Abstract:
A preferred embodiment of the present invention generally comprises a hand-held two-way radio employing digital selective calling. The hand-held two-way radio further comprises a VCO operative to modulate the radio signal frequencies of a guard channel such that the guard channel can be changed by changing the output of the VCO. In addition, the present invention comprises a hand-held two-way radio comprising circuitry operative to function according to the digital selective calling international standards, and a VCO operative to modulate the radio signal frequencies of a guard channel such that the guard channel can be changed by changing the output of the VCO. A fourth embodiment of the present invention comprises a hand-held two-way radio comprising circuitry operative to send and receive GPS data, and a VCO operative to modulate the radio signal frequencies of a guard channel such that the guard channel can be changed by changing the output of the VCO.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application claims priority under 35 U.S.C. §120 from U.S. Provisional Application Ser. No. 60/190,846, filed Mar. 20, 2000. 
     
    
     
       TECHNICAL FIELD OF THE INVENTION  
         [0002]    The present invention generally relates to electronic communication devices and, more particularly, to a handheld two-way radio with digital selective calling.  
         BACKGROUND OF THE INVENTION  
         [0003]    Digital selective calling was conceived by an international committee in the early 1970s. Its purpose was to expedite the handling of traffic in the maritime service by facilitating more efficient calling between ships and from ship to shore, and to provide a more automated distress and safety system. The international committee, known as the CCIR, comprised representatives from all countries with salt-water coastlines, both from the private and public sectors, including the FCC from the United States.  
           [0004]    A key factor in the acceptance of the DSC protocol was the safety of life at sea (SOLAC) treaty of 1974 (amended in 1988), requiring the use of DSC for distress alerting and safety calling. Current international treaties require a limited compliance with this treaty starting in 1992. Since that time, certain types of vessels have been required to have DSC equipment. Recently, many nations have been expediting the implementation of DSC systems in the VHF arena in hopes of relieving some of the congestion on the voice distress and calling channel (channel  16 ). DSC helps solve this problem as it uses channel  70  for its routine calling channel.  
           [0005]    In the DSC system, each radio is programmed with a unique identification number. The radios are carried by vessels, marinas, bridge tenders, coast stations, etc. DSC ship station identification numbers are issued by appropriate communications authorities in each country, such as the FCC (United States) and the DOC (Canada). DSC ship station identification numbers are similar to telephone in that they are unique to each station. Each DSC radio constantly monitors the calling channel (channel  70 ) looking for a broadcast of its ship station identification number. Therefore, in order to call another DSC radio, the calling radio will broadcast the ship station identification number for the receiving DSC radio, as well as the identity of a separate working channel selected by the caller. The receiving DSC radio, monitoring calling channel  70 , will see that it is being called by another radio, and will switch its receiver over to a working channel broadcast with the ship station identification number. The two radios can then communicate with one another on the selected working channel, while continuing to monitor calling channel  70  in case a call is received from another radio.  
           [0006]    It can thus be seen that the use of DSC radio completely avoids congestion on channel  16  both during the initial contact and during the subsequent conversation. If an operator is not available to answer a call placed to a DSC radio, the radio will typically log the call in an internal directory so that the call can be returned when the operator is able to do so.  
           [0007]    DSC radios have the ability to be connected to a navigation receiver, such as a LORAN-C or GPS receiver, such that the radio will be able to automatically give the radio&#39;s position to another vessel with a simple digital call. Alternatively, another DSC radio can request your position from your DSC radio. This makes DSC very useful for vessels locating one another and is particularly useful for fleet operators tracking several vessels.  
           [0008]    In the event of an emergency on a vessel, the DSC operator can press one key to broadcast an emergency distress message (on channel  16 ) using the DSC system. This message will be received by all vessels equipped with DSC equipment and will sound alarms on each one. If the DSC radio is connected to a navigation receiver, the vessel&#39;s position will also be broadcast, making it much easier for others to come to aid.  
           [0009]    DSC has therefore proved to be a valuable resource in maritime communications. However, an analogous system has never been implemented for land based communications, particularly for mobile (handheld) applications. The present invention is directed toward meeting this need.  
