Note: Descriptions are shown in the official language in which they were submitted.
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COMMUNICATION SYSTEM UTILIZING RADIATING TRANSMISSION LINE
This is a divisional of Canadian Patent
Application Serial No. 2,132,036 filed September 14, 1994.
BACKGROUND OF THE INVENTION
This invention relates to radio frequency
communication systems and in particular radio frequency
communication systems utilizing radiating or "leaky"
transmission lines. In a particular embodiment, the present
invention relates to radio frequency communication systems
used for underground communication.
Radiating transmission lines are deliberately
constructed as imperfect transmission lines so that signals
in the inner conductor radiate electromagnetic fields
outwardly from the line as the electrical signals are being
transmitted down the line. The electrical magnetic fields
radiated from the line can be picked up by mobile receivers
located remotely, but in the vicinity, of the line.
Radiating transmission lines can take on several
different forms. One form comprises an open braid coaxial
cable. Other forms comprise coaxial cables having
cylindrical outer sheaths with longitudinal slits to permit
radiation.
Radiating transmission lines are commonly used in
environments where electromagnetic waves, such as radio
frequency waves, do not propagate well. This type of
environment exists in underground mine shafts. For example,
a worker in a mine shaft using a remote mobile audio
station, such as a walkie-talkie, cannot communicate to
other workers who also have remote mobile audio stations,
because the radio waves cannot propagate long distances down
a mine shaft. However, if all of the workers were near a
radiating transmission line such that the radio waves from
the first worker's audio station could be received by the
transmission line, those signals could be transmitted down
the line and radiated near the audio stations of other
workers. In this way, communication in the mine shaft can be
effected.
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In the past, several different types of
communication systems utilizing radiating transmission lines
have been used. However, a common difficulty with all of
the prior art communication systems has been intermodulation
product interference caused by mixing of signals at
different frequencies. Intermodulation interference is
particularly prevalent in communication systems using
radiating transmission lines because the transmitted signals
must be sufficiently "strong" to radiate an appreciable
distance from the line. These "strong" signals mix and the
intermodulation products interfere with the weaker signals
which are received by the transmission line from mobile
stations.
Because of this intermodulation interference,
prior art communication systems have been limited in the
number of signals which can be transmitted down the line at
any one time. Most prior art communication systems did not
provide for multichannel communication where several mobile
stations could communicate simultaneously and independently
on the same transmission line.
In addition, in order to attempt to decrease the
effects of intermodulation interference, prior art systems
had a large spread between the frequencies of different
signals to permit more effective filtering. However, this
method of decreasing interference exhausts the usable
frequencies of the transmission line thereby precluding
additional signals from being transmitted. In particular,
such prior art devices did not permit video signals from
mobile video stations to be simultaneously transmitted on a
single transmission line along with audio signals.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to
at least partially overcome the disadvantages of the prior
art. Also, it is an object of this invention to provide an
alternative type of radio frequency communication system
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which provides for communication of audio and video signals
on a single radiating transmission line. Also, it is an
object of the present invention to provide a radio frequency
communication system having multichannel audio communication.
Furthermore, it is an object of the present invention to
provide transmission of audio signals at frequencies less than
20 MHz apart.
Accordingly, in one of its aspect, this invention
resides in providing a radio frequency communication system
for communicating audio and video signals from and to remote
mobile stations comprising:
a radiating transmission line;
a base station coupled to a first end of the
radiating transmission line;
a first mobile audio station comprising mobile
receiver means for receiving a first audio signal from the
transmission line at a first frequency and mobile transmitter
means for transmitting a second audio signal to the
transmission line at a second frequency;
a mobile video station comprising mobile transmitter
means for transmitting video signals to the transmission line
at a third frequency;
wherein the base station comprises base receiver
means for receiving signals near the second and third
frequencies from the transmission line; and
wherein the base station comprises base transmitter
means for transmitting signals to the transmission line at the
first frequency.
