Satellite Communications System for Medical Related Images

This invention relates to a satellite communications system for transmitting medical related images from mobile units to a central headquarters and then sending back diagnostic analysis from the central headquarters to the mobile units and more particularly, to an apparatus and method for converting static, high resolution, video images into low frequency signals capable of being transmitted over a narrow band width and for converting the low frequency signals back into static, high resolution, video images for analysis by a trained professional.

Systems are well known for sending medical related images, such as X-rays, ultrasound, computerized tomography (CT), nuclear magnetic resonance (NMR), EKG, etc., over phone lines and standard television communication systems. These existing medical communications systems, however, suffer from a number of disadvantages, including high costs, immobility, inaccuracy, and slow transmission communication.

The cost of sending high resolution images over phone lines is expensive due to the high costs associated with operating a phone link system. Slow transmission rates over the phone lines (9600 baud rate maximum) further causes phone charges to accumulate over time. Also, digitized images sent over phone lines must be encoded with extra parity bits to insure against errors caused by noise (20 db signal to noise ratio) during transmission. Analysis of the extra bits causes further delay in transmission. Often, errors are not detected and the images are sent with the inaccuracies anyway. In these situations doctors are left with evaluating images that have inaccuracies. Thus, the analysis provided by the doctor is inadequate due to the inaccuracies of the image. Furthermore, phone link systems cannot easily provide communication with mobile units. It is desirable to have mobile units capable of developing medical photographs and capable of sending the photographs from any location to a central headquarters, where these images can be diagnosed by a professional. However, phone link systems are constrained in that not all locations can provide the proper phone line hookups for sending the medical images to the central headquarters.

Mobile television communication systems are also used to send images from mobile units to central locations, however, these systems are very expensive to operate. Particularly, in situations where the mobile units are at large distances from the central headquarters, requiring expensive television type satellite communications equipment to complete the transmission. These systems are expensive because they transmit non-static type images over highly used band widths, at high frequencies. The higher the frequency, and the greater the band width, the more it usually costs to transmit by satellite.

Due to the high costs and the problems associated with transmitting images over phone lines and/or standard television communications equipment, incorporation of mobile medical diagnostic equipment, with the capability of sending video images back to a central headquarters for analysis, has not been developed.

The aforesaid difficulties are overcome by the present invention, which includes a mobile satellite communications system for sending high resolution, medically related, static images over narrow band width/low frequency signals to a central location for diagnosis.

More particularly, the system consists of means for converting a high resolution image into a voltage analog signal, means for converting the voltage analog signal into a narrow band width/low frequency signal, means for transmitting the narrow band width/low frequency signal to a satellite, means for receiving the narrow band width/low frequency signal, means for converting the narrow band width/low frequency signal back into a voltage analog signal, means for converting the voltage analog signal into a digital signal, means for buffering the digital signal, means for converting the buffered digital signal into a high resolution image, and means for transmitting diagnostic analysis, by a trained professional, in voice or readable form back to the sending unit.

By converting only static or single frame images, this invention overcomes the drawbacks of the prior art. Essentially, because the image does not move, (i.e., x-ray, etc.), the transmitting equipment can take more time to break down the static image and it can send a low frequency/narrow band width signals at a slower rate, thereby reducing the cost of sending images traditionally associated with standard television communication systems. This invention uses the lowest possible frequencies and narrowest possible band width to achieve the highest quality transmission of the images available, thereby keeping costs low. Additionally, the system can achieve the transmission more accurately at a 65 db signal to noise ratio and in less than 1/12 the time it takes a phone line system to operate.

Now, for the first time, mobile units can efficiently and inexpensively send medical related images back to a central location for diagnosis. Thus, necessary medical care can be brought directly to a patient at any location in the world, without having to bring the professional.

FIG. 1A shows a mobile truck equipped for sending and receiving low frequency/narrow band width signals to and from a central headquarters in accordance with this invention;

FIG. 1B is a parts diagram of the image conversion equipment located within the mobile truck;

FIG. 1C is a parts diagram of the image conversion equipment located within the central headquarters;

FIG. 2 is a schematic block diagram of the information flow from the high resolution cameras in the mobile truck to the diagnostic monitors in the central headquarters for analysis;

FIG. 3 is a plot of the voltage analog signal produced by the video compressor prior to FM modulation;

FIG. 4 is a schematic block diagram of the information flow in a second embodiment of the invention.

Referring to FIGS. 1A, 1B and 1C, a mobile truck 10 is shown transmitting low frequency/narrow band width signals to a satellite 12 which in turn transmits the low frequency narrow band signals to a central headquarters 14. Truck 10 contains equipment for generating medical related images, such as the X-ray equipment 16 as shown. The truck can also accommodate ultrasound equipment, magnetic resonance equipment, echo cardiogram equipment, etc. For discussion purposes only, however, we will focus primarily on transmitting photographic images produced by X-ray equipment 16.

