|[AMRadio] Comment from N0JEF|
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
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.
This message was typed using the DVORAK keyboard layout.
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