Abstract:
An ultra high frequency transceiver which transmits a modulated carrier wave and mixes a received signal with a locally generated signal to produce an intermediate frequency signal is tested by using the same transmitter as used during normal transceiver operation and by modulating the carrier with a wave having sudden transitions. A portion of the transmitted wave is reflected back to a receiver segment of the transmitter to produce an i.f. signal that is detected by a demodulator. Each transition causes the demodulator to detect a pulse signal. In response to the pulse signal being detected and not being detected during a testing interval, indications are derived to signal that the transceiver is and is not operating properly, respectively.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ultra high frequency transceiver with a self-testing facility. 
     2. Description of the prior art 
     A conventional ultra high frequency transceiver comprises substantially an ultra high frequency oscillator, a modulator, a mixer, a band-pass filter, and a demodulator. 
     In order to check whether the ultra high frequency transceiver is functioning normally or not, a pulse modulated signal of a given carrier frequency is fed from an antenna of the transceiver into the band-pass filter at the output of which a check is made to detect the presence of a failure within any circuit constituting the transceiver unit. 
     According to the conventional transceiver testing method, however, additional pulse modulating and ultra high frequency oscillating units are required to produce a pulse modulated signal of the same carrier frequency. 
     Therefore, if there are no such modulating and oscillating units, the presence of failure within any circuit constituting the transceiver unit could not be detected before communications begin with another transceiver station. 
     BRIEF SUMMARY OF THE INVENTION 
     The ultra high frequency transceiver of the present invention is so designed as to detect the presence or absence of a failure within any circuit constituting the transceiver unit by actuating a built-in self-testing facility prior to communications. 
     In an embodiment of the present invention, if an abnormality occurs anywhere in the ultra high frequency transceiver, the self-testing facility optically indicates the presence of a failure. 
     In another embodiment of the present invention, after indication of the a failure of the transceiver unit is detected, the power supply is automatically interrupted to prevent a partial failure from causing possible further damage. 
     In another third embodiment of the present invention, after indication of the a failure of the transceiver unit is detected the pulse modulated signal is definitely fed back to the transceiver unit to locate the trouble. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the ultra high frequency transceiver according to the present invention will be more clearly appreciated from the following description taken in conjunction with the accompanying drawings in which like reference numerals designate corresponding elements, and in which: 
     FIG. 1 is a simplified block diagram of a conventional ultra high frequency transceiver; 
     FIG. 2 is a simplifed block diagram and partial circuit diagram of a preferred embodiment of the present invention; 
     FIGS. 3 (a) to (d) are waveform charts associated with the preferred embodiment of the present invention shown in FIG. 2; 
     FIG. 4 is a simplified block diagram of a second preferred embodiment of the present invention; 
     FIG. 5 is a simplified block diagram of a third preferred embodiment of the present invention; 
     FIG. 6 is a simplified partial block diagram of a fourth preferred embodiment of the present invention; and 
     FIG. 7 is a simplified partial block diagram of a fifth preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     To facilitate understanding of the present invention, a brief reference is made to the conventional ultra high frequency transceiver depicted in FIG. 1. This conventional ultra high frequency transceiver 1 comprises, substantially, an ultra high frequency oscillator 2 such as a Gunn oscillator, isolators 3, 5, and 7, a directional coupler 4, a modulator 6, a circulator 8, an antenna 9, a mixer 10, a band-pass filter 11, and a demodulator 12. 
     A locally generated UHF signal of frequency f 1  derived from the oscillator 2 is fed into the modulator 6 via the isolator 3, directional coupler 4, and isolator 5 (shown by solid arrows). 
     The UHF signal f 1  is modulated by the modulation signal in the modulator 6 and radiated from the antenna 9 via the isolator 7 and circulator 8 (shown by a dashed line and arrows). 
     A carrier frequency signal f 2  received by the antenna 9 is supplied to the mixer 10 via the circulator 8 and directional coupler 4 (shown by a dotted and dashed line with arrows). 
     The UHF signal f 1  is also partially fed into the mixer 10 by means of the directional coupler 4. The mixer 10 serves to mix signals f 1  and f 2 . 
     The output of the mixer 10 is fed to the bandpass filter 11 which has a central frequency which is the difference between the frequencies of f 1  and f 2 . 
     In a conventional method of checking the output of the band-pass filter or demodulator to ensure that there is no failure in the apparatus, a pulse modulated signal of carrier frequency f 2  is fed to the antenna by another apparatus such as an ultra high frequency oscillator or pulse modulator. 
     This, of course, is quite expensive and time consuming. 
     In view of the above problem, reference is now made to FIGS. 2 to 7, and more particularly to FIG. 2, wherein a preferred embodiment of the ultra high frequency transceiver according to the present invention is illustrated. 
     The same reference numerals as used in FIG. 1 designate corresponding parts in the several drawings. 
     Self-testing circuit 23 (FIG. 2) detects the presence or absence of a failure in the transceiver. 
     The self-testing facility 23 comprises an OR gate 13, switch 14, AND gate 15, flip-flop 16 and differentiator 21. OR gate 13 has first and second input terminals respectively connected to a clock signal generator via a switch 14 and to a modulation signal generator; OR gate 13 has an output terminal connected to the modulator 6. AND gate 15 includes first and second input terminals respectively connected to the output of demodulator 12 and to the bias supply +V cc  via a switch 14a mechanically interconnected to the switch 14. Set and reset terminals S and R of flip-flop 16 are respectively connected to the output terminal of the AND gate 15 and to an output of differentiating circuit 21; output terminals Q and Q of flip-flop 16 are connected to control a display circuit 22. 
