Abstract:
A radio receiving apparatus has a receiving section for receiving a radio signal, a local oscillating section for generating a first local oscillation signal and a second local oscillation signal, wherein the first local oscillation signal and the second local oscillation signal have each of a first frequency and a second frequency differing from a received frequency. The apparatus also has a frequency converting section for mixing the received signal output from the receiving section and the first local oscillation signal to output an intermediate frequency signal and an orthogonal converting section for orthogonal converting the intermediate frequency signal output with the second local oscillation signal.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a radio receiving method and a radio receiving apparatus which are used to obtain baseband signals by orthogonally converting radio receipt signals after being frequency-converted, when receiving and demodulating a simultaneous paging signal such as a pager, etc. 
     2. Description of the Related Art 
     Conventionally, a pager has been known as one of radio receiving apparatus which receive a simultaneous paging signal, telephone number and business of a transmission pager (caller) and display the same. A super heterodyne system has been employed for conventional pagers. In the super heterodyne type pagers, a narrow-band filter, for example, a band-pass filter (BPF) is disposed between an antenna and a receiving amplifier. However, since the BPF is large-sized, there is such a problem where if a BPF is equipped in a pager, the pager itself is unavoidably made large in size. Therefore, in recent pagers, a direct conversion (DC) receiving system which has a simple construction and is able to be small-sized is employed. 
     FIG. 8 is a block diagram showing major parts of a DC receiving type radio receiving apparatus. FIG. 8 shows a frequency signal processing system to orthogonal conversion in a radio receiving apparatus in which a DC receiving system is employed. In the radio receiving apparatus, radio waves of FSK system coming from the base station are received by antenna Antl, and the receiving signal (f0) is amplified by a high-frequency amplifier  2 . Amplification signal (f0) coming from high-frequency amplifier  2  is inputted into mixers  3   a ,  3   b . Local oscillation signals (cosine wave signals, sine wave signals) which are of the same frequency (fL) as that of the receiving signals (f0) are inputted into these mixers  3   a ,  3   b , wherein the receiving signals (f0) are multiplied by the local oscillation signals. 
     A local oscillation signal (fL) of cosine wave signals outputted from local oscillator  7  is supplied into the mixer  3   a , and sine wave signals, in which the phase of the local oscillation signals (fL) outputted from the local oscillator  7  is shifted 90° by phase shifter  8 , is supplied into the mixer  3   b . Orthogonal conversion is carried out by multiplying the receiving signal (f0) by local oscillation signals (cosine wave signals, sine wave signals) in the mixers  3   a ,  3   b , whereby base band signals (I component signals and Q component signals) are obtained. 
     I signals and Q signals outputted from mixers  3   a ,  3   b  are inputted into a demodulation circuit  6  after they are band-limited through channel filters  4   a ,  4   b  having the center frequency corresponding to the receiving channel (ch) and limiters  5   a ,  5   b . Then, demodulation signals are outputted from the demodulation circuit. 
     Furthermore, at the local oscillator  7 , oscillation circuit  9  is caused to oscillate at the reference frequency of crystal oscillator XTAL, wherein oscillation signals of oscillation circuit  9  are given to phase locked loop (PLL) portion  10  consisting of a phase comparator, prescaler, programmable divider (counter), mixer, etc. (which are not illustrated). The oscillation frequency of voltage control oscillator (VCO)  12  is locked to a specified frequency by a control voltage which is generated by causing the output signals of PLL portion  10  to pass through a low pass filter (LPF)  11 . The oscillation signal (fV), the frequency of which is locked, is multiplied by multiplication circuit  13 , and local oscillation signals having the same frequency (fL) as that of the receiving frequency (f0) are sent out to mixers  3   a ,  3   b . In the PLL portion  10 , programmable divider, etc. receives control signals from CPU  14  to cause the receiving frequency to be established. 
