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TECHNICAL FIELD OF THE INVENTION
The present invention relates in general to video systems, and more
particularly relates to video cameras, displays and transmission apparatus
for transmitting video signals under covert conditions.
BACKGROUND OF THE INVENTION
There are many situations in which it is desirable to obtain a closeup view
of a situation or event from a remote location. In military application,
this is highly desirable for the safety of combat troops. Other situations
occurring in a civilian setting require the same type of safety
requirements.
The aiming and firing of a gun emplacement situated in the combat zone may
be controlled remotely by personnel not located at the combat zone. In
this situation, a video camera can be located at the gun site to obtain a
closeup view of defensive positions, and at the same time transmit video
signals of the combat zone scene to remotely located troops who can
control the aiming of the gun. In another situation, it would be highly
desirable to mount a video camera to the rifle of an infantryman, and a
video display to his helmet, thereby allowing the soldier to aim the rifle
without engaging the weapon in the normal aiming position. The infantryman
could even remain in a hidden position and aim the gun through the use of
the video display, all without exposing his body to the enemy.
With regard to the foregoing applications, it is often desirable that the
video transmission from the camera to the remote display remains
unavailable to the enemy so that such information cannot be used to the
enemy's advantage. While elaborate encoding or encryption techniques could
be employed to maintain the video transmission somewhat secret, such
techniques require additional equipment, thereby adding to the weight,
cost and reliability concerns to the system.
Helmet-mounted video display systems have been employed for assisting
combat pilots in maneuvering aircraft and for weapons deployment. In these
systems, control cables are generally connected between the helmet and the
aircraft cockpit so that any movement of the pilot's head results in the
corresponding movement of the weaponry. With this type of arrangement the
video display and helmet are fixed to the aircraft and thus are useless
for ground operations where mobility is important.
From the foregoing, it may be seen that a need has arisen for a field
operated video system which provides for remotely located video camera and
display equipment, as well as transmission capabilities therebetween.
SUMMARY OF THE INVENTION
In accordance with the present invention, a video system with remotely
locatable equipment is disclosed which substantially eliminates or reduces
the problems associated with the prior art techniques.
In accordance with a principal feature of the invention, a weapon-mounted
video camera operates in conjunction with a head-mounted video display,
thereby enabling military personnel to aim the weapon without assuming a
line of sight position with respect to the aiming apparatus of the weapon.
According to various embodiments of the invention, the video camera may be
responsive to visible light, infrared radiation, thermal radiation or
other particular radiation properties of the environment which enable an
accentuated view of the scene or situation.
In accordance with another important feature of the invention, the video
display may operate in conjunction with an image splitter disposed in the
person's line of sight, thereby enabling the person to observe a
superimposed scene of the object within his line of sight, as well as the
object appearing on the video display.
In accordance with a correlary feature of the invention, the head-mounted
video display can be operated in conjunction with night vision apparatus
to provide additional viewing capabilities, as well as used in conjunction
with helmet apparatus which allows the display to be easily removed out of
the person's line of sight vision.
With regard to yet another feature of the invention, the video transmission
between the camera and display equipment can be transmitted through a
physical medium, such as a metallic conductor or a fiber optic bundle, or
by free space radiation. In an embodiment of the invention, a free space
radiation frequency of about 1.39 micrometers (um) permits the
transmission of a video signal for only a short distance before the signal
becomes significantly attenuated, due to atmospheric absorption. In this
manner, the transmission of a video signal is maintained secret or has a
low probability of intercept within the immediate area of activity.