Truck 10 contains image conversion and communications equipment 18. Referring to FIG. 1B, this equipment includes a receiving and transmitting satellite antenna control (not shown), a high resolution camera 22, a light table 24, monitor 28, thermal printer 30, impact printer 32, video compressor 50, modulator/demodulator 52 and 72, computer 33 and head phones 74. Truck 10 also includes a dark room for developing medical photographs (which is not shown). The top side of the truck 10 includes a satellite antenna 34 for communication with the central headquarters 14. Although only one truck is shown in FIG. 1, any number of trucks 10 are capable of communicating with the central headquarters 14 or to the other trucks from any given location throughout the world.

Central headquarters 14 consists of a receiving and transmitting satellite antenna 36 and headquarters 37. Referring to FIG. 1C, the equipment for analyzing the received radio signals from the mobile truck 10 is shown. Receiving equipment 38, consisting of a demodulator 54, video expander 56 and buffer 58, is linked to monitors 40, 42 and to personal computer 44. The personal computer 44 is linked to mass storage 62, frame store 64, and modulator 70 which is linked to satellite antenna 36 in FIG. 1A.

Generally, referring to FIGS. 1A, 1B and 1C, the detailed operation of this satellite communication system is now explained. Truck 10 provides medical diagnostic equipment, i.e., X-ray equipment, etc., to any location and the information generated by the equipment can be analyzed at a central location. For example, the truck 10 is easily maneuvered to an accident location, where a victim is seriously injured and cannot be moved and a doctor is not available at the accident location. Medical equipment, such as X-ray equipment 16, is easily removed from truck 10 to take necessary X-ray photographs of the victim. Truck 10 has the necessary facility for developing the X-ray photographs and transmitting equipment for sending an image of the X-ray photograph to a central headquarter 14 for professional analysis.

More particularly, referring to FIG. 1B, an operator of the truck 10 takes a developed X-ray and places it on light table 24 for reviewing by a high resolution camera 22. High resolution camera 22 takes a video photograph of the X-ray and this image is converted into an analog voltage signal by video compressor 50. FM modulator 52 then converts the analog signal into a low frequency narrow band signal to be transmitted by satellite dish 34 (FIG. 1A). The signal is sent to satellite 12 where it is resent to the central headquarters satellite antenna 36. Truck 10 and the central headquarters 14 can be at any distance from each other. For example, a mobile truck in the flat plains of the desert in Arizona could transmit images by satellite to a central headquarters located in Southern California.

At the central headquarters 14 (FIG. 1A), the transmission signal is converted into an analog voltage signal by demodulator 54 and then converted into a digital image at video expander 56 (FIG. 1C). In the preferred embodiment, high resolution monitors 40, 42 are capable of displaying two different static x-ray images transmitted from the truck 10. A radiologist can then review the images displayed on the high resolution monitors 40, 42 and provide his diagnosis of the X-rays directly to the mobile truck via satellite, in either voice or readable form. Microphone 48 converts the doctor's verbal diagnosis into an analog signal which is sent directly to FM modulator 70, where it is converted into a frequency signal to be sent over satellite antenna 34 (FIG. 1A) to truck 10. Additionally, computer 44 is capable of converting the doctor's verbal analysis directly into digital text, which can be separately FM modulated and sent to truck 10.

Video expander 56 is also linked to personal computer 44 which is equipped with software algorithms for reformating the digital data for long term storage on an optical disk 62. Personal computer 44 is linked to optical disk/mass storage 62 for retaining a permanent copy of the X-ray images. In addition, the diagnosis provided by the doctor is also storable on mass storage 62 in the form of digital text. The operator at the truck will then see the diagnostic analysis on the printer 32 or hear the doctors voice via headphones 74 (FIG. 1B). Impact printer 32 will provide the operator with a hard copy of the diagnosis and thermal printer 30 will provide the operator with a detailed photographic copy of the X-ray. These hard copies can be used by an operator/paramedic for applying first aid to an accident victim or to a hospital nurse for record keeping purposes.

