Subscriber's station unit for bi-directional video and data communication services

The subject of the invention is a subscriber set for two-way communication of vision and data services, in particular for interactive networks, two-way data transmission services for carrying synchronized digital messages between particular points in the whole network.

The wireless interactive video system disclosed in US Patent No. 4,591,906 relates to interactive, real-time digital communications for a broad audience of subscribers in urban areas adjacent to a central television broadcasting station.

For example, the Federal Communications Commission (FCC) has established communication standards in the US for such interactive video data transmission services, allocating for wireless transmissions the 218-219 MHz band for public use in designated areas of local base stations, which includes interactive subscriber teams of small of maximum effective radiated power below 20 W.

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There are no known interactive data transmission and vision service systems that can support a designated area of ​​the base station with subscriber units transmitting with power of the order of milliwatts. In the case of such an improved system, battery-powered portable subscriber bands, suitable for tasks such as meter reading, would become feasible with low battery consumption, enabling interactive digital connectivity in local and fixed coverage areas, e.g. on the territory of the given country.

Wireless interactive data and video transmission services are provided without telephone lines or cable systems through the national base station network, as disclosed in U.S. Patent No. 5,101,267, via satellite transmissions between local area base stations and a data center.

Limited coverage, such as nationwide, enables video programs watched nationwide, such as world baseball games, to become interactive for individual subscribers. Mass communication becomes possible via a telecommunications system that operates essentially in real time with the participation of such a wide audience from urban areas that would block any existing public telephone network.

Each local base station in such a fixed range communication system, e.g. national, must be capable of interacting within the limits set by applicable standards with the peak participation of the local auditorium without significant commutation delays to ensure bi-directional interactive connections essentially in real time over the network serving an auditorium consisting of a large number of participants who want to essentially simultaneously connect.

The known two-way radio transmission network technology, represented for example by portable telephone communication systems, is usually incompatible with efficient communication in substantially real time with the current strong subscriber activity. This is because in telephone systems, commutation and communication operations must be compatible with commutation commands from subscriber sets with coded acoustic tones accompanying analogue audio messages. With long digital identification numbers for long-distance national connections, usually containing ten digits in decimal format, which must be manually entered with line occupancy for making inter-point connections, as part of the connection signal data, commutation circuits are occupied for very long periods of time, which is disadvantageous for connections taking place essentially in real time or for high traffic conditions. Busy signals are often encountered that limit the size of the participating auditorium for instant connection, and as a result the on-line congestion that requires redialing is annoying to potential users. The interactive response, which requires communication through a telephone exchange, tends to delay and discourage participants and introduces the critical problem of identifying and interacting inter-subscriber connections in real time without crowded switches and nervousness due to busy signals and retrying calls.

Similarly, even with a limited amount of digital data that can be transferred in digital paging system messages, where typically only some messages mean a short fixed-length message, such as a telephone call number, there is little real-time connectivity in the presence of heavy traffic due to the complexity of the telephone switching circuits needed to carry messages.

To process digital information accurately, effectively, and in a way that ensures privacy, you need to accurately synchronize and organize digital data and accompanying commands. For two-way real-time digital communication with a large auditorium wanting quick access to a system or message transfer network, signal synchronization becomes critical and absolutely necessary for real-time interactive communication. In general, telephone acoustic transmissions are non-critical analogue to synchronization and are asynchronous. Known telephone-type telecommunications systems are therefore not suitable for use in interactive data transmission and vision systems that transfer private digital messages between individual points in real time for a large audience.

Typical solutions for fixed-range communication, e.g. domestic, using such known telephone switching techniques, are briefly treated as representative of the current state of the art, using analog (acoustic) telephone communication networks and cellular technology to operate cheap, mobile, battery powered subscriber teams operating in local subdivision areas of the cells.

The telephony system disclosed in U.S. Pat. Nos. 4,481,670 and 4,550 443 provides the transmission of the best signals from portable radio apparatus in two-way acoustic analog communication between overlapping zones served by different fixed cell suppressors, which in some cases use different frequency bands to separate adjacent zones.

