistor 104 is turned fully on as is transistor 94,
hence it is no longer influenced by the continuously running
oscillator 108. Accordingly, after this second time delay period
the radiated emissions are only of the carrier modulated at the
modulation frequency of oscillator 13. The transistor 104 is an
amplifier and also a buffer to prevent the continuous conduction of
transistor 94, subsequent to the second time delay period, from
influencing the oscillator 108. This has the advantage of not
affecting the frequency of the oscillator circuit 108 and hence
maintaining the same frequency in a particular transmitter-receiver
set.
From the above it will be noted that either subcoder 66 or 106 may
be used interchangeably with the transmitter 11 and prior to
plugging a subcoder into the transmitter, the transmitter is a
completely operable unit radiating a modulated carrier wave and
usable with a receiver tuned to the same carrier and modulation
frequencies. If security is required in addition to that afforded
by the possible carrier frequencies and possible modulation
frequencies, then the subcoder 66 or 106 may easily be added to the
transmitter and a complementary decoder added to the receiver. For
example, if 10 possible transmitter frequencies are usable and 10
possible modulation frequencies are usable, this would give 100
possible codes. Adding a subcoder with another 10 possible
frequencies, this gives 1,000 possible codes. Actually it has been
found that the security achieved by the addition of this third
frequency is considerably more than merely a 10-fold increase in
security. Referring to FIG. 3 with the tuning fork 110, it will be
observed that this tuning fork could be induced into oscillation by
a physical shock. However, this alone does not establish a third
frequency output. Before the right combination of carrier,
modulation and subcoding frequencies occur, five things must be
properly established:
1. The push-button switch 15 must be closed;
2. The carrier frequency oscillator 12 must be at the right
frequency;
3. The modulation frequency oscillator 13 must be at the right
frequency;
4. The third frequency oscillator 108 must be at the right
frequency; and,
5. The capacitor 100 must not be charged. This fifth criteria above
is accomplished by the timing circuit 99 and takes only 1/10 to
three seconds to accomplish. Accordingly, a lawbreaker would have a
very short time in order to try to fulfill these five criteria.
This is why the security is increased much more than 10-fold by the
addition of a third frequency.
FIG. 4 illustrates a preferred embodiment of the receiver 211
incorporated in the transmitter-receiver system. The radio receiver
211 is adapted to be operative on a received signal of a
predetermined first frequency carrier modulated by a lower second
modulation frequency, and also subject to receiving random noise
signals. The receiver 211 includes a receiving antenna 212
supplying an input to a transistor 213 which is an isolation stage.
The signal is then passed to a superregenerative circuit 214 which
includes a transistor 215 with a parallel resonant output circuit
216. This parallel resonant output circuit 216 is tuned to a
predetermined first frequency carrier, which for example, might be
in the order of 250 MHz. The output of the super-regenerative
circuit 214 appears at a terminal 217 and contains the carrier
frequency, the modulation frequency and also a squelch frequency
intermediate these two frequencies. In this example, the modulation
second frequency may be an audio or super-audio frequency.
The squelch frequency depends upon the constants of the circuit 214
and may be 600 KHz., for example. This output is applied to
resistors 218 and 219 in series and to a capacitor 220 which
presents a low impedance to ground for the squelch frequency and
accordingly the modulation frequency signal is passed by a
capacitor 222 to the transistor 213 in a reflex circuit for
amplification of such modulation frequency signal. This amplified
output appears across a capacitor 223 and it is passed by a
coupling capacitor 224 to an input terminal 225 of a lower
frequency amplifier 227. The amplifier 227 is shown as a transistor
supplying an output to a detector circuit which includes a tuned
load 229 and an untuned load 230.
The parallel resonant circuit 216 is tuned to resonance to the
first or carrier frequency and hence is a first means responsive to
this first frequency. The tuned load 229 is tuned to resonance at
the second or modulation frequency and hence is a second means
responsive to this second frequency. The tuned load 229 includes a
transform 231 with a movable slug core 232 and the transformer has
a primary and a secondary winding 233 and 234, respectively with
the primary winding connected to the output of the transistor 227.
