JPH06197028A - Radio transmitter - Google Patents

Abstract

PURPOSE:To prevent generation of an excess transmission output at the start of AM transmission and to make transmission at a rated transmission output. CONSTITUTION:An ALC feedback loop is formed by a detection circuit 9 detecting part of a transmission output resulting from modulating a voice signal from a microphone 1, a buffer amplifier 10 having a gain changeover device 11, an integration circuit 12 having a capacitor changeover device 13, a voltage follower circuit 14 and an IF amplifier 4. A switching circuit 15 is connected to the voltage follower circuit 14 and controlled by a changeover device S3 provided between a time constant circuit 16 receiving a transmission signal TX and ground and the amplification factor of the IF amplifier 4 is controlled by the voltage follower circuit 14.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ALC circuit of a radio transmitter, and more particularly to a radio transmitter suitable for preventing excessive transmission output at the start of AM transmission.

2. Description of the Related Art Conventionally, a wireless transmitter for modulating and transmitting a voice signal from a microphone has been provided as shown in the block diagram of FIG. In the figure, reference numeral 1 is a voice signal input microphone. A voice signal input from the microphone 1 is modulated by a modulation circuit 2 to which a carrier signal is supplied from a carrier generation circuit 3, and an intermediate frequency (I
It is converted to F) and amplified by the IF amplifier 4. 5 is a mixer circuit, and this mixer circuit 5 includes a voltage controlled oscillator circuit.
A local oscillation frequency is supplied from the (VCO) 6, the output signal of the IF amplifier 4 is converted into a transmission frequency, amplified by the RF amplifier 7, and transmitted from the antenna 8. Reference numeral 9 denotes a detection circuit. This detection circuit 9 detects a part of the transmission output signal, and this detection signal is fed back to the IF amplifier 4 via the buffer amplifier 10, the integration circuit 12 and the voltage follower circuit 14. To form an ALC circuit. A wireless transmitter configured in this way, for example, an amateur wireless transmitter is generally SSB,
The transmission signals of CW, FM, AM, etc. can be set and transmitted by one radio, but in this way, when the modulation mode is different, the operation of each ALC circuit is formed differently. .
In particular, in order to perform 100% modulation transmission in AM transmission, CW output
Since it is necessary to set the carrier to 1/4 and apply modulation, the ALC feedback loop controls the carrier component level of the IF amplification stage of the IF amplifier 4.
That is, at the time of AM transmission, the gain switching device 11 provided in the buffer amplifier 10 of the ALC circuit is set to ON to forcibly reduce the output voltage of the buffer amplifier 10 to perform ALC feedback and reduce the amplification degree of the IF amplifier 4. The carrier level was controlled to 1/4. In addition, the capacitor switch 13 provided in the integration circuit 12
It was turned on and the average value of the ALC feedback voltage was taken out to perform ALC feedback, and the carrier component of the IF amplifier 4 was controlled to be constant regardless of the presence or absence of modulation. Thus, when sending AM, A
The gain level switch 11 and the capacitor level switch 13 in the LC feedback loop automatically adjust to the carrier level of the transmission output that enables 100% AM modulation, and the carrier level is not adjusted. Also, since there is no carrier component in the SSB transmission signal during SSB transmission, in order to keep the transmission output constant, level control should be performed according to the peak value of the audio signal, which is the modulation signal.
It was performing a return operation. In this way, the transmission output level of the wireless transmitter corresponds to the set output level of the wireless transmitter.
A feedback operation was performed to control the output level, and the excessive output or the excessive output of the transmission output was eliminated to transmit.

However, the above-mentioned conventional wireless transmitter, especially when performing AM transmission, sets the gain switch 11 and the capacitor of the ALC feedback loop by setting the wireless communication device to the AM transmission mode. It is set to ON by an instruction from the control circuit (not shown) built in the switcher 13, and the rise time of the feedback loop occurs at the start of AM transmission. During the delay time of this rise operation, there is no ALC feedback. There is a problem that the transmission output will be transmitted at the maximum output, which may interfere with other wireless communication,
There was a drawback that it would be a problem under the radio regulations. Also,
There is also a problem that the above-mentioned maximum output causes a problem such as destruction of the final stage transistor of the wireless transmitter. The present invention has been made in view of the above points, and an object thereof is to provide a wireless transmitter that solves the drawbacks of the conventional example and prevents excessive transmission output at the start of AM transmission.