In a further aspect, the invention provides a radio
frequency communication system for communicating audio and
video signals through a radiating transmission line to and
from a first mobile audio station comprising mobile receiver
means for receiving a first audio signal from the transmission
line at a first frequency and mobile transmitter means for
transmitting a second audio signal to the transmission line
at a second frequency, and a mobile video station comprising
mobile transmitter means for transmitting a video signal to the
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transmission line at a third frequency, and a base station
coupled to a first end of the radiating transmission line,
said system having at least one amplification unit, each such
amplification unit being connected to said transmission line
at periodic locations for amplifying the audio signals and
video signals, said amplification unit comprising:
audio amplification means for amplifying said audio
signals;
first and second filtering means connected between
said audio amplification means and said transmission line for
filtering said video signal;
video amplifier means for amplifying said video
signal in a direction toward the base station;
third and fourth filtering means connected between
said video amplifier means and said transmission line for
filtering said first and second audio signals;
wherein said first filtering means, audio
amplification means and second filtering means are connected
to said transmission line in parallel with said third
filtering means, video amplifier means and fourth filtering
means;
wherein the base station comprises base receiver
means for receiving signals near the second and third
frequencies from the transmission line; and
wherein the base station comprises base transmitter
means for transmitting signals to the transmission line at the
first frequency.
In a still further aspect, the present invention
provides an amplification unit for amplifying audio and video
signals for use in a radio frequency communication system for
communicating audio and video signals from and to remote
mobile stations, said system having a radiating transmission
line, a base station coupled to a first end of the radiating
transmission line, a mobile audio station comprising mobile
receiver means for receiving a first audio signal from the
transmission line at a first frequency and mobile transmitter
means for transmitting a second audio signal to the
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transmission line at a second frequency, a mobile video
station comprising mobile transmitter means for transmitting
a video signal to the transmission line at a third frequency,
said amplification unit comprising:
audio amplification means for amplifying said audio
signals;
first and second filtering means connected between
said audio amplification means and said transmission line for
filtering said video signal;
video amplifier means for amplifying said video
signal in a direction toward the base station;
third and fourth filtering means connected between
said video amplifier means and said transmission line for
filtering said first and second audio signals;
wherein said first filtering means, audio
amplification means and second filtering means are connected
to said transmission line in parallel with said third
filtering means, video amplifier means and fourth filtering
means;
wherein the base station comprises base receiver
means for receiving signals near the second and third
frequencies from the transmission line; and
wherein the base station comprises base transmitter
means for transmitting signals to the transmission line at the
first frequency.
In a further aspect, the present invention resides
in providing a radio frequency communication system for
communicating audio signals between remote mobile audio
stations and for communicating video signals from a remote
mobile video station to a base station comprising:
a radiating transmission line having one end coupled
to said base station;
at least one amplification means connected to the
radiating transmission line for amplifying said audio and
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video signals;
wherein each of said mobile audio stations receives
audio signals at different frequencies near a first
frequency and transmits audio signals at different
frequencies near a second frequency;
wherein each of said mobile video station transmits
video signals at a third frequency;
wherein the base station comprises base receiver
means for receiving the audio and video signals from the
transmission line; and
wherein the base station comprises base transmitter
means for re-transmitting audio signals received by the base
receiving means to the transmission line at the first
frequency.
In a still further aspect, the present invention
relates to a radio frequency communication system wherein
the first and second amplifier means utilize transistor
means operating in the linear region to amplify the signals.
Further aspects of the invention reside in
providing an improved communication system having
multichannel audio and data communication. In this way, a
radio frequency communication system can provide for several
independent audio communications between remotely located
mobile audio stations and data communication to remotely
control underground mining equipment by utilizing remotely
located video stations to visually monitor the equipment.