In paging systems, modems are used to connect to a telephone system for communication and commutation in a national network, as described in U.S. Patent Nos. 4,870,410 and 4,875,039, therefore they are subject to the same previously described, limitations of the commutation system, even if you only need a short digital connection only.

The object of the invention is to develop a subscriber assembly for a two-way communication network of vision and data services, enabling the effective use of licensed interactive communication channels to ensure synchronized digital communication in essentially real time with variable length between the geographically separated base station subscribers of an interactive data transmission and vision service system. It is important to be able to support a large auditorium without significant delays in peak load conditions in a manner consistent with the FCC standard for interactive data and vision services.

Furthermore, the object of the invention is to introduce into interactive data transmission services and vision a system ensuring effective, two-way interactive communication with the possibility of using simplified and cheap subscriber assemblies, broadcasting peak power of milliwatts and meeting FCC standards.

Another object of the invention is to provide the possibility of introducing portable digital subscriber assemblies for an interactive data transmission and vision services system intended for local and limited range communication, e.g. national.

According to the invention, the subscriber team for two-way communication of vision and data services in a system using cell repeater base stations and a local remote receiver is characterized by a digital transmitter that has a maximum output power of the order of milliwatts, and a receiver to receive synchronized signals from cellular repeater base station. The mentioned digital transmitter works in the carrier frequency band in the range of about 218-219 MHz.

The said subscriber set is a battery powered portable set.

The subscriber group has a unique identification number so that said subscriber team can be distinguished from many of the listed subscriber groups by said repeater cellular base station, so that said subscriber team can only be selected to receive a message from said repeater base station.

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In addition, the subscriber assembly includes means for transmitting messages to a local remote receiver and said repeater cellular base station in a selected one of many frequency bands.

The subscriber assembly further includes means for responding to a request sent from said repeater cellular base station to said subscriber assembly to set conditions for reverse transmission of the message from said subscriber assembly to said repeater cellular base station.

Preferably, the subscriber assembly includes setting means for selecting a transmission path for said reverse transmission of said message from said subscriber assembly to the repeater cellular base station.

The base station configuration for interactive data services provides several related features to improve the efficiency of digital communications. These features include a system using portable subscriber sets with a transmission power of the order of milliwatts and a significant increase in the number of subscriber teams cooperating with the base station. For example, 4000 subscriber teams of one base station can participate in point-to-point communication of national range with a transM k 9 prędkością speed. 9 k kk9 9 9 X data mission 5.16 kbd.

A significant advantage of the invention is the ability to quickly connect a very large number of separately identified subscribers at each base station for parallel communications and to include new subscribers in pending communication slots without significant delay.

These properties were implemented in a subscriber system of multiplication on the base station, which is synchronously connected with the carrier signal of the base station or with the images of the main TV channel. Communications and commutations are therefore synchronized across the entire network with a fixed range, e.g. domestic, for more effective and faster inter-point communication in real time. Even more important is the appropriate freedom to multiply variable-length digital messages from a large number of broadcasting subscriber assemblies at the base station, ensuring that subscribers encounter a short waiting time for access to make a call, even on national communications.

The base station includes a central transmitter and a data processing station for processing transmitted digital data to subscriber assemblies in a designated area of ​​the base station. Many reception-only stations located throughout the area and connected by a wired, cable, microwave or radio connection to a central data processing station then process and transmit transmitted digital data from subscriber assemblies in the subdivision zones in the designated area of ​​the base station. Therefore, the base station supports a network of subcellular receiving stations located in places enabling reliable response from subscribers sending digital signals at the level of milliwatts in the 218-219 MHz band allowed by FCC. Support for frozen signals between various subdivision zones is provided, so that cheap, portable, battery-powered subscriber units with a milliwatt transmitter can be moved in the geographical area of ​​the base station for reliable performance of such functions as meter reading and data transfer.

