IC-756Pro3/Quadra ALC Overshoot Test

by Adam Farson VA7OJ/AB4OJ

Fig.1: Test screenshot.
Fig.1: Test screenshot.

On 27 August 2007, I ran an ALC overshoot test on my IC-756Pro3/Yaesu Quadra station as follows:

Initial setup:

Frequency: 14140 kHz. Quadra Po = 1kW. Required drive power 70W.

Test configuration:

  1. Pro3 ANT1 Bird 4273-025 line sampler Bird 43 power meter Quadra Input 1.

  2. Sampling port of line sampler connected to Tektronix 455 oscilloscope Channel 1, terminated in 50Ω.

  3. Scope set to 0.2V/div vertical, 0.1 sec/div horizontal.

Test procedure:

  1. Key exciter in USB mode, with Mic Gain fully CCW: no RF output; no spike.

  2. Key exciter in RTTY mode: Drive drops off approx. 6% in first 100 mS, then settles.

Fig.1 illustrates what is happening. ALC settling time is approx. 100 mS, but there is no damaging overshoot.

Remarks:

References:

Copyright  2008 A. Farson VA7OJ/AB4OJ (including images). All rights reserved. 
Last revised: November 27, 2015