Still another important feature of the invention involves the network
distribution of the transmitted video signals such that an image from a
single video camera can be observed by plural persons having appropriate
display equipment. Also, video signal networking is disclosed for enabling
a single person to selectively view the image generated by plural remotely
located video cameras.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other features and advantages will be apparent from the
following and more particular description of the preferred embodiments of
the invention, as illustrated in the accompanying drawings in which like
reference characters refer to the same parts throughout the different
views. Referring to the drawings:
FIG. 1 is a block diagram of the video camera and display system according
to the invention;
FIG. 2 illustrates a typical application of a rifle-mounted video camera
operating with a free space transmission of video signals to a
helmet-mounted video display;
FIG. 3 illustrates an alternative embodiment of the invention in which both
the video camera and display are helmet mounted;
FIG. 4 illustrates a vehicle guidance system including an outside mounted
video camera transmitting a video image to the driver concealed within the
vehicle;
FIG. 5 illustrates an application of the invention utilizing an
air-to-ground free space transmission of an image, and a ground-to-ground
physical transmission medium;
FIG. 6 is an isometric view of one embodiment of a helmet-mounted image
display system employing holographic display techniques;
FIG. 7 is an isometric view of a headgear-mounted image display system
employing a beam splitter which can swing out of the user's line of sight;
FIG. 8 illustrates helmet-mounted video display apparatus for allowing
split image viewing of the video image as well as the object in the
person's line of sight;
FIG. 9 illustrates head gear incorporating both a video display and night
vision equipment;
FIG. 10 is an oblique view of a video display, hingeably mounted to a
headgear;
FIG. 11 is a side view of the headgear mounted video display of FIG. 10;
FIG. 12 illustrates night vision equipment mounted to a helmet, and coupled
by a physical transmission medium to a display;
FIG. 13 is a cross-sectional view of an armored military vehicle having
omnidirectional image transmitting capabilities within the vehicle;
FIG. 14 depicts in block diagram form the major components of the video
display equipment;
FIG. 15 illustrates alternative switchable transmission paths between a
video camera and a remotely located video display according to the
invention;
FIG. 16 graphically depicts the atmospheric absorption characteristics with
respect to transmission carrier wavelength;
FIG. 17 shows a networking scheme used between a single video camera and a
plurality of remotely located display units;
FIG. 18 shows another networking scheme used in selectively viewing one of
a plurality of images generated by plural remotely located video cameras;
FIG. 19 illustrates a helmet-mounted switching arrangement for selective
presentation of an image from one of the plural cameras shown in FIG. 18;
FIG. 20 illustrates a vehicle guidance system for use in connection with
low probability of intercept of nocturnal activities; and
FIG. 21 illustrates a nonvisible light transmitter for use in conjunction
with the system of FIG. 20.
DETAILED DESCRIPTION OF THE INVENTION
The principles and concepts of the invention are best understood by
referring first to FIG. 1 of the drawings. The video system according to
the invention is shown generally as reference character 10, and includes
an imager shown as a video camera section 12 employed separate and apart
from an imager shown as a video display 14. With regard to the example of
FIG. 1, the object to be viewed is shown as an armored vehicle 16, and the
image thereof provided by the video display equipment 14 is shown as
reference character 18.
More particularly, the video camera 12 includes an optical imaging system
20 coupled to a video processing sensor system 22 which, in turn, is
coupled to a video transmitter system 24. Optionally provided integral
with the camera is a video display unit 26. The optical imaging system 20
comprises a lens and filter assembly for providing a clear and accurate
image of the vehicle 16 to the processing system 22. The optical imaging
system 20 may be of the conventional type which provides optical
correction and adjustment of objects characterized by visible light
radiation. The system 20 may also be of the type which processes infrared
characterizations of the object. A resultant image of the particular type
of characterization is coupled to the video processing system 22. The
optical imaging system 20 may also be of the type which is responsive to
thermal radiation which is characteristic of the object, or include night
vision capabilities. The noted types of imaging systems are readily
available, and adaptable to the video camera 12 according to the
invention.
Once a visible image of the object 16 is created by the optical imaging
system 20, such image is presented to the video processing system 22 for
converting the optical image into a standard electrical video format.