     The entirety of local oscillator  7  is covered by shield case  15 , whereby unnecessary radiation is attempted to be decreased. However, especially, since the resonance frequency of antenna Ant 1  is identical to that of local oscillation signals, the local oscillation signals are radiated through antenna Ant 1 . This becomes unnecessary radiation waves and is received again. If a phase difference exists between the unnecessary radiation waves and the receiving frequency (f0), noise is generated in the demodulation signals. Furthermore, unnecessary radiation of intensive electric field strength is mixed from a circuit substrate member, at which local oscillator  7  cannot be shielded by a shield case  15 , etc., into a mixer. 
     Improvement of unnecessary radiation from an antenna in such a DC receiving system was proposed. For example, as disclosed in Japanese Laid-open Patent Publication No. 321686 of 1995, local oscillation signals inputted into a mixer where orthogonal conversion is carried out are set in a phase relationship where they are drowned each other. Thereby, unnecessary radiation power from antenna can be decreased. 
     However, in the example of the abovementioned Patent Publication, although improvement of decreasing unnecessary radiation power from antenna was attempted, it is difficult to carry out an accurate orthogonal conversion by the mixer, and simultaneously the apparatus will be made large-sized, wherein the actual mounting area of electronic components is decreased, and the process work will be made cumbersome. 
     That is, since local oscillation signals coming from the local oscillation portion are, directly or through a common earth, jumped into a mixer or antenna system, it is necessary to cover the local oscillation portion with a shield case as in the description of the former in the conventional example. Furthermore, since local oscillation signals are jumped directly into the antenna system, it is difficult to securely prevent local oscillation signals from being radiated from an antenna, the frequency of which is the same as that of the local oscillation signals. Therefore, unnecessary radiation waves are received again, wherein as a phase difference occurs between the unnecessary radiation waves and the receiving frequency, noise is caused to occur in the demodulation signals. 
     Furthermore, If the local oscillation portion is covered by a metal-made shield case, space is caused to occur between members inside the shield case and internal electronic components. In other words, the shield case is made large-sized. Resultantly, this becomes an obstacle in view of requirements of downsizing and light weight. 
     Still furthermore, since a large-sized shield case is disposed, the actual mounting area of secondary and thirdly circuit substrates of electronic components is decreased. In this case, since more electronic components can not be mounted, no high performance and downsizing can be achieved. Furthermore, since it is difficult to automatically dispose a large-sized shield case in the standard automatic surface mounting machine, manual work is requisite. That is, a shield case attaching process and soldering process are made cumbersome, wherein the assembling efficiency is worsened. 
     SUMMARY OF THE INVENTION 
     The present invention was developed in view of the abovementioned situations, and it is therefore an object of the invention to provide an excellent radio receiving method and a radio receiving apparatus, which are able to eliminate a comparatively large-sized shield case, to carry out an accurate orthogonal conversion, and enable a downsizing and light weight, and which improve the efficiency of assembling processes. 
     In order to achieve the abovementioned object, the present invention is constructed so that receiving signals are frequency-converted by local oscillation signals of the second frequency generated by a local oscillation portion after they are frequency-converted by local oscillation signals of the first frequency generated from the output of the abovementioned local oscillation portion, and they are orthogonally converted to obtain a base band signals. 
     Furthermore, the invention is constructed so that after the receiving signals are converted to intermediate frequency signals by mixing them with local oscillation signals of the first frequency, the intermediate frequency signals are directly mixed with local oscillation signals of the second frequency, wherein by orthogonal conversion, base band signals are obtained. 
     Furthermore, a radio receiving apparatus according to the invention comprises a receiving circuit for receiving radio waves; a frequency converting circuit for outputting intermediate frequency signals frequency-converted by mixing receiving signals from the receiving circuit and local oscillation signals of the first frequency; an orthogonal conversion circuit for outputting base band signals orthogonally converted by mixing the intermediate frequency signals from the frequency conversion circuit with local oscillation signals of the second frequency; and a basic frequency oscillation circuit for oscillating a basic frequency signal in order to generate local oscillation signals of the abovementioned first frequency and second frequency. 
