JPS6232661B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a superheterodyne receiver having a self-diagnosis function.

Generally, in a superheterodyne receiver used for wireless communication, it is possible to detect whether a desired wave is being received by a signal detection circuit such as a squelch circuit. When such a receiver is constantly receiving signals, it can be determined whether the receiver itself has failed based on a change in the output signal of the detection circuit. Normally, this detection circuit detects the strength of the received electric field, and when the input electric field decreases or is cut off, the detection circuit, for example, a squelch circuit, is turned on. At the same time, this sketil signal also serves as an alarm signal for the receiver, and is also useful for monitoring the receiver itself. Therefore, this receiver has the disadvantage that it is not possible to distinguish between a state in which the input electric field is cut off and a state in which the signal path from the input side to the detection circuit within the receiver is broken.

An object of the present invention is to eliminate the above-mentioned conventional drawbacks and provide a receiver having a self-diagnosis function that can determine whether or not the receiver itself is malfunctioning even when it is in a standby state for a received signal. There is something to do.

According to the present invention, in a superheterodyne receiver, there is provided a means for generating a signal of an image frequency having an image relationship with the reception frequency, and a signal demodulator connected to a stage subsequent to an intermediate frequency converter for converting the reception frequency. means for detecting the intermediate frequency signal level on the input side of the signal demodulator or the out-of-band noise level on the output side of the signal demodulator, and when the detection means detects a break in the intermediate frequency signal level, Alternatively, when the out-of-band noise level of the demodulated signal is detected to exceed a predetermined level, the signal is sent to the input side of the intermediate frequency converter through a reception filter at the time of reception under the control of the detection output. A receiver having a self-diagnosis function is obtained, characterized in that the output of the image frequency signal generating means is provided in place of the signal input of the reception frequency added by the receiver.

Next, embodiments of a receiver according to the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the structure of a first embodiment of the present invention. In this example, 1 is an antenna, 2 is a receiving filter, 3 is a relay terminal between the receiving filter 2 and the subsequent stage for guiding the output,
4 is a switch circuit, 5 is an image frequency signal oscillator, 6 is a local oscillator, and 7 is an intermediate frequency converter. Generally, the IF signal frequency-converted by the intermediate frequency converter 7 passes through the subsequent filter circuit and amplifier circuit, but these are omitted for the sake of clarity. Furthermore, 8 is a level detector for the IF signal, and 9 is a controller, which receives the output of the level detector 8 and is connected to a control input terminal of the switch circuit 4. 10 is a signal demodulator. First, when there is a constant input signal, the signal entering from antenna 1 passes through reception filter 2,
The frequency converter 7 converts the signal into an IF signal, which is input to the level detector 8 and signal demodulator 10. Level detector 8 detects this IF signal and sends a detection signal to controller 9. While the IF signal level is normal,
The output of the controller 9 controls the switch 4 to open, so that the image frequency signal is not applied to the relay terminal 3.

On the other hand, if a failure occurs in the circuit from the input side of the receiver to the detector 8, the detector 8 will not detect the IF signal. In this case, the controller 9 drives the switch 4 for a predetermined time to close it, and transmits the image frequency signal to the relay terminal 3.
is applied to the intermediate frequency converter 7 via. If the intermediate frequency converter 7 is not malfunctioning, this image frequency is frequency-converted here, and becomes an IF signal with the same frequency as the IF signal obtained by frequency-converting the original reception frequency, and its level is equal to the image ratio. However, by raising the signal level of the image frequency applied to the intermediate frequency converter 7 to some extent in advance, the signal can be easily detected by the detector 8. . Therefore, even if an image frequency signal is injected into the relay terminal 3 on the output side of the receiving filter 2, if the IF signal cannot be detected by the detector 8, it can be known that the receiver itself is malfunctioning. .

In addition, when the receiver is in a normal state and there is no reception input, the detector 8 also informs the controller 9 that there is no signal, so the controller 9
drives the switch 4 for a predetermined time,
Close this. In this case, the image frequency signal is converted into an IF signal, which is detected by the detector 8, so it can be determined that there is no receiver input, rather than a receiver failure.

FIG. 2 is a block diagram showing the configuration of a second embodiment of the present invention. In this example, a detector 11 that detects noise outside the band of the demodulated signal is
It is connected to the output side of the signal demodulator 10 shown in FIG. 1, and detects the noise level outside the band of the demodulated signal instead of detecting the IF signal. The other components are indicated by the same reference symbols as in FIG. 1 and should be understood to have the same functions. According to this embodiment, when the receiver is normally receiving a signal, the noise level of the demodulated signal obtained from the signal demodulator 10 is below a predetermined level, and the detector 11 detects the output. However, when the reception input is cut off, the noise level increases and the noise is detected by the detector 11. By operating the controller 9 and controlling the switch 4 based on this detection signal, it is possible to determine whether there is a failure in the receiver by the same method as described in the first embodiment.

In the first and second embodiments described above, a signal at the image frequency was added as a pseudo signal from the output side of the reception filter 2, but even if a signal at the same frequency as the normal reception frequency is added, the above-mentioned With such a configuration, the operating state of the receiver can be detected. However, when a signal with the same frequency as the receiving frequency is applied to the input side of the intermediate frequency converter 7 via the switch 4, this signal is simultaneously transmitted to the antenna 1 via the receiving filter 2, and may be radiated as spurious signals from the source and affect other communication systems. On the other hand, when a signal with a frequency that is an image of the receiving frequency is applied to the input side of the intermediate frequency converter 7, the signal transmitted toward the antenna is sufficiently attenuated by the receiving filter 2 on the way, and The amount of radiation emitted from the antenna is extremely small and does not affect other communication systems.

Further, in the above embodiment, the switch circuit 4 is controlled by the control signal from the controller 9, but the oscillation of the image frequency signal oscillator 5 may be directly turned on and off without using this switch circuit. Needless to say.

As is clear from the above explanation, according to the present invention, an image frequency signal is given to the intermediate frequency converter instead of the reception input, and the IF in that state is
By detecting the presence or absence of out-of-band noise in the signal or demodulated signal, it is possible to easily determine whether there is a failure in the receiver itself even when waiting for a received signal, especially in TDMA communication systems. Applying this method to receivers will have a significant effect on improving system reliability.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the structure of a first embodiment according to the invention, and FIG. 2 is a block diagram showing the structure of a second embodiment according to the invention. In the figure, 1 is an antenna, 2 is a reception filter, 3 is a relay terminal, 4 is a switch circuit, 5 is an image frequency signal oscillator, 6 is a local oscillator, 7 is an intermediate frequency converter, 8 and 11 are detectors, and 9 is a The controller 10 is a signal demodulator.

Claims (1)

[Claims] 1. In a superheterodyne receiver, means for generating a signal at an image frequency that has an image relationship with the reception frequency, and an intermediate signal at the input side of a signal demodulator connected after the intermediate frequency converter that converts the reception frequency. means for detecting the signal level of the intermediate frequency or the out-of-band noise level on the output side of the signal demodulator, and when the detection means detects a break in the signal level of the intermediate frequency, or the demodulated signal When the out-of-band noise level of is detected to exceed a predetermined level, by control using the detection output,
The intermediate frequency converter has a self-diagnosis function characterized in that the output of the image frequency signal generation means is applied to the input side of the intermediate frequency converter in place of the signal input of the reception frequency applied through the reception filter during reception. Receiving machine.