Referring to FIG. 2, a block diagram representation of the preferred embodiment of the system is shown. As discussed above, the truck 10 consists of image conversation and communications equipment 18 and satellite antenna 34. The image conversation and communications equipment can be further broken down into high resolution camera 22 and transmission equipment 21. The transmission equipment includes a video compressor 50 and modulator 52. Starting with block 22, a high resolution photograph of, for example an X-ray, is taken. High resolution cameras are well known to those skilled in the art and in the preferred embodiment, the high resolution camera 22 is a 68 -Series MTI .TM. camera designed and built by Dage-MTI Inc. In the preferred embodiment, the high resolution camera has 512 X 512 picture elements or pixels and for even higher resolution the camera has 1,024.times.1,024 pixels. Each picture element or pixel is essentially a small light detector for sensing the intensity of light at a given location. The more pixels there are on the charged coupled array (not shown) of the camera, the better the quality of the image recorded. The camera is also equipped with a focus and zoom control so that an operator can adjust the camera to obtain any desired view of the X-ray image. Additionally, it is envisioned that a doctor at the central location 14 (FIG. 1A) will be able to control the positioning, zoom and focus of the high resolution camera 22.

The high resolution camera is linked to transmission equipment 21 which converts the high resolution television signal into a narrow band with, low frequency signal so that a transmission can be made over the FM band. In the preferred embodiment, the transmission equipment 21 consists of a Video Compressor Series-262 provided by Colorado Video Inc. linked to a standard FM modulator 52. For a more detailed description of a video compressor, see Appendix I.

The video compressor essentially takes vertical row samples or an orthogonal scan of the high resolution video image provided by camera 22. As the camera scans each horizontal row of pixels once every 631/2 microseconds, the video compressor samples one pixel per row. In this way, the video compressor scans the high resolution image in a series of vertical columns, scanning the image from left to right. It takes 1/60 of a second for a single vertical scan, from the top to the bottom of the high resolution image. An entire frame period or one scan from left to right of an image having 512.times.512 pixels takes about 16 seconds. A scan of an image having 1,024.times.1,024 pixels takes approximately four times as long. As the video compressor scans a high resolution image, an analog voltage signal (FIG. 3) is produced and simultaneously sent to FM modulator 52.

Referring to FIG. 3, the left hand column of the signal graph shows a gray scale (white to black levels) and a voltage scale for each level of light detected by a pixel. When the pixel detects a very dark or black image, the video compressor sends an analog voltage signal of 35 volts to the FM modulator. When the gray scale detected by the pixel is very light or almost at a white level, the video compressor sends an analog signal near its peak voltage. In other words, for each pixel, a gray value is represented by a particular voltage and the pixels are capable of detecting 256 levels of gray, from very light to very dark.

Now referring more particularly to the voltage signal represented in FIG. 3, at the left hand side, a start burst or square wave is depicted. This start burst essentially tells the receiver 38 (FIG. 2) to get ready for a transmission. A delay of a few seconds is then allowed to enable the receiving equipment to get ready for a transmission. An impulse of 35 volts alerts the receiving equipment that an analog voltage signal representing the gray scale of the pixel, in column 1 (left most column) is being sent. Scanning a column of 512 pixels typically takes 1/60th of a second and a very short blanking period at 0 volts is followed. The beginning the analog signal (FIG. 3) represents the top of the column of pixels and the end of the analog signal represents the bottom of the column of pixels. Each column is depicted by a separate analog signal, separated by a short blanking period of 0 volts.

As stated, when the analog signal is being generated by the video compressor it is also simultaneously sent to the FM modulator 52. The FM modulator essentially converts this voltage analog signal into a frequency signal which is acceptable for standard radio transmission equipment. In the preferred embodiment, the zero voltage range of the voltage analog signal is represented by an 11 KHz band width signal and the maximum voltage is represented by a 15 KHz signal.

Essentially, the truck 10 acts as a standard FM radio station, converting the 11-15 KHz band width signal into an FM transmission. The frequency signal representative of the voltage analog signal is sent via a satellite antenna 34 at approximately an occupied band width of 180-200 KHz band width. At this band width, the signal to noise ratio of the system is 65 db. For a lower signal to noise ratio a greater deviation from the 11-15 KHz signal is made (e.g. 220-246 Khz occupied band width signal). Satellite 12 essentially acts as a repeater translating the transmitted signal into a different frequency and then sending it to satellite antenna 36 at central headquarters 14. The satellite antenna 36 is equipped with an FM filter to ensure that the receiving equipment only receives the transmitted signals from the satellite. For a more detailed description of the preferred embodiment of satellite disk antenna 34,36 satellite 12 and, refer to Appendix II. The signal is then sent to the receiving equipment 38 where demodulator 54 converts the frequency signal back to an analog voltage signal.

Video expander 56 converts the voltage analog signal into a digital signal. This digital signal is temporarily stored in a buffer 58 until enough data is accumulated to be properly read out to the high resolution monitors 60. The high resolution monitors require that each column of pixels be built within 1/60 of a second. The receiving equipment, however, does not process the pixel data fast enough to create a pixel column in 1/60 of a second. Thus, the buffer 58 provides the necessary time delay for the digital data to accumulate before the columns of pixels can be developed on the high resolution monitors 60. High resolution monitors are well known to those skilled in the art and in the preferred embodiment, the high resolution monitors are HR series 2000 provided by Dage-MTI Inc. These monitors were specifically designed for viewing X-rays, and other medically related images.

