Abstract:
A diversity receiving apparatus having a plurality of antennas, antenna feeders each being associated with respective one of the antennas, and a single diversity receiving section to which the antennas are connected via the associated antenna feeders. A breakage detecting circuit is included in the apparatus for detecting the breakage of any one of the antenna feeders. The detecting circuit uses an antenna whose radiation element is connected to ground and, by applying a predetermined DC potential to the hot line of the antenna feeder via a resistor, constantly monitors the potential. On the breakage of the antenna feeder, the detecting circuit produces an alarm in response to the resultant change in the potential. The apparatus is capable of readily detecting that the diversity reception effect has been lost and the receiving ability has been degraded due to the breakage of the antenna feeder.

Description:
This is a continuation of application Ser. No. 07/524,896 filed May 18, 1990, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a diversity receiving apparatus for receiving a signal by space diversity and, more particularly, to a vehicle-mounted space diversity receiving apparatus. 
     A diversity receiving apparatus for receiving signals transmitted by radio waves by space diversity is known in the art. This kind of receiving apparatus has a plurality of antennas for picking up radio signals. The signals picked up by the individual antennas are switched over or combined and then fed to a diversity receiver. A prerequisite with such an apparatus is that the antennas be spaced apart from each other. When the diversity receiving apparatus is mounted on a vehicle, the individual antennas are affixed to the roof, windshields and so forth of the vehicle. Each antenna is connected to the diversity receiver by an exclusive antenna feeder which propagates a signal therethrough. 
     When one of antenna circuits or channels included in the diversity receiving apparatus and constituted by an antenna, antenna feeder and so forth fails, the apparatus is capable of receiving a signal by the other antenna circuits. In this condition, despite that the receiving ability of the apparatus has been degraded, the reception seemingly remains normal. The user, therefore, often overlooks such a failure of the antenna circuit. This problem is especially serious when it comes to a vehicle-mounted diversity receiving apparatus, because antenna feeders of the apparatus are apt to break due to vibrations and impacts particular to on-road vehicles. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a diversity receiving apparatus capable of readily detecting the deterioration of a receiving ability ascribable to the breakage of an antenna feeder. 
     A diversity receiving apparatus of the present invention has a plurality of antennas for receiving signals transmitted by radio waves; diversity receiving section means for receiving one of the signals coming in through the antennas; antenna feeder means for connecting the antennas to the diversity receiving section, respectively; and means for detecting breakage of any of the antenna feeders. 
     Preferably, the detecting means has a power source connected through a resistor to one end of the antenna feeder connecting the diversity receiving section and an antenna whose radiation element is connected to ground, and a detecting circuit connected to the one end of the antenna feeder for detecting a variation in the potential appearing on the one end. On the breakage of the antenna feeder, the detecting circuit turns on a light emitting diode in response to the resultant increase in the potential. This facilitates the detection of the breakage of an antenna feeder which degrades the receiving ability of the diversity receiving apparatus. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other objects, features and advantages of the present invention will become more apparent by reference to the following detailed description of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a block diagram schematically showing a diversity receiving apparatus embodying the present invention; 
     FIG. 2 is a partly taken away perspective view of an antenna included in the FIG. 1 apparatus; and 
     FIG. 3 is a schematic block diagram showing an alternative embodiment of the diversity receiving apparatus in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, a diversity receiving apparatus includes rod antennas 1 and 2. The rod antennas 1 and 2 are connected to a diversity receiving section 5 through antenna feeders 3 and 4, respectively. The rod antenna 1 comprises a radiation element 11 whose one end is grounded through a choke coil or inductance 12 and connected to one end 101 of the hot line 31 of antenna feeder 3. The outer conductor 32 of antenna feeder 3 is connected to ground through its ends 102 and 502. Likewise, the rod antenna 2 comprises a radiation element 21 whose one end is grounded through a choke coil or inductance 22 and connected to one end 201 of the hot line 41 of antenna feeder 4. The outer conductor 42 of antenna feeder 4 is connected to ground through its ends 202 and 504. 
     The diversity receiving section 5 comprises an antenna switch 51 whose one input terminal 511 is connected to the other end 501 of hot line 31. The other input terminal 512 of antenna switch 51 is connected to the other end 503 of hot line 41. The output terminal 510 of switch 51 is connected to the input of a receiver 52. 
