JPS62264735A - Identifying signal decoder - Google Patents

Abstract

PURPOSE:To realize the decoding of an identification signal for all frequencies with excellent S/N by using a band pass filter for a fixed wave. CONSTITUTION:A mixer 11 is connected between a low pass filter 8 and a band pass filter 9 and a frequency variable oscillator 12 is connected to the mixer circuit 11. In using a microcomputer as the oscillator 12, part of the function of a detection circuit 10 is commonly used. The oscillator 12 oscillates a frequency higher than that of an identification signal f0 by a prescribed value at the time of decoding when the titled device is activated. Thus, the mixer circuit 11 mixes the oscillating frequency of the oscillator 12 and the reception frequency, and generates the difference frequency, then the result is fed to the band pass filter 9. Thus, all identification signals are identified by the band pass filter 9 having a center frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a decoding device for identification signals used in commercial communication devices such as taxi radios.

(Prior Art) In commercial communication devices, such as taxi radios, it is necessary to perform many communications using frequencies within a limited band. Furthermore, it is possible to classify by other means. A typical method is one that uses an identification signal called a CTCS S' (Continuity Tone Condroldo Squelch Condroldo) signal.

To explain this with reference to FIG. 2, reference numeral 1 denotes a high frequency amplification circuit which amplifies radio waves received by the antenna 2 over a wide band. On the output side of the high frequency amplifier circuit 1, a local oscillation circuit, a mixer circuit, an intermediate frequency amplifier circuit, etc., which are normally used in a superheterodyne circuit, are provided (these circuits are well known, so their illustrations are omitted). ,
After that, the FM detection circuit 3 is connected. The output side of the FM detection circuit 3 is connected to a low frequency amplification circuit 6 via an ipass filter 4 and a low frequency mute circuit 5, which obtains an audio signal by removing the identification signal from the FM detection output. A speaker 7 is connected to the amplifier circuit 6.

The low frequency mute circuit 5 is configured such that the degree of amplification of the signal input to the input terminal 5a and output from the output terminal 5b changes depending on the magnitude of the identification signal applied to the identification signal input terminal 5c.

This false identification signal is given from the output signal of the FM detection circuit 5 via the low-pass filter 8, the band-pass filter 9, and the detection circuit 10.

In this circuit, when an FM signal enters the antenna 2, this FM signal is high-frequency amplified by the high-frequency amplification circuit 1,
Next, the frequency is converted, the intermediate frequency is amplified, the frequency is detected by the FM detection circuit 5, the signal passes through the bypass filter 4, the low frequency mute circuit 5 enters the low frequency amplification circuit 6, the signal is amplified, and the speaker 7 is driven. Become. High frequency amplifier circuit 1
is an audio signal and a lower-frequency identification signal (6
00 hertz or less, for example R3-220 of EIA standard
A carrier wave modulated with both signals (signals with 37 types of reference frequencies determined by Of the two signals, the audio signal reaches the syspee cuff through the route described above,
As for the identification signal, the audio signal is cut by the low-pass filter 8, and the band-pass filter 9 allows only a specific frequency (one wave out of the above 37 types) to pass, improving the S/N ratio and reducing the The frequency mute circuit 5 will be controlled.

(Problem to be Solved by the Invention) In the conventional decoding device described above, when a plurality of identification signals are used, in order to reliably capture only one of the signals of interest, a very sharp bandpass filter is used. required. For this reason, bandpass filters had to be manufactured for each of the 37 reference frequencies mentioned above, and there was a problem in that it was necessary to match the assigned frequencies.The present invention solves this problem. An object of the present invention is to provide an identification signal decoding device that can easily handle identification signals of all frequencies with one bandpass filter.

(Means for Solving the Problems) The present invention, as a means for solving the above problems, receives a carrier wave modulated with both an audio signal and an identification signal in a lower frequency range than the audio signal, and In a receiving circuit that adds the detection output of the identification signal to a low frequency mute circuit and extracts only a predetermined audio signal, a mixer circuit is connected to the rear stage of the low-pass filter that separates the audio signal and the identification signal from the carrier wave. , a frequency variable oscillator is connected to the mixer circuit, and the output of the mixer circuit is passed through a bandpass filter that passes a frequency that is the difference between the passband frequency of the lowpass filter and the oscillation frequency of the oscillator. It was designed to be added to.

(Function) With this configuration, by appropriately selecting the oscillation frequency of the oscillator, one frequency is determined to be supplied to the bandpass filter for any frequency among the 37 frequencies. Therefore, it is necessary to prepare only one type of bandpass filter.

(Embodiment) Next, an embodiment of the present invention will be described with reference to FIG. 1, with the same components K as in FIG. A mixer circuit (frequency conversion circuit) 11 is connected between the low-pass filter 8 and the band-pass filter 90, and the mixer circuit 1
1 is connected to a variable frequency oscillator 12.

It is desirable to use a microcomputer as the variable frequency oscillator 12 from the viewpoint of simplifying the structure, and if a microcomputer is used in this part, it can also serve as the detection circuit 10 etc. by using part of its functions. be able to.

This device configured as described above operates as follows. During decoding when this device functions, the oscillator 12 oscillates a frequency higher (or lower) than the identification signal fo by a certain value. As a result, the mixer circuit 11 becomes the oscillator 1
The two oscillation frequencies and the reception frequency are mixed to generate a difference (or sum) frequency, which is then fed to the bandpass filter 9. Therefore, the bandpass filter 9 with one center frequency can identify all the identification signals.

(Effects of the Invention) With the configuration described above, the present invention has an advantage in that decoding of identification signals of all frequencies can be realized with a good S/N ratio only by using a fixed single-wave bandpass filter. .

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional one. 1... High frequency amplifier circuit 3... FM detection circuit 5...
・Low frequency mute circuit 8...Low pass filter 9
...Band pass filter 10...-detection circuit 11
...Mixer circuit j2. ,, Oscillator (and 1 other person) Procedural amendment June 2, 1980 Patent Application No. 108223 of 1988 2, Decoding device for signal for identifying the name of the invention 3, Relationship with the amended person case Patent applicant Name: Nippon Piezo Denki Co., Ltd. 4, Agent Address: 5, Shufunotomo Building, 1-6 Kanda Surugadai, Chiyoda-ku, Tokyo Date of amendment order: “Voluntary” 7: Details of the amendment, page 2, lines 9 to 11 Correct the line "Continuity Tone Condroldo Squelch Condroldo" to read "Continuous Tone Condroldo Squelch System."

Claims (1)

[Claims] (1) Receive a carrier wave modulated with both an audio signal and an identification signal lower than the audio signal, and add the detection output of the identification signal to a low frequency mute circuit to extract only the specific audio signal. In the receiving circuit, a mixer circuit is connected after the low-pass filter that separates the audio signal and the identification signal from the carrier wave, and a variable frequency oscillator is connected to the mixer circuit, and the output of the mixer circuit is An identification signal decoding device characterized in that the identification signal is applied to a detection circuit via a bandpass filter that passes a frequency that is the difference between the passband frequency of the lowpass filter and the oscillation frequency of the oscillator.