For maintaining a permanent copy of the transmitted image, video expander 56 is linked to a personal computer equipped with software which reformats the digital data for storage on a standard mass storage electronic device. In the preferred embodiment, this storage device is an optical disc, however, any mass storage device for large amounts of digital data is suitable. The optical disc stores the X-ray images in digital form for any desired length of time. When the X-ray information is needed at a later date, the digital data can be easily retrieved from the optical disc by a command from computer 44. Because the digital data is stored on optical disc in a computer oriented format, it is not suitable for sending directly to the high resolution monitors 60. For this reason, a frame store 64 is provided for converting the stored digital computer data into a format that the high resolution monitors can interpret.

Essentially, frame store 64 is an intelligent buffer for temporarily storing the digital data in its own memory and converting it into a format to be shown on the high resolution monitors 60. For a more detailed discussion of the preferred embodiment the frame store 64, please refer to Appendix III. In the preferred embodiment, the frame store is a Serial No. 491 Video Frame Store provided by Colorado Video Inc.

When the digital data is displayed on monitor 60, a doctor analyzes the displayed image and provides his diagnosis via a voice activated computer 44. An analog voice signal of the doctor's diagnosis is sent to modulator 70 for transmission or a digital text signal is sent to modulator 70 for transmission back to the truck 10. Additionally, the digital text signal is also sent to the mass storage device 62 for storage and/or future reference. For transmission of the diagnosis to truck 10, modulator 70 converts the voice or digital signals into a narrow band width/low frequency signal. Satellite dish antenna 36 then transmits the frequency signal to the satellite 12 which in turn repeats a different frequency signal to the satellite antenna 34 of truck 10. The narrow band width/low frequency signal representative of the voice signal or the digital text signal is then converted back to an analog or digital signal by demodulator 72 on truck 10. The digital text signal is processed and formated by computer 33 and then it is displayed on a standard monitor 28 or printer 32, the textual analysis is provided to printer 32, so that the operator has a record of the diagnosis. If voice signals are sent, then the analog voice signal is sent from demodulator 72 directly to head phones 74. The instructions and analysis provided by the doctor will then be used by the operator/nurse to administer treatment if necessary.

Up until now, a satellite communications system for sending narrow band width/low frequency signals representing voltage analog signals of video images has been described. Referring to FIG. 4, another embodiment is depicted for transmitting a frequency signal representative of a digital signal instead of a voltage signal. The only difference in the embodiments depicted in FIGS. 2 and 4, is that the video expander has been moved from the central headquarters 14 into the truck 10. Now when the video compressor 50 generates a voltage analog signal a video expander 56 will convert the analog signal into a digital signal. As mentioned previously, the voltage analog signal produced by the video compressor represents pixel gray scale values for the vertical columns of pixels in the high resolution camera. The video expander converts the voltage signal into a binary number from 0 to 256. Each binary number represents a digital signal to be converted by the FM modulator 52 into a narrow band/low frequency signal. Essentially, the video expander acts as an analog/digital converter, changing the voltage signal of the video compressor into a digital signal for FM modulation. Satellite antenna 34, on truck 10, sends the narrow band/low frequency signal to satellite 12. Satellite antenna 36 at the central headquarters 14 receives the signal reflected by the satellite 12. The frequency signal is then converted into a digital signal by the demodulator 54. Unlike the other previously described embodiments, a video expander need not be provided because the signal is already represented in its digital form. However, a buffer is still required to delay the data before it is sent to monitors 60. All other parts of this embodiment are identical to the embodiment shown in FIG. 2.

The invention has been described in exemplary and preferred embodiments, but is not limited thereto. Those skilled in the art will recognize that a number of additional modifications and improvements can be made to the invention without departure from the essential spirit and scope. For example, the preferred embodiment of the invention may be used to send other medical related images, such as CT, magnetic resonance and ultrasonic sound images, etc., from the truck to the central headquarters or vice versa. Additionally, the resolution of the images provided are only limited by the resolution of the camera and monitors available to the art. Therefore, the invention is not limited by the above disclosure, but only by the following claims.

The Video Compressor is intended to function as the transmitter in a narrow-band (sometimes called "slow-scan") video communications system. It accepts a standard, composite TV signal and reduces the signal band width to the audio range for transmission over narrow-band communication channels. The video compressor requires a channel band width of 11-15 KHz and transmits a picture in 9 to 30 seconds depending on the resolution required. The video compressor operates over voice grade FM modulated band frequency channels and requires 8 seconds for 256.times.256 resolution, 16 seconds for 512--512 resolution.

