JPS6144417B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit system for preventing the beginning of a conversation from being cut off in a pre-talk type very short wave wireless telephone device that employs a tone squelch.

Figure 1 shows a system diagram of a conventional single channel FM receiver with tone squelch, from the frequency discriminator to the speaker circuit. In FIG. 1, 1 is a frequency discriminator, 2 is a noise amplifier, 3 is a noise detector, 4 is an inverter circuit, 5 is a bandpass filter for tone detection, 6 is a tone signal amplifier, 7 is a tone signal detector, 8 is a matching circuit, 9 is an audio switch circuit,
10 is an audio amplifier, and 11 is a speaker.

In Figure 1, during standby, radio waves from the other communication station are not being received, and a noise voltage close to 100% modulation appears in the output of discriminator 1 due to the limiter operation (not shown) of the FM receiver. . Therefore, the high-frequency noise is amplified by the noise amplifier 2, and turned into a detected DC signal by the noise detector 3, which is added to the inverter circuit 4. In the inverter circuit, the output voltage disappears due to the DC input voltage, and the logic does not hold in the coincidence circuit 8, so no on command is issued to the audio switch circuit 9, so the audio is output through the audio amplifier 10 and the speaker 11. Not yet.

Now, when a radio wave is received from the other station, the noise in the output of the discriminator 1 is reduced due to the noise suppression effect, the output of the noise detector 3 is reduced, and the output of the inverter 4 becomes a logic "1" level and is added to the matching circuit 8. .

On the other hand, the tone modulation signal of the other station's radio wave is discriminated by discriminator 1, filtered by bandpass filter 5, amplified by tone amplifier 6, and detected by tone detector 7, resulting in logic level "1" and coincidence of 8. added to the circuit. The coincidence circuit obtains the logical product "1" with the output of the inverter 4, and sends an ON command to the audio switch circuit 9. The audio output from the discriminator 1 is amplified by the audio amplifier 10, and the speaker 11 outputs the sound of the other station. will be heard.

The series of circuits up to controlling the audio switch using tone signals is generally called a tone squelch circuit, and the series of circuits up to controlling the audio switch using noise detection is generally called a noise squelch circuit. Further, although the tone squelch circuit is normally used in combination with an oscillation circuit, the transmitter circuit is omitted here.

The frequency used for the tone squelch circuit is usually
The lower part of the audio band from 67Hz to 250.3Hz (300Hz to 3KHz) is used. In the concrete circuit, a high-pass filter of 300Hz or higher is inserted in the audio circuit to remove this tone that is modulated at the same time as the audio.

Now, in the single channel FM receiver with tone squelch shown in FIG. 1, considering the time from the reception of radio waves from the other station until the sound is output from the speaker, the following will be obtained.

First, the delay time t ₁ in the filter for tone detection
is generally expressed as t ₁ =1/πB. where B is the bandwidth of 3 dB reduction in Hz. Bandwidth B cannot be made wider than a certain value because of the need to remove adjacent channels of tones. Among the frequencies used for tone squelch, the lowest frequency is 67Hz, and the adjacent frequencies are
71.9Hz is used. For this reason, the Q of the filter is generally selected to be approximately 50. Therefore, at 67Hz, the bandwidth B is approximately 1.34Hz, and t ₁ ≒
It becomes 238mSEC. Next, if the time constant t ₂ of the rectifier circuit is about 3 cycles of 67Hz, t ₂ ≒ 15 mSEC
×3≒45mSEC.

Therefore, the time required for tone detection is approximately 280 mSEC at a tone frequency of 67 Hz. Also, 250.3Hz
Also, the total delay time is approximately 76mSEC. On the other hand, the delay time from noise suppression by noise squelch to audio circuit connection is usually about 20 mSEC to 50 mSEC because the frequencies handled are high.

Therefore, the time from the arrival of radio waves from the other station to the output of sound from the speaker in FIG. 1 is determined only by the tone squelch circuit, and at a tone frequency of 67 Hz, approximately 280 mSEC is required. During this time, if transmission is started at the same time as press talk control in a general press talk call, one or two sounds at the beginning of the conversation will disappear. In the press-talk communication system, this occurrence of interruptions at the beginning of a conversation occurs each time a call is made, so it is necessary to press the press-talk button and take a breath before transmitting, which has the disadvantage of impeding prompt communication. Furthermore, in an automatic relay system using tone squelch, the delay time due to tone reception is doubled between the receiver of the relay station and the receiver of the own station, which is even more detrimental.