The output from the transistor 227 is through the primary winding
233, a capacitor 235 and a resistor 236 to ground. Each of the
output signals of the transistor 227 appear across the resistor
236, and accordingly, a center conductor 238 of a test point jack
is connected to this junction of the capacitor 235 and resistor
236. The outer conductor 239 of this test point jack is connected
to ground. With all of the audio signals including the random noise
appearing across resistor 236, this may be considered the input to
the untuned load 230 and it is stated as being untuned to
distinguish it from the tuned load 229.
In this tuned load 229 capacitor 240 is connected across the
secondary winding 234 to tune it to resonance which is reflected
into the primary winding 233. The upper terminal of capacitor 240
is a first terminal 241 relative to ground 242 which may be
considered a second terminal. The lower end of capacitor 240 is
connected to a junction 243 at the untuned load 230 and passes from
there through a resistor 244 to ground. A capacitor 245 is
connected in parallel with resistor 244 and a diode 246 is
connected with a polarity to conduct current from junction 243 to
the test point center conductor 238.
A unidirectional conducting device shown as a diode 248 is
connected to the first terminal 241 to pass current to a main load
249. This main load includes a transistor 250, a relay 251 and a
time delay capacitor 252. A diode 253 connects the capacitor 252
between diode 248 and ground 242. A discharge resistor 254 is
connected across the capacitor 252. When the time delay capacitor
has been sufficiently charged positive, then current is passed
through a resistor 255 to the base of transistor 250. This occurs
when the voltage of the capacitor 252 exceeds the forward voltage
drop from base to emitter of the transistor 250.
A power supply 258 is provided such that when a switch 259 is
closed, a step-down transformer 260 is energized and the secondary
thereof energizes first and second terminals 261 and 262 of a
terminal strip 264 which also has a third terminal 263. The AC
voltage between terminals 261 and 262 is supplied through a
rectifier 265 to a filter capacitor 266 so that a supply conductor
267 is positive relative to ground 242. The relay 251 is connected
to this DC supply conductor 267. The relay controls single pole
double-throw contacts with a contact blade 268 connected to ground
242. The normally closed contacts 270 are connected to a terminal
271 at the junction of first and second bleeder resistors 272 and
273. A capacitor 275 is connected in series with resistor 273
between terminal 271 and a terminal 276, which is connected to the
base of transistor 250. The normally open contacts 276 are
connected by a lead 277 to the third terminal 263 on the terminal
strip 264. This provides an external connection controled by the
energized or de-energized condition of the load 249. Protective
capacitors 278 and 279 are connected between terminal 271 and
ground and terminal 276 and ground and a filter capacitor 280 is
connected across the relay 251. A protective diode 281 is also
connected across this relay 251.
OPERATION
The radio receiver 211 conveniently may be used in a remote control
of a physical device, for example, the remote control of a garage
door operator from a low powered transmitter. As the user
approaches the garage in driving his automobile, he presses a
button on the transmitter to place it in operation. The transmitter
emits a signal which is a selected one of a plurality of carrier
first frequencies and one of a plurality of second modulation
frequencies. As explained above, it may also contain a third lower
frequency, however, the main receiver as described so far in FIG. 1
is usable with just a singly modulated carrier frequency. The tuned
circuit 216 is responsive to the first frequency and if the
received signal on the antenna 212 is one having a carrier at this
frequency, then the signal is passed to the lower frequency
amplifier 227. Normally noise being received on the antenna 212 is
passed and is further amplified by the amplifier 227. The untuned
load 230 is that which is more responsive to this noise and
off-frequency signals than the tuned load 229, for example, there
may be four times as much voltage across resistor 236 as across the
primary winding 233 due to this noise. The polarity of the diode
246 is such that junction 243 will be negative as caused by the
audio frequency noise on this resistor 236. In a practical circuit
this may be 1 to 3 volts negative at junction 243 relative to
ground 242. The conduction by diode 246 makes the test jack
conductor 238 positive by a small amount due to this rectification
of the audio frequency noise.
When a received signal of the proper first and second frequencies
is received, then it is passed by the super-regenerative circuit
214 and the tuned load 229 resonates at this second frequency. This
means a high voltage appears across the secondary winding 234 and
hence across the primary winding 233. Diode 248 is poled to conduct
when the first terminal 241 is positive. However, it will be noted
that diodes 246 and 248 are in effect poled in opposite directions.