Further aspects of the invention will become
apparent upon reading the following detailed description and
the drawings which illustrate the invention and preferred
embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, which illustrate embodiments of
the invention:
Figure 1 shows one embodiment of a radio frequency
communication system according to the present invention;
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Figure 2 is a block diagram showing the components
of an amplification unit used in a radio frequency
communication system according to the present invention;
Figure 3 is a block diagram showing the components
of a first amplification module used for amplifying audio
signals along the radiating transmission line in a direction
away from the base station;
Figure 4 is a block diagram showing the components
of a second amplification module for amplifying audio
signals along the transmission line in a direction towards
the base station;
Figure 5 is a block diagram showing a video
amplifier module for amplifying video signals along the
transmission line in a direction towards the base station;
Figure 6 is an electrical schematic diagram of the
amplification unit according to a preferred embodiment of
the present invention;
Figure 7 is an electrical schematic diagram of the
first amplification module according to a preferred
embodiment of the present invention;
Figure 8 is an electrical schematic diagram of the
second amplification module according to a preferred
embodiment of the present invention; and
Figure 9 is an electrical schematic diagram of the
video amplifier module according to a preferred embodiment
of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
OF THE INVENTION
As shown in Figure 1, one embodiment of the
present invention comprises a radio frequency communication
system, shown generally as 10. The communication system 10
comprises a radiating transmission line 12 used for
communicating audio signals As and video signals Vs from
remote mobile audio and video stations 14, 20. It is
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understood that several such remote mobile audio stations 14
can be located near the radiating transmission line 12.
For the purposes of the present description, it
shall be assumed that the radio frequency communication
system 10 is installed in an underground mine such that a
substantial part of the radiating transmission line 12 is
located below ground. For example it will be assumed that
the vertical extension of the radiating transmission line 12
goes down a mine shaft and that each horizontal extension of
the line 12 goes down a different level of the mine.
However, it is understood that the system 10 could be used
in any environment where radio waves do not propagate well.
The radiating transmission line 12 is of the type
as discussed above wherein electromagnetic signals are both
transmitted and radiated from the transmission line 12. In
this way, remote mobile stations, such as remote mobile
audio stations 14 and video stations 20, can transmit and/or
receive radio frequency electromagnetic transmissions to
and/or from the radiating transmission line 12.
Each mobile audio station 14 has a receiver 16 for
receiving a first audio signal Asl at a first frequency F1
and a mobile transmitter 18 for transmitting a second audio
signal As2 to the transmission line 12 at a second frequency
F2. Accordingly, the audio signals As comprise the first
audio signals As2 which travel from the mine to the surface
and the second audio signals Asl which travel from the
surface into the mine. The audio signals convey audio
information but, in one embodiment, can also convey narrow
band computer data. It is apparent that the first frequency
F1 should be different from the second frequency F2.
The system 10 further comprises a remote mobile
video station 20 having a mobile transmitter 22 for
transmitting video signals Vs to the transmission line 12 at
a third frequency F3. The remote mobile video station 20
can be any type of portable video camera having a built in
transmitter for transmitting the video signals at a
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frequency. The video signals convey video information such
as images sensed by the remote mobile video station 20.
One end of the transmission line 12 is coupled to
a base station 24. It does not matter which end of the
transmission 12 is coupled to the base station 24 as long as
all of the amplification units 30 are oriented to amplify
the first and second audio signals Asl, As2 and the video
signals Vs in the appropriate direction. However, in the
embodiment where the communication system 10 is used in a
mine, such that a substantial part of the line 12 is located
below ground, it is preferable that the base station 24 is
located above ground.
As shown in Figure 1, the transmission line 12 is
preferably coupled to the base station 24 by electrically
connecting the line 12 to a part of the station 24. As
shown in Figure 1, this is preferably done by connecting the
line 12 to a header unit 29 which can receive the
transmission line 12 and separate the first and second audio
Asl, As2 and the video signals Vs.