         SUMMARY OF THE INVENTION  
         [0010]    A first embodiment of the present invention comprises a hand-held two-way radio employing digital selective calling.  
           [0011]    A second embodiment of the present invention comprises a VCO operative to modulate the radio signal frequencies of a guard channel such that the guard channel can be changed by changing the output of the VCO.  
           [0012]    A third embodiment of the present invention comprises a hand-held two-way radio comprising circuitry operative to function according to the digital selective calling international standards, and a VCO operative to modulate the radio signal frequencies of a guard channel such that the guard channel can be changed by changing the output of the  
           [0013]    A fourth embodiment of the present invention comprises a hand-held two-way radio comprising circuitry operative to send and receive GPS data, and a VCO operative to modulate the radio signal frequencies of a guard channel such that the guard channel can be changed by changing the output of the VCO.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a schematic block diagram of a prior art super heterodyne radio receiver employing selective calling.  
         [0015]    [0015]FIG. 2 is a schematic block diagram of a first embodiment super heterodyne receiver of the present invention employing digital selective calling.  
         [0016]    [0016]FIG. 3 is a graph of channel frequency versus attenuation for a prior art bandpass filter.  
         [0017]    [0017]FIG. 4 is an electrical schematic diagram for a preferred embodiment front end of the present invention.  
         [0018]    FIGS.  5 A-C are graphs of channel frequency versus attenuation illustrating the operation of adjustable bandpass filter of the present invention.  
         [0019]    [0019]FIG. 6 is an electrical schematic diagram of the IF section of a preferred embodiment of the present invention.  
         [0020]    [0020]FIG. 7 is a schematic block diagram of a main RF section of the preferred embodiment of the present invention.  
         [0021]    [0021]FIG. 8 is an electrical schematic diagram of a main RF section of the preferred embodiment of the present invention.  
         [0022]    [0022]FIG. 9 is an electrical schematic diagram of the VCO  40 ,  46  of a preferred embodiment of the present invention.  
         [0023]    [0023]FIG. 10 is a schematic block diagram of an audio module of the preferred embodiment radio of the present invention, illustrating the audio processing circuitry and data modems.  
         [0024]    [0024]FIG. 11 is an electrical schematic diagram of an audio module of the preferred embodiment radio of the present invention, illustrating the audio processing circuitry and data modems.  
         [0025]    [0025]FIG. 12 is an electrical schematic diagram of the central processing unit (CPU) and interface for controlling a preferred embodiment radio of the present invention.  
         [0026]    [0026]FIG. 13 is an electrical schematic diagram of a keypad for use in the preferred embodiment radio of the present invention.  
         [0027]    [0027]FIG. 14 is an electrical schematic diagram of the top panel connections for a preferred embodiment radio of the present invention.  
         [0028]    [0028]FIG. 15 is an electrical schematic diagram of the push-to-talk (PTT) switches for use in a preferred embodiment radio of the present invention.  
         [0029]    [0029]FIG. 16 is an electrical schematic diagram of a flex circuit for use with a liquid crystal display (LCD) of the preferred embodiment radio of the present invention.  
         [0030]    [0030]FIG. 17 is an electrical schematic diagram of a flex circuit for use with the top panel of a preferred embodiment radio of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0031]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, and alterations and modifications in the illustrated device, and further applications of the principles of the invention as illustrated therein are herein contemplated as would normally occur to one skilled in the art to which the invention relates.  
         [0032]    With reference to FIG. 1, there is illustrated a schematic block diagram of a prior art super heterodyne radio receiver employing digital selective calling, indicated generally at  10 . The radio  10  includes an antenna  12  capable of coupling electromagnetic radiation in the frequency band of interest and applying this signal to a front end  14 . The front end  14  provides standard radio processing functions as known in the art, such as filtering of the signal from the antenna  12  to a particular band of interest. The signal from the front end  14  is applied to a mixer  16 , which has a secondary input provided from a crystal  18 . The output of the mixer  16  is a first intermediate frequency (IF) signal  20  which is applied to the guard channel processing circuitry of the radio.  