While not limited to the raster/scan type of video system, such a
technique is well known in the art and can thus be easily adapted to the
present invention. In essence, the video processing system 22 produces an
electrical signal representation of the optical image and couples the
electrical signals to the video transmitter 24. The electrical video
signal is also coupled to the optional video display 26 which is integral
to the camera 12. The optional video display system 26 converts the
electrical signals of the object 16 back into an optical characterization
thereof so as to be observable by a person. With the provision of the
integral video display unit 26, a viewer can initially set up the camera
12 and use such display 26 for aligning the camera 12 with respect to a
particular scene. This can be done without operating the video transmitter
24, and thus no signal is radiated in the immediate area of the camera 12.
The video transmitter system 24 provides the transmitting equipment to
produce a video signal appropriate for transmitting over a desired medium.
In the depiction of FIG. 1, the transmitted signal 27 is shown transmitted
in a free-space medium. That is, the video signal is transmitted through
the atmosphere without a physical or hardware connection between the
camera 12 and the remote video display 14. The video transmitter system 24
can be of the type adapted for modulating the video signal onto an
electrical carrier of a desired frequency, or onto a carrier in a
frequency band which is in the visible light range, or above such range.
In those situations where the camera 12 and video display 14 are mounted
adjacently on a combat helmet, the video transmitter system 24 may be
dispensed with entirely, whereupon the electrical video signal is coupled
directly to the video display 14 by a coaxial cable, or other suitable
conductor. In other applications where the video camera 12 is located in
the immediate area of the video display 14, and where the transmission of
the video signal is to remain absolutely secure, the transmission medium
may include a fiber optic bundle. In this event, the video transmitter
system 24 would include an electrical to optical converter.
The remotely located video display 14 is provided with a video receiver
system 28 for receiving the video signal transmitted by the camera 12. The
video receiver system 28 is coupled to a video monitor system and display
30 which regenerates an optical image of the object 16 from the electrical
characterization of such image. An optical viewer 32 comprises a lens
arrangement for providing optical correction, magnification or other
adjustment for presentment of the image to the viewer 34. As noted in FIG.
1, the image 18 can be observed either from the remotely located display
14 or the optional integral video display 26, if provided.
Referring now to FIG. 2, there is shown an application of the invention
which is envisioned to be advantageous for combat personnel. A soldier 36
is equipped with a rifle 38 to which a video camera 12 is mounted. The
video camera 12 is fastened to the rear portion of the rifle barrel and
above the sight mechanism so as to provide an unobscured aim of the rifle,
should the soldier use the weapon in a conventional manner. The video
camera 12 is shown equipped with an infrared or thermal detector,
comprising the optical imaging system 20. With this arrangement, objects
can be identified by the nature and extent of the heat emitted, and
recognized by the solder 36 in the video display 14 by the solder 36.
In accordance with conventional combat protection gear, the soldier 36 is
provided with a helmet 40. Mounted to the helmet 40 is the video display
equipment 14 which receives free space video transmissions from the camera
12 to thereby provide the solder 36 with an infrared (IR) generated image
without having to continuously look through a rifle-mounted IR equipment.
The video display 14 is shown fastened to the helmet by a strap 42, which
strap is fixed to the helmet by rivets (not shown) or other suitable
means. The video display 14 is also depicted receiving free-space
transmissions of the camera-generated video image. The solder 36 is
outfitted with a screen 44, goggles or other similar eyewear on which the
image of the object can be holographically presented. The image 46 is
shown removed and disposed in a frame 48 in the manner presented by the
display 14 to the soldier 36. The image 46 can also be superimposed on a
reticle 50 which provides the soldier 36 information such as range, size,
elevation, etc. Holographic projection systems are well-known in the art
and are readily adaptable for use in the noted example.