A Video Expander is usually used at the receiver end of the channel to store and display the transmitted image.

The Video Compressor is a sampling scan converter which accepts standard, composite TV signals and reduces the video band width to the audio range. The sampling format is one sample per TV scan line starting in the upper left corner of the raster and forming a vertical column. The output is a slow-scan signal with a line rate equal to the field of the input TV signal (60 lines/second for U.S. standards), and scans vertically from top to bottom. The frame rate depends on the TV line rate and on the desired resolution and scans from left to right.

The band width of the output signal is approximately 11-15 KHz (15,750 samples/second for U.S. 525-line standards). The output signal is DC coupled and follows the TV convention of whites being positive going. Vertical resolution is equal to that of the "real-time" input TV signal, while the horizontal resolution is determined by the slow-scan frame time.

A special feature of the Video Compressor is a "real-time" monitor output signal that displays the sampling column and the resultant slow-scan video wave form superimposed on the input video. Before transmitting a picture, the operator can move this column across the picture to determine and adjust the quality of the slow-scan output signal. During transmission, the sampling column moves slowly from left to right indicating the portion of the picture remaining to be transmitted.

Single Frame Operation

In most instances, such as person-to-person communications of visual material, it is desirable to send pictures one frame at a time. Typically, a vidicon camera will be used as a video input source to the Video Compressor and the "real-time" signal will be viewed on a conventional TV monitor. The operator may thus compose to his satisfaction the image to be transmitted, ensuring that it is properly focused and clearly shows significant detail. Following a convention widely used in broadcast studios, it is preferable not to attempt to show too much detail, and closeups of subjects are to be preferred.

If a camera with automatic level control is used, adjustment of the BLACK LEVEL and VIDEO LEVEL controls should not be required after the initial adjustment. If more than one video camera is used, the output levels of all the cameras should be set to the same level if possible.

Once a satisfactory "real-time" picture is obtained, the START button is momentarily depressed to initiate transmission of that frame. The position of the sample line indicates the degree of transmission, and neither the camera nor the subject should be moved while the transmission is in progress. When the transmission is complete, the sample line returns to mid-screen (or other position set by the ANALYZE control). Although another picture may be transmitted immediately, it is important to remember that the viewer at the receiving end may wish to spend some time observing the image that was just completed.

When unattended operation is desired, such as for surveillance purposes, the SINGLE/CONT switch should be placed in the CONT position, and the Video Compressor will continuously transmit the input video signal. Again a reasonably constant input signal is desired, and cameras with automatic level control are recommended. The Video Compressor will tolerate a limited amount of motion in the scene being viewed, although geometric distortion in the reproduced image will occur in the following ways: objects moving right to left will be compressed, objects moving left to right will be expanded unless moving rapidly, in which case their direction of travel will seemingly be reversed. Objects moving vertically will be distorted diagonally, with the left hand side of subjects moving upward being lower than the right hand side, and the reverse holding for subjects moving downward.

By using a tape recorder, it is possible to store a large number of pictures at the transmit end for subsequent transmission, or to store images at the receive end for subsequent viewing on a monitor. when making recordings, care should be taken in setting recording levels properly.

(General Operation)

The dish is stowed and deployed by a hydraulic ram that is powered by a 12 VDC motor driven pump drawing approximately 200 Amperes. Limit switches are provided to stop deployment when the operating position is reached. Dish storage and deployment are accomplished automatically by the AP-1 unit.

The azimuth adjustment is effected by a 120 VAC motorized gear drive. A limit switch is located at each end of the horizontal disk travel. Two limit switches are used to centre the dish prior to stowage. Dish elevation is accomplished by a 120 VAC motor driven screw jack. Limit switches permit adjustment between 0.degree. and 90.degree. elevation. A 120 VAC motorized gear drive provides polarizing adjustment of the freedom.

(1) To raise the dish antenna from its storage position to its operational position, first select the power system to be used. When connected to shore or auxiliary generator power, first verify that the "utility light" breaker on the Power Distribution Panel is on. Next move the "Pan-Tilt Power" switch on the Power Distribution Panel to the AC position. If the truck is not connected to the shore power and the generator is not being used, move the "Pan-Tilt Power" switch to the Inverter position.

(2) To enable the system, lift the red enable switch guard on the Hubcom AP-1 "Deploy" section and move the toggle switch to the right.

(3) Depress the "UP" button located beneath the enable switch until the dish antenna is raised to its full operational position and stops automatically. Aiming

(1) To adjust the dish azimuth, press the "CCW/CW" switch in the azimuth section of the AP-1, for counter clockwise rotation of the dish assembly. A digital readout will monitor the dish azimuth heading in degrees as it is moved. The "F/S" switch in the azimuth section selects a fast or slow azimuth adjustment speed.