The base station 24 further comprises a base
receiver 26 and a base transmitter 28. It is understood
that the base receiver and transmitter 26, 28 can be
directly coupled to the line 12 or can be indirectly coupled
to the line 12 by means of the header unit 29 as shown in
Figure 1.
The base receiver 26 receives signals from the
transmission line 12 at the second and third frequencies F2,
F3. The base transmitter 28 can transmit signals to the
transmission line at the first frequency F1. In this way,
the second audio signal As2 can be received by the base
receiver 26 and re-transmitted by the base transmitter 28 at
the first frequency F1. This allows the second audio
signals As2, which are transmitted by remote audio stations
14 to the base receiver 26, to be re-transmitted by the base
transmitter 28 at the first frequency F1 and received by the
receivers 16 of all other remote mobile audio stations 14
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set at the first frequency F1. In this way, one mobile
audio station 14 can communicate to all other mobile audio
stations 14 which are set at the first frequency F1.
Furthermore, the base receiver 26 also receives
the video signal Vs at the third frequency F3. This video
signal can be reproduced on a video monitor or can be re-
transmitted above the surface to other locations.
In a further embodiment, the system 10 comprises a
base radio 27 located near the base station 24. The base
radio 27 can receive or transmit audio signals to the base
station 24 which are then received and re-transmitted down
the line 12 by the transmitter means 28. The base radio 27
generally comprises a microphone into which persons on the
surface can speak into. The audio signals transmitted by
the base radio 27 are then modulated and transmitted at the
first frequency F1 down the line 12 by the base transmitter
28. In this way, persons located on the surface of the mine
can communicate with persons located underground. In a
further embodiment, the base radio 27 can receive audio
signals from other radios located on the surface, or be
connected to telephone lines located on the surface, such
that persons distant from the base station 24 can
communicate with persons in the mine.
Standard radiating transmission lines 12 can
usually radiate and transmit electromagnetic signals in a
frequency range of 20 MHz to 500 MHz. However, in a
preferred embodiment of the present invention, the first and
second frequencies F1, F2 are above 100 MHz and preferably
between 100 and 200 MHz. Furthermore, it is preferable that
the third frequency F3 is below 100 MHz. This separation of
the frequencies allows for easier separation and
amplification of the first and second audio signals Asl, As2
and the video signals Vs.
In, a further preferred embodiment, the first
frequency F1 is about 155 MHz and the second frequency F2 is
about 170 MHz. In this way, both the first and second audio
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signals Asi, As2 are in the VHS band. In this preferred
embodiment it is also preferable that the third frequency F3
be between about 55 MHz and 68 MHz. It has been found that
these frequencies interface well with standard walkie-
talkies and transmitting portable video cameras.
The system 10 in a further embodiment comprises
branching units 90 which permit the transmission line 12 to
be "branched-off" in two different directions. In the case
of a mine, the branching units 90 allow the transmission
line 12 to extend down a shaft and horizontally along
different levels.
Furthermore, the system 10 preferably comprises
termination units 13 which are located at the end of each
branch of the radiating transmission line 12. T:~e
termination units 13 comprise impedance-matching modules in
order to terminate the transmission line 12 with a minimum
amount of reflected signal.
An important element of one embodiment of the
present invention is the amplification units 30. As seen in
Figure l, the amplification units 30 are connected to the
transmission line 12 at periodic locations. The
amplification units 30 are used to amplify the audio and
video signals As, Vs. Generally, one amplification unit 30
is placed along the line 12 at every 350m. However,
amplification units 30 may be required more frequently if
other elements, such as branching units 90 interrupt the
line 12 thereby increasing the signal loss.
The components of an amplification unit 30 are
shown in more detail in Figure 2. As can be seen, the
radiating transmission line 12 enters and leaves a typical
amplification unit 30 at either end. It is preferable to
have impedance-matching modules 36 insulating the
transmission line 12 from the components of the
amplification unit 30.