The application of the invention shown in FIG. 2 provides many advantages
to the combat solder. For example, a gunner in an armored vehicle equipped
with the camera 12 and the helmet-mounted display 14 of the invention can
reload or carry on other operations while watching a target through the
head-mounted display. As an additional advantage, the invention may
significantly reduce the time to thus aim and fire the weapon. In the case
of a foot soldier equipped with a camera-mounted rifle 38 and a
helmet-mounted video display 14, the soldier can aim the weapon from a
full defilade position and shoot from the hip. With the provision of the
head-mounted video display 14, a solder can also wear a gas mask without
impairing or making more difficult the aiming of the weapon 38. This is a
result of a soldier not having to rest the gun on his shoulder for aiming
through the conventional sights. Rather, he need only concentrate on the
head-mounted video display 14. Not only does the invention eliminate eye
and neck strain should a prolonged conventional aiming position be
required, but is also eliminates the motion or agitation of the rifle
which has the effect of losing aim on the target. This is particularly
important, for example, in an armored vehicle where a conventional control
panel-mounted video display moves to the same extent as the vehicle
according to the roughness of the terrain. Hence, it becomes very
difficult for the observer to concentrate on the wiggling video image. In
accordance with an important feature of the invention, the head-mounted
feature of the video display system secures the display, and thus the
video image of the object with respect to the observer's eyes.
FIG. 3 illustrates another embodiment of the invention wherein both the
video camera 12 and the display 14 are helmet-mounted. The video camera 12
shown in FIG. 3 is provided with a thermal or infrared detector 52. Again,
a video image of the thermal representation of the object is transmitted
by free space 54 to the video display 14. The video camera 12 can be
mounted to the helmet 40 by any suitable securing means. The image 56
displayed to the soldier 36 is shown as a motorized gun emplacement,
thereby yielding an indication of the thermal characteristics of the motor
and the personnel around the target.
FIG. 4 illustrates an additional application of the invention. A video
camera 57 is mounted exterior to an armored vehicle 58 for providing a
view of the terrain in front of the vehicle 58. The video image of the
object is again transmitted by free space techniques to a receiver 59. The
receiver 59 may be coupled by a coax or fiber optic line to a video
display (not shown) mounted to the helmet of the tank driver. The driver
(not shown) can then assume other duties within the vehicle without having
to constantly look through a periscope, peephole or at a dash-mounted CRT
display.
FIG. 5 depicts another application of the invention. An aircraft 60 can fly
into a position of surveillance of a target 61 and relay an image thereof
to ground personnel 62. Based upon the image displayed on the helmet
apparatus 63 of the ground personnel 62, appropriate gun control
parameters can be keyed into a remote fire control unit 64 to aim the
vehicle mounted weapon 65 at the target 61. The remote control 64 is
connected to the vehicle mounted weapon 65 by a secure fiber optic fire
control link 66.
FIGS. 6 and 7 illustrates other helmet-mounted video display arrangements
where the corresponding parts thereof are identified by the same reference
characters as shown in FIGS. 2 and 3. In this arrangement, the display
screen 44 is formed integral with the video display 14, and the
combination is pivotally mounted to the helmet 40 by a screw 67. The
display screen 44 and the display unit 14 can be rotated upwardly out of
the line of sight of the soldier. Display screen 44 is transparent so the
soldier may see through the screen when he is not focussing on images on
the screen. The display unit 14 houses the projection and display optics
as well as the video link receiver and power supply. A video receiver fish
eye objective lens and detector assembly 68 receive the free space optical
radiation of an image transmitted from a remote location. The remote image
transmitter may be a gun-, vehicle- or aircraft-mounted, or mounted to a
tripod.
FIG. 7 illustrates a headgear 69 equipped with the video display 14. The
headgear 69 is mounted to the user's head by a strap 70. The helmet 40
fits over the headgear strap 70 and provides conventional protection. In
this embodiment, a beamsplitter video screen 71 provides the medium upon
which the image is protected by the display unit 14. The beamsplitter
screen 71 is hinged 72 so that it can be removed from the soldier's line
of sight. A focus and lateral adjustment 73 provides three axis
adjustments to properly focus the projected image in front of the user's
eye. An off-on switch 74 is manually operated to render the electrical
circuits of the display unit 14 operational.