The base station system is designed for communications in a fixed range network, e.g. a national network, for base stations via a satellite communications network. The base station data processor locally segregates, collects and formats messages from individual subscribers for retransmission via the satellite network to the switching node and the data processing center with the ability to locate individual subscribers in remote base stations via a fixed coverage network, e.g. national.

The solution according to the invention also creates the possibility of offering additional interactive services on the network, such as reading meters and inventory control in non-alcoholic beverage dispensing machines, etc. in a way that saves human labor and costs so that it becomes a sensible solution

172 843 from an economic point of view in this type of interactive vision and data service system. Subscriber teams in a digital communications system can be implemented without the need for two video displays in the manner described below. It is also possible to implement local alarm systems for remote monitoring of door opening, 'detection of fires, damages, continuous reading of temperature values, etc. Two-way paging services or telemetric determination of the location or condition of delivery vehicles etc. are also possible. In addition, with full vision display of installations implemented in subscriber teams, it is possible to move such teams to different locations in the home, office or car. Thus, the solution according to the invention allows the creation of portable or mobile interactive subscriber stations and communication units for interactive video and data service systems compatible with the FCC standard. With the use of lower power transmitters, power regulation in subscriber sets can be avoided by the usual automatic gain control in remote receiving terminals. Smaller and portable home kits are also possible. Wvstenińe. significant advantage of longer battery life for portable subscriber assemblies.

A further important advantage of the solution according to the invention is the ability to handle connections between individual points in the entire fixed coverage area in peak traffic conditions with a very short waiting time of the subscriber for access to the system.

In addition, the system's important properties are that low power subscriber teams use the system at the external limits of the repeaters, which reduces the risk of intercell interference, and the system can be expanded by adding divided zones, 'as the subscriber base grows, there are no problems with compliance by the FCC standard system for interactive vision and data services by passive, remote receivers only for receiving, and investment costs are significantly reduced, power costs and operating costs of this system.

The subject of the invention in the embodiments is illustrated in the drawing, in which Fig. 1 shows an interactive, satellite data transmission and vision system with a fixed range, ensuring inter-point communication between subscriber response teams in local service areas and various sellers of goods and services, in a block diagram, FIG. 2 - local area repeater base station system for communication with very low power local subscriber assemblies, including mobile or portable assemblies, in the schematic, Fig. 3 - radio station repeater radio signal protocol for enabling communication with a significant number of subscriber assemblies in real time , Fig. 4 - diagram of message fields illustrating maximizing data processed at local cell stations, Fig. 5 - the link between the base cell station and the satellite for processing a fixed-length field and formulating messages of variable length from subscribers during an active connection, in a block diagram, Fig. 6A - block diagram of communication channels in the base cell station, Fig. 6b - message transfer diagram between local subscribers of a mobile data center and a network of cell stations connected via satellite, Fig. 7A - block diagram illustrating the properties of message passing time in the base cell station, Fig. 7B - typical communication fields, with showing relative times at individual cell communication stations, Fig. 8A - graph of frequency bands allocated by the FCC standard, Fig. 8B - list sub-channel bands for interactive data and video services, and 9A and 9B show respectively subscriber sets for fixed or mobile read-only communication services and the integrated digital data and video transmission service according to embodiments of the invention.

According to Figure 1, in an interactive network, via subscriber assemblies 4, subscribers connect via radio links 5 with a frequency of 218-219 MHz or with

172 843 a set of local remote receivers 20, each of which is connected by a connection 21 (Fig. 2), such as a telephone line, with repeaters 3, or with repeaters 3 of a local area base station, belonging to a set of teletransmission stations with different locations for communication via satellite 1, controlled by data center 2 and switching. Regional recipients 7 or local recipients 7 ', as participants in the service system, also connect via repeaters of the local area and control center 2. Commutation and communication are carried out by the commutation control center 14 and the associated catalog of 13 terminals, data and software delivery from control center 15 as well as billing and transaction processing 16 together with the appropriate interaction of memory and software in the subscriber team 17.