         [0033]    Because the guard channel for all prior art digital selective calling radios is channel  70  (156.525 MHz), and the crystal  18  vibrates at a fixed frequency of 135.125 MHz, the first IF signal  20  will always be at exactly 21.4 MHz. Since it is known that the first IF signal  20  will always be 21.4 MHz, the processing circuitry to which the signal  20  is applied can be designed to be optimized for processing at this frequency.  
         [0034]    The signal from the front end  14  is additionally applied to a second mixer  22 . A second input to the mixer  22  is applied by a voltage controlled oscillator (VCO)  24  because the signals in the front end can be anywhere within a predefined frequency range, a particular frequency (i.e. channel) may be selected by controlling the VCO  24  to emit a frequency that, when combined with the frequency of interest in the mixer  22 , produces a first IF signal of 21.4 MHz upon the signal line  26 . The signal upon the line  26  is applied to the voice channel processing circuitry, which preferably includes a narrow band pass filter centered on 21.4 MHz. In this way, any channel within the frequency range covered by the front end  14  may be precisely selected by controlling the frequency output of the VCO  24 .  
         [0035]    The digital selective calling radio  10  of FIG. 1 is useful in marine applications where all radios in use utilize a fixed guard channel  70 . If a different guard channel were selected, the crystal  18  would have to be physically removed from the radio  10  and replaced with a crystal that vibrated at the appropriate frequency which would produce a first IF signal  20  of 21.4 MHz for the new guard channel of interest. This presents a problem in land-based used for DSC radios. Different organizations with wish to use land-based DSC radios (such as fire departments, lifeguard departments, etc.) can potentially be located in close physical proximity to one another. Because these organizations would not necessarily be involved with one another&#39;s operations, they could potentially desire to have different guard channels, such that, for example, the fire chief could call all of the fire department radios upon their assigned guard channel without disturbing the radios of the lifeguards. For this reason, land-based DSC radios will preferably have guard channels which differ from location to location. If the prior art design of radio  10  is utilized, then a different radio needs to be manufactured for each different location.  
         [0036]    In order to solve this problem, the present invention utilizes a first embodiment super heterodyne receiver architecture as illustrated in FIG. 2 and indicated generally at  30 . The radio  30  also uses an antenna  12  which couples electromagnetic signals and applies these to a splitter  32 . The splitter  32  applies the signal from antenna  12  (at a signal power decreased by 3 dB) to front ends  34  and  36 , which contain processing circuitry as is known in the art. The signal from the front end  34  is applied to a mixer  38 . A signal from a voltage controlled oscillator (VCO)  40  is also applied to the mixer  38 . In this way, a particular frequency of interest may be selected from the signal supplied by the front end  34  by selecting a VCO  40  frequency which, when mixed with the front end signal of interest in the mixer  38 , produces a first IF signal of 21.4 MHz on the line  42 . This signal is applied to the voice channel processing circuitry, which includes a narrow band pass filter to select the 21.4 MHz signal of interest.  
         [0037]    Likewise, the signal from the front end  36  is applied to a second mixer  44 . A signal from a second VCO  46  is also applied to the mixer  44 . The signal from the second VCO  46  is chosen to be at a frequency which, when combined with the guard channel frequency of interest from the front end  36 , will produce a first IF signal of 21.7 MHz on the line  48  as an output from the mixer  44 . The signal on the line  48  may then be applied to the guard channel processing circuitry, which includes a narrow band pass filter centered on 21.7 MHz. It will be appreciated that the radio  30  may support the selection of any channel as the guard channel, by electronically varying the output frequency of the VCO  46 . This may be done as an internal adjustment, or may done as an internal adjustment or may be selectable by the user by means of any convenient radio controls. An electrical schematic diagram of a preferred embodiment VCO  40 ,  46  is illustrated in FIG. 9.  
         [0038]    It should be noted that in the first embodiment of FIG. 2, the first IF signal for the voice channel is selected at 21.4 Mhz, while the first IF signal for the guard channel is selected at 21.7 Mhz. This is done to minimize cross-talk interference between the voice channel processing circuitry and the guard channel circuitry. Because each circuit is optimized for the particular IF signal frequency, any coupling of the other IF signal frequency into the circuit will have minimal effect because that coupled frequency is outside of the circuits optimized processing frequency.  