A radio transmitter according to the present invention is turned on / off by a transmission signal in a radio transmitter having an ALC circuit which detects a transmission output and returns it to an IF amplifier via a voltage follower circuit. A switching circuit, a time constant circuit for switching control of the switching circuit, and a switcher between the time constant circuit and ground are provided in the voltage follower circuit, and the switching circuit is turned on by the on operation of the switcher. The amplification degree of the IF amplifier is reduced, and at the same time, the time constant circuit to which a transmission signal is supplied is driven to control the switching circuit to turn off after a predetermined time to perform the ALC feedback operation.

According to the present invention, a switching circuit is provided in the voltage follower circuit of the ALC feedback loop, a time constant circuit is provided for controlling the switching operation of this switching circuit, and a transmission signal is added to this time constant circuit. In addition, a switch is provided between this time constant circuit and ground to control the voltage follower circuit of the ALC circuit. In particular, during AM transmission, by setting the wireless communication device to AM transmission mode as in the conventional example, the gain switching device connected to the buffer amplifier of the ALC circuit and the capacitor switching device connected to the integrating circuit are
At the same time when it is set to ON, the switch of the time constant circuit is also set to ON. When the switch is set to ON, the transmission signal supplied to the time constant circuit controls ON of the switching circuit at the start of AM transmission, and at the same time, the capacitor of the time constant circuit starts charging. On the other hand, when the switching circuit is turned on, the base voltage of the transistor of the voltage follower circuit is forcibly set to the ground potential, and the output voltage of the voltage follower circuit is lowered to reduce the IF
Control to reduce the amplification of the amplifier. In this way, the amplification of the IF amplifier is reduced to eliminate the excessive output of the transmission output, and when the transmission signal supplied to the time constant circuit has finished charging the capacitor, the output voltage of this time constant circuit turns off the switching circuit. The transistor of the voltage follower circuit that is controlled and connected to this switching circuit enters the normal ALC feedback operation state. On the other hand, the capacitor switch provided in the integration circuit of the ALC circuit turns on at the same time as AM transmission starts to start charging the capacitor of the integration circuit.The charging time constant of this integration capacitor is the capacitor of the time constant circuit described above. Since the charging time is set to be substantially the same as the charging time of, the charging of the capacitor of the integrating circuit is completed at the same time as the charging of the capacitor of the time constant circuit is completed. In this way, the integration circuit of the ALC feedback loop also operates normally.
The average value of the ALC feedback voltage can be output, and at the same time, the operation of the voltage follower circuit also turns off the switching circuit.
The normal ALC feedback operation state, and the transmission output
ALC feedback control is performed to obtain a constant level output. That is, it is possible to forcibly lower the transmission output level at the start of AM transmission and prevent excessive output at the start of AM transmission.
After the charging time of the capacitor of the integration circuit and the capacitor of the time constant circuit, the normal ALC feedback operation is automatically activated and normal transmission output can be transmitted, preventing damage to the final-stage transistor circuit of the wireless transmitter. However, it does not interfere with the radio communication of other stations, and the problem of radio regulation due to excessive output disappears.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a wireless transmitter according to the present invention will be described with reference to FIGS. The same parts as those of the conventional example are designated by the same reference numerals and the description thereof will be omitted. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram of a main part of an ALC feedback circuit, and FIG. 3 is a waveform diagram showing a transmission output waveform at the start of AM transmission. In FIG. 1, reference numeral 15 is a switching circuit, and this switching circuit 15 is connected between the voltage follower circuit 14 and the ground. Reference numeral 16 is a time constant circuit. A transmission signal is supplied to the time constant circuit 16 from the input terminal 17, and a switch S ₃ is connected between the time constant circuit 16 and the ground. Controls the ON / OFF switching operation of the switching circuit 15. Also, FIG.
In the circuit diagram of, Q _{1 to} Q ₇ are transistors, and S ₁ to