In this system, simple and cheap subscriber assemblies 4 are widely used for a wide range of interactive functions using software control functions. This system, in its radio frequency processing part, effectively handles mass data to cope with the very high peak load of the system essentially in real time through the commutation control center 14, which stores for each subscriber current updated information that does not need to be sent with each transaction, such like area code, name, address, phone and credit card number, etc.

The array of repeaters 3 shown in Fig. 2 allows the interactive capabilities and functions of the subscriber units 4 to be expanded, while simultaneously improving performance and reducing cost. The outer ring 19 marked with dashed lines indicates the boundaries of a local area, such as may be covered by the FCC standard for interactive services related to video and data transmission. The repeaters of the 3 local area of ​​the teletransmission station are connected to the satellite system via a directional 3A parabolic antenna and send digital communications signals and television vision signals to X subscribers in the designated territory via transmitter 8.

The set, usually consisting of ten remote, receive-only, stationary 20A-20N relay stations, is located at strategic locations within this cellular area. Each remote receiver 20 is connected by a cable, microwave or rented telephone line 21 to a repeater 3. Subscriber suppressive units X4, 4 'etc. the response zones 22 located in the split zones therefore connect to the remote receivers 20 at a significantly reduced transmission path length in the split response zones 22 compared to the direct transmission to the repeater 3. This split feature, used for the first time in an interactive video and data transmission system, provides reliable transmission at radiated power levels of the order of milliwatts. Separate advantages are obtained, such as a lower risk of external interference and a long battery life supplying portable subscriber assemblies 4 that can be moved in the conventional area 19 marked by the line.

The system protocol for receiving messages and responses in subscriber sets in the form of a diagram in Fig. 3 shows a large number, typically 640, of X subscriber sets that can simultaneously be used on any repeater 3. It is assumed that each of the ten fixed remote receiving stations 20A-20N in area 19 is capable of handling 64 X radio subscriber assemblies. This is possible because the X subscriber bands powered by the order of milliwatts are intended for broadcasting in one of the ten divided zones 22, with the means of preventing interference with adjacent zones 22A, 22B etc.

For broadcasting by X subscriber teams in respective zones 22, the protocol allocates in a limited broadcast period 30 time interval 31 'of the home unit response at a cumulative response speed of 5.1 kbd. Each of these enabled user home units then sends a message

1721313 digital superimposed by modulation on a subcarrier in the 218-219 MHz band. Broadcasting interval 32 allows the repeater transmitter to broadcast a message containing a signal (e.g., ringing), which may include the address code number for starting one home unit in - area 19. Each home team has an address code associated with it that must be used to run the home team, and the central data commutation control has a directory of all such numbers in the nationwide network. The broadcasting time interval 33 provides a time slot for checking errors and providing the needed control signals. Surveillance slots 36 are introduced between consecutive broadcast periods 30, also called radio frequency fields.

Radio frequency fields enable transmission at 5.1 kbd for each of e.g. ten zones 22. Each of the repeaters thus has in the buffer memory the home unit data transmission rates multiplied by ten to enter the buffer memory at 51 kbd. The total transmission speed for the main cellular area 19 is 51 kbd with ten simultaneous responses from separate zones 22. Assuming no errors and sending 1000 bits messages from each home team, when 3000 home teams are trying to send their messages through ten channels, then the waiting time for the line would be less than one minute without having to redial.

As shown in Fig. 3, each remote receiving station 20A-20N is allocated a suitable frequency band fi-fn 'by which isolation is obtained from subscriber X in each zone 22 in area 19. The length of radio frequency fields is 12.4 milliseconds including a surveillance band 36 of approximately 120 microseconds.