This means that the outputs of the tuned and untuned loads 229 and
230 are effectively connected in opposition. The output of the
untuned load 230 appears across terminal 243 and 242 and is
negative on terminal 243 relative to ground terminal 242. The
output of the tuned load 229 is positive on the first terminal 241
relative to the ground 242. Accordingly, under normal stand-by
conditions, the output from the noise from the untuned load 230
predominates and no current is passed to the main load 249. When
the proper second frequency signal is received however, then the
output from the tuned load 229 at terminal 241 predominates and
exceeds the negative voltage at terminal 243. Under this condition
the output of the tuned load 229 is more positive than a given
value to pass current to the main load 249. The given value in this
case is a voltage, for example, 2/10ths of a volt to cause the
diode 248 to conduct. Upon conduction the time delay capacitor 252
will be charged. At the threshold of received signal, diode 248
conducts only on the crests of the positive half cycles but as the
received signals grow stronger, the diode 248 may conduct for
practically the entire positive half cycles. Resistor 254 is
connected to continually discharge capacitor 252 but at some point
the charge on capacitor 252 will reach a voltage value exceeding
the forward bias on transistor 250. This may be 7/10ths of a volt,
for example, for silicon transistors and hence transistor 250 will
conduct to energize relay 251. When this happens the normally
closed contact 270 is opened and the normally open contact 276 is
closed. This places an output signal on the third terminal 263,
which may be used for any desired purpose, for example, in a garage
door operator this may be used to control a power relay energizing
a motor which drives the garage door. The operation of this
particular part of the circuit is more fully described in my
previous U.S. Pat. No. 3,579,240.
FIG. 5 shows a preferred embodiment of a decoder 290 having a test
plug 291 which may be plugged into the test jack 238-239 of the
main receiver 211 to add a third frequency capability thereto. The
decoder 290 may be made on a printed circuit board and may be
practically small and lightweight to support itself physically when
plugged into the test point jack 238-239. Electrical connections
are also made at the same time of this physical support. The test
plug 291 includes a center conductor 292 connecting to the center
conductor 238 and an outer conductor 293 connecting to the outer
conductor 239 of the test jack. The outer conductor 293 is
connected to an internal ground 294 of the decoder 290.
The decoder 290 includes generally a disabling means 296 and a
third frequency responsive means 297. The disabling means 296 may
also be considered a bias means to bias the main receiver 211 so
that no current is passed to the main load 249. The third frequency
responsive means 297 may also be considered a tuned circuit
resonant to the third frequency, which is lower than the carrier
frequency. The decoder 290 includes a power supply means 299
including a rectifier 300 poled to conduct current through a
flexible lead 301 to the first terminal 261 on the terminal strip
264. This flexible lead 301 may readily be connected on the
terminal 261 when the decoder is plugged into the test jack. The
power supply 299 also includes a filter capacitor 302 connected
between the voltage supply conductor 303 and ground 294. This
polarity of the rectifier 300 makes supply conductor 303 negative
relative to ground 294, for example, -31 volts. The ground 294 of
decoder 290 is connected to the ground 242 of the main receiver and
with the first terminal 261 connection, this provides an operating
voltage to the decoder 290 and also provides a reference potential;
namely, ground.
The test plug center conductor 292 is connected to a terminal 305
and the disabling means 296 is connected between this terminal and
the supply conductor 303. This disabling means 296 includes
generally a voltage dropping resistor 306 and a transistor 307. A
bias resistor 308 is connected between ground 294 and the base of
transistor 307 and since ground is positive of the supply conductor
303 in this decoder 290, this biases the transistor 307 normally
into conduction. The circuit may be traced considering FIG. 5 in
conjunction with FIG. 4. Starting with ground 294 or 242, which is
positive, the current flows upwardly through resistor 244, the
diode 246, the test point center conductor 238, test plug center
conductor 292, down through resistor 306 and transistor 307 to the
negative supply conductor 303. This current flow makes the upper
end of resistor 244 at junction 243 negative with respect to
ground. In a practical circuit constructed in accordance with this
invention, this was made to be about 20 volts negative relative to
ground. This is sufficient negative bias voltage supplied by the
biasing or disabling circuit 296 such that the main receiver is
disabled. By this is meant that no current may be passed to the
main load 249. The super-regenerative circuit 214 is a senstive
circuit with a gain in the order of one million, yet irrespective
of the strength of the signal on the antenna 12, for example, even
if the proper first and second frequencies are present there will
not be sufficient positive voltage at terminal 241 relative to
ground 242 such that the output of the tuned load 229 can overcome
this negative voltage output of the untuned load 230 plus the bias
from the decoder 290. This is why the circuit is described as being
disabled by the negative bias supply from the decoder 290.
