JPH0214820B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in the squelch method of a wireless receiver (including a receiving section of a wireless transmitter/receiver).

[Conventional technology and problems]

High-gain radio receivers are equipped with an inter-office noise suppression operation that suppresses internal noise that occurs when there is no signal input or weak signal input, and outputs only a practical level signal. However, now it is often called squelch, so it will be written as squelch below.

Compensates for deficiencies in AGC operation when receiving AM or CW,
It is equipped with a gain adjuster to prevent saturation of the circuit due to strong signal strength, and by reducing the gain to a certain extent during normal reception, it is possible to suppress inter-station noise to a level that does not cause problems, but when receiving FM The machine uses a limiter (amplitude limiter) in the intermediate frequency stage to keep the output constant and reduce noise, so it has an extremely large overall gain, and because it does not use a gain adjuster, there is no strong noise between stations when selecting a station. There is a problem that this occurs, and in order to cope with this problem, a squelch circuit is necessarily provided.

As shown in Figure 2, the internal noise of an FM receiver is rapidly reduced even with a weak input of -10dB or less.
Since a S/N of about 20 dB can be obtained, this noise is used to perform a squelch operation to stop the operation of the low frequency amplification stage after detection. The outline of its configuration is shown in Figure 3. The audio component and noise component are separated and extracted from the detected output, but since the FM receiving circuit has a wide band and the distribution band of the noise component is wide, it is usually
The squelch gate installed in the low frequency amplification stage is controlled by using the rectified DC voltage that extracts only the noise output through a 50kH ₂ to 100kH ₂ tuning circuit or BPF, and closes the gate when there is noise output. The output is cut off, and when a signal is input and the noise output falls below a predetermined value, the gate opens and operates normally. The practical model is equipped with a squelch level adjuster to select the signal level at which the gate opens and closes, and the level variable range is about 10 dB.

In AM receiving circuits, the passband width of the intermediate frequency stage is set to the very edge of the sandband width in order to eliminate adjacent interference waves, and in CW, the band width is set to a narrow band of several 100 Hz, so the noise output from the detector is the same as the audio output. It is difficult to separate and detect only the noise as in the case of FM. Therefore, the squelch operation in AM receivers uses carrier squelch, which is performed by detecting the carrier strength of the signal. To detect carrier squelch, it is possible to use the control voltage of the AGC circuit that operates based on changes in carrier strength, as shown in Figure 4, without the need for a special detection circuit. Intermittent SSB or carrier without
There is an advantage that it can be applied as is when receiving CW.
Further, instead of directly using the AGC control voltage, an S meter drive voltage obtained by DC amplifying the AGC control voltage may be used.

As mentioned above, the noise squelch method is used for FM, and the carrier squelch method is used for non-FM, so multi-mode receivers including FM are equipped with both squelch methods, and the squelch method is also switched in conjunction with mode switching. Although the squelch level setting device is also provided separately, it is common to have it linked or shared due to panel space issues and convenience of use. Also, as can be seen from the characteristic example in Figure 2, the squelch operation level is different between FM and AM.
Since the radio field strength also differs, it is necessary to readjust the squelch level setting device each time you switch modes. Furthermore, AM is often used with the squelch turned off, so if you switch to FM without changing it, you will be surprised by the strong inter-station noise.

[Purpose of the invention]

An object of the present invention is to provide a squelch method that can perform more rational squelch operations in all modes in a multimode receiving circuit including FM.

[Summary of the invention]

This invention relates to a wireless reception circuit that is characterized in that it is configured such that, in a multi-mode receiving circuit including FM, it operates with carrier squelch in modes other than FM mode, and can selectively use noise squelch and carrier squelch in FM mode. This is the "squelch method of the machine".