(2) To adjust the dish elevation, depress the "UP/ON" switch in the elevation section of the AP-1 until the desired elevation is displayed in degrees in the digital readout. The "F/S" switch in the elevation section selects fast or slow elevation adjustment speed.

(3) It is necessary to know the polarization of the desired transponder prior to transmission. The "V" or "H" buttons on the Hubcom MS-2 will then route the waveguides to provided the corresponding vertical or horizontal feed port for the received signal. The transmitted signal will be automatically routed ot the orthogonal feed port.

(4 ) Once the proper receive polarization is selected, the feedhorn position can be fine tuned over a +45.degree. angle by depressing the "CCW/CW" switch in the polarity section of the AP-1 until the best signal is obtained. Use the "F/S" switch in the polarity section to select fast or slow polarization adjustment speed.

To return the dish antenna to the storage position, simply depress the "stow" button on the "AP-1" unit. The dish antenna will center and lower itself to the storage position automatically.

Dish antenna positioning is controlled from the operator area and is greatly simplified by digital readouts of elevation and azimuth on the dish aming control panel. Once the disk is roughly positioned, the transponder frequency selected and correct polarization of the feedhorn chosen watch the spectrum analyzer while slowly panning the dish in a systematic pattern until a sight display of an active transponder is seen. All satellites have characteristic spectral energy distribution. Check for narrow band communications channels, half transponder operation, scrambled signals and narrow band beacons.

To scan satellites in the Eastern hemisphere, at a longitude greater than that of your location, lower on the dish until the spectrum analyzer display flattens out, pan left to the next satellite or raise the dish to flatten the display and pan right. If the longitudes are close to equal lower the dish very little and pan left or right to the satellite longitude is less than that of your location, lower the dish and pan right or raise the dish and pan left.

To scan satelitte on the Western hemisphere, greater than that of you own location, lower the dish until the spectrum analyzer display flattens out, pan right to the next satellite or raise the dish to flatten the display and pan left. If longitude close to equal, lower the dish very little and pan left or right. If the satelitte longitude is less than that of your location, lower the dish and pan left or rise the dish and pan right.

Once the correct satellite is found, fine tune the dish position by optimizing the amplitude of the spectral display. The video waveform monitor can be used to clean up the top of the sync pulse on unscrambled channels as a means of fine tuning.

The terminal transmits at 14.0-14.5 GHz and receives at 11.7-12.2 GHz. It consists of a microwave transceiver, power supply unit, and ac and dc cables.

The preferred RF terminal is an ASAP 12161 Terminal provided by Avantek designed to interface with any modern dish having a data capability of 9.6 kbps to 1.544 <bps and any size antenna. It is used in a wide range of data distribution and collection applications, including financial data transfer, oil well and pipeline monitoring, point-of-sales systems, electronic funds transfer, electronic mail, voice store-and-forward communications, and video conferencing.

The function of the ASAT 1214 RF Terminal is the upconversion of the modulators's IF output to an RF signal for transmission via an antenna, and the downconversion of the received RF signal for use by the demodulator. Major components are an upconverter chain, a low-noise downconverter, and a frequency synthesizer. The power amplifier in the upconverter chain is made of Aventek's Gallium Arsenide Field Effect Transistor (GaAsFET) devices and Internal Matching network (IMFET) devices that provide highly stable power gain and minimal intermodulation distortion. The downconverter is built around low-noise amplifier devices, providing a system noise temperature of better than 250.degree. K. The synthesizers rely on an ovenized 10 MIIZ crystal oscillator which provides fully synthesized carrier frequency selection in 1 MHz steps over a 500 MHz bandwidth.

The RF transceiver, upconverts a 70 MHz IF signal from a modulator to a 14 GHz transmit signal. The upconversion process used two upconverters, a bandpass filter, and a power amplifier, and is controlled by an automatic level control (ALC) circuit. On the receive side, the transceiver downconverts a 12 GHz received signal to a 70 MHz IF signal for output to a demodulator. Key downconversion modules are a 12 GHz bandpass filter and a low-noise converter. Both conversion functions rely on LO signals processed by a fixed synthesizer. The system parameters are monitore by an internal summary alarm board.

The IF transmit signal enters the transceiver at a frequency of 70 MHz +20 MHz. In the first upconverter, this IF signal mixes with a 1150 MHz LO signal to produce a 1220 MHz (.+-.20 MHz) IF signal. After passing through a 1220 MHz bandpass filter, the signal is mixed in the second upconverter with a 12.78-13.78 GHz agile LO signal. When summed with the IF signal, the LO signal will produce a transmit signal with the desired RF frequency in the 14.0-14.5 GHzband.