The decoder 290 also includes the third frequency responsive means
297 which in this preferred embodiment is a tuned circuit resonant
to this third frequency. The tuned circuit includes an inductance
310 with a tunable core 311. A capacitor 312 is connected in
parallel with the inductance 310 for parallel resonance. This
circuit is tuned to resonance at the third frequency which is lower
than the first or carrier frequency and in this preferred
embodiment is also lower than the second or modulation frequency.
For example, in one practical circuit this might be in the range of
500 to 5,000 Hz. Upon parallel resonance the voltage across this
inductance 310 rises and this establishes turn-off of the
transistor 307 to terminate the negative bias on the junction 243
and thus enable the receiver 211. Since the receiver is at that
time enabled, this means that if the signal is received containing
the proper first and second frequencies, then current is passed to
the main load 249 at that time.
The third frequency responsive means 297 includes in this preferred
embodiment a buffer amplifier 313 shown as a Darlington transistor
pair. Power is supplied to this amplifier through a resistor 314
from the positive operating voltage which in this case is ground
294. The input base of the Darlington pair is connected by a
coupling capacitor 315 to the upper end of the tank circuit
310-312. The emitter output of the Darlington pair is fed through a
resistor 316 to the negative operating voltage at conductor 303.
The AC output of the Darlington pair is supplied through a coupling
capacitor 317 to the input base of a driver transistor 320. A high
impedance isolating resistor 322 connects the input terminal 305 to
the upper end of the tank circuit 310-312 to have supplied thereto
the low frequency signals present on the test jack center conductor
238. An accelerator circuit 328 is provided in the subcoder or
decoder 290. This accelerator circuit includes a diode 329
connected from the lower end of resistor 306 to a junction 330
between voltage divider resistors 331 and 332 connected between
ground and the negative supply conductor 303. A resistor 333 and a
capacitor 334 are connected in series between junction 330 and
ground. A resistor 335 and capacitor 336 are connected in series
between the junction of resistor 333 and capacitor 334 and the base
of the transistor 320. A resistor 337 is connected from the base of
transistor 320 to conductor 303.
OPERATION
When a signal is received, correct in the first frequency, this is
passed by the superregenerative circuit 214 and the tuned circuit
216 thereof to the lower frequency amplifier 227. During normal
operation the voltage across resistor 236 is approximately four
times as great as the voltage across the secondary 234. This is
because the noise and off-frequency signals generate a much larger
output from the untuned load 230 than from the tuned load 229.
However, during those periods when the correct second frequency is
applied to the amplifier 227, then the parallel resonance of the
detector circuit 229 assures that up to about 90% of the total
output of the detector appears across the secondary winding 234 and
only about 10% across the resistor 236. Also present across
resistor 236, in this example, will be the aforementioned proper
third frequency. This third frequency is applied to the decoder
290.
During the initial period that the decoder 290 is powered, there
will be a small leakage current through the high resistance 308 to
charge the large capacitor 325 so that the base of transistor 307
is positive relative to conductor 303 and transistor 307 is made
conducting. Now, when the proper third frequency is passed along
the center conductor 292 of test plug 291, it will be passed to the
third frequency responsive means 297. The voltage across the
parallel resonant circuit 310-312 thus increases considerably and
the AC signals at this third frequency are passed by the coupling
capacitor 315 to the Darlington transistor pair 313. This
transistor pair has an output at the collector of the last
transistor which is passed through the AC coupling capacitor 317 to
drive the base of the transistor 320 at this third frequency rate.
The Darlington transistor pair 313 has a high impedance input to
not load the inductance 310 and has a low impedance output to drive
the transistor 320. The turn-on of the transistor 320 on half wave
positive pulses at the third frequency rate, rapidly discharges the
capacitor 325, perhaps in about 10 miliseconds.