     In these aspects of the invention, since radio receiving signals are frequency-converted by local oscillation signals of the second frequency generated from the output of the local oscillation portion after they are frequency-converted by the local oscillation signals of the first frequency generated from the output of the abovementioned local oscillation portions and base band signals are obtained by orthogonal conversion, the resonance frequency of antenna is not the same as the frequency of the first local oscillation signals as in a conventional DC receiving system, unnecessary radiation of local oscillation signals having the same frequency as the resonance frequency of the antenna is eliminated. In other words, it is possible to suppress noise generation due to receiving unnecessary radiation waves again. 
     Furthermore, since no mixing due to jumping of local oscillation signals of intensive field strength in frequency conversion and orthogonal conversion, accurate orthogonal conversion can be carried out. Furthermore, a comparatively large-sized shield case, covering the local oscillation portion, which is not able to be automatically mounted, is not required any more, it is possible to make the apparatus small-sized and and the assembling efficiency can be improved. 
     By making the sum of the first frequency and second frequency equal to the frequency of the receiving signals, an adequate frequency conversion can be achieved by a direct conversion system. 
     In this case, in order to carry out receiving by the direct conversion system, the basic frequency signal of the local oscillation signals may be set to a frequency obtained by dividing the receiving frequency by the sum of a multiplication ratio for generating the local oscillation signal of the first frequency and a multiplication ratio for generating the local oscillation signal of the second frequency. 
     Furthermore, the invention is constructed so that the same is able to selectively receive receiving signals of a plurality of frequencies and to change at least one of the first and second frequencies corresponding to the receiving frequency. 
     Furthermore, the invention is constructed so that the same comprises an antenna varying circuit capable of selectively receiving signals of a plurality of frequencies and a variable multiplication circuit for generating local oscillation signals of the first frequency and local oscillation signals of the second frequency from the basic frequency signals corresponding to the receiving frequency. 
     Thereby, it is possible for a single receiver to receive electric waves of different frequencies, and the receiver is preferable in a case where the same type of apparatuses are exported to a plurality of countries. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing a configuration of a first embodiment of the invention; 
     FIG. 2 is a block diagram showing a configuration of a second embodiment of the invention; 
     FIG. 3 is a block diagram showing a configuration of a third embodiment of the invention; 
     FIG. 4 is a block diagram showing a configuration of a fourth embodiment of the invention; 
     FIG. 5 is a circuit diagram showing a detailed configuration of an antenna varying circuit according to the fourth embodiment thereof; 
     FIG. 6 is a circuit diagram showing a detailed configuration of a variable high-frequency amplification circuit according to the fourth embodiment thereof; 
     FIG. 7 is a circuit diagram showing a detailed configuration of a variable multiplication circuit according to the fourth embodiment thereof; and 
     FIG. 8 is a block diagram showing a configuration of major parts of a conventional radio receiving apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A description is given of embodiments of a radio receiving method and a radio receiving apparatus according to the invention, with reference to accompanying drawings. 
     FIRST EMBODIMENT 
     FIG. 1 is a block diagram showing a configuration of the first preferred embodiments of a radio receiving apparatus according to the invention. In FIG. 1, a high-frequency processing system to orthogonal conversion in a radio receiving apparatus is shown. The radio receiving apparatus has antenna Ant 2  for receiving FSK type paging signals, and a high-frequency amplifier  21  for amplifying the receiving signals (f0) from the antenna Ant 2 . Furthermore, the apparatus is provided with a mixer  22  where amplification signals (f0) are inputted from the high-frequency amplifier  21 , are mixed with the first local oscillation signals (fL1) and are converted to intermediate frequency signals of frequency (fIF). 
     Furthermore, this embodiment is provided with mixers  23   a ,  23   b  which output base band signals (I signals, Q signals) obtained by orthogonal conversion which is carried out after intermediate frequency signals of frequency (fIF) outputted by mixer  22  are multiplied by the second local oscillation signals (fL2: cosine wave signal, sine wave signals), and the same is further provided with channel filters  24   a ,  24   b  for limiting the bands of I signals and Q signals from mixers  23   a ,  23   b , limiters  25   a ,  25   b  for controlling the level of I signals and Q signals from the channel filters  24   a ,  24   b  to a fixed level, and a demodulation circuit  26  which outputs demodulation signals by which I signals and Q signals outputted by the limiters  25   a ,  25   b  are demodulated. 