Figure 4 shows a typical message transfer protocol for a fixed message length of 30 bytes of 8 bits. This fixed length is important to minimize system access time under peak load conditions, since there will be essentially no risk of dead radio time while some subscriber is waiting for a connection or disconnection. Broadcast interval 32 usually includes various functional categories. The home team identification section addresses the team to be started (similar to the telephone number), and the packet identification byte for gathering certain sequences of home team response fields into one packet. All messages and protocol are compatible with data transmission by default as part of the video signal during exp^jjvertical transmission or with transmission via a digital radio link parallel to the video channel. However, as it will be explained in more detail below, it is beneficial to synchronize the time-determined data in a nationwide system, even taking into account the differences in radio propagation time, and therefore to synchronize the transmission with the television carrier signal from the amplifier transmitter and to organize all time reproduction slots generally known technical procedures can be used to avoid idle radio time. Therefore, this system departs from all existing telephone commutation systems with asynchronous commutation.

As shown in Figs. 1, 2, 4 and 5, broadcasting with a general coverage of messages from individual subscriber units 4, longer than 240 bits, requires several fields with accumulating packets that can be identified in broadcast field 32. The cell station transmitting system processes thus, the packet of packets as shown in Fig. 5 to accumulate variable length subscriber messages into a set of serial transmissions to be transmitted to the satellite with a higher transmission frequency. The packet creation teams 41, 41A, etc. are individually assigned to one corresponding subscriber at the same time, until a variable length subscriber message containing n fields of 240 bits is completed, and after determining the price of the packet in step 42, the messages are accumulated in step 43, synchronously

172 843 timed in step 45 and broadcast in step 44 to the satellite. These accumulated messages are received by the data control center 2 for switching, adding the specific subscriber's data and receiving address, and retransmitting it via satellite to a receiving point, such as a downstream subscriber or service provider.

Figures 6A and 6B refer to the communication sequence in the cellular area of ​​the teletransmission station of the local area 19 (Fig. 2) between subscriber assemblies 4, repeaters 3 and remote fixed receivers 20. It should be noted that subscriber assembly 4 can be any interactive data transmission device, which general term includes subscriber video stations, digital alarms etc. and mobile assemblies.

The block diagram of the data flow shown in Fig. 6B refers to the juxtaposition and sequence of interconnection responses between respective subscriber units 4, remote fixed receivers 20 zones 22 and repeaters 3. Synchronization is controlled by the carrier frequency Txa of the repeater transmitter on which the unit is set subscriber 4. Subsequently, the subscriber team 4 starts a response that includes both the subscriber identification tag and repeater identification tag for transmission between repeaters with portable units or freezing of cellular stations of the area.

The remote receiver 22 receives signals transmitted by the subscriber on its frequency Rx <u and sends confirmation to repeater 3 for sampling the transmission and supervising the routing of the transmission. Amplifier 3 selects the remote unit 22, 22 'etc. which receives the best subscriber signal. It should be noted that the remote receiver 22 receives both the signal transmitted on the Rxai frequency of the repeater transmitter, and ss ^^ r ^ c ^ forwarded the same IRxs and pc ^ cD every day: the subscriber team transmits on two alternative frequencies, one of which is tuned to the frequency of the specific remote receiver 20.

The amplifier 3 then transmits the best frequency back to the subscriber set 4 for tuning and terminating communication with the best and only remote receiver 20. This is the end of the set up period and the beginning of the transmission period during which the message bits are transmitted to the repeater 3 by the remote receiver 20, which has been tuned and are processed in the repeater 3 and transferred to the data center network via the VSAT link. It should be noted that the gap 33 between the broadcasting interval 3l of the repeater 3 and the response interval 31 of the subscriber unit is used for such a combination of functions that the period of one field includes the procedure of Fig. 6B by transmitting one message field from the subscriber unit. If the transmission conditions change, the next field of the subscriber's message could therefore be transmitted from another remote receiver on a different frequency. Thus, part of the packet identification byte of Fig. 4 is important for reassembling the message fields into one message packet (also marked). Any cellular identification number 486 is similar to the code designation of a telephone exchange area when identifying a cellular address or the full address of an identifiable subscriber.