         [0039]    Another limitation in prior art DSC radios is illustrated in FIG. 3, wherein a graph of channel frequency versus attenuation is illustrated. The attenuation illustrated in FIG. 3 corresponds to the bandpass filtering that is utilized in the prior art front end  14 . As can be seen from the graph, the filtering of the prior art front end  14  comprises a bandpass function centered on the fixed guard channel  70 . In contrast, both the voice channel  42  and guard channel  48  of the present invention require filtering within the front ends  34 ,  36  that is adjustable depending upon which particular frequency is chosen as the voice channel and the guard channel. The prior art solution illustrated in FIG. 3 is therefore unacceptable for this application.  
         [0040]    [0040]FIG. 4 illustrates a preferred embodiment electrical schematic diagram for the front end  34 ,  36 . A filter section  50  provides bandpass filtering wherein the bandpass has an adjustable center frequency. An RF input, such as from the splitter  32 , is provided at the input  52 . This RF signal is bandpass filtered with a bandpass center frequency determined by a voltage applied to control terminal  54 . The filtered RF signal is available at the RF output port  56 . As is known in the art, it is common to use an LC (inductance-capacitance) circuit in order to provide filtering of an electrical signal. In the adjustable bandpass filter  50 , part of the capacitance used for filtering is a veractive diode (D 1 , D 2 ). The capacitance of the veractive diode changes with the voltage applied to the input terminal  54 .  
         [0041]    Because the receiver  30  already includes voltage signals which vary with the voice channel and guard channel frequencies, namely the outputs of VCO  40  and VCO  46  respectively, the values of the components in filter  50  may be chosen such that the VCO voltage may be applied to the front end at input terminal  54  in order to control the center frequency of the bandpass filter  50 . This is advantageous in that it simplifies the electrical design of the radio by finding another use for the voltage already being generated by the VCO  40 ,  46 . Alternatively, the control voltage applied to input  54  could be a voltage that is empirically predetermined for the front end  34 ,  36  and stored digitally (such as in an EEPROM). This stored digital information could be utilized as a look-up table which maps the desired center frequency to the voltage to be input to port  54 . The digital information retrieved from the look-up table would then be input into a digital-to-analog converter in order to create the voltage signal to be applied to input  54 .  
         [0042]    Use of the bandpass filter  50  is illustrated in FIGS. 5 a - c . As can be seen from these figures, as the channel frequency (guard channel or voice channel) changes, the center frequency of the bandpass filter  50  changes automatically to track the changing channel frequency. In the preferred embodiment, adjustment of the VCO  40 ,  46  to change the channel frequency also automatically changes the center frequency of the bandpass filter to match the selected channel frequency because the input control voltage to the VCO  40 ,  46  is used to control the adjustable bandpass filter  50 .  
         [0043]    Electrical schematic diagrams for a preferred embodiment of DSC radio of the present invention are illustrated in FIGS.  6 - 17 . FIG. 6 is an electrical schematic diagram of the IF section of a preferred embodiment of the present invention. FIG. 7 is a schematic block diagram and FIG. 8 is an electrical schematic diagram of a main RF section of the preferred embodiment of the present invention. FIG. 9 is an electrical schematic diagram of the VCO  40 ,  46  of a preferred embodiment of the present invention. FIG. 10 is a schematic block diagram and FIG. 11 is an electrical schematic diagram of an audio module of the preferred embodiment radio of the present invention, illustrating the audio processing circuitry and data modems. FIG. 12 is an electrical schematic diagram of the central processing unit (CPU) and interface for controlling a preferred embodiment radio of the present invention. FIG. 13 is an electrical schematic diagram of a keypad for use in the preferred embodiment radio of the present invention. FIG. 14 is an electrical schematic diagram of the top panel connections for a preferred embodiment radio of the present invention. FIG. 15 is an electrical schematic diagram of the push-to-talk (PTT) switches for use in a preferred embodiment radio of the present invention. FIG. 16 is an electrical schematic diagram of a flex circuit for use with a liquid crystal display (LCD) of the preferred embodiment radio of the present invention. FIG. 17 is an electrical schematic diagram of a flex circuit for use with the top panel of a preferred embodiment radio of the present invention.  
         [0044]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.