The amplification unit 30 comprises an audio
amplification module 40 and a video amplifier module 70.
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The audio amplification module 40 acts as an audio
amplification means for amplifying the audio signals As.
The video amplifier module 70 acts as a video amplification
means for amplifying the video signals Vs. As can be seen
from Figure 2, the video amplifier module 70 is connected to
the transmission line 12 in parallel with the audio
amplification module 40.
As also shown in Figure 2, there are first and
second filtering means, shown as high pass filters 32A, 32B,
connected between the audio amplification module 40 and the
transmission line 12 on either side of the audio
amplification module 40. The high pass filters 32A, 32B
filter the video signal Vs from the audio amplification
module 40.
It is understood that any type of filtering means
could be used in order to remove the video signal Vs.
However, as stated above, it is preferable that the
frequencies used for the first and second audio signals Asl,
As2, are at higher frequencies than the frequency used for
the video signal Vs. Accordingly, in a preferred
embodiment, as shown in Figure 2, the first and second
filtering means for filtering video signals comprise high
pass filters 32A, 32B for filtering signals below about 100
MH2.
Likewise, there are third and fourth filtering
means, shown in Figure 2 as low pass filters 34A and 34B,
connected between the video amplifier module 70 and the
transmission line 12 on either side of the video amplifier
module 70. As was the case with high pass filters 32A, 32H,
the third and fourth filtering means could be any type of
filtering means to filter out the audio signal As from the
video amplifier module 70. However, since in a preferred
embodiment the video signal Vs is at a lower frequency than
the audio signals As, the third and fourth filtering means
preferably comprise low pass filters for filtering signals
above about 100 141iz .
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In a preferred embodiment, the video signal Vs is
unidirectional in that it is only carried along the
radiating transmission line 12 towards the base station
24. Accordingly, as shown in Figure 2, the video amplifier
module 70 amplifies the video signal Vs in a direction
towards the base station 24 as indicated by the arrow
located above the module 70.
As stated above, the audio signals As comprise a
first audio signal Asl, which is transmitted from the base
station 24 further into the tunnel, and a second audio
signal As2, which comprises signals traveling from the
tunnel to the base station 24. To accommodate this bi-
directional amplification, the audio amplification module 40
comprises a first amplification module 50 for amplifying the
first audio signal Asl in a direction towards the tunnel and
away from the base station 24 and a second amplification
module 60 for amplifying the second audio signal As2 in a
direction towards the base station 24. The first
amplification module 50 and the second amplification module
60 are shown in more detail in Figures 3 and 4 respectively.
As shown in Figure 3, the first amplification
module 50 comprises a first amplifier 54 for amplifying the
first audio signal Asl in the direction shown by the
arrow. The first amplification module 50 further comprises
fifth and sixth filtering means, shown in Figure 3 as band
pass filters 52A, 528, for passing signals at frequencies
near the first frequency F1 only and filtering out signals
that are not at frequencies near the first frequency F1.
The band pass filters 52A, 528, are connected on either side
of the first amplifier 54 and, if Figure 3 is superimposed
on Figure 2, it is apparent that the band pass filters 52A,
52B are connected between the first amplifier 54 and the
high pass filters 32A, 32B, respectively.
The first amplification module 50 further
comprises a limiting circuit 58 for attenuating the signal
entering the first amplifier 54. The limiting circuit 58 is
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generally required to limit the first audio signal Asl. The
first audio signal Asi must be sufficiently strong so that
it can radiate from the transmission line 12, however, if
the first audio signal Asi is too strong, then the signal
Asi will not be properly amplified by the first amplifier
54. The limiting circuit 58 ensures that the first audio
signal Asl does not exceed the amplification specifications
of the first amplifier 54.
In a preferred embodiment, the first amplifier 54
utilizes a transistor 51 for amplifying the first audio
signal Asl. Because the transistor 51 has an impedance
which is generally lower than the impedance of the other
components in the system l0, it is preferable to have
impedance-matching modules 56 located on either side of the
first amplifier 54 to match the impedance of the first
amplifier 54 with the other components in the system 10.