The RF transmit signal is amplified by the power amplifier as a final step before transmission. Active bias regulators in the power amplifier ensure that each stage of amplification is performed at very nearly the optimum point regardless of temperature environment. A 2W power amplifier raises the RF signal to the output power of 23 dBm to 33 dBm, depending on the setting selected during alignment. The selected output level is held constant by the automatic level control loop, consisting of a control circuit in the first upconverter and a level detector in the power amplifier.

The incoming 11.7-12.2 GHz receive signal passes through a 12 GHz low-insertion-low bandpass filter. The filtered signal enters the low-noise converter which contains a low-noise amplifier, another filter, and two downconverters. The first downconverter mixes the receive signal with an agile LO signal at a frequency of between 12.78 and 13.28 GHz such that the produced IF signal will be 1080 .+-.20 MHz. The new IF receive signal is filtered and mixed in the second downconverter with a 1150 MHz LO signal for conversion to a 70 .+-.20 MHz IF signal. A low-noise amplifier performs final amplification of the IF signal.

The LO signals that are mixed with the tramsmit and receive signals are supplied by fixed and agile frequency synthesizers. The synthesizers use a 10 MHz ovenized crystal oscillator, designed for very low phase noise and high stability, as a reference. A X4 multiplier is used by the agile synthesizer. The signal produced by the agile synthesizer is made accessible to the customer through DIP switches that can be used to set the frequencies, and through a screw on the crystal oscillator for fine tuning. The synthesizer provides selection of transmit and receive frequencies, in 1 MHz steps, over the 500 Mhz band.

All of the transceiver's functions are monitored by alarm circuitry which activates light-emitting diodes (LEDS) on the summary alarm board. The LED alarms allow detection of power failure, loss of lock, extreme temperature, and failure of any one of the functional components in the transceiver.

(III-C) SATELLITE NETWORK

In the preferred embodiment, the satellite system is a GStar satellite network. It is a telecommunications system owned and operated by GTE Satellite Communications, and it is composed of three orbiting satellites. GStar A1 was successfully launched by an Ariane rocket on May 7, 1985. GStar A2 is scheduled to be launched in December 1985 or January 1986. These satellites are the first U.S. Ku-band communications spacecraft to offer 50-state coverage at 12 GHz, as well as regional beam coverage to the eastern or western halves of the continental United States. The GStar A2 and A3 satellites will also have the ability to transmit by way of two, high-powered spot beams.

Each GStar satellite carries 16 transponders with usable band widths of 54 MHz. Fourteen 20-watt transponders can be switched between east or west regional beams or CONUS coverage. The remaining two 27-watt transponders are connected to a combined footprint that covers CONUS, Alaska, and Hawaii. Because of their wide band widths, GStar transponders are capable of transmitting two simultaneous TV programs on multiple data and voice circuits.

Fourteen of GStar's 16 operational transponders use 20-watt TWTAs that can be tailored by ground command to provide east or west regional coverage or 48-state (CONUS) coverage. The remaining two transponders provide 50-state coverage using combined CONUS/Alaska/Hawaii beams powered by 27-watt TWTAs. The antenna subsystem comprises two offset parabolic reflectors. Polarization purity if achieved through the use of grids embedded in each reflector that are transparent to the opposite sense of polarity.

Efficient use of the communications capacity of these satellites will be obtained through digital transmission techniques. Cusomer-generated inputs will be digitalized prior to transmission through the system; a time division multiple access (TDMA) scheme will take the digitalized signals and integrate them into what is known as a "burst mode" delivery system. Periodic frame reconfiguration allocates satellite capacity in proportion to the traffic requirements of each earth satellite.

Another embodiment of the satellite network is a Hughes Galaxy which operates a Ku-band satellite system starting in 1987. The system consists of two in-orbit satellites providing coverage of the 48 contiguous states. Hughes Galaxy receives orbital assignments of 71 and 180 degrees west longitude. Galaxy K-band satellites will use the Hughes Aircraft HS 393 wide-body design derived from the Intelsat* VI spacecraft bus. Individual satellites within the system carry 16 active transponders with usable band widths of 52 MHz. Each transponder is connected by ground command to one of two shaped full-CONUS beams, or to an east or west half-CONUS beam.

The Video Expander is designed to operate over FM band frequencies. If a dedicated channel is used, the channel should have the following characteristics:

Frequency Response: 11 to 15 Khz

Signal-to-Noise Ratio: 60 db or better.

In the receiving mode, the Video Expander accepts properly formatted slow-scan TV input signals and reconstructs a conventional TV still picture using the same memory which provided frame freeze for transmission. Image retention is indefinate unless deliberately erased or power to the Video Expander is lost. A remote control box is provided for easy desk top operation. The unit can be generally locked to other video sources to provide switching, mixing, and special effects capabilities.