FIGS. 8-11 illustrate various other embodiments of the invention secured to
the head of a soldier. In FIG. 8 a video receiver 75 is mounted to a face
frame 76 which is fastened to the person's head by an adjustable headdress
strap 77. The face frame 76 is molded in the general shape of the facial
features surrounding a person's eyes and nose. A helmet 40 may be worn
over the display headdress, and thus the cranial protection of the person
need not be compromised. The helmet 40 is secured to the head of a person
by a combined chin strap 78 and a depending side strap 79.
The video receiver 75 is secured to the face frame 76 and is thus made
integral therewith so that the video receiver 75 ideally follows the
motions of the observer's head. The video receiver 75 is connected by a
cable 80 to an electrical or optical antenna for receiving transmissions
from a remotely located camera. Provided with the video receiver 75 is an
image viewer or screen 81, such as a vacuum fluorescent display, a cathode
ray tube, an electroluminescent display, or a liquid crystal display. All
such types of displays can be obtained in miniature form suitable for use
as described herein. One type of miniature display particularly suitable
for use is the vacuum fluorescent display described in U.S. Pat. No.
4,081,716, and may be obtainable from ISE Electronic's Corp., ISE, Japan.
This display is approximately 7 mm by 10 mm, operates on only 15 volts and
thus is ideally suited both as to size and weight for use with the
invention.
The optical viewer 81 is optically coupled to the receiver 75 so as to
present an image to the person corrected with respect to focus,
magnification and other appropriate parameters. As noted in FIG. 8, the
optical viewer 81 redirects the image from a horizontally directed image
plane to a vertical image plane adjacent one of the observers's eyes. A
partially reflecting mirror 82 is mounted to the optical viewer 81 at an
angle of about 45 degrees, and is disposed directly under the exit lens 83
of the optical viewer 81. The redirected image of the object is thus
reflected from the mirror 82 and presented for viewing to the observer.
Because the mirror 82 is only partially reflecting, the person can also see
objects that are disposed on the opposite side of the mirror 82. Thus, the
person has available for viewing with one eye superimposed objects, namely
the video image from the display 81, as well as objects in the line of
sight vision of the observer. The reflecting mirror 82 is mounted within a
frame which is pivotally mounted 84 to the optical display 81. The person
can thus swing the reflecting mirror 82 upwardly and out of the line of
sight vision of the eye with which it is aligned. Hence, the person can
observe the surroundings in the event a video display is not desired.
Additionally, a switch 86 is mounted to the face frame 76 for providing
electrical power control of the video receiver 75. The switch 86 is wired
to the video receiver 75 to provide on-off operation. The switch 86 is
mounted at the foremost part of the face frame 76 so as to be readily
accessible for operation by the wearer of the headdress.
FIG. 9 illustrates an adaptation of a video display 88 with night vision
equipment 90 to provide the viewer 92 with alternative image
characterizations of an object. With this arrangement, the video display
88 and the night vision equipment 90 are disposed in the line of sight
division of the respective left and right eye of the observer 92. The face
frame 94 of this embodiment fits flush against the face of the wearer 92,
and includes an outwardly extending shell 96 which houses the video
display 88 and night vision equipment 90. The video display 88 and night
vision equipment 90 are secured within the face frame shell 96 and are
thereby protected. The face frame 94 is secured to the head of the wearer
92 by an adjustable strap 98. With this arrangement, the vision equipment
88 and 90 can only be removed by removing the face frame 94 from the head
of the wearer 92.
The night vision equipment 90 includes a conventional image intensifier
tube 100 which presents an electronic light amplified presentation of the
object, with only very small amounts of light illuminating the object. In
accordance with the conventional night vision equipment, starlight is
sufficient to illuminate a distant object for easy viewing on the backside
of the image intensifier tube 100. The video display 88 has an inherent
narrow field of vision. Thus, objects peripheral to the line of sight
vision, as viewed through the video system, are generally not displayed.