As mentioned in the "Prior Art and Problems" section above, the squelch method generally uses noise squelch in FM mode and carrier squelch in non-FM modes, and its operating level As can be seen from the characteristic example in Figure 2, in FM an adequate S/N ratio is obtained that does not require squelch closure when the input is below 0 dB (0 dB = 1 μV), while in AM the input does not exceed 10 dB. Since sufficient S/N cannot be obtained, there is a 10 to 20 dB difference between the input levels in both squelch operating ranges, and the FM
In accordance with the purpose of selectively receiving radio waves with a strong input level similar to that of AM, the present invention is configured so that noise squelch and carrier squelch can be selectively used in FM mode. The range is expanded to enable switching to carrier squelch to cope with strong input level signals that cannot be covered by noise squelch.The details of the configuration will be described in the embodiment section of the present invention.

Claim 2 of the present invention is ``the squelch method according to claim 1, characterized in that all carrier squelch operations are stopped when the FM mode is set to noise squelch.'' In modes other than FM, the squelch operation is turned off for the purpose of receiving weak input signals such as amateur wireless communication, but if you switch to FM mode as it is, it eliminates the inconvenience of generating intense inter-station noise. Therefore, in the squelch method according to claim 1, the squelch operation in modes other than FM can be stopped while the noise squelch operation state remains set in the FM mode. This will be described in the section of Examples of the present invention.

[Embodiments of the invention]

FIG. 1 shows a circuit configuration of an embodiment of the present invention, and its operation will be explained below.

1 and 2 are voltage comparators that generate the squelch gate opening/closing control voltage, and the input terminals have a reference voltage for setting the squelch operation level.
A squelch operating voltage is applied to the terminal, and when the terminal voltage is in a range that is relatively negative than the reference voltage, the output is at H level, and when it is in a range that is relatively positive than the reference voltage, the output is at L level. Comparator 1 is used for noise/squelch, and comparator 2 is used for carrier/squelch.The output is passed through a negative OR gate by diodes 3 and 4 to open and close the squelch gate, but the comparator is an NPN open collector. If the shape is 3,4
is not necessary.

5 is a variable resistor for squelch level adjustment, the middle point of the resistor is grounded, +V _cc is applied to one end and -V _cc is applied to the other end, and comparators 1 and 2 are given positive and negative reference voltages. It is the composition.

For convenience, the operation of the comparators will be explained starting with carrier squelch comparator 2.

The input of comparator 2 is connected to the carrier detection voltage (as shown in Figure 4 in the AM receiving circuit) through terminal 6.
AGC voltage or S meter drive voltage,
In the FM receiver circuit, the voltage is taken out from before the limiter stage of the intermediate frequency amplification shown in Figure 3 and rectified.
(increases from 0 to the + voltage side according to the input signal strength), and also adds a + reference voltage to the input of the comparator 2 using the squelch level adjuster 5. If the input signal is 0, the voltage will increase from 0 to the + voltage side. The applied voltage is 0, the output of comparator 2 is at L level, and is applied to the squelch gate through diode 4, closing the gate and muting the output.
Next, when the input signal increases and the voltage at the terminal exceeds the set voltage (reference voltage) at the terminal, the output of comparator 2 is inverted and becomes H level, causing the squelch
The gate opens and outputs the received sound. If the squelch level adjuster is set to 0 or the negative voltage side, the squelch gate will remain open and the squelch operation will stop from input signal 0, and the higher the reference voltage goes to the positive side, the higher the signal level at which the squelch will open. Operate. This is called a deep squelch state.

Pass terminal 7 to the input of comparator 1.
A negative voltage obtained by rectifying the noise output of the FM detector (output of the noise filter in Figure 3) with the noise rectifier 8 is added to the input of the comparator 1, and a negative reference is applied to the input of the comparator 1 by the squelch level adjuster 5. When a voltage is applied, the noise output is maximum when the input signal is 0, so the input of comparator 1 is negative than the reference voltage, the output of comparator 1 is at L level, and it is added to the squelch gate through diode 3. to close the gate and mute the output. Next, when the input signal increases, the noise output decreases, and the input voltage moves to the positive side relative to the input voltage (reference voltage), the output of comparator 1 is inverted and becomes H level, and the squelch gate opens and outputs the received sound. The input of comparator 1 is switch 9 except in FM mode.
is grounded to prevent any malfunction in the carrier squelch operation.

