JPH0221797Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention relates to an AGC circuit that is particularly effective when applied to SSB receivers.

(Prior art) This type of conventional general AGC circuit is
In the AGC control section, the
After rectifying the AF signal, it is fed back to the RF amplifier circuit and IF amplifier circuit through the AGC time constant circuit consisting of a resistor and capacitor, and the gain of both amplifier circuits is controlled according to fluctuations in the received signal level, resulting in a constant output signal level. The automatic feedback control system is configured as follows.

(Problem that the invention aims to solve) By the way, in an SSB receiver, the charging time constant for generating the AGC voltage is reduced so that the AGC operation starts earlier when a signal is input, and the discharging time is reduced. A method called fast attack slow release, which has a double time consistency that maintains AGC operation for a while when the input signal disappears by increasing the constant, is considered the best and is widely used. However, when selecting a station by rotating the tuning dial, a high-level received signal can be heard better due to AGC operation, but it is locked at this level and does not drop for a while, so when the dial is rotated quickly, the signal becomes stronger. If a weak received wave is input after the received wave, there is an inconvenience that this wave cannot be heard at all.

(Means for solving the problem) This idea was made in view of the above-mentioned problems of the conventional technology. In an AGC circuit equipped with an AGC control section that controls the gain of the circuit, a speed detection circuit that detects the rotation speed of the tuning dial is connected to the AGC circuit.
We provide an AGC circuit that is connected to the time constant circuit of the control section and has a configuration in which the time constant of the AGC time constant circuit is varied according to the rotation speed of the dial, thereby solving the problems of the conventional one at once. The purpose is to resolve this issue.

(Embodiment) Hereinafter, a preferred embodiment of this invention will be described in detail with reference to the drawings.

In FIG. 1, 1, 2, 3, 4, 5, and 6 are antennas, which are the components of the SSB receiver, respectively;
It shows an RF amplifier circuit, a local oscillator circuit, a mixing circuit, an IF amplifier circuit, and a demodulation circuit, 7 is an AGC control section that is almost the same as the existing one, and 8 is a speed detection circuit that detects the rotation speed of the tuning dial 9. show,
A speed detection circuit 8 is connected in relation to an AGC time constant circuit of the AGC control section 7 to constitute an AGC circuit 10. The AGC control section 7 of this speed detection circuit 8
The connection to the AGC time constant circuit is as shown in FIG. 2 by interposing a field effect transistor F so that the drain of the transistor F is connected to the AGC time constant circuit 7a consisting of a capacitor C and a resistor R, and the gate is connected to the speed detection circuit. 8, or as shown in FIG. 3, the AGC time constant circuit 7b is configured with a capacitor C and two types of resistors R2 and R3 connected in parallel, and both resistors R2 and R3 are connected to the switch S, respectively. It is connected to each switching contact, and the switch S is configured to be switched depending on whether or not the speed detection circuit 8 detects a predetermined rotational speed.

To explain the operation of the embodiment device configured as described above, when the tuning dial 9 is turned quickly during the channel selection operation, in the example shown in FIG. A correspondingly large voltage is applied, and the time constant of the capacitor C decreases, causing it to be quickly discharged. On the other hand, in the example shown in FIG. Switch the switch S and set the AGC time constant circuit 7b.
Since the time constant is reduced by switching to the resistor R3 having a smaller resistance value, the capacitor C is quickly discharged.

(Effects of the invention) As mentioned above, according to the AGC circuit of this invention,
AGC according to the rotation speed of the tuning dial
Since the time constant is variable and the AGC operation is performed quickly, even when turning the tuning dial quickly to select a station, it is possible to reliably hear even the weak received waves that are input immediately after the strong received waves. There are noticeable effects that can be achieved.

[Brief explanation of the drawing]

The drawing shows an example of the AGC circuit of this invention.
FIG. 1 is a block diagram, and FIGS. 2 and 3 are wiring diagrams each illustrating an AGC control section. 2...RF amplifier circuit, 5...IF amplifier circuit, 6...
...Demodulation circuit, 7...AGC control section, 7a, 7b...
...AGC time constant circuit, 8...Speed detection circuit, 9...
...Tuning dial.

Claims (1)

[Claims for Utility Model Registration] (1) RF amplifier circuit and
In an AGC circuit equipped with an AGC control section that controls the gain of the IF amplifier circuit, the speed detection circuit that detects the rotation speed of the tuning dial is
The dial is connected to the time constant circuit of the AGC control section, and the time constant of the AGC time constant circuit is varied according to the rotational speed of the dial.
AGC circuit. (2) The AGC circuit according to claim 1 of the utility model registration, characterized in that the AGC time constant of the time constant circuit is continuously varied in accordance with the rotational speed of the tuning dial. (3) The AGC circuit according to claim 1 of the utility model registration claim, characterized in that the AGC time constant of the time constant circuit is switched by detecting a predetermined rotational speed of the tuning ear.