The second amplification module 60 is shown in
Figure 4. As with the first amplification module 50, second
amplification module 60 comprises a second amplifier 64 for
amplifying the second audio signal As2 in a direction
towards the base station 24, as shown by the arrow in Figure
4.
The second amplification module 60 also comprises
seventh and eighth filtering means, shown in Figure 4 as
band pass filters 62A, 62B for passing signals at
frequencies near the second frequency F2 and for filtering
out signals at frequencies not near the second frequency
F2. The band pass filters 62A, 62B are connected between
the second amplifier 64 and the high band pass filters 32A,
32B respectively. It is understood that the band pass
filters 62A, 62B can take on any form which can accomplish
this result. In a further preferred embodiment, the band
pass filters 62A, 628 comprise shorts to ground for signals
at specific frequencies, such as the first frequency F1.
This is often preferable because the first signal Asi at the
first frequency F1 is much stronger.
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Furthermore, if Figures 2, 3 and 4 are combined,
it is apparent that the second amplification module 60 is
connected between the high pass filters 32A, 32B in parallel
with the first amplification module 50.
As with the first amplifier 54, the second
amplifier 64, in a preferred embodiment, utilizes a
transistor 61 for amplifying the second audio signal As2.
Furthermore, the second amplification module 60 comprises
impedance-matching modules 66 for performing a similar
function as impedance-matching modules 56 in Figure 3.
As the second audio signal As2 is generally
received by the radiating transmission line 12 from remote
mobile audio stations 14, the second audio signal As2 is
generally not very strong in the transmission line 12.
Accordingly, a limiting circuit 58 is generally not required
in the second amplification module 60.
Figure 5 shows the video amplification module 70
in more detail. The video amplification module 70 comprises
a video amplifier 74 for amplifying the video signal Vs in a
direction towards the base station 24, as shown by the arrow
in Figure 5.
The video amplification module preferably
comprises a band pass filter 72 for passing signals at
frequencies near the third frequency F3 and for filtering
out signals at frequencies not near the third frequency
F3. The band pass filter 72 is connected between the video
amplifier 74 and the low pass filter 34B. It is understood
that the band pass filter 72 can take on any form which can
accomplish this result. In a further preferred embodiment,
the band pass filter 72 comprises circuits to ground signals
at specific frequencies, such as the first frequency F1.
This is often preferable because the first signal Asi at the
first frequency F1 is much stronger.
As with the first and second amplification modules
50 and 60, the video amplification module preferably
comprises impedance matching modules 76 for performing a
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similar function as impedance modules 56 and 66 in Figures 3
and 4 respectively. Furthermore, in a preferred embodiment,
the video amplifier 74 utilizes a transistor 71 for
amplifying the video signal Vs.
Figure 6 shows an electrical schematic diagram of
the amplification unit 30 according to a preferred
embodiment of the present invention. A preferred
arrangement of electrical components is shown in Figure 6
for forming high pass filters 32A, 32B and low pass filters
34A, 34B. However, it is understood that any combination of
capacitors, inductors and resistors could be used to form
high pass filters 32A, 32B and low pass filters 34A, 34B.
It is apparent that the relative values of these components
would depend on the frequencies used and the precise
operating characteristics of the transistors 51, 61.
Transformers T1, T2 act as the impedance-matching
modules 36 in order to match the impedance of the
amplification unit 30 with that of the remainder of the
communication system 10. Connectors Jl, J2 and J3 are used
for connecting the first amplification module 50, video
amplifier module 70 and second amplification module 60,
respectively.
Wave guides W1, W2, W3 and W4 located on either
side of connectors Jl and J3 are present to decrease noise
in a manner known to persons skilled in the art. The length
of wave guides W1, W2, W3 and W4 is preferably about a
quarter of the wave length of the audio signals As.