The setup procedure is important for transferring the mobile assembly from one stationary remote receiver 22 to another because freeze areas such as boundaries between the operating zones of the two remote receivers 22 are encountered (Fig. 2). Similarly, portable assemblies can be transferred from a repeater to a repeater when adjacent repeaters are located e.g. in urban areas, which requires a similar handover procedure. Transmission can be initiated in various ways.

As described above, the repeater 3 may initiate the forwarding of the subscriber assembly 4 from the remote receiver 20 in one zone to another station in another zone with. subdivision repeater. Measurement of RSSI signal parameters can therefore serve as a criterion for forwarding, with the repeater directing the subscriber to the program

172 843 compilation, if signals below the threshold occur, e.g. -80 dBm. Since the subscriber team 4 stores the transmitted data in memory, they are held until the end of the compilation procedure for about 50 milliseconds.

Alternatively, the subscriber unit software may cause subscriber unit 4 to enter into the set up program when RSSI drops below the selected threshold value, so that the home unit response is only sent after satisfactory connection set up with the repeater or repeater zone 20 of the repeater with the right signal strength.

When subscriber units 4 are suitable for transfer from repeater to repeater, packets (Fig. 5) should be sorted by data control center 2 rather than at repeater level 3. Each packet has a subscriber identifier for this purpose and the packet identifier is carried in the field broadcast (Figure 4) for such processing. Thus, in the data control center 2, a packet of three fields from two different repeaters, essentially geographically adjacent, can be formed. It should be noted that in subscriber transmissions (Fig. 6B) there is a repeater identifier that is used for control purposes.

As shown in Figure 2, the possibility of frozen relay errors or interfering signals between repeaters has been eliminated by allocating different transmission frequencies for communication with geographically adjacent remote receiver stations 20 in adjacent cell areas 19, 26. In the vicinity of the overlapping cellular areas 19 and 26, the respective frequencies fx, fy allocated to neighboring remote receivers 20X and 20Y can avoid interference problems between remote receiving stations 20 in different neighboring cell areas.

Important synchronizations in messages processed at the cell station (Fig. 2) are discussed based on Figs. 7A and 7B. To maintain accurate synchronization of message bits in the system, radio propagation time delays must be calculated. These propagation times are indicated in Fig. 7A, and the time parameters of the transmitted message field are given in Fig. 7B. The fields are successively separated by a 120 microsecond band. A corresponding delay of 2.7 microseconds in a cell area 19 with a diameter of about 3 km is encountered between the subscriber group 4 and the nearest remote receiver station 20 from about ten such stations arranged around the cell. This does not matter, because thanks to the use of 50 microseconds of implant width, it is less than 6% of the pulse width, so for this propagation delay no adjustment of the range is needed. Therefore, amplifier 3 sets its synchronization in the system based on the received responses of the subscriber after calculating the delay time of about 2 x 10.6 microseconds (on average) for transmission to subscriber 4 and back to repeater 3.

Figures 8A and 8B show FCC compliant interactive communication bands for which permits are obtained, thereby allocating fifteen channels with a bandwidth enabling the transmission of messages under the conditions described herein.

Figures 9A and 9B respectively show portable subscriber assemblies suitable for an interactive two-way wireless communication system in an FCC compatible repeater for interactive video and data services with a simplified digital device (Fig. 9A) and with a more complex vision imaging device (Fig. 9B).

