JPH0434334B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a radio receiver, and particularly to an S meter circuit for a receiver having an FM receiving circuit and a voice squelch circuit.

[Conventional technology]

Highly sensitive radio receivers are usually equipped with a so-called S meter, which is a kind of tuning indicator that increases or decreases the indication according to the radio wave input strength, but in the amateur radio field, the radio field strength is There is a system that displays in nine stages from S9 to S9, and the S value written on the tuning display is called an S meter.

Figure 3 is a block diagram showing the general configuration of a high-sensitivity receiver.The S-meter circuit consists of a carrier rectifier, DC amplifier, and S-value indicator from the input section of the detection stage, through an auxiliary amplifier if necessary. In the past, many S value indicators were in the form of a pointer, but now there are also many types of light display such as light emitting diodes or liquid crystal panels. In addition, part or most of the circuit can be
You can also see configurations that are shared with circuits.

[Problem to be solved by the invention]

The operation of the S meter circuit is basically to drive the display with current or voltage obtained by rectifying the carrier of the signal.
The carrier input strength at S1 is equal to or lower than the receiver's internal noise level, so when an antenna is connected, it often shows a swing greater than S1 due to external noise, so it is important to accurately display S1 and S2. This is a difficult situation.

However, when receiving FM, due to the characteristics of the discriminator detector and the use of an amplitude limiter in the intermediate frequency amplification stage, the noise suppression effect at the time of signal input works, making it possible to receive inputs that are approximately one digit smaller than AM. . However, due to the action of the amplitude limiter, the FM detector input remains constant from small input to large input, so in an FM/AM receiver, the AM S
The meter is used as is, but in FM-only machines, a circuit similar to the S-meter circuit shown in Figure 3 is added, branching off from the front stage of the amplitude limiter, so the sensitivity of the S-meter is the same as that for AM. Therefore, F.M.
In the receiver, a situation occurred in which the S meter did not move at all even though the weak signal was being received sufficiently well, and there were many dissatisfaction with this system, which was mainly used for amateur radio equipment to receive weak input signals.

Therefore, the present invention provides an FM/AM receiver with the following features:
We have corrected the drawback that the S-meter did not operate when the FM signal was a weak input signal, even though the receiving condition was sufficiently practical, and now we have created a circuit that allows FM reception and at the same time the S-meter operates. The challenge is to provide.

[Means to solve the problem]

The present invention applies the squelch control voltage to the transistor 46 in the squelch control circuit when receiving FM radio waves to a receiver capable of instructing the input strength of FM radio waves and AM radio waves.
By inverting the signal and adding it to the transistor 53 of the S meter circuit, the swing of the S meter is increased when FM radio waves are input, and the problem with the conventional FM receiver is that weak signals are well received. This was an attempt to resolve the situation where the S meter did not move at all.

〔Example〕

FIG. 1 is a circuit diagram of a general high-sensitivity FM receiver except where the present invention is applied, and represents an overview of the configuration and operation of the present invention.

The input signal from the antenna is passed through high frequency amplification stage 1.
Operates speakers, etc. through mixer stage 2, intermediate frequency amplification stage 3 (may be multiplexed conversion, but basically the same), limiter stage 4, detection stage 5, squelch gate 6, and audio amplification stage. (The AGC circuit is omitted as it is not directly related). Here, the role of the squelch stage is to suppress amplitude-varying noise during signal input in an FM receiver and generally receive the signal with a better S/N ratio than AM reception, but when the signal becomes extremely weak, the S/N ratio suddenly increases. N deteriorates and large noise is output in a no-signal state, so in order to avoid this, the audio amplification stage is closed when the noise output exceeds a predetermined value, and the squelch control circuit 9 Normally, the squelch gate 6 is closed using a DC voltage obtained by extracting noise components higher than the audio frequency from the output and rectifying the noise components.

The S meter circuit branches from the stage before the limiter stage and drives the S meter 13 through the amplifier stage 10, rectifier stage 11, and DC amplifier stage 12, but this S meter circuit is almost the same as in the case of an AM receiver.
FM/AM receivers often use the AM S meter circuit as is.

In the present invention, by adding the squelch control voltage 91 to the drive voltage of the S meter, even if the signal strength is below the noise level of the S meter, the swing of the S meter increases before and after the FM squelch operates. , the operation is the same as if the indication sensitivity of the S meter had increased.

Figure 2 illustrates the above-mentioned operational relationship, where the horizontal axis shows the input signal strength, the curve shows the FM audio output, the curve shows the voltage input to the squelch control circuit, and the curve shows the difference depending on the received signal level. FIG. 3 is a reference diagram showing the presence or absence of a noise signal. The curve shows the swing of the S meter due to the conventional signal input. The curve shows a comparison of the swing of the S meter when the present invention is applied. However, the vertical axis shows the tendency of change, and the scale between each curve is not the same.

The squelch control voltage is a voltage obtained by selecting, amplifying, and rectifying the noise component in the detection output, and is highest when there is no signal, and when a signal is input, the noise output decreases due to the noise suppression effect of the FM receiver circuit. Therefore, when the noise output drops to a predetermined level, the squelch gate 6 is opened to allow the sound to pass through.The input signal strength at this time is called the squelch level, and the squelch level is variable depending on the application. In the figure, when the noise drops to almost the same level as the signal for small signal reception, the squelch level is variable depending on the application, but in the figure, when the noise drops to almost the same level as the signal for small signal reception, the squelch level changes This shows the state where it is set to open. This can be considered the minimum practical squelch level.

As shown in the curve, when the signal strength is below the squelch level, the audio output is not output at all, including noise, and when it exceeds the squelch level, it is suddenly output.