FIG. 7 shows a graph of voltages available at different parts of
the receiver circuit 211. A curve 340 illustrates the signal
received at the antenna 212 which as an example includes the proper
first, second and third frequencies between a time t.sub.0 and a
time t.sub.2. Also a curve 341 shows the time period of a received
signal containing only the proper first and second frequencies, the
third frequency being missing. Prior to this time t.sub.0, the
voltage across the capacitor 325 is shown by a curve 342 and this
shows a voltage of 0.7 volts positive with respect to conductor 303
across this capacitor 325. From time t.sub.0 to time t.sub.1 ;
namely, about 10 miliseconds, the capacitor 325 discharges to have
essentially zero voltage thereacross at time t.sub.1 as shown at a
point 343 on this curve 342. Prior to this the transistor 307 was
conducting and this caused a large DC negative bias voltage to
appear on the center conductor test point 238. In the
aforementioned circuit this might be a -19 volt DC bias established
on the curve 344 showing the voltage at this conductor 238. During
this same period prior to time t.sub.0 this large negative voltage
at this conductor 238 causes conduction of the diode 246 so that
junction 243 and first terminal 241 is at a minus voltage, for
example, -18.8 volts as shown by curve 345 of the potential at this
terminal 241. Now at time t.sub.1 when the transistor 307 has
stopped conducting, the potential at test point 238 goes up to
about +5 volts as shown at a point 346. The reason for this
positive voltage is that the third frequency signal is now an off
frequency signal as far as the tuned load 229 is concerned.
Accordingly, a large proportion of the total output of transistor
227 appears across the resistor 236. This will be positive at the
center conductor 238. This positive voltage partially biases off
diode 246 so that the potential at the first terminal 241 remains
at about -4.8 volts.
The curves of FIG. 7 assume a condition wherein small hand-sized
transmitters may be far away from the receiver and hence be
emitting a relatively weak signal, not much more than the threshold
of sensitivity of the receiver. This might be 5 microvolts of
signal at the antenna 212, for example. During this condition the
very crests of the positive half cycles at the second frequency
rate are resonated by the tuned circuit 234-240 sufficiently so
that these crests are passed by the diode 248. These charge the
capacitor 252 relatively slowly and this capacitor is being
continuously discharged by the paralleled resistor 254. Under these
conditions the charging of capacitor 252 may be sufficiently slowly
achieved, as shown by a curve 347, so that the plus 0.7 volt charge
condition on this capacitor 252 is not reached until a time t.sub.3
which is subsequent to time t.sub.2. The time t.sub.2 is that at
which the third frequency disappears from the received signal. When
the third frequency disappears, the noise, in this case an off
frequency signal, on resistor 236 decreases to a lower level,
perhaps +2 volts as shown at a portion 348 of the curve of voltage
on this center conductor 238. During this same time period from
time t.sub.1 to time t.sub.2, the voltage at terminal 241 is about
4 to 5 volts negative because of conduction of diode 246 on the
negative half cycles of voltage on the resistor 236. This is shown
by a portion 349 on the curve of the potential at terminal 241.
This negative voltage at terminal 241 makes it difficult for the
proper second frequency to be passed by the diode 248 during
positive half cycles.
Now at the time t.sub.2 when the third frequency has disappeared
from the incoming received signals, this third frequency which is
noise insofar as the tuned circuit 229 is concerned, has now
disappeared and hence the negative bias at terminal 241 has about
disappeared as shown by a portion 350 of the curve of potential at
this terminal 241. This means that the positive half cycles of the
second frequency will be more readily passed by diode 248 to more
quickly charge capacitor 252 and hence the relay will be energized
at a time t.sub.3 by conduction of transistor 250. This relay
energization is shown by a curve 351 as occurring at the time
t.sub.3. It will be understood that with a stronger signal
containing frequencies one, two and three, then the energization
and pull-in of the relay 251 may occur prior in time to the time
t.sub.2 ; namely, prior to the time when the third frequency
disappears from the incoming signal.
