JPS605649Y2 - Transmitting/receiving device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transmitting/receiving device suitable for use in a tone squelch method that performs selective calling by superimposing a tone signal on a voice signal.

Conventionally, there has been a transmitter/receiver of this type as shown in FIG.

In the drawing, 1 is an antenna, 2 is a tuner, 3 is a bypass filter, 4 is an audio amplifier, 5 is a low-pass filter, and a limiter 6 is inserted after the low-pass filter 5.

A bandpass filter 7 and a detector 8 are connected in series to the output side of the limiter 6.

The output end of the detector 8 is connected to an audio amplifier 4, and the output end of the audio amplifier 4 is connected to an output device, for example a speaker 9.

10 is a microphone, and 11 is a transmitter.

The operating mode of the conventional device will be explained below.

First, during reception, a modulated wave received by an antenna 1 is demodulated by a tuner 2, and separated into an audio signal and a tone signal by a bypass filter 3 and a low-pass filter 5.

The separated tone signal is limited above a certain level by a limiter 6 and shaped into a waveform close to a square wave.

This limited tone signal is filtered through a bandpass filter 7.
is applied to the detector 8 via.

The output of this detector 8 is applied to the audio amplifier 4 to control the transmission of the separated audio signal to the output device 9.

On the other hand, during transmission, the audio signal from the microphone 10 is transmitted to the transmitter 11, modulated and transmitted together with the tone signal.

According to such a conventional device, the limit level is determined in relation to the operating level of the detector 8, and is appropriately set in a range equal to or higher than the operating level. The tone signal is always at a certain level or below a certain level, and even if an excessive adjacent channel tone signal is input for some reason, the excessive signal is suppressed to a certain level (limit level).

Therefore, the adjacent channel tone signal applied to the detector 8 via the bandpass filter 7 is below the operating level of the detector 8, the detector 8 does not operate, and as a result, the device does not malfunction due to an excessive adjacent channel tone signal. Effects can be obtained.

However, although the conventional device can remove malfunctions caused by the adjacent channel I---7 signal by inserting the limiter 6 as described above, the insertion of the limiter 6 causes malfunctions due to the low frequency components of the audio signal. A new drawback arises.

That is, the tone signal is set to 1 by the low-pass filter 5, but at the same time, the low-frequency component a of the audio signal below the cutoff wave number of the low-pass filter 5 may leak into the [1-bus filter 5; fa and the tone signal ft are applied to the limiter 6, and ft is subjected to FM modulation by fa in the limiter 6.

In particular, in the case of fa) ft, as shown in Fig. 3a, ft passing through the limiter 6 is suppressed to about half,
This appears to be a L/bevel under-bevel phenomenon of ft, resulting in a malfunction in which the device does not operate when it should be operating.

In addition, in the same figure a, the left figure shows the state before the limiter, and the right figure shows the state after the limiter.

The present invention has been made in view of the drawbacks of the conventional devices described above, and provides a transmitting/receiving device that can eliminate malfunctions caused by excessive adjacent channel tone signals as well as malfunctions caused by low frequency components of audio signals. Embodiments thereof will be described in detail below with reference to the drawings.

In FIG. 2, 20 is an antenna, 21 is a tuner, 2
2 is a transmission/reception selector switch, 23 is a bypass filter,
24 is an audio amplifier, 25 is a low-pass filter, 26 is a limiter, 27 is a band-pass filter, 28 is a detector, 2
9 is an output device such as a speaker, 30 is a microphone, and 31 is a transmitter.

The difference from the conventional device shown in FIG. 1 is that the audio signal from the microphone 30 is passed through a bypass filter 23 by a changeover switch 22 and then transmitted to a transmitter 31.

According to this embodiment, at the time of transmission, the low frequency component fa of the audio signal from the microphone 30 is cut off by the bypass filter 23, and although it is actually not completely cut off and remains to some extent, this level is lower than the tone level. It becomes smaller than the l novel of the signal ft.

This audio signal with reduced fa is transmitted to the transmitter 31, where it is superimposed on the 1.-tone signal, modulated, and transmitted.

When such a modulated wave is received by the device of this embodiment, the modulated wave from the antenna 20 is demodulated by the chicorer 21 and separated into a voice signal and a tone signal by the bypass filter 23 and the low-pass filter 25.

At this time, since the low frequency component of the audio signal is originally small, the low frequency component a leaked to the low pass filter 25 is
As shown in the left diagram of the figure, it is smaller than ft.

Therefore, when ft and fa pass through the limiter 26, as shown in the right figure of the figure, ft is not FM modulated and suppressed by fa as in the conventional device (on the contrary, fa is FM modulated and suppressed by ft.

Therefore, there will be no malfunction due to the low frequency component a of the audio signal.

The other operations of this embodiment are the same as those of the conventional example described above, so the explanation thereof will be omitted.

As explained above, this invention cuts off the low frequency components of the audio signal during transmission, so by simply adding a simple means such as installing a transmission/reception switch, excessive adjacent channel This has an extremely large effect of eliminating malfunctions caused by tone signals as well as malfunctions caused by low frequency components of audio signals.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional transmitting/receiving device, FIG. 2 is a diagram showing an embodiment of the transmitting/receiving device according to the present invention, and FIG.
b is a diagram showing signal levels, respectively. 23 is a bypass filter, 25 is a low pass filter, 2
6 is a limiter, 27 is a bandpass filter, 28 is a detector, and 29 is an output device.

Claims (1)

[Scope of utility model registration request] At the time of transmission, a composite signal in which a voice signal and tone signal with low frequency components cut off by a bypass filter are superimposed is transmitted to the transmitter, and at the time of reception, a modulated wave containing a composite signal similar to the composite signal from another transmitting/receiving device is transmitted to the transmitter. From the composite signal obtained by demodulating this modulated wave, the bypass filter separates the audio signal, while the low-pass filter separates the tone signal, and after limiting the separated tone signal, it is detected via the band-pass filter. a transmitting/receiving device, in addition to a detector, the output of the detector controls transmission of the separated audio signal to an output device.