ALC and alternatives for controlling your linear output stage

Ashhar Farhan VU2ESE observes that ALC is just one way of controlling output power from a linear amplifier stage and that an easier approach is to do it in software.

This needs software that can control the ‘mic volume’.  You could set the value differently for each band.  There is another pay-off with software mic gain, it can make a major difference to the transmit IMD.  At voice peaks, the tx linear chain compresses. The gain is not constant between low and high levels of modulation. This is the cause of in-channel IMD.   Now, if we have a look up table that amplifies the peaks more than the lows, we can ‘correct’ the gain back to being linear. This simple concept goes by the name of ‘pre-distortion’ in the SDR world.

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