At the time t.sub.2 when the third frequency has ceased, the
decoder 290 will be conditioned so that the third frequency voltage
across the tank circuit 310-312 disappears. This causes transistor
320 to cease conduction and hence the capacitor 325 starts to
charge as shown by portion 352 of the curve of voltage across this
capacitor. This charge is relatively slow because of the high
resistance of resistor 308. At some point in time t.sub.4, not
necessarily related to the time t.sub.5 when frequencies one and
two cease, the capacitor 325 will charge to about 0.7 volts
positive on the upper plate thereof so that transistor 307 again
starts to conduct. This establishes the aforementioned large
negative bias on center conductor 238 and on the terminal 241 as
shown by portions 353 and 354 of the voltage curves on these
terminals, respectively. This disables the receiver 211 so that no
further signals may be passed to the relay 251. The capacitor 252
is now being discharged rather rapidly by resistor 254 as shown by
curve portion 355 and when the potential thereacross falls below
0.7 volts, the transistor 250 ceases conduction and relay 251 drops
out as shown by curve portion 356. The above description is with
the frequencies one and two ceasing at a time t.sub.5 which is
subsequent to the time t.sub.4. However, should the frequencies one
and two cease prior to the time t.sub.4, then capacitor 252 ceases
charging and starts to discharge along a line 357. This would cause
dropout of the relay at a point 358 on the relay energization
curve.
The accelerator circuit 328 makes certain that once transistor 307
starts to turn off, it actually does turn off and quickly.
Resistors 331 and 332 form a voltage divider, and the potential of
junction 330 may be half way between ground and conductor 303, for
example, at a potential of -15.5 V. At some time during turning off
of transistor 307, the collector thereof will rise in potential to
a point exceeding -15.3 volts, at which time diode 329 will
conduct. This supplies a momentary current through resistors 333
and 335 and capacitor 336 to help drive the base of transistor 320
more positive and hence assure turn on thereof.
FIG. 6 shows an alternative decoder circuit 370 which may be used
in place of the decoder 290 and which has a test plug 371 with a
center conductor 372 and an outer conductor 373. This test plug 371
may be plugged into the test point jack 238-239 of the receiver
211. The decoder 370 has the same power supply 299 to establish a
negative voltage, for example, -31 volts on a negative power supply
conductor 303. This is again established by a flexible conductor
301 which may be connected to the terminal strip terminal 261. The
power supply 299 establishes this negative voltage on conductor 303
relative to a ground 374 to which the outer conductor 373 of test
plug 371 is connected. The decoder 370 includes generally a
disabling means 376 and a third frequency responsive means 377. The
disabling meand 376 is quite similar to the disabling means 396 of
the circuit of FIG. 5. This disabling means 376 includes a
Darlington transistor pair 378 connected in series with a resistor
379 between the negative supply conductor 303 and a terminal 380
which is connected to the test plug center conductor 372. Normally,
this transistor pair 378 is biased into conduction by the bias
resistor 381. This bias resistor is a large value impedance and
through a resistor 383 charges a capacitor 382 connected in series
therewith between negative supply conductor 303 and the ground
connection 374. Accordingly, normally during non-receipt of third
frequencies, the capacitor 382 will be charged enough to bias
transistor pair 378 into saturation.
The third frequency responsive means 377 is a means tuned to be
responsive to this frequency and is shown in this embodiment as a
tuning fork 385. This tuning fork may vibrate or be in resonance at
the selected third frequency rate which again may be in the order
of 300 to 5,000 Hz. The input to the tuning fork 385 is from the
terminal 380 through a high resistance 393 and a coupling capacitor
386 and upon receiving the proper third frequency this forces the
tuning fork 385 into vibration at its resonant frequency. The
output from the tuning fork is from the other fork leg at a
coupling capacitor 387 which drives the base of the transistor 388
at this third frequency rate. This transistor 388 is normally
biased partly on by current through resistors 389 and 394.
Transistor 388 amplifies the third frequency voltage and the output
appears across the resistor 389. The third frequency rate is passed
by a capacitor 390 to a resistor 391. During the negative
excursions of the upper end of resistor 391, a diode 392 will
conduct, again at this third frequency rate. This rapidly drives
the upper plate of capacitor 382 more negative so that the
transistor pair 378 ceases conduction. This stops the bias
previously developed by conduction of this Darlington transistor
pair. Accordingly, with the bias stopped, this enables the receiver
211 so that if the received signal on antenna 212 contains a proper
first and second frequencies, then the diode 248 passes this second
frequency output to energize the relay 251. This is essentially the
same operation as the circuit of FIG. 5 and as described by the aid
of the curves of FIG. 7. Again when the third frequency ceases, the
tuning fork 385 will cease oscillation, the transistor 388 will
cease amplifying, diode 392 will cease conduction and capacitor 382
will again be permitted to charge slowly through the large value
resistor 381. When about 1.4 volts forward bias appears across
capacitor 382, this will again establish forward conduction of the
transistor pair 378 to again start the negative bias which disables
the receiver 211.