     The diversity receiving section 5 also comprises a breakage detecting circuit 53 which includes a pair of low-pass filters each having a choke coil or inductance 536 or 537 and a capacitor 534 or 535. One end of coil 536 is connected to the other end 501 of feeder hot line 31 while one end of coil 537 is connected to the other end 503 of feeder hot line 41. The other end of coil 536 is connected to ground through capacitor 534 while the other end of coil 537 is connected to ground through the capacitor 535. The junction of coil 536 and capacitor 534 is connected to one of two inputs of NAND gate 533 through an inverter 531. The junction of coil 537 and capacitor 535 is connected to the other of two NAND gate 533 inputs through an inverter 532. The output of NAND gate 533 is connected to the anode of a light emitting diode (LED) 539 through a resistor 538. The cathode of LED 539 is grounded. 
     The diversity receiving section 5 further comprises a direct current (DC) voltage source 54 which applies a positive potential V to the other ends 501 and 503 through resistors 56 and 57, respectively. One end of resistor 57 is connected to the positive terminal of voltage source 54 through a terminal 55. 
     In operation, the radiating element 11 picks up a radio frequency signal and provides the picked-up-signal to the antenna switch 51 through the antenna feeder 3. The choke coil 12 blocks the picked-up radio frequency signal while passing a signal having a lower frequency than the frequency of the radio frequency signal. The radiating element 21 picks up a radio frequency signal and provides the picked-up signal to the antenna switch 51 through the antenna feeder 4. The choke coil 22 has the same function as the choke coil 12. The antenna switch provides the receiver 52 with one of radio signals from the antennas 1 and 2 under control of the receiver 52. The receiver controls the switchover of antenna switch 51 based on, for example, the field strength levels obtained from the radio frequency signals. The above-mentioned antenna diversity operation is well known in the art and thus no further description thereabout will be provided in this specification. It should be noted that the present apparatus may use other types of diversity reception, for example, a signal combining diversity reception. 
     Even if one of antenna feeders 3 and 4 fails, the receiver 52 can still receive a radio signal due to the diversity function. More specifically, if the antenna feeder 3 is broken, the antenna switch 51 provides a radio frequency signal from the antenna 2 to the receiver 52. Thus, the user overlooks the breakage of the antenna feeder 3. The present invention prevents this overlooking by adding the breakage detecting circuit 53. 
     So long as the hot line 31 of antenna feeder 3 is held in normal connection, the DC potential at the terminal 501 remains in a ground level of &#34;L&#34;, because the terminal 501 is grounded through the hot line and the coil 12. When the hot line 31 is broken, the DC potential at the terminal 501 turns to the voltage V or &#34;H&#34;. Likewise, the hot line 41 of antenna feeder 4 is held in normal connection, the DC potential at the terminal 503 remains in &#34;L&#34;, while when the hot line 41 is broken, the DC potential at the terminal 503 turns to &#34;H&#34;. It follows that the output of NAND gate 533 is in &#34;L&#34; only when both the hot lines 31 and 41 are connected normally, maintaining the LED 539 turned off. On the other hand, when at least one of the hot lines 31 and 41 is broken, the output level of the NAND gate 533 turns from &#34;L&#34; to &#34;H&#34; with the result that the LED 539 glows. The low-pass filter including the coil 536 and 537 and the capacitor 534 or 535 blocks signals having frequencies close to the frequency of signals coming in through the associated rod antenna 1 or 2, while passing signals having lower frequencies than the same. 
     In the above construction, assume that either one of the antenna feeders 3 and 4 inclusive of the hot lines 31 and 41 has been broken, but a radio frequency signal is being received by either one of the antennas 1 and 2. Even in such a condition which seemingly is normal, the user of the apparatus is alerted to the breakage of the antenna feeder 3 or 4 by the LED 539 which will be glowing then. The LED 539 may be replaced by a beeper 540 which generates an alert tone in response to the &#34;H&#34; output of NAND gate 533. 
     Referring to FIG. 2, the rod antenna 1 has a radiation element 111, a ground plate 112 made of metal, a retainer 113 also made of metal, a dielectric 114 which is inherently low in loss for a received radio signal, and the choke coil 12. The retainer 113 is welded or otherwise affixed to the ground plate 112, while the radiation element 111 is affixed to the retainer 113 with the intermediary of the dielectric 114. The choke coil 12 is connected at one terminal to the base portion of the radiation element 111 and at the other terminal to the retainer 113 by welding or similar technology. The hot line 31 of the antenna feeder 3, or the center conductor of the coaxial cable in the illustrative embodiment, is received in and connected to the base portion of the radiator 111. The choke coil 12 is welded or otherwise rigidly connected to the ground plate 112. The other rod antenna 2 has the same structure as the rod antenna 1. 