Therefore, an object of the present invention is to prevent the beginning of a conversation in alternate communication in a single channel FM transmitter/receiver with a tone squelch. It consists in combining the talk signals. Examples will be described below with reference to the drawings.

FIG. 2 shows an embodiment of the present invention, in which numerals 1 to 11 are the same as those explained in FIG. 1. 21
The pre-talk signal 22 that activates the transmitter is a delay circuit of the quick delay recovery type, and immediately transmits the signal to the matching circuit 8 by the tone detector output 7 or the pre-talk signal 21, and also outputs the tone detector output or the pre-talk signal 21. The output signal is configured to continue for a certain period of time (for example, about 10 seconds) when the press talk signal disappears.

Next, this operation will be explained.

First, when a radio wave from the other station is received, it is discriminated by the discriminator 1, the own tone is filtered by the filter 5, amplified by the tone amplifier 6, detected by the detector 7, and sent to the delay recovery type delay circuit 22. Added. This circuit is of the fast acting type and immediately adds a logic level "1" to the 8 match circuit.

On the other hand, the noise squelch signals from 2, 3, and 4 are applied as logic "1" from inverter 4 to the matching circuit by radio wave reception, so the logic is established and 9
An on command is applied to the audio switch circuit. Therefore, the incoming voice is amplified by the 10 voice amplification circuits, and the received voice can be heard from the 11 speakers.

Next, considering the case where the radio waves of the other station stop, the situation will be as follows.

When the other station's radio waves stop, the output of inverter 4 disappears due to the noise squelch, the audio switch ON command through the matching circuit 8 disappears, and the speaker output turns off. On the other hand, the tone detection output of 7 is also turned off, but 22 is for a while (approximately 10
(seconds). When the radio wave of the other station stops and a press talk is made for a response, the output of the delay circuit 22 continues to hold the output due to the press talk signal 21. After the press talk of your own station ends, you will receive the radio wave of the other station again, but the delay circuit output of 22 will hold the output for 10 seconds from the time the press talk ends. Because of this, press talk was cut off after 10
If a radio wave is received from the other station within seconds, the matching circuit 8
Since the output from the delay circuit No. 22 has already been added, the sound is output from the speaker after the response time of the noise squelch, and the delay time due to the tone has no effect. At this time, the tone signal is delayed and applied to the delay circuit 22 to continue holding the output.

In this way, the beginning of the conversation may occur only when the first call is received from the other party, but the delay caused by the tone signal after the call starts has no effect on operation, and the call can be made with only the noise squelch delay. Become. Furthermore, when transmitting from your own station, you can prevent the beginning of a conversation being received by your own station from the first time.

In addition, when the same frequency radio wave with a different tone frequency is received immediately after the end of communication, the voice will be heard from the speaker for about 10 seconds, but this only happens once and will not be received after that, so there is no particular problem.

As explained above, the embodiment can minimize interruptions at the beginning of a conversation, and is therefore most suitable for all press-to-talk communications system wireless systems using tone squelch that require prompt communications. This is particularly effective for relay systems using tone squelch.

Since the present invention has a delay circuit to prevent the start of a press talk call from being cut off, it is possible to make a quick call, and it can be used for taxi radio, service radio, and disaster prevention radio using tone squelch.

[Brief explanation of the drawing]

Figure 1 shows a conventional single communication channel with tone squelch
FIG. 2 is a circuit diagram of the FM receiver after the frequency discriminator, and FIG. 2 is a circuit diagram of the same portion according to the present invention. 1; Frequency discriminator, 2; Noise amplifier, 3; Noise detector, 4; Inverter, 5; Bandpass filter, 6;
tone amplifier, 7; tone detector, 8; matching circuit, 9; audio switch circuit, 10; audio amplifier,
11; Speaker, 21; Press talk signal, 2
2; Delay recovery type delay circuit.

Claims (1)

[Claims] 1. In the tone squelch method of a single channel FM receiver, which controls the output of audio via the audio switch circuit by operating the audio switch circuit with a noise squelch signal and a tone signal, the tone squelch method is controlled by the tone detector output. A tone squelch method characterized in that a voice switch circuit is operated via a delay recovery type delay circuit which is also controlled by a pre-talk signal.