The decoder 290 or 370 is responsive to the third frequency which
may be received on the antenna 212 of the receiver 211. The decoder
by itself has a terminal 305 or 380 which may be considered a first
terminal, ground 294 or 374 may be considered a second terminal and
input terminal 261 may be considered a third terminal of this
decoder. The bias means or disabling means 296 or 376 develops a
bias voltage and the transistor 307 or 378 is a switch means
connected to this bias means to selectively connect and disconnect
the bias voltage from the first terminal 305 or 380. The frequency
responsive means 297 or 377 is responsive to a given frequency
input; namely, the third frequency, on this first terminal 305 or
380. In each decoder there is a means connecting the output of the
frequency responsive means to the switch means to actuate this
switch means to change the bias voltage condition on the first
terminal upon the incoming presence of the given or third
frequency. This connecting means includes the transistor 320 in
FIG. 5 and the transistor 388 and diode 392 in FIG. 6. In the
preferred embodiment of FIG. 5, this change of the bias voltage
condition on the first terminal is a disconnection of the bias
voltage from this first terminal. In both FIGS. 5 and 6 there is a
power supply means with a rectifier and filter so that the bias
voltage is a DC voltage. The DC bias voltage appears between the
first and second terminals 305 and 294 and the second and third
terminals 294 and 261 are adapted to have an AC voltage applied
thereto. The capacitor 325 or 382 provides a time delay of
reapplying the bias voltage to terminal 305 or 380 upon cessation
of third frequency input to said first terminal 305 or 380.
The time period 340 during which the first, second and third
frequencies are being transmitted, as shown in FIG. 7, is a first
time period. The third frequency is terminated thereafter. In the
receiver circuit the third frequency responsive means is enabled
during at least a second time period. This second time period is
portions 349 and 350 of the voltage curve on the terminal 241. The
receiver is enabled during this period, because the disabling bias
means has been terminated during this time.
The aforementioned receiver circuit 211 and decoders 290 or 370
establish a circuit which accomplishes many objectives.
An additional advantage is achieved by having the subcoder 66 or
106 as a plug-in module rather than permanently wired into the
transmitter 11. If a customer wants only a minimum security of one
of a range of carrier frequencies and one of a range of modulation
frequencies, then the transmitter 11 is completely usable as part
of a transmitter-receiver set. However, let us assume that after
the consumer has purchased the transmitter receiver set, he desires
(1) either more security or (2) increased freedom from spurious
interference which might be operating his garage door on spurious
signals. In such a case, the serviceman or dealer may simply plug
the subcoder into the transmitter 11, cut the jumper 22, place a
similar decoder in the receiver of that set and the customer has
accomplished both things; namely, increased security and increased
freedom from spurious signal operation of his garage door. The
transmitter 11 at that time is one which has not only the two
frequencies originally built into it, but it also has the third
frequency of the subcoder.
Still another advantage is gained by the dealer or distributor
because he does not need to stock nearly as many parts as he did
before. Considering only the transmitter of the
transmitter-receiver set, and if one assumes ten possible carrier
frequencies, 10 possible modulation frequencies and ten possible
subcoding frequencies, the dealer or distributor does not need to
stock one thousand different transmitters. He needs to stock only
ten different transmitters of different carrier frequencies, plus
ninety more transmitters for the ten different modulation
frequencies of each of the ten carrier frequencies, plus ten
different subcoders 66 or 106. This is a stocking of 110 parts
rather than 1,000 parts. Actually, the stocking of the 90
additional transmitters to cover the possible 100 codes of
modulation and carrier frequencies, may be eliminated if the dealer
or distributor wishes to tune the movable cores 47 for the
particular modulation frequency desired. These are continuously
movable tuning slugs and with some frequency standard these
modulation frequencies may quickly be set by a simple screwdriver
adjustment. In such case, one would need to stock only 10
transmitters for the 10 different carrier frequencies, plus 10
subcoders for the 10 different subcoding frequencies for a total of
stocking only twenty parts rather than one thousnad parts. A
similar saving in the stocking of receivers of the
transmitter-receiver set is also effected and hence this is a
tremendous saving in cost and convenience to the dealer and
distributor who needs to stock such a materially reduced number of
units.
