Simple audio compressor for SSB HF Radio rigs

The audio signal goes through passive components C1, R1, D1, C2, R3.  Part of the speech signal charge the D3/D4 detector and creates a control voltage for T1 which is easily available for general-purpose transistor 2N3904. The fading time depends on capacitor C4 and resistor R5. With an audio input variation of 50dB, the output signal gets +-3dB.  This simple circuit can be used in SSB transceivers. I used 1N60 diodes that I could more easily find. I have not tested this using more commonly available diodes but I do not see the reason why this should not work using them.

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