In the FM reception state, depending on the position of the squelch level adjuster 5, either noise squelch or carrier squelch can be operated. That is, if the squelch level adjuster 5 is set to the negative side of the midpoint, the comparator 2 will not operate, the noise squelch will be activated by the comparator 1, and the squelch level adjuster 5 will be set to the positive side of the midpoint. For example, comparator 1 does not operate, and comparator 2 operates the carrier squelch.

Next, if you switch to FM mode with the carrier squelch operating in a mode other than FM, the carrier squelch will operate even in FM, and if you set the noise squelch operation in FM mode, the carrier squelch will not work in all modes. Do not work. For example, if you apply squelch in AM and only receive strong radio waves and switch to FM, the carrier squelch will operate on FM as well, receiving only strong signals, and the squelch will be applied to receive weak radio waves in AM. If you switch to FM while the unit is stopped, FM operates with noise squelch, which is suitable for receiving weak radio waves close to the noise level.

FIG. 5 illustrates the operating position and squelch operating state of the squelch level adjuster 5. The zero point in the figure is the midpoint position of the regulator 5, the left side of it is a negative potential, and the right side is a positive potential. Regarding squelch operation, the adjustment range is to the left of the 0 point as a noise squelch (FM mode only), and to the right of the 0 point as a carrier squelch (common to FM, AM, SSB, CW, etc.), and the adjustment position is clockwise. The carrier squelch action is deepest at the end of the rotation.
The closer you get to the 0 point, the shallower the carrier squelch becomes. To the left of the 0 point, the carrier squelch is turned off. However, in FM mode, the deepest noise squelch is applied near the 0 point, and becomes shallower as you move counterclockwise. It is shallowest at the clock end (squelch can also be turned off by voltage distribution), so you can see that you can continuously adjust from carrier squelch to noise squelch using only the level adjustment knob.

〔Effect of the invention〕

As mentioned in the prior art section, conventionally, in multi-mode receiving circuits including FM, a noise squelch is used when receiving FM, and a carrier squelch operates with the squelch stopped in modes other than FM mode. By applying the invention and selectively using noise squelch and carrier squelch in FM mode, there is an advantage that it is possible to deal with strong-level radio signals that are outside the operating range of noise squelch. Furthermore, even if you switch to FM mode with squelch stopped in a mode other than FM mode, the noise squelch will continue to operate, so there is no need to worry about inter-station noise being generated.

When implementing the present invention, if the configuration described in the embodiment section is used, all squelch-related controls can be performed only by the squelch level adjuster, and the transition from noise squelch to carrier squelch state in FM mode can be performed using only the squelch level adjuster. It can be moved smoothly and is very effective in use.

[Brief explanation of drawings]

Fig. 1 is an example of an implementation configuration of the present invention, Fig. 2 is a characteristic diagram of the squelch operating range, Fig. 3 is an example of a noise squelch configuration of an FM receiving circuit, and Fig. 4 is an example of a carrier squelch configuration of an AM receiving circuit. Figure 5 shows the squelch
FIG. 3 is an explanatory diagram of the operation of the level adjuster. 1, 2...Comparator, 3, 4...Diode, 5...Squelch level adjuster.

Claims (1)

[Claims] 1. In a multi-mode receiving circuit including FM,
A squelch system for a radio receiver characterized in that it operates with carrier squelch in modes other than FM mode, and is configured so that noise squelch and carrier squelch can be selectively used in FM mode. 2. The squelch method according to claim 1, wherein all carrier squelch operations are stopped when the FM mode is set to noise squelch.