S ₃ is a switch. In the wireless transmitter configured as described above, a part of the transmission signal transmitted from the antenna 8 is supplied to the detection circuit 9 and detected, and this detection signal forms an ALC feedback loop that is fed back to the IF amplifier 4, In this way, the radio transmitter basically controls the transmission output level by forming the ALC feedback loop even if the various types of modulation described above are used. In particular, in the case of AM modulation, the carrier level is lowered so that AM 100% modulation is possible, so that the gain switching device 11, the capacitor switching device 13, and the switching device S ₃ provided in the time constant circuit 16 are provided. Set to ON. The detection output signal detected by the detection circuit 9 is supplied to the base of the transistor Q ₁ which constitutes the buffer amplifier 10 via the variable resistor VR as shown in the figure, and is supplied to the integration circuit 12 from the collector of the transistor Q _2. Output, but a resistor is placed at the base of this transistor Q ₂ .
A switch S ₁ forming a gain switch 11 is connected via R ₁ and is grounded. When the switch S ₁ is turned on, the base of the transistor Q ₂ is grounded by the resistor R ₁ and the collector output voltage is lowered to be output. The output of the buffer amplifier 10 is supplied to the integrating circuit 12, the capacitor C ₁ of the integrating circuit 12 is grounded by the ON operation of the switch S ₂ , and the average value of the ALC feedback signal can be obtained. Like this
The average value signal of the ALC feedback signal is supplied to the voltage follower circuit 14. The final stage transistor Q ₅ of the voltage follower circuit 14
The base of the transistor is the transistor that constitutes the switching circuit 15.
Is connected to the collector of Q _7, and controls the output voltage of the transistor Q ₅ by ON / OFF switching operation of the transistor Q _7, the output voltage is supplied to the IF amplifier 4 as ALC feedback voltage. The base of transistor Q ₇ has an input terminal
The transmission signal TX (= 8V) supplied to 17 and the transistor Q ₆
Supplied via capacitor C ₂ , above, transistor Q ₇
A switch S ₃ is connected to the base of between the grounds. Automatically ON switcher S ₃ at the time of AM transmission by AM transmission mode setting
When set to, the transistor Q ₆ turns on and the input terminal
The transmission signal TX supplied to 17 starts charging the capacitor C ₂ , and at the same time turns on the transistor Q ₇ . That is, the transistor Q ₇ maintains the ON state until the capacitor C ₂ is completely charged, forcibly setting the base of the transistor Q ₅ of the voltage follower circuit 14 to the ground potential, and the emitter output voltage of the transistor Q ₅ is suppressed low. , The ALC feedback voltage to the IF amplifier 4 becomes low and the amplification degree of the IF amplifier 4 can be lowered to suppress the transmission output. Figure 3 is a waveform diagram showing an amplitude characteristic of the AM transmission signal waveform in FIG. 3, 20 is an AM transmission output waveform of the conventional example (the block diagram of FIG. 4), at the time of AM transmission start excessive output amplitude V ₁ Generated output signal waveform 20
After the time T _{1 at} which the excessive output 20a ends, the output signal waveform 20b with the output amplitude V _{2 in} the normal state is shown. 22 is the output signal waveform of the AM transmission circuit that forms the ALC feedback loop of the present invention. At the start of AM transmission, the transmission power is kept small by reducing the amplification of the IF amplifier 4 as described above. The output waveform 22a gradually increases to obtain the output signal waveform 22b having the output amplitude V _{2 in} the normal state from before the time T ₁ . That is, the transmission circuit having the ALC circuit of the present invention is an AM
The transmission output at the start of transmission is the excessive output that has been generated in the past.
You can eliminate a. When the capacitor C ₂ of the time constant circuit 16 is completely charged by the transmission signal TX of the input terminal 17, the transistor Q ₇ is turned off and the transistor Q ₅ of the voltage follower circuit 14 is returned to the normal operating state. Above, time constant circuit
The charging time of the capacitor C ₂ of 16 depends on the integration circuit 12 of ALC feedback.
Substantially by selecting the capacity to be the same time, the integrating circuit from the time AM transmission start charging time to the capacitor C ₁ of the switching device S ₂ capacitor C ₁ is turned ON has completed charging to start charging substantially simultaneously, to charge the capacitor C ₂ of the time constant circuit 16 is completed transistor and capacitor C ₁ of 12 ends charging ALC feedback circuit becomes normal feedback operation state
Q ₇ turns off. Thus, by providing the voltage follower circuit 14 of the ALC feedback loop with the switching circuit 15 that is turned on / off by the transmission signal TX, it is possible to prevent the occurrence of an excessive output at the start of AM transmission. The transmission signal output at the start of AM transmission of the wireless transmitter has been described above.
In a transmission circuit that forms an ALC feedback loop that detects an output signal and feeds back a DC feedback voltage that is integrated by using a capacitor, etc., the contents of this invention can be applied to start transmission with a better transmission output. it can.

