ARRL

AE7TO

Joined: Fri, Apr 20th 2012, 06:10 Roles: N/A Moderates: N/A

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Will use of ALC pin on IC-635 for RF power control cause distortion? Aug 1st, 21:00 1 254 on 1/8/14

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Will use of ALC pin on IC-635 for RF power control cause distortion? AE7TO on 1/8/14
I would like to control my ICOM IC-735 remotely, mostly for digital modes. Unfortunately, this radio's early CI-V interface does not allow for computer control of RF transmit power. So I have assembled an external box with a microprocessor and relays for applying negative DC voltage to the ALC pin on my rig's ACC2 connector whenever I send the appropriate commands from a remote computer.

My initial tests into a dummy load indicate that the whole setup works as intended. I leave the IC-735's RF Power slider on 100 watts and I can reduce actual output power to 10 or 50 watts by applying negative voltages to the ALC pin.

My question is this: Will this approach distort my signal (e.g. IMD or splatter) when transmitting JT65 or PSK31? I know that we don't want audio input levels so high that ALC kicks in. But I don't have a sense for whether artificially reducing power output via the ALC pin would have similar consequences. The signal looks ugly on a co-located SDR receiver. But I suspect that is because I am overloading the receiver.

73.
Mark, AE7TO

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