     Furthermore, the embodiment is provided-with local oscillation unit  30  which outputs local oscillation signals (fV) for frequency conversion and orthogonal conversion and is further provided with a multiplication circuit  28  which outputs the first local oscillation signals (fL1) obtained by multiplying “x” times the local oscillation signals (fV) outputted by the local oscillation unit  30  to the mixer  22 , and a multiplication circuit  29  which outputs the second local oscillation signals (fL2) obtained by multiplying “y” times the local oscillation signals (fV) outputted by the local oscillation unit  30  to the mixer  23   a  and phase shifter  27 . 
     The local oscillation unit  30  include oscillation circuit  31  which oscillates at the reference frequency of a crystal oscillator XTAL and a phased lock loop (PLL) portion  32  which is composed of a phase comparator, prescaler, programmable divider (counter) and mixer (which are not illustrated). The oscillation unit  30  is provided with a low pass filter (LPF)  33  which converts control signals coming from PLL portion  32  into direct current and outputs the same, a voltage control oscillator (VCO)  34  which outputs oscillation signals (fV) frequency-locked by a direct-current control voltage coming from the PLL  33  to multiplication circuits  28 ,  29 . These components constitute a closed loop circuit. 
     Furthermore, the embodiment is also provided with CPU  35  which changes a programmable divider (not illustrated) by control signals in the PLL  32  and establishes the receiving frequency. 
     Next, a description is given of actions of the first preferred embodiment. 
     Receiving signals (f0) coming from antenna Ant 2  are amplified by a high-frequency amplifier  21 . The amplification signal (f0) is inputted into the mixer  22 . In this mixer  22 , wherein the amplification signals (f0) are frequency-changed to intermediate frequency signals of frequency (fIF) by the first local oscillation signals (fL1), and the intermediate frequency signals are outputted into mixers  23   a ,  23   b.    
     In the mixers  23   a ,  23   b  of the latter stage, the intermediate frequency signals outputted by mixer  22  and the second local oscillation signals (fL2: cosine wave signal, sine wave signal) are multiplied by each other and orthogonally converted, wherein base band signals (I signals and Q signals) obtained by the orthogonal conversion are outputted. I signals and Q signals coming from mixers  23   a ,  23   b  are band-limited through channel filters  24   a ,  24   b , and are further inputted into limiters  25   a ,  25   b , wherein after the level of I signals and Q signals is suppressed to be fixed, they are demodulated by demodulation circuit  26 , and the demodulation signal is outputted. 
     In the local oscillation unit  30 , oscillation circuit  31  is caused to oscillate at the reference frequency of crystal oscillator XTAL. Oscillation signals of the oscillation circuit  31  are inputted into PPL  32 . Phase comparison differential signals between oscillation output signals (fV) of VCO  34  and multiplication oscillation signals from the oscillation circuit  31  are converted to direct current by LPF  33 , wherein VCO  34  outputs frequency-locked oscillation signals (fV) to multiplication circuits  28 ,  29  by the direct current control voltage. The first and second local oscillation signals (fL1, fL2) multiplied by the multiplication circuits  28 ,  29  are inputted into mixer  23   b  through mixers  22 ,  23   a  and phase shifter  27 . 
     The frequency relationship of frequency conversion in the mixer  22  and orthogonal conversion in mixers  23   a ,  23   b  is expressed by the following equation (1): 
     
       
         f0=fL1+fL2  (1) 
       
     
     where f0≠fL1, f0≠fL2, fL1=fV·x, fL2=fV·y, fIF=fL2 
     In such receiving processing, a programmable divider, etc. in the PLL  32  is changed and controlled by a control signal coming from CPU  35  and is set to the receiving frequency. 
     Thus, since the frequency conversion by mixer  22  and orthogonal conversion by mixers  23   a ,  23   b  are based on the relationship expressed by equation (1), no comparatively large-sized shield case which covers the local oscillation unit  30  is required any more. 