Inductors L11, L12, L13, L14 and L15 are used to
provide DC power from the radiating transmission line to the
active components of the communication system 10, such as
the transistors 51, 61.
Figure 7 shows an electrical schematic diagram of
the first audio communication module 50 according to a
preferred embodiment of the present invention. Connector J1
shown in Figure 7 connects the first amplification module 50
to the connector J1 located on the amplification unit 30 as
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shown in Figure 6. Unit blocks A1 and A2 shown on either
side of connector J1 are filter assemblies and correspond to
band pass filters 52A, 52B as shown in Figure 3.
Transformers T1 and T2 correspond to the impedance-matching
modules 56 shown in Figure 3.
Limiting circuit 58 comprises transistors Q2 and
Q3, and in association with the other electrical components
as shown in Figure 7, can limit the first audio signal Asi
entering the first amplifier 54. Transistor Q1 corresponds
to transistor 51 in Figure 3 and, in combination with the
associated electrical components as shown in Figure 7, form
the first amplifier 54.
It is understood that the circuits shown in Figure
7 are preferred embodiments of the limiting circuit 58 and
first amplifier 54 and that other specific circuits could be
used without derogating from the scope of the present
invention. It is also apparent that the actual values of
the inductors, resistors and capacitors shown in Figure 7
are dependent on the frequencies of the signals Asl, As2 and
the characteristics of transistors Q1, Q2 and Q3.
Figure 8 shows the electrical schematic diagram of
the second amplifier module 60 according to a preferred
embodiment of the present invention. Connector J1 in Figure
8 connects with connector J3 in Figure 6.
Blocks Al and A2 in Figure 8 are band pass filters
for passing signals having frequencies near the second
frequency F2 and filtering signals not having frequencies
near frequency F2 and in particular filtering signals having
frequencies near frequency F1. Blocks A1 and A2 correspond
to band pass filters 62A, 628 in Figure 4. Transformers T1
and T2 act as impedance-matching modules, shown in Figure 4
as 66, to match the impedance of the transistor Q1 in Figure
8 to the impedance of the communication system 10.
Transistor Q1 performs the amplification of the
second signal As2 in a direction towards the base station 24
and corresponds to transistor 61 in Figure 4. The
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capacitors, inductors and resistors connected to transistor
Q1 maintain transistor Q1 in the linear region with an
appropriate gain. The values for these electrical
components can be determined by persons skilled in the art
to effect the proper gain for signals having frequencies
near the second frequency F2. Transistor Q1 and the
associated electrical components form part of the second
amplifier, shown in Figure 4 as 64.
Figure 9 shows an electrical schematic diagram of
a video amplifier module 70 corresponding to a preferred
embodiment of the invention. Connector J1 in Figure 9
connects with connector J2 in Figure 6.
Band pass filter 72 as shown in Figure 9 as
comprising a series of inductors, capacitors and resistors
for passing the amplified video signal Vs from the video
amplifier 74 and for filtering out signals having
frequencies not near the third frequency F3. Transformers
T1 and T2 act as impedance matching modules, shown in Figure
as 76, to match the impedance of the transistor T1 in
Figure 9 to the impedance of the communication system 10.
As shown in Figure 9, the video amplification
module 70 comprises a video amplifier 74 which utilizes
transistor Q1 to perform the amplification of the video
signal Vs in a direction towards the base station 24. The
transistor Q1 in Figure 9 corresponds to transistor 71 in
Figure 5. The capacitors, conductors and resistors
connected to transistor Q1 in Figure 9 maintain transistor
Q1 in the linear region and within an appropriate gain. The
values of these electrical components can be determined by
persons skilled in the art to effect the proper gain for
signals having frequencies in the third frequency F3.
