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Very successful AGC The circuit is ND6T, but in some designs and different connection may be suitable. The described AGC circuit uses A244D (TCA440), an integrated circuit for receivers up to 30 MHz. We will use only and part of it for AGC, which is and four-stage MF amplifier and its control circuit. The control range can be up to 60 dB, which is really and lot. More about this integrated circuit will tell datasheet.
The principle of AGC is simple. An NF signal is fed to the input of A244D, which is amplified. The output signal is rectified by and diode and fed back to the gain control circuit of the first three amplifier stages in A244D. At the same time, the values of the variable resistor and capacitor C5 create the possibility of setting the control level and the time constant.
Perhaps the biggest disadvantage of the A244D is that the MF part of this integrated circuit only works at lower frequencies, up to 2 MHz. The idea outlined here processes the NF signal, but we can also use it to regulate the MF frequency, e.g. 455 kHz or similar. It is also possible to connect an indicator to pin no. 10. S-meter.
Source:
[1] and collection of lectures from the national seminar of radio amateurs of the Tatras Association 1983, Use available IOs in radio amateur practice
[2] MKARS80 transceiver om0aao