Contributed by Bob Lanning, W6OPO

Today, I ran a stress test on my IC-7700 to check PA integrity under high duty-cycle usage (heat). No failure occurred, and I saw what I assume to be an ICOM safety feature turn on.

I ran this test for 15 minutes using a 75% duty cycle (CW dashes) signal into a 50 + j0Ω dummy load. Ambient temperature was 70F (21C). Power output was 170W, not 200W (my choice) as measured on an LP-100A Digital Vector RF Wattmeter  which has a calibration pedigree. I had the IC-7700's multimeter display on, so I could watch all parameters simultaneously. Table 1 gives the logged data points.

Table 1: Logged IC-7700 PA data points.
Time (min) Po (W) ID (A) VD (V) Temp Ind (segments) Fan Speed
0 170 11 48 all blue low (1)
3 170 11 48 1 gray med (2)
5 170 11 48 2nd pink* high (3)
8 170 11 48 3rd pink high (3)
12 170 11 48 4th pink high (3)
14 85 8 48 4th pink high (3)
15 85 8 48 4th pink high (3)
* Pink starts after 7 gray segments.

After the test, I stopped transmitting until the temperature dropped back into the gray segments then sent dashes again. Power was back to 170W, and ID back to 11A. All other parameters remained normal.

At the highest temperature, 2 segments remained before the red zone started in the line below the segments. It is understood that the temperature indicator segments are arbitrary indicators.

It was nice seeing the radio cut back to 50% power level at the maximum temperature reached.

So there you have it. My radio (S/N 0201526) can tolerate the heat created by the test described above. What is not clear is why some of the reported PA failures are occurring at 50-100 watt levels.

73, Bob - W6OPO  

Copyright  2009 R. Lanning W6OPO. All rights reserved. 
Editing and page creation: A. Farson VA7OJ/AB4OJ
Last revised: 09/25/19.

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