In a further preferred embodiment of the present
invention, the communication system l0 comprises several
mobile audio stations 14. Each audio station 14 has a
mobile transmitter 18 for transmitting signals at separate
frequencies near the second frequency F2. Furthermore, each
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mobile audio station has a mobile receiver 16 for receiving
signals at separate frequencies near the first frequency
F1.
In this embodiment, several mobile audio stations
14 can transmit and receive audio signals As simultaneously
to and from the transmission line 12. In this way, several
different audio signals As can be transmitted and received
from all of the mobile audio units 14. In other words, this
preferred communication system 10 provides "multichannel"
communication between different mobile audio stations 14.
In this embodiment, the base receiver can
independently separate and receive each of these signals at
frequencies near the second frequency F2. These signals are
then re-transmitted at frequencies near the first frequency
F1, by the base transmitter 28.
Multichannel communication can be effected by
operating transistors 51, 61, which form part of first and
second amplifiers 54, 64, in the linear regions. The
circuit diagrams shown in Figures 7 and 8 are designed to
operate transistors 51, 61 (shown in Figures 7 and 8 as Q1)
in the linear class A region.
. It is understood that any spread of the
frequencies near the first and second frequencies F1, F2,
can be used as long as no frequencies near the first
frequency F1 overlap with frequencies near the second
frequency F2. However, it is preferable if the spread of
all of the signals near the first and second frequencies F1
and F2 be about 1 I~Iz .
Having a 1 l~iz spread permits about 10 to 20
channels to be transmitted on the radiating transmission
line 12 at any one time, whether or not a separate video
signal Vs is also being transmitted from a mobile video
station 20. The band width for each audio signal channel
can be about 6 IQiz, 12.5 IQ~iz, 25 KHz or 35 KHz, or any
combination thereof. Furthermore, having all of the
frequencies transmitted and received from the audio stations
CA 02282891 1999-09-21
18 -
14 within 1 MHz of the second and first frequencies F2, F1,
respectively, ensures that transistors 51, 61 will operate
in the linear region for all of the frequencies. In
addition, having a spread of about 1 MHz allows the band
pass filters, shown in Figures 3 and 4 as 52A, 52B, 62A,
62B, to be more precise thereby filtering out more noise.
It is understood that the audio signals As
transmitted on each of the channels, can also consist of
computer data much as a modem can transmit computer data
over telephone lines. In this way, communication system 10
uses mobile data stations 100 for receiving and sending
computer data along the transmission line 12. The data can
be transmitted as digital or analog data points.
Accordingly, the communication system 10 of the
present invention permits a data signal to be sent and
received from the base station 24 located above ground.
This data signal can be used to control machinery as well as
ventilation and other environmental controls in the mine.
Furthermore, the operation of machinery under ground can be
monitored by persons above ground by use of the mobile video
station 20. In this way, the present communication system
1o can be used to monitor and control underground mining
equipment remotely from the surface with fewer workers
located below ground. Therefore, the communication system
according to the present invention provides for mines to
be operated much more cheaply and safely.
Furthermore, the present system can increase the
level of safety in the mine. For example, the data signals
can be used to periodically or continuously locate the
personnel in the mine. In this way, should an accident
occur in a mine, there will be a record of the most recent
number of personnel in the mine, and their location in the
mine, to assist any rescue operations which are launched.
Furthermore, more dangerous mining operations, such as
triggering explosives, can be done remotely and with the
maximum number of personnel outside of the mine by use of a
CA 02282891 1999-09-21
- 19 -
data signal.
It will be understood that, although various
features of the invention have been described with respect
to one or another of the embodiments of the invention, the
various features and embodiments of the invention may be
combined or used in conjunction with other features and
embodiments of the invention as described and illustrated
herein.
Although this disclosure has described and
illustrated certain preferred embodiments of the invention,
it is to be understood that the invention is not restricted
to these particular embodiments. Rather, the invention
includes all embodiments which are functional or mechanical
equivalents of the specific embodiments and features that
have been described and illustrated herein.
