[AMRadio] Comment from N0JEF


D. Chester k4kyv at charter.net
Sun Feb 14 13:19:10 EST 2010


When running a  transceiver on AM you want to avoid hitting the ALC 
altogether.  This includes the ALC function in the radio as well as the 
linear. As soon as you trigger the ALC, the carrier level abruptly drops 
down, producing a distorted, anaemic sounding "negative controlled carrier" 
effect.  If there is an easy to do so, disable the ALC altogether when 
running AM.  Otherwise, keep the positive peaks just below the ALC 
threshold.  ALC is designed for SSB and was never intended to be run with 
AM.

If the ALC cannot be disabled, it can serve a useful purpose as a positive 
peak overmodulation indicator.  Run the output just under the point where 
you begin to see some indication of ALC action on voice peaks.

The best way to make sure the signal is fully modulated but that nothing is 
being pushed into the flat-topping/distortion region is to monitor the 
envelope pattern of the signal with an oscilloscope. At one time, all major 
manufacturers offered a monitor scope as a matching accessory to go with 
each of their transceiver lines. A modulation monitor scope is NOT the same 
thing as a modern transceiver's panoramic display.

To me, operating a phone transmitter (AM or SSB) without a monitor scope is 
like driving a car at night with the headlights turned off.

Don k4kyv
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