     That is, in comparison with a case of DC receiving system conventionally used, the resonance frequency of antenna Ant 2  is different from the frequency of the first local oscillation signals (fL1), wherein no unnecessary radiation is produced from antenna Ant 2 . Therefore, it is possible to prevent noise from occurring due to receiving unnecessary radiation waves again. Furthermore, even though unnecessary radiation of intensive field strength from the local oscillation unit  30  is mixed into the mixer  22  since the local oscillation signals (fV) which the local oscillation unit  30  outputs to mixer  22  are different from the receiving signals (f0), the influence can be eliminated. Furthermore, the second local oscillation signals (fL2) is attenuated and supplied into the mixers  23   a ,  23   b  through multiplication circuit  29  and phase shifter  27 , the influence thereof is also eliminated. In other words, an accurate orthogonal conversion can be carried out. 
     Furthermore, since no shield case is used, no space to cover electronic components of the local oscillation unit  30  is generated. Therefore, the entire of the apparatus can be small-sized, and particularly downsizing and light weight, which are requisite for pagers, are further improved. That is, since no shield case which is difficult to be automatically mounted by an automatic surface mounting apparatus is required, the attaching process and soldering process can be simplified, and the efficiency thereof can be further improved. 
     SECOND EMBODIMENT 
     FIG. 2 is a block diagram showing a configuration of the second preferred embodiment. The basic construction of the second preferred embodiment is identical to that of the first embodiment shown in FIG. 1, wherein the second embodiment differs in that a multiplication circuit  29  is removed from a pass of supplying oscillation signals from the local oscillation unit  30  to mixer  23   a  and phase shifter  27 . 
     The second preferred embodiment is provided with only a multiplication circuit  28   a  which multiplies “x” times the oscillation signals (fV) coming from the local oscillation unit  30  to sends the same to the mixer  22 . Oscillation signals (fV) coming from the local oscillation unit  30  is directly supplied to the mixer  23   b  through the mixer  23   a  and phase shifter  27 . All the other construction is identical to that of the first preferred embodiment. 
     Actions of the second preferred embodiment are the same as those of the first embodiment. However, the frequency relationship of frequency conversion in the mixer  22  and orthogonal conversion in the mixers  23   a ,  23   b  is expressed by the following equation (2): 
     
       
         f0=fL1+fL2  (2) 
       
     
     where f0≠fL1, f0≠fL2, fL1=fV·x, fIF=fL2=fV 
     In the second preferred embodiment, since a single multiplication circuit  28   a  is enough, the construction thereof can be simplified, and the other advantages are the same as those of the first preferred embodiment. 
     THIRD EMBODIMENT 
     FIG. 3 is a block diagram showing a configuration of the third preferred embodiment. 
     The basic construction of the third embodiment is the same as that of the first embodiment shown in FIG.  1 . However, the third embodiment differs in that a multiplication circuit  28  is removed from a pass of supplying oscillations from the local oscillation unit  30  to the mixer  22 . 
     The third preferred embodiment is provided with only a multiplication circuit  29   a  which supplies oscillation signals (fV) coming from the local oscillation unit  30  to the mixer  23   a  after multiplying the same “y” times, shifts the phase of oscillation signals (fV) from the local oscillation unit  30  ninety degrees (90°) by a phase shifter  27  and supplies the same to the mixer  23   b . The oscillation signals (fV) coming from the local oscillation unit  30  are directly supplied to the mixer  22 . All the other construction is identical to that of the first preferred embodiment. 
     Actions of the third preferred embodiment are the same as those of the first embodiment. However, the frequency relationship of frequency conversion in the mixer  22  and orthogonal conversion in the mixers  23   a ,  23   b  is expressed by the following equation (3): 
     
       
         f0=fL1+fL2  (3) 
       
     
     where f0≠fL1, f0≠fL2, fL1=fv, fL2=fV·y, fIF=fL2. 
     In the third preferred embodiment, a single multiplication circuit  29   a  is enough, the construction is able to be simplified, and all the other advantages are the same as those of the first embodiment. 