This creates a disorienting affect when it is necessary for a person to
freely move about. The tendency is, for the wearer who depends entirely on
the video system, to constantly look from side to side to effectively
increase the field of view. When the night vision equipment is provided
which has a much larger field of view, the wearer 92 can look through both
the video display 88 and the night vision equipment 90 and gain advantage
of both types of optical equipment. In other words, when a viewer is
equipped with the optical apparatus shown in FIG. 9, the night vision
equipment 90 can be used to view the general environment disposed in front
of the person 92, while the video display 88 permits the wearer 92 to then
focus on objects which would not otherwise be in the line of sight vision.
A headgear-mounted video display is shown in FIG. 10. A helmet may or may
not be needed with this alternative. The headgear 102 provides a headdress
to which a flat panel video monitor or display 104 is hingeably mounted.
In FIG. 11 a helmet 40 is shown worn over the video display headgear 102.
The headgear 102 is shown for mounting the video display 104 adjacent the
eyes of a wearer 106. The details of the headgear 102 are disclosed in
more detail in U.S. Pat. No. 4,703,879, and entitled Night Vision Goggle
Headgear. The video display 104 is mounted by a pivotal connection 108 to
an overhanging frame structure 110 so that the video display 104 is
cantilevered in front of the viewer's eye. The frame structure 110 is
formed integral with a headband 112 of the headgear 102. Straps 114, 116,
118 and 120 secure the headgear 102 to the wearer's head. With this
arrangement, a helmet 40 can be easily worn, if desired, over the headgear
102 and thus facilitate full vision capability as well as protection.
A video display system is shown in FIG. 12 receiving an image from
helmet-mounted night vision equipment 121. The night vision equipment 121
is fixed to the helmet 40 so that whenever the user turns his head, the
corresponding view is displayed by the display unit 14. The night vision
equipment provides an image of the object through a physical conductor 122
to the display unit 14. The physical conductor 122 may comprise a coaxial
cable or fiber optic cable. This embodiment is tailored to the exclusive
use of the display in low light conditions. However, the night vision
equipment can be replaced with a thermal or infrared sensitive unit.
FIG. 13 is illustrative of yet another application of the invention,
wherein an armored vehicle receives video transmissions 123 from a
remotely located imager (not shown). A receiver unit 124 mounted within
the vehicle retransmitts the video image omnidirectionally. In this
manner, each person within the vehicle who is equipped with a head mounted
display 125 can observe the image. There is a low probability of intercept
of the video signals retransmitted within the vehicle due to the enclosed
nature thereof.
FIG. 14 illustrates a detailed block diagram of a video display receiver
system 126 of the invention. In the exemplary receiver system 126, an
optical to electrical transducer 127 receives free space radiation 128
from a video transmitter (not shown) encoded with information relating to
the object. The radiation 128 may be characterized by a wavelength either
in the visible light range, or shorter. The optical to electrical
transducer 127 may comprise, for example, a material disposed in the path
of the radiation 128 and responsive to the particular wavelength of the
radiation 128. The material thus produces an electrical output
representative of the modulated free space video signal. A video
demodulator 129 is coupled to the transducer 127 for demodulating a video
signal into constituent electrical components suitable for driving a video
display. A video display driver 130 receives the coded signal from the
video demodulator 129 and drives a display 132 so that an image of the
object is displayed thereon. The video display driver 130 is of
conventional design and adapted to drive a raster/scan type of display, if
such type of display is employed. If a matrix type of display is used, the
driver 130 would be adapted for individually addressing each element of
the matrix with a signal having characteristics of the brightness with
which the element should be illuminated. Preferably, the display 132 is of
the miniature, lightweight, low power type suitable for mounting to the
helmet or headgear of a wearer. A vacuum fluorescent display of the type
disclosed in the noted patent has these qualities.
An eyepiece assembly 134 is disposed in the output optical path of the
display 132 and comprises plural lenses, such as 136, for interfacing the
image on the display 132 to the human eye 138. The eyepiece assembly 134
may include the various combinations of lens types to suit individual
needs. In addition, the eyepiece assembly 134 may be used in conjunction
with the partial reflecting mirror 82 of FIG. 8.
