JPH0117871Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an improvement in carrier suppression of an SSB transmitter having an output power control circuit.

[Conventional technology]

SSB communication is particularly suitable for long-distance communication due to its narrow proprietary frequency bandwidth and the high power efficiency of the power amplification stage, thus reducing the transmitter output power to at least
Usually it is 10W or more. But recently
With the spread of the SSB method, it is often used for short-distance communication, and in that case, it is desirable to reduce the output to, for example, 1W or less to prevent interference, and for that purpose, a power reduction switch is used. There are an increasing number of transmitters equipped with

[The problem that the idea aims to solve]

The simplest way to reduce the output of an SSB transmitter is to reduce the modulation input, but since this reduces the modulation depth and reduces the sandband power, it reduces the degree of carrier leakage in the SSB generation stage. This is not a desirable method because it worsens the carrier suppression shown and reduces the S/N ratio due to residual noise.

Therefore, in many conventional devices, the output power level of the transmitter is detected and fed back to the so-called pre-stage section, which is between the SSB generation stage and the output amplification stage, and the gain of the pre-stage section is controlled. A method of setting the level of output power is used. In this case, the operation up to the output of the SSB generation stage is the same, and a method is used in which the output power level is set by controlling the gain of the front stage. In this case, the operation up to the output of the SSB generation stage is the same, and the output is reduced by lowering the gain of the front stage, so neither carrier suppression nor S/N deteriorates. However, at the point when the transmission is interrupted, the gain of the front stage is not controlled and is at full gain, so there is a concern that the carrier suppression will deteriorate and the S/N ratio will be noticeably lowered. The present invention was developed to solve these problems, and aims to provide a transmission output reduction circuit that does not deteriorate carrier suppression or S/N ratio.

[Means to solve the problem]

A part of the output power is taken out by an output divider, rectified and detected by a detector, and a threshold voltage is applied to the detector with a reverse bias to control the detected value. This detection output is fed back to the preamplifier to limit the output power. Furthermore, a signal attenuation amount setting circuit and a through circuit are installed in parallel between the SSB signal generator and the preamplifier, and the selection is made by a first switch. The first switch and the second threshold setting switch are interlocking mechanisms, and are configured so that the selection of the signal attenuation amount setting circuit corresponds to the setting of the threshold value with a large feedback amount.

〔Example〕

The present invention will be explained with reference to the drawings. Reference numeral 1 denotes an SSB signal generator, which normally generates an SSB signal using a balanced modulator and a sideband removal filter. 2 is a pre-stage amplifier (also called a driver stage), which has the gain necessary to drive the SSB signal to the output (also called power) amplification stage 3, and has a gain that is reduced by the amount of output control voltage added. Operate.

The output power is sent to the antenna 4 and at the same time a part of it is taken out through the output divider 5 and sent to the detector 6.
The voltage is rectified to become a DC control voltage 61, which is fed back to the preamplifier 2 to control the gain. The depth of this control operation can be adjusted by adjusting the threshold for starting the operation of the detector 6; the lower the threshold, the deeper the control operation, and the higher the threshold, the shallower the control operation. It is also possible to stop the control. This threshold value can be easily set by adjusting the reverse bias voltage applied to the detector 6. In the figure, a resistor 10 is inserted in series with the detector 6, and a current is passed through the resistor 11 or 12 from a circuit with a constant potential, such as a power supply circuit, to generate a reverse bias voltage across the resistor 10. Since the resistor 10 is constant, the smaller the resistance value of the DC resistors 11 and 12, the greater the reverse bias voltage. Therefore, the threshold setting switch 7 switches the resistors 11 and 12 to obtain the desired output voltage level. Just set the resistance value. Furthermore, in this invention, the second threshold setting
The first switches 9A and 9B, which operate mechanically in conjunction with the switch 7, are switches between the through circuit and the signal attenuation setting device 8 , and the signal attenuation setting device 8 is connected to the SSB signal generator 1 and the front. Since the attenuation circuit is provided between the main amplifiers 2 and is an attenuation circuit after conversion to an SSB signal, there is no adverse effect due to attenuation. The interlocking condition of the first switches 9A, 9B and the second switch 7 for setting the threshold value is that when the second switch 7 for setting the threshold value sets the maximum bias voltage and the feedback voltage 61 is the minimum value, the first switch 9A , 9B are on the through circuit side, and no attenuation is performed between the first switches 9A and 9B. The second switch for threshold setting selects the smaller threshold voltage.The control voltage 61 reaches its maximum value, lowering the amplification of the front stage amplifier and
Switches 9A and 9B are switched to signal attenuation setting devices, and the input to the preamplifier 2 is also lowered, resulting in stable output reduction during low output transmission, resulting in carrier suppression and S/N reduction during no modulation or low modulation periods. prevent. The signal attenuation setting device 8 in the previous stage is connected to the SSB generator 1 and the previous amplifier 2 shown in the figure.
It may be placed between the pre-stage amplifier 2 and the output amplification stage 3, and the pre-stage amplifier 2
It is sometimes provided between stages, and is within the scope of design freedom.

[Effect of idea]

By interlocking the reduction circuit according to the present invention on both the input side and the output side, the output can be reduced in the best condition without carrier suppression or S/N deterioration, which has a great practical effect.

[Brief explanation of the drawing]

The figure is a block diagram of an output limiting circuit of an SSB transmitter according to an embodiment of the present invention. 1...SSB signal generator, 2...Pre-stage amplifier, 3
... Output amplification stage, 5 ... Output divider, 6 ... Detector, 7 ... Threshold setting switch, 8 ... Signal attenuation amount setting device.

Claims (1)

[Scope of utility model registration request] An SSB signal generator, a pre-stage amplifier, an output amplifier, and an antenna are connected in cascade, and an output divider made of a capacitor is connected to the output side of the output amplifier to detect the output power level, and the output power level is returned to the pre-stage amplifier. In a transmitting section of a transmitter or transceiver that sets the level of output power by controlling the gain of the transmitter, a signal attenuation amount setting device using a through circuit and a resistor is installed in parallel between the SSB signal generator and the pre-stage amplifier. a detection diode that outputs a negative voltage to the output side of the output divider, a resistor and a capacitor that are grounded in parallel through a coil, and fed back to the contact point between the coil and the resistor. Set the two threshold voltages to the second
means for inputting switching with a switch, the second switch and the first switch are interlocked;
When the first switch selects the through circuit, the second switch is on the threshold side with a small feedback amount, and when the first switch is on the signal attenuation setting device side, the second switch is on the threshold side with a small feedback amount. A transmitter circuit characterized in that it selects a large threshold.