General

The Video Expander has two transmission rates. when the FAST/SLOW switch is in the FAST position, a single field picture with 256.times.256 elements is transmitted in approximately 34 seconds. When the switch is in the SLOW position, a full frame picture with 256.times.512 elements, dot interlaced, is transmitted in approximately 74 seconds. Both Video Transceivers must be set to the same speed for proper operation.

The SINGLE/CONT at the transmitter only must be in a position for the desired mode of operation as explained below.

Single Frame - Transmit

In many instances, such as person-to-person communication of visual material, it is desirable to send pictures one frame at a time on command. For this mode of operation, the SINGLE/CONT switch should be set to SINGLE.

Typically, one or more TV cameras will be used as the video input sources to the video expander and the "frozen" signal will be viewed on one or more conventional TV monitors. The operator may thus compose to his satisfaction the image to be transmitted, ensuring that it is properly focused and clearly shows significant detail.

When the transmission is complete, the cursor stops at the right hand edge of the raster and the scan light goes off. Although another picture may be transmitted immediately, it is important to remember that the viewer at the receiving end may wish to spend some time observing the image that was just completed.

Single Frame - Receive

For single frame reception, the video expander at the receive end should have its FAST/SLOW switch in the same position as the transmitting video expander.

When a start burst signal is received from the transmitter, the scan lights go on. As each column is received from the transmitter, it is stored in the 290 memory and displayed as a new column on the television monitor. Thus a new picture will build up, a column on the television monitor. Thus a new picture will build up, a column at a time, as the cursor moves from left to right across the raster.

Continuous Scan Operation

When unattended operation is desired, such as for surveillance purposes, the SINGLE/CONT switch on the transmitting video expander should be placed in the CONT position. The unit will then transmit a continuous sequence of pictures, freezing a new frame (field) each time.

The receiving video expander is set up in the same manner as for single frame operation, as described in the preceding section.

Memory

By using a memory device, it is possible to store a large number of pictures at the transmit end for subsequent transmission, or to store images at the receive end for subsequent viewing on a monitor.

The Video Frame Store is a solid-state video memory with high-speed analog/digital (A/D) and digital/analog (D/A) converters, and is capable of digitizing storing, and displaying a single frame of video information. It can be used to grab and freeze one frame from a camera or video tape recorder and display it on a standard TV monitor for observation. Individual picture elements in the store picture can then be accessed by a computer, processed, and returned to the video frame store memory for redisplay.

The Video Frame Store is a digital semiconductor memory made up of random access memory (RAM) integrated circuits capable of storing one complete frame of video information. Data can be entered into this memory from a camera or other video source by means of high-speed A/D converter in the video frame store or, alternately, entered directly from a computer if a computer I/O module is installed. The contents of the memory can be continuously viewed on an external TV monitor connected to the video frame store.

The Video Frame Store utilizes standard 2:1 interlace and "dot Interlace" which increases subjective horizontal resolution.

The "frame grab" process can be initiated by means of a front panel pushbutton switch, a remote pushbutton switch, or a TTL store signal. The unit stores the first frame following the conclusion of a store command. The video output is a standard video signal synchronized with the vide input and can be switched or mixed with other video signals or recorded on conventional video tape recorders.

The Video Frame Store can be easily interfaced with most computers or other digital processing equipment. A single 16-bit duplex I/O module in the computer 491 is all that is required for interfacing to most modern computers. All digital signals to or from the unit are buffered and are TTL compatible.

Video Source

The source of the video signal for the Video Frame Store must have the following characteristics:

1. It must be composite (i.e. a mixture of video and synchronizing pulses). Most modern cameras have composite video outputs.

2. It must have 2:1 interlace scanning format All cameras meeting either U.S. standard EIA RS-170 or EIA RS-330 have 2:1 interlace. Cameras with random interlace will not work (many of the least expensive surveillance cameras have random interlace).

Video Monitor

The video monitor connected to the Video Out connector of the video frame store can be any standard monochrome television monitor designed to operate at the line rate of the video input signal. This monitor displays the image stored in the video frame store memory, or, if the STORE pushbutton is held down, can be used to view the video input signal as it is processed through the memory.

Setting the Video and Black Level Controls

The front panel BLACK LEVEL and VIDEO LEVEL controls are best set by holding the STORE pushbutton down and adjusting the BLACK LEVEL control so there is no loss of detail in the black portions of the picture and adjusting the VIDEO LEVEL control so there is no loss of detail (clipping) in the whitest portions of the picture. These controls can, of course, be set to intentionally alter the store video by clipping either blacks or whites or both.