     The display circuit 22 comprises transistors 19 and 20. Transistor 19 has a base connected to the Q terminal of the flip-flop 16 and a collector selectively connected via a light emitting diode (hereinafter abbreviated as LED) 17 and the switch 14a to bias supply +V cc . Transistor 20 has a base connected to the Q terminal of the flip-flop 16 and a collector selectively connected to bias supply +V cc   via the switch 14a and another LED 18. 
     When the switch 14 is closed prior to communications, the UHF signal from the UHF oscillator 2 is modulated by the clock signal (FIG. 3(a)). 
     A portion of the pulse modulated signal from the modulator 6 f 1  is reflected from a flange connecting antenna 9 and circulator 8 or objects near the antenna 9, or by spurious resonant circulation and arrives at the directional coupler 4. 
     This signal is supplied to the mixer 10 together with the locally generated UHF signal (FIG. 3 (b)). 
     The mixer 10 derives a signal (FIG. 3 (c)) similar to the modulated signal (FIG. 3 (a)) caused by constructive and destructive interference of the signal due to phase differences in the propagation path length. 
     This is because a similar output may be generated due to the detection capability of mixer 10. When the above output signal reaches the band-pass filter 11, only the harmonic component passes the filter and a pulse is generated when the pulse modulated signal rises or falls (FIG. 3(d)). 
     Since the switch 14 is interlocked, i.e., ganged with the switch 14a, the pulse signal is supplied to the set terminal S of the flip-flop 16 through the AND gate 15. 
     The flip-flop derives a high level (logical 1) voltage at the Q terminal and low level (logical 0) voltage at the Q terminal, respectively. 
     Then transistor 20 is turned on with the transistor 19 turned off. When the transistor 20 is turned on, the LED 18 is turned on to indicate that the ultra high frequency transceiver is functioning normally. 
     On the other hand, if there is abnormality (e.g. malfunction in, for example, the modulator 6 or mixer 10) in the ultra high frequency transceiver, the demodulator 12 does not produce the pulse modulated output shown in FIG. 3 (d). 
     Therefore, the flip-flop 16 receives the output signal from the differentiating circuit 20 at the reset terminal R and maintains a high level (logical 1) voltage at the Q terminal and low level (logical 0) voltage at the Q terminal. 
     As a result, transistor 19 and LED 17 only turns on to illuminate 17. 
     FIG. 4 is a circuit diagram of a second preferred embodiment of the present invention in which the power supply is automatically interrupted if there is any failure in the ultra high frequency transceiver. 
     In this embodiment of the present invention, the ultra high frequency transceiver comprises substantially the ultra high frequency transceiver section 1 shown in FIG. 1, a power switch 24 for the ultra high transceiver section 1, a timer 25 which operates for a predetermined period of time after the power switch 24 is closed. Relay coil 26 closes switches 14 and 14a in FIG. 2 in response to the output of timer 25. A relay coil 27 includes normally closed contact 28 which is opened when the transistor 19 is turned on, and a delay circuit 29 which provides delay for a predetermined period of time before actuation of the relay coil 27. 
     When the power switch 24 is closed, the relay coil 26 is actuated for a predetermined period of time to turn on switches 14 and 14a. At this time, the self-testing circuit 23 shown in FIG. 2 is activated. 
     Since the delay circuit 29 is provided, even if there is a delay between closing on of the switches 14 and 14a and the derivation of a pulse signal by the demodulator 11 (FIG. 2), the transistor 19 (FIG. 2) is not supplied with power. Thus the contact 28 remains closed. When there is no failure in the ultra high frequency transceiver 1, communication with another transceiver can be established by the power supplied by supply 24 to the transceiver via contact 28. 
     When, on the other hand, there is a failure in the ultra high frequency transceiver 1, the transistor 19 turns on after a period of time determined by the delay circuit 29 to actuate the relay coil 27. At this time, the normally closed contact 28 is opened to interrupt the power supplies by supply 24 to the ultra high frequency transceiver section 1. 
     In the second embodiment of the present invention, the self-testing of the transceiver unit 1 to determine whether it is operating normally is automatically determined when the power switch 24 is closed. When the failure within the transceiver unit 1 is detected, the power supply is automatically interrupted so that a partial failure cannot affect other parts of the ultra high frequency transceiver. 
     In a case where the power supply interruption circuit is applied to an automotive vehicle, the on position of an ignition key may serve as the on, i.e., closed, position of the power switch 24 and the ignition key start position may serve as the mechanism to close switches 14 and 14a. 
     In this arrangement, the timer 25 and relay coil 26 can be omitted. 
     FIG. 5 is a circuit diagram of third embodiment of the present invention in which a part of the modulated signal is positively fed back at the antenna 9 to the mixer 10. 
     A waveguide 30 provides a means for coupling the circulator 8 with an antenna 9. An adjustment screw 31 provided in the waveguide 30 provides a means for adjusting the amount of reflection of the modulated signal and the difference in the propagation path length. 
     FIG. 6 is a circuit diagram of a fourth embodiment of the present invention in which there is provided an attenuator 38 within a second waveguide 37 for attenuating ultra high frequency signals to a desired degree. Waveguide switching circuits 35 and 36 are connected across the circulator 8 to bypass the circulator 8 through the second waveguide 37 and the attenuator 38. 
     FIG. 7 is a circuit diagram of a fifth embodiment of the present invention in which a PIN diode switch 40 is connected between the circulator 8 and antenna 9. 
     The modulated signal is reflected partially by controlling bias current to the PIN diode switch 40. 
     From the foregoing description, the ultra high frequency transceiver of the present invention is a simple addition or attachment of the self-testing circuit to the ultra high frequency transceiver proper that permits speedy and accurate detection of a failure within any circuit of the transceiver unit.