     FOURTH EMBODIMENT 
     FIG. 4 is a block diagram showing a configuration of the fourth preferred embodiment. 
     The fourth preferred embodiment has a feature of greatly varying the receiving frequencies (f0 to fn), which can meet a requirement where the service frequency bands are different according to districts. 
     The basic configuration is similar to that of the first preferred embodiment shown in FIG.  1 . However, the fourth preferred embodiment is provided with an antenna varying circuit  20  for changing the tuning frequency of antenna Ant  2  by control signals to change the frequency received from CPU  35  and a variable high-frequency amplification circuit  21   a  for carrying out the high-frequency amplification by changing the tuning frequency by frequency changing control signals coming from CPU  35  to receiving signals (f0 to fn) coming from the antenna circuit  20 . 
     Furthermore, variable multiplication circuits  28   b ,  29   b  which vary multiplication frequencies corresponding to the frequency changing control signals from CPU  35  are employed therein. Still furthermore, a memory  36  which stores programs and tables for varying the receiving frequencies (f0 to fn) is provided in CPU  35 . All the other construction thereof is the same as that of the first preferred embodiment shown in FIG.  1 . 
     FIG. 5 is a circuit diagram showing a detailed construction of antenna varying circuit  20  shown in FIG.  4 . In FIG. 5, in the antenna varying circuit  20 , capacitor C 1 , variable capacity diode DC 1  and capacitor C 2  which greatly vary the tuning frequency (in every frequency band) corresponding to the frequency changing control signal from CPU  35  are connected to antenna Ant 2 . 
     Furthermore, capacitor C 3 , variable capacity diode DC 2  and resistor Ri which finely vary (in the receiving frequency steps) the tuning frequency corresponding to the frequency changing control signals coming CPU  35  are juxtaposed to antenna Ant 2 . A control signal coming from CPU  35  is supplied to the variable capacity diode DC 2  through resistor R 2 , and they are connected to the input side of variable high-frequency amplification circuit  21   a  of the next stage through capacitor C 4 . 
     FIG. 6 is a circuit diagram showing a detailed configuration of variable high-frequency amplification circuit shown in FIG.  4 . In FIG. 6, high-frequency (receiving) signals coming from antenna varying circuit  20  are inputted into the variable high-frequency amplification circuit  21 , and the same circuit  21   a  is provided with transistors Q 1 , Q 2  carrying out amplification of the high-frequency signals, resistors R 10 , R 11  and capacitor C 10 . Furthermore, the variable high-frequency amplification circuit  20  is further provided with coil L 1  which makes resonance with high-frequency (receiving) signals to be inputted, variable-capacity diode DC 3 , which is connected to the coil L 1 , for varying the tuning frequency corresponding to frequency-changing control signals coming from CPU  35 , resistor R 12  for applying the control signals to variable-capacity diode DC 3 , and capacitor  11  for cutting off direct current to send out amplification signals to the mixer  22  of the following stage. 
     Furthermore, although the variable high-frequency amplification circuit  21   a  is not provided with two changing means which greatly vary the tuning frequency (every frequency band) and finely vary (in receiving frequency steps) the tuning frequency, it may be acceptable that the same is provided with two changing means which greatly vary the tuning frequency and which finely vary the tuning frequency, as in the antenna varying circuit  20 . 
     FIG. 7 is a circuit diagram showing a detailed configuration of variable multiplication circuits  28   b ,  29   b  shown in FIG. 4, wherein the variable multiplication circuits  28   b ,  29   b  are provided with a transistor Q 3 , into which oscillation signals (fV) coming from VCO 34  are inputted through capacitor C 20 , for outputting multiplied signals, coils L 2 , L 3  for greatly varying the multiplication frequency (tuning frequency) corresponding to frequency changing control signals coming from CPU  35 , and a switch SW 1  which greatly varies the multiplication frequency (in every frequency band) by changing the coil L 2  to its independent operation or changing the coils L 2 , L 3  for an in-series connection. Furthermore, the circuits  28   b ,  29   b  are also provided with a capacitor C 21  and a variable capacity diode DC 4 , which finely vary the multiplication frequency (in receiving frequency steps) corresponding to frequency changing control signals coming from CPU  35 . 