The S-meter drive voltage is an amplitude rectification type that is proportional to the signal amplitude, and detects amplitude-changing noise and signals equally, so as the signal input increases, the AGC
As a result of this operation, the gain is reduced and the noise output and signal output become equal. The signal strength is 1 more than when receiving FM.
Since the signal becomes large by an order of magnitude, the S meter's indication will fluctuate due to noise regardless of the signal if the signal is weak below a certain level, like a curve, so the S meter cannot operate with an extremely weak signal. , the range extends to a level that is about one digit higher than the lowest squelch operation level during FM.

The curve indicates the indicated state of the S meter when the present invention is applied, and is displayed by adding the inverted squelch control voltage to the indicated drive voltage of the S meter. The S meter oscillates in response to a signal input above the squelch level, making it possible to cause the S meter to oscillate due to a signal below the noise level.

FIG. 4 shows an example of a circuit according to the present invention, in which an FM detection stage 20 converts a change in carrier frequency due to modulation into a change in voltage amplitude, and the output is sent through a squelch gate 30 to an audio output circuit. supply to. On the other hand, in the squelch control circuit 40 , a noise detection circuit 41 extracts only the noise component of about 30 kHz, which is higher than the audio frequency, and outputs a DC voltage (in the figure) obtained through a squelch sensitivity adjuster 42, a noise amplifier 43, and noise rectifiers 44, 45. + potential) In FIG. 2, the B signal is applied to the base B of the DC amplification transistor 46. The power supply voltage _Vcc is divided and applied to the collector C of the transistor 46 by resistors 47 and 48.
This voltage is also applied as a base bias voltage to the transistor 31 of the squelch gate 30. When no bias voltage is applied to the base B of the transistor 46, conduction between C and E is off, so the base B of the transistor 31 is connected to a resistor. A voltage obtained by dividing _Vcc by 47 and 48 is applied as a bias, and the squelch gate 30 opens and outputs an audio signal. However, when a noise rectified voltage is applied as a bias to the base B of the transistor 46, conduction occurs between C and E. Since it is turned on and almost in a short-circuit state, the audio input is shortened, and the bias also becomes 0, so the squelch gate closes and no audio is output. When suppressed, the squelch gate operates to open.

The S meter circuit 50 rectifies the intermediate frequency carrier that does not pass through the limiter with diodes 51 and 52, and adds the voltage (+ potential in the figure) to the base B of the meter driving transistor 53 to the collector C or emitter E circuit. Since the meter 54 connected in series is made to swing, the bias voltage applied to the base B increases in proportion to the signal strength, so the current flowing through the collector C and emitter E also increases, causing the meter 54 to swing.

The above is a conventional circuit, and in order to apply the present invention, it is sufficient to add the audio squelch control voltage to the S meter drive voltage, but since the noise rectified voltage increases as the input signal becomes smaller. , the increase and decrease of the voltage value is reversed and the S meter driving transistor 5 is
It is necessary to add it to the base B of 3, and it is enough to pass it through an inverting circuit using one transistor,
In the present invention, since the transistor 46 constitutes an inversion circuit at the same time as DC amplification, the desired purpose can be achieved by applying the voltage on the collector C side to the base B of the transistor 53. However, if the two circuits were directly connected, the balance of the circuit potential would be lost, so they are connected through a backflow prevention diode 47 and a resistor 48 for adjusting the addition amount to the S meter and eliminating audio signal interference.

Although various variations of the present invention are possible depending on the original circuit to which it is applied, in this embodiment, the desired purpose can be achieved by simply adding one diode and one resistor. This is an example of the simplest application.

〔Effect of the invention〕

As stated in the section of the prior art and summary of the invention,
With conventional FM receivers, when the input signal is weak, sufficient S/N ratio can be obtained for communication purposes, and even though the voice squelch works, there is a range in which the S meter does not work. By applying this, it is possible to make the S meter swing at least in a range above the minimum operating level of the voice squelch.

Also, although not mentioned in the previous section, in the FM/AM receiver to which the present invention is applied, when receiving AM,
A side effect is that by operating the FM squelch control circuit, it is possible to make the S meter swing with a weak signal up to the receivable limit.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram for explaining the present invention, FIG. 2 is an operational characteristic diagram of the present invention, and FIG. 3 is a conventional circuit diagram.
FIG. 4 is a circuit diagram for implementing the present invention. 1... High frequency amplification stage, 2... Mixer stage, 3...
Intermediate frequency amplification stage, 4...Limiter stage, 5...FM
Detection stage, 6...Squelch gate, 7...Audio amplification stage, 8...Speaker, 9...Squelch control circuit,
10...S meter amplification stage, 11...S meter rectifier, 12...S meter drive DC amplification stage, 13...
S meter, 20...FM detection stage 30 ...Squelch gate, 31, 43, 46, 53...Transistor, 40 ...Squelch control circuit, 41 ...Noise selection circuit, 42...Squelch sensitivity adjustment stage, 44, 4
5, 47, 51, 52...diode, 50...
S meter circuit, 54...S meter.

Claims (1)

[Claims] 1 In the S meter circuit that branches the output signal of the intermediate frequency amplifier of the AM and FM receiver, rectifies it, and supplies the signal amplified by the DC amplification transistor to the S meter to display the received signal strength, The squelch gate is controlled by a signal from a switching transistor that operates with the rectified voltage of the noise signal. When there is no noise signal in the receiving state, the switching transistor is cut off and opens the switching gate with a high collector voltage, so that the noise signal is If the squelch circuit is large, the switching transistor becomes conductive and the squelch gate is closed by a low collector voltage. In the case of FM reception, the receiver is characterized in that the S meter is displayed from the squelch operation start state in the weak radio wave region by the sum of the S meter signal generated by the output of the intermediate frequency signal and the squelch signal. S meter circuit.