The decoder 290 or 370 easily may be plugged into an existing test
point jack 238 on any one of several existing receivers. Prior to
the plug-in of this decoder, the receiver is completely operative
on two frequencies; namely, the first carrier frequency and the
second or modulation frequency. The test point jack is a valid test
point so that a serviceman in the field may readily check for
proper carrier frequency and proper modulation frequency. It is
recognized that many servicemen in the field will not have complete
laboratory test equipment, and in fact, may have only a small DC
voltmeter. Accordingly, the test point 238 has been selected with
this in mind. To test the proper operation of the receiver 211 in
the field, the serviceman merely connects a DC voltmeter from the
test point center conductor 238 to ground 239 or 242. First, the
modulation frequency is tuned considerably away from the proper
point by moving the adjustable core slug 232. Next, the variable
capacitor in the tank circuit 216 is adjusted to get a maximum
reading on the voltmeter. This will be because the
super-regenerative circuit 214 is passing a maximum of audio
frequency signals, primarily noise, when the receiver carrier tuned
circuit 216 is correctly tuned to the carrier of the transmitted
signal. Second, the modulation frequency is adjusted by the movable
core slug 232 until the voltmeter gives a minimum reading. The
reason why the voltmeter gives a minimum reading at the proper
modulation frequency is that the proportion of output voltage from
the tuned load 229 relative to the untuned load 230 is a maximum at
the second or modulation frequency. Since the test point center
conductor 238 is effectively measuring the voltage output of the
untuned load 230, this is then a minimum at the time that the
second frequency received signal is a maximum. Accordingly, it will
be seen that the decoder 290 or 370 plugs into an existing test
point jack which is a valid and operable test point for determining
the proper condition of operation of the receiver 211.
This plug-in to the test point jack establishes that the decoder
290 or 370 is operable with a minimum of electrical connections to
the receiver. The plug-in establishes two electrical connections
and additionally provides physical support for the small
lightweight decoder. A third electrical connection by means of the
flexible conductor 301 is easily made to the terminal strip 264 by
merely a screwdriver to fasten the conductor lug to this terminal
261. These minimum electrical connections provide not only an
operating voltage to the decoder but also provide a reference
potential in this case ground 242 or 294.
The above description illustrates that the decoder 290 or 370 has
three different electrical conditions all on the same test point
center conductor 238: (1) the third frequency signal is supplied to
the decoder 290 or 370; (2) the entire reciever 211 is disabled by
a bias voltage applied on this center conductor; and, (3) the
entire receiver 211 is enabled by a changed electrical condition on
this semiconductor 238.
The present invention is also greatly advantageous to the user. It
enables the user to select one simplified system at a lower cost
and later if the location of this remote control receiver is in an
area wherein spurious electrical disturbances are encountered and
the garage door goes up and down undesirably and due to spurious
electrical disturbances, then the user may merely purchase an
easily added decoder 290 or 370 to convert his receiver into one
responsive to three frequencies rather than to only two
frequencies.
Another important objective of the present invention is that it
does not change the effective band width of the receiver in order
to add the third frequency. One reason for this is that the third
frequency remains on the incoming signal for only a short time, for
example, a tenth of a second from time t.sub.0 to t.sub.2 as shown
in FIG. 7. As described above when the third frequency is present,
this acts generally as noise on the untuned load 230 to increase
the signal thereof. This is shown at the portion 349 of the voltage
at the first terminal 241 on FIG. 7. This is an establishment of a
negative bias which means that the output from the tuned load 229
must be in excess of this bias in order to have current passed to
the time delay capacitor 252. However, the existence of this proper
third frequency is received in the decoder which then terminates
the bias; namely, the disabling means, and hence the receiver is
enabled after time t.sub.2 without any change in bandwidth
reception characteristics of the entire receiver 211.
The present disclosure includes that contained in the appended
claims, as well as that of the foregoing description. Although this
invention has been described in its preferred form with a certain
degree of particularity, it is understood that the present
disclosure of the preferred form has been made only by way of
example and that numerous changes in the details of the circuit and
the combination and arrangement of circuit elements may be resorted
to without departing from the spirit and scope of the invention as
hereinafter claimed.
* * * * *