     The illustrative embodiment has two rod antennas 1 and 2 each being connected to the diversity receiving section by an exclusive antenna feeder. Of course, such an arrangement is similarly applicable to a diversity receiving apparatus having three or more antennas. Assume that some antennas are connected to a diversity receiving section via individual antenna feeders and the others are directly connected to the diversity receiving section, as practiced from time to time. Then, the circuitry responsive to the breakage of an antenna feeder will of course be associated only with those antenna circuits which have the antenna feeders. 
     The rod antennas shown in FIGS. 1 and 2 have radiation elements which are not connected to ground and, therefore, each may be implemented as a whip antenna, as desired. When use is made of an antenna whose radiation element is directly connected to ground, i.e., a unipole antenna having a grounded matching stub, the choke coil 12 for indirectly connecting the radiation element to ground is not necessary. While the choke coils 12 and 22 each serving as a lumped constant circuit are used as circuits which block signals and exhibit a low resistance for DC, they may be replaced with distributed constant circuits having a similar impedance characteristic. 
     Referring to FIG. 3, an alternative embodiment of the diversity receiving apparatus in accordance with the present invention is shown. In the figures, the same or similar components are designated by like reference numerals, and redundant description will be avoided for simplicity. In FIG. 3, the diversity receiving apparatus has two antennas 6 and 7, antenna feeders 3 and 4 connected at one ends to the antennas 6 and 7, respectively, a diversity receiving section 8 connected to the other ends of the antenna feeders 3 and 4, and a choke coil 9. 
     The antennas 6 and 7 have radiation elements 61 and 71, respectively. The choke coil 9 chokes received signals associated with the radiation elements 61 and 71 and connects the elements 61 and 71 with respect to DC. The radiation elements 61 and 71 are not connected to ground. 
     The diversity receiving section 8 has an antenna switch 51, a receiver 52 for diversity reception, a detecting circuit 81, capacitors 58 and 59, and a DC voltage source 54. The antenna switch 51 is connected at one input terminal to the other end 501 of the antenna feeder 3 through the capacitor 58 and connected at the other input terminal to the other end 503 of the antenna feeder 4 through the capacitor 59. The receiver 52 controls the switchover of the switch 51, as in the FIG. 1 apparatus. The capacitors 58 and 59 pass signals coming in through the associated antennas 6 and 7 while blocking DC. 
     The other end 501 of the hot line 31 of the antenna feeder 3 is connected to the DC voltage source 54 through a choke coil 50. The detecting circuit 81 is connected to the other end 503 of the hot line 41 of the antenna feeder 4 so as to monitor the DC potential appearing there. 
     The detecting circuit 81 includes an inverter 811, a choke coil 812 connected between the input terminal of inverter 811 and the other end 503 of the hot line 41, a resistor 813 connected between the input terminal of inverter 811 and ground, a resistor 814 connected at one end to the output of inverter 811, and an LED 815 whose anode and cathode are connected to the other end of resistor 814 and ground, respectively. The choke coil 812 blocks a signal coming in through the antenna 7 while exhibiting a low resistance for DC. 
     The input terminal of inverter 811 is connected to the voltage source 54 through the choke coil 812, antenna feeder 4, antenna 7, choke coil 9, antenna 6, antenna feeder, and choke coil 50. The output terminal of inverter 811 is connected to ground through the LED 815. In this configuration, when the hot lines 31 and 41 of the antenna feeders 3 and 4 are not broken, the level on the input terminal of inverter 811 is &#34;H&#34; while the level on the output terminal of the same is &#34;L&#34;. When at least one of the hot lines 31 and 41 is broken, the input and output terminals of inverter 811 turn to &#34;L&#34; and &#34;H&#34;, respectively. As a result, the LED 815 is turned on to alert the user of the apparatus to the breakage of the antenna feeder 3 inclusive of the hot line 31 or the antenna feeder 4 inclusive of the hot line 41. 
     In summary, it will be seen that the present invention has a breakage detection circuit detecting the breakage of an antenna feeder and thereby prevents the user from overlooking the fact that the diversity reception effect has been lost and, therefore, the receiving ability has been lowered due to the breakage of an antenna feeder.