As described above, the wireless transmitter according to the present invention is provided with the switching circuit 15 in the voltage follower circuit 14 of the ALC feedback loop, and the switching circuit 15 transmits the transmission signal.
ON / OFF by the operation of the time constant circuit 16 charged by TX
When the AM transmission is started, the feedback voltage from the voltage follower circuit 14 reduces the amplification degree of the IF amplifier 4 so that the transmission output can be controlled to be a small output. The effect is that it can be prevented. That is, since it is possible to prevent an excessive output and always operate at a normal transmission output, it is possible to prevent the transistor and the like of the final stage amplifier of the wireless transmitter from being damaged and to extend the life of the transistor and the like. . In addition, since the wireless transmitter is always operated at the rated output, problems with radio regulations can be solved, without interfering with the communication of other stations, and excessive output causes the S meter of the wireless transmitter to instantaneously swing excessively. This has the effect of eliminating such problems. Moreover, it has excellent features such as a simple structure and easy implementation because it can be constructed at low cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a wireless transmitter according to the present invention.

FIG. 2 is a circuit diagram showing an ALC circuit of the essential part of the present invention.

FIG. 3 is a waveform diagram showing a transmission output waveform at the start of AM transmission.

FIG. 4 is a block diagram showing a conventional example.

[Explanation of symbols]

 1 Microphone 2 Modulation Circuit 3 Carrier Generation Circuit 4 IF Amplifier 5 Mixer Circuit 6 Voltage Controlled Oscillation Circuit (VCO) 7 RF Amplifier 8 Antenna 9 Detection Circuit 10 Buffer Amplifier 11 Gain Switcher 12 Integration Circuit 13 Capacitor Switcher 14 Voltage Follower Circuit 15 Switching circuit 16 Time constant circuit 17 Input pin of transmission signal TX 20 Conventional transmission output waveform at the start of AM transmission 20a Excessive transmission output waveform at the start of AM transmission 20b Normal output waveform at the start of AM transmission 22 AM Transmission at the start of transmission Output waveform 22a Transmission output rising waveform at the start of AM transmission 22b Normal output waveform at the start of AM transmission

Claims (1)

[Claims] 1. A wireless transmitter having an ALC circuit that detects a transmission output and returns it to an IF amplifier through a voltage follower circuit, and a switching circuit that is turned on / off by a transmission signal,
A time constant circuit for switching control of the switching circuit and a switcher between the time constant circuit and ground are provided in the voltage follower circuit, and the switching circuit is turned on by the ON operation of the switcher to turn on the IF amplifier. A radio transmitter, characterized in that the amplification factor is lowered, and at the same time, the time constant circuit to which a transmission signal is supplied is driven to control the switching circuit to turn off after a predetermined time to perform an ALC feedback operation.