     Next, a description is given of actions of the fourth preferred embodiment. 
     In the fourth preferred embodiment, the frequency is set to a frequency band which is granted for a district of receiving, and CPU  35  controls varying and setting of the receiving frequency (f0) on the basis of control programs stored in memory  36 . All the other actions than this are the same as those of the first embodiment shown in FIG. 1, wherein the relationship between the frequency conversion in mixer  22  and orthogonal conversion in mixers  23   a ,  23   b  is the same as that shown in equation (1). 
     In a case of tuning to the frequency granted for a district of receiving, that is, in a case where the frequency is greatly varied, a control signal (voltage) is outputted from CPU  35  to a variable-capacity diode DC 1  in the antenna varying circuit  25  shown in FIG. 5, and the switch SW 1  which greatly varies the tuning frequency in the variable multiplication circuits  28   b ,  29   b  shown in FIG. 7 is changed. 
     Next, in a case of setting to the receiving frequency, that is, in a case where the receiving frequency is finely changed, a control signal coming from CPU  35  is applied to the variable capacity diode DC 2  through a resistor R 2  in the antenna varying circuit  20  shown in FIG. 5, whereby the frequency is tuned to the receiving frequency. Furthermore, in the variable high-frequency amplification circuit  21   a  shown in FIG. 6, a control signal coming from CPU  35  is applied to the variable-capacity diode DC 3  through another resistor R 12  to tune the frequency to the receiving frequency. Furthermore, in the variable multiplication circuits  28   b ,  29   b  shown in FIG. 7, a frequency changing control signal coming from CPU  35  is applied to the variable-capacity diode DC 4  in order to cause the receiving frequency steps to be effected. 
     Furthermore, although the fourth preferred embodiment is described with the same applied to the first preferred embodiment shown in FIG. 1, the fourth embodiment may be applied to the second and third embodiment respectively shown in FIG.  2  and FIG.  3 . The actions and effects thereof remain the same. In either case, it is necessary that the frequency relationship between the frequency conversion in mixer  22  and orthogonal conversion in mixers  23   a ,  23   b  meets the aforementioned equations. 
     Furthermore, antenna varying circuit  20 , variable high-frequency amplification circuit  21   a  and variable multiplication circuits  28   b ,  29   b  are changed over by control of CPU  35 . That is, although they are electrically changed, they may be mechanically changed. In this case, a semi-fixed capacitor may be used for variable-capacity diodes DC 1  through DC 4 . 
     Thus, no mechanical filter is used in the fourth preferred embodiment, and a plurality of oscillation frequencies may be generated from a single local oscillation portion. Therefore, a single pager is able to receive electric waves of completely different frequency bands. At this time, it is possible to dynamically vary the receiving frequency bands by only setting the oscillation frequency (fv) of VCO 34  to a value which can meet fv=f0/(x+y) wherein (f0) is the receiving frequency, (x) is a multiplication ratio of variable multiplication circuit  28   b , and (y) is a multiplication ratio of variable multiplication circuit  29   b.    
     As been made clear from the above description, according to the invention, since the resonance frequency of an antenna is different from the frequency of local oscillation signals inputted into a mixer, no unnecessary radiation of local oscillation signals which is the same as that of the resonance frequency of the antenna is produced, wherein it is possible to prevent noise from occurring due to receiving the unnecessary radiation waves again. Furthermore, no comparatively large-sized shield case, which covers the local oscillation portion and is difficult to be automatically mounted, is required any more. It is possible to make the apparatus small-sized and light in weight along with further improvement of the assembling efficiency. 
     Furthermore, according to the invention, since the receiving frequency band and the receiving and multiplication frequency bands corresponding to setting of the receiving frequency are changed over, and the receiving and multiplication frequencies corresponding to the receiving frequency are set, it is possible to easily set the receiving frequency in wide frequency bands where the service frequency band differs.