In the simplified version of Fig. 9A, the transceiver 50 enables bidirectional wireless communication in the 218-219 MHz bands shown in Fig. 8 compatible with the functions described previously, e.g. with reference to Fig. 6A. Two-headed arrow for radio waves at antenna 49 indicates two-way wireless communication. For digital communication, an input register 51 is provided for received data

172 843 digital and output register 52 for storing interactive subscriber messages from transducer 53, typically a hand keyboard or a digital sensor device. Digital displays can be used so that the subscriber can observe the content of one or both of these registers. The data processor 54 through the appropriate software controls the system in various modes of operation, such as manual control 55 suitable for entering data from the subscriber's keyboard or an automatic supervision control mode 56 for transmitting an alarm or indicating the slot status of the vending machine owned by the subscriber. The frequency control section 57 is used to supervise and set the transmission carrier frequency during the compilation procedures for sending to the most advantageous fixed remote receiver 20. It also serves as a system clock for synchronizing the frequency of digital data transmission with the system, e.g. by synchronization with the carrier signal of a television station. An identification number 58 is created in each subscriber team, which, similarly to the telephone number, serves as a screen for incoming messages directed to this subscriber team and as the identifier of the source of messages originated? Mvrb nr7P7 of the given subscriber

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The general software control technique for operating subscriber assemblies and systems in the described system is generally known.

This embodiment of the interactive data transmission system according to the invention has many innovative properties and significant advantages, all compatible with operations within the FCC compliant network parameters services, interactive data transmission and vision either for interactive communication within the local cell or for interactive communication within a network limited to a defined area, for example a national network. The data processor controlled by the software makes the use of such a system essentially universal in the sense of introducing operating modes matching and integrated with typical equipment or systems, and to provide various properties of the manual interaction control by the subscriber. The simplicity of communication in digital mode makes the assembly simple, cheap and small for perfect portability and long battery life with battery power. It is very important to be able to use in the interactive installation the data transmission service and the vision of the mobile subscriber's movement to ensure the connectivity capabilities previously limited to fixed-range mobile telephone systems, and to ensure that the range of interactivity previously unattainable.

The embodiment of Fig. 9B provides interactivity in conjunction with video displays, and in particular relates to broadcast television programs. A conventional television receiver 60 via a wireless link 63 connects to an interactive data transmission device 61, e.g. for typical telecommunication services. To this end, the manual control unit 62 controls the television receiver 60 and the interactive data transmission device, which in this case can be called a home unit or a subscriber unit. The portability feature enabled by the solution of the invention allows such a unit to be moved to an adjacent room or placed in a car in which it can be transported within boundaries or across cell boundaries with good digital synchronous communication within a cellular network with a fixed range.

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FIG. 5

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REMOTE RECEIVER AND MOBILE STATION

F1G.7B

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<td>15 CHANNELS 468.75 kHz</td><td>15 CHANNELS 468.75 kHz</td>

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<td>and</td><td>213.03125 ί - '. HZ.</td><td> 16</td><td>213.53125 MH2</td>

<td> 2</td><td> 213,0625</td><td> 17</td><td> 213,5625</td>

<td> 3</td><td> 213,09375</td><td> 13</td><td> 2 13,59375</td>

<td> 4·</td><td> 213.125</td><td> 19</td><td> 213,625</td>

<td>S</td><td> 213,15625</td><td> 20</td><td> 213,65625</td>

<td>έ&gt;</td><td> 213,1375</td><td></td><td>2lfe, 6 &amp; 75</td>

<td> 7</td><td> 213,21375</td><td> 22</td><td> 213,75375</td>

<td>s</td><td> 213,25</td><td>Zi</td><td> 213,75</td>

<td>e</td><td> 213,23125</td><td> 24-</td><td> 213,73125</td>

<td>IO</td><td> 213,3125</td><td> 25</td><td> 213,3125</td>

<td> 1 1</td><td> 213,34375</td><td> 26</td><td> 213,34375</td>

<td> 12</td><td> 213,375</td><td> 27</td><td> 213,315</td>

<td>ra</td><td> 213,40625</td><td> 23</td><td> 213,90625</td>

<td> 14-</td><td> 213,4375</td><td> 29</td><td> 213,9375</td>

<td> 15-</td><td> 213,4-6375</td><td> 30</td><td> 213,9637 5</td>

FIG.8B

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9A

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FIG. 9B

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