With reference now to FIG. 15, there are shown the details of an
arrangement for coupling a video camera transmitter 140 to the video
display receiver 126. The imager or camera 140 is shown mounted on a
tripod 141. As described above, the video camera transmitter 140 can be
located remotely from the head-mounted video display receiver 126, such as
on a weapon, a vehicle or also on a tripod. These suggested mounting
locations are only exemplary, and are not to be interpreted as limiting
the applicability of the invention to particular situations. The
arrangement of FIG. 15 provides dual modes of video transmission between
the video camera transmitter 140 and the video display receiver 126. In
one mode of operation, the video information is transmitted in a free
space medium 128 from the transmitter 140 to the receiver 126. In another
mode of operation, the modulated video signal is transmitted from the
transmitter 140 to the receiver 126 by a physical medium, such as a fiber
optic or a coaxial cable 144. The physical medium 144 can be
advantageously used in those situations where the utmost security of the
video signal is desired, or where the atmospheric conditions do not permit
an acceptable medium for a free space transmission.
The video camera transmitter 140 includes a video transmitter 146 for
transmitting a modulated video signal of the image on a pair of output
conductors 148 and 150. Transmitter line 148 drives an electrical to free
space transducer 152 for transmitting the free space video signal 128.
Transmitter conductor 150 drives the physical conductor 144 with
appropriate video signals. Physical conductor 144 can be of the coaxial
type, in which event the signals on video transmission line 150 are
electrical in nature. However, the physical conductor 144 can also be a
fiber optic bundle, wherein the signals in transmission line 150 would be
converted to modulated light signals.
The electrical to light transducer 152 of the video camera transmitter 140
includes a reflector 154 for providing a desired directional radiation
characteristic. When it is desired to transmit a highly directional
modulated video signal in free space 128, the reflector 154 can be shaped
in a parabolic form to focus the transmitted video signal in a beam
collimated in a desired direction. In the alternative, the video signal
may be transmitted omnidirectionally, wherein any video display receiver
in the area would be capable of receiving the video signal. The electrical
transducer 152 further includes a light transmitting element 156 which
converts the video signal on transmission conductor 148 into modulated
light signals. The nature of the materials comprising the element 156
determines primarily the wavelength of the transmitted energy in free
space 128. Materials are presently available to provide free space
transmissions from the short ultraviolet spectrum to the far infrared
spectrum.
The video display receiver 126 is provided with an optical to electrical
transducer 159 for converting the free space 128 transmission of the video
signal into corresponding electrical representations. Further details of
the transmitter transducer 156 and the receiver transducer 159 will be
disclosed below. A focusing lens 160 is disposed in the path of the free
space video signal 128 for focusing the light radiation on the electrical
transducer 159. The lens 160 is preferably constructed of a material which
has a low degree of attenuation to the particular wavelength of the free
space transmission. Of course, the material with which the optical to
electrical transducer 159 is constructed is also highly responsive to the
particular frequency or wavelength of the free space radiation.
The video display receiver 126 is provided with a feature in which the
image chosen to be displayed on the video display 132 is automatically
switchable from the free space transmission medium 128 to the physical
medium 144. An automatic selection means 160 is provided for automatically
selecting the physical medium 144 when the cable is connected to the video
display receiver 126, and for selecting the free space transmission 128
when the physical medium 144 is disconnected. To that end, the video
display receiver 126 includes a switch 162 switchable between a first
position 164 and a second position 166 in response to the electrical
energization of an associated relay coil 168. When the switch 162 is in
the first position 164, the video signal transmitted on the physical
medium 144 is coupled to the video demodulator 129. On the other hand,
when the switch 162 is switched to the second position 166, the free space
transmission 128 of the video signal is coupled to the video demodulator
129.
The automatic switching mechanism 160 further includes a physical medium
connection arrangement 170 for ohmica | | |
